Experimental Study on Free-Convection Condensation Heat Transfer From Moist Air

2005 ◽  
Author(s):  
Niro Nagai ◽  
Masanori Takeuchi ◽  
Osamu Kura ◽  
Tomoharu Masuda
Keyword(s):  
Heat Transfer ◽  
Free Convection ◽  
Inclination Angle ◽  
Pressure Ratio ◽  
Film Theory ◽  
Experimental Results ◽  
Condensation Heat Transfer ◽  
Moist Air ◽  
Transfer Coefficients ◽  
Experimental Conditions

Characteristics of free-convection condensation heat transfer from moist air under atmospheric pressure were experimentally investigated, for further improvement of physical modeling on heat and mass transfer of solar distillation device. The cooled metal surface was 50mm width × 100mm height. The experimental conditions were as follows. Moist air temperature range was 40∼100°C for saturated moist air, and 50∼70°C for non-saturated moist air. Relative humidity range was 50∼90%. Inclination angle of cooled surface was 0° (downward facing) ∼ 180° (upward facing). All experimental results of heat transfer characteristics for vertical surface (angle 90°) were well correlated into a single equation with partial air pressure ratio using classical Nusselt’s liquid-film theory. The experimental results for the effects of inclination angle show that heat transfer coefficients for angle 0°∼105° were almost constant with slight peak value at angle 45°, followed by rapid decreasing of heat transfer coefficient over angle 120°.

Effect of Temperature Difference on In-Tube Condensation Heat Transfer Coefficients

2016 ◽  
Vol 139 (1) ◽  
Author(s):  
Malcolm Macdonald ◽  
Srinivas Garimella
Keyword(s):  
Heat Transfer ◽  
Temperature Difference ◽  
Film Theory ◽  
Horizontal Tube ◽  
Condensation Heat Transfer ◽  
Effect Of Temperature ◽  
Test Fluid ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Underlying Mechanisms

The effect of temperature difference (Tsat − Tcoolant) on condensation heat transfer coefficients inside horizontal tubes is investigated in detail. Condensation experiments are conducted on propane inside a 7.75 mm horizontal tube at four temperature differences between the test fluid and coolant at three mass fluxes and four saturation temperatures. The heat transfer coefficient is shown to increase with temperature difference, with this effect diminishing with larger temperature differences, and being most significant at higher saturation temperatures. Heat transfer coefficients at the low-reduced pressures (Pr = 0.25) corresponding to lower saturation temperatures (30 °C) are mostly unaffected by the temperature difference. Subcooling of the condensate is expected to increase heat transfer coefficients at the larger temperature differences. Flow visualization studies are used to explain the inadequacy of the Nusselt film theory for the conditions investigated. The underlying mechanisms are also used to explain why the correlations from the literature do not predict the observed trend, and a new correlation to account for the effect of temperature difference is developed.

Condensation heat transfer and pressure drop of R134a inside microfin tubes: Effect of fin height and fin angle

2007 ◽  
Vol 221 (1) ◽  
pp. 43-53 ◽  
Author(s):  
R K Al-Dadah ◽  
A D Naser
Keyword(s):  
Heat Transfer ◽  
Experimental Results ◽  
Condensation Heat Transfer ◽  
Smooth Tube ◽  
Transfer Coefficients ◽  
Pressure Drops ◽  
Mass Fluxes ◽  
Wide Range ◽  
Spiral Angle ◽  
Microfin Tubes

In this paper, the effects of fin height and fin angle on condensation heat transfer inside microfin tubes were investigated. One smooth and six microfin tubes with outer diameters of 9.52 mm were used to condense R134a at 30 °C and a mass flux range 157–347 kg/m2s. Each of the microfin tubes tested had 60 fins and a spiral angle of 18°. In three of these tubes only the fin height was altered to 0.15, 0.20, or 0.25 mm while the fin angle remained at 30°. The remaining microfin tubes had altered fin angles to 40, 50, or 60°, with the fin heights remaining at 0.20 mm. Experimental results showed that microfin tubes had distinct performance advantages over the smooth tube. Particularly, the microfin tube with fin height of 0.20 mm and fin angle of 50° produced condensation heat transfer coefficients 215–250 per cent higher than those of the smooth tube, with average increases in pressure drops at 115–160 per cent. Four frequently cited correlations were used to predict the heat transfer coefficient for condensation inside smooth tubes. Of these correlations, the predictive method proposed by Cavallini et al. [1] that takes into account the wide range of flow patterns encountered in condensation at various mass fluxes was found to best predict the experimental results. For microfin tubes, the model by Yu and Koyama [2] predicted the experimental results with least deviation from experimental results compared to that of Cavallini et al. [3, 4] and that of Kedzierski and Goncalves [5].

