Saturated Refrigerant Research Articles

Heat transfer of uncoated and nanostructure coated commercially micro-enhanced refrigeration tubes under pool boiling conditions

The heat transfer performance of commercially produced micro-enhanced tubes with and without a nanocoating was investigated under pool boiling of saturated refrigerant. These multiscale enhancements were on the outside of 19 mm horizontal copper tubes heated by water to determine the effectiveness of this multiscale enhancement technique on industrially relevant tubes and geometry. The tubes tested were a plain tube roughened by sandpaper, a low finned GEWA-KS tube and two micro-enhanced re-entrant cavity tubes, the GEWA-B5 and EHPII. The tubes were tested in R134a at saturation temperatures of 5 °C and 25 °C across a range of heat fluxes from 20 kW/m2 to 100 kW/m2 under pool boiling conditions. The nanocoating applied to the tubes produced a forest of copper oxide nanostructures on the surface, increasing wickability of the surface. A Scanning Electron Microscopy showed that copper oxide nanocoatings coated all micro-enhanced tubes evenly without impeding the surface features or significantly blocking the re-entrant cavities. For the uncoated tubes in pool boiling, the heat transfer coefficients of the EHPII was up to 519 % greater than those of the plain roughened tube, the GEWA-B5 was up to 539 % higher than the roughened tube and the GEWA-KS was at best 64 % higher than those of the plain roughened tube. Increases in the saturation temperature to 25 °C produced minor improvements in heat transfer coefficients. The application of the copper oxide nanocoating resulted in generally decreased heat transfer performance by approximately 40 % on average compared to the uncoated tubes, with the GEWA-B5 tube the worst affected. Degradation of the heat transfer is thought on plain surfaces to be due to the flooding of nucleation sites, while re-entrant cavity style enhanced surfaces were thought to experience degraded sensible and latent heat transfer due to impeded flow in the microstructure capillary channel, as bubbles were noted to be trapped in the channels. It is recommended that the heat transfer at much higher heat flux ranges be explored for possible HTC enhancement.

Pool Boiling Heat Transfer in Saturated R407C Using Reentrant Cavity Surfaces

The nucleate pool boiling phenomenon has immense heat transfer applications due to the ability to remove significant quantities of heat from the heating surface with limited temperature differences. Enhancing the pool boiling heat transfer coefficient (HTC) has gained the important consideration in contemporary research for the conservation and efficient utilization of material and energy in the design of boilers. Many types of modification have been tested for enhancing the HTC. One such method is the application of reentrant cavity. An experiment investigation has been carried out to study the nucleate boiling heat transfer from reentrant cavity tubes to a pool of saturated refrigerant R407C at the saturation temperature of 7 °C and 10 °C. An analysis of experimental data shows the reentrant cavities with the mouth size of 0.21, 0.25, 0.31, 0.41, and 0.51 mm can be advantageous for enhancing the HTC of plain tubes. The mouth size of 0.21 mm for boiling R407C has shown maximum enhancement compared to other sizes. A correlation for reentrant cavity surfaces has also been developed and validated with the experimental results.

Approximate Thermal Calculation of the Superheated Steam Condenser of Heat Pumps

A comparative analysis of the methods of approximate thermal calculation of the superheated steam condenser of the steam compression heat pump of the heat supply system is presented. The working substance of the heat pump and the condensing steam is the refrigerant R410a. When the single-zone method is applied, the condenser is calculated by one area with the inclusion of the heat of overheating in the heat of condensation and the use of the overheating coefficient. The two-zone method assumes the calculation of the condenser in two separate areas, viz. the cooling of superheated steam and its actual condensation. The approbation was carried out during a numerical study of a condenser of a low-temperature heat pump system for heating and hot water supply, with a heat exchange surface in the form of a spiral coil pipe in a pipe immersed in a heated liquid. In the first approach, the flow rate and temperature of the heated water are limited by the saturation temperature of the condensing refrigerant, regardless of the flow pattern of the working media. The method of two-zone calculation of the superheated steam condenser with a counter-current or cross-counter-current flow scheme of working media makes it possible to obtain real results of the temperature of the heated water that exceeds the temperature of the saturated refrigerant vapor, taking into account the flow rate of the heated water. In this case, the wall temperature in the cooling area is higher than the saturation temperature, and during condensation it is lower, which further confirms the adequacy of the presented technique. The use of a two-zone technique with a separate averaging of the physical properties of the working media in the areas of superheated steam and condensation cooling, as well as temperature pressures, provides a more accurate value of the heat exchange surface, which in the case under consideration is reduced to 20%. Based on the conducted studies, it is recommended to use a two-zone technique that makes it possible to obtain reliable data on the parameters of the superheated steam condenser.

