4.5.Non condensable gas

Unit 4 - Refrigerants

4.5.Non condensable gas
Non condensable gases like air, chlorine, oil and water vapors and combinations of oxygen, hydrogen and nitrogen, collect within the refrigerating system. Since these gases do not condense with the refrigerant instead they usually collect in the condenser or receiver. Non condensable gases vary the condensing pressure above that required for the condensing temperature. This is so because it has been preserves scientifically that if several gases exist in the same closed container; the total pressure is the sum of the individual pressure that each gas would exist if it were alone in the container. The higher pressure (due to non condensable gases) increases the work of the compressor reduces the refrigerating effect and raises the power consumption. The sources of non condensable gases from outside the systems are Improper evacuation of a new system before charging, drawing air into the crankcase of the compressor during servicing, air may enter through the shaft seal when the system is being operated under a vacuum, some air may come from outside when the compressor is stopped for repairs, air may come from inside when the refrigerant or/and oils is decomposed under the heat of compression, air may also come from inside when refrigerant used is not 100% pure, but contains some foreign matter and through leaks in the systems when operating under vacuum. Such a presence of non-condensable gas or air in the system results in - undue increase in the condensing pressure, unnecessary increase in the work done by the compressor which means that a greater horse power is required and thereby the power consumption is increased and thereby the power consumption is increased without any benefit, a promotion in the oxidation of the oil, acting as a resistance to heat transfer, which makes a decrease in refrigeration capacity and gas also acts as an insulation. Therefore, to remove the nonconsensable gas or air) gas purgers are used.



Last modified: Monday, 29 August 2011, 7:28 AM