Characteristics Of Refrigerator Research Articles

Transient refrigerant distribution in a microchannel heat exchanger heat pump system under different reverse cycle defrosting strategies

The migration and redistribution of refrigerant are critical factors that affect the refrigeration system performance. To improve the defrosting and start-up heating performance, it is essential to investigate the transient distribution characteristics of refrigerant mass. However, quantitative studies on the transient distribution of refrigerant during defrosting and start-up heating stages in heat pump systems are scarce. The dynamic characteristics of defrosting and start-up heating cannot be deeply understood from the perspective of refrigerant migration. Therefore, the purpose of this paper is to experimentally study the transient distribution characteristics of refrigerants during defrosting and start-up heating stages for different defrosting strategies. Based on the refrigerant-side dynamic characteristics, the defrosting cycle is divided into three stages for the defrosting strategy with the indoor fan off, the indoor coil charging stage, accumulator charging stage, and wet compression stage. Additionally, for the defrosting strategy with the indoor fan on, it is divided into two stages: the indoor coil charging stage and the outdoor coil discharging stage. For the defrosting strategy with the indoor fan off, the wet compression phenomenon occurs at 240 s, which poses significant challenges to the stability of the compressor. At the end of defrosting, the accumulator retains the most refrigerant for both defrosting strategies. From the perspective of refrigerant transient distribution, the start-up heating stage is the process of refrigerant migration from the accumulator to indoor and outdoor coils. The two main factors that affect start-up heating performance are heating the indoor coil metal, and vaporizing the liquid refrigerant in the accumulator. For the defrosting strategy with indoor fan on, the energy consumption of heating the indoor coil and vaporizing the liquid refrigerant is reduced by 45.7 % and 48.9 % during start-up heating. Based on the transient refrigerant distribution experiment, some methods to improve defrosting and start-up heating are also proposed. This study can provide useful insights into the transient distribution of refrigerants and provide guidance for defrosting optimization.

Matching Characteristics of Refrigerant and Operating Parameters in Large Temperature Variation Heat Pump

Characterizing the optimal operating parameters for a heat pump with a specific refrigerant is paramount, as it provides valuable guidance for refrigerant selection. The temperature mismatch between cold and hot fluids in the evaporator and condenser can lead to degraded thermal performance in heat pumps with large temperature variations. To address these two key issues, we selected several pure refrigerants with varying critical temperature levels for use in a large temperature variation heat pump configuration. The corresponding thermal performance was then investigated using the Ebsilon code under fixed temperature lift conditions as the operating temperature varied. It indicates that the maximum coefficient of performance (COP) is typically achieved when the deviation factors of temperature and pressure from their critical parameters fall within the ranges of 0.62~0.71 and 0.36~0.5, respectively. Our research recommends the binary refrigerant mixture of R152a/R1336mzz(z) (COP = 3.54) for the current operating conditions, as it significantly improves thermal performance compared to pure R1336mzz (z) (COP = 2.87) and R152a (COP = 3.01). Through research on the impact of the compositional ratio of R152a/R1336mzz(z) on the thermal performance of the heat pump, we found that that the optimal ratio of R1336mzz(z) component to R152a component is 0.5/0.5. This study offers valuable guidance for selecting the most suitable refrigerants for heat pumps in practical engineering design scenarios.

Evaluation of adsorption characteristics of HFO-1234yf refrigerant with different adsorbents

