Showing papers on "Thermal expansion valve published in 2021"

Energy and exergy performance evaluation of a three-stage auto-cascade refrigeration system using low-GWP alternative refrigerants

Abstract: In order to seek promising refrigerants for vapor compression refrigeration system to obtain ultra-low temperatures down to -100 °C, and to determine whether the low-GWP refrigerants, R41, R170 and R1132a, are suitable substitutes for R23, this study conducted a comprehensive comparative analysis on the cycle characteristics of a three-stage auto-cascade refrigeration (ACR) system using R1234yf/R23/R14, R1234yf/R41/R14, R1234yf/R170/R14 and R1234yf/R1132a/R14. The system performances, including cooling capacity, coefficient of performance (COP), evaporation temperature, compressor discharge temperature, exergy destruction and efficiency were investigated with various compositions and vapor qualities. Results show that R41, R170 and R1132a can all be recommended to replace R23, and the alternatives present promising thermodynamic properties in theoretical simulations. Under the same operation conditions, the cooling capacity of the R1234yf/R41/R14 system is the largest, while the maximum COP and exergy efficiency occur in the R1234yf/R23/R14 system. Considering the energy shortage and environmental pollution issues, R1234yf/R41/R14 with the mass fraction of 0.64/0.17/0.19, COP of 0.2713, and exergy efficiency of 13.91% performs better and hence can be suggested as an alternative refrigerant for the three-stage ACR operating at -100 °C. The largest exergy destruction component occurs in the compressor, followed by the air-cooled condenser and expansion valve, on which future optimization work can be carried out. The results provide a basic theoretical analysis of the selection and replacement of refrigerant in three-stage ACR.

Effect of thermostatic expansion valve tuning on the performance enhancement and environmental impact of a mobile air conditioning system

Abstract: In this work, the performance enhancement of a HFO-1234yf mobile air conditioning (MAC) system with a suction/liquid line heat exchanger (SLHX) was carried out experimentally by tuning the thermostatic (constant superheat) expansion valve (TXV) and its impact on the environment was also evaluated. The optimum charge of HFO-1234yf and HFC-134a systems was found to be 670 g and 740 g, respectively. The results showed that the HFO-1234yf system with SLHX had better coefficient of performance (COP) and exergy efficiency when compared to HFC-134a system with SLHX at idling condition, whereas it had reduced performance at other speed conditions. The tuning of the TXV in the HFO-1234yf system had a positive influence on the COP, cooling capacity, and exergy efficiency and those were higher than that of existing HFC-134a system by 4.3–8.6%, 6.5–10.1%, and 3.7–5.1%, respectively, at idling and city speed conditions, whereas those were slightly lower at high-speed conditions. The total CO2 equivalent emission of tuned and un-tuned HFO-1234yf system was 27.98% and 24.64% lower than that of the existing HFC-134a system. The outcome of this study indicated that the SLHX implementation in the HFO-1234yf MAC system with tuned TXV could be a possible option to replace HFC-134a.

Performance Analysis of an Ejector Enhanced Two-Stage Auto-Cascade Refrigeration Cycle for Low Temperature Freezer

Abstract: In this paper, an ejector enhanced two-stage auto-cascade refrigeration cycle (EARC) using ternary mixture R600a/R32/R1150 is proposed for application of −80°C freezing. In EARC cycle, an ejector was employed to recover the expansion work in the throttling processes and lifted the suction pressure of the compressor. The performances of the ejector enhanced two-stage auto-cascade refrigeration cycle and conventional auto-cascade refrigeration cycle (CARC) were compared using thermodynamic analysis methods. The influences of the important operation parameters including mass fraction ratio of the mixture, fluid quality at the second separator inlet, condensation temperature, evaporation temperature, and expansion ratio of expansion valve on the performances of EARC cycle were discussed in detail. The results indicate that ternary mixture R600a/R32/R1150 has the optimal mass fraction ratio of 0.45/0.2/0.35 with respect to the maximum COP. The EARC cycle yields higher performance than the CARC cycle in terms of COP, exergy efficiency and volumetric refrigeration capacity. And 4.9%–36.5% improvement in COP and 6.9%–34.3% higher exergy efficiency could be obtained in EARC cycle comparing with CARC cycle. The finding of this study suggests that the EARC cycle has a promising application potential for low temperature freezing.

