Experimental Study of Refrigerant (R-134a) Condensation Heat Transfer and Retention Behavior on Paraffin-Coated Vertical Plates and Fin Structures

2020 ◽  
Vol 142 (8) ◽  
Author(s):  
Hong-Qing Jin ◽  
Sophie Wang
Keyword(s):  
Heat Transfer ◽  
Copper Surface ◽  
Condensation Heat Transfer ◽  
Retention Behavior ◽  
Conduction Model ◽  
Maximum Increase ◽  
Liquid Retention ◽  
Transfer And Retention ◽  
Coated Surface ◽  
R 134A

Abstract Condensation of refrigerant R-134a is experimentally investigated on a paraffin-coated copper surface and compared to condensation on a plain copper surface. Heat transfer and visualization experiments are conducted for vertical-plate samples and for two different fin structures at various degrees of subcooling. A one-dimensional heat conduction model is used to interpret the condensation heat transfer measurements, while liquid retention behavior is quantified with the aid of image processing. The experimental results on vertical plates show that the heat transfer is enhanced on the coated surface with a maximum increase of 27% in the condensing heat transfer coefficient. On fin structures, the liquid retention was reduced by up to 28% on a coated surface. The heat transfer and retention behavior vary with surface material, degree of subcooling, and fin geometry.

Condensation of Low-Surface-Tension Fluids on Microstructured Surfaces at Low Temperature

2017 ◽  
Author(s):  
Abulimiti Aili ◽  
Qiaoyu Ge ◽  
TieJun Zhang
Keyword(s):  
Heat Transfer ◽  
Surface Tension ◽  
Low Temperature ◽  
High Surface ◽  
Condensation Heat Transfer ◽  
Lubricant Oil ◽  
Microstructured Surfaces ◽  
Performance Deterioration ◽  
Coated Surface ◽  
Coated Surfaces

Filmwise condensation of a low surface tension fluid (i.e. refrigerant) on microstructured aluminum surfaces is studied to investigate the effect of the structures on condensation heat transfer at low temperature. The hypothesis is that the structures may cause thinning of the condensate film at micro-scales, thus resulting in an enhancement of condensation heat transfer. However, the structures may also decrease the mobility of the condensate near the surface due to increased friction, thus potentially leading to performance deterioration. The aim of this work is to investigate which of the two counteracting mechanisms dominate during filmwise condensation. Condensation experiments are carried out in a low-temperature vacuum chamber. Compared with the Nusselt model of condensation, the microstructured surfaces, either coated or uncoated, show similar performance, with potentially slight enhancement at low subcooling degree and slight deterioration at high subcooling degree. When the microstructured and silane-coated surface is infused with a non-volatile and very low-surface-tension lubricant oil, the lubricant is displaced by the condensate and there is almost no change in the condensation performance. Our results show that, unlike the case of dropwise condensation of high-surface tension fluids, microstructured and coated surfaces with/without infusing oil is not exciting to enhanced filmwise condensation of low-surface-tension fluids.

Predicting Heat Transfer in Long R-134a Filled Thermosyphons

2009 ◽  
Vol 131 (5) ◽  
Author(s):  
M. H. M. Grooten ◽  
C. W. M. van der Geld
Keyword(s):  
Heat Transfer ◽  
Saturation Temperature ◽  
Good Alternative ◽  
Condensation Heat Transfer ◽  
Air Cooling ◽  
Transfer Coefficients ◽  
Reduced Pressure ◽  
Evaporation Heat ◽  
Evaporation Heat Transfer ◽  
R 134A

When traditional air-to-air cooling is too voluminous, heat exchangers with long thermosyphons offer a good alternative. Experiments with a single thermosyphon with a large length-to-diameter ratio (188) and filled with R-134a are presented and analyzed. Saturation temperatures, filling ratios, and angles of inclination have been varied in wide ranges. A higher sensitivity of evaporation heat transfer coefficients on reduced pressure than in previous work has been found. Measurements revealed the effect of pressure or the saturation temperature on condensation heat transfer. The condensate film Reynolds number that marks a transition from one condensation heat transfer regime to another is found to depend on pressure. This effect was not accounted for by correlations from the literature. New correlations are presented to predict condensation and evaporation heat transfer rates.

