Refrigerant R134a Research Articles

Effect of contraction on the convective boiling heat transfer of microchannel heat sinks

The present study examines the effect of contraction before straight fin microchannels in the cold plate by using refrigerant R-134a as a working fluid. The experiments compared two test sections with the same geometry and dimension, but one has contraction before the microchannels (CBM), and another one has no contraction before the microchannels (NCBM); the mass flux ranges from 25 to 425 kg/m2⋅s while the heat flux spans from 60 to 300 kW/m2. The inlet flow conditions can be either a fully liquid inlet or with vapor qualities (from 0.1 to 0.45). Improved flow distribution is found with the introduction of the contraction. Based on the mass flux and irrespective of the inlet conditions, the test results indicated that the performance of the CBM shows a superior heat transfer coefficient (HTC) by about 3 ∼ 30 % than that of NCBM. Nonetheless, the pressure drop of CBM is lower than NCBM when the inlet is fully liquid. Conversely, the trend of pressure drop is reversed with a vapor-quality inlet. For the fully liquid inlet, the CBM contains a much lower pressure drop by 22 % compared to NCBM at a low mass flux of 36.2 kg/m2⋅s. However, the reduced pressure drop has narrowed to 3 % at a mass flux of 402.8 kg/m2⋅s. Flow visualizations were performed, and it was found that the CBM is free from flow reversal, and the fluctuations in temperature or pressure drop are much less pronounced. By contrast, the NCBM design shows flow reversal and sluggish bubble phenomena.

Experimental study on improving the performance of vapor compression cycle by using loop-type heat pipe

In this study, an experimental study was carried out on a heat pipe, whose evaporator is located between the compressor outlet and the condenser inlet of an industrial cooler on a vapor compression cycle (VCC). It absorbs heat from the new generation refrigerant fluid of 515B and transfers it to the outdoor air. The heat pipe is a looped thermosiphon-type heat pipe. R134a refrigerant is used as a working fluid in the heat pipe. By changing the condenser air inlet temperatures, the contribution of the heat pipe to the cooling cycle has been determined experimentally. While the evaporation pressure of the refrigeration cycle with the heat pipe remains approximately constant, the condensation pressure decreases, and the sub-cool temperature increases. For condenser air inlet temperatures of 30, 40, and 50°C, the COP of the cooler with heat pipe increases by 1.8%, 2.6%, and 2.76%, respectively. As the air temperature at the condenser inlet increases, the ratio of heat pipe power to the cooling capacity of the cycle also increases. In addition, the compressor outlet temperature is reduced by 1.5%–2.8% using of the heat pipe.

A study on the design of Waste Heat Recovery Unit (WHRU) for 30kW Organic Rankine Cycle (ORC) power system for ships

ABSTRACT As the improvement of ship energy efficiency is emphasized internationally, researches for this are being conducted in various ways. Accordingly, research is being conducted on the application of ORC power generation systems for ships using waste heat from the main engine exhaust gas generated during operation. The WHRU constituting the ORC system must be designed so that stable-phase change heat transfer occurs. In this study, a design study was conducted using the ANSYS CFX program for the production of a WHRU capable of generating ORC power generation output for a 30-kW ship using R134a refrigerant. A WHRU capable of achieving 30 kW generation output performance was designed while changing various design elements (shape, tube diameter, number of tubes, number of stages, etc.) of the WHRU. As a result, it was confirmed that the refrigerant (R134a) in a liquid state at a temperature of 14.8°C entered at a flow rate of 1.06 kg/s, evaporated by the exhaust gas, and was discharged from the outlet in a state of vapor fraction 1 at a temperature of 56.4°C. The heat transfer rate of the WHRU was 219.2 kW, the pressure during the evaporation process was constant at 13.9 bar in absolute pressure, and the enthalpy was 220 kJ/kg at the inlet and 426 kJ/kg at the outlet, respectively.

