Influence of magnetic field on two‐phase flow convective boiling of some refrigerant mixtures

In this paper, an experimental study on the influence of magnetohydrodynamic (MHD) on heat transfer characteristics of two‐phase flow boiling of some refrigerant mixtures in air/refrigerant horizontal enhanced surface tubing is presented. Correlations were proposed to predict the impact of MHD on the heat transfer characteristics such as average heat transfer coefficients, and pressure drops of R‐507, R‐404A, R‐410A, and R‐407C in two‐phase flow boiling inside enhanced surface tubing. In addition, it was found that the refrigerant mixture's pressure drop is a weak function of the mixture's composition. It was also evident that the proposed correlations for predicting the heat transfer characteristics were applicable to the entire heat and mass flux, investigated in the present study. The deviation between the experimental and predicted value using new and improved correlations for the heat transfer coefficient and pressure drop were less than ±20%, for the majority of data. Copyright © 2005 John Wiley & Sons, Ltd.     

Forced convective condensation and boiling of ternary non-azeotropic refrigerant mixtures inside water/refrigerant enhanced surface tubing

In this paper, an experimental study on the heat transfer characteristics of two-phase flow condensation and boiling of ternary non-azeotropic refrigerant mixtures, on water/refrigerant horizontal enhanced surface tubing, is presented. The enhanced surface tubing data showed a significant enhancement of the heat transfer compared to an equivalent smooth tube depending on the mixture components and their concentrations. Correlations were proposed to predict the heat transfer characteristics such as average heat transfer coefficients, as well as pressure drops of ternary non-azeotropic refrigerant mixture flow condensation, and boiling inside enhanced surface tubing. In addition, it was found that the refrigerant mixture's pressure drop is a weak function of the mixture's composition.     

Influence of thermophysical properties on two-phase flow convective boiling of refrigerant mixtures

In this paper, an analytical study on the influence of thermophysical properties on heat transfer characteristics of two-phase flow boiling of some refrigerant mixtures in air/refrigerant horizontal enhanced surface tubing is presented.Correlations were proposed to predict the thermophysical properties of refrigerant mixtures such as thermal conductivity and viscosity as well as their impact on the heat transfer characteristics such as average heat transfer coefficients, and pressure drops of R-507, R-404A, R-410A, and R-407C in two-phase flow boiling inside enhanced surface tubing. In addition, it was found that the refrigerant mixture's pressure drop is a weak function of the mixture's composition.It was also evident that the proposed improved correlations for predicting the thermophysical properties were applicable to the entire heat and mass flux, investigated in the present study. The deviation between the experimental and predicted value using new and improved correlations for the heat transfer coefficient and pressure drop were <±20 %, for the majority of data.     

Influence of liquid injection on two‐phase flow convective boiling of refrigerant mixtures

In this paper, an analytical study on the influence of liquid injection on heat transfer characteristics of two‐phase flow boiling of some refrigerant mixtures in air/refrigerant horizontal enhanced surface tubing is presented. Correlations were proposed to predict the impact of the liquid injection the thermophysical properties of refrigerant mixtures as well as the heat transfer characteristics such as average heat transfer coefficient of R‐507, R‐404A, R‐410A, and R‐407C in two‐phase flow boiling inside enhanced surface tubing. It was also evident that the proposed correlations and the experimental data that the liquid injection has significant impact on the heat transfer coefficient. In addition, the proposed correlations were applicable to the entire heat and mass flux, investigated in the present study under the liquid injection conditions. The deviation between the experimental and predicted under liquid injection were less than ±20, for the majority of data. Copyright © 2004 John Wiley & Sons, Ltd.     

Two‐phase flow boiling characteristics of alternatives to R‐22 inside air/refrigerant enhanced surface tubing

In this paper, an experimental study on the heat transfer characteristics of two‐phase flow boiling of alternative zeotropic refrigerant mixtures to R‐22, on air/refrigerant horizontal enhanced surface tubing is presented. The new alternatives considered in this study are: R‐507, R‐404A, R‐408A, R‐407C, and R‐410A. The experimental data showed that R‐22 has the highest heat transfer rate compared to the other blends in the range investigated. Furthermore, it was also quite evident from these data that R‐410A has the highest pressure among the blends under investigation for Reynolds number greater than 3.5×10⁴. However, for Reynolds number less than 3.6×10⁴, it appears from the data that R‐22 has the highest pressure drop compared to other refrigerants under investigation. Copyright © 2000 John Wiley & Sons, Ltd.     

