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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]

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]

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]

We present a new wide-ranging correlation for the viscosity of 1,1,1,2-tetrafluoroethane (R-134a) based on critically evaluated experimental data. The correlation is designed to be used with densities from an existing equation of state, which is valid from the triple point to 438 K, at pressures up to 70 MPa. The estimated uncertainty (at the 95 % confidence level) for the viscosity varies depending on the temperature and pressure, from a low of 0.2 % in the dilute-gas range near room temperature, to 2 % along the saturated vapor boundary, 2.5 % for the saturated liquid, and 4 % for some high-pressure regions. The correlation behaves in a physically reasonable manner when extrapolated to pressures above 70 MPa. Comparisons with experimental data at pressures to 400 MPa are given. However, care should be taken when using the correlation outside of the validated range of the equation of state. [ABSTRACT FROM AUTHOR]

Previously published experimental viscosity data at low density, originally obtained using all-quartz oscillating-disk viscometers for R134a and six vapors of aromatic hydrocarbons in the temperature range between 297 K and 631 K at most, were re-evaluated after an improved re-calibration. The relative combined expanded ( k = 2 ) uncertainty of the re-evaluated data are 0.2 % near room temperature and increases to 0.3 % at higher temperatures. The re-evaluated data for R134a as well as for the vapors of mesitylene, durene, diphenyl, fluorobenzene, chlorobenzene, and p-dichlorobenzene were arranged in approximately isothermal groups and converted into quasi-isothermal viscosity data using a first-order Taylor series in temperature. Then, the data for R134a were evaluated by means of a series expansion truncated at first order to obtain the zero density and initial density viscosity coefficients, η (0) and η (1) . For the six aromatic vapors, the Rainwater–Friend theory for the initial density dependence of the viscosity was used to derive η (0) values. Finally, reliable η (0) and also η (1) values for R134a were selected as reference values in the measured temperature range to be applied when generating a new viscosity formulation. [ABSTRACT FROM AUTHOR]

Various energy and exergy performance parameters of an automotive heat pump (AHP) with R1234yf have been investigated and compared with those of the baseline system with R134a. For this aim, an AHP system was set up from the components of an air-conditioning system employed in a compact car and equipped with instruments for mechanical measurements. It was tested with R1234yf and R134a by changing the compressor speed and air stream temperatures incoming the outdoor and indoor units. Using test data, energy and exergy analyses of the AHP were performed, and its performance parameters were evaluated. The R1234yf system provided conditioned air temperatures in the range of 29.9–59.3 °C, heating capacities in the range of 1.96–3.14 kW and coefficient of performance (COP) values in the range of 2.44–4.56. It yielded 3.3–10.8 °C lower conditioned air temperature, 9.2–15.4% lower heating capacity, 1.6–7.1% lower COP, 13.8–21.6 °C lower compressor discharge temperature, 3.1–19.2% higher total exergy destruction rate per unit heating capacity but significantly less TEWI in comparison with the system with R134a. Moreover, the R1234yf system yielded larger exergy destructions in the outdoor unit, compressor and expansion device but lower exergy destruction in the indoor unit. These findings reveal that R1234yf can be used in AHP systems in expense of less heating capacity, lower COP and higher exergy destruction rate per unit heating capacity in comparison with R134a. [ABSTRACT FROM AUTHOR]

The pressure drop around the well in the production from a gas condensate reservoir causes the formation of condensate in the area before it reaches the well and surface space. This condensate and occasionally water in the porous medium can block the well and create an additional pressure drop. Studies show that the chemical treatment of this area eliminates the problem by altering the reservoir rock wettability toward a moderate and strong gasphilicity. For this purpose, fluoropolymers-, fluorosurfactants-, and fluorochemicals-coated nanoparticles can be used. In this work, we have studied two types of fluoride gas namely R134A and R404A, which are widely used in refrigeration industry as refrigerant gases, perfumery, and industrial detergents. The basis of this study was the aging of rock samples in thin sections and plugs in these two gases at different pressures above the critical pressures of them at 70 °C at different times and then conducting the contact angle experiments by placing the drop of water and condensate on the cross sections and then performing imbibition tests using plugs. The results show that in addition to the efficiency of both gases in wettability alteration to gasphilic, the gasphilic intensity obtained at constant temperature depends on the pressure and the aging time of the samples. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study on the film condensation heat transfer characteristics of a horizontal smooth tube and an enhanced tube using R134a, R1233zd(E) and R1234ze(E). The objectives of this paper are to develop experimental correlations of heat transfer for enhanced tubes used in a film type condenser and to provide a guideline for design of the film type condenser. Tests are performed on a horizontally smooth tube with a 19.05 mm diameter and three enhanced tubes. The temperature of the saturated vapor inside the condenser is 38 °C. In the case of the horizontal smooth tube, the film condensation heat transfer coefficients of R1234ze(E) and R1233zd(E) were approximately 10.97% and 10.04% lower than those of R134a, respectively. The experimental values obtained from the horizontal smooth tube agreed well with the theoretical value of Nusselt's film which were within the ±10% error range. In the enhanced tubes experiment, the film condensation heat transfer characteristics according to the number of knurling and Fin per inch were examined. The enhanced tubes E.T(C)-1 and E.T(C)-3 exhibit a fin per inch number value of 55 and 85 and 107, respectively. Moreover, the fin per inch and knurling number of E.T(C)-5 are 60 and 117, respectively. As a result, the film condensation heat transfer coefficient was found to decrease with increasing heat flux, and E.T (C) -5 showed the highest average film condensation heat transfer coefficient for all refrigerants. Based on the experimental results, the effect of the fin per inch number on the heat transfer coefficient outside the tube is greater than that of the knurling number. In this study, the equations for film condensation heat transfer coefficient for each refrigerant and each enhanced were derived tube according to the heat flux, and a total of nine correlations were observed to have an accuracy of ±10% within the experimental range. [ABSTRACT FROM AUTHOR]

