Droplet Evaporation in High Temperature Environments

1981 ◽  
Vol 103 (1) ◽  
pp. 86-91 ◽  
Author(s):  
G. M. Harpole
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
High Temperature ◽  
Heat And Mass Transfer ◽  
Stagnation Point ◽  
Convective Heat ◽  
Temperature Effects ◽  
Simple Correlation ◽  
Fluid Properties ◽  
Pure Steam

Axisymmetric-stagnation-point convective heat and mass transfer solutions are presented for water evaporating into dry air and into pure steam for free stream temperatures from 373K to 1450K and radiative to convective heat flux ratios from 0 to 2. Effects of (1) blowing (evaporation), (2) variable fluid properties, (3) interdiffusion (binary diffusion with nonequal heat capacities), and (4) radiation are all included. A simple correlation which fits these stagnation point solutions within 3 percent is presented. Whole droplet heat transfer is shown to behave much like stagnation-point heat transfer when the Reynolds number is on the order of 100. Blowing and other high temperature effects on whole droplet heat and mass transfer can be estimated with stagnation point solutions. The ratio of stagnation point solutions with and without high temperature effects should multiply no-blowing constant-fluid-properties whole-droplet heat transfer correlations as a correction factor. Such a corrected whole-droplet correlation compares favorably with experimental data in the literature.

Heat Transfer on Nanofluid Flow With Homogeneous–Heterogeneous Reactions and Internal Heat Generation

2014 ◽  
Vol 136 (12) ◽  
Author(s):  
Raj Nandkeolyar ◽  
Peri K. Kameswaran ◽  
Sachin Shaw ◽  
Precious Sibanda
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Heat Generation ◽  
Internal Heat ◽  
Internal Heat Generation ◽  
Heterogeneous Reactions ◽  
Transfer Coefficients ◽  
Transfer Characteristics ◽  
Fluid Properties

We investigated heat and mass transfer on water based nanofluid due to the combined effects of homogeneous–heterogeneous reactions, an external magnetic field and internal heat generation. The flow is generated by the movement of a linearly stretched surface, and the nanofluid contains nanoparticles of copper and gold. Exact solutions of the transformed model equations were obtained in terms of hypergeometric functions. To gain more insights regarding subtle impact of fluid and material parameters on the heat and mass transfer characteristics, and the fluid properties, the equations were further solved numerically using the matlab bvp4c solver. The similarities and differences in the behavior, including the heat and mass transfer characteristics, of the copper–water and gold–water nanofluids with respect to changes in the flow parameters were investigated. Finally, we obtained the numerical values of the skin friction and heat transfer coefficients.

Stagnation-Point Flow of a Jeffrey Nanofluid over a Stretching Surface with Induced Magnetic Field and Chemical Reaction

2015 ◽  
Vol 20 ◽  
pp. 93-111 ◽  
Author(s):  
Naramgari Sandeep ◽  
Chalavadi Sulochana ◽  
Isaac Lare Animasaun
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Differential Equations ◽  
Ordinary Differential Equations ◽  
Heat And Mass Transfer ◽  
Stagnation Point ◽  
Chemical Reaction ◽  
Transfer Rate ◽  
Stretching Surface ◽  
Jeffrey Nanofluid

With every passing day the heat transfer enhancement in the convectional base fluids plays a major role in several industrial and engineering processes. During these process nanofluids has attained its great importance to enhance the heat transfer rate in the convectional flows. Keeping this into view, in this study we investigated the stagnation point flow, heat and mass transfer behaviour of MHD Jeffrey nanofluid over a stretching surface in the presence of induced magneticfield, non-uniform heat source or sink and chemical reaction. Using similarity technique, the governing boundary layer partial differential equations are transformed into nonlinear coupled ordinary differential equations. The ordinary differential equations are solved numerically using Runge-Kutta-Felhberg scheme. An excellent agreement of the present results has been observed with the existed literature under some special cases. The effects of various dimensionless governing parameters on velocity, induced magneticfield, temperature and nanoparticle concentration profiles are discussed and presented through graphs. Also, friction factor, local Nusselt and Sherwood numbers are computed and discussed. Dual solutions are presented for suction and injection cases. It is found that dual solutions exist only for certain range of suction or injection parameter. It is also observed that an increase in the heat and mass transfer rate for higher values of Deborah number.

scholarly journals Characteristics of supercritical heat transfer during filmboiling of nanofluids on a vertical heated wall

2018 ◽  
pp. 29-35
Author(s):  
А. Avramenko ◽  
M. Kovetskaya ◽  
A. Tyrinov ◽  
Yu. Kovetska
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Mathematical Model ◽  
Mass Transfer ◽  
Heat Flux ◽  
High Temperature ◽  
Heat And Mass Transfer ◽  
Heated Surface ◽  
Heated Wall ◽  
Film Boiling

Nanofluid using for intensification of heat transfer during boiling are analyzed. The using boiling nanofluids for cooling high-temperature surfaces allows significantly intensify heat transfer process by increasing the heat transfer coefficient of a nanofluid in comparison with a pure liquid. The properties of nanoparticles, their concentration in the liquid, the underheating of the liquid to the saturation temperature have significant effect on the rate of heat transfer during boiling of the nanofluid. Increasing critical heat flux during boiling of nanofluids is associated with the formation of deposition layer of nanoparticles on heated surface, which contributes changing in the microcharacteristics of heat exchange surface. An increase in the critical heat flux during boiling of nanofluids is associated with the formation of a layer of deposition of nanoparticles on the surface, which contributes to a change in the microcharacteristics of the heat transfer of the surface. Mathematical model and results of calculation of film boiling characteristics of nanofluid on vertical heated wall are presented. It is shown that the greatest influence on the processes of heat and mass transfer during film boiling of the nanofluid is exerted by wall overheating, the ratio of temperature and Brownian diffusion and the concentration of nanoparticles in the liquid. The mathematical model does not take into account the effect changing structure of the heated surface on heat transfer processes but it allows to evaluate the effect of various thermophysical parameters on intensity of deposition of nanoparticles on heated wall. The obtained results allow to evaluate the effect of nanofluid physical properties on heat and mass transfer at cooling of high-temperature surfaces. The using nanofluids as cooling liquids for heat transfer equipment in the regime of supercritical heat transfer promotes an increase in heat transfer and accelerates the cooling process of high-temperature surfaces. Because of low thermal conductivity of vapor in comparison with the thermal conductivity of the liquid, an increase in the concentration of nanoparticles in the vapor contributes to greater growth in heat transfer in the case of supercritical heat transfer.

