Energy Convers. Mgmt Vol. 33, No. 4, pp. 235--242, 1992 0196-8904/92 $5.00 + 0.00 Printed in Great Britain. All rights r~aervvd Copyright © 1992 Pergamon Press Ltd AN ANALYTICAL STUDY OF A LATENT HEAT STORAGE SYSTEM IN A CYLINDER N. K. BANSAL I and D. BUDDHIT~ ICentre of Energy Studies, Indian Institute of Technology, Hauz Khas, New Delhi-110 016 and 2Academic Staff College, Tubular Structure Hall, Khandwa Road, New Campus, Devi Ahilya University, Indore-452 001, India (Received 10 December 1990; receivedfor publication 19 August 1991) Abstract--The cylindrical latent heat storage system which has been considered here is a part of a domestic hot water system. During the charging mode of the phase change material, the cylindrical capsule is in the closed loop with a solar water heater, and during the discharging mode, the energy is extracted by a liquid flowing through the storage unit. A theoretical model has been developed for such a system. The calculations for the moving boundary and the fluid temperature have been done by using latent heat storage materials. Latent heat storage Solar water heater Moving boundary NOMENCLATURE Ac = Absorber area of flat-plate collector (m 2) Cs = Specific heat of solid PCM (J/kg °C) Cw--Specific heat of fluid (J/kg °C) H = Latent heat of fusion (J/kg) h, = Heat transfer coefficient from outer surface of storge unit to ambient (Vv'/m 2 °C) h t -- Heat transfer coefficient from fluid to liquid PCM (W/m 2 °C) h,s = Heat transfer coefficient from fluid to solid PCM (W/m2 °C) h m = Heat transfer coefficient from solid PCM to fluid passing through storage unit (W/m 2 °C) hm~ -- Heat transfer coefficient at liquid-solid interface (V~//m 2 °C) hs = Heat transfer coefficient at solid-liquid interface (W/m 2 °C) k s --Thermal conductivity solid PCM (W/m °C) L = Height of storage unit (m) m = Number of identical storage subunits (dimensionless) m w= Flow rate fluid in flat-plate collector (kg/s) n -- Number of harmonics (dimensionless) p = Perimeter of tube (p = 2nh0) (m) R = Radius of PCM storage sub-unit (m) r--Radius coordinate (m) r m -- Radius of melted zone (m) rmt -- Radius of solidified zone during discharging mode (m) r0 -- Radius of tube inside storage unit (m) S = Solar radiation received by absorber surface (W/m 2) T,--Ambient temperature (°C) T~0 = Average value of ambient temperature (°C) T** = n th harmonic in Fourier series expansion of ambient temperature (°C) Ts = Temperature of collector fluid at inlet of flat-plate collector (°C) Ta = Melting temperature of PCM (°C) Ts -Temperature of solid PCM (°C) T,0 := Average part of temperature of solid PCM (°C) T~ = nth harmonic in Fourier series expansion of temperature of solid PCM (°C) T o = Temperature of collector fluid at outlet of flat-plate collector (°C) T,,- Temperature of fluid passing through storage unit (°C) t --- Time (s) U L ~--- Overall heat loss coefficient of flat-plate collector (W/m 2 °C) y---Space coordinate (m) Greek letters Pl = Density of liquid PCM (kg/m 3) p, = Density of solid PCM (kg/m 3) r/= Thermal efficiency (dimensionless) tTo whom all correspondence should be addressed. 235