Experimental Analysis of Heat Transfer During the Melting of A Phase-Change Material in Triplex Tube Heat Exchanger

Experimental Analysis of Heat Transfer During the Melting of A Phase-Change Material in Triplex Tube Heat Exchanger

M. Subramaniyana T. Parameshwaranpillaib.

a Department of mechanical engineering, Anna university (BIT campus),Trichy.

bDepartment of mechanical engineering, Anna university (BIT campus),Trichy.

ABSTRACT

Triplex tube heat exchanger was fabricated and tested for analyze the heat transfer of the internal and external fins by phase change material melting behavior experimentally .The TTHX is designed by Solidworks 2010. The (TTHX) two models are fabricated by brass welding. The fin length is varied to determine the time taken for achieving the maximum temperature in the PCM and heat transfer and fin efficiency. The three experiments were conducted by varying the water charging temperature in two models of TTHX. The readings are analyzed and results are presented.

INTRODUCTION:

It is becoming increasingly difcult to ignore the mismatch between the energy supply and energy demand for solar thermal energy applications, since solar energy is

considered as a periodic energy source, which leads to low efciency of those applications. Latent heat thermal energy storage is an important component and plays a key role in the energy efciency improvement of the solar-energy applications. Recently, thermal energy storage systems, especially latent heat thermal energy storage, have gained a greater attention from the viewpoint of global environmental problems and the energy-efciency improvement. It promises an elevated performance and reliability with the advantages of high storage.The main disadvantages of PCMs that limit the using of these materials as thermal energy storage is the lowthermal conductivity,which causes a long time for the melting and solidication process.Several researchers have studied the heat transfer enhancement inPCMs, including nned tubes insertion of a metal matrix to the PCM, using multitudes , using bubble agitation in PCMs [, using a PCM

dispersed with high conductivity particles,and employing multiple families of PCMs.so we need to recover the heat and enhance the heat transfer by some of the techniques like enhancement and PCM storage.

Abduljalil A.,et.al study theHeat transfer enhancement for a triplex tube heat exchanger by using internal and external ns to accelerate the melting rate of RT82 as a PCM were investigated numerically; different design and operation parameters include the n length, TTHX materials, number of ns, n thickness, Stefan number and PCM unit geometry were analyzed. Based on the simulation results, these parameters have a signicant inuence on the time for complete melting; the effect of n thickness is small compared to the n length and number of ns, which have a strong effect on the melting rate time.Velraj,et.alinvestigated numerically and experimentally the effect of internal longitudinal ns on the solidication process of parafn (RT60) inside a vertical cylinder. They considered the heat transfer through the n tip and the circumferential wall of the cylinder. The effects of different tube radii and different numbers of ns have been studied theoreticallywith respect to the

surface heat ux on the solidication process of the parafn.IsakKotcioglu, et.alInvestigate, in addition to above given studies an experimental investigation is described by Taguchi methods, which include the enhancement of forced convection heat transfer in a rectangular channel using inclined thin plates as wing- type vortex generators.M.J. Hosseini,et.alThe focus of this study is to evaluate natural convection effects during melting of parafn wax in double pipe heat exchange systems. The main feature of this study is the detailed measurement of the temperature eld within the PCM. Theeffects of the inlet temperature of HTF on the enhancement heat transfer were studied.N.H.S. Tay,et.alexperimentally validated CFD model of a PCM thermal energy storage system with plain tubes containing the heat transfer uid wasmodied to accommodate the heat transfer enhancement techniques of pins and ns attached to the tube.This difference of the heat transfer surface area has provided the nned tube design to be able to transfer heat more effective and faster.M. Hatami,et.alinvestigated the effect of Darcy and Rayleigh Number on temperature distribution and heat transfer through longitudinal and rectangular porous n and

we showed that LSM is the most accurate method among the applied procedures.S.A.VijayPadmaraju,et.al A LHS system containing PCM in cylindrical capsules is designed and fabricated with an effective water storage capacity of about 48 liters, enough to meet the needs of a family of four. The thermal behavior of the LHS system is investigated experimentally for various operating conditions. The effects of flow rates on charging times and energy storage of the TES systems are studied ,From the literature survey of we conclude many author says to increase the heat transfer by various modification in fins and PCM to achieve our required.

METHODOLGY:

In this study the TTHX is designed by solid works, Then it is fabricated by proper suitable material, mostly many author says copper is good for the thermal energy storage system and recovery system because it has a high thermal conductivity, two models of TTHX is fabricated only the fin length is varied other parameters are same in those models. Then the suitable PCM are selected in this study the paraffin (C22-C45) was chosen by availability

criteria.The experiment was conducted by non flow of HTF(hot temperature fluid).Results validated by both experimentally and theoretical calculation.

