, Cascade systems have been used for applications where the compression ratio of the refrigerant is

Cascade Systems and Applications cascade systems have been used for applications where the compression ratio of the refrigerant is too high and / or where evaporation actually lower temperatures (<-50C) are required. Lately this type of system has become more popular to be necessary in low temperature catering food warmers applications using R744 (CO2) as a refrigerant in systems known as subcritical. Different sectors are in cascade systems the best solution for efficiency catering food warmers and performance in low temperature systems.
, Cascade systems have been used for applications where the compression ratio of the refrigerant is too high and / or where really low evaporation catering food warmers temperatures (<-50C) are required. Lately this type of system has become catering food warmers more popular to be necessary in low temperature applications using R744 (CO2) as a refrigerant in systems known as subcritical. What is a cascade system? A cascade system consisting of two independent systems of a stage, where the system with lower evaporation temperature used exchanger as condenser for rejecting catering food warmers heat therefrom, using the system evaporator with higher evaporation temperature. Usually use different refrigerants and their application is mainly for low or ultra-low temperature. (See diagram 1 and 3). Figure 1 two sets of cascaded stage = System Advantages of using a cascade system compression ratio of each system decreases, which causes the increase in volumetric efficiency of each of the stages and, therefore, the system as a whole is more efficient so that less displacement of the compressor is also needed. Also, the discharge temperature (see Figure 1) is decreased compared to a single stage system, which benefits the oil temperature and good lubrication of the compressor. Compression ratio PR, where P2 is the discharge pressure in psia and P1 is the suction pressure in psia. Compression ratio is the result of dividing the discharge catering food warmers pressure catering food warmers and suction pressure in psia. Psia = psig Psig is +14.7 psi gauge pressure. Psia is the absolute pressure including atmospheric pressure.
Furthermore, commonly used high-pressure refrigerant called whose characteristics allow the suction pressure is positive and not be necessary to work under vacuum, even when the saturated suction temperature (TSS) is very low. The R23 and R508B refrigerants catering food warmers are the most popular for these applications.
R-22 (psig)
2.6
7.4
13.2
20.1
28.2
37.7
48.8
61.5
76
92.6
121
168
226
297
382
To use a cascade system is needed to note that the compressors are within applicable limits, which are well lubricated and ensure that no liquid gets by suction. In the high system this is not a problem as it is basically a system of known MT.
For low system, other parameters have to care. For example the return gas temperature should not be less than -60 C as a precaution not to damage the compressor, as this is made of cast iron.
You should also take care of the oil temperature to ensure you have the proper viscosity for both to return the oil to adequately lubricate the compressor. Normally a temperature of the gas return overheated compressor or high (> 20K) is required. For this exchanger between the suction line and liquid used.
In the case of oil, it has to prevent this go to the system having an oil separator Generously sized and high efficiency. Failure to return the oil, perhaps necessary cycles "thaw" is to raise the suction pressure, mass flow increase and decrease oil viscosity with increasing temperature the same and so this return to the compressor. Other coolant may be used to help decrease the viscosity of the oil as the R600 (butane) or R601 (pentane). Normally this method is a must try adding only grams of these refrigerants to obtain the required result. The amount of R600 or R601 depends on the system size.
Moreover, when working with such low temperatures, both pipe insulation and all parts that are exposed and have a lower temperature than the dew and this being sufficient insulation in the parts where the temperature is below required 0 C. This is to prevent condensation and / or freezing of moisture in the atmosphere.
By high pressures with these refrigerants (R508B, R23, R744) is