An Experimental Study of Heat Transfer Characteristics of Microencapsulated Phase Change Material Slurry in a Coil Heat Exchanger

Abstract

The use of microencapsulated phase change material (MPCM) slurry as an enhanced heat transfer fluid is considered to be very promising for saving energy in thermal energy systems. However, little is known how MPCM may exhibit enhanced heat transfer performance in coil heat exchanger. Coil heat exchangers are extensively used in industrial applications including heating, ventilating and air conditioning (HVAC) systems because of their superior heat transfer performance and compactness. In this study, the heat transfer characteristics of MPCM slurry in a coil heat exchanger have been investigated experimentally. Thermal properties of MPCM slurry were measured using a differential scanning calorimeter. Pressure drop, overall heat transfer coefficient and heat transfer effectiveness in a coil heat exchanger were determined by considering different flow rates. It was found that heat transfer characteristics were positively affected by the phase change process of the phase change material in MPCM, even though MPCM exhibit reduced turbulence and increased pressure drop. The overall heat transfer coefficient for MPCM slurry is in the range of 5,000 to 9,000 W/m2-K over a Dean number range from 1,600 to 4,000 (equivalent Reynolds number range of 6,000 to 15,000). The enhancement in heat transfer performance is about 17% when compared to that for water. In addition, durability tests of MPCM slurry were conducted to evaluate the MPCM’s ability to withstand continuous pumping conditions, which is critically important in the implementation of MPCM slurry in industrial applications.

Performance characteristics of microencapsulated phase change material slurry in a helically coiled tube

“…The durability of MPCM particles can also ensure that all the results obtained from the experiments are reliable and repeatable. The effective specific heat of the slurries as a function of time was used to evaluate the stability of MPCM particles [3,26]. The effective specific heat values of the MPCM slurries remained constant after about 550 cycles of pumping for each corresponding mass fraction.…”

“…Many researchers [37][38][39][40][41] have used a performance coefficient, which includes both heat transfer and flow resistance characteristics to compare the overall performance of heat exchangers between new and base fluids. In this study, the effect of using MPCM slurry was evaluated using the performance efficiency coefficient (PEC), which is defined as the ratio of Nusselt number ratio to friction factor ratio between MPCM slurry and water, and it is calculated as follows:…”

Thermal Performance of Microencapsulated Phase Change Material Slurry in a Coil Heat Exchanger

“…The effective specific heat of the slurries was used to evaluate the stability of MPCM particles [26,27]. Recently, the effective specific heat values of MPCM slurries at mass fractions of 4.6% and 8.7% were measured using HX2 by performing energy balance calculations.…”

Field evaluation of microencapsulated phase change material slurry in ground source heat pump systems

“…The increase of the shell thickness decreased the breakage of microcapsules [21,22] but it also led to lower amount of PCM and lower heat capacity [23]. With respect to pressure drop characteristics, mass fraction of MPCM in the slurry increased pressure drop, which was greater than that of carrier fluid due to the increased viscosity [23,24]. Friction factor curve of MPCM slurry flowing through a straight tube fitted well with the correlation used for a homogeneous Newtonian fluid [12,20].…”

“…In terms of heat transfer characteristics, MPCM slurry could considerably enhance the heat capacity when compared to water due to the latent heat of fusion of PCM [24,25].…”