Effects of Tube Row on Heat Transfer and Surface Wetting of Microscale Porous-Layer Coated, Horizontal-Tube, Falling-Film Evaporator

2013 ◽  
Vol 135 (4) ◽  
Author(s):  
Batikan Köroğlu ◽  
Nicholas Bogan ◽  
Chanwoo Park
Keyword(s):  
Heat Transfer ◽  
Porous Layer ◽  
Horizontal Tube ◽  
Flow Mode ◽  
Falling Film ◽  
Surface Wetting ◽  
Solution Flow ◽  
Flow Rates ◽  
Film Evaporator ◽  
Evaporation Heat

An experimental study was conducted to investigate the effects of tube row on surface wetting and heat transfer of a horizontal-tube, falling-film evaporator. Two types of the evaporator tubes were used for comparison: plain copper and copper coated with a microscale porous-layer. Distilled water was used as solution and heating fluids. A visual observation experiment performed in ambient with no heat input showed that when solution fluid was dripped onto the evaporator tubes from a solution dispenser, the plain tubes were partially wetted, while the porous-layer coated tubes were completely wetted due to capillary liquid spreading, even at low solution flow rates. It was found from the heat transfer experiment performed in a closed chamber under saturated conditions that the porous-layer coated tubes exhibited superior evaporation heat transfer (up to 100% overall improvement over the plain tubes at low solution flow rates) due to complete solution wetting and thin-film evaporation. It was also observed that the surface wetting and heat transfer are greatly influenced by both intertube flow mode of solution fluid and tube wall superheat. The effects of the tube row on the solution wetting and heat transfer were significant, especially for downstream tubes.

Experimental Study of Tube Row Effects on Evaporation Heat Transfer Using a Micro-Scale, Porous-Layer Coating on a Horizontal-Tube, Falling-Film Heat Exchanger

2012 ◽  
Author(s):  
Batikan Köroğlu ◽  
Nicholas Bogan ◽  
Chanwoo Park
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Porous Layer ◽  
Horizontal Tube ◽  
Falling Film ◽  
Solution Flow ◽  
Micro Scale ◽  
Evaporation Heat ◽  
Evaporation Heat Transfer ◽  
Layer Coating

An experimental study was conducted to investigate the effects of tube row and a micro-scale porous-layer coating on solution fluid wetting and heat transfer of a horizontal-tube, falling-film heat exchanger using an inline tube arrangement. A uniform layer of micro-scale copper particles was directly bonded onto plain copper tubes by sintering to create a porous-layer coating on the tubes. Distilled water was used as solution and heating fluids. The visual observation performed in open ambient condition revealed that when the solution was dripped onto horizontal tubes from a solution dispenser, the conventional plain tubes were always partially wetted while the porous-layer coated tubes were completely wetted due to capillary action, even at low solution flow rates. It was shown from the comparison of the evaporation heat transfer results of the plain and porous-layer coated tubes tested in a closed chamber under saturated conditions that the porous-layer coated tubes exhibited a superior evaporation heat transfer rate (around 70% overall improvement at low solution flow rates) due to the complete solution wetting and thin solution liquid film on the evaporator tubes. It was also observed that the heat transfer and surface wetting of the horizontal-tube, falling-film heat exchanger are greatly affected by both the flow mode of the solution fluid between the tubes and tube wall superheats. The effect of the tube row of the falling-film heat exchanger on the solution wetting and heat transfer was significant.

Enhancement of Solution Wetting and Heat Transfer on Horizontal-Tube, Falling-Film Evaporator Using Porous-Layer Coating

2010 ◽  
Author(s):  
Sangsoo Lee ◽  
Chanwoo Park
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Porous Layer ◽  
Complete Solution ◽  
Horizontal Tube ◽  
Partial Solution ◽  
Falling Film ◽  
Micro Scale ◽  
Film Evaporator ◽  
Layer Coating

An experimental study using a porous-layer (wick) coating on a horizontal-tube, falling-film evaporator was conducted to investigate the solution wetting of evaporator tubes and its effects on the evaporator performance. The partial solution wetting and the local dry-out on the evaporator tubes are the commonly encountered problems for the horizontal-tube, falling-film evaporator. In this study, the porous-layer coating was used in an attempt to enhance the solution wetting on the tubes and thus the evaporator performance. An experimental setup was built to measure the solution wetting and the performance of the evaporators using micro-scale hatched tubes (baseline design) and porous-layer coated tubes. Distilled water was used as the solution and the heating fluids. The solution wetting and the falling-film flow modes were visually observed in the range of the solution Reynolds number from 6 to 61. The evaporator using the micro-scale hatched tubes had the partial solution wetting on the tubes in the range of the solution Reynolds number considered for the study. In contrast, the evaporator using the porous-layer coated tubes showed the complete solution wetting which was confirmed by a visual inspection. The evaporator performance was evaluated by a thermal resistance analysis for the ranges of the solution and the heating fluid Reynolds numbers from 18 to 154 and from 3070 to 7270 respectively. The evaporation thermal resistances for the micro-scale hatched and the porous-layer coated tubes were increased as the solution flow rates were increased. The evaporation heat transfer coefficients for the micro-scale hatched tubes were higher than those for the porous-layer coated tubes. However, the evaporation thermal resistances with the porous-layer coated tubes were lower than those with the micro-scale hatched tubes because the complete solution wetting was achieved using the porous-layer coating.

