Contoh laporan

SMK SHAHBANDARAYA, KLANG

PenilaianBerasaskanSekolah (PBS)

Physics Paper 4 (960/4)

THEME : Heat

TITLE : Determination Of Heat Conductivity Of Metals

GROUP MEMBERS : 1) James Tee Chow Sheng

2) Lee ZhiRhinn

TEACHER : Puan Fatimah Bt. MohdJamil

SCHOOL : SMK Shahbandaraya, Klang

CLASS : 6 (A) Zuhrah

1

INDEX

NO CONTENTS PAGE NO

1 Abstract 1

2 Introduction 3

3 Theory 4

4 Literature Review 5

5 Problem Statement 6

6 Objective 6

7 Methodology 8

8 Results and Observations 10

9 Discussion 11

10 Conclusion 12

11 Referencesand Bibliography 12

2

HEAT

Determination Of Heat Conductivity Of Metals

Abstract

Difference between heat and temperature in describing heat transfer problems,

we often makes the mistake of interchangeably using the terms heat and temperature.

Actually, there is a distinct difference between the two. Temperature is a measure of

the amount of energy possessed by the molecules of a substance. It is a relative

measure of how hot or cold a substance is and can be used to predict the direction of

heat transfer. The usual symbol for temperature is T. The scales for measuring

temperature in SI units are the Celsius a Kelvin temperature scales. On the other hand,

heat is energy in transit. The transfer of energy as heat occurs at the molecular level as

a result of a temperature difference. The usual symbol for heat is (q). Common units

for measuring heat are the Joule and calorie in the SI system.

What is Heat Transfer? Heat transfer is energy in transit due to temperature

difference. Whenever there exists a temperature difference in a medium or between

media, heat transfer must occur. The basic requirement for heat transfer is the

presence of temperature difference. There can be no net heat transfer between two

mediums that are at the same temperature. The temperature difference is the driving

force for heat transfer, just as the voltage difference is thedriving force for electric

current flow and pressure difference is the driving force for fluid flow. The rate of

heat transfer in a certain direction depends on the magnitude of the temperature

gradient (the temperature difference per unit length or the rate of change of

temperature) in that direction. The larger the temperature gradient, the higher the rate

of heat transfer.

3

1.0 Introduction

Heat conduction, also known as heat transfer is facilitated by mean of

molecular agitation. Molecules that are agitated create heat energy. This heat energy

is always transferred from a higher temperature to a lower temperature according to

the second law of thermodynamics. Taking different metal rods with the same

temperature on each end for example, the hot ends’s energy will transfer across the

rod to the cooler end, because the higher speed particles on the hotter end will collide

with the slower moving particles on the cooler end. These collisions will cause the

slower moving particles to move faster, thus transferring heart energy to the cooler

end. Some materials get warmer faster than others. Metal is a good conductor because

it takes heat quickly.

Diagram1 : Heat Conduction

Diagram2 : Heat Conduction

4

Diagram 3 : Heat Conduction

Metals are used in many of our everyday objects. The kitchen is full of

different metals: metal coil in heater, stainless steel sinks, silver spoons, and copper

pans. Pots and pans used for cooking are good examples of the properties of metal. At

room temperature metals are solid and sturdy with a high melting point so they can

withstand high temperatures without melting. When metals are heated up to their

melting points they become malleable, or shapeable. Pots and pans come in many

shapes and sizes but have one purpose, to transfer heat from the stove to the contents

inside. Metals have been used to manufacture cookware because of their ability to

conduct heat.

In this experiment, different types of metal rods (copper, brass, aluminium and

steel) are to be used to determine which metal rod has the highest heat conductivity.

