Refrigeration unit used for domestic purpose called locally as freezers, cold storage box and air conditions and technically called as vapor-compression refrigeration systems. Based on the application at instance for food and beverage storage at temperatures negative to 25 degree centigrade freezers are used. To maintain comfortable temperature in living rooms air conditioners terminology used.
Operation units i.e, evaporator and condenser in refrigeration circuit made with a heat exchanger design. Tubes extended with fins transfer heat to and from the refrigerant to surrounding. In case of air conditioning, a set of bent tube with fins fitted in interior of the room. A fan or blower forces air to pass through the gaps between the fine fins of evaporator where the coiled tubes are fitted compactly. Heat from the air absorbed by the refrigerant than air temperature dropped below ambient.
Similarly, condenser present at outdoor works on the principle of heat exchanger of tube with fin air circulated mode. Excess heat in the refrigerant absorbed by the air. Outdoor fan circulates the natural air through the condenser.
Split air conditions work based on above mode of operation. Window air-conditions units contains the condenser and evaporator in closed box type unit. Food storage freezers built with the storage space fitted with coils on its walls. The compressor and evaporator setup placed outside of the refrigeration unit.
Engineering design aspects to improve efficiency of Refrigeration unit:
1. Refrigerant selection and it effect on evaporator:
Propane (R290) is best refrigerant when compared to R600a (isobutene), R134a (1,1,1,2-Tetrafluoroethane), R22 (Chlorodifluoromethane), R32 (Difluoromethane) and R410A in terms of coefficient of performance when finned tube evaporator used in experiment. Energy conservation parameter if improved in design of evaporator heat exchange it could influence the concept of climate change problem. One of the mainly considered variables in the design is the selection of refrigerant that will not show high global warming potential.
Properties to consider for selection of refrigerant:
- Liquid conductivity
- Saturation vapour pressure
- Dew point temperature
- Vapour density
- Latent heat
Refrigeration equipments are indirect cause for increase in CO2 emission, by the design and good refrigerant, efficiency should be increased to control this emission.
Heat transfer operation in heat exchangers of the units depends mainly on the;
- Compatibility of lubricating oil and refrigerant
- Oil flow rate and circulation pattern in and out of the compressor
2. Energy loss prevention:
Air conditioning system consumes lots of energy and more energy is lost. Energy saving methods help to save energy and improve the performance of the compressor that used in air conditions. Heat pipe heat exchanger is one of the well-designed devices; it can save energy during the heat exchange.
Heat pipe heat exchangers are fitted as condensers that placed outside of the room to release the heat into the atmosphere. This type of heat transmission devices are simple in construction and perform heat transfer with less temperature differences. As the outside temperature increase in summer the delta temperature, decrease hence rate of heat transfer decreases. In this situation heat pipe heat exchangers work well.