Performance Of Refrigeration System Research Articles

Experimental and analytical investigation of CO2/R32 condensation heat transfer in a microchannel

Previous research has shown that CO2 mixtures can improve the thermal performance of CO2 refrigeration systems. Moreover, the use of a microchannel heat exchanger can reduce the refrigerant charge and improve the heat transfer coefficient. Therefore, in this experimental study, we investigated the condensation heat transfer characteristics of CO2/R32 in a porous flat microchannel with a hydraulic diameter of 0.715 mm. According to the results, the convective heat transfer coefficient decreased rapidly then increased slowly with an increase in the CO2 mass fraction. The minimum value was achieved when the CO2 mass fraction was approximately 55%. In addition, the convective heat transfer coefficient decreased with an increase in the condensation temperature. Higher vapour quality and mass flow rate conditions corresponded to higher convective heat transfer coefficients. The prediction correlations applicable to the in-tube condensation heat transfer exhibited low prediction results for CO2/R32, with a heat transfer coefficient prediction error for the newly established prediction model of 16.77%. This study provides theoretical support for analysis of the CO2/R32 condensation heat transfer mechanism in microchannels and the future design of microchannel condensers.

Experimental study on performance of phase change microcapsule cold storage solar composite refrigeration system

This paper proposes a solar jet-compression composite cooling system with phase change microcapsule storage and build a cooling storage-type solar composite refrigeration system and operational performance test platform. A microencapsulated suspension with a base solution of deionized water was prepared, and sodium dodecyl sulfate (SDS) 0.2%, xanthan gum 0.2%, and sodium chloride (NaCl) 0.5% were added. The operating characteristics of the solar cooling system and the variation in the storage performance of the phase change material under evaporation temperatures of −5 °C and −10 °C and suspension mass fractions of 10% and 15% were investigated. It was found that the temperature of the suspension with a 15% mass fraction decreased by 7.34 °C when the storage time reached 100 min and that of the suspension with a 10% mass fraction decreased by 8.20 °C in the same storage time. The storage capacity of the microencapsulated suspension was greater than that of water within the same storage time. The storage capacity of the 10% suspension at 33 min is 2765.01 kJ, which is 63.1% more than that of water, indicating that the suspension has better storage performance.

Influence of mixing section inlet and diffuser outlet velocities on the performance of ejector-expansion refrigeration system using zeotropic mixture

• Theoretical analysis of an ejector expansion refrigeration cycle . • Effects of mixing section inlet and diffuser outlet velocities on the system. • Effects of zeotropic mixture mass ratio on system performance. It is known that the performance of vapor compression cooling systems can be increased thanks to the ejector. In the literature, there are many studies on the subject, in which mathematical models of ejector-expansion cooling systems are developed. However, the refrigerant velocities at the mixing section inlet for the secondary flow (suction stream) and diffuser outlet were neglected in these studies. In the mathematical model used in this study, the velocities in both sections are considered and the system performance is calculated. The performance assessment of an ejector-expansion refrigeration system was realized in the case of using the R600a/R290 refrigerant mixture as a working fluid. Thus, the effect of zeotropic refrigerant mixtures on the system performance is also investigated, considering the refrigerant velocities at the mixing section inlet and diffuser outlet. According to the obtained results, it has been found that the cooling performance of the system that uses R600a/R290 mixture as a refrigerant is 5.8%-7% higher when the velocities at the mixing section inlet and diffuser outlet are considered compared to the neglected one. The exergy efficiency is also calculated to be around 4.6% lower when the ejector mixing section inlet and diffuser outlet velocities are neglected.

