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Some new, low-global warming potential refrigerants will be flammable, and the laminar burning velocity is a useful parameter for quantifying fire risk. Laminar burning velocity measurements have been made using a constant volume experiment with dry air and the refrigerant R-152a (CH3CHF2), pure and blended with R-134a (CH2FCF3), or R-1234yf (CF3CFCH2). The resulting burning velocity data deduced from the pressure rise in the chamber are presented for a range of fuel air equivalence ratio and loading of the less flammable refrigerant, for unburned gases at 298 K and 101 kPa as well as at 375 K and 253 kPa. For comparison, the 1-D, planar laminar burning velocity was numerically simulated using a recently developed kinetic mechanism that includes a wide range of refrigerants with air. The predicted burning velocities agree reasonably well with the experimental values, and the numerical results are used to understand the kinetic mechanism of the reaction of the refrigerants. Uncertainties in the experimental data from radiation heat losses as well as extrapolation to ambient conditions are explored. [ABSTRACT FROM AUTHOR]

AbstractAn experimental study of post-dryout (PDO) heat transfer in the coolant R-134a was performed in a vertical round tube with upward flow. Experiments were conducted at high pressures from 28.4 bars up to 39.8 bars, corresponding to a reduced pressure of 0.7 to 0.98, respectively. Mass flux was varied in the interval of 300 to 1500 kg/m2∙s, and overall equilibrium vapor quality was between −1.88 and 4.89. Depending on the settings of the experimental parameters, the heat flux was varied from around 11 to 100 kW/m2. The uniformly heated tube had an inside diameter of 10 mm and a heated length of 3000 mm.In total, more than 10 000 PDO data points were obtained. In the PDO region, the wall temperature distributions had similar behavior across the pressure range. At the occurrence of dryout, the wall temperature suddenly increased until it reached a peak. For higher mass flux, the wall temperature decreased after reaching the peak, followed by a second temperature increase with a lower slope. For lower mass flux, the wall temperature kept increasing after the dryout point. The temperature peak after the dryout point was smaller at higher pressure, while this effect was even stronger near the critical pressure. Likewise, the vapor quality corresponding to the first peak shifted to even lower values with increasing pressure. Furthermore, it was found that at increasing pressure and at increasing mass flux, the dryout location and the total temperature distribution shifted toward lower vapor qualities. In addition, several PDO correlations were assessed, and a new correlation for high-pressure conditions was developed and compared with the results of the existing ones. [ABSTRACT FROM AUTHOR]

In present study the effect of nano particle mixing in base refrigerant of R-152 is evaluated. Now a days two biggest environmental issues confronting the world are global warming and ozone depletion. The increasing national and international concern about global warming, as well as the importance placed on the study of this research work has been prompted by energy conservation. Hydro floro carbon is a kind of greenhouse gas that is used in air conditioning and refrigeration and it majorly contribute in global warming issue which is why it is needed to be strictly ban. In this study, we use nano particles mixed with the base refrigerant. Since we know that performance of VCRS is highly depends upon the type of refrigerant used. It is highly recommended to use a refrigerant with good thermo physical properties as they enhance the transfer of heat & increase performance for the system. Nano additives enhance the cross-sectional area of heat transfer which results in better output of the refrigeration system. Different types of metal oxide nano particles are used to compare the performance by various researchers along with carbon nano tubes. Finer the diameter of the particles less is the problem of clogging and chocking arises. Experimentation work is carried out by using different concentration of nano particles to analyze their impact on the system. The efficiency and exergy analysis of alternative refrigerants (hydrocarbon and nano refrigerants) were also investigated. Evaporating temperature, condensing temperature, and refrigerant mass along with varying nano particles concentration are the factors investigated in the refrigeration method. A Computerized refrigeration cycle test rig has been used for these experiments. Trial runs are used to determine the operating ranges of all the chosen parameters. [ABSTRACT FROM AUTHOR]

Multiwalled carbon nanotubes (MWCNTs) exhibit outstanding physical properties, including high thermal conductivity, excellent mechanical strength, and low electrical resistivity, which make them suitable candidates for a variety of applications. The work presented in this paper focuses on the pool boiling performance of refrigerant R-134a on microporous Cu-MWCNT composite surface layers. A two-stage electrodeposition technique was used to fabricate Cu-MWCNT composite coatings. In order to achieve variation in the surface properties of the Cu-MWCNT composite surface layer, electrodeposition was carried out at various bath temperatures (25 °C, 30 °C, 35 °C, and 40 °C). All surfaces coated with the Cu-MWCNT composite demonstrated superior boiling performance compared to the uncoated surface. Heat transfer coefficient (HTC) values for Cu-MWCNT composite surface layers, prepared at bath temperatures of 25 °C, 30 °C, 35 °C, and 40 °C, exhibited improvements of up to 1.75, 1.88, 2.06, and 2.22, respectively, in comparison to the plain Cu surface. [ABSTRACT FROM AUTHOR]

In this study the performance analysis of ice plant is carried out experimentally for different concentration (0.2%, 0.3% and 0.4%) of TiO2 with (POE) lubricant using R-134a as a primary refrigerant in to the system. The performance analysis is carried out based on the parameters such as temperature of brine, pressure ratio, compressor work, refrigerating effect and COP. The pressure and temperature readings are recorded by using the pressure gauge and thermocouples fitted in the test rig for the analysis. The properties of refrigerant are recorded by using the LABVIEW software in computerised test rig. In this analysis it was observed that the minimum compressor work and maximum COP found at 0.4% concentration of TiO2 compared to other concentration. At 0.4% concentration of TiO2 nanoparticles, the efficacy was found to be superior to that of a mixture of R134a and pure lubricant, consuming 16.3% less compressor power and increasing COP by 34.2%. But the thermal conductivity and the density, of the mixture of R134a and nanolubricant are observed higher in comparison with the mixture of R134a and pure lubricant and are increases with increasing the concentration of TiO2.

