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DEVELOPMENT OF A CONSTANT TEMPERATURE BATH USING PHASE

CHANGE MATERIALS FOR LOW TEMPERATURE APPLICATIONS

A PROPOSAL SUBMITTED TO

SSN EDUCATIONAL TRUST

FOR

INTERNAL FUNDING

BY

B. SRIRAM (31509114050) III MECH

K. VINOTH KUMAR (31509114058) III MECH

N. ARUNACHALAM (31509114005) III MECH

A. PADMANATHAN (31509114304) III MECH

SUPERVISOR: Dr. N. LAKSHMI NARASIMHAN

ASSOCIATE PROFESSOR (MECH)

DATE OF SUBMISSION : 14.09.2011

DEPARTMENT OF MECHANICAL ENGINEERING

SSNCE, KALAVAKKAM 603 110.


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Project title : DEVELOPMENT OF A CONSTANT TEMPERATURE BATH USING

PHASE CHANGE MATERIALS FOR LOW TEMPERATURE

APPLICATIONS

Broad Subject : MECHANICAL ENGINEERING

Sub-Area : THERMAL ENGINEERING

Duration : 1 YEAR

Total cost : Rs. 41,000/-

Principal Investigator : Dr. N. Lakshmi Narasimhan

Associate Professor, Department of Mechanical

Enginering

Co-Investigators : B. SRIRAM (31509114050) III MECH

K. VINOTH KUMAR (31509114058) III MECH

N. ARUNACHALAM (31509114005) III MECH

A. PADMANATHAN (31509114304) III MECH

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PROJECT SUMMARY

Constant temperature baths are employed in applications such as the biomedical, materials

development, solar thermal, food preservation, electronics, etc. The key parameter in the

design of an efficient constant temperature bath is its response to the temperature fluctuations

from a set value. Critical applications like the biomedical, crystal growth, etc. poses stringent

conditions on temperature variations to be as small as within 0.5 oC from a specified/set

temperature. Design and development of constant temperature baths for such applications is

more challenging than that for an application that is tolerant to relatively larger temperature

fluctuations (upto 3 oC). Accordingly, the cost of the systems also increases (nonlinearly)

with increase in the demand for high precision baths that maintain constant temperatures with

very low fluctuations. The intention of the present project is to build a cost effective constant

temperature bath integrated with an energy storage material referred as phase change material

(PCM) suited for low temperature applications (5 to 15 oC) with an acceptable temperature

fluctuation. Performance of the system shall be studied experimentally to understand its

actual response with and without incorporating a thermal storage device. It is hoped that the

results shall encourage developing such cost effective constant temperature baths for

laboratory purpose and other applications in a wide range.

Keywords: constant temperature bath, phase change material, thermal storage, low

temperature.

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Origin of the Proposal

This project is based on our past experience of designing low cost chillers for diffusion

vacuum pumps and designing of thermal storage units with phase change materials for the

purpose of thermal energy storage. The proposed system is an integration of the two concepts

with suitable modifications to enable function as a constant temperature bath.

Definition of the Problem

Development of a cost effective constant temperature bath with a reasonable temperature

fluctuation (less than 2oC) between the range 5 to 15oC finds use in various applications

like the biomedical, materials development, thermal system, etc. A constant temperature bath

employing a thermal energy storage material and operating between 5 to 15 oC is to be built

and tested. Comparison on the performance between the systems with and without a thermal

storage material shall be carried out.

Objectives

1. To design and build a unit that can maintain temperatures in the range 5 to 15 oC for

10 lit water capacity.2. To design and integrate a thermal storage device with the unit.

