Statistical models for surface renewal in heat and mass transfer. Part IV: Wall to fluidized bed heat transfer coefficients

AIChE Journal ◽  
1970 ◽  
Vol 16 (3) ◽  
pp. 464-471 ◽  
Author(s):  
L. B. Koppel ◽  
R. D. Patel ◽  
J. T. Holmes
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Fluidized Bed ◽  
Statistical Models ◽  
Transfer Coefficients ◽  
Surface Renewal ◽  
Heat Transfer Coefficients

Heat and Mass Transfer With Liquid Evaporation Into a Turbulent Air Stream

1986 ◽  
Vol 108 (1) ◽  
pp. 4-8 ◽  
Author(s):  
T. Kumada ◽  
T. Hirota ◽  
N. Tamura ◽  
R. Ishiguro
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Turbulent Heat ◽  
Transfer Coefficients ◽  
Enhancement Of Heat Transfer ◽  
Heat Transfer Coefficients ◽  
Air Stream ◽  
Liquid Evaporation ◽  
Experimental Errors

Some of the previously reported heat transfer coefficients with evaporation are fairly large as compared with those of a dry body under similar hydrodynamic conditions. In order to clarify this curious enhancement of heat transfer, a method of error evaluation was developed and applied to correct the experimental errors in the recently reported results. An experimental study was also made on turbulent heat and mass transfer of air flowing over a water surface. The present and the previously reported experimental results revealed that the heat transfer coefficient with evaporation agrees with that of a dry body without evaporation, within experimental error, if the erroneous heat inputs into the liquid are properly corrected according to the proposed method.

scholarly journals Heat and mass transfer in the process of heat treatment and drying of natural leather with the convective method of energy supply

2021 ◽  
Vol 66 (1) ◽  
pp. 84-92
Author(s):  
A. O. Ol’shanskii ◽  
A. M. Gusarov ◽  
S. V. Zhernosek
Keyword(s):  
Heat Transfer ◽  
Heat Treatment ◽  
Mass Transfer ◽  
Heat Conduction ◽  
Differential Equations ◽  
Heat And Mass Transfer ◽  
Analytical Solutions ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Unsteady Heat Conduction

In the work, the authors investigated the possibility of using the results of analytical solutions of the linear differential equations of unsteady heat conduction with constant heat transfer coefficients to calculate the temperature of the material during heat treatment of leathers. Heat treatment of natural leathers as heat-sensitive materials is carried out under mild temperature conditions and high air moisture contents, the temperature does not undergo significant changes, and the heat transfer coefficients change almost linearly. When using analytical solutions, the authors made the assumptions that for small temperature gradients over the cross section of a thin body, the thermal transfer of matter can be neglected and for values of the heat and mass transfer Biot criteria less than unity, the main factor, limiting heat and mass transfer, is the interaction of the evaporation surface of the body with the environment; so, in solving the differential heat equation we can restrict ourselves to one first member of an infinite series. In this case, a piecewise stepwise approximation of all thermophysical characteristics with constant values of these coefficients at the calculated time intervals was applied, which made it possible to take into account the change in the transfer coefficients throughout the entire heat treatment process. Processing of experimental data showed that in low-intensity processes with reliable values of the transfer coefficients, it is possible to use the results of solutions of differential equations of unsteady heat conduction in heat transfer calculations. The results of the study of heat transfer during drying of leather confirm the laws of temperature change established experimentally. Together with experimental studies of drying processes, analytical studies are of great practical importance in the development of new methods for calculating heat and mass transfer in wet bodies.

Nanofluid Heat and Mass Transfer in a Deformable and Peristaltic Pump

2019 ◽  
Vol 8 (8) ◽  
pp. 1632-1639
Author(s):  
Aamir Ali ◽  
Y. Ali ◽  
D.N. Khan Marwat ◽  
M. Awais
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Surface Deformation ◽  
Wave Number ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Flow And Heat Transfer ◽  
Diffusion Parameters ◽  
Peristaltic Movement

Flow heat and mass transfer in a deformable channel of peristaltically moving walls is investigated in this paper. Moreover, the channel is filled with nanofluids. The purpose of this study is to examine the combined effects of surface deformation and peristaltic movement of the walls on the nanofluid flow in a channel. We have considered the effects of nanofluid in the peristaltically deformable porous channel whose walls are contracting or expanding in the normal direction. Nanofluids have been used to enhance the thermo-physical properties of fluids such as thermal diffusivity, thermal conductivity and convective heat transfer coefficients on flow and heat transfer. The analytic solution of the problem have been presented. We have analyzed the effects of different involved parameters such as Reynolds number, surface deformation parameter, Prandtl number, wave number, Brownian and thermophoretic diffusion parameters and Schmidt number on the velocity profile, the temperature profile, pressure distribution and the concentration profile with the help of graphs. The results are shown graphically and discussed physically. It is observed that the deformation increases the axial velocity and temperature of the fluid.

