scholarly journals Experimental Analysis and Optimization of an R744 Transcritical Cycle Working with a Mechanical Subcooling System

Energies ◽  
2020 ◽  
Vol 13 (12) ◽  
pp. 3204 ◽  
Author(s):  
Daniel Sánchez ◽  
Jesús Catalán-Gil ◽  
Ramón Cabello ◽  
Daniel Calleja-Anta ◽  
Rodrigo Llopis ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Heat Exchanger ◽  
Critical Temperature ◽  
Computational Model ◽  
Experimental Analysis ◽  
Experimental Tests ◽  
Cooling Capacity ◽  
Operating Conditions ◽  
Coefficient Of Performance ◽  
Liquid Heat

In the last century, the refrigerant R744 (carbon dioxide) has become an environmentally friendly solution in commercial refrigeration despite its particular issues related to the low critical temperature. The use of transcritical cycles in warm and hot countries reveals the necessity of adopting different configurations and technologies to improve this specific cycle. Among these, subcooling methods are well-known techniques to enhance the cooling capacity and the Coefficient of Performance (COP) of the cycle. In this work, an R600a dedicated mechanical subcooling system has been experimentally tested in an R744 transcritical system at different operating conditions. The results have been compared with those obtained using a suction-to-liquid heat exchanger (IHX) to determine the degree of improvement of the mechanical subcooling system. Using the experimental tests, a computational model has been developed and validated to predict the optimal subcooling degree and the cubic capacity of the mechanical subcooling compressor. Finally, the model has been used to analyze the effect of using different refrigerants in the mechanical subcooling unit finding that the hydrocarbon R290 and the HFC R152a are the most suitable fluids.

scholarly journals THEORETICAL AND EXPERIMENTAL ANALYSIS OF A VAPOR-COMPRESSION REFRIGERATION CYCLE WITH A HEAT EXCHANGER BETWEEN THE SUCTION AND LIQUID LINES

2019 ◽  
Vol 18 (2) ◽  
pp. 19
Author(s):  
L. S. Santana ◽  
J. Castro ◽  
L. M. Pereira
Keyword(s):  
Heat Exchanger ◽  
Experimental Analysis ◽  
Thermodynamic Cycle ◽  
Electrical Energy ◽  
Coefficient Of Performance ◽  
Refrigeration Cycle ◽  
Vapor Compression ◽  
Vapor Compression Refrigeration Cycle ◽  
Vapor Compression Refrigeration ◽  
Liquid Heat

Vapor-compression refrigeration systems require a significant amount of electrical energy. Therefore, there is a need for finding efficient ways of operating this equipment, reducing their energy consumption. The use of heat exchangers between the suction line and the liquid line can produce a better performance of the thermodynamic cycle, as well as reduce it. The present work aims at an experimental analysis of the suction/liquid heat exchanger present in a freezer running with refrigerant fluid R-134a. Three different scenarios were used in order to evaluate the thermal performance of the refrigeration cycle. The first scenario was the conventional freezer set up to collect the required data for further comparison. Moreover, the second and third scenarios were introduced with a 20 cm and 40 cm suction/liquid heat exchanger, respectively, into the system. From the experiments, it was observed that the heat exchange does not significantly affect the coefficient of performance (COP) of the freezer. It was concluded from this work that the best scenario analyzed was the 20 cm suction/liquid heat exchanger where most of the thermodynamic properties were improved, one of them being the isentropic efficiency.

Transcritical Carbon Dioxide Refrigeration as an Alternative to Subcritical Plants

2016 ◽  
pp. 100-159
Author(s):  
Adriana Greco ◽  
Ciro Aprea ◽  
Angelo Maiorino
Keyword(s):  
Carbon Dioxide ◽  
Heat Exchanger ◽  
Critical Temperature ◽  
Experimental Analysis ◽  
Internal Heat ◽  
Refrigeration Cycle ◽  
Desiccant Wheel ◽  
Internal Heat Exchanger ◽  
Transcritical Carbon Dioxide ◽  
Vapour Compression

Carbon dioxide (R744) is as a valid alternative to classical substances such as HFCs used in vapour compression plants. A transcritical refrigeration cycle is needed because the critical temperature of carbon dioxide is usually lower than the ambient temperature. In this chapter the performances of a transcritical cycle have been evaluated with a prototype R744 system working as a classical spit-systems to cool air. An experimental analysis has been carried out on the effect of: refrigerant charge, internal heat exchanger, heat rejection pressure on the energetic performances of the transcritical plant. An experimental analysis of a hybrid trans-critical refrigerator-desiccant wheel system has been carried out in order to improve the COP. The experimental transcritical cycle has been examined in comparison with a classical vapour compression plant working with the R134a.

