Modeling an Integral Dual Solar/Gas-Fired Generator for a Water-Lithium Bromide Absorption Chiller

2000 ◽  
Vol 122 (4) ◽  
pp. 217-223 ◽  
Author(s):  
J. Cao ◽  
R. N. Christensen
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Solar Energy ◽  
Lithium Bromide ◽  
Design Procedure ◽  
Absorption Chiller ◽  
Convective Boiling ◽  
Desorption Process ◽  
The Heat Transfer Coefficient ◽  
Driving Source

This paper presents a design procedure for a dual solar/gas-fired generator of an absorption chiller. The solar energy is the primary driving source for the generator, while the natural gas serves as the backup heat when the solar energy is unavailable or insufficient. Saturated forced convective boiling for binary mixtures has been considered to account for the reduction in the heat transfer coefficient observed for most mixtures. The simultaneous solar and gas-fired desorption process was investigated. The generator constructed based on modeling results yielded good performance in the experiment. [S0195-0738(00)00704-4]

Convective Boiling of R-22 in a Flat Aluminum Multi-Minichannel Tube With Dh = 1.4 mm

2008 ◽  
Author(s):  
Nae-Hyun Kim ◽  
Wang-Kyu Oh ◽  
Jung-Ho Ham ◽  
Do-Young Kim ◽  
Tae-Ryong Shin
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Mass Flux ◽  
Saturation Temperature ◽  
High Mass ◽  
High Heat Flux ◽  
Convective Boiling ◽  
The Heat Transfer Coefficient

Convective boiling heat transfer coefficients of R-22 were obtained in a flat extruded aluminum tube with Dh = 1.41 mm. The test range covered mass flux from 100 to 600 kg/m2 s, heat flux from 5 to 15 kW/m2 and saturation temperature from 5°C to 15°C. The heat transfer coefficient curve shows a decreasing trend after a certain quality (critical quality). The critical quality decreases as the heat flux increases, and as the mass flux decreases. The early dryout at a high heat flux results in a unique ‘cross-over’ of the heat transfer coefficient curves. The heat transfer coefficient increases as the mass flux increases. At a low quality region, however, the effect of mass flux is not prominent. The heat transfer coefficient increases as the saturation temperature increases. The effect of saturation temperature, however, diminishes as the heat flux decreases. Both the Shah and the Kandlikar correlations underpredict the low mass flux and overpredict the high mass flux data.

Modeling an Integral Dual Solar/Gas Fired Generator for a Water-Lithium Bromide Absorption Chiller

1999 ◽  
Author(s):  
Jiming Cao ◽  
Richard N. Christensen
Keyword(s):  
Heat Transfer ◽  
Natural Gas ◽  
Solar Energy ◽  
Current Flow ◽  
Lithium Bromide ◽  
Absorption Chiller ◽  
Transfer Resistance ◽  
Subcooled Liquid ◽  
Bromide Solution ◽  
Lithium Bromide Solution

Abstract This paper presents a design process for a dual solar/gas fired generator. A generator fired by solar energy and/or natural gas for a water-lithium bromide absorption chiller of 25 refrigeration tons (RT) was modeled. The natural gas is considered as the backup heat when the solar energy is unavailable or insufficient. The flue gas and the water-lithium bromide solution are in co-current flow, while the solar fluid and the water-lithium bromide solution are in counter-current flow. Fifty fluted tubes were installed vertically between two concentric cylindrical tubes. A solid ceramic insert was used to enhance heat transfer on the gas side that is considered as having the dominant heat transfer resistance. The burner is installed inside the smaller cylindrical tube. The solar fluid from the solar collector enters the generator through the fluted tubes while the water-lithium bromide mixture flows in the annular channel around the fluted tubes as a subcooled liquid. The generator is divided into two regions according to the heat transfer mechanism: subcooled liquid region and desorption region. In this model, a simultaneous solar and gas fired desorption process was investigated. The amount of makeup heat needed from natural gas was determined as a function of the solar fluid flow rate. Local temperature profiles were predicted by the model.

Influence of Flow Regime, Heat Flux, and Mass Flux on Electrohydrodynamically Enhanced Convective Boiling

2000 ◽  
Vol 123 (2) ◽  
pp. 355-367 ◽  
Author(s):  
J. E. Bryan ◽  
J. Seyed-Yagoobi
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Flow Regime ◽  
Mass Flux ◽  
Electrode Design ◽  
Convective Boiling ◽  
R 134A ◽  
The Heat Transfer Coefficient

The influence of quality, flow regime, heat flux, and mass flux on the electrohydrodynamic (EHD) enhancement of convective boiling of R-134a in a horizontal smooth tube was investigated in detail. The EHD forces generated significant enhancements in the heat transfer coefficient, but the enhancements were highly dependent on the quality, flow regime, heat flux, and mass flux. The experimental data provided evidence that an optimum EHD enhancement exists for a given set of these variables with a specific electrode design. However, experimental data also provided evidence that the EHD forces can drastically reduce the rate of heat transfer at certain conditions

Convective Boiling of R-22 in a Flat Extruded Aluminum Multi-Port Tube

2004 ◽  
Author(s):  
Nae-Hyun Kim ◽  
Young-Sup Sim ◽  
Chang-Keun Min
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Mass Flux ◽  
Saturation Temperature ◽  
High Mass ◽  
High Heat Flux ◽  
Convective Boiling ◽  
The Heat Transfer Coefficient

