Search

Limited experimental research has been conducted on organic Rankine cycle (ORC) systems that use wet working fluids. Therefore, the present study examined how the performance of an ORC system that uses a wet working fluid (R134a) was affected by the superheat degree ratio (SDR) under various scroll rotation speeds. The SDR is the dimensionless ratio between superheat degree and evaporation temperature at a given heat source temperature. Experimental results indicated that at scroll rotation speeds of 900, 1350, and 1800 rpm, the maximum output power of the aforementioned system was 1103, 1464, and 1537 W, respectively, with SDRs of 0.49, 0.49, and 0.54, respectively. The maximum net efficiencies at these speeds were 5.87%, 5.91%, and 5.32%, respectively, which occurred at SDRs of 0.61, 0.49, and 0.48, respectively. This level of system performance was attributable to the high enthalpy at the expander inlet and the high mass flow rate at the high evaporation pressure under an SDR of approximately 0.5. Although increasing the SDR did not enhance the scroll expander's isentropic efficiency, this efficiency decreased considerably when the SDR fell below 0.2. These findings emphasize the importance of optimizing the SDR of ORC systems to improve their performance. [ABSTRACT FROM AUTHOR]

R134a was recognized as probably one of the most important refrigerants of the two past decades. Among the proposed alternative fluids, there are certainly isobutane (R600a) and R152a. This article presents about 200 new heat transfer coefficient and pressure drop data obtained during flow boiling of R152a and R600a inside a smooth copper tube having an internal diameter of 4 mm. Three saturation temperatures were considered for each refrigerant, from 5 °C to 20 °C. Furthermore, for each temperature studied, the heat flux was varied between 15 and 30 kW m−2 and the refrigerant mass flux from 100 to 400 kg m−2 s−1. After presenting the new data, a critical comparison was proposed between the performance of these refrigerants and R134a. Finally, some classic correlations available in the literature have been implemented. The deviations between the calculated and experimental values were reported and commented. [ABSTRACT FROM AUTHOR]

Abstract Limited experimental research has been conducted on organic Rankine cycle (ORC) systems that use wet working fluids. Therefore, the present study examined how the performance of an ORC system that uses a wet working fluid (R134a) was affected by the superheat degree ratio (SDR) under various scroll rotation speeds. The SDR is the dimensionless ratio between superheat degree and evaporation temperature at a given heat source temperature. Experimental results indicated that at scroll rotation speeds of 900, 1350, and 1800 rpm, the maximum output power of the aforementioned system was 1103, 1464, and 1537 W, respectively, with SDRs of 0.49, 0.49, and 0.54, respectively. The maximum net efficiencies at these speeds were 5.87%, 5.91%, and 5.32%, respectively, which occurred at SDRs of 0.61, 0.49, and 0.48, respectively. This level of system performance was attributable to the high enthalpy at the expander inlet and the high mass flow rate at the high evaporation pressure under an SDR of approximately 0.5. Although increasing the SDR did not enhance the scroll expander's isentropic efficiency, this efficiency decreased considerably when the SDR fell below 0.2. These findings emphasize the importance of optimizing the SDR of ORC systems to improve their performance.

This study investigates the flow boiling heat transfer characteristics of refrigerants R134a and R407c in horizontal micro-fin tubes. We conducted experiments across a range of heat flux (15–35 kW·m−2), mass flux (50–250 kg·m−2 s−1), and saturation temperature (15 °C-25°C) conditions. Our findings reveal that R134a consistently exhibits a higher heat transfer coefficient (HTC) compared to R407c, making it advantageous for applications requiring efficient heat transfer. However, R134a also shows a tendency towards premature dry-out flow patterns at higher heat fluxes, which could limit its effectiveness under certain conditions. In contrast, R407c demonstrates more stable flow regimes, maintaining wavy-annular and annular flows without early dry-out, which highlights its robustness at higher heat fluxes. Flow pattern maps indicate that higher heat fluxes promote the formation of wavy and annular flow patterns in both refrigerants, with R134a transitioning to dry-out flows more readily than R407c. The influence of saturation temperature on HTC was also significant, with lower temperatures resulting in higher HTCs for both refrigerants. This can be attributed to the increased thermodynamic driving force for phase change at lower temperatures. Our study aligns with previous research, corroborating the critical role of micro-fin tubes in enhancing HTC. The findings have practical implications for the design and optimization of refrigeration systems, emphasizing the need to carefully select refrigerants and operating conditions to achieve efficient and stable heat transfer performance. [ABSTRACT FROM AUTHOR]

The present study is focused on identifying the most suitable sequence of machine learning-based models and the most promising set of input variables aiming at the estimation of heat transfer in evaporating R134a flows in microfin tubes. Utilizing the available experimental data, dimensionless features representing the evaporation phenomena are first generated and are provided to a machine learning-based model. Feature selection and algorithm optimization procedures are then performed. It is shown that the implemented feature selection method determines only six dimensionless parameters ( S u l : liquid Suratman number, B o : boiling number, F r g : gas Froude number, R e l : liquid Reynolds number, B d : Bond number, and e / D : fin height to tube's inner diameter ratio) as the most effective input features, which reduces the model's complexity and facilitates the interpretation of governing physical phenomena. Furthermore, the proposed optimized sequence of machine learning algorithms (providing a mean absolute relative difference (MARD) of 8.84% on the test set) outperforms the most accurate available empirical model (with an MARD of 19.7% on the test set) by a large margin, demonstrating the efficacy of the proposed methodology. [ABSTRACT FROM AUTHOR]

