Journal of Heat and Mass Transfer Research
Volume:9 Issue: 2, Summer-Autumn 2022

The expected performance characteristics of a wet media in an evaporative cooler with the specified geometric and material aspects are reducing the dry-bulb temperature and increasing the moisture content of the air outlet. Inlet air conditions are not under the control of the designer or the operator, but the choice of media geometry and fabric, the external factors such as the water circulation rate, and the velocity of air passing through the media could be controlled by the designer. Based on cooling performance for the excelsior of aspen wood pad, the minimum amount of ratio of the static circulation to evaporation rates is about 8 to 12, which has been mentioned in the literature. In this work, for the cellulosic pad by considering the exergy and cooling efficiencies, the optimal ratios of circulation to evaporation rates are presented for different air velocities. It can be seen that under the constant inlet air conditions, by increasing the air velocity as: 0.5, 1.0 and 1.5 m/s, the maximum exergy efficiency values are 0.10, 0.13 and 0.18 respectively and there are some specified values (minimum) for the ratios of water circulation to evaporation rates between 2 and 2.8 for the typical cellulose pad. However, for the same air velocities, maximum cooling efficiencies occur at lower exergy efficiencies, such as 0.03, 0.04, and 0.045, respectively.

Convective heat transfer from a flat plate, which is enhanced by an oscillating blade, was numerically investigated at the present study. It was assumed that the blade is made of a rigid and thin plate and it is vertically oriented at the top of the target plate. Numerical analysis was performed using commercial software ANSYS Fluent 6.3 and the periodic oscillation of the blade was modeled by the moving mesh method. Conservation equations of mass, momentum and energy was solved in 2-D and transient form for the laminar airflow with constant physical properties. Constant temperature was considered for the plate and the details of both the flow and thermal fields were determined. The distribution of convective heat transfer coefficient was then calculated for the target plate. The effect of various parameters including the amplitude and frequency of the blade oscillation as well as the geometrical parameters was investigated on the convective heat transfer from the target plate. The results indicated that a wider area of the plate was affected by increasing the oscillation amplitude of the blade. Convective heat transfer was also enhanced over the entire target plate as the rotational Reynolds number was increased.

In this study, a carbon dioxide (CO2) absorption process in a typical rotating packed bed (RPB) reactor equipped with blade packing and under a high frequency ultrasonic field has been studied. The utilized ultrasonic transducers were ultrasonic atomizer humidifiers with a frequency of 1.7 MHz. This reactor takes advantage of both controllable high gravitational force and induced effects of high frequency ultrasound, simultaneously, in a small volume. The overall volumetric gas side mass transfer coefficient (KGa) with and without ultrasound was investigated. The effects of different parameters such as rotational speed (400-1600 rpm), liquid flow rate (20- 120 L/h), monoethanolamine (MEA) concentration (1- 4 mol/L), gas flow rate (2500- 4000 L/h), and CO2 concentration (1- 4 vol%) were investigated in the absence and presence of ultrasound. The obtained results showed that the removal efficiency increased with increasing gas and liquid flow rates, and rotational speed, as well as MEA concentration. With increasing CO2 concentration, absorption efficiency decreased. The average arithmetic value of the relative volumetric gas-side mass transfer coefficient was enhanced 11.4% under the ultrasonic field. Moreover, the average CO2 removal efficiency was enhanced from 27.4 % in the absence of ultrasound to 29.8% in the presence of ultrasound. Therefore, high frequency ultrasound can enhance CO2 absorption, even in high efficiency equipment like RPBs.

This paper investigates the unsteady magnetohydrodynamic (MHD) mixed convective fluid flow over a rotating sphere. An implicit finite difference scheme, together with quasi-linearization, is used to find non-similar solutions for the governing equations. The impact of variable physical properties and viscous dissipation are included. It is observed that the skin friction coefficient in the axial direction and the heat transfer coefficient are increasing with an increase in MHD, mixed convection and rotation parameters and with time, whereas the effect is just the opposite for the skin friction coefficient in the rotational direction. The non-uniform slot suction(injection) and the slot movement influence the point of vanishing skin friction to move in the axial direction downstream (upstream).