Convective boiling heat transfer coefficients of R-22 were obtained in a flat extruded aluminum tube with Dh = 1.41 mm. The test range covered mass flux from 200 to 600 kg/m2 s, heat flux from 5 to 15 kW/m2 and saturation temperature from 5°C to 15°C. The heat transfer coefficient curve shows a decreasing trend after a certain quality (critical quality). The critical quality decreases as the heat flux increases, and as the mass flux decreases. The early dryout at a high heat flux results in a unique ‘cross-over’ of the heat transfer coefficient curves. The heat transfer coefficient increases as the mass flux increases. At a low quality region, however, the effect of mass flux is not prominent. The heat transfer coefficient increases as the saturation temperature increases. The effect of saturation temperature, however, diminishes as the heat flux decreases. Both the Shah and the Kandlikar correlations underpredict the low mass flux and overpredict the high mass flux data.

scholarly journals A Review on Convective Boiling Heat Transfer of Refrigerants in Horizontal Microfin-Tubes: A Typical Example

2021 ◽  
Author(s):  
Thanh Nhan Phan ◽  
Van Hung Tran
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Boiling Heat Transfer ◽  
General Concept ◽  
Transfer Performance ◽  
Convective Boiling ◽  
Microfin Tubes ◽  
The Heat Transfer Coefficient

Understanding the Heat transfer performance of refrigerant for convective boiling in horizontal microfin tube and smooth tube is place an importance role on the designing of evaporator, the main equipment on refrigeration system. Reviewing the general concept especially the theory of boiling in the tube, the formation of the flow pattern map, the calculating procedure for heat transfer coefficient and pressure drop during boiling process of refrigerant in microfin tube. Besides, a typical example will be presented more detail in step by step to define the heat transfer coefficient and pressure drop for one working condition to estimate the data results without doing experiments.

Forced Convective Boiling of Nonazeotropic Refrigerant Mixtures Inside Tubes

1993 ◽  
Vol 115 (3) ◽  
pp. 680-689 ◽  
Author(s):  
K. Murata ◽  
K. Hashizume
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Vapor Phase ◽  
Saturation Temperature ◽  
Nucleate Boiling ◽  
Transfer Coefficients ◽  
Convective Boiling ◽  
Transfer Resistance ◽  
The Heat Transfer Coefficient

Forced convective boiling of nonazeotropic mixtures inside horizontal tubes was investigated experimentally. The heat transfer coefficient and pressure drop of pure refrigerant R123 and a mixture of R123 and R134a were measured in both a smooth tube and a spirally grooved tube. The heat transfer coefficient for the mixture was found to be lower than that for an equivalent pure refrigerant with the same phsycial properties, not only in the boiling-dominant region but also in the convection-dominant region. On the basis of this experiment, correlations were proposed for heat transfer coefficients in smooth and grooved tubes; the reduction in heat transfer coefficient for the mixture is attributed to the mixture effects on nucleate boiling and to the heat transfer resistance in the vapor phase. This heat transfer resistance is caused by the sensible heating of the vapor phase accompanying the rise in saturation temperature. These correlations are able to predict the heat transfer data within ± 20 percent

Pool Boiling Performance of Notched Tubes in Lithium Bromide Solution

2015 ◽  
Vol 23 (02) ◽  
pp. 1550013 ◽  
Author(s):  
Yong-Sub Sim ◽  
Nae-Hyun Kim
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Saturation Pressure ◽  
Lithium Bromide ◽  
Smooth Tube ◽  
Floral Tube ◽  
The Heat Transfer Coefficient

In the present study, pool boiling heat transfer coefficients in Lithium Bromide ( LiBr ) solution were obtained for smooth, floral, notched fin and notched floral tubes. Test range covered saturation pressure from 7.38 to 101.3 kPa, LiBr concentration from 0% to 50%. Floral tube yielded the highest heat transfer coefficient, and smooth tube yielded the lowest heat transfer coefficient. Effect of notching on heat transfer coefficient was dependent on tube shape. When applied to the smooth tube (notched fin tube), notching increased the heat transfer coefficient. When applied to the floral tube (notched floral tube), on the other hand, notching decreased the heat transfer coefficient. The reason has been attributed to the balance of advantage of added nucleation sites and disadvantage of added flow resistance. Boiling heat transfer correlations were developed which are applicable for saturation pressure from 7.38 to 101.3 kPa and LiBr concentration from 0% to 50%.

A Thermodynamic Nonequilibrium Slug Flow Model

2005 ◽  
Vol 127 (3) ◽  
pp. 323-331 ◽  
Author(s):  
Jader R. Barbosa, ◽  
Geoffrey F. Hewitt
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Slug Flow ◽  
Formation Rate ◽  
Convective Boiling ◽  
Subcooled Liquid ◽  
Calculation Methodology ◽  
Pressure Water ◽  
The Heat Transfer Coefficient

This paper presents a calculation methodology to predict the peaks in heat transfer coefficient at near zero equilibrium quality observed in forced convective boiling in vertical conduits. The occurrence of such peaks is typical of low latent heat, low thermal conductivity systems (such as refrigerants and hydrocarbons), and of systems in which the vapor volume formation rate for a given heat flux is large (low-pressure water). The methodology is based on a model that postulates that the mechanism behind the heat transfer coefficient enhancement is the existence of thermodynamic nonequilibrium slug flow, i.e., a type of slug flow in which rapid bubble growth in subcooled boiling leads to the formation of Taylor bubbles separated by slugs of subcooled liquid. Results are compared with experimental data for forced convective boiling of pure hydrocarbons and show considerable improvement over existing correlations.

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