Multiwalled carbon nanotubes (MWCNTs) exhibit outstanding physical properties, including high thermal conductivity, excellent mechanical strength, and low electrical resistivity, which make them suitable candidates for a variety of applications. The work presented in this paper focuses on the pool boiling performance of refrigerant R-134a on microporous Cu-MWCNT composite surface layers. A two-stage electrodeposition technique was used to fabricate Cu-MWCNT composite coatings. In order to achieve variation in the surface properties of the Cu-MWCNT composite surface layer, electrodeposition was carried out at various bath temperatures (25 °C, 30 °C, 35 °C, and 40 °C). All surfaces coated with the Cu-MWCNT composite demonstrated superior boiling performance compared to the uncoated surface. Heat transfer coefficient (HTC) values for Cu-MWCNT composite surface layers, prepared at bath temperatures of 25 °C, 30 °C, 35 °C, and 40 °C, exhibited improvements of up to 1.75, 1.88, 2.06, and 2.22, respectively, in comparison to the plain Cu surface.

Heat pumps are frequently used for heating, cooling, and air conditioning. It is well known that nanoparticles can improve the coefficients of conduction and convection, increasing heat transfer along with other properties. The considered heat pump was loaded with R-134a. Titanium dioxide (TiO2) and aluminium oxide (Al2O3) were blended with clean water to create a nanoscale solution used to cool the heat pump condensers. A total of three TiO2 and Al2O3 proportions (0.1%, 0.2%, and 0.3%) were used. The study's findings showed that utilizing 0.3% Al2O3 instead of conventional clean water to cool the heat pump condenser boosted the coefficient of performance by 18% while reducing energy consumption by 26%. [ABSTRACT FROM AUTHOR]

The nucleated pool boiling heat transfer experiments for plain and five different reentrant cavity copper tube surfaces in saturated R134a, R32, and R600a have been carried out. The experiments are carried for heat fluxes ranging from 6.92 to 51.71 kW/m2 at saturation temperatures of 7°C and 10°C. A significant increase in the boiling heat transfer coefficient has been observed for all tube surfaces with the reentrant cavity. The nucleate boiling heat transfer coefficient for R134a, R32, and R600a is 1.2–2.8 times more than that for plain tube surfaces. A correlation for reentrant cavity surfaces has also been developed. [ABSTRACT FROM AUTHOR]

An experimental study in condensation has been conducted to analyse the condensation phenomena. The enhancement heat transfer performance is as always highlighted phenomenon for being investigated. The modified surface is a common method for enhancing the performance of condensation since inducing the droplet on the surface. The droplet leads to increasing heat-transfer area, decreasing thermal resistance, and shorten the condensing cycle. The condensation by using water successfully induces droplets on the surface and enhances the heat transfer. But water and refrigerant have different fluid properties which induce different phenomena whereas refrigerant is widely used in industry. In this case, the condensation is conducted on the modified surface by using a commercial promotor to investigate the phenomena. The investigation results show that the surface tension immensely influences the condensate on the surface. Refrigerant is low surface tension fluid which leads to the difficulty of fluid for inducing droplets and almost no enhancement heat transfer performance since the results almost fitted well to Nusselt bare tube prediction around 2443-3063 W/m2 oC with subcooled temperature 2 up to 5 oC.

Due to ever growing 'demand of the energy' and for the capability to remove large quantities of heat from the heating surface, pool boiling heat transfer becomes the main attraction for research in search of finding the efficient means for transferring heat. Following this trend, the present study also investigated the pool boiling performance of refrigerants, mainly, pure refrigerant (R-134a) and natural refrigerant (R-600a), on the plain aluminium and two graphene nanoplatelets (GNPs) reinforced aluminium matrix composite (Al@GNPs) coated aluminium heating surface with different thickness (50 ± 5 µm and 125 ± 6 µm), which were synthesised by the help of a three-step technique involving mechanical milling, screen printing and sintering process on the plane aluminium surface. The test is conducted at a saturation temperature of 10°C and heat fluxes ranging from 8.28 kW/m2 to 75.61 kW/m2. Test results of R-134a and R-600a were compared. It is observed that thicker Al@GNPs composite coated surface showed better HTC but with reduced 'onset of nucleate boiling' (ONB) wall superheat than the plain Al surface. [ABSTRACT FROM AUTHOR]

The present work explores the pool-boiling performance of refrigerants (R-134 and R-1234yf) on the plain Cu and graphene nanoplatelets (G) reinforced Cu matrix (Cu@G) composite coated heating surface. A two-step electrodeposition technique was employed to prepare microporous Cu@G composite coatings. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) studies confirmed the successful fabrication of microporous structure of Cu@G composite coatings. Surface profilometer investigation was done to know the surface roughness of prepared Cu@G composite coatings. Pool boiling experiments were carried out with increasing heat flux from 8.80 kW/m2 to 61.25 kW/m2 at a saturation temperature of 10°C. Test results of R-134 and R-1234yf were compared. The experimental results revealed that the heat transfer coefficients (HTCs) of R-134a were higher than R-1234yf for plain Cu and Cu@G composite coated heating surfaces. [ABSTRACT FROM AUTHOR]