Improving the performance of drop-in hydrocarbon refrigerants for the increasing in-flow of conventional refrigerators to Nigeria is a necessary sustainable strategy. This experimental study investigates the enhancement limits of a liquid-line magnetic field, CNT nano-lubricant, and a combination of both on an R134a domestic refrigerator with 40–70 g each of R600a refrigerants. The study compares the performance of R600a refrigerant without enhancements (pure) and with two pairs of 3000 Gauss liquid-line mounted O-ring permanent magnets (Mag), 0.2 g L−1 concentration of CNT nano-lubricant (Nano), and both liquid-line magnet and CNT nano-lubricant (Mag-Nano). Test parameters include evaporator air temperature, discharge pressure, power consumption, coefficient of performance (COP), and total equivalent warming impact (TEWI). The results show that enhancement methods led to higher COP in the range of 16.64–42.38%. At the same time, evaporator air temperature, discharge pressure, power consumption, and TEWI were lower by 9.76% to 20.96%, 17.75% to 34.26%, 5.22% to 13.42%, and 5.88% to 10.86%, respectively. In conclusion, the proposed enhancement techniques in the refrigeration system provide normal, safe, and efficient operation. [ABSTRACT FROM AUTHOR]

Thermal energy-driven adsorption refrigeration systems are potential alternatives to the vapour compression refrigeration system. Using solar or waste heat thermal compressors over electrical compressors diminishes fossil fuel-based energy expenditure and its adverse effects on the environment. The solar thermal energy system's cost is highly dependent on the system's maximum temperature-generating capacity. The present work focuses on the experimental investigation of the adsorption thermal compressor performance by supplying source heat at different temperatures and determining the optimum desorption temperature and the supply heat cycle time resulting in the best performance. The adsorbent–adsorbate pair considered for the study is activated charcoal extra pure powder—R134a. The compressor is supplied with hot water at different temperatures, and the variation in performance parameters such as desorption pressure, desorbed mass change and average temperature is analysed. A novel index, i.e. rate of pressure change with respect to temperature (dp/dT), is introduced to evaluate the optimum desorption temperature with respect to different supply heat cycle times. The best performance of the adsorption thermal compressor is observed in the range of 50–60 °C, and the corresponding pressure change recorded is equal to 1.04 bar in 120 s. The obtained optimum temperature and pressure range can limit the thermal energy losses and increase the desorbed mass flow rate, thereby enhancing the entire system performance. The findings can be considered in design and development of an adsorption refrigeration system driven by renewable source heat or waste heat. [ABSTRACT FROM AUTHOR]

It has been proved that due to addition of nanoparticals to the refrigerant results in improvement in thermophysical properties and heat transfer characteristics of the primary refrigerant, which improves the COP of the refrigeration system. In this experimental analysis of vapour compression system, the performance study has been carried out by preparing the nanolubricant. In this experimental study, three cases are considered. The compressor of the system filled with pure polyolester (POE) oil, SUNISO-3GS oil and POE + TiO2 nanoparticles as lubricant. In the nanolubricant, the volume concentration of the nanoparticles is 0.2%. The experimental study shows that vapour compression refrigeration system works smoothly with nanorefrigerant. In this experimental study, it has observed that when nanolubricant used in place of traditional POE oil, the refrigerating effect has been increased and the compressor power consumption has reduced by 27% and the refrigeration system COP improves by 29%. The analysis shows that the enhancement factor in the evaporator is 1.2 when nanorefrigerants are used instead of pure refrigerant. The properties of refrigerant like thermal conductivity and density are also studied for the nanolubricant by using the Labview software, in which the thermal conductivity and the density of R134a and nanolubricant mixture are observed higher in comparison with the R134a and pure lubricant mixture. [ABSTRACT FROM AUTHOR]

The process of air entering the vapor compression refrigeration system is very common, and it can happen during installation, maintenance, or charging. Since air is a non-condensable gas compared to the refrigerant gas inside the system, it causes deterioration in the system mainly due to high condensing pressure. This experimental study contributes to verifying the negative effects that can be left by non-condensable gases in the vapor-compression refrigeration system via analyzing the performance of a chest freezer charged with R134a refrigerant without an air fraction and with three air fractions 1.7%, 2.5% and 3.3% under steady-state conditions and an ambient temperature of 32°C. The results revealed that the performance of the chest freezer deteriorated clearly with the increase in air fraction; at an air fraction of 3.3% the power consumption increased by 37.1% and the coefficient of performance decreased by 42.8% compared to without air fraction. In addition to high noise and vibration. [ABSTRACT FROM AUTHOR]

This paper presents local condensation Heat Transfer Coefficients (HTCs) and temperature profiles of R134a and three low-GWP replacements, R1234yf, R1234ze(E), and R152a, within Brazed Plate Heat Exchangers (BPHEs). The measurement of local temperature profiles allows to couple the evaluation of thermal and hydraulic performances of refrigerants into a single parameter named Total Temperature Penalty (TTP). The experimentation was carried out in a prototype BPHE instrumented with thermocouples inserted into the plate wall to measure the local heat flux and wall temperature. The transition from gravity-controlled condensation to mixed condensation was observed in the refrigerant mass velocity interval 15−20 kg m−2s−1. The experimental HTCs were compared with existing theoretical models finding a Mean Absolute Percentage Error (MAPE) within 10–15 %. The TTP analysis highlights similar condensation performance for R134a, R1234yf and R1234ze(E) refrigerants, while R152a performs better than R134a.