Effects of an Internal Heat Exchanger in a Refrigerant System with Carbon Dioxide on Its Cooling Coefficient of Performance and Cooling Capacity

2008 ◽  
Vol 34 (5) ◽  
pp. 505-512 ◽  
Author(s):  
Shogo Tamaki ◽  
Yuuko Fujii ◽  
Yohsuke Matsushita ◽  
Hideyuki Aoki ◽  
Takatoshi Miura ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Heat Exchanger ◽  
Internal Heat ◽  
Cooling Capacity ◽  
Coefficient Of Performance ◽  
Internal Heat Exchanger

Transcritical Carbon Dioxide Refrigeration as an Alternative to Subcritical Plants

2015 ◽  
pp. 295-359
Author(s):  
Adriana Greco ◽  
Ciro Aprea ◽  
Angelo Maiorino
Keyword(s):  
Carbon Dioxide ◽  
Heat Exchanger ◽  
Critical Temperature ◽  
Experimental Analysis ◽  
Internal Heat ◽  
Refrigeration Cycle ◽  
Desiccant Wheel ◽  
Internal Heat Exchanger ◽  
Transcritical Carbon Dioxide ◽  
Vapour Compression

Carbon dioxide (R744) is as a valid alternative to classical substances such as HFCs used in vapour compression plants. A transcritical refrigeration cycle is needed because the critical temperature of carbon dioxide is usually lower than the ambient temperature. In this chapter the performances of a transcritical cycle have been evaluated with a prototype R744 system working as a classical spit-systems to cool air. An experimental analysis has been carried out on the effect of: refrigerant charge, internal heat exchanger, heat rejection pressure on the energetic performances of the transcritical plant. An experimental analysis of a hybrid trans-critical refrigerator-desiccant wheel system has been carried out in order to improve the COP. The experimental transcritical cycle has been examined in comparison with a classical vapour compression plant working with the R134a.

scholarly journals Performance Evaluation of a Gravity-Assisted Heat Pipe-Based Indirect Evaporative Cooler

Energies ◽  
2020 ◽  
Vol 13 (1) ◽  
pp. 200 ◽  
Author(s):  
Krzysztof Rajski ◽  
Jan Danielewicz ◽  
Ewa Brychcy
Keyword(s):  
Mathematical Model ◽  
Heat Pipe ◽  
Cooling Capacity ◽  
Operating Conditions ◽  
Coefficient Of Performance ◽  
Mass Transfer Processes ◽  
Air Cooler ◽  
Evaporative Cooler ◽  
The Mathematical Model ◽  
Further Development

In the present work, the effects of different operating parameters on the performance of a gravity-assisted heat pipe-based indirect evaporative cooler (GAHP-based IEC) were investigated. The aim of the theoretical study is to evaluate accurately the cooling performance indicators, such as the coefficient of performance (COP), wet bulb effectiveness, and cooling capacity. To predict the effectiveness of the air cooler under a variety of conditions, the comprehensive calculation method was adopted. A mathematical model was developed to simulate numerically the heat and mass transfer processes. The mathematical model was validated adequately using experimental data from the literature. Based on the conducted numerical simulations, the most favorable ranges of operating conditions for the GAHP-based IEC were established. Moreover, the conducted studies could contribute to the further development of novel evaporative cooling systems employing gravity-assisted heat pipes as efficient equipment for transferring heat.

Influence of Experimental Uncertainty on Prediction of Holistic Multi-Scale Data Center Energy Efficiency

2011 ◽  
Author(s):  
Thomas J. Breen ◽  
Ed J. Walsh ◽  
Jeff Punch ◽  
Amip J. Shah ◽  
Niru Kumari ◽  
...  
Keyword(s):  
Energy Efficiency ◽  
Experimental Analysis ◽  
Data Center ◽  
Data Centers ◽  
Operating Conditions ◽  
Coefficient Of Performance ◽  
System Level ◽  
Scale Model ◽  
Multi Scale ◽  
Scale Data

