Multi-objective Optimization on Helium Liquefier Using Genetic Algorithm

Abstract

Abstract.Research on optimization of helium liquefier is limited at home and abroad, and most of the optimization is single-objective based on Collins cycle. In this paper, a multi-objective optimization is conducted using genetic algorithm (GA) on the 40 L/h helium liquefier developed by Technical Institute of Physics and Chemistry of the Chinese Academy of Science (TIPC,CAS), steady solutions are obtained in the end. In addition, the exergy loss of the optimized system is studied in the case of with and without liquid nitrogen pre-cooling. The results have guiding significance for the future design of large helium liquefier. 1.IntroductionIt's known that for a refrigeration cycle, the power needed increases sharply with lowering of the refrigeration temperature. Ideally, 70.43 W power is needed to be done on the refrigeration system to get 1W cooling capacity at 4.2 K. Certainly more power is expected to get liquid helium, so an optimization design means a lot for reducing energy consumption. Some optimization studies have already been carried out on helium liquefier and most of them are in theory. Rijo Jacob Thomas et al [1] have conducted an exergy analysis on Collins cycle, results show that the first and the last heat exchanger should be taken seriously for their low exergy efficiency. In addition, the optimal mass flow into expanders is found to be 80% of the total mass flow. Rijo Jacob Thomas et al [2] also analyzed the effect of the number of the Brayton cooling stage in a helium liquefier. It is found that the optimal number of Brayton cooling stage is four to achieve the highest exergy efficiency. There is 1 ICECICMC IOP Publishing

Low‐temperature annealing and graphitizing of white‐solidified low‐alloy cast irons

“…Consequently, the remelted layer experiences a lowtemperature annealing treatment during nitriding, which might cause microstructural changes and deteriorate the mechanical properties. Even though high-temperature graphitizing annealing of whitesolidified cast irons has frequently been investigated, little is known about the low-temperature annealing behavior of white-solidified low-alloy cast irons produced by rapid solidification processes [19][20][21][22][23]. The hardness of white-solidified surface layers produced by remelting decreases upon low-temperature annealing for 1 h [20].…”