In this study, performance characteristics of an automotive heat pump (AHP) system using R1234yf and R134a were investigated. Compressor speeds, air temperature and air flow velocity significantly influence the system performance parameters. Therefore, the effect of compressor speeds, air flow velocities and temperatures on the system performance characteristics were evaluated under various test conditions. Optimum experimental conditions were arranged to determine the performances of the AHP system. As a result, the heating performance of R1234yf is lower than R134a. The heating performance of AHP systems gets higher as air flow velocities drop. While the air flow velocities raised up from 1.2 to 4.5 m s−1, the heat capacity was decreased by 15%. Change in air velocities plays more role on the performance characteristics than the change in ambient temperature at low air flow velocities. Comparing the suction and discharge pressures of both the R134a and R1234yf, R1234yf is higher because of its vapour densities. Finally, R1234yf can be used in AHP systems for both cooling and heating applications. [ABSTRACT FROM AUTHOR]

The heat transfer characteristics of a thin porous copper-coated wickless heat pipe using R134a as a working fluid is investigated and is compared for its performance with uncoated wickless heat pipe using the same working fluid. An electroplating process was utilised to form a porous structure of copper over the inner surface of the wickless heat pipe. The experiments were carried out in the heat input range between 50 and 250 W. The thermal resistance of heat pipe at three different inclination angles such as 0°, 45° and 90° with horizontal are investigated. The results showed that 45° inclination has the lowest resistance with significant improvement in heat transfer characteristics. The coated wickless heat pipe exhibited a low thermal resistance when compared to uncoated wickless heat pipe. The condenser and evaporator heat transfer coefficients of a coated wickless heat pipe were found to be higher by about 11% and 25%, respectively, when compared to uncoated heat pipe for a heat flux of 10 kW m−2 and inclination of 45°. The magnitudes of dimensionless numbers (such as, Bo, We, Ku and Co) on coated and uncoated wickless heat pipes are also found. [ABSTRACT FROM AUTHOR]

Ejector refrigeration has the advantage of low capital cost, simple design, reliable operation, long lifespan and almost no maintenance. The only weakness is the low efficiency and its intolerance to deviations from design operation condition. R134a used in ejector refrigeration system gives better performance in comparison with many other environmental friendly refrigerants as the generation temperature is from 75°C to 80°C. The present work experimentally investigated the on-design and off-design performance of the ejector with fixed geometry using R134a as refrigerant, and cycle performance of the ejector refrigeration system. The experimental prototype was constructed and the effects of primary flow inlet pressure, secondary flow inlet pressure and ejector back pressure on ejector performance and cycle performance were investigated respectively. The operation conditions are: primary flow inlet pressure from 2.2 MPa to 3.25 MPa, secondary flow inlet pressure from 0.36 MPa to 0.51 MPa, ejector back pressure from 0.45 MPa to 0.67 MPa. Conclusions were drawn from the experimental results, and the experimental data can be used for validation of theoretical model for both critical and subcritical mode. [ABSTRACT FROM AUTHOR]

