Effect of the Thermostatic Expansion Valve Characteristics on the Stability of a Refrigeration System

2003 ◽  
Author(s):  
Veerendra Mulay ◽  
Dereje Agonafer ◽  
Roger Schmidt
Keyword(s):  
Low Temperature ◽  
Thermal Resistance ◽  
Physical Properties ◽  
Time Constant ◽  
System Performance ◽  
System Stability ◽  
Refrigeration System ◽  
Expansion Valve ◽  
The Stability ◽  
Thermo Physical Properties

The combination of increased power dissipation and increased packaging density has led to substantial increases in chip and module heat flux in high-end computers. The challenge has been to limit the rise in chip temperature. In the past virtually all-commercial computers were designed to operate at temperatures above the ambient. However researchers have identified the advantages of operating electronics at low temperatures. The primary purpose of low temperature cooling using vapor compression system are faster switching times of semiconductor devices, increased circuit speed due to lower electrical resistance of interconnecting materials, and a reduction in thermally induced failures of devices and components. Achievable performance improvements range from 1 to 3% for every 10°C lower transistor temperature, depending on the doping characteristics of the chip. The current research focuses on IBM’s mainframe, which uses a conventional refrigeration system to maintain chip temperatures below that of comparable air-cooled systems, but well above cryogenic temperatures. Although performance has been the key driver in the use of this technology, the second major reason for designing a system with low temperature cooling is the improvement achieved in reliability to counteract detrimental effects, which rise as technology is pushed to the extremes. A mathematical model is developed to determine the time constant for expansion valve sensor blub. This time constant varies with variation in thermo-physical properties of sensor element that is bulb size and blub liquid. An experimental bench is built to study the effect of variation of evaporator outlet superheat on system performance. The heat load is varied from no load to full load (1KW) to find out the system response at various loads. Experimental investigation is also done to see how the changes in thermo-physical properties of the liquid in sensor bulb of expansion valve affect the overall system performance. Different types of thermostatic expansion valves are tested to investigate that bulb size; bulb constant and bulb location have significant effect on the behavior of the system. Thermal resistance between the bulb and evaporator return line can considerably affect the system stability and by increasing the thermal resistance, the stability can be further increased.

Effect of the Location and the Properties of Thermostatic Expansion Valve Sensor Bulb on the Stability of a Refrigeration System

2005 ◽  
Vol 127 (1) ◽  
pp. 85-94 ◽  
Author(s):  
Veerendra Mulay ◽  
Amit Kulkarni ◽  
Dereje Agonafer ◽  
Roger Schmidt
Keyword(s):  
Low Temperature ◽  
Thermal Resistance ◽  
Time Constant ◽  
Thermophysical Properties ◽  
System Performance ◽  
System Stability ◽  
System Response ◽  
Refrigeration System ◽  
Expansion Valve ◽  
The Stability

The combination of increased power dissipation and increased packaging density has led to substantial increases in chip and module heat flux in high-end computers. The challenge has been to limit the rise in chip temperature. In the past, virtually all commercial computers were designed to operate at temperatures above the ambient. However, researchers have identified the advantages of operating electronics at low temperatures. The primary purpose of low-temperature cooling using a vapor compression system are faster switching times of semiconductor devices, increased circuit speed due to lower electrical resistance of interconnecting materials, and a reduction in thermally induced failures of devices and components. Achievable performance improvements range from 1% to 3% for every 10°C lower transistor temperature, depending on the doping characteristics of the chip. The current research focuses on IBM’s mainframe, which uses a conventional refrigeration system to maintain chip temperatures below that of comparable air-cooled systems, but well above cryogenic temperatures. Although performance has been the key driver in the use of this technology, the second major reason for designing a system with low-temperature cooling is the improvement achieved in reliability to counteract detrimental effects, which rise as technology is pushed to the extremes. A mathematical model is developed to determine the time constant for an expansion valve sensor bulb. This time constant varies with variation in the thermophysical properties of the sensor element; that is, bulb size and bulb liquid. An experimental bench is built to study the effect of variation of evaporator outlet superheat on system performance. The heat load is varied from no load to full load (1 KW) to find out the system response at various loads. Experimental investigation is also done to see how the changes in thermophysical properties of the liquid in the sensor bulb of the expansion valve affect the overall system performance. Different types of thermostatic expansion valves are tested to investigate that bulb size, bulb constant, and bulb location have significant effects on the behavior of the system. Thermal resistance between the bulb and evaporator return line can considerably affect the system stability, and by increasing the thermal resistance, the stability can be further increased.