scholarly journals Experimental study on enhancement characteristics of steam/nitrogen condensation inside horizontal multi-start helical channels

Open Physics ◽  
2021 ◽  
Vol 19 (1) ◽  
pp. 634-646
Author(s):  
Jianjun Wen ◽  
Zhi Dou ◽  
Jiaqi Zhong ◽  
Yonghong Niu ◽  
Zhenwei Hu ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Performance Evaluation ◽  
Cooling Water ◽  
Condensation Heat Transfer ◽  
Steam Condensation ◽  
Transfer Coefficients ◽  
Experimental Conditions ◽  
Interfacial Shearing Stress ◽  
Comparison Results ◽  
Helical Channels

Abstract The aim of this study was to reveal the internal mechanism of enhanced condensation heat transfer, by experimentally performing steam condensation with higher inlet velocity in the horizontal multi-start helical channels (HMSHCs), and investigating the influences of pressure of steam, mass flowrate of cooling water, and mass fraction of noncondensable (NC) gas on steam condensation performance. Taking steam condensation in horizontal circular condensation channel (HCCC) as a reference, the condensation heat transfer coefficients (CHTCs), the outlet condensate mass flowrates (CMFRs), and the total steam condensation pressure drops (SCPDs) were compared and discussed, respectively. The results indicated that NC gas had a strong inhibitory effect on steam condensation, and average condensation characteristics decreased with the increase in NC gas fraction for lower Rem. But for higher Rem, the gas–liquid interfacial shearing stress can likely weaken the negative effect of NC gas. In addition, increasing the cooling water flowrate can entirety promote steam condensation. The comparison results indicated that steam condensation performance of HMSHC is better than that of HCCC under same experimental conditions. For the specific experimental scope, the average CHTCs and the outlet CMFRs in HMSHC are approximately 2.35 and 1.25 times of that inside HCCC, respectively, while the overall SCPDs in HMSHC are about 1.16 times of that inside HCCC. After introducing the performance evaluation factor, the calculation results revealed that the performance evaluation factor h PEC {h}_{\text{PEC}} of the average CHTCs in HMSHC is approximately 2.02, and the performance evaluation factor m PEC {{m}}_{\text{PEC}} of the outlet CMFRs in HMSHC is approximately 1.08. The two evaluating values are reasonable.

scholarly journals Influence of Active Cooling at the Trailing Edge on the Thermal Behavior of a Tilting-Pad Journal Bearing

Lubricants ◽  
2021 ◽  
Vol 9 (3) ◽  
pp. 26
Author(s):  
Nico Buchhorn ◽  
Michael Stottrop ◽  
Beate Bender
Keyword(s):  
Heat Transfer ◽  
Thermal Behavior ◽  
Experimental Results ◽  
Transfer Coefficients ◽  
Trailing Edge ◽  
Active Cooling ◽  
Oil Supply ◽  
Tilting Pad ◽  
Carry Over ◽  
Lower Temperature

In tilting-pad journal bearings (TPJB) with a non-flooded lubrication concept, higher maximum pad temperatures occur than with a flooded bearing design due to the lower convective heat transfer at the pad edges. In this paper, we present an approach to influence the thermal behavior of a five-pad TPJB by active cooling. The aim of this research is to investigate the influence of additional oil supply grooves at the trailing edge of the two loaded pads on the maximum pad temperature of a large TPJB in non-flooded design. We carry out experimental and numerical investigations for a redesigned test bearing. Within the experimental analysis, the reduction in pad temperature is quantified. A simulation model of the bearing is synthesized with respect to the additional oil supply grooves. The simulation results are compared with the experimental data to derive heat transfer coefficients for the pad surfaces. The experimental results indicate a considerable reduction of the maximum pad temperatures. An overall lower temperature level is observed for the rear pad in circumferential direction (pad 4). The authors attribute this effect by a cooling oil carry-over from the previous pad (3). Within the model limits, a good agreement of the simulation and experimental results can be found.

