Temperature Test Chambers Requirements for Refrigeration
The refrigerant in temperature test chambers should obviously meet the basic requirements of the temperature environment test, including:
(1) Standard gasification temperature (ts).
The temperature at which a refrigerant evaporates from a liquid to a gaseous state is determined by its working pressure. The temperature at which the refrigerant evaporates from a liquid to a gaseous state at standard atmospheric pressure is called the standard vaporization temperature (ts) of the refrigerant, such as the standard vaporization temperature ts of R22 = -40.8 ° C; standard gasification temperature of R502 is ts = -45.6 ° C. The lower the working pressure of the refrigerant, the lower its vaporization temperature. On the contrary, if the evaporation temperature of a refrigerant is required to reach a certain low temperature value, its working pressure must be adjusted to be lower than a corresponding pressure, and the pressure value is saturated. steam pressure.
In order to avoid the infiltration of air into the refrigeration system and reduce the cooling efficiency, the normal operating pressure of the temperature test box refrigeration system should generally be higher than the local atmospheric environmental pressure. Therefore, the standard vaporization temperature (ts) of the refrigerant is the lowest limit temperature that the temperature test chamber can reach.
(2) The condensation pressure Pk cannot be too high.
The condensing pressure Pk is the working pressure at which the high-temperature and high-pressure steam discharged from the compressor is cooled to a liquid state during condensation. This pressure is restricted by the temperature of the cooling medium and the compressor discharge pressure. The higher the compressor discharge pressure and the lower the temperature of the cooling medium, the more easily the refrigerant vapor condenses. However, increasing the discharge pressure of the compressor will not only increase the power consumption of the compressor, shorten the working life of the compressor, but also easily cause leakage of the working fluid.
On the other hand, the temperature of the cooling medium is not too low due to the limitation of the ambient temperature and the temperature of the cooling water. Generally, the inlet temperature of the cooling medium into the condenser is 24 ° C ~ 29 ° C. The temperature is 40 ° C ~ 50 ° C, and the average temperature of the cooling medium is in the range of 30 ° C ~ 50 ° C.
(3) Oil solubility and water solubility of the refrigerant.
The refrigerant should have a certain degree of oil solubility and water solubility. After the lubricant is dissolved in the refrigerant, it is beneficial to the lubrication of various operating parts in the refrigeration system, especially the liquid refrigerant with oil solubility in the condenser will take away the oil film condensed on the inner wall of the condenser due to condensation effect It can reduce the influence of the oil film on the inner wall of the condenser on the heat exchange efficiency of the condenser.
However, when the liquid refrigerant enters the evaporator with the dissolved oil, as the liquid refrigerant evaporates and gasifies, it will be installed in the evaporator in the actual refrigeration system, and the compressor's exhaust port will be equipped with oil and gas separation. Device to limit the amount of dissolved oil in the refrigerant. At the same time, in the installation of the evaporator, some oil return measures are taken.
The oil absorbed on the inner wall of the evaporator will also return to the oil pool of the compressor under the effect of gravity and the negative pressure of the compressor suction. For shell-and-tube evaporators, the return air pipe must have a certain inclination toward the compressor suction port when installing, so that the remaining oil can be sucked back into the compressor by the suction negative pressure of the compressor depending on the oil collecting effect of gravity
The infiltration of water vapor into the refrigeration system will form "ice plugs" in some parts of the low temperature section, blocking the smooth flow of refrigerant. Therefore, a "drying filter" is installed before the condenser in the refrigeration system to absorb the moisture that may seep into the refrigeration system, and when installing and maintaining the refrigeration system, increase the vacuuming time appropriately to benefit the refrigeration system. Residual moisture is evaporated and removed under vacuum. To ensure the normal operation of the refrigeration system, the use of water-soluble refrigerants can be circulated with a small amount of residual water vapor.
In addition, it is also desirable that the refrigeration unit volume of the refrigerant is large, which can reduce the size of the refrigeration unit; has a high thermal conductivity, which can reduce the heat exchange area of the condenser and evaporator; low viscosity and low density, which can reduce Resistance in pipeline flow reduces pipeline pressure drop; stable chemical and physical properties, non-corrosive, non-toxic, non-combustible, non-explosive, and has certain anti-electrical properties.