Effect of the Thermostatic Expansion Valve Characteristics on the Stability of a Refrigeration System: Part II

2003 ◽  
Author(s):  
Amit Kulkarni ◽  
Dereje Agonafer ◽  
Roger Schmidt
Keyword(s):  
Load Condition ◽  
Transient Behavior ◽  
System Stability ◽  
Stable Operation ◽  
Refrigeration System ◽  
Expansion Valve ◽  
System Part ◽  
Suction Line ◽  
The Stability ◽  
Experimental Bench

The combination of increased power dissipation and increased packaging density has led to substantial increases in chip and module heat flux in high-end computers. The challenge has been to limit the rise in chip temperature. In the past virtually all-commercial computers were designed to operate at temperatures above the ambient. However researchers have identified the advantages of operating electronics at low temperatures. The current research focuses on IBM’s mainframe, which uses a conventional refrigeration system to maintain chip temperatures below that of comparable air-cooled systems, but well above cryogenic temperatures. An experimental bench was built to study the effect of variation of evaporator outlet superheat on system performance. Three different types of thermostatic expansion valves were tested in order to verify that the bulb size and bulb location have significant effect on the transient behavior of the system. Bulbs of each of the three thermostatic expansion valves were mounted at five different locations on the suction line. It was observed that the overall system stability increases as we move closer to the evaporator exit. It was also observed that there exists a region in the suction line at which the superheat variation is the least and placing the bulb at this region gives maximum stable operation of the system. This region can be defined as the minimum stable superheat point. Tests were conducted at five different load conditions 1000W, 750W, 500W, 250W and no load condition. It was observed that the system was the most stable at full load condition for all three types of valves and system stability consistently decreased as the load was decreased.

To Improve the Performance and Efficiency of Refrigeration Systems by Using Refrigerant Pumps

2013 ◽  
Vol 385-386 ◽  
pp. 233-236
Author(s):  
Qing Jiang Liu ◽  
Zeng Zhi Yuan ◽  
Jin Ting Sun ◽  
Fang Han
Keyword(s):  
Pressure Difference ◽  
System Performance ◽  
Low Pressure ◽  
System Stability ◽  
Refrigeration System ◽  
Expansion Valve

In order to improve refrigeration system stability and efficiency of the low pressure difference between thermostatic expansion valve, it is researched that the refrigeration system is the refrigerate capacity of the HSN7471-75 compressors. The system performance is analyzed and compared in the case of with and without refrigerant pumps. The results indicate that the COP of the refrigeration system with a pump can increase 31%. The reliability of system is also improved.

Design and Build of Teaching and Experimental Marine Cold Store

2014 ◽  
Vol 556-562 ◽  
pp. 907-911
Author(s):  
Chang Wei He ◽  
Meng Zhang ◽  
Xiao Ping Jia ◽  
Yuan Liu
Keyword(s):  
Thermal Performance ◽  
System Performance ◽  
Heat Load ◽  
Refrigeration System ◽  
Electrical System ◽  
Technology Application ◽  
Design Scheme ◽  
Expansion Valve ◽  
Cold Store ◽  
Practical Teaching

In the paper, the design scheme of the new cold store is proposed firstly, with the consideration of the latest technology application and the convenience and maneuverability of practical teaching. Then the refrigeration system is designed based on the calculation of the heat load of the cold store. The suited components such as compressor, evaporator, condenser and expansion valve are selected and the electrical system is designed. After that the whole unit is installed and adjusted to make sure that the installation is propitious to improve the system performance and convenient for training. Finally the thermal performance of the new cold store system is tested and compared with the old system test. The result shows that the matching of the new refrigeration system is reasonable and the new cold store is up to the mustard. With the help of training on the cold store, the students will meet the essential requirements of STCW 78/95 convention on application and management of the marine cold store.