The global critical issue in energy scarcity should be appropriately solved to realize a sustainable society. Effective use of Rankine cycle is one possible way since it provides most of worldwide electricity production. In this paper, theoretical analysis model of organic working fluids R717, R134a, R1234yf, R290, R245fa and R1233zd in Rankine cycle for maximum power generation in optimization operation using low-temperature heat sources are proposed and studied for development next generation green and zero-carbon energy generation system to promote the race to zero. Results show that temperatures of warm and cold water at inlet, mass flow rate of the warm water and performance of the evaporator play a key role to obtain the theoretical optimization operation conditions for maximum power generation. In the case of same initial conditions of temperatures of warm water (85°C) and cold water (15°C) at inlet, mass flow rate of the warm water (10 kg/s) and performance of the evaporator (100 kW/K), R717 has the best performance in terms of the maximum power output 56.0 kW with thermal efficiency of 8.6%, and the next is the R1233zd (54.4 kW, 8.3%), R245fa (54.0 kW, 8.2%), R134a (52.8 kW, 7.9%), R290 (52.7 kW, 7.9%), and R1234yf (51.7 kW, 7.7%). Here, it should be noticed that other optimization conditions are almost the same (mass flow rate of the cold water 9.1–9.2 kg/s; performance of the condenser 91∼92 kW/K) to get their maximum power output of ORC. In addition, it also known that low-GWP R1233zd (GWP: 1) can deserve the best option to replace R245fa (GWP: 950) and R1234yf (GWP: 4) also can replace r134a (GWP: 1430) since their optimization operation conditions are almost same.

Synthetic refrigerants are being phased out gradually in accordance with international environmental protection protocols because of global warming and ozone layer depletion. Adopting R290/R600 refrigerant, an environmentally friendly refrigerant, to replace R134a, a high global warming potential refrigerant, provides one of the solutions. In this study, exergy analysis of R134a and TiO2 suspended with lubricant and R290/R600 with a composition of 60% R290 and 40% R600 (60:40) was investigated in vapour compression system (VCRS) using R290/ R600 in TiO2 nanomixture lubricant and compared with R134a and R290/ R600 in pure lubricant. At the inlets and outlets, the main components of the VCRS are connected to temperature and pressure sensors to measure the inlet and outlet temperatures and pressures. The results obtained were used to analyses the exergy losses at various VCRS components (compressor, condenser, evaporator, expansion valve) were investigated to determine the refrigerator’s total exergy destruction (E·xdest.Total) and efficiency (ηex). The E·xdest.Total of R290/R600 in pure lubricant and R290/R600 TiO2 nanomixture lubricant was reduced by 26.9% and 42.3%, respectively, and system ηex increased by 27.7% and 38.9% respectively when compared to R134a in the system. Hence, TiO2 suspended with R290/R600 is potential a substitute for R134a.

In the present study, an experimental investigation is conducted to study the nucleate boiling characteristics on a smooth tube having a low-GWP azeotropic refrigerant, R513A. The heat flux ranges from 5 to 90 kW/m2, and saturation temperatures are 0, 6, 10, 16, and 22 °C, respectively. The performance of R513A is compared against that of R134a. The performance is in terms of heat transfer coefficient (HTC). HTCs normally increased with the rise of heat flux and saturation temperature. However, the HTCs of R513A exceed those of R134a by approximately 20–25 %. Additionally, comparative analysis of the test data and some existing correlations are made. The compared correlations include three correlations based on reduced pressure (Cooper, Ribatski and Jabardo, and Jung), as well as two correlations based on thermophysical properties. It is found that the Jung correlation gives the best overall predictive ability against the R513A data with a deviation ranging from 5 % to 10 %. [ABSTRACT FROM AUTHOR]

The process of phasing out of medium and high global warming potential refrigerants is accelerating in all areas of refrigeration, particularly since the European F-Gas Regulation No. 517/2014 and the ensuing Kigali amendment went into effect. Hydrocarbon refrigerants are being considered as suitable alternatives due to their low global warming potential and excellent thermal properties, but due to their flammability, safety precautions must be followed. This theoretical study contributes to the evaluation of the thermal and environmental impact of hydrocarbon refrigerants as drop-in alternatives to R134a in domestic refrigerator. In order to conduct an analysis of energy, exergy, and environmental factors, R134a and all hydrocarbons refrigerants proposed by ASHRAE--R290, R600, R600a, R601, R601a, and R1270--were examined as operating fluids used in a domestic refrigerator with a cooling capacity of 157 W and constant condenser temperature of 40°C and variable evaporator temperature every 5°C between -5 and -30°C. The results revealed that all the alternative refrigerants except R601 and R601a have higher thermal and environmental performance than R134a and can be used after refrigerator compressor replacement. [ABSTRACT FROM AUTHOR]

The performance of a new mixed refrigerant R1234yf/R13I1 with a mass ratio of 90/10 under basic refrigeration cycle and refrigeration cycle with internal heat exchanger is calculated in comparison with the performance of R134a under basic refrigeration cycle at different condensation temperature and evaporation temperature. The results show that R1234yf/R13I1 is virtually non-flammable with global warming potential of less than 4. Under basic refrigeration cycle, the compressor power consumption, cooling capacity and COP of R1234yf/R13I1 are lower than these of R134a by about 4.5%, 9.5%, and 7.5%, respectively. Under refrigeration cycle with internal heat exchanger, the compressor power consumption, cooling capacity, and COP of R1234yf/R13I1 are lower than these of R134a by about 2%, 4.5%, and 3%, respectively. The R1234yf/R13I1 is a beneficial refrigerant of replacing R134a in vapor compression system. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the effect of changing the indoor unit air flow rate on the performance of an automobile heat pump with a suction line heat exchanger. Using a four-way valve, the automotive heat pump system was developed by reversing the refrigerant direction in the automobile air conditioning system, excluding the compressor. A suction line heat exchanger was added to the test system to enhance heat transfer between the liquid and suction lines of the automotive heat pump system. Performance comparisons were first performed for R134a and R1234yf by disabling the suction line heat exchanger. Then, the suction line heat exchanger was activated for R1234yf, and the tests were repeated. Performance comparisons were made for two different compressor speeds and three different indoor unit airflow speeds. It was found that using the heat exchanger in R1234yf operations improved the heating capacity, compressor discharge temperature and coefficient of performance by approximately 1.8 %, 5.1 % and 5.9 %, respectively. The heating capacity of the heat pump system using R134a, R1234yf, and R1234yf with the suction line heat exchanger was determined to be in the range of 2.46–3.29 kW, 2.35–3.04 kW, and 2.39–3.11 kW, respectively. An increase in the airflow speed of the indoor unit from 1.4 m s−1 to 3.2 m s−1 resulted in an average decrease of approximately 12.3 % in the compressor discharge temperature. In contrast, the heating capacity and coefficient of performance increased by approximately 11.8 % and 14.4 % on average, respectively, for R1234yf operations with the heat exchanger. This study revealed that by optimizing the air flow rate in the R1234yf heat pump system with a suction line heat exchanger, improvements in the heating capacity and coefficient of performance can be achieved, thus providing better thermal comfort in the passenger compartment.

