Journal of Heat and Mass Transfer Research
Volume:7 Issue: 1, Winter Spring 2020

Mixing tanks equipped with mechanical stirrer are broadly applied in chemical and petrochemical industries, due to their variety of industrial process requirements. In this study, helical single blade mixer was designed applying CATIA and then mixing of fluid and solid particles, in a tank with this agitator was examined by OpenFOAM. For velocity distribution in the mixing tank, continuity, momentum equations, boundary conditions and coding were performed applying​ C++ language scripts in the software. The results of velocity distributions in three directions coordinates indicated that the efficiency of helical blade mainly correlated to axial and tangential flows.  The radial flow has less important role in mixing operation. Moreover, solid particles concentration distribution were computed in the fluid phase .It was exhibited that the particles were distributed homogeneously in the tank. In addition, temperature distribution was obtained applying continuity, momentum and energy equations as well as utilizing necessary code and boundary conditions in the software. Consequently, a correlation for Nusselt number as a function of Re, Pr and Vi was acquired by using temperature profile and dimensional analysis. The results achieved are in good agreement with those available in literature.

The low conversion efficiency of solar cells produces large amounts of thermal energy to the cells, and with an increase in the temperature of solar cells, their electrical efficiency decreases. Therefore, a hybrid photovoltaic thermal system improves the overall efficiency of the system by adding thermal equipment to the solar cell and removing excessive heat from these cells. In this paper, we study the effect of SiO2/water nanofluids on thermal and electrical efficiency of domestic photovoltaic thermal systems (DPVT) theoretically and experimentally. In the theoretical part, based on the control-volume finite-difference approach, an explicit dynamic model was developed for a single-glazed flat-plate water-heating photovoltaic thermal collector with closed loop cooling system with withdrawing urban water from the storage tank. The model accuracy was verified in comparison with the measured experimental data. Experimental results show that by increasing concentrations of nanofluid, the thermal and electrical performance has improved and overall efficiency decreased by increasing the diameter of the nanoparticles. The overall efficiency of the DPVT for 0 and 3 weight percent of SiO2/ water nanofluids with a diameter of 11-14 nanometers increased to 5.4% and 7.76% compared to base fluid, respectively.

Abstract. In this paper, a Cascaded Lattice Boltzmann Method with second order slip boundary conditions is developed to study gas flows in a microchannel in the slip and transition flow regimes with a wide range of Knudsen numbers. For the first time the effect of wall confinement is considered on the effective mean free path of the gas molecules using a function with nonconstant Bosanquet parameter instead of the constant one. The constant-force driven and pressure-driven gas flows in a long microchannel are simulated under different conditions. The results of the velocity profile, pressure distribution, and mass flow rate are in good agreement with the benchmark solutions and experimental data reported in the literature. The Knudsen minimum phenomenon is also well captured by the present model. The proposed Cascaded Lattice Boltzmann Method shows a clear improvement in predicting the flow behaviors of microchannel gas flows for the previous classic and Cascaded Lattice Boltzmann Method

This study presents an innovative and simple way to increase the rate of heat transfer in a spiral plate heat exchanger model. Several circular cross-section rods, as continuous vortex generators, have been inserted within the spiral plate heat exchanger in the cross-stream plane. The vortex generators are located at various azimuth angles of α=30◦, 60◦, 90◦, and 120◦ with non-dimensional diameters of d/H=0.3, 0.4, and 0.5. Computations have been carried out numerically by means of the finite volume approach under different Dean numbers (De) ranging from 500 to 1500 in the laminar regime. The flow physics within the advanced spiral heat exchanger model has been discussed using several velocity and temperature contours. It was found that by inserting the continuous vortex generators in the cross-stream plane of a spiral plate heat exchanger, the unsteady flow develops within the channel in which the rate of unsteadiness is proportional to d/H and De directly and to azimuth angle inversely. The maximum heat transfer enhancement with respect to the conventional spiral plate heat exchanger (without continuous vortex generators) is found to be 341% for α=30◦, d/H=0.5, and De=1500. Additionally, values of pressure drop penalty and thermal-hydraulic performance have been determined accordingly.

In this paper, the effect of adding hydrogen to the composition of methane and air in a micro combustor is investigated by a three-dimensional numerical method. First, the results of the current study in determining the wall temperature of the micro combustion chamber are compared with those obtained from the experimental and numerical results of the previous research. By confirming the numerical solution of this study, the effect of adding hydrogen to the mixture of methane and air on the distribution of temperature, pressure and outlet velocity of the gases is calculated numerically. The numerical results show that increasing the percentage of hydrogen to the mixture of methane and air leads to nonlinear changes in the outlet velocity, pressure, and temperature. In addition, the results show that by increasing the percentage of hydrogen to 2.5% and 5%, the maximum outlet velocity of the gases and minimum temperature are produced in the micro combustor, respectively.

The objective of this study is to present a mathematical modeling and solution approach for the drying process of spheroidal solids with the application of microwave in capillary porous media based on the Luikov equations, composed of a system of linear and coupled partial differential equations arising from the energy, mass and pressure balances inside the solid matrix. Additionally, the power generation term from the application of microwaves is added to this differential system. The solution to this problem is achieved through a Coupled Integral Equations Approach (CIEA), whose objective is the transformation of the initial PDE system into an ODEs one. A computer code was developed in FORTRAN 90/95 programming language, which uses the subroutine IVPAG from the IMSL library to solve the system of ODEs from the application of the CIEA. The results obtained were compared with other previously reported in the literature to verify the methodology and showed satisfactory agreement.

This study investigates the effect of ZnO nanoparticles to transformer oil on the thermal conductivity and dynamic viscosity. The consequence of the temperature and nanofluid concentration as an important parameters have been explored on the thermal conductivity and viscosity of the samples. The results indicated that the thermal conductivity of the nanofluid was higher than that of the pure transformer oil at the temperature of 25°C. Also, a rise in the nanoparticle concentration of transformer oil increased the thermal conductivity of nanofluid. Besides, the thermal conductivity at the volume fractions of 0.05% and 1% increased by approximately 4.61% and 11.53%, respectively. The dynamic viscosity reached the highest level at maximum volume fraction in all temperatures. In addition, an increase in the temperature reduced the dynamic viscosity of both the pure transformer oil and the nano-oil. At a given temperature, a rise in the volume fraction of ZnO nanoparticles enhanced the dynamic viscosity. Moreover, to predict the dynamic viscosity of nanofluid, a new correlation has been presented as a function of temperature and volume fraction with R-Sq=0.9913.

In present paper, heat transfer of pulsatile flow in ribbed tube was investigated numerically by considering the effect of thermal inertia of solid wall thickness. To this purpose, CVFV (Control Volume Finite Volume) technique with collocated grids arrangement was adopted to discretize momentum and energy equations. Rhie and Chow interpolation method was employed to avoid checker-board of pressure field in numerical simulation. The well-established SIMPLE (Semi-Implicit Method for Pressure Linked Equations) method was utilized to deal with the coupling of pressure and velocity in momentum equation. Stone’s Strongly Implicit Procedure (SIP) was used to solve the set of individual linear algebraic equations. Womersley number, Reynolds number, velocity amplitude and wall thickness ratio are four essential parameters which influence heat transfer and Nusselt number in pulsatile flow in a ribbed tube. It was deduced by varying Womersley number Nu does not change. Nu enhances almost 19% by augmentation of wall thickness ratio from 0.125 to 1. It was shown by increasing velocity amplitude from 0.1 to 0.8, Nu reduces almost 4.7%.