" Refrigeration " refers to the artificial reduction of the temperature of a cooled object ( such as an object or space ) below ambient temperature and maintaining this temperature.
The difference between the cooling process and the cooling process is that the direction of heat transfer is different. The cooling process is a process in which heat spontaneously passes from a high temperature heat source to a low temperature heat source. The refrigeration process is the reverse of the cooling process, so it is also called the reverse heat transfer process. The process of taking out heat from a low-temperature heat source is also referred to as the process of releasing cold to a low-temperature heat source, that is, cooling.
According to the second law of thermodynamics, the refrigeration process is impossible to proceed spontaneously. In order for the refrigeration process to be realized, a certain amount of external energy must be consumed to compensate. This energy can be electrical energy, thermal energy, solar energy or other energy. Machines and equipment that implement manual refrigeration are collectively referred to as " refrigerators " . A chiller is an energy-consuming machine that uses the state of matter to achieve refrigeration. Such media that operate in a chiller are referred to as refrigerants ( or refrigerants ) . The continuous research and development of refrigerators and refrigerants has made refrigeration technology increasingly effective in various fields and has been widely used in various fields.
From the definition of refrigeration, it can be known that the temperature range from below the ambient temperature to near OK is the temperature range studied by refrigeration technology, and people use various refrigeration methods to achieve different low temperatures. According to the research object, refrigeration method and people's habits, the majority of the refrigeration industry's point of view is to divide the cooling temperature zone into the following three areas:
1) Ordinary refrigeration: 120K or more.
2) Low temperature refrigeration: 120 ~ 4 . 2K .
3) Ultra-low temperature refrigeration: 4 . 2K or less.
Conventional refrigeration methods commonly used are liquid gasification refrigeration, gas expansion refrigeration, and thermoelectric refrigeration. Liquid gasification refrigeration utilizes the vaporization of a low-temperature refrigerant liquid to absorb the heat of the object to be cooled to achieve the purpose of refrigeration, such as vapor compression refrigeration, absorption refrigeration, adsorption refrigeration, and steam injection refrigeration. The gas expansion refrigeration uses the high-pressure refrigerant gas to absorb the heat of the object to be cooled after the pressure drop and temperature expansion. After the thermoelectric refrigeration uses the semiconductor thermocouple to pass the direct current, there is a phenomenon in which one end absorbs heat and one end releases heat to achieve refrigeration. Other refrigeration methods such as magnetic refrigeration are under development.
At present, the refrigeration methods applied in air-conditioning engineering are mainly vapor compression refrigeration and absorption refrigeration. The refrigeration part of this course is written for these two parts. Refrigeration technology is based on the principles of thermal engineering and fluid mechanics. In the process of learning, we must pay attention to theoretical practice and lay a good foundation for engineering practice.
1-1 refrigeration principle
The ideal refrigeration cycle - there is no irreversible loss in the inverse Carnot cycle. The ideal refrigeration cycle operating between two constant temperature heat sources can be achieved with an inverse Carnot cycle. The inverse Carnot cycle consists of two isothermal processes and two isentropic processes . In theory, it can be composed of a compressor, a condenser, an expander and an evaporator in a wet steam region, and a refrigeration system can be realized by isothermal evaporation and isothermal condensation of the refrigerant in the wet vapor zone. It should be noted here that the inverse Carnot cycle is based on the assumption that there is no heat transfer temperature difference between the two processes of evaporation and condensation and the low temperature heat source and the high temperature heat source. The high and low temperature heat sources are constant, there is no flow resistance when the refrigerant flows, and the compression and expansion processes are equal. Under the reversible condition of the entropy process, the whole process of the cycle is a reversible process, so it is called an ideal refrigeration cycle.
The inverse Carnot cycle schematic is shown in Figure 1-1 . The refrigerant expands along the 3 '' → 4 '', the temperature drops from T '' k to T '' o ; then, it expands along the constant temperature line 4 '' → 1 '', and the refrigerant is in the T during the constant temperature expansion . '' o absorbs heat from the substance to be cooled q '' o ; the refrigerant is adiabatically compressed from state 1 '' to state 2 '', temperature rises from T '' o to T '' k ; constant temperature along line 2, a 3, compression, constant temperature in the compression process, the refrigerant 'q emit heat to the coolant temperature at k' is T '' k. The four state points in the loop 1 '' → 2 '' → 3 '' → 4 '' → 1 '' are represented on the T-S map ( temperature - entropy map ) , as shown in Figure 1-2 . According to the knowledge of thermal engineering, the expression of the coefficient of refrigeration can be
The refrigeration coefficient is the ratio of the cooling capacity to the power consumption of the decompression work. It is an economic indicator. The larger the refrigeration coefficient, the better the economy. The ideal refrigeration cycle has a large coefficient of refrigeration, so it is used as a standard for refrigeration cycles. The actual cooling cycle the irreversible loss coefficient is lower than the ideal refrigeration cycle refrigeration coefficient with heat sophistication? To represent the actual extent of the refrigeration cycle close to the ideal refrigeration cycle indicators. Its expression is
Characteristic
1.Seeds type F1 hybrid chilli seeds
2.Fruit skin red.yellow.green
3.maturity days 90 days after sowing
4.Resistance Virus disease, blight
5.Indoor or outdoor Both
6.Yield 2000 to 2500kgs/667㎡
7.Germination rate More than 85%
8.Tags Hybrid chilli seeds
Green Pepper And Hot Pepper Seed
Green Pepper Seed,Hot Pepper Seed,Horn Pepper Seed, Capsicum Seed, Bell Pepper Seed
Ningxia Zhongqing Agricultural Technology Co. Ltd. , https://www.zq-vegetableseeds.com