The detection of gaseous refrigerants, necessary for industrial control and environmental monitoring, is explored using rotational spectroscopy in the THz wave region. Rotational absorption spectra for two widely used commercial hydrofluorocarbon (HFC) refrigerants, 1,1,1,2-tetrafluoroethane (R-134a or HFC-134a) and 2,3,3,3-tetrafluoropropene (R-1234yf or HFO-1234yf), are characterized in the 220–330 GHz frequency range at room temperature (297 K) and modest pressures (0.25–8 Torr) using a compact microelectronics-based THz wave spectrometer. The absorption spectra illustrate complex, broad, and repeating structures that result from the blending of hundreds of pressure-broadened rotational lines. The unique and distinct spectra for R-134a illustrate potential for its detection in the present frequency region with estimated detection limits approaching 15 ppm per meter path length in 1 atm of air. The spectra for R-1234yf are less distinct than those for R-134a and illustrate complex structured rotational absorption features in combination with an underlying quasi-continuous absorption that increases in strength to higher frequencies. To our knowledge, this is the first experimental characterization for the spectra of R-134a and R-1234yf in this frequency region. [ABSTRACT FROM AUTHOR]

Pool boiling has been widely employed in electronic, power production and refrigeration systems due to its high efficiency in heat transfer. However, the investigation and application of microporous Al matrix composite coatings to enhance the pool boiling heat transfer (BHT) are very limited. In this study, graphene nanoplatelets reinforced Al matrix (Al@GNPs) composite coatings are fabricated by combining mechanical milling, screen printing and sintering techniques to investigate the pool boiling heat transfer using R-134 as working fluid. The experimental data were obtained at a saturation temperature of 10 °C for heat fluxes ranging from 9.04 kW·m−2 to 73.57 kW·m−2. The effect of various coating thicknesses on boiling characteristics and heat transfer coefficient (HTC) of R-134a were studied and presented in detail. Our results demonstrate that the HTC obtained for Al@GNPs-4 composite coated heating surface is 143% higher than the plain Al heating surface. Enhanced nucleation sites and increased bubble pumping action are the main reasons for the augmented BHT performance on the Al@GNPs composite coated heating surfaces. [ABSTRACT FROM AUTHOR]

The fabrication of porous metallic composite coating on the heating surface to improve pool boiling heat transfer (BHT) performance has received significant attention in recent years. In this work, Cu-GNPs nanocomposite coatings, which were prepared on a copper substrate using various current densities through a two-step electrodeposition technique, were used as heating surfaces to study the pool BHT performance of refrigerant R-134a. The surface morphology, elemental composition, thickness, surface roughness, and porosity of prepared Cu-GNPs nanocomposite coatings are studied and presented in detail. All Cu-GNPs nanocomposite coated surfaces exhibited improved boiling performance compared to the plain Cu surface. The heat transfer coefficient (HTC) values for Cu-GNPs nanocomposite coated Cu surfaces prepared at 0.1, 0.2, 0.3, and 0.4 A/cm² were improved up to 1.48, 1.67, 1.82, and 1.97, respectively, compared with the plain Cu surface. The enhancement in the HTC is mainly associated with the increase in surface roughness, active nucleation site density, and micro/nanoporosity of the heating surface. [ABSTRACT FROM AUTHOR]

• Evaluation of the force convection boiling heat transfer coefficient and pressure drop of a R134a/nano oil mixture in a horizontally-aligned tube with an aluminum helical fin. • SiO 2 –TiO 2 nano particles-based nanocomposites are selected for the preparation of nano oil. • Several values of mass flow rate, and concentration of SiO 2 –TiO 2 nanoparticles have been used. • 89% increase in boiling convection heat transfer coefficient and 16% increase in pressure drop using nano oil (0.4%) and a helical fin. The present study investigates experimentally heat transfer of the forced convection boiling of a R134a/nano oil mixture in a horizontally-aligned tube with an aluminum helical fin. The effects of various parameters including refrigerant mass flow, vapor quality, star-shaped fin, oil concentration and volume fraction of nanoparticles are studied. SiO 2 –TiO 2 nanoparticles are synthesized by applying both ultra-sound irradiation and sol–gel methods. Morphology and size of nanostructures are portrayed through the exact use of scanning electron microscopy, while the phase of the product is investigated by an X-ray diffraction pattern (XRD). The findings indicate that as the mass flow enhances, the heat transfer coefficient rises. The heat transfer coefficient and pressure drop have increased by using a helical fin. Regarding the oil-refrigerant mixture, the heat transfer coefficient augments at low vapor quality and reduces at high vapor quality. By adding nanoparticles, heat transfer increases, but a decreasing trend in heat transfer is observed from a certain vapor quality. The highest percentage of increase in heat transfer at a mass velocity of 380 kg/m2.s is for the case with a fin and a mixture of R134a/nano oil, and this amount is equal to 89%. [ABSTRACT FROM AUTHOR]

Chlorofluorocarbons and hydro chlorofluorocarbons (HCFCs) are replaced by hydroflourocarbons (HFCs) which is not harmful to the ozone layer. However, few of HFCs have a relatively high global warming potential (GWP) and are subject to further examination due to growing concerns about global climate change. The goal now is to find the next generation of environmentally sustainable work fluids with an insignificant direct environmental impact in terms of ozone depletion and global warming potential. This document introduces the mixture of low-GWP refrigerants like R440A, R430A, R1234ze (E)/152a (50:50 by mass), R290/600a (40/60), R290/600(60/40), R290/600(50/50), ARM 42,ARM 42a and AC5 are used to replace R-134a in a domestic refrigeration system without doing any modifications to the system. The performance of the refrigerator was observed in terms of volumetric cooling capacity, blower discharge temperature, and coefficient of performance, refrigeration effect and energy consumption of a blower.

