Energy Transfer– Thermoelectric · Energy Transfer–Thermoelectric Introduction 8 ® 9....

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Instruction Manual No. 012-08745A Instructions Experiments Sample Data Energy Transfer– Thermoelectric ET-8782

Transcript of Energy Transfer– Thermoelectric · Energy Transfer–Thermoelectric Introduction 8 ® 9....

Page 1: Energy Transfer– Thermoelectric · Energy Transfer–Thermoelectric Introduction 8 ® 9. Temperature Sensor Clamps When modeling a refrigerator it is useful to observe the heat

Instruction ManualNo. 012-08745A

Instructions

Experiments

Sample Data

Energy Transfer–

ThermoelectricET-8782

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Energy Transfer–Thermoelectric Model No. ET-8782

Table of Contents

Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Experiment 1:

Conservation of Energy and the First Law of Thermodynamics . . . . . . . . . . . . . . . . . . . . . 9

Experiment 1:

Teachers’ Notes–Conservation of Energy and the First Law of Thermodynamics . . . . . 15

Experiment 2:

Load Resistance and Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Experiment 2:

Teachers’ Notes–Load Resistance and Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Experiment 3:

A Model Refrigerator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Experiment 3:

Teachers’ Notes–A Model Refrigerator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Experiment 4:

Coefficient of Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Experiment 4:

Teachers’ Notes–Coefficient of Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Experiment 5:

Teachers’ Notes–Carnot Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Technical Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Copyright and Warranty Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

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Model No. ET-8782 Energy Transfer–Thermoelectric

Energy Transfer–ThermoelectricModel No. ET-8782

Included Equipment Replacement Part Number

1. Thermoelectric circuit board ET-8782

2. Foam insulators (qty. 2) 648-08724

3. Heat sink 624-013

4. Thumbscrew 617-018 and 615-031

5. Temperature cables (qty. 2) PS-2515

6. Banana patch cords (qty. 8) SE-7123

7. CD-ROM containing editable experiment instructions

and DataStudio® files (not pictured)

Contact Tech Support

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Energy Transfer–Thermoelectric Introduction

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Note

The most convenient combination of interface and sensors for use with the Thermoelectric circuit

board is:

• PS-2001 PowerLink interface

• PS-2143 Quad Temperature Sensor

• PS-2115 Voltage/Current Sensor

• PS-2135 Fast Response Temperature Probes (3-pack), optional

This is the equipment called for by the experiments in this manual and on the CD-ROM. There are

other options for PASPORT™ and ScienceWorkshop® sensors and interfaces, and stand-alone

multimeters. Please contact Tech Support, or see the PASCO catalog or website for details.

Introduction

The Energy Transfer–Thermoelectric circuit board provides students with a hands-on example of

a thermoelectric heat engine. Using measurements from temperature, voltage and current sensors,

students will quantitatively study the energy, work and heat flow associated with heat engines,

heat pumps and refrigerators.

This manual includes instructions for five experiments with sample data and teachers’ notes. You

can photocopy the student instructions or print them from the editable copy of this manual

included on the CD-ROM. Experiment #5 is a DataStudio workbook, which contains the student

instructions within the DataStudio file.

In addition to the experiments detailed here, the Thermoelectric board is well-suited for self-

guided exploration. The following sections will familiarize you with the components of the

experimental set-up.

Additional Equipment Required Model Number

DC Power Supply (10 V, 1 A minimum) SE-9720A or equivalent

Temperature Sensor(s), compatible with 10 kΩ thermistors Various, see note below

Voltage and Current Sensor(s) Various, see note below

PASCO Computer Interface Various, see note below

DataStudio software See PASCO catalog

Optional Equipment Model Number

Fast Response Temperature Probes PS-2135 (3-pack)

Decade Resistance Box SE-7122 or equivalent

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Model No. ET-8782 Introduction

1. Peltier Device with Hot and Cold Reservoirs

The Peltier Device is constructed of two ceramic plates with p and n semiconductors in between.

As DC current passes through the device, it pumps heat from one side to the other. Aluminum

blocks are fastened to each side of the peltier in thermal contact with the ceramic plates. These

blocks add thermal mass to the system and act as the traditional Hot and Cold Reservoirs. When

there is a temperature difference across the peltier, it can be switched to Heat Engine Mode, in

which spontaneous heat flow through the device generates an electric current. Do not touch the

hot aluminum block when it is running in Heat Pump Mode. The temperature of this block can

reach 90 °C or higher.

Do not allow the peltier device to reach temperatures above 100 ºC. Always monitor the

temperature of the hot side when the peltier is operating in Heat Pump Mode. Operation between

80 °C and 100 °C will shorten the life of the device; if you operate the device in that temperature

range, do so for the briefest possible time. You can operate the peltier device without damage at

temperatures below 80 °C.

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Energy Transfer–Thermoelectric Introduction

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2. Input Power

Input Power for the board must be supplied from an external DC power supply capable of 1 amp

at 10 volts. Connect the power supply via the red and black banana jacks on the right-hand side of

the board. Note the polarity: red must be positive. Do not input more than 10 volts.

3. Load Resistors

In Heat Engine Mode, a jumper cable must be connected from the bottom banana jack terminal to

one of the terminals labeled A through D. The load resistance depends on how you connect the

jumper cables. If, for example, the jumper is connected to terminal A, then all of the resistors are

in series in the circuit, and the total load resistance is 20 Ω + 7 Ω + 3 Ω = 30 Ω. If the jumper is

connected to terminal C, the load resistance is 3 Ω. A second jumper can also be used across a

resistor to remove it from the circuit. For example, if the main jumper from the bottom connector

is plugged into terminal A, and a second jumper is connected between B and D, the total load

resistance is 20 Ω; the 7 Ω and 3 Ω resistors are bypassed.

The possible combinations are 3 Ω, 7 Ω, 10 Ω, 20 Ω, 23 Ω, 27 Ω and 30 Ω. If you use a decade

resistance box instead of the on-board resistors, you can supply any value you want. You can also

connect the jumper from the bottom terminal directly to terminal D, which reduces the load

resistance to a few tenths of an ohm (due to the internal resistance of the circuit).

4. Knife Switch

The single pole double throw Knife Switch on the right side of the board is used to select the

mode of operation. In Heat Pump Mode, external power is applied to the peltier device, and heat

is pumped from the aluminum block on the cold side to the block on the hot side. In Heat Engine

Mode, the external power is disconnected, and heat flows back through the peltier, generating

electric current through the load resistor.

5. Voltage and Current

Voltage and current sensors connected to the banana jacks at the top of the board will measure

voltage across and current through the peltier. Note the polarity when you connect the sensors. A

single PASPORT Voltage/Current sensor can be used for both measurements. If you plan to run

the peltier without a current sensor, you must connect a jumper between the current terminals to

complete the circuit.

From the measured voltage and current, DataStudio will calculate the power supplied to the

peltier (in Heat Pump mode) or power generated by the peltier (in Heat Engine mode). DataStudio

will plot a graph of power versus time, which it will use to calculate input or output energy.