(1) Standard gasification temperature (ts).
The temperature at which a refrigerant evaporates from a liquid to a gaseous state is determined by its working pressure. The temperature at which the refrigerant evaporates from a liquid to a gaseous state at standard atmospheric pressure is called the standard vaporization temperature (ts) of the refrigerant, such as the standard vaporization temperature ts of R22 = -40.8 ° C; standard gasification temperature of R502 is ts = -45.6 ° C. The lower the working pressure of the refrigerant, the lower its vaporization temperature. On the contrary, if the evaporation temperature of a refrigerant is required to reach a certain low temperature value, its working pressure must be adjusted to be lower than a corresponding pressure, and the pressure value is saturated. steam pressure.
In order to avoid the infiltration of air into the refrigeration system and reduce the cooling efficiency, the normal operating pressure of the temperature test box refrigeration system should generally be higher than the local atmospheric environmental pressure. Therefore, the standard vaporization temperature (ts) of the refrigerant is the lowest limit temperature that the temperature test chamber can reach.
(2) The condensation pressure Pk cannot be too high.
The condensing pressure Pk is the working pressure at which the high-temperature and high-pressure steam discharged from the compressor is cooled to a liquid state during condensation. This pressure is restricted by the temperature of the cooling medium and the compressor discharge pressure. The higher the compressor discharge pressure and the lower the temperature of the cooling medium, the more easily the refrigerant vapor condenses. However, increasing the discharge pressure of the compressor will not only increase the power consumption of the compressor, shorten the working life of the compressor, but also easily cause leakage of the working fluid.
On the other hand, the temperature of the cooling medium is not too low due to the limitation of the ambient temperature and the temperature of the cooling water. Generally, the inlet temperature of the cooling medium into the condenser is 24 ° C ~ 29 ° C. The temperature is 40 ° C ~ 50 ° C, and the average temperature of the cooling medium is in the range of 30 ° C ~ 50 ° C.
(3) Oil solubility and water solubility of the refrigerant.
The refrigerant should have a certain degree of oil solubility and water solubility. After the lubricant is dissolved in the refrigerant, it is beneficial to the lubrication of various operating parts in the refrigeration system, especially the liquid refrigerant with oil solubility in the condenser will take away the oil film condensed on the inner wall of the condenser due to condensation effect It can reduce the influence of the oil film on the inner wall of the condenser on the heat exchange efficiency of the condenser.
However, when the liquid refrigerant enters the evaporator with the dissolved oil, as the liquid refrigerant evaporates and gasifies, it will be installed in the evaporator in the actual refrigeration system, and the compressor's exhaust port will be equipped with oil and gas separation. Device to limit the amount of dissolved oil in the refrigerant. At the same time, in the installation of the evaporator, some oil return measures are taken.
The oil absorbed on the inner wall of the evaporator will also return to the oil pool of the compressor under the effect of gravity and the negative pressure of the compressor suction. For shell-and-tube evaporators, the return air pipe must have a certain inclination toward the compressor suction port when installing, so that the remaining oil can be sucked back into the compressor by the suction negative pressure of the compressor depending on the oil collecting effect of gravity
The infiltration of water vapor into the refrigeration system will form "ice plugs" in some parts of the low temperature section, blocking the smooth flow of refrigerant. Therefore, a "drying filter" is installed before the condenser in the refrigeration system to absorb the moisture that may seep into the refrigeration system, and when installing and maintaining the refrigeration system, increase the vacuuming time appropriately to benefit the refrigeration system. Residual moisture is evaporated and removed under vacuum. To ensure the normal operation of the refrigeration system, the use of water-soluble refrigerants can be circulated with a small amount of residual water vapor.
In addition, it is also desirable that the refrigeration unit volume of the refrigerant is large, which can reduce the size of the refrigeration unit; has a high thermal conductivity, which can reduce the heat exchange area of the condenser and evaporator; low viscosity and low density, which can reduce Resistance in pipeline flow reduces pipeline pressure drop; stable chemical and physical properties, non-corrosive, non-toxic, non-combustible, non-explosive, and has certain anti-electrical properties.
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