• A drop-in replacement of R-134a with R-152a in a domestic refrigerator was performed. • The energy performance of the system was improved with R-152a. • An environmental impact assessment was carried out by TEWI and LCCP approaches. • Both environmental metrics showed great environmental benefits with R-152a. • The effect of carbon intensity variation on LCCP was investigated. In the European Union F-gas Regulation limited the use of some refrigerants in several applications. Regarding the domestic refrigeration sector, the F-gas Regulation banned the use of refrigerants with GWP values higher than 150. This fact led the scientific community to search for a replacement of R-134a, that is the most common refrigerant used in domestic refrigerators in USA. In this work, a comprehensive environmental analysis of the drop-in substitution of R-134 with a low GWP refrigerant (R-152a) in a no-frost domestic refrigerator was performed. The comparison, based on experimental data, between the environmental performance of the refrigeration system with the two refrigerants was carried out developing two different evaluation methods, which led to the evaluation of TEWI and LCCP, respectively. Both these metrics consider both direct and indirect contributions to global warming. Historical data of different countries were used to forecast the carbon intensity values for the next 15 years, which were then used to evaluate indirect emissions of the system during its lifetime. Considering the Italian case study, the results showed that the refrigerator working with an optimal charge of R-152a, identified as the mass charge that minimises TEWI and/or LCCP index, has better environmental performance than the system working with R-134a, with a reduction of TEWI and LCCP values of 10.3% and 9.4%, respectively. The same comparison, in terms of LCCP, was also performed for other European countries, showing a strong dependence of the LCCP index on carbon intensity values. [ABSTRACT FROM AUTHOR]

The influence of air humidity on flame propagation in mixtures of hydrofluorocarbons (HFCs) with air was studied through numerical simulations and comparison with measurements from the literature. Water vapor added to the air in mixtures of fluorine rich hydrofluorocarbons (F/H ≥ 1) can be considered as a fuel additive that increases the production of radicals (H, O, OH) and increases the overall reaction rate. The hydrofluorocarbon flame is typically a two-stage reaction proceeding with a relatively fast reaction in the first stage transitioning to a very slow reaction in the second stage which leads to the combustion equilibrium products. The transition to the second stage is determined by the consumption of hydrogen-containing species and formation of HF. Despite a relatively small effect of water on the adiabatic combustion temperature, its influence is significant on the reaction rate and on the temperature increase in the first stage of the combustion leading to the increase in burning velocity. The main reaction for converting H 2 O to hydrogen-containing radicals and promoting combustion is H 2 O + F = HF + OH, as demonstrated by reaction path analyses for the fluorine rich hydrofluorocarbons R-1234yf, R-1234ze(E), and R-134a (F/H = 2). The calculated burning velocity dependence on the equivalence ratio ϕ agrees reasonably well with available experimental measurements for R1234yf and R-1234ze(E) with and without the addition of water vapor. In agreement with experimental data, with water vapor, the maximum of burning velocity over ϕ is shifted to the lean mixtures (near ϕ = 0.8). [ABSTRACT FROM AUTHOR]

Two-phase closed thermosiphon system for cooling high heat flux electronic devices was constructed and tested on a lab scale. The performance of the thermosyphon system was investigated using R-134a as a working fluid. The effect of heat flux and the refrigerant pressure on the evaporator side heat transfer coefficient were investigated. It was found that the heat transfer coefficient increases by increasing the heat flux on the evaporator or by reducing the inside pressure. The effect of heat transfer mode of the condenser (natural or forced) also affected the overall heat transfer coefficient in the cycle. At the 200W heating load, the values of the heat transfer coefficients were 32 and 1.5 kW/m². °C, for natural and forced convection modes, respectively. The temperature difference between the evaporator and the refrigerant saturation pressure was found to be dependent on heat flux and the pressure inside the system. At 40W heating load, the heat transfer coefficient was calculated to be 500, 3000 and 7300 W/oC.m2 at 0.152, .135 and 0.117 reduced pressure, respectively. It can be concluded that such a thermosyphon system can be used to cool high heat flux devices. This can be done using an environmentally friendly refrigerant and without any need for power to force the convection at the condenser. [ABSTRACT FROM AUTHOR]