6. Temperature Ports

Each aluminum block has a 10 kΩ thermistor embedded in it. Use the provided Temperature

Cables to connect temperature sensors to the thermistors through the hot-side and cold-side

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Model No. ET-8782 Introduction

Temperature Ports. The temperature sensor measures the resistance of the thermistor and

translates it into a temperature reading. If you are using a PASPORT Quad Temperature sensor,

you will connect both temperature ports (and up to two additional probes) to a single sensor.

From the measured temperature change, DataStudio will calculate the heat flow into or out of the

aluminum blocks.

7. Foam Insulators and Heat Sink

The Foam Insulators are used to insulate one side or both sides of the peltier. For conservation of

energy studies, use both insulators to minimize heat exchange with the environment. If needed,

you can put a rubber band around them to hold them tightly together.

The Heat Sink, which helps to dissipate heat, fastens to the hot-side aluminum block with the

provided thumb screw. For more efficient cooling, the fins of the heat sink should be vertical. Be

careful when removing the heat sink because it can get very hot.

In some experiments, you will have an insulator on the cold side, and the heat sink on the hot side.

8. Cooling Fan

The Cooling Fan and heat sink act together to dissipate heat from the hot reservoir. The fan is used

when demonstrating a refrigerator. You can also use it to cool the aluminum blocks back to room

temperature, which is a required initial condition in some experiments.

The fan is operated through a switch in the center of the board and it is powered by the same

external power supply that powers the peltier. The fan has a built-in regulator, so it will run at a

constant speed when the input voltage is 6 volts or higher. Do not use the fan when the input

voltage is below 4 volts.

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Energy Transfer–Thermoelectric Introduction

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9. Temperature Sensor Clamps

When modeling a refrigerator it is useful to observe the heat flow around the heat sink. Two

Temperature Sensor Clamps (one high, one low) are provided to position Fast Response

Temperature Probes (not included) in the air stream from the fan before and after the air has

passed through the heat sink.

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Model No. ET-8782 Energy Transfer–Thermoelectric

Experiment 1:

Conservation of Energy and the First Law of

Thermodynamics

Introduction

In this activity you will study the flow of energy in the experimental set-up as you run it through a

cycle.

First you will operate the apparatus in Heat Pump mode, in which energy is supplied to the peltier,

and the peltier pumps heat from one aluminum block to the other. After a temperature difference

has been established between the blocks, you will switch the peltier into Heat Engine mode, in

which heat flows from the hot block, through the peltier, and into the cold block. The peltier will

convert some of the heat that flows out of the hot block to electrical energy, which it will supply to

the load resistor.

During this cycle you will follow the energy as in moves in different forms from the power supply

to the peltier (electrical energy), in and out of the aluminum blocks (heat or thermal energy), and

into the load resistor (electrical energy). As you do the experiment, bear in mind the law of

conservation of energy and the first law of thermodynamics. How do they relate to the transfer of

energy within the system?

Set-Up

1. Input Power: Set the Heat Pump/Heat Engine switch to the neutral position (straight up).

Connect the power supply using banana patch cords to the input power terminals on the

circuit board as shown in picture below. Note the polarity.

Equipment Required Part Number

Thermoelectric circuit board part of ET-8782

Foam insulators (qty. 2) part of ET-8782

Banana patch cords (qty. 5) part of ET-8782

Temperature cables (qty. 2) part of ET-8782

DC Power Supply (10 V, 1 A minimum) SE-9720A or equivalent

PASPORT Voltage/Current Sensor PS-2115

PASPORT Quad Temperature Sensor PS-2143

PASPORT interface(s) PS-2001 or equivalent

DataStudio software See PASCO catalog

“Conservation of Energy” configuration file for DataStudio part of ET-8782

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Energy Transfer–Thermoelectric Conservation of Energy and the First Law of Thermodynamics

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2. Load Resistance: Connect a jumper from

the terminal at the bottom of the board to

Terminal B. This makes the load resistance

3 Ω + 7 Ω = 10 Ω.

3. Insulators: Place both foam insulators on

the aluminum blocks.

4. Temperature: Connect the cables from the

temperature ports to the Quad Temperature

Sensor. Connect the Cold Side to Channel 1

of the sensor and the Hot Side to Channel 2.

5. Voltage: Connect the voltage leads of the

Voltage/Current Sensor to the Voltage Ports

on the board. Note the polarity.

6. Current: Connect separate red and

black banana patch cords from the

current input of the Voltage/Current

sensor to the Current Ports on the

board. Note the polarity.

7. Computer: Connect the sensors to the

computer through the PASPORT

interface. Open the pre-configured

DataStudio file “Conservation of

Energy”. The display should look as

shown here.

Background

DataStudio has been configured to measure and record the temperature of both aluminum blocks,

the voltage and current applied to the peltier during Heat Pump mode, and the voltage and current

generated by the peltier during Heat Engine mode. From these measured quantities, DataStudio

will calculate and display heat flow, power and work. The following sections explain how

DataStudio makes those calculations.

Heat vs. Temperature

Each digits display shows the heat (Qhot or Qcold) that flows into or out of the aluminum block on

either the hot or cold side of the peltier. The relationship between heat flow and temperature

change is given by

Q = mc∆T

where:

Power Supply

Voltage/CurrentSensor

TemperatureSensor

Ch 1

Ch 2

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Model No. ET-8782 Experiment 1: Conservation of Energy and the First Law of Thermodynamics

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Q = heat transferred,

m = mass of the aluminum block,

c = specific heat of aluminum = 0.90 J/(g·°C),

∆T = change in temperature.

A positive value of Q may represent heat transferred into or out of the aluminum block,

depending on whether the block is on the hot side or the cold side of the peltier, and whether the

peltier is operating as a heat pump or a heat engine.

The temperature of each block is measured by the embedded thermistor. DataStudio calculates the

heat flow from the measured temperature change, and pre-entered values of m and c. Click on the

calculator icon in the tool bar and look at the equations used; note the constants, m and c, in the

bottom section of the calculator window. (The mass of each block is about 19 g. If you would like

to enter your own value for the mass, measure the blocks with calipers and use the density of

aluminum, 2.7 g/cc, to calculate the mass, then enter it in the calculator.)

Input Power and Work Done by the Peltier Heat Pump

In Heat Pump mode, Input Power from the power supply equals the rate at which the peltier does

work to pump heat out of the cold reservoir and into the hot reservoir. The Voltage/Current Sensor

measures the voltage applied to the peltier, and the current that flows through it. DataStudio

calculates the Input Power using the equation: Power = Voltage × Current.

The area under the plot of Input Power versus time equals the energy supplied to the peltier, which

equals the work done by the peltier.

Power Generated and Work Done by the Peltier Heat Engine

In Heat Engine mode, Power Generated is the rate at which the peltier does work on the load

resistor. The Voltage/Current sensor measures the voltage across the resistor and the current

through it. From these measurements, DataStudio calculates the power supplied to the load

resistor. The area under the plot of Power Generated versus time equals the work that the peltier

has done on the resistor.