3. To test the performance of the unit with and without the thermal storage unit.

State of Knowledge

Though the art of designing constant temperature bath is well understood and numerous

commercial systems are readily available, for a wide range of temperatures, a simple cost

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effective unit with an acceptable performance is needed for numerous noncritical

applications in the laboratories elsewhere. Two chiller units for diffusion vacuum pumps

were recently built under the supervision of the principal investigator and put into operation

at the crystal growth facility at SSN campus. The chillers demonstrated a successful

operation with operating hours exceeding 2000 over a period of one year for the first while it

is about 400 for the recently developed second chiller over a period of

4 months. The lowest temperature achieved with the chilling unit was about 18 oC at low load

while it was about 23-25oC with a thermal load of about 550-600 W. The performance of the

unit was studied experimentally and discussed elsewhere in the design and fabrication report

[1]. Thermal storage devices employing phase change materials are used in many

applications for energy storage and retrieval. A great deal of work is available elsewhere in

the open literature on phase change materials [2-5]. Seeniraj and Narasimhan [4] studied

numerically the influence of an encapsulated phase change material as a cold storage for an

airconditioning application considering heat leak into the system. Fang et al. [5] investigated

the performance of an ice storage for an airconditioning system and reported an appreciable

enhancement in the performance of the thermal storage system with a heat pipe. Azzouz et

al. [6] studied the performance of a phase change material (PCM) slab attached to a

refrigerator. They have found that the addition of a PCM resulted in a continuous operation

of the refrigerator for several hours without power supply. An elaborate review on the types

of PCMs has been presented by Gil et al. [7] recently. The present work involves building a

portable chiller unit with heater and thermal storage facility to function as a constant

temperature bath in the operating temperature range between 5 to 15 oC.

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References

1. Design and Fabrication of a chiller unit for a diffusion vacuum pump,

P. Ashwath, Harish Krishnamoorthi, G. Ramachandran and S. Viajyaragavan Design

and Fabrication Project report, May 2011, SSNCE.

2. Seeniraj, R.V., Velraj, R., and Lakshmi Narasimhan, N., 2002, Heat Transfer

Enhancement Study of a LHTS unit containing Dispersed High Conductivity

Particles, ASME Jl. Solar Energy Engng.,- Vol. 124, No: 3, pp. 243-249.

3. Seeniraj, R.V., Velraj, R., and Lakshmi Narasimhan, N., 2002, Thermal Analysis of

a Finned-Tube LHTS module for a Solar Dynamic Power System, Heat and Mass

Transfer, (German Journal) Vol. 38, pp. 409-417.

4. Seeniraj, R.V and Lakshmi Narasimhan, N., 2008, Performance Enhancement of a

Solar Dynamic LHTS Module having Both Fins and Multiple PCMs, Solar Energy,

82, pp. 535-542.

5. Fang G., Xu Liu, Shuangmao Wu, 2009 Experimental investigation on performance

of ice storage air-conditioning system with separate heat pipe, Experimental Thermal

and Fluid Science 33, 11491155.6. Azzouz K., D. Leducq, D. Gobin, 2009, Enhancing the performance of

household refrigerators with latent heat storage: An experimental investigation,

International Journal of Refrigeration 32 1634 1644.

7. Gil A, Marc Medrano, Ingrid Martorell, 2010, Ana Lazaro, Pablo Dolado, Belen

Zalba, and Luisa F. Cabeza, State of the art on high temperature thermal energy

storage for power generation. Part 1-Concepts, materials and modellization,

Renewable and Sustainable Energy Reviews 14, 3155.

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Importance of the proposed project/ Justification for subject area

This project provides a means for adopting the concept of thermal management using phase

change materials for developing a low cost constant temperature bath.

The successful development of the unit could promote future market prospects for such units

to a wide range of non critical applications in the operating temperature range between 5 and

15 oC.

Review of Expertise

The principal investigator carried out research in the area of cryogenics during his doctoral

programme at IIT Madras and gained expertise in the design and development of

refrigerators suited for very low temperatures (-200 oC) using mixture of refrigerant gases.

He has sufficient experience in the design and development of low cost chillers for portable

systems such as the cooling systems for diffusion vacuum pumps. In addition, he has carried

out research on thermal energy storage using phase change materials and co-authored four

papers during his pre Ph.D. tenure. With this background, the principal investigator is

positive in developing the proposed unit which is an amalgamation of refrigeration and

thermal storage technology.

Methodology

An existing analytical and numerical modeling code developed by the investigator shall be

employed for the design of heat exchanger for the chiller unit. A low temperature bath based

on the design shall be fabricated and tested for its performance and response to various loads.