Forced convective boiling of nonazeotropic refrigerant mixtures inside enhanced surface tubing

An experimental study on the characteristics of two phase flow boiling of pure refrigerants such as R12 and R22 as well as nonazeotropic refrigerant mixtures R22/R114 and R22/R152a inside horizontal enhanced surface tubing is presented. The enhanced surface tubing results showed a significant improvement of the heat transfer over that of an equivalent smooth tube, depending on the mixture components and their concentrations. Correlations are proposed to predict the heat transfer characteristics such as average heat transfer coefficients as well as pressure drops of nonazeotropic refrigerant mixture flow boiling inside enhanced surface tubing. In addition, it was found that the refrigerant mixtures pressure drop is a weak function of the mixture compositions.     

Boiling characteristics of alternatives to R‐502 inside air/refrigerant enhanced surface tubing

In this paper, an experimental study on the heat transfer characteristics of two‐phase flow boiling of alternative zeotropic refrigerant mixtures to R‐502, on air/refrigerant horizontal enhanced surface tubing is presented. The new alternatives considered in this study are: R‐507, R‐404A, R‐407B, and R‐408A. It was evident from the experimental data that R‐502 has the lowest heat transfer rate compared to the other blends in the range investigated. Furthermore, it was also quite evident from these data that R‐407B has the highest pressure among the blends under investigation. However, at a Reynolds number less than 3.6×10⁴, it appears from the data that R‐404A has the lowest pressure drop compared to other refrigerants under investigation. Copyright © 2000 John Wiley & Sons, Ltd.     

Flow boiling and condensation of tetrary refrigerant mixtures inside water/refrigerant enhanced surface tubing

This work presents the results of an experimental study concerning the heat transfer characteristics of two-phase flow condensation and boiling of tetrary (R-32/R-125/R143a/R134a) refrigerant mixtures inside water/refrigerant horizontal enhanced surface tubing. Heat transfer characteristics such as average heat transfer coefficients, as well as pressure drops of the tetrary refrigerant mixtures, have been predicted and compared with other mixtures during flow condensation and boiling inside enhanced surface tubing. It was found that the tetrary refrigerant blend has higher transfer coefficients than R-502, and the lowest pressure drop among the refrigerants studied. © 1997 by John Wiley & Sons, Ltd.     

Prediction of two‐phase condensation characteristics of some alternatives to R‐22 inside air/refrigerant enhanced surface tubing

The results of an experimental study on the heat transfer characteristics of two‐phase flow condensation of some azeotropic refrigerant mixtures, proposed as alternatives to R‐22, on air/refrigerant horizontal enhanced surface tubing are presented. The condensation data indicated that the heat transfer coefficient of the blend R‐408A has the highest heat transfer rate among the blends under investigation. The condensation data also showed that R‐507 and R‐404A have similar heat transfer rates to that of R‐22 when plotted against the refrigerant mass flow rate. It can also be observed that, as the mass flux increases, the heat transfer coefficient increases. Correlations were proposed to predict the heat transfer characteristics such as average heat transfer coefficients as well as pressure drops of alternatives to R‐22 such as R‐507, R‐404A, R‐407C and R‐408A, as well as R‐410A in two‐phase flow condensation inside enhanced surface tubing. In addition, proposed correlations were found to fairly predict the two‐phase flow heat transfer condensation data. Copyright © 2000 John Wiley & Sons, Ltd.     

Prediction of convective boiling characteristics of alternatives to R-502 inside air/refrigerant enhanced surface tubing

In this paper, an experimental study on the heat transfer characteristics of two-phase flow boiling of alternative azeotropic refrigerant mixtures to R-502 on air/refrigerant horizontal enhanced surface tubing is presented. Correlations were proposed to predict the heat transfer characteristics such as average heat transfer coefficients, as well as pressure drops of alternatives to R-502; such as R-507, R-404A, R-407B, and R-408A in two-phase flow boiling inside enhanced surface tubing. In addition, it was found that the refrigerant mixture’s pressure drop is a weak function of the mixture’s composition. It was found that the correlations were applicable to the entire heat and mass flux, investigated in the present study for the proposed blends under question. The deviation between the experimental and predicted values for the heat transfer coefficient and pressure drop were less than ±20% and 35%, respectively, for the majority of data.     

