Heat Transfer Coefficients Of R407C Research Articles

Tube-in-Tube 미세관내 R-22 및 R-407C의 응축열전달 특성

This paper focuses on the results of an experimental study of condensation heat transfer coefficients with the refrigerants R-22 and R-407C, and looks at the pressure gradient and heat transfer coefficients of horizontal tube-in-tube heat exchangers with the use of small tubes with inner diameters of 4 mm, 3 mm and 2 mm, in a 16.91 mm tube and length of 3,000 mm. Experiments were performed at an inlet saturation temperature of 35 to 45℃ and mass flux ranges from 200 to 600 kg/m²s. The use of an inner tube with a diameter of 4.0 mm resulted in a pressure gradient that was 2.5 times higher than that of an inner tube with a diameter of 8.0mm. In tube-in-tube HEX, the pressure gradients of R-22 measured higher than those of R-407C. The condensation heat transfer coefficients increase with an increase in mass flux, but they decrease with an increase in saturation temperature. Condensation heat transfer coefficients of R-407C were a little higher than those of R-22, and the condensation heat transfer coefficients of double tube HEX were about 40% higher than those of tube-in-tube HEX. The experimental results of this study were also compared with five existing correlations. New condensation heat transfer correlations were developed, and successfully predicted the experimental results with mean deviations of 10.6% and 10.1%, and average deviations are -0.92% and -0.31%, for R-22 and R-407C, respectively.

Experimental study on flow boiling characteristics of pure refrigerant (R134a) and zeotropic mixture (R407C) in a rectangular micro-channel

In the present study, the flow boiling characteristics of pure refrigerant R134a and zeotropic mixture R407C are experimentally investigated in a single visualized rectangular micro-channel heated on three sides with the cross-sectional area of 1mm×1mm and length of 106mm. Boiling heat transfer coefficients are obtained at the saturation temperature of 21°C under the heat flux and mass flux ranging from 30–150kW/m2 and 35–1400kg/m2s, respectively. The boiling curves of the two refrigerants are also discussed. Based on the visualization results, seven flow types are identified and the flow pattern maps are plotted. Through the comparative study, the phenomena of advance into churn-annular flow and coexistent bubbles with the flow patterns from confined bubble to annular are observed for R407C. The boiling heat transfer coefficient of R407C is slightly higher than that for R134a at lower vapor quality while the opposite situation appears with the increasing vapor quality after that. During churn-annular to annular flow stage, the boiling heat transfer coefficient of R407C presents a declining trend which is obviously different from the relatively stable value of R134a. The nucleate boiling heat transfer of R407C is suppressed during bubbly flow but promoted in confined bubble to slug flow stage compared with R134a. The CHF of R407C is higher than that of R134a. A correlation for the flow boiling heat transfer coefficient of mixtures is proposed in consideration of Ma number and predicts satisfactorily the database of R407C and R404A.

Flow boiling heat transfer characteristics of R407C inside a smooth tube with different tube inclinations

This paper presents the results of experimental investigations carried out with refrigerant R407C during flow boiling inside a smooth tube of inside diameter 7.0 mm at different tube inclinations. The experiments included five different tube inclination angles from 0° to 90° of the direction of refrigerant flow. The test runs were carried out at inlet temperature range of 6 °C to 9 °C, refrigerant mass velocities from 100 to 300 kgm−2 s−1 and heat fluxes between 3 and 6 kW m−2. The average quality of boiling refrigerant was between 0.1 and 0.9. The influences of the above parameters on the boiling heat transfer coefficient with tube inclinations are presented. The heat transfer coefficients predicted by some available models and correlations in the open literature are compared with the present data. An empirical correlation has also been developed to predict the heat transfer coefficient of R407C during flow boiling inside an inclined plain tube.

Prediction model of flow boiling heat transfer for R407C inside horizontal smooth tubes based on RBF neural network

The flow boiling heat transfer inside horizontal smooth tubes is studied for refrigerant mixture R407C and a prediction model is proposed based on RBF neural network. The factors strongly affecting the flow boiling have been assumed as the inputs, such as mass flux (G), heat flux (q), quality (x), saturation temperature (Tsat) and tube inner diameter (D). At the same time, the flow boiling heat transfer coefficient (h) as the output. The K-means clustering algorithm is applied to design RBF network. In addition, the prediction results is significantly improved compared with the four frequently used conventional correlations. For the network model of heat transfer, the average deviation, absolute average and root-mean-square deviations are -0.9%, 5.5% and 10.9%, respectively. Hence, the simulation results prove that the model based on RBF neural network is feasible to forecast the flow boiling heat transfer coefficient of R407C, and optimization design evaporators used R407C.