Experimental Analysis on PV/T-SAHP Performance under the Influence of the Electronic Expansion Valve

2013 ◽  
Vol 641-642 ◽  
pp. 117-122
Author(s):  
Hai Tao Wang
Keyword(s):  
Solar Radiation ◽  
Experimental Analysis ◽  
System Performance ◽  
System Stability ◽  
Pv Module ◽  
Expansion Valve ◽  
Compressor Power ◽  
Maximum Opening

Under different Electronic Expansion Valve (EXV)opening degree at the fixing frequency of 50hz of the compressor，we had test the system performance. When the cooling refrigerant influence to the PV module and the heating air influence to the collector／evaporator reached the balance，the photoelectric efficiency achieved the maximum．When the EXV opening degree fixing, with the raising of the solar radiation, the compressor power values appeared oscillation，and the oscillation was especially evident when the EXV at the maximum opening degree． So we put forward the PV/T-SAHP system stability principle．At the same time，we found that the key of the PV／T-SAHP research is to discover the relation between the solar radiation and the superheat of collector／evaporator．

scholarly journals Low-Speed Stability Optimization of Full-Order Observer for Induction Motor

2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Xiangsheng Liu ◽  
Lin Ren ◽  
Yuanyuan Yang ◽  
Jun He ◽  
Zhengxin Zhou
Keyword(s):  
Induction Motor ◽  
Control Strategy ◽  
System Performance ◽  
System Stability ◽  
Feedback Gain ◽  
Unstable Region ◽  
Low Speed ◽  
Gain Matrix ◽  
Adaptive Law ◽  
The Stability

In terms of the instability of the full-order observer for the induction motor in the low-speed regenerative mode, the low-speed unstable region which leads to the extension of the commissioning cycle cannot be eliminated by the traditional adaptive law which aims at good system performance. It is proposed that the feedback gain matrix can control both the unstable region and the system performance both. To make a trade-off between the stability and performance by designing the feedback gain matrix is still an open problem. To solve this problem, first we analyze the cause of instability and derive constraints to ensure system stability by establishing a transfer function of the adaptive observing system for the speed. Then, with the derived constraints as the design criteria for the feedback gain matrix, a control strategy combining the weighted adaptive law with the improved feedback gain matrix is proposed to improve the stability at low speed. Finally, by comparing the traditional control strategy with the proposed control strategy through simulations and experiments, we show that the proposed control strategy achieves better performance with higher stability.

Experimental Investigation of Vapor Compression Refrigeration System Performance Using Nano-Refrigerant

2014 ◽  
Vol 2 (2) ◽  
pp. 12-27
Author(s):  
Ahmed J. Hamad
Keyword(s):  
Experimental Investigation ◽  
System Performance ◽  
Cuo Nanoparticles ◽  
Working Fluid ◽  
Vapor Compression ◽  
Refrigeration System ◽  
Test Rig ◽  
Vapor Compression Refrigeration ◽  
R 134A ◽  
Thermo Physical Properties

     Experimental investigation of vapor compression refrigeration system performance using Nano-refrigerant is presented in this work. Nano-refrigerant was prepared in current work by mixing 50 nanometers diameter of copper oxide CuO nanoparticles with Polyolester lubrication oil and added to the compressor of the refrigeration system to be mixed with pure refrigerant R-134a during its circulation through refrigeration system. Three concentrations (0.1%, 0.25%, and 0.4%) of CuO-R134 a Nano-refrigerant are used to study the performance of the refrigeration system test rig and to investigate the effect of using Nano-refrigerant as a working fluid compared with pure refrigerant R-134a. The results showed that, the increasing in concentration of CuO nanoparticles in the Nano-refrigerant will significantly enhance the performance of the refrigeration system, as adding nanoparticles will increase the thermal conductivity, heat transfer and improve the thermo-physical properties of Nano-refrigerant. Investigation of performance parameters for refrigeration system using Nano-refrigerant with 0.4% concentration compared with that for pure refrigerant R-134a shows that, Nano-refrigerant has reflect higher performance in range of 10% and 1.5% increase in COP and refrigeration effect respectively and 7% reduction in power consumption for refrigeration system. It can be concluded that, Nano-refrigerants can be efficiently and economically feasible to be used in the vapor compression refrigeration systems.