Common fault effects on a natural refrigerant, variable-speed heat pump

Abstract: The European heat pump market is growing every year as European legislation moves towards the use of natural refrigerants that have less global warming potential than conventional refrigerants. Even though heat pumps are very efficient, the appearance of hard-to-detect faults increases energy consumption. The present study emulated some of the most common faults on a variable-speed heat pump charged with propane. The faults tested were evaporator fouling, compressor valve leakage, liquid line restriction and refrigerant overcharge. The effect of these faults on performance and several heat pump features are described. Evaporator fouling was the fault with least COP degradation and compressor valve leakage with the most (7% and 56% COP reduction, respectively). The results are compared with the results from a comparable study. The heat pump covered the demand generated by nearly all the faults at the expense of increasing the power consumption. The features of each fault are summarized in a chart, which could be used as table for diagnosing faults.

Improved Superheat Control of Variable-Speed Vapor Compression Systems in Provision of Fast Load Balancing Services

Abstract: Utilization of renewable energy resources, such as solar and wind, has seen rapid growth on the power grid worldwide. To mitigate the adverse impact of these volatile generation on the reliability of the power grid, fast balancing services are increasingly procured by system operators from various resources, such as flexible air-conditioning and space heating loads. Recent work of the authors has demonstrated technical feasibility and various benefits of using variable-speed vapor compression equipment for two fast load balancing services, namely frequency regulation and solar photovoltaic power smoothing. A major control issue was also identified in prior experimental tests: the drastic changes of the compressor speed for fast load balancing have caused severe superheat regulation issues including oscillations and even wet compression. To this end, a gain-scheduled feedforward and proportional integral (PI) controller is proposed and presented in this paper, which uses the real-time compressor speed in determining compensating control actuation of the expansion valve to mitigate the disturbance effect. Both simulation and experimental validations of the proposed control strategy were carried out with a 3-ton variable-speed heat pump. Test results have shown that the proposed controller is effective in improving the superheat regulation performance for three load balancing scenarios, i.e., compressor speed step changes, frequency regulation and photovoltaic smoothing. The demonstrated performance gains include fast post-disturbance recovery of the superheat with the settling time shortened by 63% to 83%, complete avoidance of wet compression and enhanced transient energy efficiency.

Low global warming potential (GWP) refrigerant supermarket refrigeration system modeling and its application.

Abstract: As an environmentally friendly low global warming potential (GWP) refrigerant, Carbon dioxide (CO2) has continuously gained popularity and research attention as alternative refrigerant for supermarket refrigeration system. In this paper, to fulfill the increasing need of accurate Low-GWP supermarket refrigeration models for development of supervisory level control and optimization strategies, a high fidelity model is developed for CO2 transcritical supermarket refrigeration system which includes compressor rack of low temperature (LT) compressors and medium temperature (MT) compressors, air-cooled gas cooler, evaporator, expansion valves and other auxiliary equipment. A resistance-capacity model structure is proposed to simulate the display cases. Semi-thermodynamic models are proposed to estimate reciprocating compressors volumetric efficiency and power consumption. The zone modeling approach is used for evaporator simulation, and air-cooled gas cooler is modeled with distributed modeling method. The expansion valve simulation is based on orifice flow model. To calibrate these models, both manufacture performance data and experimental data are used. The experiments are conducted with a full instrumental CO2 supermarket refrigeration system installed in Oak Ridge National Lab Flexible Research Platform (FRP). The simulation model can predict the system performance, including power consumption, cooling capacity, mass flow rate, temperature, and pressure, with high accuracy (within ±4%) compared to experimental data. In addition, this developed model has been used to create the system optimum high side pressure for high side expansion valve control, and to generate wide operating range simulation data for developing the batter-equivalent commercial refrigeration system model which can be used in grid interactive control development.

Experimental performance evaluation of an R1234yf automobile air conditioning system employing an internal heat exchanger

Abstract: A bench-top automobile air conditioning (AAC) system using a thermostatic expansion valve was developed. The system was equipped with a coaxial internal heat exchanger (HEX) and charged with R1234yf, a new refrigerant used as an alternative to R134a. The system was tested at the compressor speeds ranging between 1000 rpm and 2600 rpm with increments of 400 rpm. For each compressor speed, the air temperatures at the evaporator and condenser inlets were concurrently changed between 30 °C and 40 °C with increments of 5 °C. The system was operated for the cases of employing and not employing the HEX, and totally 30 test runs were performed. Then, the first law of thermodynamics was applied to the system components to evaluate various steady state performance parameters. The considered parameters were the refrigerant mass flow rate, evaporating temperature, cooling capacity, compressor power, coefficient of performance (COP), condenser heat dissipation rate and discharge temperature of the compressor. It was determined that the experimental system employing the HEX yielded on average 0.8 °C lower evaporating temperature, 2.2% higher cooling capacity, 2.0% lower compressor power and 3.0% higher COP values relative to the system not employing the HEX. These findings reveal that the use of HEX causes a better system performance in terms of the cooling capacity, compressor power and COP. Consequently, the performance of R1234yf AAC systems can be improved with the use of HEX, and thus, the AAC systems using R1234yf can be more competitive with those using R134a.