The refrigerant R134a is to be phasing out soon in automobile air conditioning applications due to its high global warming potential of 1430. Hence, it is essential to identify a sustainable alternative refrigerant to phase out R134a in automobile air conditioners. This paper presents the experimental thermodynamic performance of R430A (composed of R152a and R600a, in the ratio of 76:24, by mass) as a drop-in substitute to replace R134a in automobile air conditioners. The experiments were carried out in an automobile air conditioner test setup equipped with a variable frequency drive electrical motor. During experimentation, the ambient temperature and ambient relative humidity were maintained at 35 ± 1 °C and 65 ± 5%, respectively. The compressor speed was varied in the range between 1000 and 3000 rpm. The results showed that the coefficient of performance of an automobile air conditioner working with R430A was found to be 12–20% higher with 6–11% reduced compressor power consumption when compared to R134a. The R430A has 2–6 °C higher compressor discharge temperature when compared to R134a. The physical stability of the lubricant used in the compressor was retained while operating with R430A. The maximum exergy destruction occurs in the compressor (0.28 kW for R134a and 0.24 kW for R430A) followed by evaporator (0.16 kW for R134a and 0.14 kW for R430A), condenser (0.14 for R134a and 0.12 kW for R430A) and expansion valve (0.043 kW for R134a and 0.039 kW for R430A) at a compressor speed of 1000 ± 10 rpm. The exergy destruction of the system operating with R430A was found to be 12–28% lower when compared to R134a systems due to its favorable thermo-physical properties. The total equivalent warming impact of R430A was found to be lower when compared to R134a by about 47.3%, 35% and 32.4% for LPG, petrol and diesel vehicles, respectively. The results confirmed that R430A is a good drop-in substitute to replace R134a in existing automobile air conditioning systems. [ABSTRACT FROM AUTHOR]

This paper experimentally investigated exergetic performance analysis of vapor compression refrigeration system using R450a as a replacement for R134a at different evaporator and condenser temperatures within controlled environmental conditions. The exergetic performance analysis of the vapor compression refrigeration system with test parameters including efficiency defects in the components, total irreversibility, and exergy efficiency of the refrigeration system was performed. Findings showed that the total irreversibility and exergy efficiency of the vapor compression refrigeration system using R450A refrigerant were lower and higher than R134a by about 15.25–27.32% and 10.07–130.93%, respectively. However, the efficiency defect in the condenser, compressor, and evaporator of the R450A refrigeration system was lower than R134a by about 16.99–26.08%, 5.03–20.11%, and 1.85–15.85%, respectively. Conversely, efficiency defect in the capillary tube of the R450A refrigeration system was higher than R134a by about 14.66–78.97% under similar operating conditions. Overall, it was found that the most efficient component was the evaporator, and the least efficient component was the compressor for both refrigerants. [ABSTRACT FROM AUTHOR]

This study investigates numerically the thermodynamic analysis of various refrigerants on the basis of vapor compression refrigeration cycle. The refrigerants studied are R134a, R152a, R1234yf, R404A, R407C, R410A and R507A. The aim of this research is to find the alternative refrigerant of R134a numerically. EES Professional V9.944-3D is used in the modeling of thermodynamic cycle of VCRC and calculating the performance parameters of VCRC. The comparison of thermodynamic VCRC for all the refrigerants is made. The performance parameters include: cooling capacity, input power of compressor, COP, compression ratio and discharge temperature. These parameters are calculated at engine speeds of 1000 rpm, 2000 rpm and 3000 rpm, condenser temperature of 50∘C and evaporator temperature of 5∘C. The compressor volumetric efficiencies are taken as 0.75, 0.65 and 0.55 corresponding to engine speeds of 1000 rpm, 2000 rpm and 3000 rpm. The results of performance parameters for all refrigerants studied are exported to MATLAB R2017a software where the comparative analysis is performed. Results show that R152a is the only refrigerant which can be used as alternative in current AACS with minimum modification. The cooling capacity of R152a is slightly less than that of R134a, while its COP is found to be higher than that of R134a. R152a shows the highest COP improvement of 5.33% at engine speed of 1000 rpm. It has very low GWP and almost same saturation pressure corresponding to condenser and evaporator temperature as that of R134a, so it can serve as alternative refrigerant in current AACS. [ABSTRACT FROM AUTHOR]

This paper experimentally investigated and also modeled using artificial neural networks (ANN) approach the energy analysis of a domestic refrigerator using selected charges of LPG refrigerants (40, 50, 60 and 70 g) and different concentrations (0, 0.2, 0.4 and 0.6 gL−1) of TiO2-based nanolubricants as replacement for R134a refrigerant. The parameters for energy analysis include: compressor power consumption, cooling capacity, COP, compressor discharge temperature and pressure ratio. The findings showed that cooling capacity and COP of the domestic refrigerator using LPG refrigerant with TiO2 nanoparticles dispersed in a mineral oil lubricant was found to be higher than that of R134a by around 18.74-32.72 and 10.15-61.49%, respectively. Furthermore, compressor power consumption and pressure ratio of the domestic refrigerator using LPG refrigerant with TiO2-mineral oil lubricant were also found to be lower than that of R134a by about 3.20-18.1 and 2.33-8.45%, respectively, under similar conditions. The compressor discharge temperature was also found to be lower using LPG refrigerant with lubricant TiO2-mineral oil than R134a. The results further suggested that the best energetic performance of the domestic refrigerator was obtained using 40 g charge of LPG refrigerant with TiO2-mineral oil lubricant at 0.4 gL−1 of TiO2 concentration under similar operating conditions. The predictions from ANN models had excellent alignment with experimental results giving a range of values for R2 from 0.914 to 0.970, RMSE from 0.111 to 2.317, and MAPE from 0.865 to 3.148%. [ABSTRACT FROM AUTHOR]