Experimental investigation of dehumidification performance of a vapor compression refrigeration system

The dehumidification performance of a vapor compression refrigeration system (VCRS) is investigated in this work, including total refrigerating capacity (TRC), total dehumidification capacity (TDC), latent heat ratio (RLH), and power consumption per unit dehumidification capacity (PCPDC). Experiments were performed for the VCRS with the rated refrigerating capacity of 7 kW. The influence of indoor air parameters including the temperature, humidity and flowrate on the dehumidification performance were studied. TDC and RLH decreased with an increase in the air temperature at a fixed humidity ratio, and increased with an increase in the air humidity at a fixed temperature. PCPDC decreased with an increase in the air humidity. The effect of the air flowrate was more complex than that of the air temperature and humidity. There was a maximum value in TDC and a minimum value in PCPDC with an increase in air flowrate for each humidity. For example, TDCmax was 2.45 kg/h for 38% rh and 6.62 kg/h for 80% rh, accordingly, PCPDCmin was 3383.48 kJ/kg for 38% rh and 1286.5 kJ/kg for 80% rh at 26 °C. As the humidity increases, the maximum and minimum values shifted towards larger flowrates. The experimental results are useful for the operation of VCRS and the design and control of convection-radiation air conditioning (CRA/C) system for the improvement of the environmental comfort.

Study on the performance of an energy-efficient three-stage auto-cascade refrigeration system enhanced with a pressure regulator

This paper proposed a modified three-stage auto-cascade refrigeration cycle (MTARC) associated with an intermediate pressure regulator. The energy and exergy analyses indicate that the MTARC can acquire lower evaporating temperature, greater cooling capacity and higher COP. Under a typical operating condition, the MTARC using the alternative ternary zeotropic mixture of R1234yf/R41/R14(0.66/0.17/0.17) has an evaporator inlet temperature of −90.90 °C, COP of 0.4509 and exergy efficiency of 40.67%, which are 4.63 °C lower, 32.93% and 15.38% higher than those of the conventional three-stage ARC, respectively. Further research shows that with the decreasing intermediate pressure, the thermodynamic performance of the MARC can be improved significantly, but the compressor exhaust temperature also increases. When the intermediate pressure decreases from 1.8 MPa to 1 MPa, the cooling capacity, COP and exergy efficiency of the MTARC increase by 30.34%, 22.10% and 13.79% respectively, while the exhaust temperature increases 18.59 °C from 116.66 °C to 135.25 °C, which indicates that the selection of intermediate pressure needs to be comprehensively considered. The proposed new approach is valuable for optimizing the design and application of the refrigerator at an ultra-low temperature level of −80 °C.

A Comprehensive Thermodynamic Assessment of Cascade Refrigeration System Utilizing Low GWP Hydrocarbon Refrigerants

The thermodynamic performance of a two-stage vapor compression cascade refrigeration system using hydrocarbon refrigerants is studied extensively in this study. The selection of hydrocarbon refrigerants for the cascade refrigeration system is conducted based on the molecular weight, freezing point, vaporization, density, global warming potential and ozone depletion potential. In the lower temperature circuit, Trans-2-butane (T2BUTENE) is utilized while Toluene (toluene), Cyclopentane (CYCLOPEN) and Cis-2-butane (C2BUTENE) are used on the higher temperature circuit. The performance of the system is evaluated considering three major operating temperature such as evaporator temperature, condensation temperature of lower temperature circuit (LTC), and condensation temperature of higher temperature circuit (HTC). Furthermore, comparisons between the presented work and the previous established work are conducted to show the improved performance of cascade refrigeration utilizing the hydrocarbon refrigerants. The results from the simulations suggest that highest COP and exergy efficiency is achieved when Trans-2-butane is employed in lower temperature circuit while Toluene is implemented on the higher temperature circuit. The results also suggest that the highest exergy destruction occurs at the condenser and the lowest can occur either at the lower circuit expansion valve or the evaporator for different refrigerant pairs. In addition, utilizing hydrocarbon refrigerants on cascade refrigeration systems can achieve a minimum 7.21 % higher COP than the recently employed refrigerants in previously established published works.

Cooling performance of modular fish hold for 30 gross-tonnage fishing vessel

This study analysed cooling performance in the fish holds of 30 gross tonnage fishing vessels to optimise the temperature distribution through the cargo volume in the fish hold. A field survey determined the calculation parameters and the fish hold's geometric design. The fluid flow characteristics and product cooling times were determined using a computational fluid dynamic simulation and a performance coefficient of the refrigeration cycles. The simulation result shows that the fastest cooling time occurs when the velocity inlet is 8 m/s at 100% cargo loads. The estimated cooling time until the product load reaches a temperature of −5°C is 2 hours 15 minutes. The required power consumption of the compressor is 3.22 kW and of the condenser is 16.29 kW. The refrigeration system performance coefficient is 4.06. These performance results indicate that the designed fish hold is effective in fish cooling.