Corresponding-state principle model for the correlation of temperature dependent difference of coexisted densities of refrigerants at equilibrium

A simple and new correlation model based on the corresponding state principle is proposed for the difference of coexisted densities (DCD) of the saturated refrigerants fluids. It requires three physical properties as inputs. They are the critical temperature Tc, the minimal temperature Tmin at which data of the DCD is available in the NIST database, and the corresponding DCD value at Tmin. This proposed correlation has a simple analytical expression and includes only one adjustable parameter. It can accurately reproduce the DCD data in the NIST database in the temperature range from the triple point to the critical point with AAD values less than 1.92% for 47 out of 48 refrigerants considered. Large deviations only stand in a tiny temperature range very close to the critical point.

Effect of Thermophoresis on Heat Diffusion in Isobutane/Copper‐Oxide Nanofluid under Pool Boiling Condition: Numerical Investigation

Understanding thermophoresis in nanorefrigerants stands challenging for a long period despite the phenomenon is attributed for the motion dynamics of particles in nanofluids. Influence of thermophoretic mobility of copper‐oxide nanoparticles on the heat transfer behavior of isobutane (R600a) refrigerant is reported in this work. Pool boiling of the isobutane/copper‐oxide nanofluid is numerically simulated in computational fluid dynamics utilizing both single and two‐phase approaches. Mobility of particles in the saturated refrigerant is studied, and the time scales associated with (Brownian and momentum) diffusions are numerically solved. The temperature contour of the liquid pool is validated with the experimental data, and the properties of the nanorefrigerant such as thermal conductivity, viscosity, and specific heat are estimated in ANSYS Fluent. 5% increase in thermal conductivity and marginal reduction in specific heat of the nanorefrigerant for 0.01% volume fraction of copper‐oxide nanoparticles is witnessed. Mobility of particles due to temperature gradient is found higher near the heater; however, thermophoretic velocity is predicted to be lower because of the narrow temperature gradient. Numerical results showed that the time scale for momentum diffusion is shorter (in the order of e+03) than Brownian diffusion, and hence the momentum diffusion is found to be the predominant mode of heat transfer in nanorefrigerant.

New corresponding states correlation for the temperature-dependent surface tension of refrigerant liquids

We collected data of the surface tension versus the temperature of 28 saturated refrigerant fluids available in the NIST database. These data are used to build a new corresponding state-based correlation. Compared with other previously proposed correlations, the current one has the advantages of both simplicity and accuracy. To check the ability of correlations, we compared the numerically calculated/predicted results with the data in the NIST database. It is found that the average absolute deviations are less than 10% for 26 refrigerants and less than 1% for 8 refrigerants.

Isothermal compressibility of saturated refrigerants: Chlorodifluoromethane and 1,1,1,2-tetrafluoroethane

A new five-parameter generalized van der Waals equation of state is employed for calculating the isothermal compressibility of saturated refrigerants such as chlorodifluoromethane and 1,1,1,2-tetrafluoroethane in the liquid and vapor states over a temperature range from the boiling point to the critical point. This generalized van der Waals equation of state differs from the known van der Waals equation by the modified repulsive and attractive terms. The parameters of the equation of state are determined through the characteristic thermodynamic parameters of the refrigerants. The generalized van der Waals equation-of-state parameters are compared with the known van der Waals equation-of-state parameters.