The adsorption refrigerator system with HFO-1234yf refrigerant (2,3,3,3-tetrafluoropropene) has a global warming potential of less than 4 and activated carbons (MaxsorbIII, MH-00), mesoporous silica (TMPS-2), and metal organic frameworks (MOF-177). We measured the adsorption isotherm under diverse temperature and pressure conditions experimentally, and evaluated the adsorption characteristics of these adsorbents. In this study, we designed an experimental apparatus using a volumetric method and measured the adsorption equilibrium uptake. The MaxsorbIII/HFO-1234yf pair has an adsorption uptake as high as 1.30 g-HFO-1234yf/g-ads at 40 °C and 300 kPa. The adsorption uptake is approximately equivalent to that of the MaxsorbsIII/HFC-134a pair. The experimental data of the adsorption/desorption isotherms show that there is no hysteresis for the studied pair. The experimental results were reproduced using the Dubinin–Astakhov model (D–A model). The D–A model fits the experimental results precisely within 7%. A diagram of the relationship between HFO-1234yf and MaxsorbsIII also generated the D–A model, and the adsorption uptake capacity between the adsorption and desorption steps was obtained as 0.07 kg-HFO-1234yf/kg-ads at 40 and 80 °C. The adsorption capacities of MOF-177, MaxsorbIII, TMPS-2, and MH-00 were evaluated under similar operating conditions to be 0.19, 0.08, 0.11, and −0.03 kg/kg respectively.

Explosion risk analysis of isobutane leakage in the freeze and cold storage system

The leakage and explosion of flammable refrigerant in household air-conditioning, domestic refrigerators, and heat pump system, which could pose huge threats to the building, ecological environment and the human health. Isobutane (R600a) is expected to be employed in the small-sized freeze and cold storage (FCS) system, nevertheless, the flammability slows down its development. Leakage, diffusion, distribution, and deposited characteristics of refrigerant in limited space are essential for explosion risk analysis in public places. To promote the safety application of R600a, a three-dimensional refrigerant leakage numerical model based on refrigerant leakage and diffusion (RLD) is established for RLD process, and the reliability of the model is verified by the experimental results. On this basis, the effects of different factors on the RLD process are analyzed by the numerical simulation. The results indicate that there is pessimism in the fan speed of the supply-air fan to obtain the highest average R600a concentration of defrost heater (DH) in the deposition process. The refrigerant explosion risk with the system door opened in the deposition process is markedly superior to that of the system door closed. As the leakage hole diameter increases from 1.0 mm to 2.5 mm, the average R600a concentration of the DH at the simulated time of 300 s is increased by 1.71 vol%. This study, not only reaffirms the benefit of using a three-dimensional refrigerant leakage numerical model for flammable refrigerant of the FCS system in a limited space, but also provides some rules of the RLD process with different factors.

Mass flow characteristics prediction of refrigerants through electronic expansion valve based on XGBoost

In an effort to enhance the prediction accuracy of the mass flow characteristics of refrigerants through electronic expansion valves (EEVs), this study develops a mass flow model using the XGBoost machine learning algorithm. Utilizing experimental data from open literature for refrigerants R1233zd(E) and R245fa, the model aims to accurately predict the mass flow coefficient in EEVs, a crucial aspect for improving the performance and efficiency of refrigeration systems. The model's performance is evaluated using the coefficient of determination (R2) on the training and test datasets, revealing a minimal performance gap and no overfitting issue. Remarkably, our model's predictions for R1233zd(E) and R245fa datasets align consistently with experimental data, with 96.4 % and 90.6 % of the predicted data deviating from the experimental ones within ±5 %, respectively. Further, the root-mean-square error (RMSE) and coefficient of variation of the root mean square error (CV-RMSE) values are quite low, with 2.2 % and 2.33 % for R1233zd(E), and 4.23 % and 4.47 % for R245fa, indicating high prediction accuracy. Compared to the original models, the paper approach with the XGBoost algorithm significantly improves prediction accuracy. This advancement provides a promising direction for developing more efficient and reliable control strategies for refrigeration systems in various applications.