This paper experimentally investigates the factors influencing the flow boiling heat transfer of R134a refrigerant within smooth and micro-fin tubes having an outer diameter of 9.52 mm. The tube has a peculiar micro-fin shape with a 46° apex angle and 22° helix angle, producing a surface area 1.62 times bigger than a smooth tube of identical diameter. The main goal of the study is to understand the influences of mass flux, heat flux, saturation temperature, and average vapor quality on heat transfer characteristics. The findings are initially compared with known flow boiling correlations; moreover, performance index, penalty factor, and enhancement factor considerations are also made. The heat transfer coefficient (HTC) relies on mass flux, with significant improvements at G = 200 kg m−2 s−1, despite dry-out difficulties at high vapor quality. Intensified flow velocity from higher mass flux causes a rise in frictional pressure drop (FPD), with micro-fin tubes demonstrating superior heat transfer, owing to their larger surface area and improved swirl formation. Compared to smooth tubes, FPD is significantly influenced by vapor quality for micro-fin tubes. The study analyses the importance of micro-fin tubes to improve heat transfer in industrial applications, as well as the effects of saturation temperature and vapor quality on HTC.

A mathematical model for an air conditioning system used in five‐seater cars is developed with R1234ze(E) and R134a refrigerants, consisting of real system geometry like an evaporator, compressor, condenser, and thermostatic expansion valve. The mathematical model includes refrigerant properties, heat transfer, and pressure loss correlations for two‐phase and single‐phase regions. The performance parameters of a system like evaporator cooling duty, condenser heat loss, compressor power, refrigerant flow rate, and compressor volumetric efficiency obtained from a mathematical model are validated with the results of an experimental facility developed with R134a. The uncertainty analysis performed for the testing facility showed below 11% deviation. The simulation and experimental results showed an overall 10%–15% difference. It is found that the experimental cooling capacity with R134a and numerical cooling capacity with R134a show a 4%–12% variation, experimental cooling capacity with R134a and numerical cooling capacity with R1234ze(E) show a 7%–20% variation, and numerical cooling capacity with R134a and numerical cooling capacity with R1234ze(E) show a 5%–15% variation for the given range of compressor speed (500–1500 rpm), and condensing temperature (26–45°C). The study concluded that R1234ze(E) could potentially replace R134a because it has similar thermophysical properties and an average performance difference of up to 10% with R134a. Due to the limitations of the electric motor used to drive the compressor, tests in the current study were conducted at modest compressor speeds (500–1500 rpm). Future research will focus on experiments with high compressor speed (in the range of 1500–4000 rpm) and R1234yf and R1234ze(E) refrigerants for performance evaluation of automobile air conditioning systems. [ABSTRACT FROM AUTHOR]

This paper analyzes the developing adiabatic two-phase flow after an expansion valve in an air conditioning system. R245fa and POE 32 mixture is used as the working fluid. The developing two-phase flow patterns are visualized in an 8 mm straight tube after the expansion valve from 15 to 595 mm. To explore the effect of fluid properties on the developing two-phase flow, the experimental results from previous research by the same authors are compared with those of R245fa in this paper. An image analysis technique and a one-dimensional developing two-phase flow model proposed in a previous paper by the same authors (Yao & Hrnjak, 2023c) are applied to both R134a and R245fa. The flow patterns near the expansion valve exhibit some similarities when comparing the two refrigerants. However, a significant contrast emerges in the presence of a greater number of droplets suspended within the vapor phase in the case of R245fa flow. This disparity is primarily attributed to R245fa's higher vapor velocity. Furthermore, R245fa exhibits a shorter developing length than R134a. For fully developed flow, R245fa showcases a more pronounced turbulent behavior, and the transition to annular flow happens at a lower vapor quality in comparison to R134a. All of these distinctions can be adequately accounted for by the proposed model. The developed flow patterns of both refrigerants are compared with some existing flow pattern maps. At last, a new flow pattern map is proposed based on the observed flow patterns in this research. [ABSTRACT FROM AUTHOR]