Numerical Simulation of the Liquid Flowing and Heat-Transfer outside the Tube of the Horizontal-Tube Falling Film Evaporator

2012 ◽  
Vol 614-615 ◽  
pp. 296-300 ◽  
Author(s):  
Wei Kang Hu ◽  
Li Yang ◽  
Lei Hong Guo
Keyword(s):  
Heat Transfer ◽  
Horizontal Tube ◽  
Water Desalination ◽  
Falling Film ◽  
Transfer Enhancement ◽  
Film Evaporation ◽  
Film Evaporator ◽  
Spray Density ◽  
Performance Of Heat Transfer ◽  
Falling Film Evaporation

This paper mainly studies the falling film evaporator in the field of water desalination. Using the method of fluent simulates the process of the liquid flowing and heat-transfer on the horizontal-tube falling film evaporation. The author analyses the distribution of the liquid film, and obtain the rule that spray density, evaporation temperature, temperature difference and pipe diameter affect the performance of heat-transfer in a certain range. So the paper plays a guiding role in heat transfer enhancement in the falling film evaporator.

Second Law Based Optimization of Falling Film Single Tube Absorption Generator

2002 ◽  
Author(s):  
Saeid Jani ◽  
Mohamad H. Saidi ◽  
Ali Heydari ◽  
Ali A. Mozaffari
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Entropy Generation ◽  
Horizontal Tube ◽  
Heat Transfer Fluid ◽  
Falling Film ◽  
Efficient Design ◽  
Single Tube ◽  
Evaporation Heat ◽  
Dimensionless Correlations

The objective of this paper is to provide optimization of falling film Li/Br solution on a horizontal single tube based on minimization of entropy generation. Flow regime is considered to be laminar, the effect of boiling has been ignored and wall temperature is constant. Velocity, temperature and concentration distributions are numerically determined and dimensionless correlations are obtained for predicting the average heat transfer coefficient and average evaporation factor on the horizontal tube. Thermodynamic imperfection due to passing lithium bromide solution is attributed to non-isothermal heat transfer; fluid flow friction and mass transfer irreversibility. Scale analysis shows that the momentum and mass transfer irreversibilities can be ignored at the expense of heat transfer irreversibility. In the process of optimization, for a specified evaporation heat flux, the entropy generation along with the developed heat and mass transfer dimensionless correlations is minimized and the optimal geometry and the optimum thermal hydraulic parameters are revealed. The investigation cited here indicates the promise of entropy generation minimization as an efficient design and optimized tool.

Falling Film Transitions on Plain and Enhanced Tubes

2002 ◽  
Vol 124 (3) ◽  
pp. 491-499 ◽  
Author(s):  
J. F. Roques ◽  
V. Dupont ◽  
J. R. Thome
Keyword(s):  
Heat Transfer ◽  
Low Flow ◽  
Film Condensation ◽  
Flow Mode ◽  
Water Mixture ◽  
Falling Film ◽  
Flow Rates ◽  
Enhanced Tubes ◽  
Plain Tube ◽  
Enhanced Boiling

In falling film heat transfer on horizontal tube bundles, liquid flow from tube to tube occurs as a falling jet that can take on different flow modes. At low flow rates, the liquid film falls as discrete droplets. At higher flow rates, these droplets form discretely spaced liquid columns. At still higher flow rates, the film falls as a continuous sheet of liquid. Predicting the flow transitions between these flow modes is an essential step in determining the heat transfer coefficient for the particular flow mode, whether for a single phase process or for falling film condensation or evaporation. Previous studies have centered mostly on falling films on plain tube arrays. The objective of the present study is to extend the investigation to tubes with enhanced surfaces: a low finned tube, an enhanced boiling tube and an enhanced condensation tube. The effect of tube spacing on flow transition has also been investigated. The test fluids were water, glycol and a glycol-water mixture. The adiabatic experimental results show that the flow mode transition thresholds for the enhanced boiling tube are very similar to those of the plain tube while the fin structure of the other two enhanced tubes can significantly shift their transition thresholds.

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