دکتر علی اکبر عباسیان آرانی

The great attention and interest of researchers to use ammonia in combustion systems as a carbon-free fuel for gas turbines, as well as the existence of developed infrastructure for its production, show the importance of present fuel and this issue. In addition, one of the best candidates for storing renewable energies on large scales or transporting them for long distances is doubtlessly Ammonia (NH3). In gas turbines and boilers, adding landfill gas improve NH3 reactivity effectively. The present effort studies NH3/landfill mixtures’ laminar flame propagation from 1 to 10 atm in an 11-liter constant volume combustion chamber using experimental approaches such as Mach-Zehnder and Schlieren interferometry method. The numerical study was performed using the Ansys Chemkin-Pro package via San Diego, Okafor, and GRI-Mech 3.0 mechanisms which can provide very accurate predictions for laminar burning velocities. The results indicated that the most considerable influence on increasing laminar burning velocities could be attributed to Ammonia concentration in the mixture. The experiments also showed that laminar burning velocity is reduced when the pressure is increased.

This paper introduces solar radiation estimation function based on air mass and the statistics information about sunny and cloudy days for use in numerical modeling of solar ponds. Solar ponds are one of the methods of absorbing solar radiation and storage it with long storage periods. By using one-dimensional simulation, the performance of salt gradient solar pond is investigated. By removing the usual assumptions, it is attempted to take into account the effects of environmental conditions more realistically. These conditions included the variability of ambient temperature by day and hour, the solubility of salt depend on temperature and concentration, the variability of radiation intensity with respect to the angle of elevation of the sun, and the effect of wall shading on the pond. The analysis is transient and the day and night conditions are included. The innovation was to estimate the intensity of solar radiation using the concept of air mass and the amount of cloudy sky. A relation for the calculation of cloud cover factor, which was extracted using the statistics of cloudy and semi-cloudy days and was compared with empirically amount. The ability of this relationship is to estimate the radiation intensity for locations where statistics or tools and equipment for recording radiation intensity are missing. Presented results show that the radiation intensity is in good agreement with the existing experimental data.

Today, the issue of increasing heat transfer has attracted a great deal of attention from researchers for the development of a variety of heat exchangers to achieve high efficiency, low cost, lightweight. In this paper, the hydrothermal performance is investigated by incorporating vortex generator and hole and their proper positioning on trapezoidal fin. For this purpose, numerical modeling of water flow in a rectangular channel is performed in two laminar and turbulent flow regimes and for 5 models with different positions of vortex generator and hole in constant size geometric parameters. The results showed that in both flow regimes, the pressure drop was increased by inserting the hole on top and bottom. To create a better comparison, the ratio of the Colburn factor to friction factor was defined and applied in two simple and powerful ways and the best hydraulic-thermal performance was obtained for the trapezoidal fin with the vortex generator on the right and the hole in the middle, so that in the turbulent flow regime, the highest value for the ratio of Colburn factor to friction factor (simple ratio and power ratio) was reported as 0.0539 and 0.01504 for this position, respectively.

In this paper, the thermal behavior of a living biological tissue during electromagnetic radiation thermal therapy is investigated. While, a large number of studies devoted to the Fourier and non-Fourier heat transfer in living tissue are anavilible for different boundary condition, less analytical asnd semi-analytical works exist on the heat transfer in the multilayears tissue. In the present study, semi analytical Galerkin weighted residual method is used to solve the DPL non-Fourier heat transfer equation in the multilayer tissue with a tumor placed in. The results show that considering a multilayer tissue with temperature dependent properties for each layer is very effective on temperature distribution in the tissue, so that 2°C difference in tumor temperature after 1800 s is observed. The effect of the Vernot number on the temperature distribution shows that increasing the flux relaxation time results in reducing the temperature signal velocity and the tumor temperature. The results concerning the skin surface temperature and the blood perfusion rate indicate with lowering the surface temperature, the maximum temperature acces deeper in the tissue. Moreover, the reduction in the blood perfusion rate that accures in the hypoxy tumors results in the increase of the tumors temperatures during the thermal therapy.

The closed-circuit cooling tower is described as the combination of both wet and dry cooling towers that hot water passes through the bundle of tubes as in the dry cooling towers and surrounding air passes around them in a forced or natural regimes. Thus, secondary water circulates as an open cycle and is sprayed on the bundle of tubes to preserve the tower cooling process. In the present research, the operation of a model of the closed-circuit wet cooling tower has been investigated numerically and experimentally. The effects of environmental condition on process water temperature, sprayed water temperature and air temperature have been evaluated, and the mass and heat transfer coefficients on the surface of hot water tubes have been calculated. According to these results, surrounding air temperature and humidity increasing decreases the tube outer surface mass and heat transfer coefficients. The mass and heat transfer coefficients rates are decreased by about 3% and 4% between the 278 and 288 K and are 6% and 7% between the 288 and 298 K inlet air temperature, respectively. The mass and heat transfer coefficients are both 18% for air inlet temperature between the 298 and 308 K. After 308 K these values are 4%. The decreasing rate of heat and mass transfer coefficient with increasing relative humidity from 10% to 20% is very low and from 20% to 40% is almost constant, and from 40% to 50% a 16% decrease in heat and mass transfer coefficients is observed.

Use of a magnetic field, wavy wall heat exchanger and dispersion of nanoscale particles are the new methods for improving the thermal systems performance. Flow vortex, which is formed by means of chips, or appendages such as blades or fins, is very effective in improving the heat transfer rate. In this study, the effect of magnetic field and vortex generator in compulsory displacement is investigated separately and simultaneously. In the present work, a wavy wall heat exchanger is simulated in various geometries of the Vertex generator under magnetic fields in various Hartmann and Reynolds numbers filled with nanofluid. For this propose fluid flow and heat transfer were simulated using Navier Stokes, conservatism of mass, momentum and energy with incompressible flow assumption. The system of nonlinear governing equations is solved explicitly using a fluent software based on the basic pressure solver and finite volume method. Turbulent equations are discriminated using the first order upstream method, as well as momentum, continuity and energy equations with upstream second order method. The results show that with increasing Reynolds number, the Nusselt number and friction coefficient increase and decrease respectively. As the Hartman number increases, the Nusselt number increases and the friction coefficient decreases.

In this work, influence of the twisted tape insertion on heat transfer rate and pressure drop characteristics in a double pipe has been numerically investigated. For this purpose, a 3-D double pipe heat exchanger with several types of twisted tape designed with two twist ratio (3, 5). The results obtained from the heat exchanges with twisted tape insert are compared with those without twisted tape that is plain heat exchanger. The numerical results revealed that the increase in heat transfer rate of twisted tape inserts with twist ratio 3 and 5 at Re=20000 is found to be 28% and 14% more than plain tube, respectively. It was found that with decrease twisted ratio, the amount of heat transfer rate and pressure drop increase rapidly. And by the point of pressure drop, at Re=20000, the amount of pressure drop of twisted tape inserts with twist ratio 3 and 5 are 58%  and 34% higher than plain tube, respectively.