Engineering analysis of refrigeration process in t

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Engineering analysis of refrigeration process of chemical operation

I. the refrigeration operation of compressed steam refrigeration cycle is a process of taking heat from low-temperature materials and transferring this heat to high-temperature objects. According to the second law of thermodynamics, this heat transfer process cannot be carried out automatically. Only when the consumed energy is supplemented from the outside, i.e. the outside must do work, can the heat be transferred from low temperature to high temperature

when the liquid is vaporized into steam, it is necessary to absorb heat from the outside, so as to reduce the outside temperature. The boiling point (or condensing point) of any substance changes with the change of pressure. For example, see table 16-1 for the change of ammonia boiling point with pressure

it can be seen from the table, especially in the field of medical devices or automobiles, that the lower the pressure of ammonia, the lower the boiling point; The higher the pressure, the higher the boiling point. Using this characteristic of ammonia, liquid ammonia vaporizes at low pressure (101.325kpa), absorbs heat from the cooled substance and reduces its temperature, so as to achieve the purpose of cooling the cooled substance. At the same time, the vaporized gaseous ammonia is compressed to increase the pressure (e.g. to 1220kpa). At this time, the condensation temperature of gaseous ammonia (30 ℃) is higher than that of general cooling water. Therefore, normal temperature water can be used to condense gaseous ammonia into liquid ammonia

refrigeration uses the 2009 feature that the boiling point of the refrigerant changes with the pressure. 5. The upper jaw holder is pushed backward, so that the refrigerant vaporizes and absorbs the heat of the cooled substance at low pressure to reduce its temperature, so as to achieve the purpose of cooling the cooled substance. The vaporized refrigerant condenses into a liquid under high pressure. This circulation operation achieves the purpose of refrigeration with the help of the heat absorption and heat release process of the refrigerant when the state changes. If the refrigerant breaks and leaks due to the equipment under the pressure of high and complex corresponding circuit, the liquid refrigerant will vaporize rapidly and explode

II. Refrigeration cycle process

refrigeration cycle is a cycle operation process that uses a working medium refrigerant to make it absorb heat at low pressure and release heat at high pressure, so as to achieve the refrigeration of cold substances

for the refrigerant in the refrigeration cycle, the low-pressure gas must be compressed to do work before it can become a high-pressure gas, that is, the outside world must consume compression work to realize the refrigeration cycle. If the above refrigeration cycles are connected with appropriate equipment to make the heat transfer working medium refrigerant (ammonia) continuously recycled, a basic working process of compressed steam refrigeration will be formed, as shown in figure 16-4

the ideal refrigeration cycle (reverse Carnot cycle) consists of reversible adiabatic compression process (compressor), isobaric condensation process (condenser), reversible adiabatic expansion process (expander), isobaric isothermal evaporation process (evaporator), etc. The actual refrigeration cycle is as follows

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