A Transient Nucleate Boiling Model Including Microscale Effects and Wall Heat Transfer

2006 ◽  
Vol 128 (12) ◽  
pp. 1257-1265 ◽  
Author(s):  
Thomas Fuchs ◽  
Jürgen Kern ◽  
Peter Stephan
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Transient Heat Conduction ◽  
Nucleate Boiling ◽  
Vapor Bubbles ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Rising Bubble ◽  
Transient Heat Flow

A new model is presented to compute nucleate boiling heat and mass transfer. It is based on a previous one (Kern, J., and Stephan, P., 2003, ASME J. Heat Transfer, 125, pp. 1106–1115) for quasi-stationary heat transfer to single vapor bubbles. In contrast to the preceding model, fully transient heat and fluid flow is computed with a free surface of the rising bubble and a periodic calculation of repeated cycles of bubble growth, detachment, and rise, requiring only specification of the waiting time between successive bubbles. Additionally, microscopic effects at the foot of the bubble are considered. The model is verified by comparing computed with measured heat transfer coefficients. Typical results for heat and mass transfer to a single vapor bubble are shown at all time steps of the bubble cycle. By means of the model the transient heat flow through different interfaces, e.g., wall/liquid or liquid/vapor, is computed for the whole bubble cycle. Thus, it was possible to evaluate the influence of transient heat conduction, heat storage, and convection in liquid as well as heat transfer in the wall on overall heat transfer performance.

Hybrid Modeling of Modified Mathematical Model for Gas Phase Olefine in Fluidized Bed Catalyst Reactors Using Artificial Neural Networks

2009 ◽  
Vol 4 (1) ◽  
Author(s):  
Ahmmed Saadi Ibrehem
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Fluidized Bed ◽  
Hybrid Model ◽  
Operating Conditions ◽  
Transfer Coefficients ◽  
Mass And Heat Transfer ◽  
Artificial Neural

The complex flow patterns induced in fluidized bed catalytic reactors and the competing parameters affecting the mass and heat transfer characteristics makes the design of such reactors a challenging task to accomplish. The models of such a process rely heavily on predictive empirical correlations for mass and heat transfer coefficients. Unfortunately, published empirical based correlations have the common shortcoming of low-prediction efficiency compared with experimental data. In this work, an artificial neural network approach is used to capture the reactor characteristics in terms of heat and mass transfer based on published experimental data. The developed ANN-based heat and mass transfer coefficients relations were used in a conventional FCR model and simulated under industrial operating conditions. The hybrid model predictions of the melt-flow index and the emulsion temperature were compared to industrial measurements as well as published models. The predictive quality of the hybrid model was superior to other models. This modeling approach can be used as an alternative to conventional modeling methods.

scholarly journals Calculation of the kinetics of heat transfer using the experimental data of moisture exchange in the process of convective drying of thin flat materiаls

2018 ◽  
Vol 63 (3) ◽  
pp. 333-341
Author(s):  
A. I. Ol’shanskii ◽  
S. V. Zhernosek ◽  
A. M. Gusarov
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Moisture Content ◽  
Heat And Mass Transfer ◽  
High Reliability ◽  
Surrounding Medium ◽  
Convective Drying ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Experimental Values

In the paper, the authors analyzed the solution of the differential equation of non-stationary heat conduction for an unbounded plate during the heat exchange of plate surfaces with the surrounding medium according to Newton’s law at a constant temperature of the medium. To use the results of solving the equations in the drying of thin flat materials, the dependence of the heat transfer coefficients on temperature and moisture content was studied. As a result of studying and analyzing a number of literature sources, the regularities of the change in the heat transfer coefficients during drying are established with high reliability. Studies of drying of thin wet plates of white and red clays with known heat transfer coefficients have shown that for small values of the heat transfer criterion of the Bio and small temperature gradients over the section of a thin material, application of the results of solutions of the heat transfer equations gives completely satisfactory agreement between the calculated and experimental values of the temperatures and the duration of drying. It is established that for small Bio numbers, the main factor is the external heat and mass transfer of the surface of the material with the surrounding medium and the rate of drying depends little on internal mass transfer. It is shown that the use of numerical methods for solving differential equations is possible with varying degrees of approximation only for accurate and reliable dependences of heat and mass transfer coefficients on moisture content and temperature. For a number of materials with known heat transfer coefficients, the use of analytical methods in calculations is of considerable interest and brings the theory closer to the practice of drying.