Adsorption Characteristics of Refrigerants for Thermochemical Energy Storage in Metal–Organic Frameworks

Adsorption Characteristics of Refrigerants for Thermochemical Energy Storage in Metal–Organic Frameworks

Design and Building of a Two-Stage Cascade Refrigeration System for Storage of Blood Plasma

Daily life-saving transfusions rely on the usage of blood products in clinical and research settings. With its proteins used for replacement treatment, human blood plasma serves as the main source for a variety of therapeutic transfusions. During the COVID-19 pandemic, plasma-based therapy was one of the treatment modalities used to treat infectious infections and as a source of neutralizing antibodies in patients. The specialty of transfusion medicine was adversely impacted and faced a stockpile shortage because plasma must be quickly frozen within six hours of collection in order for its proteins and coagulation components to be of the optimum quality. As a result, the cascade refrigeration system is an innovative technology that can provide the required ultra-low freezing temperature and maintain the same temperature in storage for plasma management. The paper concentrated on the design and construction analysis of a two-stage cascade refrigeration system for quick freezing time, and storing plasma proteins at extremely low temperatures to prolong their limited shelf life in a sensitive, temperature-controlled storage system. The choice of refrigerants R404A and R410A is made for high temperature and low temperature circuits which are carefully selected based on study and analysis of the characteristics of different refrigerants for short-term freezing. The ultra-low temperature evaporator is achieved using a blend of two vapour compression refrigeration cycles thermally connected by a heat exchanger to produce a freezing temperature of -35 0C. For analysis, the system was charged with various weights of plasma weighing between 1 kg and 4 kg for two hours and a half hour and kept at a temperature of -35 0C. The system's dependability and practicality for extending plasma shelf life were assessed. After 72 hours of temperature-controlled storage, the results showed 75% efficiency and a negligible (0.4) plasma quality drop.

Evaluation of flammability characteristics of mixed refrigerants R134a/R1270, R134a/R170, and R170/R1270

Hydrocarbons (HCs) are considered promising alternative refrigerants due to their excellent thermodynamics, transport properties, and environmental friendliness. However, hydrocarbons are flammable. Conversely, R134a is a widely used non-flammable refrigerant but was listed in the Montreal Protocol-Kigali Amendment due to its relatively high global warming potential (GWP). Therefore, in order to reduce the GWP of R134a and inhibit the flammability of hydrocarbon refrigerants, this study investigated the flammability characteristics of mixed refrigerants R134a/R1270, R134a/R170, and R170/R1270. The flammability limits of different concentrations of R170/R1270, R134a/R1270, and R134a/R170 were measured under standard conditions, and the inhibition mechanism of R134a was briefly analyzed. Additionally, the flammability limits of R170/R1270, R134a/R1270, and R134a/R170 were predicted using the polynomial fitting method. Subsequently, the flame propagation speed and the flame color of R1270 and R170, with and without R134a, were compared and analyzed. Furthermore, the cycle performance of R134a/HCs was calculated. The research results are expected to provide guidance for the safe and effective utilization of R1270, R170, and their mixtures in refrigeration systems.

Numerical Study on Refrigeration Characteristics of Refrigerated Cabinet Based on SIMPLE Algorithm

Numerical Study on Refrigeration Characteristics of Refrigerated Cabinet Based on SIMPLE Algorithm

A unified approach for the thermodynamic comparison of heat pump cycles

The flexible heat pump cycle introduces a heat storage device into the Evans-Perkins cycle to recover, store, and reuse part of the sensible heat carried by the hot liquid refrigerant from the condenser, achieving a higher coefficient of performance than the latter. In this paper, we develop a unified approach, namely cycle superposition to allow comparison of the flexible heat pump cycle with other performance-enhancing cycle layouts including two-stage cycles with intercooling, subcooling, flash gas removal, or their combinations. We show that under ideal conditions, the flexible heat pump cycle is thermodynamically similar to two-stage heat pump cycles with full subcooling or flash gas removal, but no intercooling. From the energy recovery perspective, the two-stage cycles recover and reuse some sensible heat carried by hot liquid refrigerant simultaneously using their high-stage compressor, whereas the flexible heat pump cycle decouples the recovery and reuse of such heat in time using a heat storage. However, the irreversible heat transfer via real heat exchangers during charging and discharging processes will reduce the benefits of the flexible heat pump cycle. The effectiveness of all these performance-enhancing methods strongly depends on the characteristics of refrigerants.

