Leakage Detection of refrigerants

 Leakage of refrigerant from a refrigeration system affects the performance of a sealed system  adversely.  Both suction as well as discharge pressures reduce due to loss of refrigerant. There will be less liquid and more flash gas, which has negative effect on several components of the system. For example, it is possible that in stead of liquid, a mixture of liquid and vapour may enter into the expansion valve leading to its malfunctioning. Due to lower suction pressures, the lubricating oil return becomes difficult. If the suction pressure due to refrigerant leakage falls below atmospheric pressure, then there is a possibility of air leaking into the system. This will bring moisture into the system and the presence of moisture affects the system adversely.

Two widely used leak detection methods are:

i.  HALIDE DETECTION

ii. ELECTRONIC DETECTION

The halide leak detector works on the principle of change of colour of a flame in the presence of the refrigerants. When a fluorocarbon based refrigerant such as R12 or R22 is sucked through a sampling tube and passed over a surface whose surface temperature is high (around 500^oC), then the refrigerant vapour breaks down and forms a foul smelling gas known as phosgene (COCl₂). When this gas is passed over a glowing copper (heated by the flame of the torch itself) it forms copper chloride, which changes the colour of the flame from pale blue to bright green. The halide torch usually burns methyl alcohol, butane gas or acetylene and is similar in construction to that of a blow lamp with a provision to draw the air for combustion through a sampling tube. If the air consists of refrigerant (due to leakage) then it is detected by the change in the colour of the flame. Using halide leak detectors leaks as small as 1.5 to 2 oz. Per year could be detected. However, use of halide leak detectors requires certain precautions to be taken while using. It cannot be used with hydrocarbon refrigerants.

Electronic leak detector is based on the principle that when halogen vapour is heated, positive ion concentration is increased and this increase is suitably magnified to an audible or visual signal. Thus the leak detector consists of a sampling tube through which air around the refrigeration system is drawn by means of a small fan. The air sample is passed over a heated platinum element. Under normal (clean air) conditions positive ion current flows under a voltage of 240 V between the ion emitter and collector (anode and cathode), However, when a sample containing halogens is drawn into the probe, an immediate increase in positive ions results and this is magnified by the electrical circuit so that an audible or visual signal is produced. Exact location of the leak can be determined as the strength of the signal increases as the probe is moved towards the leak and decreases when it is moved away from the leak. In some leak detectors a reference leak is built for comparison and adjustment of sensitivity of the detector. It is also possible to make compensation for background contamination. Electronic leak detector is highly sensitive and it can detect leaks as small as 0.25 to 0.50 oz. Per year. The operation is clean, quick and free from any fire hazard. However, it is important to maintain the input voltage for good sensitivity of the detector. They are designed to detect refrigerant leaks but should not be immersed are kept in refrigerant streams, for example from the refrigerant cylinder.