New correlation for the temperature dependent viscosity of saturated refrigerants liquids

In this paper, we proposed a new correlation for the temperature dependent viscosity of saturated refrigerants liquids based on the recent progresses on the relation between surface tension and viscosity of liquids [J. X. Tian et al., Industrial & Engineering Chemistry Research, 53, 9499, 2014] and the temperature dependent surface tension of liquids [S. G. Yang et al., Industrial & Engineering Chemistry Research, 59, 6336, 2020]. By comparing with the experimental data of 80 saturated refrigerants liquids in the DIPPR database, it is found that the proposed correlation can predict the DIPPPR data with average absolute relative deviation (AARD) less than 5% for all the 80 liquids, AARD less than 3% for 76 liquids. These results indicate superior accuracy of the proposed correlation compared to other well-known correlations including the Arrhenius equation and the Vogel-Fulcher-Tamman equation.

Automated process design and integration of precooling for energy-efficient BOG (boil-off gas) liquefaction processes

As awareness on air pollution in marine environment increases, transition of ship fuel to natural gas has been recognized as a practical solution for emission minimization. It is realized with LNG-fueled ship, whose implementation in practice demands cost-effective and energy-efficient re-liquefaction of BOG. The purpose of this study is to introduce precooling cycle to BOG re-liquefaction process to enhance energy efficiency and explore the most appropriate usage of pre-cooling refrigerants between CO2 and NH3. Three different configurations for precooling are compared, and operating conditions are optimized with an objective function to minimize energy consumption. Pre-screening based on sensitivity analysis, before optimization, is carried out to exclude any potential infeasible solution space. It allows robust optimization, leading to high quality optimal solution. Up to 7.9% reduction in overall energy consumption is achieved with the integration of precooling cycles, illustrated by high dependence on physical properties of saturated refrigerants. The modeling and optimization framework proposed in this study can serve as an effective application to the wide range of refrigeration systems subject to various refrigerants.

Surface wettability change on TF nanocoated surfaces during pool boiling heat transfer of refrigerant R-141b

Experiments were performed to demonstrate the impact of surface wettability on the nucleate boiling heat transfer of Silicon Dioxide (SiO2) Thin Film (TF) nanocoated surfaces using the saturated refrigerant R-141b at atmospheric pressure. Six numbers of circular flat type test sections of copper material having thickness of 0 nm (plain surface), 125 nm, 250 nm 375 nm, 500 nm and 625 nm surface coating thicknesses were fabricated with the Sol-Gel method followed by spin coating process and characterized through atomic force microscope (AFM), field emission scanning electron microscopy (FE-SEM), Telescope Micro-Goniometer (TMG), and Energy – Dispersive X-Ray spectroscopy (EDX) etc. The experimental results from plain and nanocoated copper surfaces were validated with well-established correlations to predict the pool boiling curve. In comparisons with plain surface, results obtained from other surfaces show that the reduction of wall superheat and additional improvement of heat transfer coefficient (HTC), for all TF nanocoated surfaces at atmospheric pressure. It has been revealed that surface wettability improves the vapor bubble departure radius for hydrophilic surfaces and decreases the frequency of bubble emissions.

Effect of pipes in heat pump system on electric vehicle energy saving

ABSTRACT Refrigerant pressure drop and temperature change in pipes are normally ignored in the thermodynamic analysis of traditional vehicle air conditioning system, this will result in serious errors. In this Paper, pressure drop and temperature difference are simulated in different pipes of electric vehicle (EV) heat pump system to analysis the effects of pipes in the actual EV heat pump system. The results indicate that the greater the mass flow, the faster pressure drop increases, the temperature difference decreases. Pressure drop of saturated liquid refrigerant is smaller than that of saturated gas refrigerant at the same saturation pressure and mass flow rate. The higher the refrigerant pressure (no phase change), the slower pressure drop decreases, the faster the temperature difference decreases. Pressure drop decreases with the increment of bending angle of the pipe. For EV heat pump system, suitable valves and less branches are helpful for energy saving of the system. Shortening the pipe between compressor and condenser can reduce temperature change obviously. Pressure drop per unit length in the pipe between evaporator and compressor is large especially in heating mode because of lower refrigerant density. It even reaches to over 100 times of that in the pipe between condenser and throttle valve in heating mode and has negative effects on the performance of the system. If the evaporator is closer to the compressor and the number of branches is less, then pressure drop will decrease a lot, which will be advantageous for energy saving of the heat pump system.