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Similarly, a latent heat thermal storage unit with a phase change material (PCM) suited for

low temperature shall be chosen based on the (i) results from our initial experiments and (ii)

energy calculations based on the thermophysical properties of the chosen PCM. The actual

performance of the low temperature bath with the PCM and an auxiliary heater shall be

studied experimentally for the cases with and without PCM separately.

Work Elements

(i) Design of heat exchanger running the code

(ii) Selection of PCM

(iii) Procurement of materials for the low temperature unit

(iv) Procurement of PCM

(v) Fabrication of the unit

(vi) Experimentation

(vii) Analysis

(viii) Documentation

Time Schedule of Activities

Activity Period Milestone

Literature

Survey onPCMs

0-1 months

Design of heatexchanger and

PCM

1-2 months Fixing the size of theunit and capacity

Procurement ofmaterials 3 months Preparation of quotes,procurement

Fabrication of

the unit

3 months Construction of the

unit and making it

ready for testing

Experimentation 3 months Testing the actual

performance of the

unit.

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Documentation 1 month Preparing the final

report.

Utilization of research results

Based on the performance of the system built and cost analysis, development of similar units

to our biomedical and crystal growth departments can be proposed / recommended as a first

phase. Consultancy opportunities for developing such units at a nominal cost to various R&D

labs and other clients shall be sought in the second phase.

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BUDGET ESTIMATE

(i) Non Consumables

S. No Items Approximate

Cost (Rs.)

1. Compressor 6000/-

2. Condenser 1200/-

3. Heat Exchanger 4000/-

4. Evaporator Vessel 1300/-

5. Heater 1500/-

6. PID 3000/-

7. RTD 1000/-8. Temperature Indicator 5000/-

9. Refrigerant Gas 3000/-

10. PCM 2000/-

11. Insulation 1500/-

12. Pressure Gauges 1000/-

13. Thermocouple 1500/-

Total (A) 32000/-

(ii) Consumables

S. No Items Approximate Cost(Rs)

1. Copper and Silver Brazing Rods 1000/-

2. Adhesives 500/-

3. Thermal Paste 500/-

4. Miscellaneous 1000/-

Total (B) 3000/-

(iii) Charges towards fabrication and labour

S. No Items Approximate Cost(Rs)

1. Fabrication and labour charges 6000/-

Total (C) 6000/-

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Total Budget Estimate (A+B+C) : Rs.41, 000/-

Time Schedule of Activities

TIME SCHEDULE OF EVENTS

0 2 4 6 8 10 12

Literature survey

Design of Heat

Exchanger

Procurement of

Materials

Fabrication

Experimentation

Documentation

Events

Months

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Justification for purchase of Major items

Compressor

The compressor forms an important component for the operation of the chiller unit. The

refrigerator unit cannot operate without a compressor. The proposed refrigeration capacity of

the compressor is about 1500-1750 W.

Condenser

The condenser is another important integral unit to compressor without which the refrigerator

of the constant temperature bath system cannot reject heat to ambient during its operation.

Heat Exchanger

The heat exchanger mentioned here is the evaporator of the refrigerator unit where heat

exchange between the refrigerant and the medium (water) to be cooled is achieved.

Evaporator Vessel

This is the container where water (10 lit) is to be maintained at a constant temperature.

Heater

Heater is needed to raise the temperature when the desired bath temperature is more than the

refrigeration temperature in the evaporator.

PID controller

A PID controller is very much essential to make the temperature bath respond automatically

to variations in the temperature from a set value. This controller controls the heater. A

separate PID controller is to be provided to switch on/off the compressor automatically with

respect to the bath temperature.

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RTD Temperature sensors

A RTD temperature sensor (Pt100) is used to sense accurately the bath temperature that is

connected to the PID.

Refrigerant Gas

The refrigerator unit cannot operate without a refrigerant which is its prime need. Atleast

three kilograms of refrigerant (R-134a) is required for our project.

PCMs

The thermal storage unit to be built in this work employs a phase change material that

melts/solidifies at specific temperatures. Atleast three different PCMs (freezing temperatures

below 15 oC) are to be tested in this work suitable for our low temperature application.

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