As the energy footprint of data centers continues to increase, models that allow for “what-if” simulations of different data center design and management paradigms will be important. Prior work by the authors has described a multi-scale energy efficiency model that allows for evaluating the coefficient of performance of the data center ensemble (COPGrand), and demonstrated the utility of such a model for purposes of choosing operational set-points and evaluating design trade-offs. However, experimental validation of these models poses a challenge because of the complexity involved with tailoring such a model for implementation to legacy data centers, with shared infrastructure and limited control over IT workload. Further, test facilities with dummy heat loads or artificial racks in lieu of IT equipment generally have limited utility in validating end-to-end models owing to the inability of such loads to mimic phenomena such as fan scalability, etc. In this work, we describe the experimental analysis conducted in a special test chamber and data center facility. The chamber, focusing on system level effects, is loaded with an actual IT rack, and a compressor delivers chilled air to the chamber at a preset temperature. By varying the load in the IT rack as well as the air delivery parameters — such as flow rate, supply temperature, etc. — a setup which simulates the system level of a data center is created. Experimental tests within a live data center facility are also conducted where the operating conditions of the cooling infrastructure are monitored — such as fluid temperatures, flow rates, etc. — and can be analyzed to determine effects such as air flow recirculation, heat exchanger performance, etc. Using the experimental data a multi-scale model configuration emulating the data center can be defined. We compare the results from such experimental analysis to a multi-scale energy efficiency model of the data center, and discuss the accuracies as well as inaccuracies within such a model. Difficulties encountered in the experimental work are discussed. The paper concludes by discussing areas for improvement in such modeling and experimental evaluation. Further validation of the complete multi-scale data center energy model is planned.

INFLUENCE OF THE SOLUTION HEAT EXCHANGER EFFICIENCY ON THE PERFORMANCE OF A SINGLE EFFECT H2O-LiBr ADIABATIC ABSORPTION SYSTEM

2011 ◽  
Vol 19 (02) ◽  
pp. 107-112 ◽  
Author(s):  
GEYDY GUTIÉRREZ URUETA ◽  
PEDRO RODRÍGUEZ AUMENTE ◽  
MARIA RODRÍGUEZ HIDALGO ◽  
ANTONIO LECUONA NEUMANN
Keyword(s):  
Heat Exchanger ◽  
Strong Solution ◽  
Heat Transfer Process ◽  
Operating Conditions ◽  
Coefficient Of Performance ◽  
Test Facility ◽  
Absorption System ◽  
Experimental Conditions ◽  
Single Effect ◽  
Absorption Cycle

This work analyzes the effect that particular operating conditions of a single effect H2O - LiBr adiabatic absorption system have on a plate-type solution heat exchanger efficiency. The corresponding influence of such efficiency on the performance of facility under study is evaluated. As a result of the design of experimental test facility, the functioning of the strong solution circuit leads to take into account some particular operating conditions which affect the correct performance of the solution heat exchanger. For some experimental conditions, the strong solution side is not completely filled by the solution fluid. As a consequence of this, the heat transfer process is affected, reducing the solution heat exchanger efficiency and changing greatly the resulting coefficient of performance (COP) of the absorption facility. In order to illustrate this phenomenon, this paper offers graphical results including: solution working temperatures, solution heat exchanger efficiency and COP in a time sequence of an experiment, as well as for fixed steady-state operating conditions. These results show the importance of a correct functioning of the solution heat exchanger on the performance of an absorption system. The results are useful for researchers interested in new absorption cycle designs.

Performance Investigation of Single Adsorption Refrigeration System Driven by Solar Heat Storage

2018 ◽  
Vol 26 (03) ◽  
pp. 1850025
Author(s):  
Hicham Boushaba ◽  
Abdelaziz Mimet
Keyword(s):  
System Performance ◽  
Heat Storage ◽  
Cooling Capacity ◽  
Operating Conditions ◽  
Coefficient Of Performance ◽  
Solar Irradiation ◽  
Cooling Power ◽  
Condensation Temperature ◽  
Adsorption Refrigeration ◽  
Solar Heat