Procedure

Before you start, the aluminum blocks should both be at room temperature. The knife switch

should be in neutral position (straight up) and the fan should be switched off.

Set the DC Voltage to between 3 and 4 volts.

Start data recording, then set the knife switch to Heat Pump.

You will see Input Power data appear in the top section of graph. The area under the graph equals

the energy supplied to the peltier, which equals the work done by the heat pump. The Heat Pump

digits display shows the heat pumped out of cold reservoir (Qcold) and the heat deposited into the

hot reservoir (Qhot).

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Energy Transfer–Thermoelectric Conservation of Energy and the First Law of Thermodynamics

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Observe how the temperatures of the aluminum blocks change.

Run the peltier in Heat Pump mode for about a minute (or until the cold side appears to reach a

minimum temperature), then switch to Heat Engine mode.

Again, observe how the temperatures of the aluminum blocks change.

Power Generated data now appears in the bottom section of the graph display. The area under the

graph equals the energy generated by the heat engine and supplied to the load resistor. The Heat

Engine digits display shows the heat that has flowed out of the hot reservoir (Qhot) and the heat

that has flowed into the cold reservoir (Qcold).

Continue to record until the aluminum blocks are close to the same temperature.

Analysis

Heat Pump Mode

In Heat Pump mode the peltier does work to pump heat out of the cold reservoir

and into the hot reservoir.

W = work done by the peltier (equal to the area under the Input Power curve),

Qhot = heat pumped into the hot reservoir,

Qcold = heat pumped out of the cold reservoir.

By the first law of thermodynamics,

Qhot = Qcold + W

1) Where did the heat pumped out of the cold reservoir go? Where did the heat pumped into the

hot reservoir come from? Why was more heat pumped into the hot reservoir than was pumped

out of the cold reservoir?

2) Compare your observed values of (Qcold + W) and Qhot. If they are not equal, where did the

“lost energy” go?

3) Write an equation in terms of the “lost energy”, Elost, and your observed data, W, Qhot and

Qcold.

Heat Engine Mode

In a heat engine, heat flows out of the hot reservoir, some of the heat is

converted to work, and the rest of the heat flows into the cold reservoir.

W = work done by the heat engine,

Qhot = heat flow out of the hot reservoir,

Qcold = heat flow into the cold reservoir.

By the first law of thermodynamics,

Qhot

W

Qcold

Hot Reservoir

Cold Reservoir

Heat Pump

Qhot

W

Qcold

Hot Reservoir

Cold Reservoir

Heat Engine

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Model No. ET-8782 Experiment 1: Conservation of Energy and the First Law of Thermodynamics

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W = Qhot – Qcold

4) Compare your observed value of work, Wobserved (which is the area under the Power vs. Time

plot) to the quantity Qhot – Qcold. Are they equal?

5) In a real heat engine, only part of the heat that flows out of the two-reservoir system

(Qhot – Qcold) is converted to useful work. In this experiment, the work that you observed (the

useful work) was the work done on the load resistor. Can you account for all of the energy

that flowed out of the hot reservoir with your values of Wobserved, Qhot and Qcold? If not, where

did the “lost energy” go?

6) Calculate the proportion of net heat flow from the aluminum blocks that was converted to

useful work;

7) Write an equation in terms of the “lost energy”, Elost, and your observed data, Wobserved, Qhot

and Qcold.

8) In this experiment the “useful work” was the work done on the load resistor. What was the

result of doing work on the resistor? How could you modify the circuit in order to make better

use of the work done by the heat engine?

Conservation of Energy

In the Heat Pump phase of the cycle the power supply put energy into the system. Then, in the

Heat Engine phase heat flowed out of the hot reservoir and part of it was converted into electrical

energy, which was supplied to the load resistor.

9) Calculate the percentage of energy put in during the Heat Pump phase that was recovered as

useful work during the Heat Engine phase;

10) Is this a good way to store energy?

Conduction and Heat Flow Through the Insulators

One of the losses of energy in this experiment has to do with heat flow by conduction through the

polyethylene foam insulators. The rate of heat flow through the insulator is

where:

% of useful workWobserved

Qhot Qcold–---------------------------- 100 %×=

% recoveredenergy generated

energy put in----------------------------------------- 100 %×=

Qi t⁄ kAT∆

x-------=

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Energy Transfer–Thermoelectric Conservation of Energy and the First Law of Thermodynamics

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Q i/t = heat flow rate through the insulator,

k = thermal conductivity of the polyethylene foam = 0.036 W/(m·°C),

A = area through which the heat flows,

∆T = temperature difference across the insulator,

x = thickness of the insulating material.

You will estimate the amount of heat that flowed through the foam in contact with the front face

of the cold block.

Measure the height and width of the cavity in the insulator that surrounds the aluminum

block. Calculate the cross-sectional area, A in m2.

Measure the thickness, x, of the foam that covers the front face of the block. Do not include the

sides of the foam (you are only calculating the heat flow through the front face). Record your

measurement in meters.

From the temperature graph, determine the difference, ∆T, between the temperature of the cold

block and room temperature. This value changed during the experiment, so record the maximum

difference, when the cold block was at its coldest. This will give you an estimate of the maximum

heat flow rate through the insulator.

11) Calculate the heat flow rate through the foam, Q i/t. This is the heat flow rate in joules/second.

To find the total amount of heat in joules, multiply this number by the total time in seconds

that the experiment ran; Qi = (heat flow rate) × (time).

12) How does your estimate of Q i compare to the heat, Qcold, that was pumped out of the cold

block in the Heat Pump phase? Is it much larger, much smaller, or similar?

13) Is your estimate of heat flow through the insulator too high or too low? Remember that you

ignored the sides in your estimate, and that you used the maximum temperature difference for

∆T.

14) How would the flow of heat through the insulator on the hot side compare to heat flow

through the insulator on the cold side? Consider both the magnitude and direction of heat

flow.

15) Is heat flow through the insulators (on the hot and cold sides) a significant factor in this

experiment? Could the heat flow through the insulators account for the discrepancy between

your observed results and the first law of thermodynamics?

16) How would your results have differed if you had not used the insulators?

Further Investigation

What are some factors that you could vary in the experimental apparatus and procedure? Predict

how changing those factors would affect the results. Do an experiment to test one of your

predictions.

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Model No. ET-8782 Energy Transfer–Thermoelectric

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Experiment 1:

Teachers’ Notes–Conservation of Energy

and the First Law of Thermodynamics

This sample data is in the file “Conservation of Energy Data”.

Heat Pump Mode

Qhot = 172.8 J

Qcold + W = 233.1 J

1) Most of the heat pumped out of the cold reservoir went into the hot reservoir. The heat

pumped into the hot reservoir is greater than the heat pumped out of the cold reservoir

because Qhot also includes the work done by the peltier.