Heat Transfer in Direct Contact Condensation of Steam to Subcooled Water Spray

2001 ◽  
Vol 123 (4) ◽  
pp. 703-710 ◽  
Author(s):  
Minoru Takahashi ◽  
Arun Kumar Nayak ◽  
Shin-ichi Kitagawa ◽  
Hiroyuki Murakoso
Keyword(s):  
Heat Transfer ◽  
Flow Direction ◽  
Condensation Heat Transfer ◽  
Saturated Steam ◽  
Internal Circulation ◽  
Conduction Model ◽  
Subcooled Water ◽  
Hollow Cone Spray ◽  
Contact Condensation ◽  
Condensation Heat Transfer Coefficient

The condensation heat transfer of saturated steam to a hollow-cone spray of subcooled water was investigated experimentally and analytically. The spray water temperature rose more steeply in flow direction than those in the previous studies, because of the use of smaller thermocouple which was capable of measuring the temperature in a thin water sheet and water droplets more accurately. The result of the condensation heat transfer coefficient suggested the breakup of the water sheet into droplets. A pure conduction model underpredicted the heat transfer in the sheet region significantly, which was better predicted by considering turbulence in the sheet. The heat transfer in the droplet region was well estimated by considering internal circulation and mixing inside the droplets.

Condensation Heat Transfer and Pressure Drop of R-134a Flowing in Annular Helical Pipes at Different Orientations

2003 ◽  
Author(s):  
B. Yu ◽  
C. X. Lin ◽  
M. A. Ebadian ◽  
R. C. Prattipati
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Cooling Water ◽  
Saturation Temperature ◽  
Condensation Heat Transfer ◽  
Working Fluid ◽  
Transfer Coefficients ◽  
Cooling Water Temperature ◽  
Helical Pipe ◽  
R 134A

This paper presents an experimental investigation of condensation heat transfer and pressure drop characteristics of refrigerant R-134a flowing through an annular helicoidal passage with the hydraulic diameter of 8.5 mm. The angles of helix axis are oriented at 0, 45, 90 degrees to gravity. The overall and refrigerant-side heat transfer coefficients and pressure drops are experimentally determined at saturation temperature 35°C, refrigerant mass flux 35–180 kg/s·m2, and cooling water temperature 27°C. The results show that orientation has significant influence on the thermal and hydraulic behaviors of the helical pipe. The results can be employed for reference in the effective design of annular helicoidal heat exchangers with R-134a as the working fluid.

Condensation Heat Transfer on a Partially Hydrophobic Surface

2014 ◽  
Author(s):  
Ramana Saketh Vanga ◽  
Sunwoo Kim
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Copper Surface ◽  
Copper Sample ◽  
Heterogeneous Surface ◽  
Condensation Heat Transfer ◽  
Transfer Coefficients ◽  
Heterogeneous Sample ◽  
Heat Transfer Coefficients

Renewable energy systems operated by a thermal energy resource such as geothermal power plants and solar thermal power systems are demanding improvement in their condensation performance [Kutscher & Costenaro, 2009]. While their energy resources are naturally obtained at almost no cost, heat rejecting components become relatively expensive to maintain and operate. In this research, a heterogeneous condensing surface is proposed to enhance the condensation heat transfer coefficient in vapor-to-liquid heat exchangers. On its surface, parallel stripes with hydrophobic feature and ones without it alternate. The effect of the partially hydrophobic condensing surface on the dropwise condensation heat transfer of saturated steam on the flat plate copper surface is experimentally investigated. A vertical flat plat condenser is constructed to evaluate the performance of the heterogeneous condensing surface in comparison with a plain copper sample and a homogeneous hydrophobic-treated copper sample. Experimental results show that condensation heat transfer of steam on the homogeneous hydrophobic-treated sample is superior to that on the plain copper surface despite the fact that both the surfaces stably promote dropwise condensation. The heat transfer coefficients for the heterogeneous surface at lower subcooling temperatures, when its stripes situate horizontally, are as high as the heat transfer coefficients for the homogeneous hydrophobic-treated surface. The enhancement for the horizontal heterogeneous sample over the plain copper sample is approximately 100%. The heat transfer coefficient for the heterogeneous sample with its stripes being vertical at 4 K subcooling is 25% greater than that of the plain copper sample. Higher heat transfer coefficients are observed at lower subcooling temperatures for all the samples. The results and observations of this project suggest that the heterogeneous surface has the potential to enhance the heat transfer coefficients.

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