R134a, which is used as a working fluid in Vapor Compression Refrigeration Systems (VCRS), is one of the refrigerants that is planned to be discontinued the usage due to the global warming. For this reason, researchers have tended to developing alternatives to R134a. In this context, in this study, the usage of R134a and its alternatives R1234yf, R450A, R513A, and R515B refrigerants were theoretically examined with the help of a theoretical model developed in the Engineering Equation Solver (EES) program using experimental data in terms of first and second laws of thermodynamics in a mechanical vapor compression refrigeration system. Analyses were performed for constant cooling capacity at various evaporation and condensation temperatures. In this study, the effects of the refrigerant type on the compressor power, heat rejection rate from the condenser, Coefficient of Performance (COP), second law efficiency, and mass flow rate of the refrigerant were determined. In addition, the results obtained under the same conditions for R134a and its alternatives were compared. As a result, compressor power increased by 5.62% for R1234yf, 2.35% for R450A, 3.41% for R513A, and 2.88% for R515B compared to R134a. Thus, it was observed that COP decreased by 5.32% for R1234yf, 2.30% for R450A, 3.30% for R513A, and 2.80% for R515B compared to R134a. Similarly, it was observed that the second law efficiency decreased by 5.32% in case of the usage of R1234yf, 2.30% in case of the usage of R450A, 3.29% in case of the usage of R513A, and 2.80% in case of the usage of R515B compared to R134a. Hence, it has been determined that the closest refrigerant to R134a in terms of the COP and the second law efficiency is R450A. [ABSTRACT FROM AUTHOR]

A major portion of the worldwide emissions arise from mobile air-conditioning systems with hydrofluorocarbon refrigerant as working substance and which is one of major cause for the greenhouse effect. R134a refrigerant having GWP of 1400 has been extensively used in car air conditioning. To reduce greenhouse gas emissions, the current R134a refrigerant must be phase out as per Kigali Amendment. The present study deals with cooling load calculation of car model by heat balance method as per ASHRAE standard using local climate condition. Further, thermodynamic analysis of R1234yf as an alternate refrigerant to R134a has been carried out for automobile air conditioning system. The required properties of refrigerants are extracted from Engineering Equation Software. The thermodynamic analysis is carried out to study the effect of operating parameters viz. condensing temperature, evaporating temperature, degree of superheating and degree of subcooling on COP, EDR, exergy efficiency and entropy generation. The previous literature reports mainly focus on separate study of either cooling load calculation or energy analysis or exergy analysis of R1234yf and R134a for automobile air conditioning system, while this paper presents the comprehensive study of new low GWP R1234yf as an alternate refrigerant to R134a in automobile air conditioning system with cooling load calculation including the concept of energy, entropy and exergy analysis. The percentage difference in COP between R134a and R1234yf system varies from 2.44 % to 4.78 % while percentage difference in EDR varies from 6.79 % to 2.87 % when evaporating temperature varied from -10 °C to 10 °C. With 12 °C of superheating at compressor inlet, the COP of R134a is 3.9 whereas COP of R1234yf is 3.75, which makes 3.85 % lower than that of R134a. The R1234yf has 4.78 % lower value of exergy efficiency as compared to that of R134a at evaporating temperature of -10 °C and it is found that maximum exergy destruction takes place in compressor. [ABSTRACT FROM AUTHOR]

The most common refrigeration system is the vapor compression refrigeration (VCR) system for a household refrigerator. The challenges for researchers are to minimize the power consumption of the compressor to improve the performance of the refrigeration system. This study aimed to assess and compare the energy and exergy analysis of VCR systems using multi-walled carbon nanotubes (MWCNT) and graphene nanosheets (GN) based hybrid nano-lubricants. The mass concentrations of each nanoparticle 0.3 g/L, 0.5 g/L, 0.7 g/L, and 0.9 g/L are mixed with 250 ml of polyolester oil (POE) separately and charged with 200 g of R134a refrigerant. Furthermore, the MWCNT and GN nanoparticles are mixed in a 50:50 proportion to prepare the same concentration of hybrid nanoparticles. The properties of refrigerants are obtained with the help of REFPROP 9.1 software. The pull-down time, compressor power, pressure ratio, exergy loss, relative irreversibility (RI), and second law efficiency (SLE) are variables that have been examined. The mass concentration of 0.7 g/L of hybrid nano-lubricants (GN-MWCNT /POE) is found to be optimal. It is noted that the pull-down time, power consumption, and pressure ratio of the refrigerator are lowered by 9.01%, 16.09%, and 5.68% respectively when compared to the pure refrigerant, whereas the actual COP and SLE improved by 11.29% and 8.22% at 0.7 g/L hybrid nano-lubricants. In addition, exergy loss and relative irreversibility are decreased for hybrid nano-lubricants. [ABSTRACT FROM AUTHOR]

Synthetic refrigerants are being phased out gradually in accordance with international environmental protection protocols because of global warming and ozone layer depletion. Adopting R290/R600 refrigerant, an environmentally friendly refrigerant, to replace R134a, a high global warming potential refrigerant, provides one of the solutions. In this study, exergy analysis of R134a and TiO2 suspended with lubricant and R290/R600 with a composition of 60% R290 and 40% R600 (60:40) was investigated in vapour compression system (VCRS) using R290/R600 in TiO2 nanomixture lubricant and compared with R134a and R290/R600 in pure lubricant. At the inlets and outlets, the main components of the VCRS are connected to temperature and pressure sensors to measure the inlet and outlet temperatures and pressures. The results obtained were used to analyses the exergy losses at various VCRS components (compressor, condenser, evaporator, expansion valve) were investigated to determine the refrigerator's total exergy destruction (Exdest.Total) and efficiency (ηex). The E·xdest. Total of R290/R600 in pure lubricant and R290/R600 TiO2 nanomixture lubricant was reduced by 26.9% and 42.3%, respectively, and system ηex increased by 27.7% and 38.9% respectively when compared to R134a in the system. Hence, TiO2 suspended with R290/R600 is potential a substitute for R134a. [ABSTRACT FROM AUTHOR]