• New method for characterization of wetting behavior based on spreading velocities. • Increase in spreading velocity of PAG-based lubricant in R-134a atmosphere. • Non-uninform spreading accessible by optical analysis. • Decreasing interfacial tension with increasing R-134a pressure at constant temperature. • Temperature dependence of interfacial tension affected by solubility. In the present study, the wettability of ground AISI 321 steel and PTFE surfaces with a polyalkylene glycol-based lubricant in air and 1,1,1,2-tetrafluoroethane (R-134a) atmospheres is characterized. For this, spreading velocities are determined from videos recorded during the continuous dosing of lubricant on the solid surfaces. The results are compared with interfacial tension data for the lubricant measured by the pendant-drop method in air and R-134a atmospheres. Significantly higher wettability was found in the presence of refrigerant atmosphere, on the steel surface and along its grinding grooves, whereas no consistent temperature-dependent trends could be identified. The interfacial tension of the lubricant decreases with increasing temperature at ambient air atmosphere as well as with increasing R-134a pressure at a fixed temperature. The temperature-dependent behavior of the interfacial tension for a given refrigerant pressure is affected by the temperature itself and by the resulting solubility of the refrigerant in the lubricant. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Highlights • Experiment measurements of supercritical R-134a were performed in a horizontal tube. • Two new analytical methods were developed based on the field synergy principle. • Numerical simulations of R-134a were conducted. • The simulation results were analyzed using the two newly-developed methods. Abstract Experimental studies on convective heat transfer characteristics of supercritical R-134a flowing in a horizontal tube with an inner diameter 8 mm were conducted in the range of mass flux 500–1000 kg m−2 s−1, heat flux 20–100 kW m−2 s−1 and pressure 4.3–4.8 MPa. Local wall temperatures and convective heat transfer coefficients of the top and bottom surfaces of the test tube were obtained, and their variational trends with increasing heat flux and mass flux were discussed within the experimental range. To have a quantitative and more comprehensive analysis of convective heat transfer behaviors of supercritical fluids as compared with the conventional methods, two new field synergy analytical methods designated as TCEH and FCEH respectively were developed, motivated by the two basic concepts of the field synergy principle respectively, i.e., the analogy of convective heat transfer to conductive heat transfer and the three general criteria associated with convective heat transfer enhancements. Numerical simulations were performed within the identical parameter ranges, and the effects of buoyancy, heat flux and mass flux on convective heat transfer were analyzed using these two new methods. Finally some new insights into supercritical convective heat transfer were obtained. [ABSTRACT FROM AUTHOR]

In this study, heat transfer coefficients and pressure drops of R-134a inside round and flat tubes are investigated experimentally with mass flux of 450, 550, and 650 kg m−2 s−1 at saturation temperatures of 35°, 40°, and 45°C. The effects of mass flux and saturation temperature on heat transfer coefficient and pressure drop are examined. The maximum enhancement factor and pressure drop penalty are obtained by flat tube (FT-2) up to 2.101 at 450 kg m−2 s−1 and 3.01 at 650 kg m−2 s−1, respectively. The correlation for flat tubes is proposed to predict the heat transfer coefficient within ±20% error. [ABSTRACT FROM AUTHOR]

Highlights • An experimental comparison between R-134a and R-152a is presented. • A domestic refrigerator made to work with R-134a is analysed. • The annual energy consumptions of the device are reported. • The energy saving achievable after the drop-in is evaluated. • A theoretical analysis provides a support to the experimental results. Abstract Among all sectors of refrigeration, one of the most affected by the latest international regulations is the domestic refrigeration. Although for it has been suggested some solutions, such as the construction of household refrigerator operating with the hydrocarbons, there remains the need to find a substitute for R-134a. With the aim of finding a simple implementation solution, in the present work, it is reported an experimental investigation carried out on a domestic no-frost refrigerator designed and built to operate with R-134a and for which a drop-in with R-152a has been realised. Different tests have been performed with the aim to identify the right charge of R-152a too. In line with the standard ISO 15502:2005 (2005), pull-down and 24 h energy consumption experiments have been run to evaluate the performance of R-152a as the drop-in replacement of R-134a in a domestic refrigerator. Also, a theoretical model has been proposed with the aim to give support to the observed energy change. [ABSTRACT FROM AUTHOR]

Abstract In the present work, nucleate boiling heat transfer characteristics of R-134a and R-1234ze refrigerants subject to the influence of lubricant oil on a plate surface were experimentally examined. Eight types of lubricants, including POEA68, POEA120, POEA170, POEB68, POEB120, POEB170, POEC170, and POED 150, were used for investigations; the experiments were carried out at saturated temperatures of 0 °C and 10 °C, respectively. The oil concentrations range from 0% to 10% and heat fluxes vary from 10 kW/m2 to 70 kW/m2. The test results for pure refrigerants are in line with the existing data and correlations. With the presence of lubricant, the heat transfer coefficient may be slightly higher or lower than those of pure refrigerants, depending on the lubricant and operating pressure. However, all the heat transfer coefficients deteriorate appreciably as compared to the pure refrigerants when the oil concentration exceeds 5%. A correlation is developed that is capable of describing the influence of lubricant oil. The proposed correlation not only can predict the influence of the lubricants of this study but also can extend to predict existing data with a good accuracy. [ABSTRACT FROM AUTHOR]

A literature survey revealed that no prior investigation has been conducted on the horizontal distribution of a two-phase refrigerant in mini-channel tubes, which may be of importance for the cooling of heat-generating objects. In this study, we investigated R-134a distribution into four flat tubes inside a horizontal plane. In order to simulate the battery of an electric vehicle, a 600-W power supply was used during our tests. Tests were conducted with mass fluxes ranging from 280 to 480 kg m −2 s −1 and an inlet quality of 0.2. The effects of inlet port orientation and heat exchanger inclination on flow distribution were investigated. Results indicated that the effects of heat exchanger inclination on flow distribution were more prevalent than those of inlet port orientation. However, these effects are weakened as mass flux increases. Flow distribution deteriorated as the inclination of the heat exchanger increased. Header pressure drop constituted a significant portion of heat exchanger pressure drop and became more pronounced as mass flux increased. [ABSTRACT FROM AUTHOR]