EXPERIMENTAL STUDY TO EVALUATE EFFECT OF SOURCE TEMPERATURE ON COP AND COMPRESSOR STATUS IN WATER-TO-AIR HEAT PUMPS

Heat pump devices have been researched and analyzed from different aspects, which indicates the importance of these devices. In fact, these devices transfer heat energy effectively from one source to another by consuming power. In this work, the importance of source temperature and its effect on system performance and compressor status has been investigated. It is shown that if the temperature of the heat source is low, the refrigerant at the inlet of the compressor will be in the two-phase region, which could cause damage to the compressor. In these cases, the evaporator design can be changed as available solutions or a high-temperature heat source can be provided in the present study. On the other hand, in the two-phase region, calculating the work of the compressor with enthalpy values will be a problem and may cause a computational error in the power consumption of the compressor. The reason for this is that the enthalpy of refrigerant in the compressor cannot be obtained with two properties, i.e., temperature and pressure. This issue has been considered and the rate of computational error has been obtained. R134a refrigerant was used as circulating gas in the used water-to-air heat pump. The results obtained in the experiments performed showed that the COP value of the heat pump increased by 172% when the source temperature increased from 6°C to 34°C. As the source temperature increases, more energy is transferred to the system. This issue raises both high-pressure and low-pressure values. This increase was recorded as 34% for high pressure and 17% for low pressure when the source temperature increased from 6°C to 34°C.

AN EXPERIMENTAL INVESTIGATION TO PREDICT OPTIMUM CHARGE OF A HEAT PUMP SYSTEM

Working principles of heat pumps is an important matter from a thermodynamic point of view that has been researched from various aspects. In this study, undercharged, optimum charged, and overcharged conditions of a heat pump were investigated using R134a refrigerant. Variations in temperature, pressure, and the coefficient of performance have been evaluated and it was aimed to find out the optimum charge condition considering different parameters. According to the experimentally obtained findings, the coefficient of performance was increased by more than three times when the refrigerant amount increased from 2000 g to ~ 7300 g. The general outcomes of the present study indicated that optimum refrigerant charge amount can notably affect the performance of heat pump apparatus. It was shown that the P-h diagram of all heat pump systems depends on the working conditions and the refrigerant charge is a very important criterion that can make significant changes in the P-h diagram. It was found that, by increasing refrigerant charge, after the downtrend starts in the compressor inlet temperature, 20% refrigerant can be added to achieve the maximum COP value. Additionally, the critical point in expansion valve outlet temperature was used to find the optimum charge. It was revealed that if 140% refrigerant is added to the given refrigerant at critical point, the optimum COP value can be achieved.

Energy-Saving Individual Heating Systems Based on Liquid-Vapor Ejector

The problem of increasing the efficiency of individual heating systems is solved by using heat pumps based on a liquid-vapor ejector with the working fluid R718 (water). The research object was the working process of the liquid-vapor ejector, based on the principle of jet thermal compression. It involves the generation of vapor in the nozzle of the motive flow of the liquid-vapor ejector and does not require its supply from an external source. Schemes and descriptions of the traditional system and the proposed scheme were given. Their difference from the traditional ones was indicated according to the schematic solution and working cycle. The article compared the proposed schemes’ thermodynamic calculation with the working flow R718 and traditional heat pump systems with carried-out refrigerants R134a, R410a, and R32. As a result, the values of the thermodynamic parameters of all system components were obtained. The coefficients of performance (COP) for the traditional and proposed cycles were determined. Applying the new scheme made it possible to increase the COP by an average of 40 %. An exergy analysis assessed the expediency of implementing vacuum units based on liquid-vapor ejectors in individual heating systems. This made it possible to compare systems that use several types of energy (e.g., electrical, thermal) and to determine their efficiency with high accuracy. As a result of the exergy analysis, the value of the proposed scheme’s exergy efficiency was obtained.

ENERGY PERFORMANCE ANALYSIS OF R32 AND R134A REFRIGERANT FOR SPRING POOL WATER HEATER

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.

Improving the performance of the vapor compression cycle using an internal heat exchanger

The main additional consumer of electrical energy in an electric bus is the climate system, which can consume up to 30% of electrical energy. This problem is especially relevant in Russia at low ambient temperatures. The optimal solution is to switch the vapor compression unit to heat pump mode. However, at low temperatures, its efficiency decreases and performance is insufficient. One way to improve efficiency is to use an internal heat exchanger. In this paper, we studied the effect of an internal heat exchanger on the performance of a vapor compression cycle using R290, R410a and R507a refrigerants. The influence of geometry on the performance of the internal heat exchanger is determined. The use of an internal heat exchanger makes it possible to increase coefficient of performance by 10-13%.

