2.3. Design of Heat Exchanger

Heat exchanger is required to transfer the heat without mixing system hot water with the chemicals (liquid) available in the process tank. Following points have been considered while designing the heat exchanger.

a. Quality of the chemical (for selecting the material of H E)

b. Temp. rise required in the liquid.

c. Heat transfer co efficient of The H E material.

d. Time available to increase the temp to set level.

e. Volume of the chemical tank.

f. Evaporation losses during heating from the top portion.

g. Make up liquid volume

2.4. Control System & Piping layout designing

i) Control System & instrumentation: The system is designed such a way that max. Heat is to be collected even during the rainy season when sunshine is not with constant intensity. So we have used the differential controller system with the difference set point. As per the above calculation procedure we come to the requirement of 95 collectors for the process of 60 trolleys per day. To save the space for solar collector installation it has been decided to fabricate a SUPER STRUCTURE on the asbestos roof of the factory shed.

There are two Temp. sensors (PT100) provided to sense the hot water outlet temp of collector outlet and at the bottom of Hot Water storage tank. When the temp. of water at the collector outlet crosses the difference set, the pump gets started and forces the low
temp water of the storage tank to the collector and the process continues till the difference comes down below the set point the pump gets off and stops the circulation. Suitable capacity pump is used for circulation of water with mechanical seal to handle high temp. Liquid.

ii) Piping layout Designing ( Лв per the schematic diagram )

a. Solar Collector & Tank Piping (Solar Loop): Solar collectors are connected in series and parallel and cold-water inlet is connected at the bottom of the each row of the collectors. Hot water outlet has been taken from the top of the solar collector of each row. There is temp. sensor is fixed at solar collector outlet and bottom of the hot water storage storage tank. The pump is used at the inlet side of the collector, which sucks the water from the tank bottom (lowest temp. ) and pushes to the collector inlet. The size of the piping is design to circulate the required quantity of water within the average sunshine hours.

b. Chemical tank and hot water storage tank piping ( Process loop ) : The function of this loop is to carry the hottest water from the tank and circulate through the heat exchanger of the three tank where chemicals have to be heated. The rate of flow is decided by the calculation of heat exchanger and accordingly the pump capacity and pipe size has been decided. The complete piping is insulated by rock wool with aluminum cladding on it to prevent heat loss. The tube type heat exchanger is used so that it can occupy the minimum space with max heat exchange as well as it should be removable to clean the scaling formed due to the deposition of chemical on the tube. The on-off valves have been provided at the inlet of the heat exchanger of each tank to control the hot water flow as per requirement. This has been done manually and temp indicators with electronic buzzers are provided to indicate the temp and removal time of each batch. Compressed air is also circulated to mix the chemical uniformly & to get uniform temp. at every point in the tank.