In this study, condensation heat transfer coefficients and frictional pressure drops of R-134a inside a micro-fin helical coiled tube with the cooling water flowing inside the shell in opposite flow direction are experimentally investigated. The inner tubes comprise of one smooth straight tube and one micro-fin helical coiled tube, which are made of copper. The experimental measurements are carried out at mass fluxes of 75, 115, 156 and 191 kg m −2  s −1 and saturation temperatures of 35° and 45 °C. In addition, the experimental data of a micro-fin helical coiled tube have been plotted on the mass flux versus vapor quality flow map and Tailtel and Dukler flow map. The transitions between different flow regimes inside micro-fin helical coiled tube have also been discussed. Moreover, the effect of mass flux, vapor quality and saturation temperature of R-134a on the heat transfer coefficients and pressure drops are examined. Comparisons between smooth straight tube and micro-fin helical coiled tube are also discussed. The experimental results show that the micro-fin helical coiled tube produces a higher heat transfer coefficient and a frictional pressure drop compared to smooth straight tube. The new correlations have been proposed to predict the Nusselt number and frictional pressure drop multiplier during condensation of R-134a inside micro-fin helical coil tube. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study of an adiabatic flow of R-134a through a capillary tube. The paper discusses the details of experimental facility for testing a capillary tube with sub-cooled and two phase inlet conditions of R-134a. The effect of diameter, capillary length, inlet refrigerant quality and inlet pressure on mass flow rate were investigated. The experiments for testing the capillary tubes were proceeded by an integrity test. The vapour quality varied from 0.05 to 0.25. All the experiments were done by varying the pressure from 655 to 724 kPa. The effect of two phase inlet conditions on mass flow rate of R-134a through an adiabatic capillary tube is observed. A correlation to predict the mass flow rate of refrigerant flowing through an adiabatic capillary tube is proposed for two phase inlet conditions. The proposed correlation predicts the measured data with an error band of ±25%. [ABSTRACT FROM AUTHOR]

An investigation into the effect of mass flow rate oscillation on the R-134a evaporation heat transportation in a horizontal annular duct was experimentally conducted. The experiments were performed at different amplitudes (10, 20, and 30%) and periods (20, 30, 60, and 120 s) of the mass flux oscillation in a duct with different gap sizes (1.0, 2.0 and 5.0 mm). In this regard, the time variations of evaporation heat transportation coefficient and the heated wall temperature were also analyzed for the thermal characteristics of the oscillatory evaporation heat transfer. Measured results showed that the amplitude and period of the mass flux oscillation insignificantly affected the time-average heat transportation coefficient for the R-134a oscillatory evaporation heat transfer. However, the larger amplitudes and longer periods of the mass flux oscillation led to stronger wall temperature oscillations. [ABSTRACT FROM AUTHOR]

An experimental study was conducted on the gas–liquid two-phase flow distributions in a multi-pass channel that simulated a compact evaporator in a heat-pump system, with a focus on the similarity between the refrigerant (R-134a) flow and the air–water flow. The body of the test channel was made of transparent polyvinyl chloride to allow optical access, and multiport aluminum tubes were used as branches. Horizontal dividing and combining headers with cross sections of 20 mm × 20 mm were connected by 22 upward branches with cross sections of 20 mm × 2 mm, lengths of 120 mm, and pitches of 12 mm. Initially, the refrigerant two-phase flow was visualized to clarify the characteristics of the flow in the headers. Then, using the same test channel, the air–water flow in the headers was observed under four air and water velocity conditions at the dividing header entrance to investigate the similarity with the flow pattern of the refrigerant flow: (i) superficial gas and liquid velocities equal to those of the refrigerant flow, (ii) equal kinetic energies, (iii) equal quality and mass flow rate, (iv) equal Baker's flow pattern map parameters. A comparison of the flow patterns in the dividing header revealed that the air–water flow under the inlet conditions of the equal kinetic energies and equal Baker's flow pattern map parameters simulated the refrigerant flow closely. Then, based on this result, the air and water distribution ratios in the branches were measured under these two conditions to examine the influence of the flow inlet conditions on the flow-distribution characteristics. A close comparison of the air–water distributions and the refrigerant flow in the combining header revealed that the inlet condition of equal Baker's flow pattern map parameters yielded better results than the equal-kinetic energy condition. [ABSTRACT FROM AUTHOR]

This work presents the experimental evaluation of energy consumption and refrigerant charge reduction when a commercial direct expansion refrigeration system is converted into an indirect system. The evaluation (with R-134a and R-507A) used a commercial cabinet with doors for medium temperature and a single-stage refrigeration cycle using a semi-hermetic compressor and electronic expansion valve; 24-h energy consumption tests were performed at laboratory conditions for each refrigerant and configuration at three heat rejection levels (23.3, 32.8 and 43.6 °C), maintaining an average product temperature inside the cabinet of 2 °C. The work analyses the impact of the conversion on temperature and pressure indicators, as well as, in the energy performance of each element. For R-134a the refrigerant charge was reduced in a 42.9%, but the energy consumption rose by 22.0%-22.8%; for R-507A the charge reduction was of 32.8% with an increase in energy consumption of between 27.7% and 38.7%. [ABSTRACT FROM AUTHOR]

