THERMAL PERFORMANCE OF A COMBINED PACKED-BED SOLAR POND SYSTEM - A NUMERICAL STUDY

Solar ponds have recently become an important source of energy that is used in many different applications. The technology of the solar pond is based on storing solar energy in salt-gradient stratified zones. M any experimental and numerical investigations concerning the optimum o perational conditions and economical feasibility of solar ponds have b een published in the last few decades. In the present study a modified solar pond with a rock bed inserted at the bottom is suggested and in vestigated. In order to conduct this study and predict the thermal per formance of the combined system, a one-dimensional transient numerical model is developed. The boundary conditions are based on measured amb ient and ground temperatures at Kuwait city. The model is validated fo r standard plain salt-gradient solar ponds and is then used to examine the thermal performance of the combined storage system for different rock material and bed geometry. It has been shown that the storage tem perature is remarkably increased when low thermal diffusivity rocks (s uch as Bakelite) are used in the packed bed. Meanwhile, when high cond uctive rocks are used, the thermal storage temperature considerably de teriorates and the temperature variations amplitudes are almost flatte ned out. The bed geometry also plays a significant role in the storage process. As expected, an appreciable gain in the storage temperature was obtained for thicker rock beds. Low porosity rock beds, as well, p roduce higher storage temperatures in the storage zone. (C) 1998 Elsev ier Science Ltd. All rights reserved.