Journal of Heat and Mass Transfer Research
Volume:8 Issue: 1, Winter-Spring 2021

This article aims to evaluate the effect of three types of Sardab (Cellars) on thermal comfort conditions. Two vernacular buildings in Yazd have been selected as case studies. In the Rasoulian house, a sardab with a water pond has been defined as case A and a Sardab without pond has been chosen as case B. Case C is a Sardab without pond in Mortaz house. Using experimental data, environmental parameters were analyzed for a month in two consecutive years. Using measured data, the values for Predicted Mean Vote (PMV) and Predicted Percentage Dissatisfied (PPD) have been calculated. The results show a considerable reduction in the air temperature (up to 20 oC) and an increase in the relative humidity of the air (up to 50%) in case A (the Sardab with pond). The sardabs without pond (Case B and C) presented lower efficiencies. Variations in daily temperatures have been presented in three cases with ceilings elevated at different heights. While the sardab that is placed completely underground presented the lowest temperature, in two other sardabs, the average air temperature was 2-3 degrees higher. According to the results, in a hot and dry climate, application of all sardab types, either with or without a pond, elevated or underground, would improve the thermal comfort condition and the energy efficiency of buildings.

It is known that slip flow and temperature jump phenomena play a significant role in micro-scale investigations. In this paper, exact analytical solutions for the flow and the convective heat transfer of gaseous flow passing through microtubes are derived for the first time in form of the Whittaker function. Here, it is assumed that both flow and heat transfer is fully developed in a microtube with constant wall temperature. The solution is obtained by considering the Navier-slip conditions for flow and heat transfer at walls. Here, a modal analysis technique is employed to achieve possible solutions for this scenario. Due to the eigenvalue form of governing equations, obtaining the closed-form exact solution for this problem is too difficult from the mathematical point of view and previous studies have been restricted to numerical and approximate series expansion solutions. In this study, an additional constraint is introduced using the definition of the mean temperature and employed to obtain possible eigenvalues related to this problem. Finally, by implementing a scaling law of the Nusselt number of laminar flow in closed conduits, an exact analytical solution for temperature distribution and the heat transfer are derived. It was found that increasing the Prandtl number increases the Nusselt number and increasing the Knudson number decreases the Nusselt number. Based on the obtained solution, the effect of Prandtl number and Knudsen number on heat convection of microtubes are studied in detail.

COVID-19 has become a health threat around the world. Mask deficiency can be expected during a pandemic infection. The stability of viruses at different temperatures and relative humidity was assessed according to the type of contaminated surface material. With increasing temperature, the permanence of viruses decreases, and in proportion to the increase in temperature should not be damage to the quality of objects. Solar disinfection is one of the new methods of using renewable resources. By designing an integrated solar drying system with the phase change material, the internal temperature of the system reaches 54 ̊ C in April and the masks are disinfected with 3036 Wh/m2 internal cumulative solar radiation. By using the appropriate equipment in the system, the temperature difference inside and outside the system was reached 30 ̊C. A correlation coefficient of 95% in the MATLAB confirmed that the curve fit was good. The main purpose of this research is to identify appropriate solutions for disinfection and consultation with scientific literature. The results showed that the most appropriate hygienic and economical disinfection method was the use of solar energy.

In this study, a statistical experimental design method (the Taguchi method with L9 orthogonal array robust design) was performed to optimize experimental conditions such that to maximize the Nusselt number of Al2O3-water nanofluids in a double tube counter flow heat exchanger. The controllable factors were selected at three sets of conditions including temperature (45, 55, and 65℃), concentration (0, 0.05, and 0.15 vol.%), and flow rate (7, 9, and 11 l/min) of the nanofluid. Analysis of the obtained results revealed that the flow rate plays a key role in the Nusselt number of nanofluid with 63.541%. The optimal levels were defined for the three factors including the nanofluid concentration of 0.15 vol.%, the nanofluid temperature of 65℃,and the nanofluid flow rate of 11 l/min. The predicted Nusselt number of nanofluid under these conditions was 322.633. The confirmation test was also performed at the optimal conditions, by which good consistency was found between the experimental and the predicted results.