Experimental investigation on split type window Air conditioner using HFC and HC mixture as ecofriendly refrigerant alternate to HCFC-22

This paper reports on an experimental study evaluating a window air conditioner's performance when R152a/R290/R600/R600a refrigerant mixture (by various mass percentages) is used as a possible alternative to R-22. Alternative refrigerants are local, cheap, and environmentally friendly. Unmodified R-22 window AC was charged with R152a/R290/R600/R600a. During the experiment, parameters such as coefficient of performance, refrigeration effect, pressure ratio, compressor discharge temperature, refrigerant mass flow rate, and compressor power are analyzed. The present work shows that R152a-15%/R290-15%/R600-35%/R600a-35% is the best-performing alternative refrigerant. Proposed blends and R22's performance were compared.

Energy performance assessment of virtually non-flammable mixtures for R134A applications

In this study, three new mixed refrigerants with low GWP values, R1234yf/R134a, R1234yf/R125, and R1234yf/R13I1, were evaluated as replacements for R134a refrigerant using two vapor compression configurations. The experiment revealed that these mixtures can be used as environmentally friendly alternatives for this configuration.

Performance of refrigeration system using Al2O3, CuO and TiO2 nano-enhanced refrigerants: A review

Refrigeration is an ever-growing field where we are always looking for environmentally cleaner, more efficient and more usable ways to enhance and discover substances and materials for refrigeration. Nanoparticles are one way to achieve this goal of great energy savings and resulting emissions reductions. The refrigeration interaction becomes more proficient and protected as contrasted with the past in the environment. The key objective of this article is to review the performance of refrigeration systems with Al2O3, CuO and TiO2 nano-enhanced refrigerants. The Review revealed that when the TiO2 nanoparticle was introduced to the R134a refrigerant, the maximum enhancement in coefficient of performance is 18.75%. On the other hand, Al2O3/R134a offers a 27% reduction in power usage when compared to traditional fluids. Compared to R134a/CuO, the Al2O3/R134a nano-refrigerant offers energy savings that are more than five times greater and 80% more effective.

Comparative Analysis of Air Conditioning Performance with 0.5 PK Capacity Using Environmentally Friendly Refrigerants

In accordance with the Montreal Protocol, R22 will be completely banned from its use from January 1, 2030. Research looking for alternative refrigerants replacing R22 has experienced a significant increase. One of the replacement refrigerants that have gradually expanded their use are hydrocarbon refrigerants, few of which are R32, R290, and R410a. However, there are no experiments using the same test equipment for use on R32, R410a and R290 refrigerants. In addition, a more detailed study comparing the respective those refrigerants has not been found. This study aims on knowing the performance of machines that use R32, R290, and R410a refrigerants. This research uses 0.5 PK air conditioner. This research has begun with the preparation of tools and materials. Preparatory steps include assembly and setting up test installations, vacuuming, refrigerant filling and leak tests. The testing and the data retrieval steps are carried out after the system operates for about 30 minutes, i.e. until the system is working normally. Data collection is carried out with the change parameter or replacing the refrigerant. After obtaining data, analysis on Coefficient of Performance (COP), electricity costs, and economical refrigerant needs is carried out. The results have shown that the COP of R32 had the highest value from the 1-hour test, which has been 49.1. The most economical electricity cost is assumed to live for 24 hours in 1 month, namely in R32 refrigerant with a total amount of $12.46. The most economical refrigerant capacity operational cost is R290 refrigerant with a total amount of $9.01.

Performance Evaluation of Split Air Conditioner with Consideration of Pressure Drop in Evaporator and Condenser

In this research, a split air conditioner's performance has been evaluated using exergy analysis on three different low global warming potential (GWP) refrigerants, namely R32, R447A, and R447B, to find a replacement for the GWP-high refrigerant R410A. With regard for pressure loss in the evaporator and condenser, a computational model is built to recreate the operational conditions of a split air conditioner. GENETRON Properties 1.4 software is used to calculate performance metrics such as coefficient of performance (COP), exergy destruction ratio, exergetic efficiency, and efficiency defect. Result shows that pressure drop in evaporator alone has an adverse effect on COP and total exergy destruction and it is higher at higher pressure drop. Effect of pressure drop on exergetic efficiency and exergy destruction ratio is found to be less significant with condenser pressure drop compared to evaporator pressure drop. Exergy efficiency is found to be maximum with R447A followed by R447B, R32, and R410A.

