Environmental chamber used to test the performance of materials in a variety of environments, equipment and testing, various materials, heat resistance, cold resistance, dry resistance, moisture resistance. For electronic, electrical, telecommunications, meters, vehicles, plastic products, metals, food, chemicals, building materials, medical, aerospace and other products testing quality.
Cascade refrigeration cycle
1.Cascade refrigeration cycles of two single stage refrigeration systems
2.Cascade refrigeration cycle of two stage compression system
3.Three element cascade refrigeration cycle
In order to obtain low temperature below 20 degrees, a cascade refrigeration cycle system is adopted to obtain low temperature, and two stage cascade refrigeration is adopted
Causes of circulation:
1. limitations of thermophysical properties of refrigerants
The temperature of refrigerant now constant temperature and humidity test machine in the single-stage refrigeration cycle basically is used in R404A, in an atmosphere of the evaporation temperature is -46.5 DEG C (R22/-40.7 C), but the air cooling condenser heat transfer temperature about 10 degrees Celsius (usually in the forced air cooling cycle, the evaporator and the temperature inside the box), is only for the -36.5 low temperature, of course, through the evaporation pressure to reduce the compressor, can reduce the minimum evaporation temperature of refrigerant R404A to -50 DEG C.
2. single stage compression steam refrigeration cycle pressure ratio limit
The minimum evaporating temperature of single stage vapor compression refrigeration machine, condensing pressure mainly depends on its compression ratio. And the condensing pressure refrigerant refrigerant by category and environmental media (such as air or water) temperature, under normal circumstances, it is in the range of 0.7~1.8Mpa. The compression ratio and the condensing pressure and evaporation pressure and when the condensate pressure is constant, with the decrease of evaporation temperature, evaporation pressure also decreased, so that the compression ratio increases, it will increase the exhaust temperature of the compressor, lubricating oil thinning, the lubrication condition is bad, serious when even appear coking and scuffing phenomenon; on the other hand, the increase of the compression ratio will cause the gas compressor transmission coefficient is reduced, the refrigeration amount is reduced, the actual compression process from isentropic process farther, compressor power increases, the refrigeration coefficient decreased, the economy decreased. Some will have the following effect:
A. the lower the evaporation temperature of any refrigerant, the lower the evaporation pressure, and the low evaporation pressure may sometimes cause the compressor to be difficult to breathe in, or to allow the outside air to enter the refrigeration system
B. when the evaporation temperature is too low, some common refrigerants have reached the solidification temperature, and can not achieve the refrigerant flow, circulation
C. evaporation pressure decreases, the specific volume of refrigerant increases, the mass flow rate of refrigerant decreases, and the cooling capacity drops greatly. In order to obtain the required cooling capacity, the volume of air suction must be increased and the volume of the compressor is too large.
Climate Instrument has over 10 years of industry experience in designing and manufacturing environmental chambers and temperature controlled products. If you have questions,contact us please.