Partial condensation of R407C and R410A refrigerants inside a plate heat exchanger

This work investigates the condensation heat transfer of two refrigerants mixtures, R407C and R410A, in a brazed plate heat exchanger (BPHE) reporting the experimental measurements of the heat transfer coefficient. The prototype consists of six plates with two refrigerant ducts and three water channels. The condensation heat transfer coefficients of R407C and R410A have been measured at constant inlet saturation pressure of 1.6 MPa and 2.2 MPa, respectively. For both refrigerants, the superheating at the inlet of the heat exchanger was around 15 K; the mass flux has been varied from 15 to 40 kg m −2 s −1 whereas the outlet vapour quality has been changed between 0.07 and 0.58 in order to investigate the effect of vapour quality. The experimental measurements have been compared against three models suggested in the open literature; moreover, a new computation procedure for the design of BPHE condensers has been developed and validated against the present experimental database.

External condensation heat transfer coefficients of R22 alternative refrigerants on enhanced tubes at three saturation temperatures

In this study, external condensation heat transfer coefficients (HTCs) of R22, R410A, R407C, and R134a are measured on a 1024 fins per meter (26 fins per inch) low fin tube and Turbo-C tube at saturation temperatures of 30, 39, and 50 °C with wall subcooling of 3–8 °C. Test results show that condensation HTCs of all refrigerants decrease as the saturation temperature increases from 30 to 50 °C. This trend is due to the degradation of thermophysical properties of the liquid phase with an increase in saturation temperature. For the low fin tube data, Beatty and Katz's prediction equation showed a reasonably good agreement for all fluids with less than 20 per cent deviation. The performance of Turbo-C tube is better than that of the low fin tube for R22, R410A, and R134a due to the efficient removal of the condensate. For Turbo-C tube, HTCs of R407C were much lower than those of the other three fluids due to a unique condensation phenomenon associated with non-azeotropic mixtures at vapour—liquid interface. The average heat transfer enhancement ratios for the low fin tube and Turbo-C tube against the plain tube are 4.0–5.5 and 3.0–8.1, respectively, for all refrigerants tested.

Condensation heat transfer coefficients of HCFC22, R410A, R407C and HFC134a at various temperatures on a plain horizontal tube

In this study, external condensation heat transfer coefficients (HTCs) of HCFC22, R410A, R407C, and HFC134a were measured on a smooth horizontal tube at 30, 39, and 50℃ with the wall subcooling of 3-8℃. The results showed that condensation HTCs decreased for all fluids tested with an increase in temperature. This is due mainly to such properties as the saturated liquid density and liquid thermal conductivity. These properties decrease as the temperature increase and accordingly HTCs decrease. The condensation HTCs of R410A are 9.2~19.7% higher than those of HCFC22 while those of R134a are 2.5~10.2% lower than those of HCFC22. Condensation HTCs of R407C, nonazeotropic mixture, are 29.4~34.3% lower than those of HCFC22. Overall, the HTCs of R407C are much lower than those of HCFC22, HFC134a and R410A due to the mass transfer resistance in a diffusion vapor film. Condensation HTCs of HCFC22 and HFC134a are higher than those calculated by Nusselt’s equation by 7.7~11.8% and 4.0~11.1% respectively. On the other hand, HTCs of R407C measured on plain tube, however, are not well predicted by these well-known prediction correlations due to the introduction of mass transfer resistance associated with non-azeotropic mixtures.

Flow condensation heat transfer coefficients of R22, R134a, R407C, and R410A inside plain and microfin tubes

Flow condensation heat transfer coefficients (HTCs) of R22, R134a, R407C, and R410A inside horizontal plain and microfin tubes of 9.52 mm outside diameter and 1 m length were measured at the condensation temperature of 40 °C with mass fluxes of 100, 200, and 300 kg m−2 s−1 and a heat flux of 7.7–7.9 kW m−2. For a plain tube, HTCs of R134a and R410A were similar to those of R22 while HTCs of R407C are 11–15% lower than those of R22. For a microfin tube, HTCs of R134a were similar to those of R22 while HTCs of R407C and R410A were 23–53% and 10–21% lower than those of R22. For a plain tube, our correlation agreed well with the present data for all refrigerants exhibiting a mean deviation of 11.6%. Finally, HTCs of a microfin tube were 2–3 times higher than those of a plain tube and the heat transfer enhancement factor decreased as the mass flux increased for all refrigerants tested.