scholarly journals Recent Progress on Stability and Thermo-Physical Properties of Mono and Hybrid towards Green Nanofluids

Micromachines ◽  
2021 ◽  
Vol 12 (2) ◽  
pp. 176
Author(s):  
S.N.M. Zainon ◽  
W.H. Azmi
Keyword(s):  
Physical Properties ◽  
Visual Observation ◽  
Particle Volume ◽  
Factors Affecting ◽  
Practical Applications ◽  
Long Term Stability ◽  
Thermal Fluids ◽  
Vis Spectroscopy ◽  
The Stability ◽  
Thermo Physical Properties

Many studies have shown the remarkable enhancement of thermo-physical properties with the addition of a small quantity of nanoparticles into conventional fluids. However, the long-term stability of the nanofluids, which plays a significant role in enhancing these properties, is hard to achieve, thus limiting the performance of the heat transfer fluids in practical applications. The present paper attempts to highlight various approaches used by researchers in improving and evaluating the stability of thermal fluids and thoroughly explores various factors that contribute to the enhancement of the thermo-physical properties of mono, hybrid, and green nanofluids. There are various methods to maintain the stability of nanofluids, but this paper particularly focuses on the sonication process, pH modification, and the use of surfactant. In addition, the common techniques to evaluate the stability of nanofluids are undertaken by using visual observation, TEM, FESEM, XRD, zeta potential analysis, and UV-Vis spectroscopy. Prior investigations revealed that the type of nanoparticle, particle volume concentration, size and shape of particles, temperature, and base fluids highly influence the thermo-physical properties of nanofluids. In conclusion, this paper summarized the findings and strategies to enhance the stability and factors affecting the thermal conductivity and dynamic viscosity of mono and hybrid of nanofluids towards green nanofluids.

scholarly journals Stability Analysis for Distributed Secondary Control with Consideration of Diverse Input and Communication Delays for Distributed Generations in a DC Integrated Energy System

2021 ◽  
Vol 8 ◽  
Author(s):  
Tao Wang ◽  
Chunyan Rong ◽  
Shuai Tang ◽  
Yinqiu Hong
Keyword(s):  
Stability Analysis ◽  
System Performance ◽  
Energy System ◽  
System Stability ◽  
Communication Delays ◽  
Secondary Control ◽  
Efficient Operation ◽  
Integrated Energy System ◽  
The Stability ◽  
Input Delays

An integrated energy system is a promising approach to synthesize various forms of energy, where cooperative control is indispensable for stable and efficient operation. During the information exchange of cooperative distributed secondary control (DSC) in an integrated energy system, the effect of time delays on system performance cannot be ignored, which mainly consist of input delays and communication delays. Compared with most of the existing literature which only address DSC considering communication delays, this paper investigates the stability robustness of an integrated energy system in the case of both input and communication delays. First, the impacts of input and communication delays on DSC are analyzed based on the Gerschgorin theorem and Nyquist criterion, where the system stability is principally dependent on input delays while has little correlation with communication delays and the inconsistency of the two delays may result in steady-state deviation. Then, on the assumption of identical input and communication delays, a closed-loop small-signal model equipped with a distributed secondary controller is established for stability analysis and the delay-dependent criteria are formulated to determine the stability margin of the system based on critical characteristic root tracking. By a series of trial declarations, the delay margins with regard to different controller gains are determined and the qualitative relationship between delay margins and controller gains can be utilized to guide the controller design for improved system performance. The effectiveness of the theoretical results is verified by case studies on a test system.

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