A Simplified Graphical Model of Air Cooler Using Mollier Diagram and Implementation in a Design Tool

2008 ◽  
Author(s):  
Fatemeh Esfandiari Nia ◽  
Dolf van Paassen
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat And Mass Transfer ◽  
Graphical Model ◽  
Design Tool ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Air Cooler

A validated heat and mass transfer model for an air cooler is developed and implemented in a design tool. The overall heat transfer coefficient is derived from the experiments, which can be written as a function of the heat transfer coefficients on the water and air side. For a good agreement between the measurements of a wet cooler and model solutions a correction in the heat transfer coefficients substantially is done. In addition, results obtained from the measurements indicate the heat transfer coefficient itself and the correlation between heat and mass transfer need to be adapted. Acceptable results are obtained when mass transfer coefficient is adjusted by a correction factor. The decrease in heat transfer is observed with increase in dehumidification and the same is concluded from the coupling of heat and mass transfer. The fins are not completely wet, which means an analogy between sensible and latent heat only exists partly. The corrected model is implemented in the studies of advanced evaporative air conditioning systems where it is used to construct a graphical model based on rules for transients in the Mollier diagram of humid air. Preliminary calculations show that it is very accurate and useful for the simulation of controlled air handling systems although it is very fast resulting of the short calculation time of the simplified models.

Determination of Heat and Mass Transfer Coefficients by Condensation in an Air Cooler

2007 ◽  
Author(s):  
Fatemeh Esfandiari Nia ◽  
Dolf van Paassen
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Transfer Coefficient ◽  
Mass Transfer Coefficient ◽  
Heat And Mass Transfer ◽  
Lewis Number ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Air Cooler ◽  
Air Conditioning Systems

This paper describes an improved class of heat and mass transfer air cooler model. The model is based on the approach of Green [1]. It delivers a compact and fast model that is appropriate for year round simulations of air conditioning systems. The model is validated through a set of experiments in the laboratory with an air cooler of eight rows. The heat transfer coefficients have been derived from the standard relations. For a good agreement between the measurements of a wet cooler and the model solutions, a substantial correction in the heat transfer coefficients is needed. In addition, the results obtained from the measurements indicated that the heat transfer coefficient itself and the correlation between heat and mass transfer had to be adapted. Acceptable results were obtained when mass transfer coefficient was adjusted by a correction factor. The decrease in heat transfer has been observed with an increase in dehumidification and the same could be concluded from the coupling of heat and mass transfer. The fins are not completely wet, which implies that an analogy between sensible and latent heat only partly exists. The model does not take wetness of the pipe into account. To overcome this problem, the Lewis number is modulated, based on the degree of dehumidification. In other words, the smaller mass transfer coefficient, there is the higher the dehumidification.

The Condensation Heat Transfer Characteristics of Zeotropic Hydrocarbon Mixtures in a Helical Pipe

2020 ◽  
Author(s):  
Shulei Li ◽  
Rui Zhu ◽  
Gongnan Xie ◽  
Yiqiang Jiang ◽  
Weihua Cai
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Saturation Pressure ◽  
Condensation Heat Transfer ◽  
Vapor Quality ◽  
Transfer Coefficients ◽  
Transfer Resistance ◽  
Hydrocarbon Mixtures ◽  
Heat Transfer Coefficients

Abstract In order to explore tube-side heat transfer characteristics in the spiral wound heat exchange (SWHE) used in liquid natural gas (LNG) plants, the study on zeotropic hydrocarbon mixtures condensation heat transfer in a helical pipe is proposed. Firstly, based on two-fluid model and thermal phase change model, a numerical method coupling with empirical correlations is established to predict condensation heat transfer for zeotropic mixtures, in which the mixed effects are taken into account. Meanwhile, the rationality of the above methods is verified based on existing experimental results. Then, the effects of refrigerant components and operating parameters on flow patterns, heat transfer coefficients and heat and mass transfer resistance are discussed as the ranges of mass flux, saturation pressure and vapor quality are 200–800 kg/(m2·s), 2–4MPa and 0.15–0.90, respectively. It can be found that the predicted results coincide with the experimental ones, with deviations within ±15%. For different zeotropic hydrocarbon mixtures, as the vapor quality increases, the stratified flow, half-annular flow and annular flow appears in turn. The condensation heat transfer coefficients are always smaller than film heat transfer coefficients owing to the existence of heat and mass transfer resistance in vapor core. Besides, both film and condensation heat transfer coefficients increase with the increase of vapor quality and mass flux, while decrease with the rise in saturation pressure. Further, heat and mass transfer resistances increase as the vapor quality and saturation pressure increase and the mass flux decreases. In addition, compared to methane/ethane/propane/nitrogen (65/25/5/5, mole%) mixture, the averaged heat transfer performance for methane/ethane (90/10, mole%) mixture improves by 19.55%, whereas, the average heat and mass transfer resistance decreases by 53.51%. This study is helpful for understanding the zeotropic mixtures condensation in tubes and gives some suggestions for the choice of refrigerant components used in LNG SWHE, to design more effective SWHE.

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