Samuel M. Sami

Numerical prediction of capillary tube behaviour with pure and binary alternative refrigerants

Abstract In this paper, a numerical model is presented for predicting capillary tube performance using new alternative refrigerants, namely pure and/or binary mixtures. The model has been established after the fluid flow conservation equations written for a homogeneous refrigerant fluid flow under saturated, subcoooled and two phase conditions. Numerical results showed that the proposed model in question fairly simulated our experimental data as well as others and fairly predicted the capillary tube behaviour under the investigated conditions.

An improved model for predicting the dynamic behaviour of adsorption systems

An improved lumped parameter model has been developed to predict the dynamic performance of adsorption cycles with a single and/or double adsorber with heat recovery. The mathematical formulation of this model is based on the conservation equations and the isosteric equation of state. Several constitutive relationships have been integrated into the model to enhance its capability to predict the thermal phenomena taking place inside the adsorber and the heat exchangers. New submodels have been added to predict the performance of air-cooled evaporator and condenser-type heat exchangers. Numerical results compared to experimental data on single and/or double adsorbers with heat recovery, indicate that the model predicts the dynamic performance of adsorption systems well, and compares well with the experimental data.

Heat transfer and pressure drop characteristics of HFC quaternary refrigerant mixtures inside horizontal enhanced surface tubing

Heat transfer characteristics of two-phase flow condensation and boiling of quaternary (four components) refrigerant mixtures, on air/refrigerant horizontal enhanced surface tubing are presented, discussed and compared to other refrigerants proposed as substitutes for CFC-502, such as R-507 and R-407B. Heat transfer characteristics, such as average heat transfer coefficients, as well as pressure drops of ternary azeotropic refrigerant mixtures, flow condensation and boiling inside enhanced surface tubing, were predicted. Experimental data showed that our proposed quaternary blend has a superior boiling heat transfer coefficient and higher pressure drop compared to CFC-502.

Numerical prediction of dynamic performance of vapour-compression heat pump using new HFC alternatives to HCFC-22

In this study, the dynamic performance of an air-source heat pump using alternatives to HCFC-22 is presented under different conditions. The HFC alternatives covered in this study are: R-407a, R-507, as well as NARM-502. Predicted numerical results of the heat-pump performance have been compared with experimental data under various conditions. The comparison showed that our dynamic model accurately predicted the experimental data. Furthermore, our proposed model was employed to predict the dynamic performance key parameters, such as cooling, heating capacities, COPs, pressures and temperatures at the system components, using new alternatives to HCFC-22.

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

Abstract 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 mixtures pressure drop is a weak function of the mixtures 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

Numerical modelling of alternative refrigerants to HCFC-22 through capillary tubes

In this paper, a numerical model is presented for predicting capillary tube performance using new alternative refrigerants to HCFC-22. The model has been established after the fluid flow conservation equations written for a homogeneous refrigerant fluid flow under saturated, sub-cooled and two-phase conditions. Numerical results showed that the proposed model in question fairly simulated our experimental data and fairly predicted the capillary tube behaviour under different conditions. The results also indicated that a system using R-407C would experience smaller pressure drop compared to R-410A and R-410B.

Energy efficiency analysis of a new ternary HFC alternative

In this paper, energy efficiency results are presented for a new HFC ternary blend proposed as a substitute for CFC 502 and HCFC 22. The blend is composed of R-23/R-32/R-125. Performance evaluation test results were obtained after an experimental heat pump set up with a 3 kW rotary compressor. The refrigerants tested in this study under different conditions were HCFC-22, as a reference base refrigerant and R-410a (HFC-32/HFC-125), R-407c (HFC-32/HFC-125/HFC-134a), as well as quaternary mixture; HFC-32/HFC-125/HFC-143a/HFC-134a. The experimental data showed that our proposed HFC ternary blend R-23/R-32/R-125 has superior performance compared to other proposed HFC alternatives such as R-410a and R-407c, under the same conditions. Pressure ratios and head pressures were compatible with new compressors to be used in new systems. Furthermore, experimental results demonstrated that the ternary blend R-23/R-32/R-125 is the best performing replacement for R-22 in heat pump applications and low temperature equipment. Experiments also showed that the heat pump system using R-23/R-32/R-125 was stable and experienced reasonable head pressures.

Heat transfer prediction of air‐to‐refrigerant two‐phase flow boiling of alternatives to HCFC‐22 inside air/refrigerant enhanced surface tubing

In this paper, an experimental study on the heat transfer characteristics of two-phase flow boiling of some alternative refrigerants to HCFC-22, on air/refrigerant horizontal enhanced surface tubing, is presented. Correlations have been 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, R-410A and R-408A in two-phase flow boiling inside enhanced surface tubing. In addition, it was found that the refrigerant mixtures pressure drop is a weak function of the mixtures 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 per cent, respectively, for the majority of data.

Prediction of condensation 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 condensation of alternative azeotropic refrigerant mixtures to R-502, on air/refrigerant horizontal enhanced surface tubing, is presented. The condensation data indicated that the heat transfer coefficient on the blend R-408A has the highest heat transfer rate among the blends under investigation. The condensation data also showed that R-502 and R-407B have similar heat transfer rates when plotted against the refrigerant mass flow rate. It also can be observed that, as the mass flux increases, 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-502; such as R507, R404A, R407B and R408A 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.

Modelling of capillary tubes behaviour with HCFC 22 ternary alternative refrigerants

In this paper, a numerical model is presented for predicting capillary tube performance using new ternary mixtures proposed as alternatives to R 22. The model has been established after the fluid flow conservation equations written for a homogeneous refrigerant fluid flow under saturated, subcooled and two- pase conditions. Numerical results showed that the proposed model in question fairly simulated experimental on ternary refrigerant mixtures and fairly predicted the capillary tube behaviour under the investigated; subcooled, saturated, and two-phase flow conditions.