In this paper, a novel exergy based charge optimisation technique is proposed instead of coefficient of performance (COP) based method for a mobile air conditioning system. The exergy destructions in each of the components in the system as a function of compressor speed and refrigerant charge level were estimated based on experimental data. It was found that the COP of the system decreases as the compressor speed increases, while the total exergy destruction in the system increases. The exergetic analysis of performance data showed that the percentage loss in the compressor, evaporator, condenser and thermostatic expansion valve lies in the range of 59.88-69.9%, 17.53-25%, 7.80-16.36% and 3.05-15.73%, respectively. Based on COP, the optimum charge varied with respect to compressor speed. The exergy based optimisation is found to be more reliable and consistently yielding a single optimum charge of 620 g irrespective of the compressor speed. The maximum exergetic efficiencies at 620 g were 43.32% and 38.15% for 900 rpm and 1800 rpm respectively. [ABSTRACT FROM AUTHOR]

This paper presents effects of heating directions on heat transfer performance of R134a flow boiling in micro- channel heat sink. The heat sink has 30 parallel rectangular channels with cross-sectional dimensions of 500μm width 500μm depth and 30mm length. The experimental operation condition ranges of the heat flux and the mass flux were 13.48 to 82.25 W/cm and 373.3 to 1244.4 kg/ms respectively. The vapor quality ranged from 0.07 to 0.93. The heat transfer coefficients of top heating and bottom heating both were up to 25 kW/m2 K. Two dominate transfer mechanisms of nucleate boiling and convection boiling were observed according to boiling curves. The experimental results indicated that the heat transfer coefficient of bottom heating was 13.9% higher than top heating in low heat flux, while in high heat flux, the heat transfer coefficient of bottom heating was 9.9%.higher than the top heating, because bubbles were harder to divorce the heating wall. And a modified correlation was provided to predict heat transfer of top heating. [ABSTRACT FROM AUTHOR]

The effects of different refrigerants on heat transfer performance of pulsating heat pipe (PHP) are investigated experimentally. The working temperature of pulsating heat pipe is kept in the range of 20°C-50°C. The startup time of the pulsating heat pipe with refrigerants can be shorter than 4 min, when heating power is in the range of 10W?100W. The startup time decreases with heating power. Thermal resistances of PHP with filling ratio 20.55% were obviously larger than those with other filling ratios. Thermal resistance of the PHP with R134a is much smaller than that with R404A and R600a. It indicates that the heat transfer ability of R134a is better. In addition, a correlation to predict thermal resistance of PHP with refrigerants was suggested. [ABSTRACT FROM AUTHOR]

A thermodynamic analysis is performed on three different configurations of R134a two-stage vapor compression refrigeration systems designed to equip cold store rooms. For economic and commercial reasons relating to agricultural activities in southern Tunisia, two seasonal food products, dates and poultry, are selected for storage at different temperatures. Performance optimization of the refrigeration systems is investigated under various operating conditions in order to choose the most efficient for a given situation. The three-stage vapor compression refrigeration systems have the same main components, but they differ in the arrangement of the flash separator. For the first considered system, the flash separator is installed before the first evaporator. In the second system, the flash separator is introduced before the second evaporator. For the third refrigeration system, the flash separator is placed before the two evaporators. An analytic study is performed in order to analyze the influence of the condensing temperature, the inter-stage pressure, the subcooling, and the superheat on the system performances. For the same operating conditions, each cycle is optimized with regard to energy performance, refrigeration efficiency, total compressor power consumption, and specific cooling capacity. A comparison between the obtained results for the three considered cycles is established. Optimum values of evaporators' superheat and inter-stage pressure are determined. [ABSTRACT FROM AUTHOR]

A new refrigerant is needed because the GWP of the R404A and R134a that are used in existing refrigerated trucks and automotive air conditioners is so high. This study predicts cooling performance by using an analytical model, for refrigeration systems using R404A and R134a. Furthermore, the performances of those systems were compared with those of alternative refrigeration systems using R1234yf and R744. The performance data of the analytical model had a trend similar to that of the experimental data: the average error between the analytical and experimental results was within 5.4%. The frost thickness of the R404A system for all operating conditions was about 2.4-3.7% larger than that of other systems because the evaporating temperature of the R404A system was lower than that for other refrigerants. For various operating conditions, the coefficient of performance (COP) of the R134a system was higher than that of other systems, while the R744 system showed the lowest performance. However, the COP reduction of the R744 system with operating time was the smallest because the thermodynamic properties of R744 were very superior. In addition, the frost thickness was seriously affected by the variations of indoor air temperature and compressor rotation speeds, and the system performance decreased significantly for severe operating conditions. [ABSTRACT FROM AUTHOR]

