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RESEARCH PAPERS: Heat Exchangers

# Performance of Phase Change Materials in a Horizontal Annulus of a Double-Pipe Heat Exchanger in a Water-Circulating Loop

[+] Author and Article Information
J. R. Balikowski

Mechanical and Aerospace Engineering, School of Engineering, State University of New York at Buffalo, Buffalo, NY 14214-3078

J. C. Mollendorf

School of Engineering, State University of New York at Buffalo, Buffalo, NY 14260-4400; Professor of Physiology and Biophysics School of Medicine, State University of New York at Buffalo, Buffalo, NY 14214-3078, and Center for Research and Education in Special Environments, State University of New York at Buffalo, Buffalo, NY 14214-3078molendrf@buffalo.edu

J. Heat Transfer 129(3), 265-272 (Jun 13, 2006) (8 pages) doi:10.1115/1.2426359 History: Received May 17, 2005; Revised June 13, 2006

## Abstract

Phase change materials (PCMs) are used in applications where temperature regulation is important because they absorb and release a large amount of energy at a fixed temperature. In the experimental part of this investigation, PCM was placed in the annular region of a double-pipe heat exchanger with water circulated in the inside pipe. Experiments were performed in which the PCM would absorb (charge) and then release (discharge) energy at various temperatures and water flows. Two materials, Climsel 28 (C28) by Climator and microencapsulated Thermasorb 83 (TY83) by Outlast Technologies, were each tested in smooth and spined annuli to observe which configuration facilitated heat transfer. The latent heats and thermal conductivities of C28 and TY83 are $126kJ∕kg$ and $186kJ∕kg$ and $0.6W∕m∕°C$ and $0.15W∕m∕°C$, respectively. The experimental data were analyzed to verify which PCM transferred more heat. The effect of different water flow rates on the heat transfer rate was also examined. In the theoretical part of this investigation, heat transfer theory was applied to C28 in the smooth-piped heat exchanger in order to better understand the phase change process. The presence of spined fins in the phase change material accelerated charging and discharging due to increased fin contact with the outer layers of the PCM. The spined heat exchanger charged and discharged in $180min$ and $120min$, respectively, whereas the temperature in the smooth heat exchanger remained below the fully charged/fully discharged asymptote by about $3°C$ and thus failed to fully charge or fully discharge. Also, higher water flows increased heat transfer between the PCM and water. TY83 in the spined heat exchanger transferred more heat and did it faster than C28 in the spined heat exchanger. The heat transfer rate from the water to TY83 while charging was 25% greater during the transient period than in C28. While discharging, the heat transfer from TY83 to the water was about 20% greater than in C28. There was generally good agreement $(±1.5°C)$ between theory and experimental data of C28 in the smooth-piped heat exchanger in terms of the trends of the temperature responses. The differences are expected to be a result of approximations in boundary conditions and uncertainties in how the temperature variation of the specific heat is formulated.

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## Figures

Figure 1

Experimental setup of water-circulating loop with the double-pipe heat exchanger storing PCM

Figure 2

Cross section of the smooth double-pipe heat exchanger at x=l2

Figure 7

Comparison of T0 in the smooth-piped and spined heat exchangers for TY83 discharging to 24°C at 1L∕min water flow

Figure 8

Comparison of T0 for C28 and TY83 charging to 30°C at 3L∕min water flow in the spined heat exchanger

Figure 9

Comparison of time-averaged q for C28 and TY83 charging to 30°C at 3L∕min water flow in the spined heat exchanger

Figure 10

Comparison of T0 for C28 and TY83 discharging to 24°C at 3L∕min water flow in the spined heat exchanger

Figure 11

Comparison of time-averaged q for C28 and TY83 discharging to 24°C at 3L∕min water flow in the spined heat exchanger

Figure 12

Time-averaged q for three water flows in the spined heat exchanger with TY83 charging to 30°C

Figure 13

Comparison of theory and experimental data of T0 for C28 in the smooth-piped heat exchanger charging to 32°C at 3L∕min water flow

Figure 14

Comparison of theory and experimental data of T0 for C28 in the smooth-piped heat exchanger discharging to 24°C at 3L∕min water flow

Figure 15

Predicted theoretical distribution of temperature in the radial direction for various times with C28 in the smooth-piped heat exchanger charging to 32°C at 3L∕min water flow

Figure 16

Predicted theoretical distribution of temperature in the radial direction for various times with C28 in the smooth-piped heat exchanger discharging to 24°C at 3L∕min water flow

Figure 3

Photograph of the spined copper pipe used as the inner tube in the double-pipe heat exchanger

Figure 4

Specific heat of C28 within the phase change temperature limits for b=2.3, adapted from Ref. 9

Figure 5

Temperature response of thermocouples located in region 3 of Fig. 3 for C28 charging in the smooth-piped heat exchanger to 34°C at 2L∕min water flow

Figure 6

Comparison of T0 in the smooth-piped and spined heat exchangers for C28 charging to 32°C at 2L∕min water flow

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