2) Qhot < Qcold + W. Some energy was lost. Part of it flowed through the insulator to the

environment. Part of it was dissipated in other parts of the circuit.

3) Qhot = Qcold + W – Elost

Heat Engine Mode

Wobserved = 0.572 J

Qhot – Qcold = 3.3 J

4) Wobserved < Qhot – Qcold

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Energy Transfer–Thermoelectric Teachers’ Notes–Conservation of Energy

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5) Most of the heat that flowed out of the two-reservoir system was lost. Some of it flowed

through the foam insulators to the environment. Some of it was dissipated in other parts of the

circuit.

6)

7) Wobserved = Qhot – Qcold – Elost

8) The result of doing work on the resistor was that the resistor dissipated heat to the

environment. For a more practical use of the useful work, the resistor could have been

replaced with a light bulb, an electric motor, or some other electrical device.

Conservation of Energy

9)

10) This is not a good way to store energy.

Conduction and Heat Flow Through Insulator

11)

Q i = (0.031 J/s) × (150 s) = 4.6 J

12) Q i is small compared to Qcold.

13) This is an estimate of the heat that flowed from the outside air, through the insulator, and into

the front face of the aluminum block on the cold side. Some more heat flowed in through the

sides that we ignored. Q i is likely an overestimate because the actual temperature difference

was not always as large as the ∆T that was used in the calculation, and the surface area of the

front face is larger than that of the sides.

14) Heat flow through the insulator on the hot side would be larger in magnitude because there

was a greater temperature difference between the block and the outside air. Since the block

was hotter than the air, heat would have flowed out to the environment.

15) The amounts of “lost energy” in the Heat Pump and Heat Engine phases were 12.5 J and 2.7 J.

The estimate of Q i suggests that heat flow through the insulators was a significant

contribution to this unaccounted-for energy. Another possible contribution to the lost energy

is heat dissipated by other components of the circuit, especially the material inside the peltier.

16) Without the insulators, it is likely that the net heat flow to the environment would have been

greater, thus increasing the amount of lost energy.

% of useful work0.572 J( )

3.3 J( )---------------------- 100 %× 17 %= =

% recovered0.572 J

60.3 J----------------- 100 %× 0.9 %= =

Qi t⁄ 0.36 W/(m·°C)[ ] 0.033 m( ) 0.037 m( )×[ ]7 °C( )

0.01 m( )---------------------×× 0.031 J/s= =

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Model No. ET-8782 Energy Transfer–Thermoelectric

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Experiment 2:

Load Resistance and Efficiency

Introduction

In this experiment you will examine the relationship between output load resistance and the

power generated by the peltier when it is operating in heat engine mode.

You will observe the output power as you vary the load resistance while keeping everything else

constant (the temperature difference between the blocks, for instance). Since it is not possible to

hold the blocks at a steady temperature difference, you will take the peltier through several

identical cycles of heating and cooling, and measure the power each time a certain temperature

difference occurs. You will repeat the cycle for each value of load resistance that you test, ranging

from slightly over 0 Ω to 30 Ω.

Before you start, predict what you will discover about the relationship between output power and

load resistance. Record your prediction using words, numbers and a graph. Explain your

reasoning.

Set-Up

1. Input Power: Set the Heat Pump/Heat Engine switch to the neutral position (straight up).

Connect the power supply using banana patch cords to the input power terminals on the

circuit board as shown in picture. Note the polarity.

Equipment Required Part Number

Thermoelectric circuit board part of ET-8782

Foam insulators (qty. 2) part of ET-8782

Heat sink and thumbscrew part of ET-8782

Banana patch cords (qty. 6) part of ET-8782

Temperature cables (qty. 2) part of ET-8782

DC Power Supply (10 V, 1 A minimum) SE-9720A or equivalent

PASPORT Voltage/Current Sensor PS-2115

PASPORT Quad Temperature Sensor PS-2143

PASPORT interface(s) PS-2001 or equivalent

DataStudio software See PASCO catalog

“Load Efficiency” configuration file for DataStudio part of ET-8782

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Energy Transfer–Thermoelectric Load Resistance and Efficiency

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2. Temperature:

Connect the

cables from the

temperature ports

to the Quad

Temperature

Sensor. Connect

the Cold Side to

Channel 1 of the

sensor and the Hot

Side to Channel 2.

3. Voltage: Connect

the voltage leads

of the Voltage/

Current Sensor to

the Voltage Ports

on the board. Note

the polarity.

4. Current: Connect

separate red and black banana patch cords from the current input of the Voltage/Current

sensor to the Current Ports on the board. Note the polarity.

5. Computer: Connect the sensors to the computer through the PASPORT interface. Open the

pre-configured DataStudio file “Load Efficiency”. The display should look as shown below.

PowerSupply

Voltage/CurrentSensor

TemperatureSensor

Ch 1

Ch 2

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Background

This section explains some of the details of the DataStudio configuration file.

Calculations: DataStudio will measure the temperature of both blocks (Thot and Tcold), the voltage

across the load resistor, and the current through the load resistor. From these measurements it will

make two calculations, temperature difference (∆T) and output power (P), using the following

equations:

∆T = Thot – Tcold

P = current × voltage

Start and Stop Conditions: DataStudio has been configured with start and stop conditions, which

control when it records data. The start condition is that ∆T must drop below 35 °C. Before the

beginning of each cycle (when ∆T < 35 °C) you will click the Start button; DataStudio will display

live data, but it will not start recording. Data recording will not start until the ∆T has increased

above 35 °C and then dropped back below that level. The start condition will enable you to view

the temperature measurements without recording them. The stop condition will cause data

recording to stop when ∆T drops below 5 °C.

Changing the Name of a Data Run: DataStudio will record a separate data run for each load

resistance. In order to keep track of them, you will rename each data run. By default, the runs are

named Run #1, Run #2, etc. In order to rename a run, find it in the Summary window (on the left

side of the screen), click on it once to select it, then click on it again to edit it (be careful to single-

click twice, and not to double-click). Enter the new name (for instance, “7 ohms”). When

DataStudio asks if you would like to rename all the data from this run, select Yes.

Procedure

1. Click the Start button. DataStudio will show live temperature readings in the Digits display,

but it won’t start recording yet.

2. Observe the temperature of both sides of the peltier; both should be close to room

temperature. During the experiment, you will take the peltier through several cycles of

heating and cooling. You must ensure that both sides of the peltier are close to room

temperature before each cycle starts. Note the room temperature for future reference.

3. Set the voltage on power supply to about 6 volts. Set the switch to Heat Pump mode for about

2 seconds, then return it to the neutral position. If the voltage/current sensor beeps, then the

current is too high (over 1 amp) and you should decrease the voltage (then close the switch

again to test it).

4. Set the switch to the Heat Engine position and allow the blocks to cool. Wait until both sides

are within a few degrees of room temperature. (To cool faster, install the heat sink on the hot

block and turn on the cooling fan. It also helps to put a metal object in contact with both

blocks.)