Towards a Miniaturized Photoacoustic Detector for the Infrared Spectroscopic Analysis of SO2F2 and Refrigerants

Sulfuryl fluoride (SO2F2) is a toxic and potent greenhouse gas that is currently widely used as a fumigant insecticide in houses, food, and shipping containers. Though it poses a major hazard to humans, its detection is still carried out manually and only on a random basis. In this paper, we present a two-chamber photoacoustic approach for continuous SO2F2 sensing. Because of the high toxicity of SO2F2, the concept is to use a non-toxic substituent gas with similar absorption characteristics in the photoacoustic detector chamber, i.e., to measure SO2F2 indirectly. The refrigerants R227ea, R125, R134a, and propene were identified as possible substituents using a Fourier-transform infrared (FTIR) spectroscopic analysis. The resulting infrared spectra were used to simulate the sensitivity of the substituents of a photoacoustic sensor to SO2F2 in different concentration ranges and at different optical path lengths. The simulations showed that R227ea has the highest sensitivity to SO2F2 among the substituents and is therefore a promising substituent detector gas. Simulations concerning the possible cross-sensitivity of the photoacoustic detectors to H2O and CO2 were also performed. These results are the first step towards the development of a miniaturized, sensitive, and cost-effective photoacoustic sensor system for SO2F2.

Comparative Analysis of the Environmental Load of Natural Refrigerant (R290)

Due to the detrimental environmental consequences of synthetic refrigerants, natural refrigerants have gained renewed interest as alternative refrigerants for a variety of applications due to their minimal ozone depletion potential (ODP) and insignificant global warming potential (GWP). This study compares the performance characteristics of R32-based Air Source Heat Pump (ASHP) to those of R290 and R410A refrigerants. In this study, analyses of the cooling effect, heat output, compressor work input, and coefficient of performance (COP) for various refrigerants will be undertaken. Additionally, the environmental consequences of R32, R410A, and R290 are discussed. The results indicate that R290 is the most efficient refrigerant in terms of performance coefficient, followed by R410A and R32. Considering environmental protection aspects, R290 is a favorable substitute medium.

Effect of Variation in Evaporator Inlet Air Temperature on Coefficient of Performance in an Automotive Air Conditioning System

Because of its superior thermal properties and multiple prospective uses, nanofluids had sparked the interest of investigators. Addition of nanoparticles to refrigerants and lubricants improves thermal characteristics and lowers power wastage. In this paper R134a refrigerant is added with nanoparticle CuO in the concentration of 0.1%v to 0.5%v and its performance is evaluated. The suction pressure of R134a at 32C is 9% higher than R134a+0.1nm and 17% higher than R13a+0.5nm.The discharge temperature of R134a is more than nano refrigerant. Due to this, the power consumption of R134a is more than nano refrigerant. By adding nanoparticles to refrigerant, the power consumption at 28C is 23% less than R134a which shows nanoparticles works normally when mixed with R134a. Due to high thermal conductivity of nanoparticles, the coefficient of performance of R134a is 35% less than R134a+0.1nm and 41% less than R134a+0.5nm.

Evaluation and quantification of compressor model predictive capabilities under modulation and extrapolation scenarios

Testing and evaluation of select semi-empirical and black-box compressor models is carried out to quantify performance in modulation (variable speed), extrapolation, and additionally, variable superheat scenarios. Three representative literature models and an artificial neural network (ANN) model are benchmarked against the industry standard AHRI model. A methodology quantifying model performance, compared against experimental data, in said scenarios is presented. High-fidelity test data taken from either a hot-gas bypass load stand or compressor calorimeter. Scroll, screw, reciprocating, and spool compressor technologies were collected with R410A, R1234ze(E), R134a, and R32 refrigerants totaling 434 experimental points. Data is divided into training, extrapolation, variable speed, and variable superheat data splits to examine model performance. Mean Absolute Percentage Error (MAPE) is computed for mass flow rate and power after training models with training data and evaluating them against the other data splits. Two literature models are true semi-empirical formulations while the other, the ANN, and AHRI model are more empirical in nature. Neither semi-empirical model predicted all compressors. When the compressor type is predicted, the semi-empirical models yield MAPE’s less than 8%, 5%, and 4% for mass flow rate and power prediction in extrapolation, modulation, and variable superheat scenarios, respectively. The exception is the Popovic and Shapiro model performing at 21% MAPE in variable superheat power prediction for the spool compressor with R1234ze(E). The ANN showed highest errors of 9.3%, 12%, and 17% in extrapolation, modulation, and variable superheat scenarios, respectively. All models outperformed the AHRI model by several orders of magnitude in these scenarios.

