~ Pergamon Renewable Energy, Vol. 13, No. 1, pp. 105-119, 1998 © 1998 Elsevier Science Ltd. All rights reserved Printed in Great Britain PII : S0960-1481 (97)00056---6 0960-1481/98 $19.00 + 0.00 TECHNICAL NOTE Regeneration of silica gel in multi-shelf regenerator SUKHMEET SINGH and PARM PAL SINGH Department of Mechanical Engineering, Punjab Agricultural University, Ludhiana-141004, India (Received 25 April 1997; accepted 31 July 1997) Abstract--In the present paper an investigation on the regeneration of solid desiccant (silica gel) in a modified design of dehumidifier called "Multi-shelf Dehumidifier", has been reported. A "Packed Bed Dehumidifier" was used as control. Both the dehumidifiers were fabricated and tested simultaneously. The effect of regeneration air temperature, bed-air velocity and number of shelves on regeneration of silica gel was investigated. The range of regeneration air temperature was 42-72°C, while bed- air velocity varied from 0.175~).55 m/s and number of shelves from 2 to 4. The regeneration time decreased with the increase in regeneration air temperature, bed- air velocity as well as number of shelves. The values of regeneration air temperature and bed-air velocity for minimum energy input were found to be 52°C and 0.175 m/s irrespective of the number of shelves. The effect of the rest period was investigated for these optimum values of regeneration air temperature and air velocity for a number of shelves varying from 2 to 4. The rest periods used were 30, 60 and 180 rains. The regeneration time reduced with increase in rest period for all the values of number of shelves, but the reduction in regeneration time was not appreciable. © 1998 Elsevier Science Ltd. 1. INTRODUCTION Desiccant cooling and air dehumidification is a good alternative to the conventional vapour com- pression system for air conditioning. With the desiccant system, indoor air humidity and temperature can be directly controlled in an open cycle and the use of chloroflurocarbon (CFC) is eliminated. The desiccant system consists of a desiccant dehumidifier, evaporative cooler and air heater to regenerate the desiccant. Into this, ambient air passes through the dehumidifier and emerges as hot and dry, because of adsorption of water by desiccant. It is then passed through a heat exchanger and an evaporative cooler. The cooled air is supplied to the air-conditioned room. To regenerate the desiccant in the regenerator/dehumidifier, ambient air passes through a heat exchanger and air heater. This brings the regeneration air temperature up to a value that allows the desiccant to be regenerated. This air passes through the desiccant to be regenerated. The regeneration air leaves regenerator/ dehumidifier as hot and wet air, thus regenerating the desiccant. Many desiccant materials are available, such as silica gel, activated alumina, molecular sieve, alumina gel, etc. However, silica gel, activated alumina and molecular sieve have a higher adsorption capacity [1]. Of these, molecular sieve requires relatively higher regeneration temperature for desorp- tion. If solar energy is used for regeneration then a higher regeneration temperature is a disadvantage because an expensive high performance solar collector needs to be used. On the other hand, silica gel and activated alumina can be desorbed at relatively low temperatures. This makes these desiccant materials useful for use with solar energy as efficiency of solar collectors decreases with the increase in collection temperature. An investigation on simultaneous dehumidification of silica gel and activated 105