Corresponding state principle based correlation for the thermal conductivity of saturated refrigerants liquids from Ttr to 0.90Tc

We here report that the corresponding state principle well stands for the temperature dependent thermal conductivity of the saturated refrigerants liquids by using the reduced quantities proposed here. A corresponding state principle based correlation is proposed and proven to be accurate in the temperature range from the triple point temperature to 0.90 times the critical temperature. Additionally, this correlation also stands for the saturated n-alkanes liquids. For the 23 refrigerants and 11 n-alkanes considered here, the proposed correlation can reproduce the REFPROP data with AAD<2% for 21 liquids, and AAD<5% for all the liquids considered.

Two-phase flow distribution of saturated refrigerants in microchannel heat exchanger headers

Mini- and microchannel heat exchangers have the potential to drastically decrease the size and cost of thermal systems, but they often underperform because of flow maldistribution. Maldistribution can be particularly acute when a two-phase mixture enters a heat exchanger header, which is difficult to address because the flow phenomena in these situations are poorly understood. In the present study, flow distribution in microchannel heat exchanger manifolds is investigated. The work focuses on two-phase flow regimes and distribution characteristics of saturated R134a in heat exchanger headers. The results quantify the effects of inlet mass flux (23.9 < Gin < 95.7 kg m−2 s−1), inlet quality (0.10 < xin < 0.90), header flow regime and header pressure drop on distribution. Additionally, several header geometries (rectangular, triangular, and vane) are investigated to identify pathways to mitigate maldistribution in heat exchangers.

Application of Carnahan-Starling-vdW-β Equation of State for Refrigerant Fluids

Herein, the application of Carnahan-Starling-vdW-β equation of state (EoS) for 13 refrigerant fluids was investigated. The EoS could predict the saturated liquid densities of these refrigerants over the temperature range of 100-400 K and pressures from zero up to187 MPa with the average absolute deviations of 2.66%. The accuracy of Carnahan-Starling-vdW-β EoS in liquid density prediction was also compared with Peng-Robinson EoS and a perturbed hard-sphere-chain EoS. The surface tension and sound velocity of the saturated refrigerants were also calculated using the Carnahan-Starling-vdW-β EoS within 4.76%. and 5.66%, respectively. Finally, Carnahan-Starling-vdW-β was employed to predict Joule-Thomson inversion curve for some studied refrigerant fluids

Horizontal convective boiling of R1234yf, R134a, and R450A within a micro-fin tube

This paper presents local convective boiling heat transfer and Fanning friction factor measurements in a micro-fin tube for R134a and two possible low global warming potential (GWP) refrigerant replacements for R134a, namely R1234yf and R450A. Test section heating was achieved with water in either counterflow or in parallel flow with the test refrigerant to provide for a range of heat fluxes for each thermodynamic quality. An existing correlation from the literature for single and multi-component mixtures was shown to not satisfactorily predict the convective boiling measurements for flow qualities greater than 40%. Accordingly, a new correlation was developed specifically for the test fluids of this study so that a fair comparison of the heat transfer performance of the low GWP refrigerants to that of R134a could be made. The new correlation was used to compare the heat transfer coefficient of the three test fluids at the same heat flux, saturated refrigerant temperature, and refrigerant mass flux. The resulting example comparison, for the same operating conditions, showed that the heat transfer coefficient of the multi-component R450A and the single-component R1234yf were, on average, 15% less and 5% less, respectively, than that of the single-component R134a. Friction factor measurements were also compared to predictions from an existing correlation. A new correlation for the friction factor was developed to provide a more accurate prediction. The measurements and the new models are important for the evaluation of potential low-GWP refrigerants replacements for R134a.

Tribology Characteristics of HFO and HC Refrigerants with Immiscible Oils

Hydro fluoro olefin (HFO) and hydro carbon (HC) refrigerants have been considered for use in air-conditioning systems and refrigerators as low global warming potential (GWP) refrigerants. These refrigerants are determined the lubrication performance of the sliding parts in compressor. To clarify lubrication performance of unsaturated and saturated refrigerants for these low GWP refrigerants, seizure and wear tests were done in the compound of liquid refrigerant and refrigeration oil. Immiscible oils to refrigerants were used for lubrication. We confirmed that antiwear and antiseizure characteristics of unsaturated refrigerants (HFO-1234yf and R1270) are better than those of saturated refrigerants HFC-134a and R290.