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Energy Transfer–Thermoelectric Load Resistance and Efficiency

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5. Connect the output load jumper to terminal D. This bypasses all of the resistors and reduces

the load resistance to almost zero. Note that the resistance is not exactly zero because the

wires and traces on the board have some resistance.

6. Place both insulators on the blocks.

7. Set the switch to Heat Pump mode. Watch the difference in temperature between the two

blocks (∆T). You are waiting for ∆T to reach 35 °C, which will take about one minute.

8. When ∆T reaches 35 °C, change the switch to Heat Engine Mode. The temperature difference

will start to decrease. When ∆T drops below 35 °C, DataStudio will automatically start

recording. You will see data appear on the graph of Power Generated vs. ∆T.

9. When ∆T drops below 5 °C, data recording will stop automatically.

10. Change the name of the data run to indicate the load resistance.

11. Click Start. DataStudio will display temperature data, but it won’t start recording yet.

12. Remove the insulators and use the fan and heat sink to cool the blocks to within a few degrees

of room temperature.

13. Change the output load to 3 Ω (connect the jumper to terminal C).

14. Replace the insulators and repeat the cycle of heating and cooling. (Go back to step 7.)

15. Repeat the cycle again for the following values of output load:

• 7 Ω (Connect the jumper to B, but also connect a shorting jumper from C to D.)

• 10 Ω (Connect the jumper to B.)

• 20 Ω (Connect the jumper to A, but also connect a shorting jumper from B to D.)

• 30 Ω (Connect the jumper to A.)

When you are finished, you will have acquired power and temperature data for six different

values of output load resistance.

Analysis

From the data that has been recorded you will extract the data needed to plot a graph of Power

Generated (P) versus Load Resistance (RL) at ∆T = 30 °C.

On the graph of P vs. ∆T use the smart cursor to read the power generated at ∆T = 30 °C for each

value of load resistance. (Use the zoom select tool to change the scale of the graph and enlarge the

area around the data at 30 °C in order to read the data precisely.)

Enter the values in the Power vs. Load table. As you enter data into the table, they will be plotted

on the Power vs. Load Resistance graph.

1) At what value of RL is the maximum power generated?

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Model No. ET-8782 Experiment 2: Load Resistance and Efficiency

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2) For output loads less than and greater than the optimal value, why does the peltier generate

less power?

All real electrical power supplies (including the peltier heat engine) have an internal resistance,

Ri. They can be modeled as an ideal voltage source in series with a resistor, as shown below (with

an output load connected).

The voltage of the ideal voltage source, VNL, is called the no-load voltage. For a peltier heat

engine VNL depends only on ∆T.

3) Under what condition does the output voltage (Vout) equal VNL?

4) How would you directly measure VNL at ∆T = 30 °C?

5) Write a theoretical equation for output power, P, in terms of VNL, Ri and RL. Make a graph of

P vs. RL (choose some arbitrary values for VNL and Ri). Based on your equation and graphs,

under what condition is P at its maximum?

6) In this experiment, one of the data points was taken with RL = 0. According to your equation,

what is the theoretical power generated when RL = 0? Was this the case in your experiment?

There is another source of resistance that we haven’t considered yet, which is the resistance of the

traces, leads and sensors in the circuit. Let’s call it RT. If we add in RT, the circuit can be modeled

thus:

7) Rewrite the theoretical equation for P taking RT into account.

8) Fit this equation to your experimental data. What is the no-load voltage at ∆T = 30 °C? What

is the internal resistance of the peltier? What is RT?

Further Investigation

1. Make a direct measurement of the no-load voltage at ∆T = 30 °C.

2. Make a direct measurement of RT (or measure as much of it as possible).

PeltierHeat Engine

VNL

RiRLVout

+

+

PeltierHeat Engine

VNL

RiRLVout

+

+

RT

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Energy Transfer–Thermoelectric Load Resistance and Efficiency

22 ®

3. Predict how your results would differ if you repeated your analysis for a different value of

∆T? Test your prediction.

4. For your graph of Power vs. Load Resistance, what did you do to ensure that only RL and P

varied, and that all other experimental parameters stayed constant? Evaluate how successful

these measures were. Discuss how you could improve them.

5. In the analysis we assumed that Vout was constant for all values of ∆T = 30 °C. Do an

experiment to test that assumption.

6. For any given output load, quantitatively describe the relationship between P and ∆T.

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Model No. ET-8782 Energy Transfer–Thermoelectric

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Experiment 2:

Teachers’ Notes–Load Resistance and Efficiency

This sample data is in the file “Load Efficiency Data”.

For instructions on using the Smart Tool and Zoom Select in the graph display, click on the

DataStudio Help menu, select Search and look up those terms in the Index.

1) Power generated was greatest for RL = 7 Ω.

2) For other values of RL, the peltier generated less power because the load resistance did not

match the internal resistance.

3) Vout = VNL when there is no load connected (or when RL = ∞).

4) To measure VNL, run the cycle with all of the load resistors disconnected, (or leave the knife

switch open for the cooling phase).

5) PVNL

2RL

Ri RL+( )2

-------------------------=

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Energy Transfer–Thermoelectric Teachers’ Notes–Load Resistance and Efficiency

24 ®

6) Theoretically P = 0 when RL = 0. Experimentally this was not the case.

7)

8) Experimental data with curve fit:

RL (W)

P (

W)

Max P when

RL = Ri

Theoretical P vs. RL

(with arbitrary values)

VNL = 10 V

R i = 5 Ω

PVNL

2RL RT+( )

Ri RL RT+ +( )2

--------------------------------------=

RL (W)

P (

W)

VNL = 1.49 ± 0.1 V

R i = 7.4 ± 0.1 Ω

RT = 0.90 ± 0.04 Ω

Root MSE = 0.011 W

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Experiment 3:

A Model Refrigerator

Introduction

In this activity you will use the peltier device to model a refrigerator. As you run your model

refrigerator, DataStudio will display the voltage and current supplied to the peltier, the

temperature of both blocks, and the temperature of the air flowing past the heat sink. You will use

these measurements to investigate some of the factors that affect the temperature of a refrigerator

Set-Up

1. Input Power: Set the Heat Pump/Heat Engine switch to the neutral position (straight up).

Connect the power supply using banana patch cords to the input power terminals on the

circuit board. Note the polarity.

2. Insulator: Place a foam insulator on the aluminum block on the Cold Side of the peltier.

3. Block Temperature: Connect the cables from the temperature ports on the circuit board to the

Quad Temperature Sensor. Connect the Cold Side to Channel 1 of the sensor and the Hot Side

to Channel 2.

