[Mechanical Equipment Technology Edition] Daily Question 201806013: Refrigeration Systems – Refrigeration Parameters (6)

The exhaust superheat should be the temperature difference between the temperature at the compressor exhaust pipe or the inlet of the condenser and the saturation temperature corresponding to the actual condensing pressure; it indicates by how many degrees the current actual temperature is higher than the saturation temperature associated with the actual pressure. It can be handled in this way: the exhaust temperature is generally around 2 degrees higher than the condensation temperature, and such an excess temperature is referred to as effective superheat. A certain degree of superheat is necessary to ensure that the refrigerant entering the compressor is free of liquid, thereby preventing wet strokes.

1. The exhaust superheat should be the temperature difference between the temperature at the compressor exhaust pipe or the inlet of the condenser and the saturation temperature corresponding to the actual condensing pressure; it indicates by how many degrees the current actual temperature is higher than the saturation temperature associated with the actual pressure. A certain degree of superheat is necessary to ensure that the refrigerant entering the compressor is free of liquid, thereby preventing wet strokes. Generally, at the evaporator outlet and the compressor exhaust, the actual temperature of the working fluid is higher than the saturation temperature corresponding to the actual pressure. This is where superheat comes into play. Superheat is divided into intake superheat and exhaust superheat. 2. Calculation method: Superheat = Suction temperature of the compressor – Evaporation temperature of the refrigerant in the evaporator.

The exhaust superheat should be equal to the exhaust temperature minus the saturated temperature of the cooling water, and it should remain between 16.6 and 22.2 degrees. The small temperature difference in the evaporator is considered normal when it is between 1 and 3 degrees, provided that the slide valve of the unit is at 80% capacity

The exhaust superheat is equal to the exhaust temperature minus the saturation temperature corresponding to the exhaust pressure; it can be calculated based on the temperature and pressure monitored in real time

The intake pressure is too low or the exhaust pressure is too high

The exhaust superheat should be the temperature difference between the temperature at the compressor exhaust pipe or the inlet of the condenser and the saturation temperature corresponding to the actual condensing pressure; it indicates by how many degrees the current actual temperature is higher than the saturation temperature associated with the actual pressure. It can be handled in this way: the exhaust temperature is generally around 2 degrees higher than the condensation temperature, and such an excess temperature is referred to as effective superheat. A certain degree of superheat is necessary to ensure that the refrigerant entering the compressor is free of liquid, thereby preventing wet strokes.

“\"Exhaust superheat\": The difference between the temperature of the compressor’s exhaust pipe (or the inlet temperature of the condenser) and the saturation temperature corresponding to the condensing pressure. The exhaust superheat of a normal refrigeration system is 20~30°C. The exhaust superheat is related to the following factors: 1. Intake temperature ； 2. Inlet superheat ； 3. Compressor lubrication status ； 4. Refrigerant entropy value.

Can’t understand the question. . . . . . . . .

This post was last edited by Hasty Passer on June 14, 2018, at 16:57. 1. The exhaust superheat is closely related to the type of refrigerant, the compression method, as well as the evaporation and condensation temperatures, and the cooling method. Some sources say it is related to the suction temperature, suction superheat, lubrication conditions, and type of refrigerant (it is not certain which statement is correct). 2. After consulting some information, the turbine manufacturer should provide a similar diagram: by referring to the operating conditions of the turbine (the relevant range), it is possible to roughly determine the range within which an appropriate superheat level exists. 3. According to various data sources, it is stated that a exhaust superheat of 20–30°C is normal for a refrigeration system ； Some also say that setting the exhaust temperature at condensation temperature + 2°C is sufficient ； 4. Another view is that once an appropriate suction superheat is determined, the exhaust superheat can be ensured. To ensure that the thermal expansion valve operates at the optimal matching point, it is necessary to provide it with an appropriate superheat. The superheat of a thermal expansion valve consists of the static assembly superheat and the effective superheat. The superheat required to start opening the valve is called the opening superheat, or static assembly superheat; generally, the static assembly superheat is around 3°C. The increase in superheat required for a thermal expansion valve to start opening up to its rated opening degree is referred to as the effective superheat or variable superheat of the thermal expansion valve. Its value is related to the stiffness of the spring and the stroke of the valve element; generally, the effective superheat is around 2–5°C. The sum of the static assembly superheat of the thermal expansion valve and the effective superheat is referred to as the operating superheat, which is what is commonly meant by superheat. Therefore, only by ensuring that the superheat is within an appropriate range can the refrigeration system achieve maximum cooling capacity without causing a wet stroke. The superheat of industrial oil coolers is required to be between 5 and 8°C. If it is found that the superheat is not within this range, adjustments must be made. 5. Another approach is to calculate the superheat based on the operating conditions, and then set a value by adding a margin to it: the exhaust temperature of the refrigeration compressor corresponds to the temperature of the superheated steam after compression. It is closely related to the type of refrigerant, the compression method, as well as the evaporation and condensation temperatures, and the cooling method. For example, the exhaust temperature of an ammonia refrigeration compressor can be calculated using the following formula: Single-stage compression: Exhaust temperature = (tk-to) × 2.4; Two-stage compression: Exhaust temperature of the high-pressure stage = (tk-to) × 2.4 ； Low-pressure stage exhaust temperature = (to1-to2) X 2.4, where tk = condensation temperature ； to=evaporation temperature ； to1=intermediate temperature ； to2 = two-stage evaporation temperature. The exhaust temperature of the R22 refrigerant is about 30% lower than that of the R717 (ammonia) refrigerant. Calculate the exhaust superheat: For single-stage compression of R717 (ammonia), the exhaust superheat is as follows: if the evaporation temperature is to = -15 degrees and the condensation temperature is tk = 30 degrees, then the exhaust temperature = X2.4 = 45 × 2.4 = 108 degrees. At that time, the condensation temperature was 30 degrees, and the calculated (measured) exhaust superheat temperature was 108 degrees; therefore, the exhaust superheat = 108 – 30 = 78 degrees. I’m not sure if I have understood the question correctly; it seems to me that the above response is not precise enough. Please advise, teacher.

Haha, this formula must have been developed by the old man from Rongchang Refrigeration~~ You can learn more about pressure-enthalpy diagrams here; I’ll explain it to you in detail later