Investigation of Working Fluid Performance through a Centrifugal Compression System

Commonly, researchers have investigated many factors that impact the performance of air conditioning and refrigeration systems, such as varied cooling configurations, operating conditions and optimization of specific system components. Although there is an abundance of research detailing the importance of working fluid selection, very few studies focus on how the working fluid selection influences the performance of the individual components of the system, such as the compressor. In this paper, the performances of a selection of working fluids are compared through a centrifugal compressor using CFD. The working fluids considered are R1234ze, R1234yf, R152a, R444a, R445a, R290 and R600a and were selected due to suitability as replacements to R134a. Each fluid, including R134a, was compared based on the performance of a centrifugal compressor with fixed inlet conditions across two operational speeds. The results indicate that R1234ze and R1234yf demonstrated the best performance as replacements to R134a, achieving the highest overall pressure ratios. Additionally, R1234ze also displayed similar power required through the compressor to R134a indicating greater suitability as a drop-in replacement. The working fluids R444a and R445a both displayed performance similar to that of R134a across both operational speeds, indicating reasonable suitability as a replacement to R134a. Alternatively, R152a, R290 and R600a displayed reduced performance compared to R134a and subsequently, are not suitable replacements based on the compression system considered in this study. As well as considering the observed differences in the performance from the selected working fluids, the implications of the results for industrial applications are also considered, along with avenues for further work.

Experimental investigation on the performance of a novel thermo-mechanical refrigeration system driven by an expander-compressor unit

• 1st experimental investigation of innovative thermomechanical refrigeration system. • Operational expander-compressor unit for thermal to mechanical energy conversion. • Detailed design, operation and performance of TMR system not reported before. • COP is 3 times higher than the ejector and 2.70 times higher than the ORC systems. • Procedure to determine optimum refrigerant mass for various operating frequencies. Operating thermos-mechanical refrigeration (TMR) ejector-based and organic Rankine cycle-based refrigeration systems at ultra-low temperature heat source (60 °C to 100 °C) is challenging and limited by their low coefficient of performance (COP), instability, and high cost. To overcome these limitations, an innovative TMR system consists of a power loop coupled with a cooling loop through an expander-compressor unit (ECU) was introduced. To ensure the efficient operation, reliability, and flexibility, of the ECU-based TMR system, a thorough experimental investigation is presented in this study. In the present setup, an air compressor is used to provide pressurized air to drive the ECU at a desired pressure of 620 kPa. Using R134a as a refrigerant, the performance of the ECU-based refrigeration system is systematically tested for various operating conditions including refrigerant mass, evaporator pressure, temperature and flow rate of the water used for evaporation and condensation loads. All tests are performed at two operating frequencies of the ECU (0.50 Hz and 0.33 Hz). Over a wide range of testing conditions, the results show that the average COP Hz varies from 1.57 to 2.73 at 0.50 Hz and from 1.56 to 2.39 at 0.33 Hz. Moreover, the evaporator temperature reaches less than −10 °C at 0.50 Hz and −9.60 °C at 0.33 Hz. These experimental results prove that the COP of the ECU-based refrigeration system is three times higher than the ejector-based systems and 2.70 times higher than the organic Rankine cycle-based systems.

Study of a Thermoacoustic Refrigeration System with a Spiral Rubber Stack

Thermoacoustic refrigeration technology converting sound energy into thermal energy offers environmental benefits including zero risks of ozone depletion or global warming potential due to the absence of hazardous refrigerants in the process. This study aims to investigate the effects of a spiral rubber stack on the cooling performance of a thermoacoustic refrigeration system made from an acrylic resonator tube. Air is used as a working gas. The results show that as time progresses, the temperature on the hot side of the stack increases, while that on the cold side of the stack reduces, leading to an increase in temperature difference across the stack. The findings of this study can potentially further expand knowledge and scientific experimental data in the field of thermoacoustic refrigeration.