4. Air Temperature: Set up two Fast Response Temperature Probes to measure the temperature of

the air before and after it flows through the heat sink. Use the temperature clamps to position the

probes below and above the heat sink (as shown in the picture). The probes should not touch the

Equipment Required Part Number

Thermoelectric circuit board part of ET-8782

Foam insulator part of ET-8782

Heat sink and thumbscrew part of ET-8782

Banana patch cords (qty. 4) part of ET-8782

Temperature cables (qty. 2) part of ET-8782

Fast Response Temperature Probes (qty. 2) PS-2135 (3-pack)

DC Power Supply (10 V, 1 A minimum) SE-9720A or equivalent

PASPORT Voltage/Current Sensor PS-2115

PASPORT Quad Temperature Sensor PS-2143

PASPORT interface(s) PS-2001 or equivalent

DataStudio software See PASCO catalog

“Refrigerator” configuration file for DataStudio part of ET-8782

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Energy Transfer–Thermoelectric A Model Refrigerator

26 ®

heat sink or the aluminum block. Connect the probe below the heat sink to Channel 3 of the Quad

Temperature Sensor; connect the other probe to Channel 4.

5. Voltage: Connect the voltage leads of the Voltage/Current Sensor to the Voltage Ports on the

board. Note the polarity.

6. Current: Connect separate red and black banana patch cords from the current input of the

Voltage/Current sensor to the Current Ports on the board. Note the polarity.

7. Computer: Connect the sensors to the computer through the PASPORT interface. Open the

pre-configured DataStudio file “Refrigerator”. The display should look as shown below.

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Model No. ET-8782 Experiment 3: A Model Refrigerator

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Procedure

As you follow this procedure take notes of your observations and write down the answers to the

questions.

1. Put the knife switch in the neutral position (straight up). Set the DC Voltage to about 6 volts.

2. Turn on the fan.

3. Start data recording. Set switch to Heat Pump mode. (Check that the current is not more than

1 amp; if it is, the sensor will beep and you should open the switch, decrease the applied

voltage, then close the switch again.)

4. Observe the temperatures of the hot and cold sides of the peltier device. Which side has the

bigger temperature difference from room temperature? Why are they not the same?

5. Let the refrigerator run in this mode for at least 5 minutes while the temperatures reach

equilibrium. Meanwhile, continue on to the next section.

Air Flow and Heat Transfer

6. Observe the air temperatures below and above the heat sink. By how much does the air

temperature increase when it passes through the heat sink? This increase in temperature is

caused by the heat flowing from the heat sink to the air.

You will now estimate the rate of heat transfer from the heat sink to the air. For a gas, we can write

Q = nc∆T

where, in this experiment:

Q = heat transferred from the heat sink to the air (in joules),

n = number of moles of air (not the mass),

∆T = change in temperature of the air,

c = specific heat of air.

The specific heat of a gas depends on whether it is heated at constant volume or constant pressure.

In this case the air is heated at constant pressure, so the specific heat is cair = 29.1 J/(mol·°C).

The manufacturer's specification for the air flow generated by the fan is about 2 liters per second.

At room temperature, one mole of gas occupies about 24.3 liters, so in one second the quantity of

gas is

7. After the temperatures of the hot and cold blocks have stabilized, calculate the heat, Q,

transferred to the air every second. Is your estimate likely too high or too low? Explain your

reasoning.

The power supplied to the heat pump is

n2 L

24.3 L/mol--------------------------- 0.082 mol= =

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Energy Transfer–Thermoelectric A Model Refrigerator

28 ®

P = IV

where:

P = power (in watts = joules/second),

I = current (in amps),

V = voltage (in volts).

8. From the measured values of applied voltage and current, calculate the energy used to run the

heat pump for one second. How does the energy supplied to the peltier every second compare

to your estimate of the heat transferred from the heat sink to the air every second? Which is

bigger? Explain your observations in terms of conservation of energy.

Insulator, Fan and Heat Sink

9. When the hot and cold blocks have reached equilibrium, write down the temperatures. Did

you make a good refrigerator?

10. Remove the foam insulator (continue recording data). Can you see a change in the cold

temperature? Put the foam insulator back on. Why did the temperature change?

11. Turn off the fan (continue recording data). Observe the effect on the temperatures for a few

minutes. How have the temperatures of both sides changed? How has the temperature

difference between the hot and cold sides changed? Can you explain why?

12. Observe the air temperatures. Have they changed from when the fan was on? Do you think

that the rate of heat transferred from the heat sink to the air has increased, decreased, or

stayed the same? Explain your reasoning.

13. If the blocks were allowed to reach equilibrium with the fan off, what do you think the final

temperature of the “cold” block would be? Would that represent a good refrigerator?

14. Before the hot side reaches 80 °C open the knife switch or turn the fan back on.

15. What part of a real refrigerator is represented by the cold block on your model?

16. In general terms, what does a refrigerator do to make the inside cold? Why does it need

insulation? Why does it need a heat sink?

Further Investigation

1. Let the refrigerator run for several minutes with the insulator removed and the fan switched

on. What is the equilibrium temperature of the cold block in this mode?

2. Without increasing the power supplied to the peltier, can you make the cold side colder?

Propose a modification to your model refrigerator and do an experiment to test it.

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Experiment 3:

Teachers’ Notes–A Model Refrigerator

This sample data is in the file “Refrigerator Data”.

The data shown in the digits displays occurred at Time = 5 minutes.

Answers to Questions

(Step 4) The hot side of the peltier has a larger temperature difference from room temperature than

the cold side. Once equilibrium is reached, the heat being pumped out of the cold block is equal to

the heat flowing into it from its surroundings. The heat flowing out of hot block is equal to the

heat pumped out of the cold block plus the work done by the peltier. Since the heat flow rate out

of the hot block is higher than the heat flow rate into the cold block, and heat flow rate is

proportional to temperature difference, the hot block must have a higher temperature difference.

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Energy Transfer–Thermoelectric Teachers’ Notes–A Model Refrigerator

30 ®

Air Flow and Heat Transfer

∆T = 2.6 °C

Q = (0.082 mol) [29.1 J/(mol·°C)] (2.6 °C) = 6.2 J (every second)

(Step 7) This estimate is likely to be high because we are measuring the air that goes straight

through the heat sink. Much of the air from the fan misses the heat sink, so the average

temperature rise for all of the air from the fan would be less than 2.6 °C.

P = (0.60 A) (7.1 V) = 4.3 J/s

(Step 8) The energy supplied to the peltier every second is less than the estimate of energy

transferred to the air by the heat sink. According to conservation of energy, they would be the

same if all of the heat lost by the system were transferred to the air through the heat sink. In fact,

some heat is lost through radiation, and through other parts of the system. It is likely that most of

the discrepancy between Q and P is due to error in the estimate of Q.

Insulator, Fan and Heat Sink

(Step 9) With the cold block at 5 °C (or 18 °C below room temperature) the model represents an

effective refrigerator.

(Step 10) With the insulator removed, the temperature of the cold block increases due to increased

heat flow from the air to the block.

(Step 11) With the fan turned off, the temperature of the hot block increases because the rate of

heat transfer to the air decreases. The temperature of the cold block increases at a similar rate.

The temperature difference between the blocks increases from 41 °C to 47 °C within 3 minutes of

the fan switching off, after which the difference decreases slowly.