Performance analysis of micro-fin tubes compared to smooth tubes as a heat transfer enhancement technique for flow condensation

• Entropy generation of R134a flow condensation inside micro-fin and straight tubes is studied and compared. • Geometrical parameters impact on entropy generation is investigated. • Flow conditions impact on entropy generation is analyzed. • Favorable geometrical and flow conditions at which the micro-fin tube has superior performance are identified. Heat transfer enhancement techniques are accompanied by pressure drop amplification, detrimentally affecting their performance; entropy generation analysis is an effective approach to assess heat transfer enhancement along with resulting pressure drop. Current study investigates and compares the performance of micro-fin (as a passive enhancement technique) and smooth tubes during flow condensation (for R134a refrigerant) through conducting entropy generation analysis. First, the impact of geometrical and operating variables on pressure losses and heat transfer contributions to entropy generation and total generated entropy inside both types of tubes is examined. Then, the conditions at which the application of micro-fin tubes in lieu of smooth ones is justifiable and of superior performance are identified utilizing entropy generation number. The simulation results indicate that entropy generation enhances in the micro-fin tubes as tube diameter, mass velocity, vapor quality, and wall heat flux rise, and saturation temperature declines. The same is observed in the smooth tube except for the mass velocity; an increase in this parameter leads to a decreasing-increasing trend in entropy generation. Moreover, the entropy generation number results indicate that applying micro-fin tubes rather than smooth ones is justifiable, i.e., has better performance, at lower mass velocities and vapor qualities, but higher saturation temperatures and wall heat fluxes.

Evaluation and Analysis of an Agro-Based Nano Refrigerant to Improve the Performance of a Domestic Refrigeration System

The use of nanoparticles along with the conventional refrigerant in a vapor compression cycle is relatively a new idea, where nano-refrigerants are found to have improved thermo-physical properties over the conventional refrigerants. Nano-refrigerant is the combination of nanoparticles with the refrigerant to improve the performance of the refrigeration process. In this study, a developed nanofluid from agricultural source (rice husk) was applied in a domestic refrigerator and its performance investigated. The pre-developed nanofluid which was prepared using the synthesis, centrifugation and calcinations processes was administered in the compressor of the refrigerator at concentrations of 0.2wt%, 0.3wt%, 0.5wt% and 0.6wt% to form a mix with refrigerant R600a used in the compressor (as control) and allowed to run for 4 hours. Performance evaluation was measured using parameters such as pull down time, discharge temperature and coefficient of performance (COP). Results show an increase in the COP by 31, 23 and 35% compared to the control sample for the 0.2wt%, 0.3wt% and 0.5wt% concentrations respectively. The sample 0.6wt% and 0.5wt% showed the best pull down time with temperatures of -6.1 and -3.1℃ at 240 minutes respectively and a reduced discharge temperature of 7-16% by the 0.2wt%, 0.3wt% and 0.5wt% concentrations in respect to the control sample. Hence, the use of rice husk based nanofliud resulted in an enhanced performance for the domestic refrigerator.

Effects of injection styles on heating performance of a heat pump with sub-cooler refrigerant injection: Experimental and thermodynamic analysis

The performance improvement of heat pump depends on the appropriate injection style such as liquid injection, vapour injection and two-phase injection. In this work, experimental and theoretical investigation on the heat pump with R410A refrigerant reveals three kinds of injection styles can be selectively achieved in the same injection device by suitable control of the sub-cooling electronic expansion valve. Liquid injection and vapour injection improve the heating capacity (Qh), mainly due to the increase of heat exchange in the sub-cooler and compressor compression work, respectively. Two-phase injection lifts the Qh owing to these two effects. Subsequently, the effect of two-phase injection on improving the heat pump performance is superior to the other two injection styles. For instance, the maximum Qh were 14.4 kW at 60 rps with the liquid injection, 12.5 kW and 13.4 kW at 85 rps with vapour injection and two-phase injection, and 8.1%, 7.0% and 18.3% higher than those without injection, respectively. The corresponding coefficient of performance was improved by 10.4%, 4.5% and 10.6%, respectively. Furthermore, the model based on the pressure-enthalpy diagram has been developed to analyze the experimental results and expound the main factors affecting the heat pump performance under different ambient temperatures.