Cascade cycle is widely applied to heat pumps operating at low ambient temperature to overcome problems such as low heating capacity and Coefficient of performance (COP) deterioration A number of researches have been conducted on cascade cycle heat pumps, but most of those studies were focused on system optimization to determine optimal intermediate temperature in air-to-water heat pumps. However, experimental optimization in regard to air and water heating simultaneously using a cascade cycle has been an understudied area. Therefore, we focused on experimental analysis for a cascade system with Variable refrigerant flow (VRF) heat pumps. Experiments were conducted under a variety of operating conditions, such as ambient and water inlet temperature. COP increased up to 16% when water inlet temperature decreased. COP of VRF heat pumps with cascade cycle is three-times higher compared with conventional boilers as well as 17% higher compared to single heat pumps. [ABSTRACT FROM AUTHOR]

The present study reports an experimental evaluation of heat transfer characteristic of R134a flow boiling in micro-channel heat sink. The heat sink is composed of 30 parallel rectangular micro-channels with cross-sectional dimensions of 500μm width and depth, as well as total length 30mm. Experiments were conducted with heat flux up to 80.212 W/cm, mass velocity ranging from 373.33 to 1244.44 kg/ms, vapor quality ranging from 0.06 to 0.9. The wall temperature of heat sink heated could be controlled at around 50°C. Heat transfer coefficient could be up to 180 kW/mK. Two dominating flow patterns were observed by analyzing boiling curves. The heat transfer characteristics of nucleate boiling and convective boiling were presented in the study. Revised correlations of R134a flow boiling in micro-channel heat sink were carried out with the consideration of nucleate boiling and convective boiling mechanisms. [ABSTRACT FROM AUTHOR]

In our earlier studies, it has been stated that the validity and limits of correlations developed for the calculation of heat transfer processes in the evaporator and condenser of heat pumps are not published in general. The values yielded for model structures and process characteristics indicate extreme ranges of standard deviation. While the description and physical and mathematical modeling of phenomena occurring in heat pump components have developed really much and the mathematical accuracy of solutions can be increased at one's own discretion, descriptions of changes in heat transfer and heat transfer coefficients in the course of refrigerant flow are quite uncertain. At the same time, these factors highly influence the accuracy of the solution. Our study presents the measurements and the new proposed heat transfer correlations, developed on the basis of such measurements, which can be used for calculating heat transfer in heat pump evaporators and condensers with higher accuracy than existing correlations in the literature. [ABSTRACT FROM AUTHOR]

The Reynolds analogy and its modifications are applied to forced convection laminar in-tube condensation to predict the heat transfer coefficient of R134a by means of well-known two-phase friction factors and agreed void fraction models and correlations explained in the authors' previous works. The vertical test section is a 0.5 m long countercurrent flow double tube heat exchanger with refrigerant flowing in the inner smooth copper tube (8.1 mm i.d.) and cooling water flowing in the annulus (26 mm i.d.). The test runs are performed at average saturated condensing temperatures of 40 °C ( Pr = 0.92) and 50 °C ( Pr = 0.97). The heat fluxes are between 10.16 and 66.61 kW m while the mass fluxes are between 260 and 515 kg m s for the vertical test sections. The Reynolds' model is modified by various two-phase flow models and correlations to account for the partial condensation inside the tube. The refrigerant side heat transfer coefficients are determined within ±30% using the two-phase friction factors of Wallis, Moeck, Fore et al., while all the proposed friction factor correlations for the Reynolds analogy, Prandtl and Taylor analogy, and Colburn analogy predict the experimental friction factor within a ±20% deviation band. The importance of altering the Prandtl number to the Reynolds analogy ( Pr = 1) is also shown in the paper. [ABSTRACT FROM AUTHOR]

Viscosity measurements have been carried out with a falling-cylinder instrument in the compressed liquid and supercritical regions of the hydrofluorocarbon 1,1,1,2-tetrafluoroethane (R134a). A highly pure sample was used. The measurement region at temperatures from 293.15 K to 438.15 K with pressures from 10 MPa to 400 MPa extends the existing data range substantially. With estimated uncertainties of 3.5 % for viscosity, the greater of 1 MPa or 0.5 % for pressure, and 0.4 K for temperature, the new results can be used to reconcile inconsistencies between literature data sets. They also provide a test of the extrapolation capability of existing viscosity correlations for this fluid and enable the development of a more accurate and wider ranging formulation. [ABSTRACT FROM AUTHOR]