An experimental investigation of oil circulation ratio influence on heating performance in an air condition heat pump system for electrical vehicles

Abstract: Oil, lubricating and cooling the sliding parts of the compressorcomponents exposed to friction, could prevent refrigerant gas leakage in compressor chamber of vapor compression air conditioning system. For air condition heat pump system in electric vehicles, no oil circulating routes and oil separator are used to drive oil from system to compressor, making oil retainedmore difficult to control. Oil accumulated in heat exchanger and expansion valve would enhance pressure drops and reduce heat transfer capacity, leading to decrease of entire heating performance in cold climate. In this paper, a newly designed air conditioning heat pump system with R134a and PAG46 oil is introduced firstly, and oil circulation experiments were conducted on a full-scale electric vehicle. Typical heat transfer characteristics and system performance parameter were recorded and analyzed subsequently under different compressor oil charge conditions, including excessive charge and insufficient charge. Oil circulation rates in system were also measured and exhibited an increasing trend with compressor oil charge mass. Furthermore, heating performances of the system under different oil circulation rate were compared by various heating capacity and pressure drops. Results showed that both excessive and insufficient charge might decrease heating performance, i.e., determination of suitable oil charge is quite important for air condition heat pump system.

Modeling and Simulation of a Retail Commercial Refrigeration System

Abstract: Commercial food outlets in the UK are responsible for 3% of the UK total energy consumption, with refrigeration systems account for 29% of this total. This highlights the potential and importance of huge energy saving within commercial refrigeration systems. In this paper, a validated model that simulates a commercial refrigeration system installed over 2000 sqft to mimic a real express store installed at Riseholme Refrigeration Research Centre at the University of Lincoln, UK, is developed and presented. The detailed modelling of the display case using a temperature model comprising of three states include air inside the display case, products, and the evaporator. Additionally, the model presents a holistic view of the whole system with each subsystem cohesively linked together. Further focus has been given on the high temperature (HT) system due to the high level of installations of this system found in retail commercial refrigeration stores as well as low temperature (LT) systems featuring doors which decrease the heat transfer from the store into the cases. It is concluded that the trends of the simulation results for the display case temperatures, expansion valve opening degree, suction line pressures, and compressors power consumption, all have high resemblance to the trends of collected data obtained from Riseholme Refrigeration Research Centre. This supports the validation of the developed model.

Modeling and Optimal Control of Vehicle Air Conditioning System

Abstract: Due to the proprietary nature of automotive software development, the control logic, plant models as well as physics-based models used for simulations are closed sources. For the most part, OEMs use Simulink® to develop their control and diagnostic logic (Khaled et al. Multivariable Control of Dual Loop EGR Diesel Engine with a Variable Geometry Turbo, SAE Technical Paper 2014–01-1357, 2014 and Khaled and Pattel, Practical Design and Application of Model Predictive Control: MPC for MATLAB® and Simulink® Users” Elsevier, ISBN: 978–0,128,139,189, 2018). As for plant models of the vehicle and its various subsystems, OEMs use many simulation packages such as ANSYS, COMSOL, SimScale in addition to MathWorks. This creates significant software integration challenges and revision control complexities. In this paper, we recommend the utilization of Simscape® toolbox from Simulink as a platform for simulating the vehicle air conditioning system. Moreover, we demonstrate the development of model predictive controller based on the two-phase model of the air conditioning system. The controller relies on a model that predicts the rate of change of temperature rather than the temperature when the compressor command is manipulated. Both the controller and the plant model are available for free download. The model leverages recent improvements in the two-phase modeling in Simscape and is an extension to the basic refrigeration model provided by MathWorks. The model includes variable displacement compressor, condenser, evaporator and expansion valve components that are provided in the library of Simscape. Issues faced during development and sizing of the refrigeration model are highlighted. Lessons learned are highlighted to aid the reader to scale the model for bigger vehicles. R134a is used as the refrigerant. The linearized model is used to develop a model predictive control (MPC) to minimize energy consumption while maintaining a good temperature reference tracking in the cabin. Simulation results for the controller are provided. Future work and recommendations are provided to conclude the work.

