This paper presents a numerical investigation for laminar FORCED CONVECTION flow of a radiating gas in a rectangular duct with a solid element that makes a backward facing step. The fluid is treated as a gray, absorbing, emitting and scattering medium. The governing differential equations consisting the continuity, momentum and energy are solved numerically by the computational fluid dynamics techniques. Since the present problem is a conjugate one and both gas and solid elements are considered in the computational domain, simultaneously, the numerical solution of Laplace equation is obtained in the solid element for temperature calculation in this area. Discretized forms of these equations are obtained using the finite volume method and solved by the SIMPLE algorithm. The radiative transfer equation (RTE) is also solved numerically by the discrete ordinate method (DOM) for computation of the radiative term in the gas energy equation. The streamline and isotherm plots in the gas flow and the distributions of convective, radiative and total Nusselt numbers along the solid-gas interface are presented. Besides, the effects of radiation conduction parameter and also solid to gas conduction ratio as two important parameters on thermo hydrodynamic characteristics of such thermal system are explored. It is revealed that the radiative Nusselt number on the interface surface is much affected by RC parameter but the radiation conduction parameter has not considerable effect on the convective Nusselt number. Comparison between the present numerical results with those obtained by other investigators for the case of non-conjugate problems shows good consistency.

This paper presents mathematical models of thin layer FORCED CONVECTION solar drying of Cuminum cyminum using two drying methods (mixed and indirect) at different operating conditions. The average initial moisture content of the seeds for all tests was about 43% d.b. and the drying was performed continuously, in each test, for a uniform period of 90 minutes drying time in a solar cabinet dryer to obtain an average final moisture content of 8% d.b. Three airflow rates (0.084, 0.127 and 0.155 m3 s-1) were adopted and the experiments were run each sunny day from 11:30 to 13:00 with an average solar intensity of 750 W m-2 (±50 W m-2), ambient air temperature of 27°C (±1°C) and relative humidity of 30% (±1%). In order to find the most suitable form of thin layer solar drying model, eleven different mathematical models were selected using the experimental data to determine the pertinent coefficients for each model by applying the non-linear regression analysis technique. The goodness of fit was evaluated by calculating and comparing the statistical values of the coefficient of determination (R2), reduced chi-square (c2) and root of mean square error (RMSE) for any model and for the two drying methods. The best results were found for the approximation of diffusion model with R2= 0.995, c2=0.0023 and RSME= 0.0199 in mixed mode type, and the Midilli model with R2= 0.994, c2=0.0045 and RSME= 0.0225 in indirect mode type thin layer solar drying.

Based on preliminary investigations under controlled condition of drying experiments, a mixed-mode solar dryer with FORCED CONVECTION using smooth and rough plate solar collector was constructed. This paper describes the development of dryer considerations followed by the results of experiments to compare the performance of the smooth and the roughed plate collector. The thermal performance of solar collector was found to be poorer because of low convective heat transfer from the absorber plate to air. Artificial rib roughness on the underside of the absorber plate has been found to considerably enhance the heat transfer coefficient. The absorber plate of the dryer attained a temperature of 69.2oC when it was studied under no-load conditions. The maximum air temperature in the dryer, under this condition, was 64.1oC. The dryer was loaded with 3 kg of grapes having an initial moisture content of 81.4%, and the final desired moisture content of 18.6% was achieved within 4 days while it was 8 days for open sun drying. This prototype dryer was designed and constructed to have a maximum collector area of 1.03 m2. This solar dryer been be used in experimental drying tests under various loading conditions.

In this paper, a numerical study of a 2-D combined CONVECTION-radiation heat transfer in a horizontal rectangular duct with two sudden contractions is presented. Contractions in duct are created by two inclined forward facing steps. To simulate the incline surfaces of the FFS, the blocked- off method was employed for both fluid mechanic and radiation problems. The fluid was treated as a gray, absorbing, emitting and scattering medium. To solve the governing equations, the 2-D Cartesian coordinate system was used. These equations were solved numerically, using the CFD techniques and SIMPLE algorithm. For computation of radiative term in energy equation, the radiative transfer equation (RTE) was solved numerically by discrete ordinates method (DOM) to find the divergence of radiative heat flux distribution. The effects of optical thickness, radiation-conduction parameter and albedo coefficient on heat transfer behavior of the system were carried out. Comparison of numerical results with available credential data shows good consistency.