Superheated emulsion detector is known to detect neutrons, γ-rays and other charged particles. The present work includes the study of nucleation efficiency of superheated drops of one of the CFC-free liquids, R134a (CHF), to fast neutrons, its response to γ-rays from Am and Cs and compare its nucleation efficiency with that of R12. The observation indicates that because of the presence of hydrogen, the nucleation efficiency is less in R134a than in R12 in the present neutron energy range of consideration. R134a is one of the most environment-friendly, commercially available liquid that is suitable for superheated drop detector, specially in neutron dosimetry and one needs to investigate it in detail. [ABSTRACT FROM AUTHOR]

Thermal conductivity and thermal diffusivity of “ozone-safe” refrigerant R134a in liquid state within the range of temperatures 295.9–354.9 K and pressures from the liquid — vapor equilibrium line up to 4.08 MPa have been studied by high-frequency thermal-wave method. The experimental uncertainties of the temperature, pressure, thermal conductivity and thermal diffusivity measurement errors were estimated to be 0.1 K, 3 kPa, 1.5 and 2.5 %, respectively. Values of thermal conductivity and thermal diffusivity of liquid R134a on saturated line have been calculated. Approximation dependences for thermal conductivity and thermal diffusivity within the whole studied range of temperatures and pressures as well as on the saturated line have been obtained. [ABSTRACT FROM AUTHOR]

Light scattering by thermally excited capillary waves on liquid surfaces or interfaces can be used for the investigation of viscoelastic properties of fluids. In this work, we carried out the simultaneous determination of the surface tension and the liquid kinematic viscosity of some alternative refrigerants by surface light scattering (SLS) on a gas–liquid interface. The experiments are based on a heterodyne detection scheme and signal analysis by photon correlation spectroscopy (PCS). R23 (trifluoromethane), R32 (difluoromethane), R125 (pentafluoroethane), R143a (1,1,1-trifluoroethane), R134a (1,1,1,2-tetrafluoroethane), R152a (1,1-difluoroethane), and R123 (2,2-dichloro-1,1,1-trifluoroethane) were investigated under saturation conditions over a wide temperature range, from 233 K up to the critical point. It is estimated that the uncertainty of the present surface tension data for the whole temperature range is less than ±0.2 mN·m−1. For temperatures up to about 0.95 Tc, the kinematic viscosity of the liquid phase could be obtained with an absolute accuracy of better than 2%. For the highest temperatures studied in this work, measurements for the kinematic viscosity exhibit a maximum uncertainty of about ±4%. Viscosity and surface tension data are represented by a polynomial function of temperature and by a van der Waals-type surface tension equation, respectively. The results are discussed in detail with comparison to literature data. [ABSTRACT FROM AUTHOR]

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The thermal conductivities of ternary refrigerant mixtures of difluoromethane (R32), pentafluoroethane (R125), and 1,1,1,2-tetrafluoroethane (R134a) in the liquid phase have been measured by the transient hot-wire method with one bare platinum wire. The experiments were performed in the temperature range of 233 to 323 K and in the pressure range of 2 to 20 MPa at various compositions. The measured data are correlated as a function of temperature, pressure, and composition. From the correlation, we can calculate the thermal conductivity of pure refrigerants and their binary or ternary refrigerant mixtures. The uncertainty of the measurements is estimated to be ±2%. [ABSTRACT FROM AUTHOR]

The p– ρ– T relationships and constant volume heat capacity Cv were measured for ternary refrigerant mixtures by isochoric methods with gravimetric determinations of the amount of substance. Temperatures ranged from 200 to 400 K for p– ρ– T and from 203 to 345 K for Cv, while for both data types pressures extended to 35 MPa. Measurements of p– ρ– T were carried out on compressed gas and liquid samples with the following mole fraction compositions: 0.3337 R32+0.3333 R125+0.3330 R134a and 0.3808 R32+0.1798 R125+0.4394 R134a. Measurements of Cv were carried out on liquid samples for the same two compositions. Published p– ρ– T data are in good agreement with this study. For the p– ρ– T apparatus, the uncertainty is 0.03 K for temperature and is 0.01% for pressure at p>3 MPa and 0.05% at p<3 MPa. The principal source of uncertainty is the cell volume (∼28.5 cm3), with a standard uncertainty of 0.003 cm3. When all components of experimental uncertainty are considered, the expanded relative uncertainty (with a coverage factor k=2 and, thus, a two-standard deviation estimate) of the density measurements is estimated to be 0.05%. For the Cv calorimeter, the uncertainty of the temperature rise is 0.002 K and for the change-of-volume work it is 0.2%; the latter is the principal source of uncertainty. When all components of experimental uncertainty are considered, the expanded relative uncertainty of the heat capacity measurements is estimated to be 0.7%. [ABSTRACT FROM AUTHOR]

