Energy Efficient Solar Milk Chiller

Renewable Resource, Hybrid Inverter, Capacitor Technology, Inverter Technology, Solar PV Module, Milk Chiller, Data Logger, Rotary Compressor, Reciprocating Compressor.

ABSTRACT

Life stock is the major sector of agriculture which is of great importance for Pakistan. It has a major contribution towards the economy of Pakistan with a 55.9 % participation in agriculture sector. Pakistan is fourth largest country in milk production with 50.9 Billion tons per annum out of which only 5% is processed and pasteurized hardly and remaining milk is handled by milk men under non-hygienic conditions which causes milk borne diseases. Milk is perishable food having shelf life of few hours therefore milk processing is done to deactivate the microorganisms in the milk and increase its shelf life for future use. It is an energy intensive process and mostly conventional form of energy is used for this purpose. Solar power is the sustainable source of energy and there is an average solar global radiation of 5.3kWh/m2/day persist in the country with more than 300 sunny days in a year. The objective of the study was to design and develop a solar assisted milk pasteurizer and to evaluate its performance. The developed solar assisted milk pasteurizer consisted of heating and cooling unit. Heating unit made of shell and tube type coil to heat up the milk up-to 730C for 15 seconds. Cooling unit has a chiller for sudden cool down the milk from 350C to 40C within 2 hours. Solar milk chiller had capacity of 200 liters, chiller semicircular pug mill type SS-304, a 2kWp PV system having eight PV modules each of 250Wp, a hybrid inverter 3kVA that convert 24V DC current into 220V AC current and two batteries 150Ah each as a backup source to meet weather fluctuations. One ton of vapor compression refrigeration system was filled with R410a refrigerant with inlet pressure of 118psi and the outlet pressure of 300psi was coupled with the chiller through coils at bottom side of the vessel. An agitator was installed with a lid on the tank to stir the milk continuously inside the chiller to make sure that homogeneous milk cooling to avoid freezing of the milk in the bottom of the chiller. Inverter technology was also coupled with the chiller to eliminate the torque load of 9-10 ampere to a uniform torque load of 3.2 ampere which is a big hurdle in using solar PV system. Efficiency of the system was achieved up-to 69%. The Coefficient of Performance (COP) of the system was found to be 3.18 and the cost of the processing milk was calculated1.17Rs/liter.

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