JEMS INDUSTRIES

Chinchwad, Pune, Maharashtra

A domestic refrigerator is one of the simplest of refrigeration devices widely used all over the world. It uses a fractional HP hermetically sealed compressor, a natural convection condenser, a capillary tube as an expansion device, and direct expansion type roll-bond evaporator. As far as the controls are concerned, an ON-OFF type thermostat controls the average temperature of the refrigerator. The inside heat transfer takes place by natural convection and convective currents set due to density difference of cold and warm air.

List Of Experiments:

1. To study construction and working of a domestic refrigerator.
2. To plot the cycle on P-H Chart.

Rating conditions * : Ambient temperature= 35^o C, atmospheric pressure = 1.01 bar, suction pressure=35 psig, discharge pressure= 180 psig, evaporation temperature=7.7^o C, discharge temperature=55^o C

Vapour Absorption Refrigerator earlier known as Electrolux refrigerator is an self contained refrigerator working on absorption technology.In the absence of a compressor or pump, the circulation takes place by density difference. The system is pre-charged with three fluids namely water, ammonia and hydrogen. Hydrogen is used as an inert gas and does not undergo any phase change and heat transfer processes. Its purpose is to keep the pressure of the system constant. It uses an electrically operated generator, where, the ammonia vapours dissolved in water are separated and pure ammonia vapours enter the condenser. In the condenser, the high pressure vapours reject its latent heat to the surroundings and get liquefied. The liquid ammonia expands through expansion device where its pressure and temperature is reduced and cold low pressure vapour enters the evaporator where it absorbs heat from the space to be cooled and then vaporized ammonia absorbs in water. This strong solution then enters the generator and the cycle repeats. PRINCIPLE OF OPERATION:Electrolux principle works on 3-fluid system. There is solution circulation pump. Total pressure is the same throughout the system. The third fluid remains mainly in the evaporator thus reducing partial pressure of refrigerant to enable it to evaporate at low pressure and hence low temperature.The schematic diagram of the Electrolux refrigerator working on NH3-H2O system with H2 as the third fluid is shown in figure. Liquid NH3 evaporates in the evaporator in the pressure of H2.Hydrogen is chosen as it is non corrosive and insoluble in water.A thermosyphon bubble pump is used to lift the weak aqua from the generator to the separator. The discharge tube from the evaporator the generator is extended down below the liquid level in the generator. The bubbles rise and carry slugs of weak NH3-H2O solution into the separator.Two U-bends are provided as vapour- locks to prevent H2 from getting into the high side or solution circuit.Partial pressure of H2 provides the pressure difference of NH3 between the condenser and evaporator. Accordingly, we have:In condenser pure NH3 vapour pressure = Total pressure In evaporator NH3 vapour pressure = Total pressure - partial pressure H2For example, consider the condenser temperature at 50 C , and evaporator temperature as -15 C. The corresponding vapour pressures of NH3 are:Condenser, Pk = 20.33barEvaporator outlet, Po2 = 2.6barThe approximate pressures in various parts of the system, then will be as given in the table.

It has been assumed that vapours leaving generator top are in equilibrium with entering rich solution at 40 C, at which temperature saturation pressure of NH3is 15.45bar. It has also been assumed that the temperature at evaporator inlet is -25 C at which temperature saturation pressure of NH3 is 1.516bar.

Specifications subject to change without any notification.

LIST OF EXPERIMENTS:

1. To study construction and working of a vapour absorption refrigerator
2. To evaluate performance of the refrigerator by calculating the C.O.P of the system.