the flat solar heating transpired collector can be used for heat buildings and large spaces, industrial applications, and drying of agricultural products. The flow structure and convection heat transfer mechanisms are very important to the air performance of uncovered flat solar heating transpired collector. In these solar air heaters, the air is usually heated by a perforated absorber plate (metal). In this research, copper adsorbent plate has been used and numerical simulation has been performed for mass flow rate (0.007, 0.01, 0.0125, 0.015) kg/s. In order for the simulation to be consistent with the physical reality of the problem, the simulation is three-dimensional, non-continuous with a large computational range and continuous suction. Thermal efficiency, mass flow rate, and outlet temperature parameters were investigated. According to the obtained results, with decreasing mass flow rate, the temperature of the absorber plate and consequently the temperature of the outlet air increases; But increasing the temperature of the absorber plate is more than increasing the temperature of the outlet air. As the mass flow rate increases, the thermal efficiency of the flat solar heating transpired collector increases. The lowest efficiency in mass flow rate is 0.007 kg / s with 66.51 % and the highest efficiency in mass flow rate is 0.015 kg / s with 78.02 %.

Thermal run-away of lead acid batteries is one of the destruction modes of lead-acid battery. This phenomenon is a thermal-fluid dynamics instability problem that needs to be solved via direct numerical procedures. High-order simulation of lead-acid battery is the first step of direct numerical simulation (DNS) methods for research on thermal run-away phenomenon. In this study, due to simple geometry of lead-acid-cell, spectral methods which are very common in DNS simulation of thermal and fluid dynamics instability problems is implemented on lead-acid cell. A full cycle of discharge, rest and recharge process of a lead-acid cell is simulated by Chebyshev spectral collocation method combined with fourth order Runge-Kutta time integration. Due to complexities, the simulations are performed to find the possible numerical difficulties of this method as the first step. Two coarse and fine grids with Chebyshev polynomials of 8 and 12 order are selected to perform numerical simulations. Comparison of the error shows that the accuracy will be decreased up to 200 times just by adding two points to grid. Also numerical results show that this method is sufficiently able to predict the cell behavior in the high rates of cell current. The results indicate that spectral methods and Runge-Kutta time integrations are promising tool for direct numerical simulation of lead-acid batteries to study complex physical phenomena such as thermal run-away problem.

Boilers are one of the most important parts of the power plants. Superheater tubes have the main role in boilers and are subject to degradation because of many working conditions. According to the pressure and temperature of the working condition of the superheater tubes in boiler, failure is usually reported from the superheater tubes. Therefore, identifying the causes of this failure and its prevention is quite important. The reports on the failure of platen superheaters in several similar boilers whose inlet and outlet header is the same for all tubes indicate that a particular part of the tubes is more vulnerable than the rest in tubes and the failures are concentrated there. Location of the most failures is at the end of the 135-degree bend of the platen superheater. Therefore, this case was investigated at a special 320 MW power plant where there were seven units. The objective of this investigation is to find the cause of the failure and solve the problem for working in a long time with safety. The preliminary examination showed that the damaged point in this group had a higher temperature than the other groups in the same position. To prove the existence of the higher temperature at these points, three methods were used: metallography, oxide layer thickness measurement, and CFD analysis and all the three methods confirm the results. In this paper, different solutions were introduced for the 320 MW power plant issue. Each of the solution methods is subject to certain advantages and disadvantage. Following the analysis, among the solution methods, one of them was selected as the best solution. Based on the method, some schemes were offered as suggested plans as an alternative to the platen superheater tubes. These schemes were validated in comparison to the power plant superheater. Then, the investigation focused on the geometry of schemes. In addition, all of the three schemes were analyzed by CFD method. Based on the analytical results, one of the schemes was chosen as an alternative plan to the platen superheater for the power plant.

Gas turbine power and thermal efficiency increase with inlet temperature. Considering the temperature limitations for the alloys used in gas turbine components, employment of techniques for reduction of these components temperatures seems to be an essential subject. Based on the research conducted on this subject, among all the proposed methods, rib cooling yields higher heat transfer coefficient and among various types of ribs, V-shaped ribs have higher heat transfer compared to angled rib. The purpose of this feasibility study is to investigate the two proposed ribs for use in gas turbine from heat transfer and fluid flow view and compare their thermal performance. In this work, 3-D numerical simulation has been performed for V-shaped ribs with an angle of 〖60〗^° for the two cases of staggered and inline ribs in two opposite walls in a rectangular channel. Experimental results have been used for validation. The results indicate an enhancement of ~22% in heat transfer if V-shaped ribs with an angle 〖60〗^° and downstream orientation are located in staggering form in two opposite walls of a channel. In this case, an increase of 10% is observed for pressure drop, however, its thermal performance increases 12% which is positive and considerable.

