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Refrigeration Cycles
Published in Kavati Venkateswarlu, Engineering Thermodynamics, 2020
Liquefaction of gases plays a vital role in engineering applications that involve temperatures below −100°C such as cryogenics (a low-temperature technology) and superconductivity. It is also used in the production of liquid propellants for rocket engines such as liquid oxygen and liquid nitrogen. The low temperatures below −100°C cannot be produced by ordinary refrigeration techniques. There are two prominent methods in which a gas can be cooled below the temperatures of that magnitude: One is by isentropic expansion through an expander and the other is by Joule–Thomson (Joule–Kelvin) expansion through a throttle valve. In the former method, temperature essentially drops, while it is not always the case with the second method. A substance exists in gas phase above its critical point only. For example, nitrogen has a critical point of −147°C; thus, it does not exist in liquid phase at atmospheric temperatures. Similarly, there are other gases such as hydrogen and helium that behave in the same way as nitrogen gas does. Therefore, the expansion of a gas through a throttle valve results in a temperature drop only when the temperature before throttling is below (maximum inversion temperature) its critical point value.
Refrigeration and Heat Pumps
Published in John Newman, Vincent Battaglia, The Newman Lectures on Thermodynamics, 2019
John Newman, Vincent Battaglia
An important technological process closely related to refrigeration is the liquefaction of gases. Combinations of three principles are used for this purpose, and these involve: Throttling or Joule–Kelvin expansion of the substance to be liquefied.Expansion of the substance to be liquefied, accompanied by the low-temperature extraction of work approaching 80% of the theoretically possible work.Cooling and condensation of the process fluid by a refrigeration system generally involving a different working fluid as the refrigerant.
Full-scale collapse testing of a steel stiffened plate structure under axial-compressive loading triggered by brittle fracture at cryogenic condition
Published in Ships and Offshore Structures, 2020
Jeom Kee Paik, Dong Hun Lee, Sung Hwan Noh, Dae Kyeom Park, Jonas W. Ringsberg
Steel stiffened plate panels are used in naval, offshore, mechanical and civil engineering structures as their primary strength parts. While in service, there may be hazardous situation that such structures are exposed to cryogenic condition due to unwanted release of liquefied gases: Liquefied gas carriers are used to transport natural and hydrogen gases at sea. While the building history of LNG (liquefied natural gas) carriers is long, the world’s first liquefied hydrogen carrier was launched in 2019 at Kawasaki Heavy Industries’ Kobe Works shipyard in Japan. The vessel, named Suiso Frontier, is due for completion in late 2020 and will be equipped with a 1250 cubic metres of liquefied hydrogen cooled to −253°C. (https://www.maritime-executive.com/article/world-s-first-liquefied-hydrogen-carrier-launched). Natural or hydrogen gas is increasingly used as energy source. To efficiently transport or manage such gases, they are usually liquefied at cryogenic condition while keeping atmospheric pressure because the liquefaction of gases can reduce the volume by 1/600. Natural gas can be liquefied at a temperature below −161.5°C at 1 atm, while hydrogen gas is liquefied at −253°C. It is noted that another way to liquefy gases is also applicable by compressing them with high pressure. In addition, LNG is now also adopted as an alternative of fuels for ship propulsion in association with the issues of CO2 emissions. There are always hazards that liquefied gases at cryogenic condition are released from cargo containments or fuel tanks of ships (Petti et al. 2013), as illustrated in Figure 1. Similar hazards can also be considered in bunkering of liquefied gases at cryogenic condition to ships or offshore power plants (Park et al. 2020).