The efficiency of R600a, an eco-friendly refrigerant with TiO2, Al2O3, and SiO2 nanolubricants, was investigated and evaluated as a substitute for R134a in a vapour compression refrigerator system. Pressure gauges and K-type thermocouples were used to monitor the temperature and pressure. The power consumption of the refrigerator was observed using the digital wattmeter. Using NIST refprop version 9.0, the refrigerant's enthalpy was determined. The results showed that R600a with nanolubricant TiO2, Al2O3, and SiO2 had lower evaporator temperatures and pull-down times than R134a and pure R600a. For R600a in the based lubricant, TiO2, Al2O3, and SiO2 nanolubricant concentrations in the system, respectively, evaporator temperatures of − 5, − 10, − 7, and − 11 °C were attained after 210, 210, 240, and 240 min of pull-down time. TiO2, Al2O3, and SiO2 nanolubricants increased R600a cooling capacity by 9.7%, 0.5%, and 12.2%, respectively, while lowering power consumption by 23.3%, 17.5%, and 20.2%. R600a/nano mixtures can therefore replace R134a and R600a with pure lubricant in a household refrigerator system.

In view of the heat dissipation of electronic components with high heat flux, five phase change heat transfer cold plates with different structures and processing methods were designed, the effects of cold plate structural parameters, heat flux, refrigerant flow rate, and heat source layout on heat transfer performance, resistance of cold plate, and the pump power consumption were experimentally studied. The results show that the designed perforated cold plate has excellent heat transfer performance. The designed perforated cold plate maintains a temperature difference of less than 25 ℃ between the heat source surface and the refrigerant inside the cold plate when dissipating a total heat output of 5 000 W and a heat flux of 38 W/cm2, with cold plate resistance less than 30 kPa and pump power consumption less than 35 W. The processing method of cold plate has a significant influence on its heat transfer effect. The cold plate should adopt integrated design as far as possible to reduce the link of heat transfer and avoid the contact thermal resistance caused by the chimerism of different materials. When multiple heat sources have different heat flux densities, placing the higher heat flux heat source closer to the inlet of the cold plate achieves better heat transfer efficiency.

The present study is focused on identifying the most suitable sequence of machine learning-based models and the most promising set of input variables aiming at the estimation of heat transfer in evaporating R134a flows in microfin tubes. Utilizing the available experimental data, dimensionless features representing the evaporation phenomena are first generated and are provided to a machine learning-based model. Feature selection and algorithm optimization procedures are then performed. It is shown that the implemented feature selection method determines only six dimensionless parameters (Sul: liquid Suratman number, Bo: boiling number, Frg: gas Froude number, Rel: liquid Reynolds number, Bd: Bond number, and e/D: fin height to tube’s inner diameter ratio) as the most effective input features, which reduces the model’s complexity and facilitates the interpretation of governing physical phenomena. Furthermore, the proposed optimized sequence of machine learning algorithms (providing a mean absolute relative difference (MARD) of 8.84% on the test set) outperforms the most accurate available empirical model (with an MARD of 19.7% on the test set) by a large margin, demonstrating the efficacy of the proposed methodology.

For a country with a tropical climate, such as Indonesia, heat pump technologies are usually necessary in high-altitude regions, where the temperatures tend to be cooler, such as a pool heater for an artificial hot spring swimming pool. A vapor compression heat pump's optimal performance relies on its working fluid's characteristics. This paper aimed to assess the performance and compare the time required to heat a hot spring pool using heat pumps with two different refrigerants: R32 and R134a. A thermodynamic modeling approach was employed to determine the better refrigerant choice between R32 and R134a for the heat pump, aside from other important factors that are considered when selecting the refrigerant, such as safety and environmental impacts. Comparing the results of R134a and R32 refrigerants, R134a has a higher GWP value than R32, indicating that R32 is more environmentally friendly. Regarding safety, R134a has low toxicity and flammability, while R32 exhibits low toxicity and mild flammability. Thus, R134a is considered safer than R32. Furthermore, the COP value of R134a was found to be higher than that of R32, indicating that R134a offers greater efficiency for the heat pump compared to R32.

In this study, the use of the alternative refrigerant R513A instead of R134a in a mechanical vapor compression refrigeration system was experimentally investigated in terms of the first and second laws of thermodynamics on the basis of the Kigali Amendment. The investigations were carried out approximately at a cooling medium temperature (TL) of 0, 4, and 8 °C and a heating medium temperature (TH) of 30, 35, and 40 °C without any modifications to the system. The energetic and exergetic performance parameters obtained in this study were related to the amount of refrigerant in accordance with the criteria restricting the use of fluorinated greenhouse gases after the Kigali Amendment. Accordingly, the required refrigerant mass flow rate per unit energetic (power input, cooling capacity, COP value) and exergetic (total exergy destruction rate and exergy efficiency) performance parameters were determined. As a result, the system was found to operate safely when R513A was used instead of R134a without any modification. In addition, the refrigerant mass flow rate per unit power input was almost the same for both refrigerants. However, R513A was found to have approximately 15 % more refrigerant mass flow per unit cooling capacity than R134a. This resulted in the refrigerant mass flow rate per unit COP being approximately 20 % higher for R513A. On the other hand, the refrigerant mass flow rate per unit exergy efficiency calculated for R513A was found to be about 15 % higher than R134a.