Method for operating a heat pump

Abstract: The device has a pair of change over valves (50, 60) arranged in such a manner that a compressor (10), a condenser (20), an expansion valve (40) and an evaporator (30) are respectively coupled with the change over valves at a pair of ends. The change over valves are a four or two way-change over valve and connected in such a manner that the condenser is coupled with the compressor at one end and with the expansion valve at another end when an operating mode is activated.

Heat source unit and freezing apparatus

Abstract: According to the present invention, an oil recovery operation comprises a first operation of reducing the opening degree of a heat source expansion valve (28) and a second operation of increasing the opening degree of the heat source expansion valve (28) after the first operation. A controller (80) is configured to execute the second operation when a first condition is satisfied during the first operation. The first condition includes at least a condition in which a difference ΔP between the pressure of a refrigerant on the downstream side of the heat source expansion valve (28) in a liquid pipe (43) and the pressure of a suction refrigerant of a compression element (C) is smaller than a predetermined value.

Heat pump system

Abstract: This heat pump system is provided with: a tank unit having a hot water storage tank for storing hot water; and a drawer unit that is drawable from the tank unit, that has a refrigerant circuit having a compressor, a condenser, an expansion valve, and an evaporator, and that supplies hot water to the hot water storage tank of the tank unit by using heat of the refrigerant circuit.

Air conditioning apparatus and outdoor unit

Abstract: Provided is an air conditioning apparatus that exhibits the effect of making it possible to reduce the amount of refrigerant needed to fill both a first refrigerant circuit in which a load-side heat exchanger is made to function as an evaporator and a heat-source-side heat exchanger is made to function as a condenser, and a second refrigerant circuit in which the heat-source-side heat exchanger is made to function as an evaporator and the load-side heat exchanger is made to function as a condenser. An air conditioning apparatus 100 comprises a compressor 10, an expansion valve 15, an outdoor heat exchanger 12, an indoor heat exchanger 20, a first cooler 13 and a second cooler 14, and a four-way valve 11 for switching the refrigerant circuit in which refrigerant circulates. The four-way valve 11 switches between: a first refrigerant circuit 5a through which refrigerant circulates in the order of compressor 10, outdoor heat exchanger 12, first cooler 13, expansion valve 15, indoor heat exchanger 20, and compressor 10; and a second refrigerant circuit in which refrigerant circulates in the order compressor 10, indoor heat exchanger 20, second cooler 14, expansion valve 15, outdoor heat exchanger 12, and compressor 10.

Novel dehumidifying and drying device

Abstract: The invention belongs to the technical field of dehumidification and drying, and particularly relates to a novel dehumidifying and drying device. The dehumidifying and drying device comprises a dryingbox, a compressor, a condenser, an expansion valve and an evaporator, wherein all the devices are arranged in the drying box, a refrigerant working medium R290 is vaporized in the evaporator to absorb heat of surrounding air, water vapor in the air is condensed on the pipe wall, a refrigerant becomes gaseous R290 to be sucked and compressed into high-temperature and high-pressure gas by the compressor and then is discharged into the condenser; R290 in the condenser continuously releases heat to the surrounding space to be condensed into liquid, and clothes and the like are dried through the released heat to accelerate water evaporation; and high-pressure liquid passes through the expansion valve, and slowly enters the evaporator after being throttled and depressurized. The process is repeated.

Integrated hybrid thermostatic expansion valve and method for providing uniform cooling of heat generating devices

Abstract: An apparatus and method are disclosed for ensuring adequate and uniform cooling for any heat-generating device that experiences large heat pulses by integrating parallel expansion devices and their control directly into each of a discrete cooling load or cold plate. One of the parallel expansion devices is an integrated cartridge thermostatic expansion valve (TXV) and the other is an electrically-actuated valve. The TXV is positioned such that a sensing element is located directly within an exit refrigerant stream, thereby improving time-response of the valve and eliminating the need for a capillary tube. The electrically-actuated valve provides a sudden burst of refrigerant while the TXV is responding to sudden heat pulses and operates at the command of the heat generating system or triggered by a temperature rise. The disclosed operational method leads to an order of magnitude reduction in settling time after a heat pulse.