One of the most important sources of aerosol production in a controlled space is the human. The flow around the individual and the particles on the garment play an essential role in aerosol distribution in the environment. Such spaces are simulated from a Lagrangian or Eulerian point of view. In this research, particle resuspension from a user’s garment under horizontal and vertical unidirectional systems was studied. For this purpose, a computer program was developed and used for examination of the impacts of different particle turbulence dispersion models, such as Discrete Random Walk, in a controlled space. Moreover, the effects of flow direction, velocity, and particle density on the probability of resuspension of particles with different diameters were investigated. The results demonstrated that the vertical unidirectional system had advantages over its horizontal variant, and that increased flow velocity provided positive feedback in the vertical system but negative feedback in the horizontal one. In the horizontal system, the resuspension probability for the sizes of 5 and 0.5 microns has increased by 177 and 355 percent, respectively, compared to the vertical system. It is worth noting that the results of the isotropic and non-isotropic models for particles size below 5 microns were quite the same. For the particles size over 5 microns, the maximum percentage discrepancy of 138 in resuspension probability between the non-isotropic and isotropic models is obtained.

The objective of current study is to discuss the effects of the Soret and Dufour with radiation absorption, applied heat source and viscous dissipation on an unsteady MHD mixed convective flow with velocity slip condition across a semi-infinite vertical permeable plate in porous medium.

A similarity transformation is used to turn the governing partial differential equations with proper boundary conditions into coupled, non-linear ordinary differential equations with variable coefficients. The inbuilt MATLAB solver bvp4c is used to generate numerical solutions.

The effects on momentum, thermal and solutal boundary layers for various parametric values are graphically depicted. Skin friction, Nusselt number and Sherwood number are all tabulated and discussed in detail. An improvement in radiation absorption corresponds to enhancement of the heat transfer rate up to 59% while leading to a decline in mass transfer rate around 20%. The momentum, thermal and solutal boundary layers are all found to be boosted when the Soret effect is higher. For higher estimation of slip effect, the skin friction is found to decay around 23%. Also, as more time goes by the thermal and concentration boundary layers are enhanced.

Results obtained in this studied has also been compared and verified with available scientific literature and is found to be in good agreement, which establishes assurance in the numerical results reported in the study.

Magnetohydrodynamic application in the biomedical field made the researcher work more on this field in recent years. The major application of this concept is in scanning using laser beams, delivering a drug to the targeted points, cancer treatment, enhancing image contrast, etc. These applications are depending on the flow and heat transfer properties of the magnetic conducting fluid and on the geometry of the flow field. An increase in the demand for the miniature in the shape and size of the clinical devices attracts the researcher to work more on design optimization. In this study optimization of magnetic field strength, geometry of domain, Prandtl number, Reynolds number for a steady, incompressible double-diffusive flow is performed using Taguchi and Analysis of variance technique. Linear regression model is used to predict the average Nusselt and Sherwood numbers. Numerical simulations were performed using finite volume method (FVM) based numerical techniques.  Experiments are designed based on Taguchi orthogonal array and FVM based numerical codes were used to obtain the results. Results show that an increase in the aspect ratio from to 0.5 to 2.0 improves the heat transfer rate by 62.0% and the mass transfer rate by 38.5%. As the Prandtl number increases from 0.7 to 13.0, heat transfer rate increases by 80.0% and mass transfer by 75.0%. This specific study could be applied in designing of solar ponds and to investigate heat and mass transfer effects during cancer treatments.

In this present work, we examine the fluid of double-layered blood flow through a tapered overlapping stenosed artery with a porous wall. This two-layered blood flow problem comprises the peripheral layer as Newtonian fluid flows and the central core layer of suspension of the erythrocytes as another Newtonian fluid flows and was analytically solved which the numerical results are shown graphically and discussed. It was found that resistance to flow accelerates with rising slip parameter, blood viscosity, and artery length while a rise in Darcy number and radius of the centre core to the tube radius in the unobstructed region decreases the resistance to flow.
Also, the resistance to flow rises with increasing stenosis height whereas it increases with a rise in values of artery shape. The wall shear stress drops as the Darcy number accelerates and rises with rising viscosity of the blood and slip parameter. Furthermore, fluctuation of wall shear stress at the neck of the stenosis drops as the Darcy number increases. Moreover, it is observed that the shear stress increases with rising viscosity of the blood and slip parameter. This work is able to forecast the major attribute of the physiological flows which have played an important role in biomedical researches.

