Variation of Heat and Mass Transfer Coefficients During Drying of Granular Beds

1990 ◽  
Vol 112 (3) ◽  
pp. 668-674 ◽  
Author(s):  
J. A. Rogers ◽  
M. Kaviany
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Evaporation Rate ◽  
Ambient Air ◽  
Spherical Particles ◽  
Convective Drying ◽  
Transfer Processes ◽  
Surface Areas ◽  
Mass Transfer Processes

During convective drying of initially fully saturated granular beds, the solid matrix is gradually exposed to the ambient air, resulting in heat transfer to both the liquid and solid. In an attempt to examine the heat and mass transfer processes occurring on the surface and to examine the influence of particle size and Bond number on the drying rate, experiments are performed in which granular beds constructed of spherical particles (which range from d = 0.2 mm to d = 25.4 mm) are convectively dried. For beds constructed of very small particles (d = 0.2 mm, Bo = 0.0035) the surface areas of the liquid and solid are difficult to estimate due to the random arrangement of the particles. The experimental results confirm existing knowledge that the evaporation rate is nearly constant during the funicular state of drying. For beds constructed of large particles (d = 25.4 mm, Bo = 21.7) an estimate of the surface areas of the liquid and solid reveals that the surface areas and the evaporation rate are highly dependent on surface saturation, contact angle, and surface tension. The results indicate that heat transfer from the solid to the liquid is significant and that the heat and mass transfer processes are not analogous.

Heat and Mass Transfer Processes and the Performance Evaluation in Single-Slope Solar Stills

2019 ◽  
Vol 141 (6) ◽  
Author(s):  
David A. Aderibigbe
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat And Mass Transfer ◽  
Glass Cover ◽  
Transfer Processes ◽  
Mass Transfer Processes ◽  
Basin Water ◽  
The Heat Transfer Coefficient

The paper reviews the present understanding of the analysis of the heat and mass transfer processes in single-slope solar stills. By using the results of published experiments, it is proposed that the heat and mass transfer phenomena from the basin water to the glass cover are coupled. This coupling makes it possible to derive the dependence of the heat transfer coefficient for condensation on the inclination of the glass cover of the still. The derived relation, i.e., Nucon = 0.738 (Grcon*Prcon*sin β/Ja*)¼ A−1 where A is the aspect ratio, has been demonstrated to be an important expression for predicting the heat transfer coefficient for condensation hcon necessary for a more realistic evaluation of the overall efficiency of single-slope solar still of a given cover angle β.

scholarly journals Numerical Investigation of Natural Convective Condensation with Noncondensable Gases in the Reactor Containment after Severe Accidents

2019 ◽  
Vol 2019 ◽  
pp. 1-12 ◽  
Author(s):  
Wen Fu ◽  
Li Zhang ◽  
Xiaowei Li ◽  
Xinxin Wu
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Mass Fraction ◽  
Transfer Processes ◽  
Noncondensable Gases ◽  
Mass Transfer Processes ◽  
Convective Condensation

The heat and mass transfer processes of natural convective condensation with noncondensable gases are very important for the passive containment cooling system of water cooled reactors. Numerical simulation of natural convective condensation with noncondensable gases was realized in the Fluent software by adding condensation models. The scaled AP600 containment condensation experiment was simulated to verify the numerical method. It was shown that the developed method can predict natural convective condensation with noncondensable gases well. The velocity, species, and density fields in the scaled AP600 containment were presented. The heat transfer rate distribution and the influences of the mass fraction of air on heat transfer rate were also analyzed. It is found that the driving force of natural convective condensation with noncondensable gases is mainly caused by the mass fraction difference but not temperature difference. The natural convective condensation with noncondensable gases in AP1000 containment was then simulated. The temperature, species, velocity, and heat flux distributions were obtained and analyzed. The upper head of the containment contributes to 35.1% of the total heat transfer rate, while its area only takes 25.4% of the total condensation area of the containment. The influences of the mass fraction of low molecular weight noncondensable gas (hydrogen) on the natural convective condensation were also discussed based on the detailed species, density, and velocity fields. The results show that addition of hydrogen (production of zirconium-water reaction after severe accident) will weaken the intensity of natural convection and the heat and mass transfer processes significantly. When hydrogen contributes to 50% mole fraction of the noncondensable gases, the heat transfer coefficient will be reduced to 45%.

scholarly journals The matrix method for calculating complex heat and mass transfer systems with multicomponent coolants

Vestnik IGEU ◽  
2020 ◽  
pp. 59-68 ◽  
Author(s):  
A.E. Barochkin ◽  
V.P. Zhukov ◽  
M.S. Shumilova ◽  
E.V. Barochkin ◽  
A.N. Belyakov
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Physical Properties ◽  
Heat And Mass Transfer ◽  
Process Model ◽  
Transfer Processes ◽  
Multi Stage ◽  
Mass Transfer Processes ◽  
The Matrix ◽  
Thermo Physical Properties

Earlier, we obtained a solution to the heat transfer problem in multi-threaded multi-stage heat-exchanging units with one-component heat carriers. However, in the energy, food, and petrochemical industries, often heat and mass transfer processes involve coolants consisting of components whose heat and physical properties differ significantly. For carrying out heat engineering calculations with such coolants, averaging of the indicated properties of the components is usually performed. However, in a number of industrial technologies based on distinguishing thermo-physical properties, in particular, differences in the boiling temperature of the components, processes for their separation by distillation are used. In this case, when calculating heat and mass transfer processes to obtain pure components with acceptable impurities, it is necessary to take into account the difference in their thermo-physical properties precisely. The development of calculating methods for the systems of multi-threaded multi-stage heat transfer processes with multi-component coolants to analyze the efficiency of their separation is a topical issue facing the energy sector and related industries. To study and simulate heat and mass transfer systems, the equations of mass and energy balances and linear algebra methods of are used. Within the framework of the matrix approach, for the case of using a mixture of components with different boiling points as heat transfer agents, a heat and mass transfer process model has been obtained. The model allows evaluating the degree of separation of components and the quality of the finished product by the content of impurities in it for various methods of organizing the process. The solutions of the model equations have been obtained and analyzed. The results can be used to increase the efficiency of resource and energy-saving technologies in solving problems of the optimal distribution of temperatures at the system stages due to recirculation of the selected components and to obtain pure components with an acceptable content of impurities in the energy, chemical and food industries.

Sign in / Sign up

Export Citation Format

Share Document