As the hot block gets hotter and the temperature difference between the blocks increases, the

tendency for heat to flow from the hot block to the cold block by conduction increases, canceling

the heat-pumping effect of the peltier.

(Step 12) When the fan is turned off the temperature change of the air flowing through the heat

sink increases to about 10 °C. Since the hot block gets hotter, it is evident that the rate of heat

transfer to the air has decreased. The increased temperature change is due to the decreased air

flow.

(Step 13) With the fan turned off, the “cold” block would stabilize at about 40 °C. That is higher

than room temperature, so it would not be a good refrigerator.

(Step 15) The cold block corresponds to the interior of a real refrigerator.

(Step 16) A refrigerator makes the interior cold by pumping heat out of it. It needs insulation to

reduce the rate of heat flow back into it from the surrounding air. It needs a heat sink to transfer

away the heat that it has pumped out of the interior, and the heat resulting from the work that it

does.

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Experiment 4:

Coefficient of Performance

Introduction

Some heat pumps, such as refrigerators and air conditioners, are used for their cooling effect.

They pump heat out of a container or a building, making the interior cooler than the surrounding

environment. But a heat pump can also be used to pump heat into a building, making the interior

warmer than the surrounding environment.

An important property of a heat pump is how much energy it uses to move a certain amount of

heat. In this activity you will measure the Coefficient of Performance of a heat pump working in

both modes, and discover how a heat pump can be more efficient at heating a building than

conventional methods.

Set-Up

1. Input Power: Set the Heat Pump/Heat Engine switch to the neutral position (straight up).

Connect the power supply using banana patch cords to the input power terminals on the

circuit board as shown in picture. Note the polarity.

2. Heat Sink and Insulator: Attach the heat sink to the aluminum block on the Hot Side of the

peltier. Place a foam insulator on the other block.

Equipment Required Part Number

Thermoelectric circuit board part of ET-8782

Foam insulator part of ET-8782

Heat sink and thumbscrew part of ET-8782

Banana patch cords (qty. 4) part of ET-8782

Temperature cables (qty. 2) part of ET-8782

DC Power Supply (10 V, 1 A minimum) SE-9720A or equivalent

PASPORT Voltage/Current Sensor PS-2115

PASPORT Quad Temperature Sensor PS-2143

PASPORT interface(s) PS-2001 or equivalent

DataStudio software See PASCO catalog

“Coeff of Performance” configuration file for DataStudio part of ET-8782

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32 ®

3. Temperature: Connect the cables from the temperature ports on the circuit board to the Quad

Temperature Sensor. Connect the Cold Side to Channel 1 of the sensor and the Hot Side to

Channel 2.

4. Voltage: Connect the voltage leads of the Voltage/Current Sensor to the Voltage Ports on the

board. Note the polarity.

5. Current: Connect separate red and black banana patch cords from the current input of the

Voltage/Current sensor to the Current Ports on the board. Note the polarity.

6. Computer: Connect the sensors to the computer through the PASPORT interface. Open the

pre-configured DataStudio file “Coeff of Performance”. The display should look as shown

below.

PowerSupply

Voltage/CurrentSensor

TemperatureSensor

Ch 1

Ch 2

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Background

DataStudio has been configured to measure and record the temperature of both aluminum blocks,

and the voltage and current applied to the peltier. From these measured quantities, DataStudio will

calculate and display heat flow, power and work. The following sections explain how DataStudio

makes these measurements and calculations.

Heat vs. Temperature

The digits displays show the heat that flows into the hot block (Qhot) and out of the cold block

(Qcold). The relationship between heat flow and temperature change is given by

Q = mc∆T

where:

Q = heat transferred,

m = mass of the aluminum block,

c = specific heat of aluminum = 0.90 J/(g·°C),

∆T = change in temperature.

A positive value of Qhot represents heat flowing into the hot block, but a positive value of Qcold

represents heat transferred out of the cold block.

The temperature of each block is measured by the embedded thermistor. DataStudio calculates the

heat flow from the measured temperature change, and pre-entered values of m and c. Click on the

calculator icon in the tool bar and look at the equations used; note the constants, m and c, in the

bottom section of the calculator window. (The mass of each block is about 19 g. If you would like

to enter your own value for the mass, measure the blocks with calipers and use the density of

aluminum, 2.7 g/cc, to calculate the mass, then enter it in the calculator.)

Input Power and Work Done by the Peltier

Input Power from the power supply equals the rate at which the peltier does work to pump heat

out of the cold reservoir and into the hot reservoir. The Voltage/Current Sensor measures the

voltage applied to the peltier, and the current that flows through it. DataStudio calculates the Input

Power using the equation: Power = Voltage × Current.

The area under the plot of Input Power versus time equals the energy supplied to the peltier, which

equals the work, W, done by the peltier.

Start Condition

The configuration file contains a start condition; when you click the Start button (with the knife

switch open) DataStudio will display live data, but it will not start recording until you close the

knife switch. This will allow you to monitor the measurements and confirm that both blocks are at

the same temperature before data recording starts.

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Procedure

Refrigerator

Before you start, the knife switch should be in the neutral position (straight up) and the fan should

be switched off. Make sure that the foam insulator is on the cold block, and that the heat sink is on

the hot block.

Set the DC Voltage to about 5 volts.

Click the Start button.

Observe the temperatures of the hot and cold blocks; they should be within 0.1 °C of each other.

(If they are not, turn on the fan and wait until the temperatures have equalized. Then turn the fan

off and proceed.)

Set the knife switch to Heat Pump mode. Allow the heat pump to run for 10 to 15 seconds, then

open the switch. Watch the temperature graphs; once the temperatures have peaked out, stop data

recording. You need to give the blocks a few seconds to reach a maximum or minimum before

you stop recording.

Heat pumps are rated by the Coefficient of Performance, k. In the case of a heat pump used for

cooling (such as a refrigerator) the Coefficient of Performance is

(for cooling)

The Coefficient of Performance expresses how much heat the heat pump removes from the cold

side compared to how much energy it uses to move the heat.

1) Use your values for the heat pumped out of the cold block (Qcold) and the area under the

Power versus time curve (W) to calculate the Coefficient of Performance, k, for your model

refrigerator.

2) For real heat pumps k is usually expected to be greater than 1. Is this the case for your model?

3) Your heat pump can also be thought of as a model air conditioner, a device used to keep the

inside of a building cooler than the outside air. In terms of moving heat, what does an air

conditioner do to keep a building cool? (Keep in mind that an air conditioner does not

necessarily move air into or out of the building.)

4) Compare your model to a building being cooled by an air conditioner. What does the peltier

represent? What does the cold block represent? What does the hot block represent?

5) If you were selecting an air conditioner to keep your home cool, would you choose one with a

high or low coefficient of performance? Explain why.

kQcold

W------------=

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Reversible Heat Pump

A certain kind of air conditioner, known as a reversible heat pump, can also be used to heat a

building. You will now use the peltier to model a reversible heat pump being used to keep a

building warmer than the surrounding air.

