[Mobile Equipment Technology Edition] Daily Question 20191129 Refrigeration Basics - Refrigeration Pressure-Enthalpy Diagram - Refrigeration Cycle (8)
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This post was finally edited by Zhang Xinlin of Binglun Environment on 2019-12-10 22:55. The basic section of refrigeration - pressure enthalpy diagram - refrigeration cycle (8) 1. Overview continues to extend based on the previous one. First, let’s understand subcooling and superheating, and talk about subcooling. Subcooling mainly acts after the liquid is discharged from the condenser and before the evaporator supplies liquid. question: Talk about your understanding of subcooling. What is the role of subcooling? What is subcooling? answer: Action position: The refrigerant liquid comes out of the condenser and before the throttling element. Subcooling: The difference between the temperature of this part of the liquid and the condensation pressure corresponds to the saturation temperature: Increase cooling capacity and enhance refrigeration efficiency (Picture 1) (Picture 2) ================================ Premium Promotion: Moving equipment---Daily questions about value and function in the direction of refrigeration https://bbs.hcbbs.com/thread-2848974-1-1.html Moving equipment---screw refrigeration compressor manufacturer internal training materials https://bbs.hcbbs.com/thread-2850090-1-1.html
A liquid whose temperature is lower than the freezing point but still does not solidify or crystallize is called a supercooled liquid. Supercooled liquids are unstable. As long as a small amount of crystals of the substance are added, crystallization can be induced and the temperature of the supercooled liquid rises back to the freezing point. This unstable state that will change quickly under minor disturbances is called a metastable state. This is because the arrangement of molecules or atoms in the crystal is regular, and liquids The body is irregular. The crystallization center contributes to this disorder-to-order transformation. The purer the liquid, the more difficult it is for the crystallization center to form. If it is lowered below the freezing point and is not formed, it is supercooling. When a saturated solution is slowly cooled in an appropriate way, it can become supersaturated without crystallization of the solute. This phenomenon is also called supercooling, and this solution is called a supercooled solution. Supercooling The solution is also unstable. The so-called supercooling refers to the difference between the temperature of the condensed water under a certain pressure and the saturation temperature under the corresponding pressure. The difference between the phase transition temperature in the equilibrium state of the molten metal and the actual phase transition temperature. The supercooling of a pure metal is equal to the difference between its melting point and the actual crystallization temperature, and the supercooling of an alloy is equal to the difference between the liquidus temperature in the phase diagram and the actual crystallization temperature. Each A substance has its own equilibrium crystallization temperature or theoretical crystallization temperature. However, in the actual crystallization process, the actual crystallization temperature is always lower than the theoretical crystallization temperature. This phenomenon is called supercooling. The temperature difference between the two is called supercooling. The degree of supercooling is closely related to the cooling speed. The faster the cooling speed, the lower the actual crystallization temperature and the greater the degree of supercooling.； On the contrary, the slower the cooling rate, the smaller the degree of supercooling, and the actual crystallization temperature is closer to the theoretical crystallization temperature. During continuous cooling, the level of cooling rate affects the degree of supercooling during phase change. It is the degree of supercooling that affects the structure morphology and crystal type. When cooling slowly, the alloy undergoes phase transformation at a small degree of supercooling.
The phenomenon of supercooling refers to the phenomenon that when the crystal solidifies, the solidification temperature is slightly lower than the solidification temperature, because the solidification temperature is a stable state when the liquid and solid state exist at the same time. If solidification is to be carried out, a driving force needs to be applied. This temperature difference slightly lower than the solidification temperature is the driving force of the solidification process, which is called supercooling. The smaller the supercooling, the longer the solidification time, allowing the crystal grains to have sufficient growth time, so the smaller the supercooling, the larger the crystal grains, and the larger the supercooling, the smaller the crystal grains. But when the degree of supercooling reaches a certain level, the atoms have no time to arrange and solidify to form quasicrystals or amorphous crystals.
The difference between the liquid subcooling temperature and the saturated liquid temperature corresponding to its pressure is called subcooling. The degree of increase in unit cooling capacity and refrigeration coefficient is proportional to the degree of subcooling. By using liquid subcooling, the unit cooling capacity and refrigeration coefficient of the cycle can be increased.