• The flammability limits of R134a/R1270, R134a/R170 and R170/R1270 were measured. • R134a demonstrates a significant flame-retardant effect at volume ratios above 0.75. • The flame color and propagation speed of refrigerants were compared and analyzed. 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. [ABSTRACT FROM AUTHOR]

Refrigerant R12, or Freon 12, has been a predominant choice in various refrigeration and air conditioning applications due to its versatility across a broad spectrum of operating conditions. However, R12, a chlorofluorocarbon (CFC) with the chemical formula CCl2F2, poses a significant threat to the ozone layer, contributing to the greenhouse effect. Consequently, the phasing out of R12 is imperative. This study explores viable alternatives to R12, focusing on the impact of external temperature and other parameters on capillary tube length. A detailed comparison between refrigerant R-134a and R-12 is conducted using Engineering Equation Solver (EES) software at Q=366.5 W, d= 1.2 mm, Tconf =45°C and tsurr=35°C. The software utilizes refrigerant thermodynamic and transport properties, including dynamic viscosity, density, thermal conductivity, and specific enthalpy, in the analysis. The research is aimed at understanding the flow dynamics in a capillary tube based on a model that aligns with the requirements of contemporary refrigerator design. Parameters such as operating conditions and tube diameter are scrutinized, with an emphasis on the direct relationship between them. The study also investigates the performance variability of the two refrigerants under identical conditions. A key finding is the superior quality of R-134a over R-12 in the two-phase region, coupled with the observation that the capillary tube length for R-134a is approximately 20% shorter than that for R-12. These results underscore the intricate relationship between refrigerant type, capillary tube dimensions, and overall system efficiency, thereby informing the design and optimization of next-generation refrigeration systems. [ABSTRACT FROM AUTHOR]

Copyright of Advances in New & Renewable Energy is the property of Editorial Office of Advances in New & Renewable Energy and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Chemistry & Industry of Forest Products is the property of Chemistry & Industry of Forest Products Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

At temperatures below 60 °C, the best way to use geothermal sources for heating is to use heat pumps. A heat pump can provide air conditioning for a residential, commercial, etc., all year round by heating in winter and cooling in summer using a low temperature source. Also, a heat pump can be used for water distillation through evaporation. The ground source heat pump with a high COP and low temperature thermal energy sources is one of the best technologies for using RES. In the present study, the effects of changing ambient temperature and soil temperature on a heat pump's overall COP and energy efficiency are investigated using a simulated geothermal heat pump with an economizer. The system's thermodynamic simulation is first performed in the engineering equation solver software for R134a and R513a working fluids. The exergy destruction of different components for both working fluids was calculated and displayed as a figure. The COP of the heat pump for R134a working fluid is equal to 3.916, equal to 3.729 for R513a working fluid, which indicates that R134a fluid has about 5% better performance. The COP of the system for R134a working fluid is equal to 3.662, which is equal to 3.504 for R513a working fluid, which indicates that R134a fluid has about 4.5% better performance. [ABSTRACT FROM AUTHOR]

• Performance of an ice plant is investigated with nano-refrigerant (R134a/MWCNTs). • Effect of varied mass of MWCNTs (0.05 g-0.25 g) and R134a (175 g-225 g) is studied. • Pull-down time and power consumption are reduced by 17.9%, 21.46%. • COP and cooling capacity improved by 40.09% and 11.29% respectively. • Economic analysis is also carried out, the operational cost is reduced by 7.12%. Ice plant is used for producing ice at a large scale from water filled in standard cans placed inside rectangular tanks filled with brine solution. Ice plant works on the vapour compression refrigeration (VCR) cycle, the researchers are focusing on minimizing compressor work and improving the cycle's performance by introducing nanoparticles with higher thermophysical properties. In this experimental investigation, the performance analysis of the test rig of an ice plant using varied masses of 0.05 g, 0.10 g, 0.15 g, 0.20 g, and 0.25 g of multi-walled carbon nanotubes (MWCNTs), dispersed in 250 ml polyolester (POE) oil charged with masses 175 g, 200 g, and 225 g of tetrafluoro ethane (R134a) refrigerants is carried out separately. REFPROP 9.1 software is used to obtain the properties of refrigerants. The evaluated parameters are pull-down time, cooling capacity, coefficient of performance (COP), Compressor work input, economic analysis, pressure ratio, thermal conductivity, absolute viscosity, and density. It is observed that in comparison to the pure refrigerant, the refrigerator's pull-down time and compressor work are reduced by 17.9% and 21.46%, whereas, COP and cooling capacity improved by 40.09% and 11.29% for 225 g mass of R134a with 250 ml POE respectively. In addition, thermal conductivity, density, and absolute viscosity improved at both the suction side and discharge side of the compressor. [ABSTRACT FROM AUTHOR]

Liquefied petroleum gas (LPG), like other hydrocarbon gases, has good thermo-physical and ecological properties, but its high-flammability has limited its direct use in refrigeration applications. Therefore, this paper investigates the thermodynamic performance of low flammable and ecological-save mixtures of LPG and tetrafluoroethane refrigerant in a refrigeration system. The computational results of global warming potential (GWP) and low flammability limit shown that the blends with 50 – 90 % LPG contents have GWP below 750 and fall within the lower flammability safety class of which five were selected for further analysis. The results showed that the thermal conductivity and the refrigerating effects produced by the selected blends are greater than those of the reference refrigerant (R134a). Also, the selected blends exhibited appropriate lower pressure ratio, discharge temperature and specific power than R134a refrigerant. Four of the blends required low power input and exhibited higher coefficient of performance which are clear indication that they are more energy efficient than R134a in the refrigeration systems. [ABSTRACT FROM AUTHOR]