5

1.1 Theory

The theory of heat transfer seeks to predict the energy transfer that may take

place between material bodies as a result of temperature difference. This energy

transfer is defined as heat. In conduction, heat is carried by means of collisions

between rapidly moving molecules closer to the hot end of a body of matter and the

slower molecules closer to the cold end. Some of the kinetic energy of the fast

molecules passes to the slow molecules, and as a result of successive collisions, heat

flows through the body of matter from the hot end to the cold end. Solids, liquids, and

gases all conduct heat. Conduction is poorest in gases because their molecules are

relatively far apart and so interact less frequently than in solids and liquids. Metals are

the best conductors of heat because some of their electrons are able to move about

relatively freely and can interact frequently by collisions. Thermal conductivity: Note

that a heat flow rate is involved, and the numerical value of the thermal conductivity

indicates how fast heat will flow. In general, thermal conductivity is strongly

temperature dependent. It has the units of watts per meter per Kelvin. Heat transfer by

conduction in a solid can be realized through the support of phonons, electrons and

photons. The individual contributions of these carriers widely depend on material and

its temperature.

6

2.0 Literature Review

Heat transfer from hot bodies such as steel, aluminum and other metals is

vitally important for a wide range of industries such as chemical, nuclear and

manufacturing. Heat transfer research related to conduction has been the source of

fundamental studies since the early work by Fourier (Fourier, 1820).Conduction is the

transfer of heat through a medium by virtue of a temperature gradient in the medium.

It is a microscopic–level mechanism, andresults from the exchange of translational,

rotational, and vibrational energy among the moleculescomprising the medium.

The first law of thermodynamics states that under steady conditions the rate of

heat flow will be constant. Second law of thermodynamics shows that the direction of

this flow is from the higher temperature surface to the lower one. These two

fundamental rules lead to Fourier’s law of general heat conduction:

dQd θ

=−kAdtdx

Where ‘dQ/dθ’ (quantity per unit time) is the rate of flow of heat, ‘A’ is the area at

right angles to the direction in which the heat flows, and -dt/dx is the rate of change of

temperature with the distance in the direction of the flow of heat, i.e., the temperature

gradient. The factor ‘k’ is called the thermal conductivity; it is a characteristic

property of material through which the heat is flowing and varies with temperature.

Problem Statement

7

There are variety of metal materials can be found in the earth. However, in

many metal industries and manufacturer, a problem has been raised which is on the

selecting the metal as the heat conductor especially in the making of the coil in water

heater. In this project, an experiment is to be carried out to determine which is the best

heat conductor to be selected as the coil in water heater.

Objective

The main objective is to determine the heat conductivity of metal rods. In this

experiment, it is how the various type of metal rods vary the time for the thumbtacks

to fall off the metal rod as happens in the metal coil of water heater whereby different

metals have the different heat conductivity which can affect the time taken for the

water to get heated.

Methodology

8

Experiment Setup

Model setup is used to represent the water heat used in kitchen. The metal rods

(copper, brass, aluminium and steel) are as the materials in the making heating coil in

water heater. As to function a water heater, electricity as the source supply is needed

in order for the heater to work, the Bunsen burner used in the experiment is taken to

represent the source supply which is the heat supply to enable the heat is transferred

throughout the metal rods. The clamps stands used is to hold the metal rods as a

holder is built to hold the heating coil in the water heater while the heat shield used is

for supporting purpose between the Bunsen burner and the thumbtacks. The uses of

stopwatches and thumbtacks are to determine the time for the thumbtacks to fall off

the metal rods as in real, time taken for the water to boil whereas the wax is used to

attach the thumbtacks to the metal rods.

Diagram 4 : Illustration of water heater with inner copper coil

Procedure

9

The wax is put in a small container and placed in the middle of the Pyrex dish

on a heat-proof mat. By using a potholder, the hot water is carefully poured around

the container until it is surrounded but does not float. The wax is left until the heat

from the hot water has caused it to soften.The softened wax is lifted out of the

container by using the spatula onto the cutting board. The softened wax is cut into

four pieces using the spatula. These pieces are used to attach five thumbtacks onto

one end of the metal rod about 2.5 cm apart which labelling A, B, C, D and E.

The experiment was setup as shown in the Diagram 4. A 25.0cm copper rod is

clamped at a distance of 25.0cm from the table and is supported horizontally by

holding it in one of the clamps at one end of the rod. The Bunsen burner is positioned

about 8.0 cm from this clamp and stand as shown in diagram above. Using the other

stand and two clamps, the heat shield is supported under the rod between the Bunsen

burner and the thumbtacks. The Bunsen burner is lighted and five stopwatches are

started at the same time when it began to heat the end of the copper rod on the side of

the screen away from the thumbtacks. The time taken for each thumbtack to fall off

the rod is taken and recorded. The processes are repeated again by replacing the

copper rod with brass rod, aluminium rod and steel rod. The experiment is repeated

again for all rods. All the data collected are recorded in the table below.