Numerical simulation on flow boiling heat transfer of R1234ze(E)/R152a in a horizontal smooth tube

The understanding of two-phase flow and heat transfer characteristics of refrigerants in tubes is important for guiding the design and optimization of heat exchangers. Based on the volume of fluid (VOF) multiphase model, this paper established a numerical model of R1234ze(E)/R152a (mass ratio of 0.4/0.6) flow boiling heat transfer in a horizontal smooth copper tube with an inner diameter of 6 mm and a length of 900 mm. The distribution of vapor volume fraction is obtained, and the influence of mass flux, heat flux, saturation temperature, and vapor quality on heat transfer coefficient (HTC) are studied. Bubble flow, plug flow, stratified flow, and wavy flow can be observed during the whole process and the fluid temperature increases along the tube. Local and time-averaged heat transfer coefficients and temperature distribution along the axial direction were studied. And the results indicate that the HTC decreases first and then increases with the augmentation of mass flux while increasing with the rise of heat flux. In addition, the HTC rises along with saturation temperature and decreases along with vapor quality. The largest related standard deviation between the simulation value and the testing data is 6.31%. Thus, the numerical simulation has a high level of accuracy.

Dynamic characteristics of refrigerant and lubricant in R290 rolling piston compressor of low-temperature air to water heat pump (LT-AWHP) during defrosting cycle

The dynamic characteristics of refrigerant and lubricant in R290 rolling piston compressor used in LT-AWHP (ambient temperature (ta) of 7 ∼ −30 °C) are not clear at present. In this study, the changing characteristics of suction and discharge pressure and temperature, physical properties of oil sump (temperature, viscosity, solubility) and oil sump liquid level in the high pressure shell double-cylinder rolling piston compressor during defrosting cycle (steady state→ defrosting→ steady state) were experimentally researched in a R290 LT-AWHP with the rated power consumption of 1.9 kW using PAG40 and POE68 lubricants at ta of −12 and −20 °C. The results show that, the defrosting time and the change rule of oil sump physical properties are different when completely miscible oil and partially miscible oil used, but the defrosting time (about 3 – 5 min) is less than that of the R290 air to air heat pump (about 8 min). After defrosting, the fluid in the upside of compressor shell remains liquid and gas mixture for a long time, which would decrease total heating performance of the heat pump. After defrosting, oil sump viscosity is lower than the steady state value for a long time after discharge pressure is stabilized again. Within a period after the four-way valve reversing, the oil sump liquid level drops a lot, which may result in metal wear for insufficient oil supply on the side of sliding vane. This research would promote the improvement of defrosting process and provide guidance for the lubricant selection of R290 LT-AWHP.

Condensation heat transfer characteristics and generalized correlations of R404A, R448A, and R454C in a plate heat exchanger

Although numerous studies have been carried out on alternatives to R134a and R410A to cope with regulations, the heat transfer characteristics of refrigerants with a low-global warming potential to replace R404A in a plate heat exchanger (PHE) have not yet been intensively investigated. Generally, R448A has been considered as a short-term alternative to R404A, while R454C has been nominated as a long-term alternative to R404A. In this study, the thermal and hydrodynamic characteristics of R404A, R448A, and R454C in a PHE during condensation are experimentally investigated at vapor qualities (x) of 0.2–0.8, mass fluxes (G) of 15–35 kg m−2 s−1, heat fluxes (q”) of 3–7 kW m−2, and saturation temperatures (Tsat) of 20–27 °C. The results of the analysis show that the condensation heat transfer coefficient (HTC) and frictional pressure drop (FPD) are predominantly affected by the x and G, while the q” barely affects the FPD. The average condensation HTC and FPD of R448A and R454C exceed those of R404A by 17.25–20.57% and 9.6–10.72%, respectively. Additionally, new generalized correlations of the condensation Nusselt number and frictional pressure drop for R404A, R448A, and R454C in a PHE are developed with mean relative deviations of −1.905% and 1.01%, respectively.

