Condensation Of R134a Research Articles

Condensation heat transfer of herringbone micro fin tubes

Experiments of in-tube condensation of R410A were carried out for a smooth tube, a helical micro fin tube and three types of herringbone micro fin tubes, which have different fin height and helix angle. In the herringbone micro fin tube, the micro fins work to remove liquid at fin-diverging parts and collect liquid at fin-converging parts. In the high mass velocity region the heat transfer coefficients of all the herringbone tubes are higher than those of the helical micro fin tube. In the low mass velocity region, however, the heat transfer coefficients of the herringbone micro fin tubes are slightly lower than those of the helical micro fin tube. The heat transfer coefficient is lower for smaller helix angle tube and effect of fin height on the heat transfer is small. Pressure drop of the herringbone tube of which helix angle is small is lower than that of the helical micro fin tube, while that of other tubes is higher. Flow configurations of the herringbone tubes were observed with R123 as working fluid and the heat transfer enhancement mechanism is discussed.

Fully coupled solution of a two-phase model for laminar film condensation of vapor–gas mixtures in horizontal channels

Detailed results are presented for laminar film condensation of vapor–gas mixtures in horizontal flat-plate channels using a fully coupled implicit numerical approach that achieves excellent convergence behavior. These results correspond to steam–air and R134a–air mixtures over wide ranges of the independent parameters, and they include velocity, temperature, and gas concentration profiles, as well as axial variations of film thickness, pressure gradient and Nusselt number. Effects of the four independent variables (inlet values of gas concentration, Reynolds number and pressure, and the inlet-to-wall temperature difference) on the film thickness, pressure gradient, and the local and average Nusselt numbers are carefully examined. It was found that the condensation of R134a–air corresponds to thicker liquid films, lower heat transfer rates, and lower algebraic values of the pressure gradient when compared with steam–air at the same operating conditions.

Two-phase flow regimes in round, square and rectangular tubes during condensation of refrigerant R134a

An experimental investigation of two-phase flow mechanisms during condensation of refrigerant R134a in six small diameter round (4.91 mm), square ( D h=4 mm, α=1), and rectangular (4×6 and 6×4 mm: D h=4.8 mm, α=0.67 and 1.5; 2×4 and 4×2 mm: D h=2.67 mm, α =0.5 and 2) was conducted. Unique experimental techniques and test sections were developed to enable the documentation of the flow mechanisms during phase change. For each tube under consideration, flow mechanisms were recorded over the entire range of qualities for five different refrigerant mass fluxes between 150 and 750 kg m −2 s −1. The flow mechanisms were categorized into four different flow regimes: intermittent flow, wavy flow, annular flow, and dispersed flow. In addition, the large amount of data enabled the delineation of several different flow patterns within each flow regime, which provides a clearer understanding of the different modes of two-phase flow. Transition lines between the respective flow patterns and regimes on these maps were established based on the experimental data. It was found that for similar hydraulic diameters, flow regime transitions are not very strongly dependent on tube shape or aspect ratio. These maps and the transition lines can be used to predict the particular flow pattern or regime that will be established for a given mass flux, quality and tube geometry.

Prediction of heat transfer coefficient during condensation of water and R-134a on single horizontal integral-fin tubes

This paper presents a few salient features of an investigation carried out to study the heat transfer augmentation during condensation of water and R-134a vapor on horizontal integral-fin tubes. The experimental investigation was performed on two different experimental set-ups for water and R-134a. The test-sections were manufactured by machining fins over plain copper tubes of 24.4 ± 0.6 mm outside diameter. The performance of two types of finned tubes viz. circular integral-fin tubes (CIFTs) and spine integral-fin tubes (SIFTs) was studied for the condensation of water and R-134a. These tubes were positioned one by one inside the test-condenser to perform the experiments. All together the experiments were conducted for the condensation on 10 different test-section tubes. With the help of the experimental results, authors have developed an empirical equation. This equation predicts the condensing heat transfer coefficient from their own experimental data for the condensation over CIFTs and SIFTs within a range of ± 15% and experimental data of other thirteen investigators in a range of ± 35% for condensation of water and different refrigerants.

Augmentation of heat transfer during filmwise condensation of steam and R-134a over single horizontal finned tubes

An experimental investigation has been carried out to augment the heat transfer rate by enhancing the heat transfer coefficient during the condensation of pure vapours of steam and R-134a over horizontal finned tubes. The study was conducted for plain tubes, circular integral-fin tubes (CIFTs), spine integral-fin tubes (SIFTs) and parially spined circular integral-fin tubes (PCIFTs). The SIFT out performed the CIFT for the condensation of R-134a by approximately 16%. However, the spines were found most effective in the bottom side of the CIFT. The PCIFTs with the spines only in the bottom side of the tube augmented the heat transfer coefficient by 20% and 11% for the condensation of steam and R-134a, respectively, in comparison to the CIFT.

