Effects of capsule conduction and capsule outside convection on the thermal storage performance of encapsulated thermal storage tanks

• Published in: Solar energy Vol. 110; pp. 56 - 63
• Main Authors: Lee, Y.T., Hong, S.W., Chung, J.D.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01-12-2014; Elsevier; Pergamon Press Inc
• Subjects: Applied sciences; Boundary conditions; Capsule; Conduction; Convection; Energy; Energy. Thermal use of fuels; Enthalpy method; Exact sciences and technology; Heat conductivity; Mathematical models; Phase change; Porosity; Solar energy; Storage tanks; Thermal conductivity; Thermal storage performance; Thermodynamics; Transport and storage of energy; Conduction; Enthalpy method; Thermal storage performance; Capsule; Phase change; Convection; Performance evaluation; Isothermal condition; Enthalpy; Thermal behavior; Thermal energy storage; Boundary condition; Porous material; Phase transformation; Thermal conductivity; Constant temperature; PCM material; Porosity; Storage tank
• ISSN: 0038-092X; 1471-1257
• DOI: 10.1016/j.solener.2014.08.034

•We investigate the constrained melting of PCM (phase change material) inside a spherical capsule using three numerical models.•We examine the effects of capsule conduction and natural convection taking place on the discharging performance.•Temperature distribution at the inner wall of the capsule shows considerable differences for the three numerical models.•The total melting time is increased 16.4% and 25.7% by the capsule conduction and convection outside the capsule.
The present study investigates the effects of capsule conduction and capsule outside convection of a spherical capsule on the thermal storage performance. The enthalpy–porosity method is employed to account for the phase change phenomenon. Three numerical models are examined. The first model is to apply the commonly used isothermal boundary condition on the outer surface of spherical PCM (phase change material). The second model is to apply constant temperature uniformly to the external surface of the capsule to examine the effect of capsule conduction. The last model takes into account the convection outside the spherical capsule. The results show that the effects of capsule conduction and capsule outside convection are substantial to the thermal storage performance. The effects of capsule conduction and capsule outside convection result in much lower discharging performance than the commonly used approach of the isothermal boundary model. This observation is more significant in real situation when the capsule material has low thermal conductivity.