Many investigators have presented mathematical work on desiccant wheels but there is a considerable discrepancy between published values and experimental values. A mathematical model based  on the two-dimensional  Navier-Stokes   equation has been derived to show the dehumidification trend of desiccant dehumidifier concerning air stream velocity. In this model the effect of air stream velocity on wheel performance as a momentum equation combined with heat and mass transfer has been studied.
The current model is capable of predicting the transient and steady-state transport in a desiccant wheel. It reveals the moisture and temperature in both the airflow channels and the sorbent felt, in detail, as a function of time. The predicted results are validated against the data taken from experimental results, with reasonable accuracy. Therefore, the numerical model is a practical tool for understanding and accounting for the complicated coupled operational process inside the wheel. Consequently, it is useful for parameter studies.

Heat transfer enhancement in a car radiator using different nano fluids has been performed very often, but use of artificial roughness has been seldom done. In the present work, artificial roughness in the form of ribs has been incorporated in car radiator. A numerical comparative study has been performed between the ribbed automobile radiator and conventional radiator (flat tube). The nanofluid (Al2O3/Pure Water) has been used as a coolant in the car radiator configuration. The pitch is kept 15 mm (constant) for all the studies performed. The Reynolds number of the flow is selected in the turbulent regime i.e. ranging from 9350 to 23000 and the concentration of the nanofluid is taken from 0.1 to 1.0 %. It has been observed that the heat transfer rate improved with the ribbed roughness as compared to conventional configuration, but the pumping power has also increased. Furthermore, heat transfer rate also increased with increase in nano-particle concentration. The maximum heat transfer enhancement of 79% reported at nanofluid concentration of 1.0% and Reynolds number of 9350 for ribbed configuration.

In this work, a mathematical model is adopted to predict the breakthrough curve in a fixed bed adsorption process, neglecting radial dispersion effects in the bed, with properties such as interstitial velocity and porosity being constant, linear adsorption kinetics and equilibrium relationship represented by the Langmuir isotherm. The resulting partial differential equation is numerically solved by the Method of Lines (MOL), while the Markov Chain Monte Carlo method is employed to estimate the model parameters, using simulated measures and a priori Gaussian probability distribution for the parameters, varying the mean and standard deviation. A convergence analysis was performed to look for numerical convergence between the number of nodes (N) used and the computational cost (CPU time) and it was observed that N = 100 obtained the lowest computational cost (less than 0.2 s). The estimated values of Peclet's number (Pe) and Langmuir's constant (KL) showed deviations of 7% and 0.01%, respectively, compared to their exact value which shows that the estimates were accurate, i.e., the parameters are close to the exact value. Also, the estimated values were within the credibility interval of 99 % established, which shows precise estimates. The information taken from these estimates has become of fundamental importance in predicting the behavior of the breakthrough curve at different points in the bed, showing that the MOL in combination with the MCMC are efficient tools in the direct and inverse analysis of models of breakthrough curves.

In this study, the performance of a solar combisystem using glazed thermal photovoltaic-thermal systems is investigated and optimized to provide the thermal and electrical demands of a five-story building in Hot/Dry climatic conditions (Tehran, Iran). Dynamic simulation of the system performance is carried out using TRNSYS software. Since there is no type for a glazed thermal photovoltaic-thermal system in TRNSYS, it is modeled in MATLAB software and then the modeling results are coupled with the TRNSYS model. The system optimization using a stochastic economic analysis based on the Monte Carlo method showed the solar combisystem with a photovoltaic-thermal system area of 31.93 m2 and a thermal storage tank of 400 l provides the building energy demands optimally. For the optimum system, the probability that the payback time is less than 5 years, the internal rate of return is more than 20% and the life cycle savings is more than the initial cost is 74.2%, 11.5%, and 97%, respectively. The thermoelectric analysis of the optimum solar combisystem indicates that, in August, the maximum electrical, thermal, and total solar fractions of the system are obtained, which are 11%, 87%, and 39%, respectively.