The aim of this paper is to provide a global study of an adsorption refrigeration machine driven by solar heat storage and collected by parabolic trough collector. The system operates with ammonia (as refrigerant) and activated carbon (as adsorbent). A mathematical model interpreting the progression of the heat and the mass transfer at each element of the prototype has been developed. The solar irradiation and the real ambient temperature variations corresponding to a usual summer day in Tetouan (Morocco) are considered. The system performance is evaluated trough specific cooling power (SCP) as well as solar coefficient of performance (SCOP), which was estimated by a dynamic simulation cycle. The pressure, temperature and adsorbed mass profiles in the Adsorber have been calculated. The effects of significant design and operating parameters on the system performance have been investigated. The results show the capability of our system to realize an encouraging performance and to overcome the intermittence of the adsorption refrigeration machines. For a daily solar irradiation of 18[Formula: see text]MJ[Formula: see text]m[Formula: see text] and operating conditions of evaporation temperature [Formula: see text]C, condensation temperature [Formula: see text]C and generation temperature [Formula: see text]C, the results show that the process could achieve an SCP of 115[Formula: see text]W[Formula: see text]kg[Formula: see text] and it could produce a daily specific cooling capacity of 3310[Formula: see text]kJ[Formula: see text]kg[Formula: see text], whereas its SCOP could attain 0.141.

scholarly journals CALCULATION MODEL OF THE SYSTEM OF THERMAL STABILIZATION OF THE ELEMENTS OF RADIO ELECTRONIC EQUIPMENT

2019 ◽  
Vol 46 (1) ◽  
pp. 42-52
Author(s):  
T. A. Ismailov ◽  
A. M. Ibragimova
Keyword(s):  
Heat Exchanger ◽  
Melting Point ◽  
Computational Model ◽  
Flow Rate ◽  
Fluid Motion ◽  
Thermal Stabilization ◽  
Maximum Flow ◽  
Cooling Capacity ◽  
Electronic Equipment ◽  
Stable Operation

Objectives. The aim of the study is to develop a computational model of the system of thermal stabilization of elements of electronic equipment (REA), based on the joint use of working substances with a stable melting point and the liquid method of heat sink, the study of the thermophysical processes occurring during its operation.Method. A computational model of the REA thermostabilization system based on the use of working substances with a stable melting point has been created. The model includes a description of the heat exchange processes during laminar fluid motion in a heat exchanger, determining the duration of stable operation of the REA elements, depending on the flow rate and cooling capacity of a thermoelectric battery (TEB).Result. The graphs of dependences reflecting the main characteristics of the developed system were obtained, in particular, the dependence of the change in the duration of maintaining the stable temperature of the REA element on its power, the temperature of the cold junctions of the thermopile, scattering at different maximum flow rates of the heat exchanger.Conclusions. The results of the calculations determine that the duration of complete penetration of the working substance, corresponding to the duration of stable operation of CEA elements, can be within the required limits only if certain very specific conditions are met: using a sufficient amount of the working substance in the heat stabilizing system, corresponding to the temperature and flow rate of the liquid in the heat exchanger. These parameters of the thermal stabilization system must be selected based on the amount of heat emitted per unit of time by the REA element, the duration of its operation, and the characteristics of the thermopile used to cool the fluid.

scholarly journals Effects of Evaporator and Condenser Temperatures on the Performance of a Chiller System With a Variable Speed Compressor

2021 ◽  
Vol 39 (1A) ◽  
pp. 45-55
Author(s):  
Ahmed H. Al-Hassani ◽  
Alaa R. Al-Badri
Keyword(s):  
Power Consumption ◽  
Water Temperature ◽  
Experimental System ◽  
Cooling Capacity ◽  
Pi Controller ◽  
Operating Conditions ◽  
Coefficient Of Performance ◽  
Rotary Compressor ◽  
Variable Speed ◽  
Control Loops

The operation and performance of heat-pump systems are affected by indoor and outdoor operating conditions. Power consumption and system efficiency are related to evaporator and condenser working pressures. Intelligent controllers such as a proportional integral (PI) controller improve the performance of variable speed refrigeration systems (VSRs) with electronic expansion valve (EEV). Evaporator and condenser pressures affect the system power consumption and efficiency. In this study, the influence of evaporator and condenser temperatures on the performance of a variable speed refrigeration system with an EEV was experimentally investigated at constant cooling load. The experimental system comprises of a rotary compressor, shell-and-coil condenser, EEV, and shell-and-coil evaporator for one-ton cooling capacity with refrigerant R410. Compressor speed and EEV opening are controlled by a PI controller with two control loops and the refrigerant superheat (DS) is maintained at 7°C. The results show that at constant cooling capacity, the refrigerant flow rate rises with the increase in the compressor speed. The coefficient of performance (COP) is improved with low compressor speed. The System COP is increased by 3.3% with increasing evaporator inlet water temperature for 2°C due to the reduction in the compressor speed and compression ratio. High condenser inlet water temperature promotes the refrigerant subcooling.

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