Performance Evaluation of Mobile Liquid Cooled Thermoelectric Refrigeration System for Storage-Cum-Transportation of Fruits and Vegetables.

The performance of a liquid-cooled thermoelectric refrigeration (LCTR) system for the storage of summer fruits and vegetables, viz., bitter gourd, okra, mango, and papaya, indicated notable results for physiological loss in weight, firmness, and colour values and overall acceptability of the crop. The LCTR system significantly reduced (p < 0.0001) the physiological loss in weight (PLW) of bitter gourd, okra, mango, and papaya to 11.51%, 10.99%, 12.29%, and 19.17%, respectively, compared to conventional ambient storage of the crop. A lesser change in colour was observed for the crop subjected to LCTR, recording 14.04, 11.46, 16.41, and 23.68 for bitter gourd, okra, mango, and papaya, respectively. All the crops witnessed no significant effect (p < 0.0001) on the quality attributes of the crop stored in LCTR and a vapour compression refrigeration system. LCTR enabled a pronounced increment in the shelf life of bitter gourd, okra, mango, and papaya by 7, 8, 10, and 13 days, respectively, compared to storage at ambient conditions. The invention provides a mobile thermoelectric refrigeration system useful for marketing fruits and vegetables efficiently. The system is economical, has a higher coefficient of performance (0.85) compared to the coefficient of performance (COP) of the existing thermoelectric refrigeration system, and maintains the freshness and quality of perishable agricultural produce during marketing and transportation.

Experimental Performance of R134a/SiO2 in Refrigeration System for Domestic Use

Nanofluids are considered as a new invention of fluids having superior thermal physical properties to improve efficiency of the refrigeration system. Nanofluids are the colloidal suspensions of nanoparticles in base fluid. Nanoparticles having higher thermal conductivity compared to pure refrigerant such as R134a can be added to pure refrigerant to improve the performance of refrigeration system. This study focuses on producing nanolubricant (SiO2/POE) and implementing the nanolubricant into refrigeration system. The nanoparticles will be homogenized in refrigerant to produce nanoRefrigerant (R134a/SiO2) at the attached reservoir. The aim of the research is to study the thermal physical properties of nanolubricant and to find the relationship between nanoparticles’ volume fraction to the Coefficient of Performance (COP) of the refrigeration system. The investigations are focused on the effects of nanoparticles with 0.1, 0.3%, 0.7% and 0.9% volume fraction to the performance of the refrigeration system. The results show that the usage of nanolubricant creates higher thermal conductivity with slightly higher dynamic viscosity which eventually increase the performance of the refrigeration system by 8.62% in term of COP.

Experimental investigation of a two-phase ejector installed into the refrigeration system for performance enhancement

In this paper, the performance enhancement of the two-phase ejector installed into the refrigeration system called an ejector-expansion refrigeration system (EERS) is investigated experimentally. A comparative performance of an ejector expansion refrigeration system (EERS) with a conventional vapour-compression refrigeration (VCRS) system is proposed. The main purpose is to demonstrate the ability to mitigate the throttling loss or to demonstrate the expansion work recovery in which the theoretical work is limited. The experimental test bench which can be operated with both VCRS and EERS is designed and built for investigations. It is designed to produce chilled water under various cooling loads which allows it to produce the desired cooling temperature for performance assessment. The condenser is cooled by the cooling water whose temperature can be controlled precisely. The test results indicate that the EERS gives better performance over the VCRS when the expansion pressure ratio must be large enough. Therefore, there is limitation of using the EERS for the expansion work recovery. The system COP can be increased by 5.3–12.7% when the cooling temperature is decreased from 12 to 2 °C. The pressure lift effect of the two-phase ejector causes a reduction in the compressor’s pressure ratio which results in a lower specific work and the refrigerant discharge temperature. This yields a longer life-time of the compressor and better lubrication. It is also found that the working condition has a significant impact on the ability to enhance the system performance of the two-phase ejector installed into the refrigeration system.

