Fundamental principles for sizing and design of gravity separators for industrial refrigeration

Throughout the past decades, the industrial refrigeration industry has developed various “rule of thumb” methods for sizing gravity liquid separators for ammonia and other common refrigerants. However, to date a uniform systematic approach or an agreeable standard has not been established. For commonly used refrigerants such as ammonia, the large installed base of separators can be used as a benchmark for sizing separators. But, when using a less common refrigerant such as CO₂, the designer faces new challenges. In this paper, a systematic approach is presented for sizing horizontal and vertical gravity liquid separators for industrial refrigeration applications. To compute separation velocities and separation distances, a theoretical model is presented. The model is used as a basis for comparison with observations from 85 operating gravity separators surveyed in the field. Criteria and formulas are presented for estimating the required liquid volume for storage. An example is provided demonstrating the use of the methods presented in this paper.     

Performance optimization of three-heat-source irreversible refrigerators based on a new thermo-ecological criterion

This paper presents an optimization study of an irreversible refrigeration absorption system based on a new thermo-ecological criterion. The considered objective function is the ecological coefficient of performance (ECOP). It takes into account the first and second law of thermodynamics and is defined as the cooling load per unit loss rate of availability. The ecological coefficient of performance has been expressed and maximized according to the temperatures of the working fluid in the main components of the system. The corresponding optimal temperatures and other optimum performance parameters have been derived analytically, and the effects of the internal irreversibility, the heat leakage coefficient and the source temperature ratio on the global and optimal performances are discussed. The results show that the maximum coefficient of performance (COP) and ecological coefficient of performance (ECOP) occurs for the same operating conditions.     

磁制冷器

磁制冷是一种以磁热效应为基础的制冷方法.最早是由德国物理学家于1880年发现。早期用于制取极低的温度。近年来,室温磁制冷取得了较大的突破,已经研制出适合家用的磁制冷冰箱,同时由于它的制冷系数高和对大气的全球气候变暖影响小等优点,将成为一种很有发展前途的制冷方式。本文论述磁制冷和磁制冷冰箱的基本原理。     

Production of biogenic amines by lactic acid bacteria and enterobacteria isolated from fresh pork sausages packaged in different atmospheres and kept under refrigeration

The occurrence of in vitro amino acid activity in bacterial strains associated with fresh pork sausages packaged in different atmospheres and kept in refrigeration was studied. The presence of biogenic amines in decarboxylase broth was confirmed by ion-exchange chromatography and by the presence of the corresponding decarboxylase genes by PCR. From the 93 lactic acid bacteria and 100 enterobacteria strains analysed, the decarboxylase medium underestimates the number of biogenic amine-producer strains. 28% of the lactic acid bacteria produced tyramine and presented the tdc gene. All the tyramine-producer strains were molecularly identified as Carnobacterium divergens. Differences on the relative abundance of C. divergens were observed among the different packaging atmospheres assayed. After 28 days of storage, the presence of argon seems to inhibit C. divergens growth, while packing under vacuum seems to favour it. Among enterobacteria, putrescine was the amine more frequently produced (87%), followed by cadaverine (85%); agmatine and tyramine were only produced by 13 and 1%, respectively, of the strains analysed. Packing under vacuum or in an atmosphere containing nitrogen seems to inhibit the growth of enterobacteria which produce simultaneously putrescine, cadaverine, and agmatine. Contrarily, over-wrapping or packing in an atmosphere containing argon seems to favour the growth of agmatine producer-enterobacteria. The production of putrescine and cadaverine was associated with the presence of the corresponding amino acid decarboxylase genes. The biogenic amine-producer strains were included in a wide range of enterobacterial species, including Kluyvera intermedia, Enterobacter aerogenes, Yersinia kristensenii, Serratia grimesii, Serratia ficaria, Yersinia rodhei, Providencia vermicola and Obesumbacterium proteus.     

Two-phase flow in high-heat-flux micro-channel heat sink for refrigeration cooling applications: Part II—heat transfer characteristics

This paper is the second of a two-part study concerning two-phase flow and heat transfer characteristics of R134a in a micro-channel heat sink incorporated as an evaporator in a refrigeration cycle. Boiling heat transfer coefficients were measured by controlling heat flux (q″ = 15.9 − 93.8 W/cm²) and vapor quality (x_e = 0.26 − 0.87) over a broad range of mass velocity. While prior studies point to either nucleate boiling or annular film evaporation (convective flow boiling) as dominant heat transfer mechanisms in small channels, the present study shows heat transfer is associated with different mechanisms for low, medium and high qualities. Nucleate boiling occurs only at low qualities (x_e < 0.05) corresponding to very low heat fluxes, and high fluxes produce medium quality (0.05 < x_e < 0.55) or high quality (x_e > 0.55) flows dominated by annular film evaporation. Because of the large differences in heat transfer mechanism between the three quality regions, better predictions are possible by dividing the quality range into smaller ranges corresponding to these flow transitions. A new heat transfer coefficient correlation is recommended which shows excellent predictions for both R134a and water.     

提高家用空调器能效比优化设计方案

通过实验确定优化目标范围,根据安全性、可靠性、舒适性、经济性以及相关部件的性能等要求确定约束条件,再根据系统各组成部分之间的相互关系,对技术参数进行调整,最终确定制冷系统的优化配置参数,从而达到提高能效比的目的.     

浅谈回热器在制冷系统中的作用

介绍回热器的作用、方式及由此产生的过冷循环、过热循环、回热循环。     

天然气深冷处理中丙烷辅助制冷节能流程技术分析

文章对天然气深冷处理装置中丙烷辅助制冷节能流程进行了介绍 ,就压缩机级数和冷凝剂冷凝温度对压缩机功率的影响进行了对比分析 ,提出了确定压缩机级数的优化方案