The p– ρ– T relationships were measured for binary refrigerant mixtures by an isochoric method with gravimetric determinations of the amount of substance. Temperatures ranged from 200 to 400 K, while pressures extended up to 35 MPa. Measurements were conducted on compressed gas and liquid samples with the following mole fraction compositions: 0.4997 R32+0.5003 R134a, 0.3288 R32+0.6712 R134a, 0.4996 R32+0.5004 R125, 0.5001 R125+0.4999 R134a, and 0.5000 R125+0.5000 R143a. Most published p– ρ– T data are in good agreement with this study. The uncertainty is 0.03 K for temperature and is 0.01% for pressure at p>3 MPa and 0.05% at p<3 MPa. The principal source of uncertainty is the cell volume (∼28.5 cm3), with a standard uncertainty of 0.003 cm3. When all components of experimental uncertainty are considered, the expanded relative uncertainty (with a coverage factor k=2 and, thus, a two-standard deviation estimate) of the density measurements is estimated to be 0.05%. [ABSTRACT FROM AUTHOR]

Molar heat capacities at constant volume Cv were measured for binary refrigerant mixtures with an adiabatic calorimeter with gravimetric determinations of the amount of substance. Temperatures ranged from 200 to 345 K, while pressures extended up to 35 MPa. Measurements were conducted on liquid samples with equimolar compositions for the following binary systems: R32/R134a, R32/R125, R125/R134a, and R125/R143a. The uncertainty is 0.002 K for the temperature rise and is 0.2% for the change-of-volume work, which is the principal source of uncertainty. The expanded relative uncertainty (with a coverage factor k=2 and thus a two-standard deviation estimate) for Cv is estimated to be 0.7%. [ABSTRACT FROM AUTHOR]

This paper reports the results of an international project coordinated by the Subcommittee on Transport Properties of Commission I.2 of the International Union of Pure and Applied Chemistry. The project has been conducted to investigate the large discrepancies between the results reported by various authors for the transport properties of R134a and culminates the effort which was initially described in 1995. The project has involved the remeasurement of the transport properties of a single sample of R134a in nine laboratories throughout the world in order to test the hypothesis that at least part of the discrepancy could be attributed to the purity of the samples. This paper provides an intercomparison of the new experimental results obtained for the viscosity and thermal conductivity in the vapor, liquid, and supercritical gas phases. The viscosity measurements were made with a variety of techniques including the vibrating wire, oscillating disk, capillary flow, and falling body. Thermal conductivity was measured using transient bare and anodized hot wires, steady-state anodized hot wires, and light scattering. Agreement between a variety of experimental techniques using the standard round-robin sample is necessary to demonstrate that some of the discrepancies in earlier results were due to sample impurities. Identification of disagreement between data using one experimental technique relative to other techniques may suggest modifications that would lead to more accurate measurements on these highly polar refrigerant materials. It is anticipated that the new data which have been measured on this IUPAC round-robin sample will aid in the identification of the reliable data sets in the literature and ultimately allow the refinement of the IUPAC reference-data correlations for the transport properties of R134a. [ABSTRACT FROM AUTHOR]

The saturated liquid viscosity of ammonia (NH3) and of the hydrofluorocarbons, difluoromethane (CH2F2, R32) and 1,1,1,2-tetrafluoroethane (CF3–CH2F, R134a), was measured in a sealed gravitational viscometer with a straight vertical capillary. The combined temperature range was from 250 to 350 K. The estimated uncertainty of the ammonia measurements is ±3.3 and ±2 to 2.4% for the hydrofluorocarbons with a coverage factor of two. The results are compared with literature data which have been measured with capillary viscometers of different design. Agreement within the combined experimental uncertainty is achieved when some of the literature data sets are corrected for the vapor buoyancy effect and when a revised radial acceleration correction is applied to data which were obtained in viscometers with coiled capillaries. An improved correction for the radial acceleration is proposed. It is necessary to extend inter-national viscometry standards to sealed gravitational capillary instruments because the apparent inconsistencies between refrigerant viscosity data from different laboratories cannot be explained by contaminated samples. [ABSTRACT FROM AUTHOR]

This paper reports the results of the measurement of the viscosity of R134a close to the saturation line in the vapor phase. The new measurements were carried out in a vibrating-wire viscometer specially constructed for the purpose, and the results have an accuracy of ±2%. In addition, the opportunity is taken to present a reevaluation of earlier measurements along the saturation line of the viscosity of R32 and R125. Improved equations of state for these fluids are now available and can be employed to generate improved values for the viscosity. [ABSTRACT FROM AUTHOR]

