Ejector design and theoretical study of R134a ejector refrigeration cycle

In the present paper, a mathematical model is developed to design R134a ejector and to predict the performance characteristics of a vapor jet refrigeration system over a wide range of the investigated parameters. These parameters include boiling temperature (65–85 °C), condensing temperature (25–40 °C), evaporating temperature (0–10 °C), degrees of superheat (0–15 °C), nozzle efficiency (0.75–0.95) and diffuser efficiency (0.75–0.95). Simulated results showed that the present model data are in good agreement with experimental data in the literature with an average error of 6%. It is found that the ejector area ratio at boiling temperature of 85 °C is about double that at boiling temperature of 65 °C for various evaporating and condensing temperatures. The present results confirm that waste heat sources of temperature ranging from 65 to 85 °C are adequate to operate vapor jet refrigeration system for air-conditioning applications.     

Investigation of an experimental ejector refrigeration machine operating with refrigerant R245fa at design and off-design working conditions. Part 1. Theoretical analysis

The ejector refrigeration machine (ERM) offers several advantages over other heat-driven refrigeration machine, including simplicity in design and operation, high reliability and low installation cost, which enable its wide application in the production of cooling. In this paper the theoretical analysis of ejector design and ejector refrigeration cycle performance is presented. It is shown that ERM performance characteristics depend strongly on the operating conditions, the efficiency of the ejector used, and the thermodynamic properties of the refrigerant used. A 1-D model for the prediction of the entrainment ratio ω, and an optimal design for ejectors with cylindrical and conical-cylindrical mixing chambers are presented in this paper. In order to increase ERM performance values, it is necessary first of all to improve the performance of the ejector.     

Investigation of an experimental ejector refrigeration machine operating with refrigerant R245fa at design and off-design working conditions. Part 2. Theoretical and experimental results

The main results of a theoretical and experimental investigation of the performance characteristics of an ejector and an ejector refrigeration machine (ERM) operating with refrigerant R245fa at design and off-design working conditions are presented. The ejector and ERM were explored theoretically using improved 1D model and the calculated results were validated experimentally on ejector test rig that has been assembled and operated at National Taiwan University. For typical cases, the performance characteristics variation with condensing, generating and evaporating temperatures along with performance maps are presented. The theoretical results are compared with the results of a set of experiments and good qualitative and quantitative agreement is observed.     

混合室轴向结构参数对蒸汽喷射器性能的影响

在实际环境条件下,采用变几何喷射器是提高喷射器性能的重要途径。基于喷嘴距可调式的喷射器实验测试平台,采用实验和数值分析相结合的方法,研究不同无量纲混合室喉部长度下,无量纲喷嘴距对喷射器的性能及不可逆性影响。结果表明：在测试范围内,喷射器的临界喷射系数随着喷嘴距的增加先增加后减小,当达到最佳无量纲喷嘴距5.83时,临界喷射系数达到最大值0.45,合理的喷嘴距应避免激波链出现在混合室收缩段;喷射器的临界冷凝压力随喷嘴距的增加逐渐下降,当无量纲混合室喉部长度为4时,其临界冷凝压力下降7.36%,下降速度最慢,原因是较大的射流冲量提高了扩压室的压力恢复能力,使流体动能衰减速度有所减缓;当无量纲混合室喉部长度为4,无量纲喷嘴距为5.83时,热力学完善度达到最大值0.21;由喷嘴距引起的喷射器熵产主要来源于两股入口流在混合室收敛段的混合和第二冲击波向扩压室出口的移动,提高扩压室的压力恢复能力能有效避免熵产的急剧增加。研究结果对喷射器的结构及综合性能进行多目标优化,以减小喷射器不可逆性提供重要参考。

     

6000m~3/h制氧机变工况减气增液的探析与实践

介绍了 6 0 0 0m3 /h制氧机为适应用户气量变化 ,进行变工况操作 ,减少气体产量 ,增加液体产量 ,降低能耗的探索与实践。     

Design and evaluation of a carbon-11 gas target having auxiliary cooling fins in the target cavity for the stable production of carbon-11

The utilization of carbon-11 (¹¹C) has rapidly grown since the introduction of positron emission tomography (PET) in Korea in 1994. A ¹¹C gas target with auxiliary cooling fins has been designed, manufactured and evaluated to compare its performances to other targets. The target was assembled from individual fin disks. The fin disks were installed inside the cavity and the cooling jacket. Four targets of different designed have been tested using the KIRAMS-13 cyclotron (13 MeV P⁺; KIRAMS, Korea). In this study, we report the comparative results for these types of ¹¹C targets.