"THE POTENTIAL OF GEOTHERMAL SOURCES IN SOUTHERN KAZAKHSTAN FOR HEAT SUPPLY TO RURAL CONSUMERS, the case OF THE ZHAMBYL REGION"

"The article presents the characteristics of geothermal deposits in the south of Kazakhstan and the analysis of the potential of geothermal waters of the Zhambyl region. Moreover, the study carries out the review of various types and methods of using geothermal water for household and its needs. Consequently, it outlines information on thermal boreholes. During the elaboration, manufacture and testing of these combined power units, several scientific and technical issues, such as the choice of the optimal low-boiling working fluid for heat and hot water supply systems were solved. An overview of the refrigerants and vapor compression fluids currently available have been made. The classification and characteristics of secondary heat carriers of various types and temperatures of their use are given. Therefore, it is proposed to use non-azeotropic binary mixtures as working bodies of a closed heat-power circuit. Moreover, an analysis was carried out on the use of non-azeotropic mixtures for heat pumps. It is proposed to use mixtures of refrigerants as working bodies for the second circuit. The specific characteristics of refrigerants are outlined. As a result, a description of the operation scheme of a steam compression heat pump operating in the mode of heat and hot water supply is highlighted. "

Experimental determination of the role of roughness and wettability on pool-boiling heat transfer of refrigerant

In order to investigate pool boiling heat transfer characteristics of refrigerants on different surfaces, an experimental rig is established and verified in this study. The pool boiling heat transfer experiment is conducted with R134a at three saturation temperatures. Six surfaces with Ra roughness ranging from 0.133 to 5.742 μm and two types of wettability are tested in the study. The heat flux varies from 40 to 280 kW/m2. Experimental results indicate that higher roughness is favorable to boiling heat transfer. Shieldex coating on copper surfaces can deteriorate heat transfer by 20% approximately. Visualization analysis was carried out with a high-speed camera to study bubble behavior. A new-found mode of bubble departing was observed at lower heat flux. Besides, the data were correlated in the form of Rohsenow correlation, and comparison and supplement are concluded based on data obtained in this study.

A simulation study on the condensation flow and thermal control characteristics of mixed refrigerant in a dimpled tube

In this study, the condensation flow and heat transfer characteristics of ethane/propane in the dimple tube have been numerically investigated, and the liquid droplet entrainment caused by the dimple structure was considered. The effects of operation and structure parameters on flow and heat transfer were analyzed, including different dimple depths, helical pitch, and dimple pitch. The results showed that the dimple tube had a higher heat transfer coefficient compared to the smooth tube, which increased with the increase in the mass flow rate and the decrease in the saturation temperature. The effect of dimple depth on heat transfer is greater than that of the dimple pitch or helical pitch, and the dimple depth will cause the local mass transfer rate to increase under high vapor quality. Meanwhile, the existing heat transfer correlations for smooth tubes were compared, and a condensation heat transfer correlation suitable for the mixed refrigerant in the dimple tubes was proposed with an average deviation of 6.3%.The conclusions obtained can provide support for the optimization design of liquefied natural gas plants.