Influence of gas/liquid injection on two‐phase flow convective boiling of refrigerant mixtures

An analytical study on the influence of gas/liquid injection on heat transfer characteristics of two‐phase flow boiling of some refrigerant mixtures in horizontal enhanced surface tubing is presented. Correlations were proposed to predict the impact of the gas/liquid injection on the heat transfer characteristics such as average heat transfer coefficient of R‐507, R‐404A, R‐410A and R‐407C in two‐phase flow boiling inside enhanced surface tubing. The data also revealed that gas/liquid injection is beneficial at certain gas/liquid injection ratios to the heat transfer coefficient depending upon the Reynolds number and the boiling point. It was also evident that the proposed correlations and the experimental data that the gas/liquid injection has significant impact on the heat transfer coefficient. In addition, the proposed correlations were applicable to the entire heat and mass flux, investigated in the present study under gas/liquid injection conditions. The deviation between the experimental and predicted under gas/liquid injection were less than ±20, for the majority of data. Copyright © 2004 John Wiley & Sons, Ltd.     

Flow boiling characteristics of refrigerant mixture R22/R114 in the annulus of enhanced surface tubing

The paper presents an experimental study of flow boiling heat transfer characteristics of refrigerant mixture R22/R114 in the annuli of a horizontal enhanced surface tubing evaporator. The test section had an inner tube bore diameter of 17.3 mm, an envelope diameter of 28.6 mm and an outer smooth tube of 32.3 mm internal diameter. The ranges of heat flux and mass velocity covered in the tests were 5–25 kW/m² and 180–290 kg/m²/s, respectively, at a pressure of 570 kPa. The enhanced surface tubing data shows a significant enhancement of the heat transfer compared with an equivalent smooth tube depending on the mixture components and their concentrations. Correlations are proposed to predict such heat transfer characteristics as the average heat transfer coefficients as well as pressure drops of R22/R114 nonazeotropic refrigerant mixture flow boiling inside enhanced surface tubing. In addition, it was found that the refrigerant mixture's pressure drop is a weak function of the mixture composition.     

Two‐phase flow convective condensation of refrigerant mixtures under gas/liquid injection

The influence of gas/liquid injection on two‐phase flow condensation heat transfer characteristics of some refrigerant mixtures in horizontal enhanced surface tubing is presented. Correlations were proposed to predict the impact of the gas/liquid injection on the heat transfer characteristics such as average heat transfer coefficient of R‐507, R‐404A, R‐410A, and R‐407C in two‐phase flow condensation inside enhanced surface tubing. The data also revealed that gas, liquid and gas/liquid injection is beneficial at certain gas/liquid injection ratios to the heat transfer coefficient depending upon the Reynolds number and the condensation point of the refrigerant mixtures in question. It was also evident that the proposed condensation correlations and the experimental data were applicable to the entire heat and mass flux, investigated in the present study under gas/liquid injection conditions. The deviation between the experimental and predicted under gas/liquid injection were less than ± 10, for the majority of data. Copyright © 2005 John Wiley & Sons, Ltd.     

Behaviour of new refrigerant mixtures under magnetic field

The behaviour of some new alternative refrigerant mixtures such as R‐410A, R‐507, R‐407C, and R‐404A under various conditions of magnetic field are discussed, analysed and presented. The effect of magnetic field on mixture behaviour varies from one mixture to another depending upon the mixture's composition and its boiling point and consequently on the thermophysical properties. Furthermore, the use of magnetic field appears to have a positive influence on the thermal capacities of the condenser and the evaporator depending upon the refrigerant mixture's thermophysical properties. Copyright © 2005 John Wiley & Sons, Ltd.     