Experimental studies that investigate the utilization of ultra-low temperature (between 48 °C and 120 °C) waste heat, which forms 25 % of the global unrecovered waste heat, to drive thermal cooling systems are rare. Thus, this study fills a significant gap in the literature by (i) experimentally evaluating the performance of a new full-scale thermo-mechanical refrigeration (TMR) system at ultra-low temperatures ranging from 50 °C to 85 °C, (ii) characterizing its operation with different commercial refrigerants, and (iii) identifying optimal operating conditions and working fluids for the investigated TMR system. An organic Rankine cycle (ORC), vapor compression cycle (VCC), and expander-compressor unit (ECU) make up the TMR system. To ensure its efficient operation, flexibility, and reliability, a full-scale ECU-based TMR system with a design capacity of 1 kW at a heat source temperature of 85 °C is built and put through a series of tests. Furthermore, the TMR system is tested with different commercial refrigerants (R134a, R410A, R407C) over a wide range of operating conditions of the power loop. The results reveal that the ECU-based TMR system can work with ultra-low temperatures of 65 °C with an energy efficiency of 5.92 % and COP of 2.36, for the ORC and VCC, respectively. At a heat source temperature of 85 °C, a condenser water temperature of 15 °C, and an evaporator water temperature of 33 °C, the energy efficiency of the ORC and COP of the VCC are increased to 9.85 % and 3.99, respectively. For the cooling quality, the TMR system shows a minimum evaporator temperature of −10 °C using R134a in both the power and cooling loop, which is improved to lower than −20 °C by using R407C in the cooling loop. The results presented herein will be beneficial to the development, design, and optimization of refrigeration and power systems that utilize low-temperature waste heat.

Aiming at the heat dissipation of electronic components with high heat flux, five phase change heat transfer cold plates with different structures and processing methods were designed, the effects of cold plate structural parameters, heat flux, refrigerant flow rate, and heat source layout on heat transfer performance, resistance of cold plate, and the pump power consumption were experimentally studied. The results show that the designed perforated cold plate has excellent heat transfer performance. The designed perforated cold plate maintains a temperature difference of less than 25 ℃ between the heat source surface and the refrigerant inside the cold plate when dissipating a total heat output of 5 000 W and a heat flux of 38 W/cm~2, with cold plate resistance less than 30 k Pa and pump power consumption less than 35 W. The processing method of cold plate has a significant influence on its heat transfer effect. The cold plate should adopt integrated design as far as possible to reduce the link of heat transfer and avoid the contact thermal resistance caused by the chimerism of different materials. When multiple heat sources have different heat flux densities, placing the higher heat flux heat source closer to the inlet of the cold plate achieves better heat transfer efficiency. [ABSTRACT FROM AUTHOR]

• Establishment and verification of a rig for refrigerants' pool boiling. • Heat transfer coefficients were obtained for the R134a pool boiling on 6 surfaces with various roughness and wettability under 3 saturation temperatures. • A phenomenon of bubble behavior above the boiling surface was spotted and observed with a high-speed camera. 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. [ABSTRACT FROM AUTHOR]

This study investigates the potential of using R134a as a working fluid in a low-emission power plant instead of the conventional power plant to mitigate the greenhouse effect. The study explores the thermodynamic properties of R134a and its suitability for use in an Organic Rankine Cycle (ORC) power plant. A simulation model was developed using Aspen Hysys to evaluate the power plant's performance using this working fluid. The results indicate that the ORC power plant can significantly reduce greenhouse gas emissions compared to conventional power plants while maintaining high energy efficiency. About 18.17 kW of electric power can be obtained at a working condition of 10 bar and an evaporator temperature of 130 °C with the highest thermal efficiency of 3.43%. The study provides valuable insights into the potential of R134a as a sustainable working fluid for low-emission power generation. [ABSTRACT FROM AUTHOR]

For a country with a tropical climate, such as Indonesia, heat pump technologies are usually necessary in high-altitude regions, where the temperatures tend to be cooler, such as a pool heater for an artificial hot spring swimming pool. A vapor compression heat pump's optimal performance relies on its working fluid's characteristics. This paper aimed to assess the performance and compare the time required to heat a hot spring pool using heat pumps with two different refrigerants: R32 and R134a. A thermodynamic modeling approach was employed to determine the better refrigerant choice between R32 and R134a for the heat pump, aside from other important factors that are considered when selecting the refrigerant, such as safety and environmental impacts. Comparing the results of R134a and R32 refrigerants, R134a has a higher GWP value than R32, indicating that R32 is more environmentally friendly. Regarding safety, R134a has low toxicity and flammability, while R32 exhibits low toxicity and mild flammability. Thus, R134a is considered safer than R32. Furthermore, the COP value of R134a was found to be higher than that of R32, indicating that R134a offers greater efficiency for the heat pump compared to R32. [ABSTRACT FROM AUTHOR]

This study embarks on a comprehensive exploration of the influence exerted by refrigerant purity characteristics on vapor-compression refrigeration systems performance. The investigation particularly delves into the effects on domestic applications, such as chest freezers. Deviations from the ideal refrigerant characteristics, as stipulated by the AHRI-700 standard, can provoke detrimental repercussions, including augmented power consumption and diminished coefficient of performance. In this empirical analysis, three R134a refrigerant samples, each with varying degrees of conformity to the AHRI-700 standard, were scrutinized. Sample 1 with superior characteristics, sample 2 with medium characteristics, while sample 3 with substandard characteristics. The samples were subjected to identical ambient conditions within a 145-liter chest freezer operating at a temperature of 32°C. The findings unequivocally underscored a correlation between refrigerant purity and system performance. Sample 1, with optimal characteristics, demonstrated superior performance, consuming less power (120.7 W) and delivering a higher coefficient of performance (2.33) in comparison to sample 2 (138 W, 2.07) and sample 3 (147 W, 1.93). These results emphatically emphasize the necessity of stringent refrigerant selection, predicated on purity characteristics, to best performance of vaporcompression refrigeration systems. [ABSTRACT FROM AUTHOR]