Influence of Void Ratio on Phase Change in Thermal Storage Canister of Heat Pipe Receiver

Abstract

In this paper, with both void cavity and phase change considered, influence of void ratio on phase change in thermal storage canister of heat pipe receiver under microgravity is numerically simulated. Accordingly, physical and mathematical models are built. A solidification–melting model upon the enthalpy–porosity method is specially provided to deal with phase changes. The change of liquid fraction with respect to void ratio and the liquid fraction distribution of different void ratios in a thermal storage canister of a heat pipe receiver are shown. Numerical results are compared with experimental ones. Research results indicate that the void cavity prevents the process of phase change significantly. Phase-change material (PCM) melts slowly during sunlight periods and freezes slowly during eclipse periods as void ratio increases. The utility ratio of PCM during both sunlight periods and eclipse periods decreases obviously as the void ratio increases. The void cavity prevents the heat transfer between the PCM zone and canister wall. The void cavity blocks the processes of both melting and solidification during cycle orbital periods.

NOMENCLATURE

A	=	area (m2)
Amush	=	mushy zone constant
CP	=	specific heat capacity at constant pressure (J/kg-K)
H	=	enthalpy (J/kg)
h	=	sensible enthalpy (J/kg)
k	=	thermal conductivity (W/m-K)
L	=	axial length (m)
Q	=	heat flux (W)
r	=	radial direction
R	=	radial length (m)
RCO	=	radial length of canister outer wall (m)
RhO	=	radial length of heat pipe outer wall (m)
Rthick	=	radial thickness of PCM (m)
S	=	source term
t	=	time(s)
T	=	temperature (K)
	=	fluid velocity
	=	solid velocity due to the pulling of solidified material out of the domain (m/s)
z	=	axial direction

Greek Symbols

β	=	liquid volume fraction
ΔH	=	latent heat of phase change (J/kg)
ϵ	=	a small number (0.001) to prevent division by zero
φ	=	turbulence quantity
ρ	=	density (kg/m3)
μg	=	microgravity (m2/s)

Subscripts

hw	=	heat pipe wall
lqs	=	liquidus
ref	=	reference
sds	=	solidus
v	=	vapor

Additional information

Notes on contributors

Xiange Song

Xiange Song is a senior engineer at Beijing International Studies University. She received her master's degree in 2006 from Beijing Jiaotong University. Her research contributions were in the field of evaporation and condensation heat transfer. Her current interests focus on building energy efficiency under theoretical and experimental aspects.

Qiue Song

Qiue Song is an engineer in the Beijing Coal Group Property Management Company. Her research contributions were in the field of air conditioning. Her current interests focus on the measurement of thermophysics properties under experimental aspects.

Xiaohong Gui

Xiaohong Gui is a vice-professor at the Institute of Engineering Thermophysics, Chinese Academy of Sciences. He received his Ph.D. in 2009 from the Beijing University of Aeronautics and Astronautics. His research is about phase change, high-temperature heat pipes, and solar power generation. He has published more than 30 academic articles in national and international scientific and technological journals.

Shiqiang Liang

Shiqiang Liang is a vice-professor at the Institute of Engineering Thermophysics, Chinese Academy of Sciences. He received his Ph.D. in 2002 from Zhejiang University, China. His current research interests focus on theory and application of phase change, energy-saving technology in waste heat and pressure utilization of absorption refrigeration, and advanced thermal management technology in gas turbine blades.

Dawei Tang

Dawei Tang is a professor at in Institute of Engineering Thermophysics, Chinese Academy of Sciences. He received his Ph.D. in 1999 from Shizuoka University, Japan. Now he is the head of the Research Centre for Heat and Mass Transfer. He is currently working on microscale heat transfer under theoretical and experimental aspects.