Heat transfer characteristics of ternary blends inside enhanced surface tubing

In this paper, an experimental study on the heat transfer characteristics of two phase flow boiling of ternary non-azeotropic refrigerant mixtures, as well as HFC-134a, inside water/refrigerant horizontal enhanced surface tubing, is presented. Correlations were proposed to predict the boiling heat transfer coefficients and pressure drop, as a function of the flow key parameters.     

Effect of magnetic field on the performance of new refrigerant mixtures

Performance test results of new alternative refrigerant mixtures such as R-410A, R-507, R-407C, and R-404A under various conditions of magnetic field are discussed, analysed and presented. The test results were obtained using an air-source heat pump set-up with enhanced surface tubing under various magnetic field conditions. Performance tests were conducted according to the ARI/ASHRAE Standards. The test results demonstrated that as magnetic field force increases, compressor head pressure and discharge temperature slightly increase as well as less liquid refrigerant is boiling in the compressor shell. This has a positive effect in protecting the compressor. The effect of magnetic field on mixture behaviour varies from one mixture to another depending upon the mixture's composition and its boiling point. Furthermore, the use of magnetic field appears to have a positive influence on the system COP as well as thermal capacities of condenser and evaporator. Copyright © 2002 John Wiley & Sons, Ltd.     

Performance study on the evaporation and pressure drop of low‐temperature refrigerant blends in porous media

An experimental investigation on the performance of different low‐temperature refrigerant blends is presented in this work. Five different low‐temperature refrigerant blends are put on display to replace the R22 refrigerant, which has a high ozone depletion potential. These five blends are R404A, R407C, R410A, R417A, and R422A. Different performance studies have been performed on these alternative refrigerants to replace R22. A comparative experimental performance study is performed during the evaporation of these refrigerant blends in porous media. A porous metallic heat transfer medium is used with different porosities (40%, 43%, and 45%) in the evaporator during the test experiments. The evaporator superheat and the condenser subcool are maintained constant throughout the experiments at 8°C (±0.5°C) and 6°C (±0.5°C), respectively. The condensing temperature is kept constant at 38.5°C, and the mean evaporating temperatures were selected to be from ?33 to ?18°C. The effect of the above‐mentioned given operating conditions on the compressor discharge temperature, evaporation pressure drop, evaporation capacity, and coefficient of performance of these five low‐temperature refrigerant blends has been analyzed for different porosities. This experimental study showed that the refrigerant R422A can give a similar or greater performance to R22 and R404A with a global warming effect and zero ozone depleting potential.     

Heat transfer in forced convection boiling of oil–non-azeotropic binary refrigerant mixtures

In this paper, the results of the heat transfer, forced convection, boiling characteristics of non-azeotropic refrigerant mixtures and oil are presented. This includes heat transfer coefficients for pure and binary mixtures under boiling conditions outside enhanced surface tubing. Local convective heat transfer coefficients have been determined using a modified Wilson-plot technique. Heat transfer correlations were established as a function of the binary mixture mass flow rate, and oil concentration, as well as key flow parameters.     

Prediction of the condensation and boiling characteristics of R12 substitutes R22/r152a/R114 and R22/R152a/R124 inside enhanced-surface tubing

In this paper, the heat-transfer behaviour of two ternary refrigerant blends proposed as an R12 substitute, has been studied during condensation and boiling inside horizontal enhanced surface tubing. Correlations are proposed to predict the average heat transfer coefficients as well as pressure drops of newly proposed ternary refrigerant blends flow, inside enhanced surface tubing.     

Experimental investigation of two phase flow condensation of alternatives to HCFC-22 inside enhanced surface tubing

This paper presents an experimental study of two phase flow condensation of some alternative zeotropic refrigerant mixtures to R-22, inside air/refrigerant horizontal enhanced surface tubing. The alternatives considered in this study are; R-507, R-404A, R-407C, and R-408A as well as R-410A. It was evident from the condensation experimental data that R-408A has the highest heat transfer rate compared to the other blends under the investigated range of refrigerant mass flow rates and heat flux. However, when the thermophysical properties are factored in, the condensation data showed that R-410A has the highest heat transfer rate at Reynolds number higher than 2.35E+7 Furthermore, experimental data of two phase condensation pressure gradient data across the test section at different Reynolds numbers showed that R-410A has the highest convective pressure drop among the blends under investigation.