Performance of a four-intersecting-vane expander in a R134a refrigeration cycle

• Experiments with expanders installed at different locations were performed. • Expander located after the condenser produces the highest power and efficiency. • The effects of expander speed, cooling and heating loads are analyzed. • Cycle behaviors with a throttle valve and an expander were compared. • The expander was able to improve the COP by up to 6.2%. • The expander exhibited an expander efficiency of 34.9%. The use of an expander is a promising technique to improve the performance of vapor compression refrigeration systems, but its use in a system with HFC refrigerants has not been extensively explored. This paper studies the performance of a four-intersecting-vane expander prototype and the effect of different expander location arrangements to the overall system performance. A customized R134a vapor compression test rig was constructed for the experiments. The rig’s coefficient of performance was determined when using either a throttling valve or an expander for the same operating conditions. The relationships between expander placement arrangements, expander rotational speed, evaporating load and condensing load on the performance of the expander and the thermodynamic behaviors of the system were also investigated. Transient behaviours of the system are discussed too. The experimental results show that the expander could improve the performance of the system by 6.4% in comparison with a system with a throttling valve. The maximum expansion power efficiency was 34.9% at 500 rpm. Of the four expander arrangements, that in which the expander is located right after the condenser exhibited the highest performance. The results show the potential benefits of using a four-intersecting-vane rotary expander for energy recovery of a vapor compression refrigeration system, and the importance of the correct placement of the expander in the system.

Forecasting the performance of a diffusion absorption refrigeration system using optimal fluid blend—A neural network approach

AbstractIn recent years, the diffusion absorption system has gained special attention in several types of research due to its ability to promote sufficient cooling effect from the use of low‐grade heat. Normally, in the diffusion absorption refrigeration (DAR) system, ammonia works as a refrigerant, helium as an inert gas, and water as an absorbent. These refrigerant combinations cause certain environmental issues such as global warming, ozone layer depletion, toxic gas formation, etc. This work aims to formulate an environment‐friendly DAR system from among six different alternative refrigerant blends. The refrigeration performances such as coefficient of performance (COP), exergy analysis, heat supplied in the generator, mass flow rate, refrigeration effect, and cooling capacity are determined for different evaporator temperatures. Harris hawk optimization (HHO) screened the optimal refrigerant blend and validated using hybrid Elman recurrent neural network (ERNN)‐based HHO methods. It is observed that the performance of the DAR is optimal when isobutane + dimethylformamide + helium is used as the working fluid.

The effects of CuO/CeO2 mixture nanoparticles on the performance of a vapor compression refrigeration system

This study was built on the basis of experimental results from a simple refrigeration system using R134a as a refrigerant. Based on the real dimensions of the system and the experimental results, Ansys fluent software was used to simulate the system to prepare the system to introduce the nanoparticles theoretically. Since the nanoparticle preparation process is expensive, this research presents a simple, easy, and inexpensive method for the preparation process based on, distilled water, ammonia, copper nitrate, and cerium nitrate to synthesize seven types of nanoparticles as a single oxide and as a mixture from two different oxides The results of preparing using X-ray diffraction and scanning electron microscopy confirmed that the particles were spherical in shape, with suitable average diameters ranging between 78.95 nm, 79.9 nm, 44.15 nm and 63.3 nm for copper oxide, cerium oxide, the first mixture, and the second mixture respectively. The theoretical study confirmed that both copper oxide, cerium oxide, and the mixture consisting of both improved the performance of the refrigeration system and reduced energy consumption. Moreover using the numerical equations available in the literature to calculate the thermophysical properties proved an improvement in these properties with an increase in the nanoparticle concentration when mixed with R134a.

