1, condensation temperature
The condensation temperature of the compressor system refers to the temperature when the refrigerant condenses in the condenser, and the corresponding refrigerant vapor pressure is the condensation pressure. The condensation temperature is one of the main operating parameters in the refrigeration cycle. For the actual refrigeration device, the condensation temperature can be said to be the most important operating parameter because of the small variation range of other design parameters, which is directly related to the refrigeration effect, safety and reliability and energy consumption level of the refrigeration device.
2. Evaporation temperature
Evaporation temperature refers to the temperature when the refrigerant evaporates and boils in the evaporator, which corresponds to the corresponding evaporation pressure. Evaporation temperature is also an important parameter in the refrigeration system. The evaporation temperature is the refrigeration temperature in an ideal state, but in actual operation, the evaporation temperature of refrigerant is slightly lower than the refrigeration temperature by 3 to 5 degrees.
3, suction temperature
The suction temperature refers to the temperature when the refrigerant enters the compressor, which is generally higher than the evaporation temperature. Because the evaporation temperature is the saturation temperature of refrigerant, and the suction temperature is the temperature of superheated gas, the refrigerant becomes superheated gas at this time. The difference between the suction temperature and evaporation temperature at this time is the suction superheat.
4. Excessive heat
Definition of superheat: refers to the temperature difference between the low pressure side and the steam in the temperature sensing package. Measurement method of superheat: Measure the evaporation pressure as close as possible to the bulb, convert the reading into temperature, and then subtract the temperature from the actual temperature measured at the bulb. The degree of superheat should be between 5 and 8℃.
5, supercooling degree
Definition of supercooling: the difference between the saturated liquid temperature corresponding to the condenser condensation pressure and the actual liquid temperature at the condenser outlet. In engineering, the exhaust pressure is generally regarded as the condensation pressure, and the difference between the saturated liquid temperature corresponding to the exhaust pressure and the liquid temperature at the outlet of the condenser is regarded as the degree of supercooling. The reason for this approximation is that the pressure drop of the condenser is smaller than that of the evaporator. For air-cooled condensers, the degree of supercooling of 3~5 degrees is more suitable. When the refrigeration system circulates normally, the outlet of the condenser usually has a certain degree of supercooling.
6. What is the use of inspiratory superheat?
If there is no excessive heat in the suction, it may produce back gas with liquid, and even cause wet stroke liquid impact to damage the compressor. In order to avoid this phenomenon, a certain degree of suction superheat is needed to ensure that only dry steam enters the compressor (because of the nature of refrigerant, the existence of superheat indicates the complete evaporation of liquid refrigerant).
However, too high superheat also has disadvantages. Too high superheat will cause the compressor exhaust temperature (exhaust superheat) to rise, and the compressor operating conditions will deteriorate and its service life will be reduced. Therefore, the suction superheat should be controlled within a certain range. The expansion valve senses the temperature difference between the return air temperature and the actual evaporation pressure (corresponding to the saturation temperature) through the temperature sensing part placed at the compressor return pipe or the evaporator outlet, and adjusts the opening of the expansion valve based on the set superheat, which is equivalent to adjusting the liquid supply of the evaporator, and finally can control the suction superheat. When the refrigerant evaporates in the evaporator, the temperature has a great influence on the refrigeration efficiency. Every time it is reduced by 1 degree, it needs to increase the power by 4% to produce the same cooling capacity. Therefore, if conditions permit, it is beneficial to improve the efficiency of the refrigeration system by appropriately increasing the evaporation temperature.
7. How to adjust the evaporation temperature?
Evaporation temperature adjustment is to control evaporation pressure in actual operation, that is, to adjust the pressure value of low-pressure pressure gauge. In operation, the low-pressure pressure is adjusted by adjusting the opening of thermal expansion valve (or throttle valve). When the opening of expansion valve is large, the evaporation temperature and low pressure increase, and the refrigeration capacity will increase; If the opening of the expansion valve is small, the evaporation temperature and low pressure will be reduced, and the refrigeration capacity will be reduced.
8. Factors affecting evaporation temperature
In the actual operation of refrigeration equipment, the change of evaporation temperature is very complicated, which is not only directly controlled by expansion valve (throttle valve), but also related to the heat load of the cooled object, the heat transfer area of evaporator and the capacity of compressor. When one of these three conditions changes, the evaporation pressure and temperature of the refrigeration system will inevitably change accordingly. Therefore, in order to ensure the stable operation of the evaporation temperature within the specified range, the operator needs to know the change of the evaporation temperature in time and adjust the evaporation temperature timely and correctly according to the change law of the evaporation temperature.
9. Influence of heat load on evaporation temperature
Heat load refers to the heat released by the cooled object. When the heat load increases and other conditions remain unchanged, the evaporation temperature will increase, the low pressure will also increase, and the superheat of suction will also increase. In this case, only the expansion valve can be turned up to increase the circulation of refrigerant, and the expansion valve cannot be turned down to reduce the low pressure because of the increase of low pressure. Doing so will increase the suction superheat, increase the exhaust temperature and worsen the operating conditions. When adjusting the expansion valve, the adjustment amount should not be too large each time, and it must be run for a certain time after adjustment to reflect whether the heat load and refrigeration capacity are balanced.
The influence of the energy change of the refrigeration compressor on the evaporation temperature. When the energy of the refrigeration compressor is increased, the suction capacity of the compressor will increase accordingly. Under other conditions unchanged, the high pressure will increase, the low pressure will decrease, and the evaporation temperature will also decrease. In order to keep the evaporation temperature needed by the production process, it is necessary to open the expansion valve to make the low pressure rise to the specified range. After the refrigeration compressor runs with increased energy for a period of time, the evaporation temperature and low pressure will gradually decrease with the decrease of the temperature of the cooled object (the expansion valve does not make any adjustment), which is because the heat load is reduced due to the decrease of the temperature of the cooled object. In this case, the pressure drop should not be mistaken for the fact that the expansion valve is opened to increase the liquid supply due to insufficient liquid supply, but the expansion valve should be turned down to reduce the energy operation of the refrigeration compressor.
10. Influence of heat transfer area change on evaporation temperature
Heat transfer area mainly refers to the evaporation area of evaporator, and the change of heat transfer area mainly refers to the change of evaporation area. In a complete refrigeration device, the evaporation area is usually fixed, but in actual operation, the evaporation area is constantly changing due to insufficient liquid supply or oil accumulation in the evaporator. The influence of the increase and decrease of evaporation area on evaporation temperature is basically similar to that of the increase and decrease of heat load. When the evaporation area increases, the evaporation temperature will increase; When the evaporation area decreases, the evaporation temperature will decrease. In order to maintain the required temperature, we should adjust the energy and expansion valve, and clean the evaporator to keep the relative balance between heat transfer area and refrigeration capacity.
11, the relationship between evaporation pressure and evaporation temperature
The lower the evaporation pressure (low pressure), the lower the evaporation temperature. The relationship between evaporation temperature and refrigeration capacity is: when the refrigerant flow rate is constant, the lower the evaporation temperature, the greater the temperature difference with the heat load (hot air) and the greater the refrigeration capacity. In other words, the lower the evaporation pressure, the greater the refrigeration capacity. Moreover, the same refrigerant with the same quality evaporates at different temperatures, and its evaporation latent heat is different. The lower the evaporation temperature, the greater the evaporation latent heat and the stronger the heat absorption capacity.
The influence of evaporation temperature change on the refrigeration capacity, power and COP of compressor under the conditions of condensation temperature: 40℃, superheat degree: 10℃, subcooling degree: 5℃ and other conditions unchanged.
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