Discussion on heat exchange
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I would like to ask: can an air-cooled heat exchanger liquefy a Freon refrigerant with a boiling point of -29°C? Even if the wind keeps blowing, in the end the temperature inside and outside the tube will be at room temperature, with no temperature difference, right? Can a temperature of -29°C really be achieved just by having the wind blow continuously to carry away heat? ； This Freon is likely under pressure, which will raise the boiling point. But what are these fins exactly? I was wondering if there could be reverse heat transfer?
I don’t think this will work; I’m not an expert in this area, and I’m hoping to get a professional answer.
Pressure must be applied, unless it is only used in the northeast during winter; the fins serve to increase the heat exchange area
Whether an air-cooled heat exchanger can liquefy the Freon refrigerant depends on the ambient temperature and the pressure of the Freon. If the ambient temperature is low enough and the heat exchanger is properly designed, liquefaction is possible. The boiling point of Freon increases as pressure rises. Ribs are structures that increase the heat dissipation area of a heat exchanger, helping to improve heat exchange efficiency. Reverse heat transfer is generally unlikely, as heat usually flows from high temperatures to low temperatures. .
So can I understand that the cooling principle of devices similar to refrigerators and dehumidifiers is not based on directly providing cooling energy for heat exchange, but rather on utilizing the heat absorbed during phase change, namely vaporization? This is quite different from the principle behind expanders
So can I understand that the cooling principle of devices similar to refrigerators and dehumidifiers is not one of directly providing cooling energy for heat exchange, but rather relies on the heat absorbed during phase change, specifically vaporization, which is quite different from the principle behind expanders?
Yes, you understand correctly. The cooling in refrigerators and dehumidifiers is usually achieved through the heat-absorbing process of vaporization of the refrigerant in the evaporator; during this process, the refrigerant absorbs heat from its surroundings and undergoes a phase change from liquid to gas, thereby lowering the temperature of the surrounding air. The expander, on the other hand, causes the gas to expand and cool through mechanical work. The principles of the two are indeed different. .
It makes use of the heat of phase change, but it is still a form of heat exchange. I’m not sure which type of expansion engine you are referring to, but the principle of heat exchange remains the same
I see that before the refrigerant enters the heat exchange chamber, that is, before cooling and heat exchange take place, it passes through a throttling tube to have its pressure reduced, or it goes through an expansion valve; I’m not sure whether this is due to free expansion causing pressure and temperature reduction； Thus, the refrigerant that ultimately enters the heat exchange chamber is necessarily a gas-liquid mixture with a certain amount of cooling capacity. There are two sources from which heat is absorbed during heat exchange: one is the cooling energy generated by the pressure drop and work done by the refrigerant itself, with heat exchange taking place due to temperature differences; the other is the heat required for the vaporization phase change of the low-pressure refrigerant, which also leads to heat being carried away. In essence, both processes involve heat exchange