In this study, the convective heat transfer of supercritical carbon dioxide in a long vertical mini-pipe has been investigated numerically. The numerical solution has been performed with the finite volume method and by developing a CFD code. The pipe has a length of 5.5 m and a diameter of 1 mm which is exposed to a constant heat flux at the wall with values of 300, 400, 500, and 600 W/m2 or step changes. In addition to the wall heat flux, the effects of gravity and flow direction have also been examined. Furthermore, some differences between the results of laminar and turbulent flows have been addressed. The results show that in the laminar flow, unlike the turbulent flow in the improvement regime of heat transfer, the system's thermal performance increases with increasing the wall heat flux, while in the deterioration mode, the two have similar behavior. Moreover, in part of the downward flow, reverse flow occurs, and its length can be understood by using the negative amount of wall shear stress. Furthermore, the thermal efficiency of the supercritical carbon dioxide is better at the upward flow and near the critical point than the constant property flow. In addition, from the applied stepped wall heat flux, it is concluded that the deterioration can be partially controlled or reduced by correctly determining the location of the step or any wall heat flux variations.

With the increasing population and heightening quality levels of life in the world, the use of freshwater resources has increased to such an extent that their shortage is considered a serious crisis. Today, manufacturing and untiring solar stills, which produce freshwater without polluting the environment, besides, at a low cost, have been considered a suitable solution to eliminate the shortage of fresh water. In recent years, water desalination has been at the center of interest more than ever in Iran because of the drought and water shortage crisis. For this reason, the design and manufacture of distilled solar still suitable for the geographical conditions of Ahvaz were accomplished. And a device with two inclined planes was selected after studying different types of distilled solar stills. In the first step, a thermal model of different heat transfer phenomena including radiation, conductivity, evaporation, and condensation was employed so that it was utilized to predict the performance of the device in various conditions and the heat analysis of the system. The governing equations in MATLAB software were then implemented and solved. According to the results of the software, which estimates the amount of the produced water using meteorological data consisting of radiation intensity and ambient air temperature, as well as the material features of different parts of the device, the dimensions of the device were designed and the device was manufactured. This device was tested on one of the winter days in January and the production amount of freshwater, as well as temperatures of glass coatings, water, and absorbent surface, were recorded. The production amount of freshwater on the 4th of January in a practical test was 0.98 L/m2.

The present paper seeks to examine a numerical method of solution called spectra quasi-linearization method (SQLM) to the problem of unsteady MHD boundary layer flow of Casson fluid due to an impulsively stretching surface under the influence of a transverse magnetic field, which is an important physical phenomena in engineering applications. The study extends the previous models to account for a classical non-newtonian fluid called Casson fluid under the influence of a transverse magnetic field. The flow model is described in terms of a highly nonlinear partial differential equations. The method of solution Spectral quasi-linearization methods(SQLM) seeks to linearised the original system of PDEs using the Newton-Raphson based quasilinearization method (QLM). The numerical results for the surface shear stress are compared with those of the analytical approach results, and they are found to be in good agreement. The flow controlling parameters are found to have a profound effect on the resulting flow profiles. It is observed that there is a smooth transition from the small time solution to the large time solution. The magnetic field significantly affects the flow field and skin friction coefficient. Indeed, skin friction coefficient is found to decrease rapidly, initially, in small time interval before attaining a steady state for large time.

The catalysts with valve metals had been modified to use in the reforming process. Furthermore, there is a trend to the cheaper materials due to the deactivation and high price of the mentioned catalysts. In this case, at the present research work, the Nickel/CMK-3 catalysts with La2O3 as the promoter were synthesized by an impregnation method with 3 wt. % of La2O3. Also, the Nickel catalysts/CMK-3 and Nickel catalysts-La2O3/CMK-3 were characterized by N2 adsorption-desorption, X-ray diffraction (XRD), Transmission electron microscopy (TEM), Field emission scanning electron microscopy(FE-SEM), Temperature programmed reduction (TPR), and the performance of the catalysts for CO2 reforming of CH4. In addition, the temperature programmed reduction (TPR) technique was selected to evaluate the catalyst properties for the CO2 reforming of CH4. In final, the obtained results demonstrated that the formation of amorphous mesoporous Carbon with NiO nanoparticles inside the channels of the supported base and also the Lantana oxide addition induced better Nickel oxide dispersion and increased the interaction of the catalyst particles with support. As a result, the Nickel catalysts supported on the Carbon mesoporous has shown enough activity for the CO2 reforming of CH4 at 650 ºC. However, the mentioned samples were deactivated due to Carbon oxidation according to the TGA results. Therefore, the addition of La2O3 with 3 wt. % as a promoter improved the catalytic activity up to 57% and enhanced the catalytic stability at a duration time of 2 hr.