Weak current College】 【refrigeration system for two-stage compression refrigeration cycle analysis.

<br> A, adopt the reasons of the two-stage compression <br> <br> Refrigeration systems for condensing temperature (or condensing pressure) decided to coolants (or environmental) of temperature and evaporation temperature (or evaporation pressure) depends on cooling .requirements. Due to the development of production, the requirements for refrigeration temperature getting lower and lower, therefore, in many practical applications, refrigeration compressor pressure to high pressure side (condensing pressure) for low-voltage-side pressure (evaporation pressure) ratio ( .ie compression ratio), high conditions. The ideal gas equation of State for Pv / T ≡ C, this time using the single-stage compression refrigeration cycle, the compression of superheated steam ended temperature must be very high (V, PT ↑ ↑ → .), so he will produce the following many problems. <br> <br> 1. compressor gas coefficient λ significantly lower, and when the compression ratio ≥ 20, λ = 0. <br> <br> 2. the compressor unit refrigeration .quantity and unit volume cooling capacity is greatly reduced. <br> <br> 3. the increase in power consumption of the compressor, refrigeration coefficient decreases. <br> <br> 4. must adopt the high fire point of lube lubricant viscosity with .temperature rise. <br> <br> 5. high temperature steam out of lubricating oil increases, increasing the load oil separation, and reduces heat transfer performance of the condenser. <br> <br> To sum up, when the compression ratio is .too high, the use of single-stage compression cycle, not just not economical, and even impossible. In order to solve the above problem, meet production demands, reality often used with intercooler and two-stage compression refrigeration cycle. However, two- .stage compression refrigeration cycle required equipment investment by large multiple-stage compression, and also more complex. Therefore, the use of two-stage compression refrigeration cycle is not under any circumstances are favourable, generally when the compression ratio ≥ 8, adopts two-stage .compression, more economic and reasonable. <br> <br> Second, two-stage compression refrigeration cycle of composition and common form <br> <br> Two-stage compression refrigeration cycle, from the evaporator of refrigerants to be low and high pressure .compressors compress twice before entering the condenser. And in the middle of two compression settings for the intercooler. Two-stage compression refrigeration cycle is made up of two compressors, double machine (one for low level compressor, another for high grade compressor), two .-level system or one standalone compressor consists of two-level system, one or two cylinders as high pressure cylinder, the remaining few cylinder as the low pressure cylinder, its high and low pressure cylinder number than average of 1: 3 or 1: 2 .. <br> <br> Two-stage compression refrigeration cycle because the throttling and intermediate cooling degree days depending on different cycle, usually divided into two throttle intermediate full cooling, two throttle intermediate incomplete cooling, a full throttle intermediate cooling and a throttle intermediate .incomplete cooling four two-stage compression refrigeration cycle. Of these, two throttle is the refrigerant from the condenser out to successively after two expansion valve and then enters the evaporator, namely by condensing pressure, the throttle to intermediate pressure by intermediate pressure, the throttle .to evaporation pressure and a throttle only after an expansion valve, the majority of the refrigerant from condensing pressure directly, evaporation of the throttle to contrast, single throttling system is relatively simple, and can use its large pressure difference achieving distance or high cold storage for .fluid. So practice in basically a throttling level compression refrigeration cycle. As for which an intermediate cooling; the type of refrigerant from the selection. Usually two-stage compression using ammonia refrigeration systems, and intermediate full cooling two stage compression freon cooling system, you .often use intermediate does not completely cool. <br> <br> 1. a full throttle intermediate dual-stage cycle of cooling <br> <br> This system is characterized by coil coolers. It has two-level throttling loss effect of reducing .the throttle, and played on low level exhaust full cooling effect. Its work is: <br> <br> In the evaporator of low-temperature refrigerant vapour (status 1), the low pressure compressor suction and compressed into intermediate pressure of superheated steam .(status 2), and then enter the same pressure of the cooler intercooler cooling inside into dry saturated vapor (status 3). Saturated vapor pressure dry and high pressure compressors for breathing and compression to the condensing pressure of superheated steam (status 4), .then enter the condenser is condensed into a refrigerant liquid (State 5). And then divided into two road, all the way through the expansion valve F after the throttle buck (State 8) into the intercooler, most liquids from the other way to enter .the intercooler coil in supercooled (State 6), but because of the heat temperature, it is not in the coil can be cooled to an intermediate temperature, rather than an intermediate temperature generally high △ t = 3-5 degrees centigrade. Supercooled liquid after .after primary expansion valve throttle down into low temperature and low pressure of supercooled liquid (State 7), and finally enters the evaporator heat absorption and evaporation, produces cold effect. <br> <br> This system applies only to R22 and R717 two- .stage refrigeration cycle. <br> <br> 2. the intermediate single throttling is not fully double-loop cooling <br> <br> A throttle intermediate incomplete cooling two stage circulation, mainly applies to the freon cooling device, the use of a .heat cycle. This system is characterized by: refrigerant mainstream first coil coolers too cold, then by recuperators further cooling; and low pressure compressor suction-greateropportunities superheat; in addition, the low level of exhaust not completely cooled to saturation. <br> < .br> Its working process: from the evaporator from the steam as a regenerator was low pressure compressor suction pressure, compression to intermediate and intercooler from dry saturated steam in the pipes for the hybrid machine from low pressure, discharge of superheated steam is cooled and then .enter the high-pressure compressor, the compression to the condensing pressure and enter the condenser, the condensation of refrigerant liquid after the pressure has entered the intercooler snake coil for cooling, and then enter the recuperator and from the evaporator from the low temperature and low .pressure steam for heat, bring to cooler snake coil in the supercooled liquid cooled again, and finally through the expansion valve enters the evaporator heat absorption and evaporation. <br> <br> The circulatory system, only applies to R12 or R22 two-stage .refrigeration cycle, and must not be usedAmmonia refrigeration systems. This is because although the high and low voltage level inhalation steam superheat is relatively large, but because of the heat index freon K values smaller than ammonia, the compressor discharge temperature is not high. < .br> <br> 3. two full throttle intermediate dual-stage cycle of cooling <br> <br> This system features a selection of the MSF intercooler. It plays two roles, one of which is the equivalent of two throttle intermediate accumulators, .the second is the use of a small part of the thermal evaporation of liquid, low voltage machine full intermediate cooling exhaust. This type of refrigeration system, only applies to R717 or R22 's two-stage compression refrigeration cycle. In order to prevent it .from intercooler saturated liquid in pipelines in Flash into steam, often require the intercooler and the distance between the evaporator to close. <br> <br> The analysis shows that IMIS on two-stage compression refrigeration cycle, not only reduces exhaust temperature high pressure .machine, improves compressor lubrication conditions, but also because of the levels of compression ratio is smaller, the compressor oil vapor coefficient increased substantially. In addition, the use of two-stage compression cycle power consumption than single-stage compression cycle less power. < .br> <br> <br>.