Experimental setup:

ASSUMPTION & CONDITION:

• The water is charging at temperature of 800C, 850C, 90 0C.

• Steady-state;

• 1-D conduction in x direction;

• Constant properties.

• Negligible radiation;

Uniform heat transfer coefficient;

The water is heated up to a corresponding temperature by electric heater or LPG.Then the heated water is charged in the TTHX by the tube 1.At the charging time the opening is closed by the PVC end cup. After the charging the another end is also closed by the end cup. At that time the stop watch is switched on.Then the TTHX is placed on the stand for without any disturbance.The digital thermometer is placed on the tube 2 to measure the temperature rise. After 5mins the temperature rise in the thermometer is noted. The temperature rise in the thermometer is noted for an hour.After the completion of the experiment the TTHX is to be cooled. First discharge the hot water inside the TTHX by opening the end cup.Then it is cooled by atmosphere air.After the complete cooling of the TTHX then the water is charged again with the corresponding temperature. Repeat this procedure.Same procedure were followed for model(2).

The designed TTHX is validated theoretically by some predetermined equation for fins.Theequation are derived from some databook.

Qf = (h*P*k*Ac) *tan h (mL)*(Tb-Tf) equation (1)

Fin efficiency = tan h (mL) / mL equation (2)

Using the design parameter values and results are obtained.

Hot water charging temperature= 80oCHot water charging temperature= 85oC

0

Hot water charging temperature= 90oC

60

50

40

30

20

FIN LENGTH=15

mm

FIN LENGTH

=20mm

10

0

0 10 20 30 40 50 60

At first the water is charging at the temperature of 80oC.the readings observed, and graph is plotted between time and temperature. From the graph and readings the maximum temperature attained in the model1 is 52.1oC at 10mins after charging. Similarly the model (2) attains the maximum temperature of 53.8oC at 15mins from the charging. Compared to those models the maximum temperature attained in model (2) only. The heat is dissipated gradually decrease 1oC interval of 5mins.The lowest temperature in the model (1) and model (2) were 43.9 oC& 44.2 oC. The model (1) dissipate the heat in a quick manner. The dwell time of steady state is achieved in the model (2). The dwell time it may be 5 to 7 mins. but in the model(1) less than 3mins.

The water is charged at 85oC. The readings were obtained. The graph is plotted between time and temperature. The model

(1) attained the maximum temperature of

53.3 oC at 10mins from the charging. Model(2) is attained the temperature of 54.3 oC at 15mins from the charging. The heat is dissipated gradually decrease of 1oC at

5mins interval in model(2). The model (1) dissipates the heat in a quick manner. The dwell time of steady state is achieved in the model (2). The dwell time it may be 5 to 7 mins. but in the model(1) less than 3mins.

The model (1) attained the maximum temperature of 56.2oC at 10mins after the charging. The model (2) is attained the maximum temperature 55.3oC at 20mins after the charging. The lowest temperature in the model (1) & model 2 were 49 oC& 51.1oC.The model (1) attained the maximum temperature of 56.2oC at 10mins after the charging. The model (2) is attained the maximum temperature 55.3oC at 20mins after the charging. The lowest temperature in the model (1) & model 2 were 49 oC& 51.1oC.

The graph shows that short fin that means model (1) attain the maximum temperature in a short time duration and also dissipate the heat to the surrounding in a quick manner compared to model (2).but in the long fins have a high heat transfer area compared to model (1).so it attain the steady state at 20 mins from the charging and also it dissipate or decrease of the temperature slowly compared to model (1).

The theoretical calculation shows that the heat transfers by the fin of the model

(1) and model (2) were 36.53 W & 41.99 W. the fin efficiency of the model (1) and model (2) were 77.27 % & 66.66 %.The values shows that fin length increase the heat transfer. The fin length increased it

decrease the fin efficiency.so the effective fin length is only to achieve the maximum heat transfer as well as increase in fin efficiency.

In the present work from the experimental and theoretical result shows that if the fin length increased the heat transfer is also increased if the fin length is decreased the time taken to achieve the maximum temperature was also decreased. In the long fin takes more times to dissipate the heat, the short fin dissipate the heat shortly. If the fin length is over the effective length it decreases the heat transfer. The results also show that if the fin length increases the efficiency is also decreased. Fin efficiency depends upon the width and thickness of the fins.

The long fins are most suitable for solar thermal application because the sun radiate in moderately. The short fins are suitable for instantaneous heating from heat energy sources.

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