This work presents the experimental evaluation of R-513A (GWP = 573) and R-450A (GWP = 547) as R-134a (GWP = 1301) drop-in replacements and as R-507A (GWP = 3987) retrofits in a commercial direct expansion refrigeration system for medium temperature applications (2 °C). The evaluation covered 24-hour tests using a single-stage cycle with semi-hermetic compressor, an electronic expansion valve customized for each refrigerant and a commercial vertical cabinet with doors placed inside a climatic chamber. The tests were performed at three water dissipation temperatures (23.3, 32.8 and 43.6 °C). Experimental results indicate that R-513A and R-450A can operate with R-134a plants, with increments in energy consumption between −1.6 to +1.2% for R-513A and from +1.3 to +6.8% for R-450A, whereas in comparison with R-507A, R-513A offered reductions in energy consumption between 4.4 to 8.2% and R-450A between 0 to 3.3%. The paper analyzes the modification of the operating pressures/temperatures and the energy indicators using the four refrigerants. [ABSTRACT FROM AUTHOR]

The performance analysis of a modified vapour compression refrigeration system has been carried out in this paper based on energy and exergy analysis and compared with the combined effect of two separate systems. The system is modified combining two conventional systems through a heat exchanger. Heat exchanger in the modified system acts as a condenser in the secondary loop and super heater in the primary loop. A computational model has been developed in EES using energy and exergy equations to calculate different parameters for evaluating the system performance. Simulation results show that modified system gives better result compared to separate systems. [ABSTRACT FROM AUTHOR]

An experimental study was carried out to examine the time periodic evaporation heat transfer for refrigerant R-134a flowing in horizontal narrow annular ducts subjected to wall heat flux oscillation in the form of triangular waves. The experiment was performed for the gap of the annular duct δ = 1.0, 2.0 and 5.0 mm. Besides, the amplitude of the imposed heat flux oscillation Δq was set at 0, 10, 30, 50, 80 and 100% of mean imposed heat flux q ¯ . Moreover, the period of the heat flux oscillation t p was fixed at 2, 20, 30, 60, 120 and 600 s. Attention was mainly paid to examining the effects of the amplitude and period of the wall heat flux oscillation on the time periodic evaporation heat transfer in the narrow annular pipe. The measured evaporation heat transfer data are expressed in terms of the evaporation heat transfer coefficient. The thermal characteristics of the oscillatory evaporation heat transfer were illustrated by showing the time variations of the instantaneous heated pipe wall temperature T w and evaporation heat transfer coefficient h r . Measured results showed that the time-average heat transfer coefficients for the oscillatory evaporation heat transfer of R-134a were not affected to a noticeable degree by the amplitude and period of the imposed heat flux oscillation. Besides, the stronger wall temperature oscillation was noticed for a longer period and a larger amplitude of the imposed heat flux oscillation and for a higher mean imposed heat flux. [ABSTRACT FROM AUTHOR]

The time periodic saturated boiling heat transfer in a horizontal annulus was investigated experimentally where the walls are under an oscillating heat flux. The fluid enters the duct with zero vapor quality (saturated liquid state). The amplitude of the imposed heat flux oscillation Δ q varies from 0% to 50% of mean imposed heat flux q ¯ and four different periods of heat flux oscillation t p , including 20, 30, 60 and 120 s are applied to the system. The measured data display that when the applied heat flux is close to that for the onset of stable flow boiling, intermittent flow boiling appears in which nucleate boiling on the heated surface only exists in a partial interval of each periodic cycle and the heat flux oscillation does not noticeably affect the time-average boiling curves and heat transfer coefficients. Besides, the heated wall temperature and evaporating flow pattern are found to oscillate periodically in time as well and at the same frequency as the imposed heat flux oscillation. Furthermore, in the persistent boiling the resulting oscillation amplitudes of the heated surface temperature, heat transfer coefficient gets larger for a longer period and larger amplitude of the imposed heat flux oscillation and for a higher mean imposed heat flux. The substantial time lag in the heated surface temperature oscillation is observed. In the first half of the periodic cycle in which the heat flux reduces with time, after the time lag the heated wall temperature decreases with time. The inverse processes occur in the second half of the cycle in which imposed heat flux increases with time. Finally, flow regime maps are provided to explain the boundaries separating different boiling regimes for the R-134a saturated boiling in the duct. [ABSTRACT FROM AUTHOR]

The recycling of depleted high global warming mixtures of fluorinated gases (F-gases) with close-boiling or azeotropic behavior requires advanced separation processes to obtain effectively the pure components. Herein, several types of PIM-1 membranes were tested for the first time towards the separation of hydrofluorocarbons and hydrofluoroolefins, showing extraordinarily high permeability coefficients for the value-added difluoromethane (R-32), up to 4100 barrer, coupled with high selectivity for the F-gas pairs of interest. Additionally, the solubility of selected F-gases in PIM-1 was measured and fitted to the dual-mode and Guggenheim, Anderson and de Boer sorption models. The separation performance of the standard PIM-1 and a highly branched PIM-1 was examined with the mixture R-410A (containing R-32 and pentafluoroethane R-125) to assess the influence of the membrane topology on the mixed-gas permeation properties over time (physical aging). Considering that the branched PIM-1 membrane was the least impacted by the aging phenomena, it was used to recover high purity R-32 (concentration in the permeate side as high as 98.9 vol % was achieved) from refrigerant gas mixtures R-410A and R–454B (mixture of R-32 and R-1234yf) in continuous long-term experiments. Results showed the great potential of PIM-1 membranes for the separation of R-32 from refrigerant mixtures collected from end-of-life equipment. [Display omitted] • F-gas permeation in PIM-1 membranes is assessed for the first time. • Performance of conventional PIM-1 is compared with highly branched PIM-1 polymers. • R-32 permeability up to 4100 barrer coupled with high selectivity are achieved. • Aged membranes achieved separation factors four times higher than fresh membranes. • Branched PIM-1 is less affected by the aging phenomenon. [ABSTRACT FROM AUTHOR]

