Heat transfer of two-dimensional, hydrodynamically developed, thermally developing, single phase, laminar flow inside a microtube is studied analytically with constant wall temperature thermal boundary condition. The flow is assumed to be incompressible and thermo-physical properties of the fluid are assumed to be constant. Viscous dissipation and the axial conduction are included in the analysis. Rarefaction effect is imposed to the problem via velocity slip and temperature jump boundary conditions for the slip flow regime. The temperature distribution is determined by solving the energy equation together with the fully developed velocity profile. Analytical solutions are obtained for the temperature distribution and local and fully developed Nusselt number in terms of dimensionless parameters / Peclet number, Knudsen number, Brinkman number, and the parameter &amp / #954 / . The results are verified with the well-known ones from literature.

The objective of this thesis is to predict numerically the optimal spacing between parallel heat generating boards. The isothermal boards are stacked in a fixed volume of electronic package enclosed by insulated lateral walls, and they are cooled by laminar forced convection of air with prescribed pressure drop. Fixed pressure drop assumption is an acceptable model for installations in which several parallel boards in electronic equipment receive the coolant from the same source such as a fan. In the numerical algorithm, the equations that govern the process of forced convection for constant property incompressible flow through one rectangular channel are solved. Numerical results of the flow and temperature field in each rectangular channel yield the optimal board-to-board spacing by which maximum heat dissipation rate from the package to the air is achieved. After the results of the optimization procedure are given, the correlations for the determination of the maximum heat transfer rate from the package and optimal spacing between boards are, respectively, derived in terms of prescribed pressure difference, board length, and density and kinematic viscosity of air. In conclusion, the obtained correlations are compared and assessed with the available two-dimensional studies in literature for infinite parallel plates. Furthermore, existing two-dimensional results are extended to a more generalized three-dimensional case at the end of the thesis.

The problem of condensation of steam on a vertical tier of horizontal tubes is investigated by both analytical and experimental methods in this study. A computer program is written to perform the analysis of laminar film condensation on the horizontal tubes. The program is capable to calculate condensate film thickness and velocity distribution, as well as the heat transfer coefficient within the condensate. An experimental setup was also manufactured to observe the condensation phenomenon. Effects of tube diameter and temperature difference between steam and the tube wall on condensation heat transfer have been analytically investigated with the computer program. Experiments were carried out at different inclinations of the tier of horizontal tubes. Effects of the steam velocity and the distance between the horizontal tubes are also experimentally investigated. Results of the experiments are compared to those of the studies of Abdullah et al., Kumar et al. and Nusselt as well as to the analytical results of the present study.

The steady-state natural convection heat transfer from vertical rectangular fins extending perpendicularly from vertical rectangular base was investigated experimentally. The effects of geometric parameters and base-to-ambient temperature difference on the heat transfer performance of fin arrays were observed and the optimum fin separation values were determined. Two similar experimental set-ups were employed during experiments in order to take measurements from 30 different fin configurations having fin lengths of 250 mm and 340 mm. Fin thickness was maintained fixed at 3 mm. Fin height and fin spacing were varied from 5 mm to 25 mm and 5.75 mm to 85.5 mm, respectively. 5 heat inputs ranging from 25 W to 125 W were supplied for all fin configurations, and hence, the base and the ambient temperatures were measured in order to evaluate the heat transfer rate from fin arrays. The results of experiments have shown that the convection heat transfer rate from fin arrays depends on all geometric parameters and base-to-ambient temperature difference. The effect of these parameters on optimum fin spacing was also examined, and it was realized that for a given base-to-ambient temperature difference, an optimum fin spacing value which maximizes the convective heat transfer rate from the fin array is available for every fin height. The results indicated that the optimum fin spacings are between 8.8 mm and 14.7 mm, for the fin arrays employed in this work. Using the experimental results of present study and experimental results in available literature [2,3,9,10,11,12,14], a correlation for optimum fin spacing at a given fin length and base-to-ambient temperature difference was obtained as a result of scale analysis.