Condensation and evaporation heat transfer of R410A inside internally grooved horizontal tubes

Heat transfer coefficient and pressure drop were measured for condensation and evaporation of R410A and HCFC22 inside internally grooved tubes. The experiments were performed for a conventional spiral groove tube of 8.01 mm o.d. and 7.30 mm mean i.d., and a herring-born groove tube of 8.00 mm o.d. and 7.24 mm mean i.d. To measure the local heat transfer coefficients and pressure drop, the test section was subdivided into four small sections having 2 m working length. The ranges of refrigerant mass flow density was from 200 to 340 kg/(m2 s) for both condensation and evaporation of R410A and HCFC22, and the vapour pressure was 2.41 MPa for condensation and 1.09 MPa for the evaporation of R410A. The obtained heat transfer data for R410A and HCFC22 indicate that the values of the local heat transfer coefficients of the herring-bone grooved tube are about twice as large as those of spiral one for condensation and are slightly larger than those of spiral one for the evaporation. The measured local pressure drop in both condensation and evaporation is well correlated with the empirical equation proposed by the authors.

A Comprehensive Study of Modified Wilson Plot Technique to Determine the Heat Transfer Coefficient during Condensation of Steam and R-134a over Single Horizontal Plain and Finned Tubes

In the present investigation a comprehensive study of the modified Wilson plot technique has been made and a stepwise methodology has been evolved. This technique can be used to determine the condensing-side heat transfer coefficient during condensation of vapor over a horizontal tube. The necessary experimental data have been acquired by conducting experiments for the condensation of steam and R-134a over a plain tube and different finned tubes (CIFTs and SIFTs). The experimental heat transfer coefficient, based on the test-section wall temperature measurement (wall temperature was measured with thermocouples), ho, has been compared with that predicted by the modified Wilson plot technique, hmw. The modified Wilson plot technique underpredicted the condensing-side heat transfer coefficient for the condensation of steam in a range of 7.5-15%. The heat transfer coefficient for the condensation of R-134a is also underpredicted in a range of 13-25% by this technique.

Effect of Hydraulic Diameter on Condensation of R-134A in Flat, Extruded Aluminum Tubes

Effect of Hydraulic Diameter on Condensation of R-134A in Flat, Extruded Aluminum Tubes

Condensation of R134a flowing inside helicoidal pipe

Condensing heat transfer and pressure drop characteristics of an ozone-friendly refrigerant HFC-134a (hydrofluorocarbon 134a) flowing inside a 12.7 mm helicoidal tube were investigated experimentally to obtain heat transfer data and correlations. For long helicoidal pipe, heat transfer measurements were performed for the refrigerant flow mass fluxes from 100 to 400 kg/m 2/s, in the cooling water flow Reynolds number range of 1500<Re w <9000 at fixed system temperature (33°C) and cooling tube wall temperature (12°C and 22°C). With the increase of mass flux, the overall condensing heat transfer coefficients of R134a increased, and slowly the pressure drops also increased. However, with the increase of mass flux (or the cooling water flow Reynolds number), the refrigerant side heat transfer coefficients decreased. The effects of cooling wall temperature on heat transfer coefficients and system pressure drops were considered. Predictive correlations valid over the above water flow Reynolds number ranges and refrigerant flow mass flux were proposed. Helicoidal pipe heat transfer characteristics were compared with data for horizontal straight pipe from literature reports.

An Analytical Model to Predict Condensation of R-410A in a Horizontal Rectangular Channel

An analytical model to predict condensation heat transfer coefficient in a horizontal rectangular channel was developed. The total local condensation heat transfer coefficient was represented as the weighted average of heat transfer coefficients for each wall. The analytical predictions compared well with the experimental data on the condensation of R-410A in a rectangular channel. The mean deviation was 6.75 percent. [S0022-1481(00)00503-X]

Effect of Fin Geometry on Condensation of R134a in a Staggered Bundle of Horizontal Finned Tubes

Effect of Fin Geometry on Condensation of R134a in a Staggered Bundle of Horizontal Finned Tubes

EHD-assisted external condensation of R-134a on smooth horizontal and vertical tubes

In this paper, results of an experimental study on the EHD-assisted external condensation of R-134 over a plain tube will be presented and discussed. The experiments performed can be divided into two groups: (1) EHD-assisted external condensation on a vertical smooth tube and (2) EHD-assisted external condensation experiments on a horizontal smooth tube. In each case, experiments were conducted as a function of parametric values such as heat flux, electrode gaps and applied electric field potential. All of the experiments were conducted using a specially designed helical electrode and with R-134a as the working fluid. Experimental results demonstrate a remarkable potential in utilizing EHD to enhance external condensation heat transfer. It is concluded that the enhancement is driven by the effective removal of the condensate through EHD-induced liquid extraction and dispersion phenomena.