Nowadays, the shipping sector has growth rapidly as followed by the increasing of world population and the demands for public transportation via sea. This issue entails the large attention on emission, energy efficiency and fuel consumption on the ship. Waste Heat Recovery (WHR) is one of the solution to overcome the mentioned issue and one of the WHR method is by installing Organic Rankine Cycle (ORC) system in ship. ORC demonstrate to recover and exploit the low temperature waste heat rejected by the ship power generation plant. The main source of heat to be utilized is obtained from container ship (7900 kW BHP, DWT 10969 mt) ship jacket water cooling system and use R-134a as a refrigerant. The main equipment consists of evaporator, condenser, pump and steam turbine to generate the electricity. The main objective is to quantifying the estimation of electrical power which can be generated at typical loads of the main engine. As the final result of analysis, the ORC system is able to generate the electricity power ranged from 77,5% - 100% of main engine load producing power averagely 57,69 kW.

This study presents a simple multi-fluid model for Helmholtz energy equations of state. The model contains only three parameters, whereas rigorous multi-fluid models developed for several industrially important mixtures usually have more than 10 parameters and coefficients. Therefore, the model can be applied to mixtures where experimental data is limited. Vapor-liquid equilibrium (VLE) of the following seven mixtures have been successfully correlated with the model: CO2 + difluoromethane (R-32), CO2 + trifluoromethane (R-23), CO2 + fluoromethane (R-41), CO2 + 1,1,1,2- tetrafluoroethane (R-134a), CO2 + pentafluoroethane (R-125), CO2 + 1,1-difluoroethane (R-152a), and CO2 + dimethyl ether (DME). The best currently available equations of state for the pure refrigerants were used for the correlations. For all mixtures, average deviations in calculated bubble-point pressures from experimental values are within 2%. The simple multi-fluid model will be helpful for design and simulations of heat pumps and refrigeration systems using the mixtures as working fluid.

The evaporation heat transfer coefficient of the refrigerant R-134a in a vertical plate heat exchanger was investigated experimentally. The area of the plate was divided into several segments along the vertical axis. For each of the segments, the local value of the heat transfer coefficient was calculated and presented as a function of the mean vapor quality in the segment. Owing to the thermocouples installed along the plate surface, it was possible to determine the temperature distribution and vapor quality profile inside the plate. The influences of the mass flux, heat flux, pressure of system and the flow configuration on the heat transfer coefficient were also taken into account and a comparison with literature data was performed.

The evaporation heat transfer coefficient of the refrigerant R-134a in a vertical plate heat exchanger was investigated experimentally. The area of the plate was divided into several segments along the vertical axis. For each of the segments, the local value of the heat transfer coefficient was calculated and presented as a function of the mean vapor quality in the segment. Owing to the thermocouples installed along the plate surface, it was possible to determine the temperature distribution and vapor quality profile inside the plate. The influences of the mass flux, heat flux, pressure of system and the flow configuration on the heat transfer coefficient were also taken into account and a comparison with literature data was performed.

The objective of this study is to design and briefly investigate the cooling performances of an air conditioning system for a special purpose vehicle under various experimental conditions. An air conditioning system with two parallel refrigeration cycles consisting of two compressors and two condensers for satisfying the required cooling performance of the special purpose vehicle was tested under extremely hot weather conditions and high thermal load conditions and then optimized by varying the refrigerant charge amount. The optimum refrigerant charge amount of the tested air conditioning system was 1200 g with the consideration of the cooling speed and cooling capacity. The indoor temperatures of the suggested air conditioning system at the refrigerant charge amounts of 1200 g, 1400 g, and 1600 g were 24.7 °C, 25.2 °C, and 26.4 °C, respectively, at the elapsed time of 300 s. The cooling time required to reach a 15.0 °C inner temperature in the suggested air conditioning system increased by 13.3% with the decrease of the refrigerant charge amount from 1600 g to 1200 g. The cooling capacity and the coefficient of performance (COP) of the suggested air conditioning system increased by 37.9% and 10.9%, respectively, due to a decrease of the refrigerant charge amount from 1600 g to 1200 g. The observed cooling performance characteristics of the air conditioning system with two parallel refrigeration cycles means it could be suitable for cabin cooling of special purpose vehicles. In addition, the designed special air conditioning system with two parallel refrigeration cycles for a special purpose vehicle was built to ensure a sufficient cooling performance for equipped passengers. [ABSTRACT FROM AUTHOR]

The effects of operating conditions on the air-side heat transfer, and pressure drop of a micro-channel heat exchanger under wet surface conditions were studied experimentally. The test section was an aluminum micro-channel heat exchanger, consisting of a multi-louvered fin and multi-port mini-channels. Experiments were conducted to study the effects of inlet relative humidity, air frontal velocity, air inlet temperature, and refrigerant temperature on air-side performance. The experimental data were analyzed using the mean enthalpy difference method. The test run was performed at relative air humidity's ranging between 45% and 80%; air inlet temperature ranges of 27, 30, and 33 0C, refrigerant-saturated temperatures ranging from 18 to 22 0C, and Reynolds numbers between 128 and 166. The results show that the inlet relative humidity, air inlet temperature, and the refrigerant temperature had significant effects on heat transfer performance and air-side pressure drop. The heat transfer coefficient and pressure drop for the micro-channel heat exchanger under wet surface conditions are proposed in terms of the Colburn factor and Fanning factor. [ABSTRACT FROM AUTHOR]