Effect of Various Parameters on Working Condition of Chiller

Abstract The present work aims to find out the effect of various parameters on evaporator, compressor and condenser in vapour compression cycle using “high performance tube manufacturer's software” for evaporator and condenser and using “compressor selection software of a reputed manufacturer” for compressor. The present work includes the effect of number of tubes, number of passes and fouling factor on saturated refrigerant temperature (SST), tube side velocity, pressure drop and temperature approach in evaporator and condenser. Effect of SST on power input to compressor, cooling capacity, condenser capacity and coefficient of performance (COP) and also effect of condensing temperature on power input to compressor, cooling capacity and condenser capacity is studied using software.

Horizontal convective boiling of R448A, R449A, and R452B within a micro-fin tube

This article presents local convective boiling measurements in a micro-fin tube for three low global warming potential refrigerants: R448A, R449A, and R452B1R452B is the pending ASHRAE designation for the mixture R32/R125/R1234yf (67/7/26), which has the developmental designation DR-55.. An existing correlation was modified to predict multi-component mixtures, which predicted 98% of the measurements to within ±20%. The new correlation was used to compare the heat transfer coefficient of the three test fluids at the same heat flux, saturated refrigerant temperature, and refrigerant mass flux. The resulting comparison showed that refrigerant R452B exhibited the highest heat transfer, in large part due to its approximately 28% larger liquid thermal conductivity and smaller temperature glide as compared to the tested low-global warming potential refrigerants. For the example case, the heat transfer coefficient for R449A was approximately 8% larger than that for R448A, while the heat transfer coefficient for R452B was more than 59% larger than either R448A or R449A. The heat transfer coefficients for R448A and R449A were roughly between 26 and 48% less than that of R404A for the example case. In contrast, the model predicts that the R452B heat transfer coefficient was approximately 13% larger than that of R404A for the same conditions.

Investigation on aqua-ammonia based solar cooling cogeneration plant

Purpose – The proposed solar thermal cooling cogeneration cycle is well suited for industrial as well as domestic needs and it eliminates need of electricity for refrigeration system. The purpose of this paper is to integrate power and cooling to minimize the energy usage. Design/methodology/approach – The proposed plant has double turbine with superheater and reheater to extract more energy, operating on single generator. The saturated refrigerant from the exit of the generator is used to run the primary turbine and the exit mass of refrigerant is split into 50:50 cooling to power ratio. Findings – It produces additional power of 24 kW at absorber concentration of 0.42 and turbine inlet concentration of 0.95, with separator temperature of 145°C and atmosphere temperature of 30°C. Research limitations/implications – The proposed cooling cogeneration cycle is possible to run on all the refrigerant working fluid mixture and it overcomes the problem of Goswami cycle which is not possible to run in hot climatic countries. Originality/value – The cycle can operate individually as refrigeration cycle, power cycle and both and it will run all climatic conditions.

Nucleate boiling of pure and quasi-azeotropic refrigerants from copper coated surfaces

The present experimental study deals with boiling heat transfer enhancement over surfaces fabricated by gas flame spraying. The copper powder was used as a coating material applied to the outer surfaces of copper tubes of 25.4 mm diameter and an effective length of 116 mm. The surfaces having coating thickness of 42.2 µm and 95.4 µm were used. Pool boiling experiments for saturated refrigerants under pure fluid category R-134a and R-600a and, quasi-azeotropic mixture R-410A (mixture of R-32 and R-125) were carried out for heat fluxes ranging from 5 to 50 kWm−2 for their respective saturation pressure corresponding to temperature of 10 °C. A significant enhancement of boiling heat transfer coefficients due to coating were found for all three refrigerants. For R-600a, the nucleate boiling heat transfer coefficients were approximated 1.35–1.52 times and 1.09–1.2 times higher than those of R-134a and R-410A respectively. The experimental data for coated surfaces were correlated in terms of relevant parameters and also compared with the existing correlations in the literature.