Low temperature refrigeration calculation and gas-liquid exchange

by:CBFI     2020-10-13
Low temperature part of the compressor refrigeration flow ( To consider the actual use of cold mass loss) To:

q * d = Qcj/( h1 - h7) = 40001 ( 325. 98 - 111. 04) kg/s= 18. 61 kg/s

high temperature part of the refrigeration cycle at least shall be provided to the low temperature part of cold quantity for

Q. = my mouth. d( h4 - hs) = 18. 61× ( 386 - 128. 6) KW to 24800 kW

cascade refrigeration system operating characteristic analysis

( 1) Circular form and energy efficiency when evaporating temperature is low, - 80 - - 100℃) Worketh for with freon qualitative, auto-cascade type generally use two stage compression in high temperature part, the low temperature part of the pressure ratio, temperature and part of low-pressure compressor pressure ratio is equal, this indicated efficiency of each compressor and gas transmission coefficient is higher, and work under favorable conditions; When the evaporation temperature lower ( - 100℃) , high and low temperature can be used for the cascade of two stage compression type, high temperature and part two stage compression low temperature part of the single stage compression cascade system, reduce the r t compressor pressure ratio, increasing the gas transmission coefficient, improves the evaporation pressure, reduce the compressor capacity and friction power, make the economy improved.

cooling evaporation temperature is lower, the greater the irreversible loss of heat transfer temperature difference. Condensation heat transfer temperature difference, the size of the evaporator, therefore, not only affects its heat transfer area and cold energy loss, but also affect the efficiency of the whole machine. Therefore, low temperature cascade refrigerating machine condensing temperature difference of heat transfer in the evaporator should take smaller values, had better not more than 5 0 c. In order to improve the performance index of auto-cascade cooling mechanism of cold, or improve the compressor's working conditions, often in the cascade refrigeration system using some of the heat exchanger. Such as:

1) water-cooled or air-cooled chillers, for low temperature part of the compressor exhaust temperature is higher, the gas cooled to 30 - 45 0 c, entering the condenser evaporator, again in order to reduce the heat load of condenser evaporator, improve the efficiency of the cycle. Use water or air cooling after cooling, according to the refrigeration of different evaporation temperature technology, refrigeration coefficient can be improved 7% Total capacity can be reduced 6% - 18%, compressor 12/7e。

2. Steam heat exchanger, faw, raise the temperature of the compressor suction vapor for low temperature part, improve the working conditions of the compressor, but also reduce the heat load of condenser evaporator role.

3. Steam a liquid heat exchanger ( Often referred to as regenerator) , it is to use low temperature steam out of the evaporator, industrial ice machine liquid before cold throttle valve. Supercooled liquid increase the refrigerating capacity of the unit, suction superheat improved the working conditions of the compressor. Inhalation of vapor superheating temperature should be 612 - 63cc。 High for small values, on. Low take great value. When steam - in the cryogenic system Liquid heat exchanger cannot achieve this degree of superheat, steam will then use a faw heat exchanger. Regenerator could also be used in high temperature cascade refrigerating machine part, but in the single stage ammonia refrigeration system is harmful.

in the refrigeration system using the above some of the heat exchanger, although able to achieve different purposes, but the system is complicated, the flow resistance and increase the possibility of leakage, produce cold damage of increase in the number of places. Therefore, in the design can be used according to the size and conditions, as far as possible to simplify. Especially for small refrigeration laughed and using mixed working medium run chillers, even can not L any kind of heat exchanger.

( 2) Variable condition features cascade refrigeration y1 evaporation temperature regulating range is relatively small, this is because the condensation temperature of low temperature level not especially limit to improve. According to the CB - 10875 89 of the regulation, the maximum working pressure of piston compressor is about 1 & 6 times; 10 kPa。 Compressor matching series products, for example, made of cascade refrigerating machine, if in the cryogenic system

the highest condensation temperature of R23 as lO ℃, the corresponding pL. d=1 545× 10 ' KPa, and C. H6 is - 17 ℃ and 1. 57× 10 kpa。 In such cases, low temperature evaporation temperature adjustable cap, should take a test or calculation to determine.
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