Diagram 5 : Heating the metal rod with attached thumbtacks

Results and Observations

10

Table 1 :Brass Rod

Table 2 : Copper Rod

Table 3 : Aluminium Rod

11

ThumbtackTime Taken For Thumbtack To Fall, T / (±0.1 s)

I II AverageA 108.5 102.1 105.3B 149.4 139.0 144.2C 204.6 197.2 200.9D 228.2 216.2 222.2E 291.6 280.4 286.0





Table 4 : Steel Rod

Table 5 : Average Time For Thumbtack To Fall From Each Metal Rod

12



Metal Rods

Average Time For Thumbtack to Fall, T' / (±0.1 s)A B C D E

Brass 105.3 144.2 200.9 222.2 286.0Copper 94.1 114.1 164.2 206.0 232.5

Aluminium 41.4 56.3 69.4 98.1 102.1Steel 165.2 273.0 390.1 520.7 547.0

A B C D E0

100

200

300

400

500

600

BrassCopperAluminiumSteel

Graph 1 : Average Time For Thumbtack To Fall From Each Metal Rod

13

Average Time For Thumbtack to Fall, T '/s

Thumbtack

Discussion :

Based on the results above, aluminium rod takes the shortest time for all

thumbtacks to fall off the rod. This can be explained by aluminium is a good heat

conductor because it allows heat to pass through it quickly. The rate of heat

conduction of aluminium is the highest among the metal rods causing delocalised

electron to move to the cold end and collides with a cold ion making it vibrates thus

heating up the cold end and thus the heat is transferred throughout the aluminium rod.

However, there are disadvantages in aluminium metal rod. One of the disadvantages

of aluminium is easily bent or change in shape when it is heated at high temperature.

Steel takes the longest time for all thumbtack to fall off the rod. This is simply

because the purer a metal is the higher is it's thermal conductivity, steel is made up of

components of iron and carbon and this means it has fairly poor conductivity,not even

as good as a pure metal.

Between copper and brass, copper is a better heat conductor. It is because

copper conducts heat more than brass because of the difference in how far the

delocalised electrons go before they hit the other electrons. Brass has an alloy

structure, an electron bounce off the irregularities in the arrangement of different

atoms and is thus not a good conductor.Further experiment could be studying how

impurities in different metals affect the conductivity.

14

Conclusion

In short, from this project, it is found that aluminium is the best heat

conductor among the metals as it takes the shortest time to heat up the rod. However,

due to its softness, aluminium is easily bent or change in shape at high temperature.

Thus, it is not suitable to be chosen as the heating coil in the water heat as it can

damage the heater. Hence, copper is the best choice of making of the coil in water

heater as it can conserve more energy because it transfers heat faster and boils the

water in shorter time and it is strong and long lasting to stand at high temperature.

References and Bibliography

Book

1.Glen E.Myers (January 1971). Analytical Methods in Conduction Heat

Transfer.Mcgraw-Hill College.

2. Kern, D. Q.,1950.Process Heat Transfer, McGraw-Hill Book.

3. Shah, R. K. and E. C. Subbaro,1988.Heat Transfer Equipment Design, Hemisphere

Publishing Co.

4. Welty, J.R., Wicks, C.E., and Wilson, R.E., 1984.Fundamentals of Momentum, Heat

and Mass Transfer, 3rd edition, John Wiley & Son.

5. GE Consumer & Industrial.A COMPARISON OF ALUMINUM VS. COPPER AS

USED IN ELECTRICAL EQUIPMENT. Retrieved from

http://www.geindustrial.com/Newsletter/Aluminum_vs_Copper.pdf

15

http://www.geindustrial.com/Newsletter/Aluminum_vs_Copper.pdf

Contoh laporan

Documents

Transcript of Contoh laporan