Measurement and Modeling of Condensation Heat Transfer Coefficients in Circular Microchannels

2006 ◽  
Vol 128 (10) ◽  
pp. 1050-1059 ◽  
Author(s):  
Todd M. Bandhauer ◽  
Akhil Agarwal ◽  
Srinivas Garimella
Keyword(s):  
Heat Transfer ◽  
Flow Rate ◽  
Heat Transfer Model ◽  
Condensation Heat Transfer ◽  
Low Flow ◽  
Transfer Model ◽  
Shear Stresses ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Circular Microchannels

A model for predicting heat transfer during condensation of refrigerant R134a in horizontal microchannels is presented. The thermal amplification technique is used to measure condensation heat transfer coefficients accurately over small increments of refrigerant quality across the vapor-liquid dome (0<x<1). A combination of a high flow rate closed loop primary coolant and a low flow rate open loop secondary coolant ensures the accurate measurement of the small heat duties in these microchannels and the deduction of condensation heat transfer coefficients from measured UA values. Measurements were conducted for three circular microchannels (0.506<Dh<1.524mm) over the mass flux range 150<G<750kg∕m2s. Results from previous work by the authors on condensation flow mechanisms in microchannel geometries were used to interpret the results based on the applicable flow regimes. The heat transfer model is based on the approach originally developed by Traviss, D. P., Rohsenow, W. M., and Baron, A. B., 1973, “Forced-Convection Condensation Inside Tubes: A Heat Transfer Equation For Condenser Design,” ASHRAE Trans., 79(1), pp. 157–165 and Moser, K. W., Webb, R. L., and Na, B., 1998, “A New Equivalent Reynolds Number Model for Condensation in Smooth Tubes,” ASME, J. Heat Transfer, 120(2), pp. 410–417. The multiple-flow-regime model of Garimella, S., Agarwal, A., and Killion, J. D., 2005, “Condensation Pressure Drop in Circular Microchannels,” Heat Transfer Eng., 26(3), pp. 1–8 for predicting condensation pressure drops in microchannels is used to predict the pertinent interfacial shear stresses required in this heat transfer model. The resulting heat transfer model predicts 86% of the data within ±20%.

Application of Artificial Neural Network for the Heat Transfer Investigation Around a High-Pressure Gas Turbine Rotor Blade

2011 ◽  
Author(s):  
Ibrahim Eryilmaz ◽  
Sinan Inanli ◽  
Baris Gumusel ◽  
Suha Toprak ◽  
Cengiz Camci
Keyword(s):  
Neural Network ◽  
Heat Transfer ◽  
Artificial Neural Network ◽  
High Pressure ◽  
Rotor Blade ◽  
Incidence Angle ◽  
Transfer Coefficients ◽  
Experimental Conditions ◽  
Heat Transfer Coefficients ◽  
Artificial Neural

This paper presents the preliminary results of using artificial neural networks in the prediction of gas side convective heat transfer coefficients on a high pressure turbine blade. The artificial neural network approach which has three hidden layers was developed and trained by nine inputs and it generates one output. Input and output data were taken from an experimental research program performed at the von Karman Institute for Fluid Dynamics by Camci and Arts [5,6] and Camci [7]. Inlet total pressure, inlet total temperature, inlet turbulence intensity, inlet and exit Mach numbers, blade wall temperature, incidence angle, specific location of measurement and suction/pressure side specification of the blade were used as input parameters and calculated heat transfer coefficient around a rotor blade used as output. After the network is trained with experimental data, heat transfer coefficients are interpolated for similar experimental conditions and compared with both experimental measurements and CFD solutions. CFD analysis was carried out to validate the algorithm and to determine heat transfer coefficients for a closely related test case. Good agreement was obtained between CFD results and neural network predictions.

Characterization of the Effect of Corrugation Angles on Hydrodynamic and Heat Transfer Performance of Four-Start Spiral Tubes

2001 ◽  
Vol 123 (6) ◽  
pp. 1149-1158 ◽  
Author(s):  
X. D. Chen ◽  
X. Y. Xu ◽  
S. K. Nguang ◽  
Arthur E. Bergles
Keyword(s):  
Heat Transfer ◽  
Evaluation Criteria ◽  
Geometry Optimization ◽  
Longitudinal Direction ◽  
Experimental Results ◽  
Neural Network Modeling ◽  
Transfer Coefficients ◽  
Correlation Models ◽  
Friction Factors ◽  
Double Pipe

A series of four-start spirally corrugated tubes has been subjected to heat transfer and hydrodynamic testing in a double-pipe heat exchanger. The study has been focused on the non-symmetric nature of the corrugation angles along the longitudinal direction. Both friction factors and heat transfer coefficients inside the tubes have been correlated against various process parameters. It can be shown that by altering the internal non-symmetric wavy shapes of the tubes, one is able to manipulate heat transfer and friction characteristics. The experimental results have been compared with some popular correlation models developed previously for both friction and heat transfer for corrugated tubes. Considerable differences between the experimental results and the predictions made using the existing correlations have been found and the probable causes have been discussed. Performance evaluation criteria are presented using the standard constant power criterion. A neural network modeling approach has been taken so that, based on the limited data, one can generate the contour showing the effect of corrugation angle on heat transfer coefficient for geometry optimization purposes.

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