This paper describes a numerical study of FORCED CONVECTION laminar flow of air past different staggered tube arrays in a patented tubular heat exchanger. The study is based on a patented (APU, UK May 2001) tubular heat exchanger design using implanted vortex generators on the internal flow and change of fluid momentum in a turbulent jet on the external flow side. The finite-volume method is used to solve the governing Navier-Stokes and energy equations for ES (Equal Spacing), ET (Equal Triangle), and RS (Rotated Square) geometric arrangements. The results are obtained at three different nominal pitch-to-diameter ratios (S*D = 1.33, 1.60, 2.00) for the range of 20≤Rein<270. Variations of pumping power (W) due to change in pressure loss and total heat transfer rate (q) from tube bundle are investigated for various arrangements and inlet Reynolds numbers. The efficiency A is also defined based on pumping power and total heat transfer rate and is used to obtain the optimum model.

Nanofluids, in which nano-sized particles (typically less than 100 nm) are suspended in liquids, have emerged as a possible effective way of improving the heat transfer performance of common fluids. In this paper a numerical study is performed to analyze the wall shear stress and heat transfer coefficient of gAl2O3-water nanofluids under laminar FORCED CONVECTION through a circular pipe. It is assumed that the distribution of nanoparticles in the flow field is nonhomogeneous. The results obtained show that addition of gAl2O3 nanoparticles to pure water effectively enhances the convective heat transfer. Moreover, the wall shear stresses are increased. The increasing rate of heat transfer depends on the volume concentration such that for the lowest and highest values of particle volume concentration 0.03 and 0.05, considered in this study, the heat transfer enhancement is approximately 23% and 40%, respectively. Also, compared with the available experimental data, the model used in this work is capable to predict the increasing rate of heat transfer of nanofluids properly.

This research study presents a numerical study on FORCED CONVECTION heat transfer of an aqueous ferrofluid passing through a circular copper tube in the presence of an alternating magnetic field. The flow passes through the tube under a uniform heat flux and laminar flow conditions. The primary objective was to intensify the particle migration and disturbance of the boundary layer by utilizing the magnetic field effect on the nanoparticles for more heat transfer enhancement. Complicated CONVECTION regimes caused by interactions between magnetic nanoparticles under various conditions were studied. The process of heat transfer was examined with different volume concentrations and under different frequencies of the applied magnetic field in detail. The convective heat transfer coefficient for distilled water and ferrofluid was measured and compared under various conditions. The results showed that applying an alternating magnetic field can enhance the convective heat transfer rate. The effects of magnetic field, volume concentration and Reynolds Number on the convective heat transfer coefficient were widely investigated, and the optimum conditions were obtained. Increasing the alternating magnetic field frequency and the volume fraction led to better heat transfer enhancement. The effect of the magnetic field in low Reynolds numbers was higher. The results showed that the modeling data were in a very good agreement with experimental data. The maximum error was around 10%.

In present study, the flow and heat transfer of Water-Cu nanofluid in micro-tube with slip regime with constant wall heat flux numerically simulated with low Reynolds numbers. Slip velocity and temperature jump boundary conditions are also considered along the microtube walls, for first time. The results are presented as the profiles of temperature and velocity. Nusselt number and pressure drop coefficient calculated in interance and full developed region. The effect of slip and using nano particle considerd.It is observed that Nusselt number increases with slip velocity coefficient and pressure drop coefficient decreases; at intrance region the Raynolds of flow has effect on Nusselt and pressure drop coefficient, too.Likewise observed nano particle adding to water has low effect to increases Nusselt number and pressure drop coefficient.

Monitoring the effective parameters of drying crops is necessary to evaluate and determine system performance under real conditions. Hence, a monitoring system was constructed to determine the performance of a vegetation FORCED-CONVECTION solar dryer. Digital temperature sensors were set up in the air inlet and outlet of the collector and the air outlet of the drying chamber. A program was written using visual Basic 6 software to register sensor data and make calculations. To evaluate the dryer, experiments were carried out over eight hours between 10 am and 6 pm during the summer. Mint was used for drying in all experiments on 5Cm high trays of the dryer chamber. The results showed that the radiation energy, the heat energy absorbed by the collector and the energy required for product evaporation had linear relationships with temperature. Radiation energy increased at first and decreased later during the drying time. The results showed that the average temperature in the collector air inlet, outlet and drying chamber air outlet were 38.1oC, 54.7oC and 45.5oC, respectively. The average maximum and minimum energy efficiency were 49% and 14.7%, respectively. The average radiation energy and required energy for product evaporation were 4572.4 and 2772.2 KJ, respectively. The drying curve was Mwb=1.827e-0.4857t with R2=0.945.