Road and railways tunnels are constructed for decreasing the transportation time inside city or intercity. The fire safety systems are mounted for the safe use of tunnels. Therefore, it is important to accurately predict the fire-induced air velocity,temperature and smoke concentrations in tunnel fires in order to design efficient fire protection systems. To this end, scaled tunnel models are used and experiments are carried to understand the phenomena on these tunnel models. In addition, the studies for investigating the tunnel fire phenomena and their methods of modeling techniques for fire experiments are mentioned. In the literature, there is no sufficient information about vehicles&#039 / blockage effect on heat release rate and temperature distribution inside tunnel with different ventilation velocities. As a result, in order to research this subject, the scaled model tunnel is constructed in Fluid Mechanics Laboratory. Based on the Froude number scaling, wood sticks with different configuration inside the model tunnel are burned in a controlled environment. The heat release rate measurement, sampling of gases after combustion, mass loss rate of burning models and temperature distribution along the tunnels with different longitudinal ventilation velocities are measured to investigate the effect of different cross-sectional areas of the burning substances. Furthermore, the model vehicles having a square base area are built according to wood crib theory. The results are investigated with statistical techniques called &quot / Analysis of Variance&quot / and general results have been tried to be reached. It is determined that the variation of air velocity inside tunnel is not so effective, but model vehicle&#039 / s cross sectional area is directly proportional to heat release rate.

Numerical solutions of mathematical modelizations of heat and mass transfer in cubical and cylindrical reactors of solar adsorption refrigeration systems are studied. For the resolution of the equations describing the coupling between heat and mass transfer, Bubnov-Galerkin method is used. An exact solution for time dependent heat transfer in cylindrical multilayered annulus is presented. Separation of variables method has been used to investigate the temperature behavior. An analytical double series relation is proposed as a solution for the temperature distribution, and Fourier coefficients in each layer are obtained by solving some set of equations related to thermal boundary conditions at inside and outside of the cylinder.

Climate models are the primary tools used for understanding past climate variations and for future projections. The atmospheric radiation is the key component of these models. Accurate modeling of atmosphere necessitates reliable evaluation of the medium radiative properties and accurate solution of the radiative transfer equation in conjunction with the time-dependent multi-dimensional governing equations of atmospheric models. Due to difficulty in solving the equations of atmospheric and radiation models simultaneously, radiation equations have been solved when input data such as concentration, temperature etc. were made available upon solution of equations of atmospheric models. Generally, time step of conservation equations are 10-30 minutes but radiative transfer equation is called only once every 1-3 hours. However, there is inaccuracy due to the fixed radiation fluxes over the intervening time steps. To overcome this problem, the equations of atmospheric and radiation models have to be solved simultaneously and the solution methods have to be compatible. For this purpose, a radiative-convective model with radiation model based on method of lines (MOL) solution of discrete ordinate method (DOM) with wide band correlated-k (WBCK) was developed. To achieve this objective, a previously developed MOL solution of DOM with WBCK model was adapted to 1-D longwave clear sky atmosphere and its predictive accuracy and computational efficiency was examined on the test problem by using benchmark solution obtained from Line-by-line Radiative Transfer Model (LBLRTM). The radiation code was then coupled with radiative-convective model and the predictive accuracy of this model was examined for several coupling intervals. Comparisons reveal that as coupling interval increases, although the computation time of the model decreases, the predicted temperature profiles diverge from the one obtained when equations of radiative-convective model and the radiation model are solved simultaneously and percentage relative error in temperature increases an order of magnitude when coupling time between radiative-convective model and the radiation model increases from 2 to 10 hours. Therefore, it can be concluded that the equations of the radiation model have to be solved simultaneously with the equations of the climate model. Overall evaluation of the performance of the radiation model used in this study points out that it provides accurate and computationally efficient solutions and can be used with confidence in conjunction with the climate models for simultaneous solution of governing equations with radiation transfer equation.