ABSTRACTThis present study discusses the contributions of the presence of hematocrit level on wall shear stress and flow resistance in a tapered and overlapping stenosed artery with permeable wall. It enables the prediction of the main property of the physiological flows which plays an important role in biomedical investigations. The equation governing the flow in a tapered overlapping stenosed artery was simplified and solved analytically for resistance to flow and wall shear stress. The results highlight that the resistance to flow increases with an increase in either stenosis height or artery shapes while It decreases slightly with a rise in hematocrit level within normal range. Darcy number rises as the resistance to flow decreases for non-tapering, diverging tapering and converging tapering artery shapes. There is a significant hike in wall shear stress as slip parameter or Darcy number increases for diverging tapering, non-tapering and converging tapering. Also, the wall shear stress is increasing with an increase in stenosis height and a decrease in artery shapes.

In this study, the physical perspectives on three-dimensional flow of base fluids with nanoparticles are comparatively investigated under the effect of viscous dissipation using Runge-Kutta 4th order numerical procedure. With the help of similarities transformations, the mathematical model which are described as partial differential equations are transmuted into ordinary differential equations. As said, the Runge-Kutta method, assisted by the shooting strategy, is designed to deal numerically with the resulting set of non-linear differential equations. Highlights of the flow-field and thermal field are illustrated quantitatively in plots. Results for local skin friction coefficients and local Nusselt number are reported and analyzed tabularly. The accuracy of present study is verified in comparison to existing literatures and we have identified an astounding understanding. Also, results indicate that, the velocity profile is enhanced by the modified Hartmann number and stretching ratio parameters. The nanofluid, in fact, has elevated skin friction values and is also more suitable for increasing the rate of heat transfer.

Owing to their lower adverse environmental impacts, natural refrigerants have recently attracted a huge deal of attention. In this regard, the present study is aimed to evaluate the thermodynamic properties of different gaseous natural refrigerants at the molecular level using molecular dynamics (MD) simulations. In this context, the density (as a representative of structural features), enthalpy, and specific heat capacity (as representatives of energy properties) of several natural gaseous refrigerants including helium, nitrogen, methane, and ethane were assessed. Lennard-Jones potential was used for simulation of helium and nitrogen while AIREBO potential and OPLS-AA force-fields were employed for simulation of methane and ethane as polyatomic hydrocarbon refrigerants. Simulations are carried out at various temperatures above the boiling point and pressures of 1, 2, and 5 bar. MD results were in good agreement with the experimental data. Among the applied potentials, AIREBO potential offered results closer to the experimental data as compared with OPLS-AA force-field. The methane-ethane mixture was also addressed at different pressures and compared with the Peng-Robinson equation of state. The results of this study indicated that molecular dynamics can be employed as a reliable tool for predicting the thermodynamic properties of natural refrigerants. The results can be used in the refrigeration cycles.

Effects of different volumetric fractions and Reynolds number on forced convection heat transfer through water/aluminum oxide nanofluid in a horizontal tube are investigated. The flow regime is laminar and the method of simulation is the axisymmetric lattice Boltzmann method (ALBM). The profiles of velocity and temperature were uniform at the input section, on the tube walls the uniform heat flux was considered; moreover, hydrodynamic, and thermal development conditions at the output section were applied. It was observed that an increase in the volumetric concentration of the nanoparticles added to the forced convection heat transfer coefficient and Nusselt number of the nanofluid, as compared to the base fluid. For a volumetric fraction of 5% and Reynolds number of 100 at the input section of the tube (0.1≤X/D≤7) the forced convection heat transfer coefficient increased by 24.165%, while an average increase of 21.361% was observed along the entire length of the tube (0≤x/D≤30). A comparison between the improvements in heat transfer at the two input temperatures, it was found that the forced convection heat transfer coefficient and Nusselt number will increase further at the lower input temperature; Moreover, with increasing the Reynolds number, the percent improvements in forced convention heat transfer coefficient and Nusselt number increased.