The prediction for optimum combination of high pressure and intermediate pressure on a small refrigerated cabinet with CO2 transcritical two-stage cycle

It is universally acknowledged that the use of two-stage cycle can effectively improve the comprehensive performance of the CO2 refrigeration system. There exists an optimum combination of high pressure and intermediate pressure in a CO2 refrigeration system with transcritical two-stage cycle where the system yields the best coefficient of performance (COP). In this paper, a novel double-iteration method is used to predict the optimum combination of high pressure and intermediate pressure of a CO2 refrigerated cabinet system with transcritical two-stage cycle and the accuracy of prediction is experimentally verified. Then, the validated thermodynamic model is employed to identify the calculation accuracies of related existing correlations for calculating the optimum high pressure and the optimum intermediate pressure under various conditions. The results show that the thermodynamic model has enough accuracy to predict the optimum combination of high and intermediate pressures with an error less than 2.07%. Among the several major existing correlations, ′′Sarkar + Yari′′ (-10 °C≤Te≤10 °C, 30 °C≤Tgc,o≤50 °C) display the most accurate results to calculate the combination of high and intermediate pressures of a CO2 transcritical cycle. Meanwhile, the difference of thermodynamic performance predicted by the model and ′′Sarkar + Yari′′ correlations can be negligible (approximate to 0).

Investigation on the density of Al2O3/R1234yf, TiO2/R1234yf and CuO/R1234yf nano-refrigerants

Nano-enhanced refrigerant is one of the promising heat transfer fluids in refrigeration systems. It has the capability to boost the efficiency of vapour compression refrigeration and air conditioning systems. In heat transfer application, the density of the fluid plays a crucial role in identifying various heat transfer characteristics such as the Reynolds number, Nusselt number, the friction factor and the pressure loss. Compared to thermal conductivity and viscosity, determining the density of nanofluids has received very less attention in research. The liquid and vapour densities of alumina (Al2O3), titanium dioxide (TiO2) and cupric oxide (CuO) nanoparticles suspended in 2,3,3,3-tetrafluoropropene (R1234yf) are investigated in this study. The Pak and Cho model was adopted to examine the densities of nano-refrigerants as the volume concentration of particles in the base refrigerant and temperature varies from 1% to 5% and 273 to 323 K respectively. The models are validated using the experimental studies conducted by various researchers on different nano-refrigerants. The analysis results indicated that the liquid and vapour densities of CuO/R1234yf nano-refrigerant are 10.3% and 62.93% greater than that of Al2O3/R1234yf at 5% particle concentration. From the liquid and vapour density point of view, the CuO/R1234yf nano-refrigerant is superior over Al2O3/R1234yf and TiO2/R1234yf. Results also indicated that at 308 K the liquid phase density of CuO added with R1234yf nano-refrigerant is higher by 12.99% and 8.65% than R134a and R141b respectively. Hence CuO/R1234yf significantly enhances the performance of refrigeration systems.

Reactive fluids for intensified thermal energy conversion

Reactive fluids for intensified thermal energy conversion With the aim to effectively increase the performances of power plants, refrigeration systems and heat pumps, this project proposes the use of equilibrated reactive working fluids instead of inert ones. It applies an original methodology that integrates thermodynamic and kinetic predictive tools to discover and characterise suitable reactive fluids, allowing for the quantification of the effects of reaction features on system performance and optimal architecture.

Improving the Engine Efficiency Using a New Combined Refrigeration Cycle for Low-Temperature Heat Source (Waste Heat Recovery)

Passenger and commercial internal combustion engines have relatively large dissipated thermal energy sources that can be used for initiating thermodynamic refrigeration cycles at low temperatures while improving engine efficiency. Researchers have focused on combined power-refrigeration cycles in past studies. This paper presents the operation and performance of a new combined refrigeration system driven by waste heat recovery within the internal combustion engines. For this purpose, the effects of several parameters on the performance of the cycle are examined. Results show that an increase in the engine water temperature, exhaust gas temperature, part-load ratio (PLR), generator temperature, as well as adsorption evaporator temperature had a positive effect on the performance of the cycle. However, the rise in condenser temperature of the adsorption cooling system leads to bad performance. Also, the results indicate that the application of the adsorption refrigeration cycle in the combined cooling cycle, along with the increase in the refrigeration cycle performance by up to 65%, also improves the efficiency of the internal combustion engine.