A numerical investigation of thermal prediction of double-pass solar air heater of-counter flow is developed in the present study. The main idea of the current study is that the collector consists of two layers of glass so that the middle layer is glass instead of the usual metal plate. The performance of double-pass solar air heater is studied for a wide range of solar radiation intensities (600, 750 and 900 W/m 2 ). A FORTRAN-90 program is built to simulate the mathematical model of double-pass solar air heater based on solving steady state two-dimensional Navier-Stokes equations and energy equation based on finite volume method. Turbulence effect is simulated by two equations 𝑘-𝜀 module. The results are compared with the results of a previous experimental study and a good agreement was found. From compression calculating efficiency of the present and traditional collector for each solar intensity, it was found that the efficiency of the current collector is higher than that of the traditional one, where the efficiency of the current collector at the solar intensity of (600, 750 and 900) W/m 2 are (0.529, 0.514 and 0.503), respectively, while those of the traditional collector (0.508, 0.492 and 0.481), respectively. In addition to this, the effect of the mass flow rate on the temperature difference of the current proposed collector was studied. Three values of the mass flow rate were studied (0.009, 0.018, and 0.027) kg/s at solar intensity of 750 W/m 2 . From this it was found that the temperature difference decreases with increasing mass flow rate. Accordingly, the efficiency decreases.

Using solar energy to cover heating loads of building is a clean and unconventional way that can help reduce electricity consumption. Problems of the cost of energy and environmental pollution are among the most important challenges facing humanity at the present time. And as most of the energy is used for heating and ventilation, thus the need to find renewable sources of energy has become a pressing need. In this direction Trombe wall, which is a classical passive solar wall, has become one of the most important heating and ventilation technologies of buildings.  In the present work a three-dimensional numerical study of thermal energy performance for Trombe wall utilizing paraffin wax as PCM was presented. The effect of PCM thickness was studied as (2, 3, 4 and 5 cm). A FORTRAN-90 computer program was built to solve a three-dimensional, turbulent Navier stokes and energy equations in addition to enthalpy transforming method for PCM with explicit scheme based on finite volume method. Numerical results of the present code were validated by comparing them with previous experimental results and a good agreement was noted. The results show that a 2 cm thick PCM is an optimal thickness, where the percentage rates of increasing in air temperature over ambient temperature at day hours (10 am, 12 pm, 5 pm, 10 pm and 7 am of the next day) were (37.8, 19.5, 30.7, 60 and 69.2%) respectively, compared to (33.5, 15.2, 25.9, 53.3 and 65.3) % respectively for a 5 cm wax calculated at the same hours.

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A numerical study of three-dimensional, steady, turbulent and incompressible natural convection of air (Pr=0.72) within a rotating cubic enclosure is presented. The present code is based on solving partial differential equations for conservation of mass, momentum and energy equations for a rotating frame. The turbulence effect is introduced by using two equations turbulence model of k-ε . Finite volume method is used in solving the governing equations. SIMPLE algorithm is applied to solve the set discretization equations. To verify the validity of present method, present results is compared with those of previous published work under the same conditions. The influence of changing rotation Rayleigh number ( ) r Ra as a result of chancing angular velocity of enclosure, and temperature difference of enclosure walls on the average Nusselt number (Nu) is presented and correlated.