Journal of Heat and Mass Transfer Research
Volume:7 Issue: 2, Summer-Autumn 2020

A numerical solution is presented for unsteady coupled heat and mass transfer by natural convection from a vertical plate embedded in a uniform porous medium in the presence of thermal radiation and chemical reaction effects. The governing equations for this problem were developed and non-dimensionalized and the resulting equations were then solved numerically by an explicit finite-difference scheme. The Roseland approximation is used to describe the radiative heat flux in the energy equation. The solutions at each time step have been found to reach the steady state solution properly. The numerical results are presented in the graphical form to show the effects of material parameters including the thermal buoyancy, the solutal buoyancy, Reynolds number, the inverse thermal radiation parameter, the permeability parameter, Prandtl number, Schmidt number and the chemical reaction parameter on the skin-friction coefficient, the Nusselt number, the Sherwood number, the velocity profiles, the temperature profiles and the concentration profiles in the boundary layer.

In this study, effects of viscous dissipation and variable physical properties on steady natural convection heat and mass transfer flow through a vertical channel were investigated. The variability in viscosity and thermal conductivity are considered linear function of temperature. The governing equations are transformed into a set of coupled nonlinear ordinary differential equations and solved using Differential Transformation Method (DTM). Results obtained were compared with exact solution when some of the flow conditions were relaxed and results from DTM show an excellent agreement with the exact solution which was obtained analytically. The influence of the flow parameters on fluid temperature, concentration and velocity are presented graphically and discussed for variations of the governing parameters. From the course of investigation, it was found that increasing viscous dissipation causes fluid temperature, velocity as well as the skin friction on the surface of both channels to increase. However, increasing the fluid viscosity retards the fluid motion and causes fluid temperature to decrease.

Hyperthermia is a form of cancer treatment where the temperature of the tumor is elevated to levels that induce its elimination. This paper discusses using a heating power source to destroy breast cancer cells. The geometry of the breast tissue is represented as a hemisphere containing three layers; muscle, gland, and fat. The conjugate gradient method that is one of The most powerful iterative methods was used to solve the inverse heat conduction problem via the Pennes bioheat equation in an axisymmetric coordinate system, where the irregular region in the physical domain (r,z) was transformed into a rectangle in the computational domain (ξ, η). The performance of the algorithm was evaluated on a tested point located at the (5, 2) position, accounting for two temperature increments. The results confirmed the accuracy and viability of the algorithm, which makes this approach promising for the actual application for breast cancer treatment soon.

AbstractAnalytical solutions of gaseous slip flow in a microchannel with different cross-sections play an important role in the understanding of the physical behavior of gases and other phenomena related to it. In this paper, the fully developed non-ideal gaseous slip flow in circular sector microchannel is investigated using the conformal mapping and the integral transform technique to obtain the analytical exact solution. Van der Waals equation is used as the equation of state for a non-ideal gas.It is developed the models for predicting the local and mean velocity, normalized Poiseuille number,and the ratio of density for conditions where the small radius of the circular sector cross-section is zero (r1*→0) and is the opposite of zero (r1*≠0, r1*=10µm).Rarefication process and effects of wall slippage are important physical phenomena that are studied. The results show that the rarefication process depends on Knudsen number, and cross-section geometry. In order to validate the analytical solution, the results of the problem are compared to the analytical and numerical solutions. Good agreement between the present study and other solutions has confirmed.

Natural gas stream must be preheated before pressure reduction takes place at natural gas pressure reduction station (PRS). It ensures that the natural gas stream remains above hydrate-formation zone. Heaters are used to prevent this problem. There is no precise method for determining the adjustment points of heaters; and the gas is usually heated to a temperature higher than the required temperature leading to the energy loss in heaters. In the present paper, the outlet gas temperature of regulator was predicted to prevent the energy dissipation by an applied analysis through thermodynamics equations and considering the deviation of natural gas from the ideal gas state using MATLAB software. The prediction of outlet temperature and application of control mechanisms made the temperature close to the standard temperature, so that avoiding the formation of destructive hydrate phenomenon, prevented the dissipation of 7983.7 standard cubic meter of natural gas and reduced 15.29 tone greenhouse gas emissions in a year at the PRS under study. The economic analysis of the proposed system has been carried out using Payback ratio method. The payback period of implementation of this control system is only less than one year. Results of comparison between the measured output temperature and calculated temperature through the software indicated an average difference of 9%.

In the present study, the thermal and rheological behavior of power-law non-Newtonian CMC-based CuO nanofluid in a tube is studied using ANSYS FLUENT software. Constant heat flux of 6000 W/m2 is subjected to the tube walls and the viscosity of nanofluid is assumed to be a function of shear rate, and temperature simultaneously. Two velocity profiles are considered as an inlet boundary condition: fully developed velocity and uniform velocity. Volume fractions of 0%-4%, and the Reynolds numbers of 600-1500 are considered in the simulations. For both velocity profiles, temperature and shear rate have considerable influence on the viscosity. Local heat transfer coefficient along the tube increases with the volume fraction, however, volume fractions less than 1.5% has an effect on local heat transfer slightly. It is revealed that as the Reynolds number enhances, local heat transfer and the average Nusselt number decrease. In conflict with previous investigations, the present results show that average Nusselt number is reduced by increasing the volume fraction of nanoparticles.

This paper is concerned with longitudinal vortex rolls in fluids. The longutudinal rolls are observed in the sea surface, desert, and atmosphere. However, origin of the vortical motions are not clear, so that in this study laboratory experiments and theoretical analyses have been conducted to elucidate the formation mechanism of the longitudinal vortex rolls in laboratory . As the results, it becomes clear that these vortex rolls are generated by the interaction of the thermal convection and the shear force by the flow. That is, as far as these two effects are existed, irrespective of other conditions are different, quite similar longitudinal vortex rolls appear. Take for example, in dayly our lives when it is fine, we often ovserve longitudinal vortex rolls in the sky, when we look through the outside from the airplane window, we see the longitudinal rows of clouds, and when wo go on board , we notice the longitudinal wave lines on the sea surface.

Predicting the dynamics of aerosols in the respiratory tract is crucial for the analysis of toxic effects of particulate matters and to the respiratory targeted drug delivery. The present work focuses on evaluating the transient absorption of drug particles on the airway walls of the respiratory tract. For this purpose, simulations of airflow and particulate matters inside a three-dimensional model of respiratory airways were coupled to a one-dimensional drug absorption model. The drug absorption from mucus to the respiratory walls was studied using the transient mass transfer equations in a multilayer model. Different breathing rates of 5, 7.5, and 10 Lit/min were considered in the simulations. Particles with different sizes of 2, 5, 10, and 30µm were released at the entrance of the oral cavity during the inspiration phase. The airflow velocity distribution, particle concentration, and flux of drugs at the interface of mucus-tissue were studied in detail. The transient absorption process that occurred over the breathing time considered of 4 s was evaluated. The results showed that the drug mass flow rate at the mucus-tissue interface and the drug concentration in the tissue layer decreases with time. Also, it was found that after inspiration, the location of the maximum concentration changes from mucus to the tissue layer.