Double Diffusive Magnetohydrodynamic (MHD) Natural Convection and Entropy Generation in a Discretely Heated Inclined Dome-Shaped Enclosure Filled with Cu-Water Nanofluid

2021 ◽  
Vol 10 (4) ◽  
pp. 564-579
Author(s):  
Rujda Parveen ◽  
Priyajit Mondal ◽  
Tapas Ray Mahapatra
Keyword(s):  
Magnetic Field ◽  
Heat Transfer ◽  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Convective Heat ◽  
Entropy Generation ◽  
Inclination Angle ◽  
Hartmann Number ◽  
Substantial Impact ◽  
Double Diffusive

This research presents an investigation of laminar two-dimensional double-diffusive free convection and entropy formation in an inclined enclosure under the influence of an inclined magnetic field. The performance of natural convective heat transfer can be improved by doing modifications in enclosure geometry that impact the flow structure. We have considered a dome-shaped enclosure to examine the heat and mass transfer performance. The enclosure is saturated with Cu-water nanofluid and the two sidewalls of the enclosure are maintained at constant temperature Tc(<Th) and concentration cc(<ch). The top-curved wall is adiabatic, and the lower wall is discretely heated and concentrated. The governing equations are first non-dimensionalized and then written in stream function-velocity formulation that is solved numerically using the Bi-CGStab method. A comparison with previously published work in literature is presented and found to be in excellent agreement. Numerical simulations are performed for various values of considered parameters such as Rayleigh number (Ra), Hartmann number (Ha), the orientation of magnetic field (γ), volume fraction of nanoparticles (Φ), and inclination angle of the enclosure (δ). The mentioned parameters have a substantial impact on the cavity flow characteristics. The obtained results demonstrate that the average Sherwood number and Nusselt number are decreasing functions of both the Hartmann number and inclination angle of the enclosure. The minimum heat and mass transfer took place at δ = 135° as the angle of inclination of the enclosure restrains the fluid velocity and reduces the heat transfer rate. Also, entropy generation analysis is conducted for all the considered parameters. The results show that the dome-shaped enclosure has a substantial impact on the fluid flow that enables a smoother and more effective flow inside the cavity, which improves the natural convective heat and mass transmission.

scholarly journals Tomography-Based Heat and Mass Transfer Characterization of Reticulate Porous Ceramics for High-Temperature Processing

2009 ◽  
Author(s):  
Sophia Haussener ◽  
Patrick Coray ◽  
Wojciech Lipin´ski ◽  
Peter Wyss ◽  
Aldo Steinfeld
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
High Temperature ◽  
Heat And Mass Transfer ◽  
Diffusion Tensor ◽  
Porous Ceramics ◽  
Interfacial Heat Transfer Coefficient ◽  
Flow Characterization ◽  
Scattering Phase Function

Reticulate porous ceramics employed in high-temperature processes are characterized for heat and mass transfer. The exact 3D digital geometry of their complex porous structure is obtained by computer tomography and used in direct pore-level simulations to numerically calculate their effective transport properties. Two-point correlation functions and mathematical morphology operations are applied for the geometrical characterization that includes the determination of porosity, specific surface area, representative elementary volume edge size, and mean pore size. Finite volume techniques are applied for conductive/convective heat transfer and flow characterization that includes the determination of the thermal conductivity, interfacial heat transfer coefficient, permeability, Dupuit-Forchheimer coefficient, residence time, tortuosity, and diffusion tensor. Collision-based Monte Carlo method is applied for the radiative heat transfer characterization that includes the determination of the extinction coefficient and scattering phase function.

Entropy Generation in Convective Heat Transfer and Isothermal Convective Mass Transfer

1987 ◽  
Vol 109 (3) ◽  
pp. 647-652 ◽  
Author(s):  
J. Y. San ◽  
W. M. Worek ◽  
Z. Lavan
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Boundary Conditions ◽  
Convective Heat Transfer ◽  
Heat And Mass Transfer ◽  
Convective Heat ◽  
Entropy Generation ◽  
Ideal Gas ◽  
Convective Mass Transfer ◽  
Plate Spacing

The irreversible generation of entropy for two limiting cases of combined forced-convection heat and mass transfer in a two-dimensional channel are investigated. First, convective heat transfer in a channel with either constant heat flux or constant surface temperature boundary conditions are considered for laminar and turbulent flow. The entropy generation is minimized to yield expressions for optimum plate spacing and optimum Reynolds numbers for both boundary conditions and flow regimes. Second, isothermal convective mass transfer in a channel is considered, assuming the diffusing substance to be an ideal gas with Lewis number equal to unity. The flow is considered to be either laminar or turbulent with boundary conditions at the channel walls of either constant concentration or constant mass flux. The analogy between heat and mass transfer is used to determine the entropy generation and the relations for optimum plate spacing and Reynolds number. The applicable range of the results for both limiting cases are then investigated by non-dimensionalizing the entropy generation equation.

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