The effect of variation of extra fan condenser and engine speed to COP of mobile air conditioners

Abstract: Efforts to increase coefficient of performance (COP) of Mobile Air Conditioners (MAC) still continue to be done, including by increasing the extra fan condenser speed. The problem is whether it can improve the COP, it needs to be tested further. This study focuses to examine the effect of extra fan condenser and engine speed variations to COP. This study was conducted on a MAC engine stand which able to measure the pressure and temperature of MAC system. The data measured at inlet compressor (P1, T1), outlet compressor (P2, T2), outlet condenser (P3, T3), and outlet expansion valve (P4, T4), at engine speed of 1.000, 1.500, 2.000, 2.500 and 3.000 rotation per minute (RPM), respectively with variations extra fan condenser speed of 0.15, 1.74, and 2.22 m/sec. The data was plotted on p-h diagram to obtain enthalpy value, so that obtained COP value by calculation. The major result obtained are the variations of extra fan condenser and engine speed had an effect on the COP. The highest COP (4.48) was achieved at an engine speed of 2,000 RPM with extra fan condenser speed 2.22 m/sec. Increasing extra fan condenser speed causes better cooling at condenser and cooling effect on the evaporator.

Server cooling system and method for cooling

Abstract: Server cooling system comprising: a condenser 50, an evaporator 60, an expansion valve 80 and a compressor 90, wherein, the outlet 64 of the evaporator 60 is connected to the inlet 91 of the compressor 90 by means of a tube or conduit 75. The outlet 92 of the compressor 90 is connected to the inlet 52 of the compressor 50 by means of a conduit 76. In addition, the outlet 54 of the condenser 50 is connected to the inlet 81 of the electronic expansion valve 80 by means of the tube or conduit 73. While the outlet 82 of the electronic expansion valve 80 is connected to the inlet 62 of the evaporator 60 by means of the tube 74. A server cooling system is achieved with an energy requirement much lower than other systems and is safer, as it avoids the presence of water and furthermore, by using a high evaporation temperature ‰¥ 14°C.

Enrichment of Cop Of Vapour Compression Refrigeration System By Using Diffuser And Nozzle

Abstract: this investigational analysis exemplifies the design and test of diffuser at compressor inlet and nozzles at condenser outlet and expansion valve outlet in VCR with the help of Rl34a refrigerant. The diffuser with divergence angle of l5°, l7° and the nozzle with convergent angle l5°, l7° are designed for same inlet and outlet diameters. Initially diffusers are tested at compressor inlet diffuser is used with inlet diameter equal to exit tube diameter of evaporator and outlet tube diameter is equal to suction tube diameter of the compressor. Diffuser helps to increases the pressures of the refrigerant before entering the compressor it will be helps to reduces the compression work and achieve higher performance of the vapour compression refrigeration system. Then nozzles are testing at condenser outlet and expansion valve outlet, where as nozzle inlet diameter equal to discharging tube diameter of condenser and outlet diameter equal to inlet diameter of expansion valve. Extra pressure drop in the nozzle helped to accomplish higher performance of the vapour compression refrigeration system. The system is analyze using the Ist and IInd laws of thermodynamics, to resolve the refrigerating effect, the compressor work input, coefficient of performance(COP)..

Condensation device for a motor vehicle, and condensation method

Abstract: The invention relates to a condensation device (1) for a motor vehicle for obtaining water from the air surrounding the motor vehicle, comprising a heat exchanger (11) and an expansion valve (14), a collecting device (20) and an operating fluid container (25), wherein the collecting device (20) is designed to collect water condensed on the heat exchanger (11) and the expansion valve (14), wherein the operating fluid container (25) is designed to store water, wherein the collecting device (20) and the operating fluid container (25) are connected to one another via a connecting line (22, 24), wherein the connecting line (22, 24) is designed to allow fluid communication to be established between the collecting device (20) and the operating fluid container (25). The condensation method for operating a condensation device describes that the heat exchanger (11) and/or the expansion valve (14) are/is sprayed with a spray mist.

Combinational pump for cooling, heating and hot water production

Abstract: The invention relates to a new type of combinational pump designed for cooling and heating purposes as well as for the production of hot usage water. It is composed of a compressor (1) and an expansion valve (2) both interconnected with pipes (3) into which a refrigerant is flowing. Between the compressor (1) and the valve (2) there are alternators (5) with or without inertia containers (4). In a complete cycle, the refrigerant is compressed by the compressor (1), liquefied, heated and expelling heat to be exploited by the alternator (5); in the sequel, the refrigerant passes through the expansion valve (2) where it evaporates, cools and takes heat from the other alternator (5) so that the wasted energy is not lost in the environment but used as compensatory energy.