Thermal conductivities of zeotropic mixtures of R125 (CF3CHF2) and R134a (CF3CH2F) in the liquid phase are reported. Thermal conductivities have been measured by a transient hot-wire method with one bare platinum wire. Measurements have been carried out in the temperature range of 233 to 323 K and in the pressure range of 2 to 20 MPa. The dependence of thermal conductivity on temperature, pressure, and composition of the binary mixture is presented. Measured thermal conductivity data are correlated as a function of temperature, pressure, and overall composition of the mixture. The uncertainty of our measurements was estimated to be better than 2%. [ABSTRACT FROM AUTHOR]

A bibliographic compilation is given on thermophysical properties of the environmentally acceptable hydrofluorocarbon blends R404A, R407C, and R410A. These refrigerant blends are still under investigation and meant to replace the transitional hydrochlorofluorocarbon R22 and the azeotrope R502. In a second part reliable formulations to calculate thermophysical-property surfaces of some selected well investigated fluids used in refrigeration are recommended. The fluids water, air, carbon dioxide, ammonia, R134a, R123, and R152a are subjects of that part. [ABSTRACT FROM AUTHOR]

An apparatus is described which is capable of measuring the enthalpy of vaporization in the temperature range from 100 to 250 K. The sample (R134a; purity, at least 99.999%) is located in the measuring cell at the saturated vapor pressure, p = ps. A control circuit allows p to be kept constant by opening a motor-operated valve to a weighing cylinder after having switched on the electrical measuring cell heater. During the experiment, the temperature is kept constant within a 10mK. In the range 180 to 230 K, the data for R134a are compared with calculated values from the fundamental equation given by Tillner-Roth and Baehr, which is recommended by Annex 18 of the International Energy Agency (IEA) as an international standard. Good agreement within a standard uncertainty of 1.6×10−3 is obtained. At temperatures of only 10 K above the triple-point temperature, the enthalpy of vaporization calculated from the Clausius–Clapeyron equation shows considerable uncertainty due to the determination of the small vapor pressure. It is chiefly in this range that it is advantageous to have the new apparatus. [ABSTRACT FROM AUTHOR]

Measurements of the viscosity of refrigerants R124, R125, R134a, and R152a in the vapor phase are presented. The measurements, performed in a new vibrating-wire instrument, cover a temperature range from 273 to 333 K from about atmospheric pressure up to below the saturation pressure. The uncertainty of the reported values is estimated to be better than ±1%. Comparison with measurements of other investigators reveals a lack of reliable data in the vapor region for these compounds. [ABSTRACT FROM AUTHOR]

Measurements of the thermal conductivity of refrigerants R124, R125, and R134a in the vapor phase are presented. The measurements, performed in a newly developed transient hot-wire instrument, cover a temperature range from 273 to 333 K and a pressure range from about atmospheric up to below the saturation pressure. A finite-elements program developed allowed the reexamination of the major corrections employed in the analysis of the results. The uncertainty of the reported values is estimated to be better than ±1%. Comparisons with measurements of other investigators along the saturation line show a lack of reliable thermal conductivity data in the vapor phase for these compounds. [ABSTRACT FROM AUTHOR]

A model for estimating second and third virial coefficients, which has been used successfully to represent the behavior of pure gases and binary mixtures, was applied to a ternary mixture. An estimate for the ternary third virial coefficient. C 123, was added to the model. Three experimentally determined binary interaction parameters were also used. The model has been applied to the ternary mixture CH2F2+CF3CHF2+CF3CH2F (R32+R125+R134a). The results are useful for calculating gas-phase densities, thermodynamic properties, and fugacities for phase equilibrium calculations. The use of such models leads to a considerable economy of effort in the case of multicomponent mixtures. Examples of the thermodynamic properties are given for the equimolar ternary mixture in the range from the dew-point temperature to 400 K at pressures of 0.5, 1, and 2 MPa. Calculated densities and speeds of sound are compared with new experimental values for a near-equimolar composition. [ABSTRACT FROM AUTHOR]

The idea of adsorption based refrigerator was conceived in the year 1961 by Vickers. The present work reports development of a sorption compressor based J-T refrigerator with R134a alone as a working fluid and a three component mixture of R134a, Ethane and Methane. Commercially available activated carbon, obtained from coconut shell, is used as an adsorbent. The reported compressor is a four cell structure and uses isenthalpic expansion of R134a for cooling purpose. A lowest temperature of −8°C is obtained giving 5 W of refrigeration effect for R134a. The work is further extended to study the effect of various parameters like adsorption-desorption cycle time, heater power input and capillary tube length on the low temperature obtained from the refrigerator. Experiments are then carried out using a three component mixed refrigerant, a low temperature of −54°C at no load is achieved. Also a continuous trouble-free operation is observed. [ABSTRACT FROM AUTHOR]