Place the heat sink on the cold block, and the foam insulator on the hot block.

Delete the data that you have previously recorded. (Click on the Experiment menu and select

Delete All Data Runs.)

Click the Start button. Make sure that the hot and cold blocks are within 0.1 °C of each other

before proceeding. (If they are not, remove the insulator, turn on the fan and wait for the

temperatures to equalize. Then turn off the fan, replace the insulator and proceed.)

Set the switch to Heat Pump mode. Allow the heat pump to run for 10 to 15 seconds, then open

the switch. Watch the temperature graphs; once the temperatures have peaked out, stop data

recording.

For a reversible heat pump heating a building, we are interested in the heat pumped into the

building, Qhot. (This is opposed to the previous case where we were interested in the heat pumped

out of the building.) Thus the Coefficient of Performance is

(for heating)

6) Use your values for the heat delivered to the hot block (Qhot) and the area under the Power

versus time curve (W) to calculate the Coefficient of Performance, k.

7) If you had used a simple resistor (rather than the peltier) to heat the aluminum block, and used

the same amount of energy (W), what would have been the maximum amount of heat

transferred to the block?

8) Compare your model to a building being heated by a reversible heat pump. What does the

peltier represent? What does the cold block represent? What does the hot block represent?

9) Why is it important for k to be greater than 1 for a reversible heat pump? Compare this to a

simple electrical heater. How much heat is delivered to a building using a simple heater

supplied with 100 J of electrical energy? How much heat is delivered to a building using a

heat pump, with k = 2, that uses 100 J of electrical energy to pump heat from outside to inside

the building?

Further Investigation

Think of a factor that you can vary in the experimental set-up. Predict how varying that factor

would affect the coefficient of performance in heating or cooling mode. Do an experiment to test

your prediction.

kQhot

W----------=

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Energy Transfer–Thermoelectric Coefficient of Performance

36 ®

Page 37: Energy Transfer– Thermoelectric · Energy Transfer–Thermoelectric Introduction 8 ® 9. Temperature Sensor Clamps When modeling a refrigerator it is useful to observe the heat

Model No. ET-8782 Energy Transfer–Thermoelectric

37®

Experiment 4:

Teachers’ Notes–Coefficient of Performance

Refrigerator

This sample data is in the file “Coeff of Performance Data Refrig”.

1)

2) This coefficient of performance is similar to that of real heat pumps.

3) An air conditioner pumps heat out of the building and into the outside air.

4) The peltier represents the heat pump, the cold block represents the interior of the building,

and the hot block represents the outside air.

5) You would choose an air conditioner with a high coefficient of performance because it would

use less energy to remove heat from the building (and cost less to run).

k76.0 J

47.8 J-------------- 1.59= =

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Energy Transfer–Thermoelectric Teachers’ Notes–Coefficient of Performance

38 ®

Reversible Heat Pump

This sample data is in the file “Coeff of Performance Data Heat Pump”.

6)

7) If you used a simple resistor to heat the block with the same amount of work, the maximum

heat transferred to the block would be W = 48.4 J.

8) The peltier represents the heat pump, the cold block represents the outside air, and the hot

block represents the interior of the building.

9) The coefficient of performance must be greater than 1 in order for the heat pump to be more

efficient than a simple heater. A simple heater supplied with 100 J of electrical energy would

transfer 100 J of heat to the building. A heat pump with k = 2 supplied with 100 J of electrical

energy would transfer 200 J to the building.

Qhot = kW

k116.6 J

48.4 J----------------- 2.41= =

Page 39: Energy Transfer– Thermoelectric · Energy Transfer–Thermoelectric Introduction 8 ® 9. Temperature Sensor Clamps When modeling a refrigerator it is useful to observe the heat

Model No. ET-8782 Energy Transfer–Thermoelectric

39®

effic

iency (

%)

Carn

ot effic

iency (

%)

DT (°C)

Experiment 5:

Teachers’ Notes–Carnot Efficiency

With the electronic workbook

contained on the CD-ROM,

students will study the efficiency

of the peltier heat engine. They

will record data for ∆T, power

generated and heat flow, calculate

efficiency, and discover the

relationship between efficiency

and ∆T. Finally they will compare

the actual efficiency of the heat

engine to the Carnot efficiency.

Have your students open the

DataStudio file “Carnot Efficiency

Workbook” and follow the on-

screen instructions. As they go

through the electronic workbook

they should take notes and record

their answers to questions on paper.

You can find sample data in the file

“Carnot Efficiency Workbook with

Data”.

Equipment Required Part Number

Thermoelectric circuit board part of ET-8782

Foam insulators (qty. 2) part of ET-8782

Banana patch cords (qty. 5) part of ET-8782

Temperature cables (qty. 2) part of ET-8782

DC Power Supply (10 V, 1 A minimum) SE-9720A or equivalent

PASPORT Voltage/Current Sensor PS-2115

PASPORT Quad Temperature Sensor PS-2143

PASPORT interface(s) PS-2001 or equivalent

DataStudio software See PASCO catalog

“Carnot Efficiency Workbook” file for DataStudio part of ET-8782

Time (s)

Tem

pera

ture

(°C

)P

ow

er

Genera

ted (

mW

)

Page 40: Energy Transfer– Thermoelectric · Energy Transfer–Thermoelectric Introduction 8 ® 9. Temperature Sensor Clamps When modeling a refrigerator it is useful to observe the heat

Energy Transfer–Thermoelectric Teachers’ Notes–Carnot Efficiency

40 ®

Page 41: Energy Transfer– Thermoelectric · Energy Transfer–Thermoelectric Introduction 8 ® 9. Temperature Sensor Clamps When modeling a refrigerator it is useful to observe the heat

Model No. ET-8782 Energy Transfer–Thermoelectric

Safety

Read the instructions before using this

product. Students should be supervised by

their instructors. When using this product,

follow the instructions in this manual and all

local safety guidelines that apply to you.

Technical Support

For assistance with any PASCO product,

contact PASCO at:

Copyright and Warranty

Information

Copyright Notice

The PASCO scientific 012-08745A Energy

Transfer–Thermoelectric Instruction

Manual is copyrighted and all rights

reserved. However, permission is granted to

non-profit educational institutions for

reproduction of any part of this manual,

providing the reproductions are used only for

their laboratories and are not sold for profit.

Reproduction under any other

circumstances, without the written consent

of PASCO scientific, is prohibited.

Limited Warranty

For a description of the product warranty, see

the PASCO catalog.

Address: PASCO scientific

10101 Foothills Blvd.

Roseville, CA 95747-7100

Phone: (916) 786-3800

(800) 772-8700

Fax: (916) 786-3292

Web: www.pasco.com

Email: [email protected]

Page 42: Energy Transfer– Thermoelectric · Energy Transfer–Thermoelectric Introduction 8 ® 9. Temperature Sensor Clamps When modeling a refrigerator it is useful to observe the heat