I have a question regarding the throttling expansion of gases
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Dear sea friends, I have a few questions regarding gas throttling expansion that I’d like to ask you all. 1. Gas throttling expansion: In practical engineering applications, are the pressures before and after throttling determined based on process requirements? In other words, is it the process that determines to what extent the pressure should be reduced through throttling expansion? 2. During gas throttling expansion, why does a positive, negative, or zero Joule-Thomson effect occur? In other words, why can throttling expansion be used for cooling or heating? How can the specific principle be explained? 3. The principle of cooling after gas expansion is the Joule-Thomson effect. From what perspective should it be understood? Energy conservation? Or? 4. Why do most gases exhibit a positive Joule-Thomson effect at room temperature, while hydrogen, helium, and neon exhibit a negative Joule-Thomson effect? What’s the difference? How should it be understood in essence? 5. Taking a single gas, such as nitrogen, as an example: when it undergoes throttling expansion from 10 MPa and 293.15 K to 5 MPa, why does its temperature decrease? How can the principle behind this temperature drop be analyzed?
For purely theoretical matters, it is difficult for engineering and technical personnel to explain them as thoroughly as school teachers can. Taking expansion with nitrogen at 10 Mpa to 5 Mpa as an example, the volume doubles after expansion; during this expansion process, pressure is exerted on the outside, work is done on the surroundings, internal energy decreases, and the temperature drops. My understanding isn’t deep enough, so this is all I can comprehend
These are all pure theoretical concepts from the book; it’s better to go back to the book to understand them. If you don’t understand the principles behind a device, it’s best to post your questions for discussion. Because what’s in the book is based on the explanation of a certain example given in it, and it is relatively abstract. If it’s a real device, it’s relatively intuitive. Furthermore, knowledge of the throttling effect is best understood by taking into comprehensive consideration the environmental parameter conditions after expansion. For reference.
Thank you for your answer. I’m learning the *propylene refrigeration process – starting with refrigerator cooling, then moving on to throttling expansion, and finally various types of refrigerants. It’s getting increasingly confusing, so I came to the forum to ask for help from everyone
Thank you for the answer; you’re right. I still need to study the theoretical knowledge thoroughly from the books
1. The extent to which the pressure decreases after throttling is determined by the process. 2–5. In throttling expansion, there is no heat exchange or work done; the enthalpy remains unchanged before and after. Only (most) substances are liquefied, with no cooling effect. There is an attractive force between most gas molecules; during expansion, potential energy increases and the temperature drops ； A few gas molecules exhibit repulsive forces; during expansion, the potential energy decreases and the temperature drops (such as in hydrogen).
It is recommended to abandon these theoretical aspects and simply focus on learning the processes*. It’s never too late to learn it again once you’re familiar with it.
Design the back pressure based on process requirements. Isenthalpic throttling. To understand these theories, one needs to have a certain theoretical foundation. Please refer to the university textbook – Physical Chemistry; it contains detailed calculation procedures and explanations for everything you want to know.