 In this paper, multi-objective optimization (MOO) of heat transfer and flow field in cross-flow heat exchangers with triangular and square arrangement is performed using Computational Fluid Dynamics (CFD) techniques and Non-dominated Sorting Genetic Algorithms (NSGA II). At first, fluid flow is solved numerically in 150 various heat exchanger using CFD techniques. Finally, the CFD data will be used for Pareto based multi-objective optimization of fluid flow in cross flow heat exchanger using NSGA II algorithm. In the MOO process there are two geometrical parameters and the conflicting objective functions are to simultaneously maximize the amount of heat transfer and minimize the pressure drop. The Pareto front including optimum design variables and objective functions for two triangular and square heat exchangers are shown in results. It is shown that the achieved Pareto solution includes important design information on fluid flow in the heat exchangers.

The interaction of the thermal and velocity boundary layers of 2D cylinder at is modeled in ANSYS Fluent. Heating elements different positions as well as various temperature effects on the flow characteristics are investigated. Temperature variation of the cylinder surface changes the fluid properties including density, viscosity, specific heat and conductivity. Their dependencies are modeled in the form of polynomials as the function of temperature. The velocity inlet boundary condition of 0.6 m/s, the pressure outlet with 0 Pa and no-slip condition for cylinder wall are set. The lateral boundaries are freestream walls while the sidewalls are symmetric. The pressure-velocity coupling is modeled with Coupled method and is used for turbulence modelling. The surrounding temperature is . The comparison of the heating element application on the windward and leeward sides of the cylinder show that its usage on the leeward side is more efficient on the flow control and reduces the aerodynamic forces significantly. By increasing the fluid viscosity due to the temperature enhancement, the Reynolds number decreases while the surface friction increases. With surface friction enhancement under leeward side heating, vorticity strength is reduced and the vortices lengths are elongated downstream. Consequently, free shear layers interaction and vortex shedding are delayed forming a relatively symmetric velocity pattern and pressure distribution. The symmetry of the pressure distribution reduces the oscillation amplitude of the aerodynamic forces that leads to the flow control. Increasing the cylinder surface temperature on the leeward side rises the intensity aerodynamic forces variation. The results indicate that the location, size, and temperature of the heating elements influence the separation points of flow and the aerodynamic forces acting on the body. The utilization of the heating element with a temperature of on the leeward side leads to lift force and drag force reduction; while using them on the lateral sides, despite delaying the separation points of the flow, leads to flow instability. The size of vortices is decreased resulting in the higher shedding frequency. The cause of this phenomenon is related to the changes in the characteristics of flow and vortices that alter the velocity and pressure fields.

In this paper, thermal-viscous fingering instability of miscible flow displacements in anisotropic porous media is studied .for the first time An exponential dependence of viscosity on temperature and concentration is represented by two parameters β_T and β_C, respectively. The effect of anisotropic properties of permeability tensor, Lewis number and thermal lag coefficient are investigated. Creation and propagation of these fingers are playing an important role in displacement of fluids and especially on oil transformation from discovered oil reservoirs in enhanced oil recovery process. In nonlinear simulation, a spectral method based on the Hartley transforms are used to model the thermal-viscous fingering instability in anisotropic porous media. The results include concentration and temperature contours, sweep efficiency, and mixing length. The results indicated that by increasing the anisotropic permeability ratio, the fingers arrive later to the end of the front, instability decrease and more stable flow is obtained. Also, by increasing the Lewis number, thermal front appears without any fingers. Decreasing the thermal lag coefficient causes to the thermal front stays behind the flow front and increasing the stability of the flow field.

The use of microfluidic systems for various applications such as lab-on-chip, drug delivery, and micro chemical reactors is increasing day by day and several sensors have been provided to control and develop these microsystems. In this paper, a biosensor based on microelectromechanical systems was introduced with direct application in liquid environment for digital microfluidic systems that have the ability to be integrated with various fluidics components such as delivery, separation, and mixing. The proposed sensor comprises  semi-sized coupled microresonators which vibrate in parallel to the substrate so that it can be integrated between the plane electrodes in digital microfluidics systems. Active area of the sensor is located in the center of the structure and immobilized for capturing any special biological targets. Due to in-plane vibration of the sensor, the viscous damping is low enough to achieve measurable quality factor by resonator. The total system is simulated by finite element methods and the results demonstrate that the appropriate vibration frequency for in-plane motion of the sensor is 16.5kHz. In addition, the quality factor and mass sensitivity are 49 and 100Hz/µg, respectively, which are comparable to sensors with similar fluidics applications.