Response to the comment “Numerical simulation of steam condensation on the surface of a horizontal tube using the VOF method. A comment on the results from Li Shu and Yonglin Ju paper ‘Numerical study on the Condensation Characteristics of Various Refrigerants Outside a Horizontal Plain tube at Low temperatures’, International Journal of Thermal Sciences, 2022”

Response to the comment “Numerical simulation of steam condensation on the surface of a horizontal tube using the VOF method. A comment on the results from Li Shu and Yonglin Ju paper ‘Numerical study on the Condensation Characteristics of Various Refrigerants Outside a Horizontal Plain tube at Low temperatures’, International Journal of Thermal Sciences, 2022”

Numerical simulation of steam condensation on the surface of a horizontal tube using the VOF method. A comment on the results from Li Shu and Yonglin Ju paper “Numerical Study on the Condensation Characteristics of Various refrigerants outside a horizontal Plain tube at low temperatures”, International Journal of Thermal Sciences, 2022

In the present comment, the results of recently published by Li Shu and Yonglin Ju “Numerical Study on the Condensation Characteristics of Various Refrigerants Outside a Horizontal Plain Tube at Low Temperatures” in International Journal of Thermal Sciences 2022 are discussed. It is shown that one of the conclusions of the work that “at low saturation temperatures, the periodic-averaged heat transfer coefficient in the numerical simulation is lower than that calculated with Nusselt's equation, especially at large wall subcooling”, is not supported by the results of simulation performed by the author of this comment.

Experimental investigations of the flow boiling characteristics of green refrigerants in a novel petaloid micropin-fin heat sink

Although micropin-fin heat sinks (MPFHSs) are widely regarded as an effective way to dissipate heat in microelectronic equipment, the pin fin structure has not changed much over the years. Inspired by the flower of Clematis montana, a novel petaloid structure was designed. The flow boiling characteristics of green refrigerants, including R1234ze(E) and R1234yf, in the petaloid MPFHS were investigated under mass fluxes of 100–200 kg/m2 s, heat fluxes of 20–40 kW/m2 and saturation pressures of 0.4–0.6 MPa and compared with those of R134a. In the nucleate boiling zone, the heat transfer coefficient (HTC) rises with saturation pressure, vapor quality, and heat flux; in the convective boiling region, it rises with mass flux. With mass flux and vapor quality, the frictional pressure drop (FPD) rises; with saturation pressure, it falls; with heat flux, it keeps constant. R1234ze(E) shows the largest HTC and the smallest FPD, and R1234yf and R134a have similar HTC and FPD. Specific bubbles, slugs, confined slugs and liquid films yielded by the petaloid micropin fins are identified, and the flow behaviors, including coalescence and separation of bubbles/slugs, are described. Comparing the existing empirical correlations for flow boiling HTC and FPD in plain and micropin-fin channels with the experimental data yields unsatisfactory mean absolute deviations (MADs). Hence, new correlations for petaloid MPFHS are developed, which yield satisfactory MADs of 12.6% and 9.9% for HTC and FPD, respectively.

Numerical study on two-phase supersonic expansion refrigeration in novel CO2 refrigeration technology

The serious environmental problems have promoted the development of CO2 natural working fluid refrigerants. The supersonic two-phase expander with supersonic nozzle as the key component is proposed. A novel CO2 supersonic two-phase expansion refrigeration cycle is constructed and its cycle performance is also calculated. Then, the numerical simulation of the flow condensation and liquefaction process of CO2 in the nozzle is carried out. The results show that the inlet parameters of the supersonic two-phase expander have an important effect on the cycle performance. With the increase of inlet pressure, COP first increases and then decreases. The optimal inlet pressure of the system is 5.3 MPa with the corresponding maximum COP by 2.50, and the Relative Carnot Efficiency decreases from 0.809 to 0.755. With the inlet temperature increase, the maximum COP and the Relative Carnot Efficiency are 2.49 and 0.826, respectively. The established model can reasonably describe the supersonic expansion refrigeration characteristics and condensation phase transition characteristics of CO2. With the increase of nozzle inlet pressure and the decrease of temperature, the inlet degree of supercooling increases, while the initial nucleation position moves forward further and the peak nucleation rate decreases. Meanwhile, the droplet number decreases, both the droplet radius and the liquid mass fraction increases. The ideal cycle performs well, which provides a valuable reference for CO2 utilization.