[Mechanical Equipment Technology Edition] Daily Question 201709028: Refrigeration Systems
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Starting today, in order to enhance communication among those interested in marine equipment, we have launched the 【Daily Question】 initiative on the Mechanical Equipment Technology forum. We hope everyone will participate actively so as to progress and improve together! ! ! Rewards: 3 wealth for active participation, 10-15 wealth for complete answers. This question is valid for two days; no scoring will be given after that period. \"Small temperature difference\" or \"approaching temperature\" is a parameter that indicates the heat transfer efficiency of a heat exchanger. How can a small temperature difference be expressed? For shell-and-tube heat exchangers, what is the approximate small temperature difference? ================================ Event Promotion: Petrochemical Zone – “Creative Ideas for Energy Savings” event (the second phase is currently in full swing) http://bbs.hcbbs.com/thread-1666758-1-1.html (Source: Haichuan Chemical Industry Forum) 2017 Coal Chemical Industry Event – “My Technical Upgrades” http://bbs.hcbbs.com/thread-1786290-1-1.html (Source: Haichuan Chemical Industry Forum)
A small temperature difference refers to a very small difference in the temperature at the ends. For shell-and-tube heat exchangers, the small temperature difference is approximately 1–2 degrees Celsius.
The small temperature difference in the evaporator refers to the difference between the saturated temperature of the refrigerant in the evaporator and the outlet temperature of the chilled water. The small temperature difference in the condenser refers to the difference between the saturated temperature of the refrigerant in the condenser and the outlet temperature of the cooling water
The difference between the “saturation condensation temperature of the refrigerant” in the condenser and the “temperature of the cooled water exiting the system” is referred to as the “small temperature difference,” which is usually 1-2°C.
The small temperature difference is also known as the approach temperature difference. The approach search temperature refers to the fact that the cold and hot fluids in a heat exchanger, from the moment they enter the heat exchanger, move towards a common temperature through heat exchange with each other. The hot stream cools down, and the cold stream warms up, both moving toward the same temperature point. However, due to practical constraints (such as the need for an infinitely large heat exchange area or an infinitely long heat exchanger), it is impossible for them to reach this temperature; thus, the target temperature is a hypothetical value. The small temperature difference is about 1-2 degrees
For the evaporator, the small temperature difference = chilled water outlet temperature – evaporation temperature； For the condenser, the small temperature difference = condensation temperature – cooling water outlet temperature ； For shell-and-tube heat exchangers, the temperature difference is roughly 1-2℃