Condensation of R-410A in a Rectangular Channel

A two-phase loop to measure the condensation heat transfer coefficient of R-410A was designed, built, and calibrated. The test section was a 3 m (10 ft) long horizontal, rectangular brass (63% Cu, 37% Zn by mass) tube 12.7 mm (0.5 in.) wide and 25.4 mm (1.0 in.) high. Uncertainty analysis was performed for each set of collected data. Any experimental data with an uncertainty greater than 10% was discarded. Also, any experimental data that failed to satisfy the energy balance for the test section within 5% was discarded. Over three hundred experimental runs were made. They covered a mass flux range of 30 to 200 kg/(s·m2) (2.2×104 to 1.48×105 lbm/h·ft2), a refrigerant saturation temperature range of 7.8 to 36.7°C (46 to 98°F), and a saturation pressure range of 1.02 to 2.23 MPa (147.4 to 323.4 psi). From this experimental database, 173 sets of data, which satisfied both the heat balance requirement and uncertainty requirement, were selected for further analysis. This study focused primarily on measurement and prediction of condensation heat transfer coefficients and the relationship between heat transfer coefficients and two-phase flow regimes. Flow pattern studies showed that the condensation was predominantly in the wavy stratified flow regime at a mass flux of less than 200 kg/(s·m2). For higher mass flux rates, the condensation was in the annular flow regime. The regionally averaged heat transfer coefficient for condensing R-410A in a rectangular channel decreased with a decrease in quality, and increased with an increase in mass flux. Using the experimental database a correlation was developed to predict the regionally averaged condensation heat transfer coefficient. In the same experimental study, the effect of oil contamination on the heat transfer performance of condensing R-410A was also investigated. Tests were conducted with two different oil concentrations (1.26% and 2.51% by mass). Results indicated that the presence of oil decreased the condensation heat transfer coefficient by 10 to 20%.

Thermodynamic property formulations and heat transfer aspects for replacement refrigerants: R-123 and R-134a

This paper reports analytical relations for the thermodynamic properties enthalpy, entropy, heat capacities at constant pressure and temperature of the replacement refrigerants R-123 and R-134a. These refrigerants are considered promising as substitutes for the fluids R-11 and R-12, respectively, which are two of the most widely used CFC refrigerants. In addition to the properties, the three real gas isentropic exponents kp,v,kv,T, kp,T are calculated, which may be used instead of the classical exponent k=cp/cv in the ideal gas isentropic change equations to describe with good accuracy the real gas behaviour. A systematic study to research the influence of various parameters on heat transfer during condensation of R-123 and R-134a on horizontal integral-fin tubes is also carried out. The results are useful in refrigeration applications to improve the basic design, as a significant concern about new refrigerants to replace the CFCs has increased very rapidly due to the destruction of stratospheric ozone and global warming. © 1997 John Wiley & Sons, Ltd.

Transfert thermique pour la condensation du R123, du R134a et de leurs mélanges, en écoulement forcé entre deux plaques planes horizontales. Etude numérique.

Heat transfer for forced convection condensation of R123, R134a and their mixtures flowing between two horizontal parallel plates. Numerical study. Film condensation of pure and binary mixtures flowing between parallel plates is treated numerically. The coupled equations of mass, momentum, species and energy conservations for the two phases are solved with an implicite scheme. In this study, we retained the pressure forces, the liquid and vapor interfacial shear stress, the Dufour effect, the inertia and enthalpy convection terms, the turbulence in the two phases and the variation of the physical properties with the temperature and concentration. The results obtained for the condensation of refrigerants R123 and R134a, show strong influence of the composition of mixture on the mean heat transfer coefficient and the total pressure loss. The calculated mean Nusselt number is in good agreement with the experimental correlations of Mochizuki and Inoué [6] and Akers and Rosson [24]. A new correlation for the mean heat transfer for forced convection condensation of pure refrigerants R123 and R134a and their mixtures between horizontal flate plates is proposed.