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.

Second Law Based Optimization of Falling Film Single Tube Absorption Generator

2004 ◽  
Vol 126 (5) ◽  
pp. 708-712 ◽  
Author(s):  
S. Jani ◽  
M. H. Saidi ◽  
A. A. Mozaffari
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Entropy Generation ◽  
Lithium Bromide ◽  
Horizontal Tube ◽  
Heat Transfer Fluid ◽  
Falling Film ◽  
Efficient Design ◽  
Single Tube ◽  
Evaporation Heat

The objective of this paper is to provide optimization of falling film LiBr 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 to predict the average heat transfer coefficient and average evaporation factor on the horizontal tube. Thermodynamic imperfection due to passing lithium bromide solution is attributed to nonisothermal 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 accompanying the developed dimensionless heat and mass transfer correlations has been 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 optimization tool.

scholarly journals CFD studies on the influence of un-wetted area on the heat transfer performance of the horizontal tube falling film evaporation

2021 ◽  
pp. 56-56
Author(s):  
Dilli Balaji ◽  
Ramalingam Velraj ◽  
Malavarappu Ramanamurthy
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Heat Transfer Performance ◽  
Horizontal Tube ◽  
Published Data ◽  
Transfer Performance ◽  
Falling Film ◽  
Film Evaporation ◽  
Falling Film Evaporation ◽  
Wetted Area

This paper discusses about the effect of un-wetted area of tube on the heat transfer performance of horizontal tube falling film evaporation. A 2D CFD model was developed to perform simulations and investigate the output and validated them with published data available in the literature. In the present study the VOF method is used to track the boundary of the liquid vapour from the contours of volume fraction. Effect of varying tube wall temperature or wall super heat (6 to 11?C) on un-wetted area, heat transfer co-efficients and mass transfer co-efficients of the circular tube were obtained from the simulation model and the results were analysed and reasons were identified and discussed here. The threshold value of wall super heat above which phase change occurs between liquid film and tube surface is identified as 6?C. Also it is noted that mass transfer rate increases and then decreases with increase of wall super heat and heat transfer co-efficient showed declining trend.

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.

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.

scholarly journals Modeling of conjugated heat and mass transfer in the entrance region of falling liquid film at various values of the Froude number

2018 ◽  
Vol 194 ◽  
pp. 01007
Author(s):  
Maria V. Bartashevich
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Liquid Film ◽  
Froude Number ◽  
Heat And Mass Transfer ◽  
Water Solution ◽  
Lithium Bromide ◽  
Entrance Region ◽  
Falling Film ◽  
Falling Liquid Film

Mathematical model of conjugated heat and mass transfer in absorption on the entrance region of the semi-infinite liquid film of lithium bromide water solution is investigated for different values of Froude number. The calculations shown that larger values of Froude number corresponds to a smaller thickness of the falling film. It was demonstrated that for large values of the Froude number the heat transfer from the surface is greater than for smaller values.

Combined Effects of Temperature and Velocity Jump on the Heat Transfer, Fluid Flow, and Entropy Generation Over a Single Rotating Disk

2010 ◽  
Vol 132 (11) ◽  
Author(s):  
A. Arikoglu ◽  
G. Komurgoz ◽  
I. Ozkol ◽  
A. Y. Gunes
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Entropy Generation ◽  
Rotating Disk ◽  
Heat Transfer Fluid ◽  
Combined Effects ◽  
Jump Conditions ◽  
Governing Equations ◽  
Velocity Jump ◽  
Effects Of Temperature

The present work examines the effects of temperature and velocity jump conditions on heat transfer, fluid flow, and entropy generation. As the physical model, the axially symmetrical steady flow of a Newtonian ambient fluid over a single rotating disk is chosen. The related nonlinear governing equations for flow and thermal fields are reduced to ordinary differential equations by applying so-called classical approach, which was first introduced by von Karman. Instead of a numerical method, a recently developed popular semi numerical-analytical technique; differential transform method is employed to solve the reduced governing equations under the assumptions of velocity and thermal jump conditions on the disk surface. The combined effects of the velocity slip and temperature jump on the thermal and flow fields are investigated in great detail for different values of the nondimensional field parameters. In order to evaluate the efficiency of such rotating fluidic system, the entropy generation equation is derived and nondimensionalized. Additionally, special attention has been given to entropy generation, its characteristic and dependency on various parameters, i.e., group parameter, Kn and Re numbers, etc. It is observed that thermal and velocity jump strongly reduce the magnitude of entropy generation throughout the flow domain. As a result, the efficiency of the related physical system increases. A noticeable objective of this study is to give an open form solution of nonlinear field equations. The reduced recurative form of the governing equations presented gives the reader an opportunity to see the solution in open series form.

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.

Thermodynamic Analysis of Freezing and Melting Processes in a Bed of Spherical PCM Capsules

2009 ◽  
Vol 131 (3) ◽  
Author(s):  
David MacPhee ◽  
Ibrahim Dincer
Keyword(s):  
Heat Transfer ◽  
Entropy Generation ◽  
Flow Rate ◽  
Present Model ◽  
Spherical Geometry ◽  
Heat Transfer Fluid ◽  
Inlet Temperature ◽  
Main Mode ◽  
Solidification Temperature ◽  
Flow Phenomena

The solidification and melting processes in a spherical geometry are investigated in this study. The capsules considered are filled with de-ionized water, so that a network of spheres can be thought of as being the storage medium for an encapsulated ice storage module. ANSYS GAMBIT and FLUENT 6.0 packages are used to employ the present model for heat transfer fluid (HTF) past a row of such capsules, while varying the HTF inlet temperature and flow rate, as well as the reference temperatures. The present model agrees well with experimental data taken from literature and was also put through rigorous time and grid independence tests. Sufficient flow parameters are studied so that the resulting solidification and melting times, exergy and energy efficiencies, and exergy destruction could be calculated. All energy efficiencies are found to be over 99%, though viscous dissipation was included. Using exergy analysis, the exergetic efficiencies are determined to be about 75% to over 92%, depending on the HTF scenario. When the HTF flow rate is increased, all efficiencies decrease, due mainly to increasing heat losses and exergy dissipation. The HTF temperatures, which stray farther from the solidification temperature of water, are found to be most optimal exergetically, but least optimal energetically. The main reason for this, as well as the main mode of loss exergetically, is due to entropy generation accompanying heat transfer, which is responsible for over 99.5% of exergy destroyed in all cases. The results indicate that viewing the heat transfer and fluid flow phenomena in a bed of encapsulated spheres, it is of utmost importance to assess the major modes of entropy generation; in this case from heat transfer accompanying phase change.

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