Refrigerators and freezers are commonly used for food preservations. Also refrigerated truck trailers and open-type refrigerator display cabinets appliances used for keeping the food in special conditions. These appliances need to be low energy consumer with having good temperature conditions for keeping the food compartments in a desired temperature range. One solution to this end is using cold storage materials called phase change materials (PCMs). PCMs have high latent heat of fusion and phase change in a narrow temperature range which makes them possible solution in energy saving field. This paper reviews cold storage techniques in food preservation appliances such as refrigerators, freezers, refrigerated truck trailers, open-type refrigerated display cabinets. Different thermal storage techniques beside different materials used in this field are briefly introduced. The main drawback of PCMs are their low thermal conductivity which is enhanced using enhancement techniques such as fins and extended surfaces, PCM embedded metal foams, using nanoparticles and Multiple PCM method techniques are discussed. Finally, researches in the field of employing cold storage materials in food preservation devices are reported and tabulated.

The Samaria-promoted of 10wt% Nickel-CMK-3 and 10wt% Nickel-SBA-15 were synthesized by the Samarium (3wt %) addition, and using the two-solvent impregnation technique. The N2 adsorption-desorption, field emission scanning electron microscopy, energy dispersive x-ray analysis, x-ray diffraction and the transmission electron microscopy analysis were used to characterize of the Samaria modified and unmodified catalysts. Furthermore, the catalyst performances were tested under the carbon dioxide reforming of methane. As a result, the x-ray diffraction and surface area investigation revealed that the addition of Samaria (Sm2O3) into the Nickel (Ni) catalysts/silica (SBA-15) and carbon (CMK-3) mesostructures decreased the particles size and surface area according to the TEM micrographs; however, mproved the catalysts activity and catalysts stability. The role of investigation of support in the dry reforming reaction indicated that the activity and catalysts stability of the Ni/CMK-3 catalysts were lower than the Ni/SBA-15 catalysts due to the agglomeration of Ni nanoparticles on the CMK-3 support, the sintering of Ni nanoparticles, the burning of the mesoporous carbon support in the higher temperatures and the blocking of Ni nanoparticles into the deposited carbon nanotubes (CNTs).

In this paper, simulation of non-Newtonian fluid flow in a two-dimension lid driven cavity is investigated. In this simulation Lattice Boltzmann method is used to solve computational fluid dynamics equations numerically. The particular approach of this research is to simulate non-Newtonian fluid flow by Sisko and Hershel Bulkley extended models for the first time beside other non-Newtonian models, by means of Lattice Boltzmann technique. The results of different models including x and y- velocity profiles and streamlines were presented. Then the simulation results of different non-Newtonian fluid flow by Sisko and Hershel Bulkley extended models have been compared with Power Law, Herschel Bulkley and Bingham plastic models. Also, the effect of the Reynolds Number and Power Law parameter (n) on the velocity profiles were studied. Increase of n parameter and Reynolds number leads to moving center of main vortex toward center of cavity. By increasing the parameter n, the maximum value of velocity increases and this indicates while n parameter is increased, vortex strength is excessed.

In this research, gas-liquid-solid three-phase flow in the annulus during under-balanced drilling operations is simulated numerically. One-dimensional form of steady-state governing equations including mass and momentum conservation equations for each phase, gas equation of state, and saturation constraint equation in the Eulerian frame of reference are solved by a proposed algorithm. The computational code is validated by using experimental data from a real well, gas-liquid two-fluid numerical simulation, and also some mechanistic models of WellFlo software. Moreover, the results are compared with the experimental data from a laboratory study. The numerical code succeeds in predicting bottom hole pressure and obtaining the characteristic flow behavior during under-balanced drilling. Due to the importance of controlling flow characteristics during the drilling operations, the effects of change in the injected liquid flow rate, gas injection flow rate, choke pressure on the gas, liquid, and solid volume fractions, as well as gas, liquid, and solid velocity distributions along with the annulus, are investigated. According to the obtained results, the effects of liquid injection flow rate and injected gas flow rate on the flow characteristics are decreased along the annulus in the flow direction, but the effects of choke pressure on the flow characteristics are increased along the annulus in the flow direction. Consequently, to change the flow characteristics in the wellhead area, it is better to change the choke pressure and to affect the flow characteristics in the bottom-hole area, it is preferred to change the gas and liquid injection flow rate. In other words, depending on the required situation of flow characteristic changes, the appropriate operational parameter can be used.