Numerical and experimental investigation of forced filmwise condensation over bundle of tubes in the presence of noncondensable gases

Ramadan, Abdul-Ghani M
The problem of the forced film condensation heat transfer of pure steam and steam-air mixture flowing downward a tier of horizontal cylinders is investigated numerically and experimentally. Liquid and vapor-air mixture boundary layers were solved by an implicit finite difference scheme. The effects of the free stream non-condensable gas (air) concentration, free stream velocity (Reynolds number), cylinder diameter, temperature difference and angle of inclination on the condensation heat transfer are analyzed. Inline and staggered tubes arrangements are considered. The mathematical model takes into account the effect of staggering of the cylinders and how condensation is affected at the lower cylinders when condensate does not fall on to the center line of the cylinders. An experimental setup was also manufactured and mounted at METU workshop. A set of experiments were conducted to observe the condensation heat transfer phenomenon and to verify the theoretical results. Condensation heat transfer results are available in ranges from (U = 1 - 30 m/s) for free stream velocity, (m1, = 0.01 -0.8) for free stream air mass fraction, (d = 12.7 -50.8 mm) for cylinder diameter and (T -Tw =10-40 K) for temperature difference. Results show that; a remarked reduction in the vapor side heat transfer coefficient is noticed when very small amounts of air mass fractions present in the vapor. In addition, it decreases by increasing in the cylinder diameter and the temperature difference. On the other hand, it increases by increasing the free stream velocity (Reynolds number). Average heat transfer coefficient at the middle and the bottom cylinders increases by increasing the angle of inclination, whereas, no significant change is observed for that of the upper cylinder. Although some discrepancies are noticed, the present study results are inline and in a reasonable agreement with the theory and experiment in the literature. Down the bank, a rapid decrease in the vapor side heat transfer coefficient is noticed. It may be resulted from the combined effects of inundation, decrease in the vapor velocity and increase in the non-condensable gas (air) at the bottom cylinders in the bank. Differences between the present study results and the theoretical and the experimental data may be resulted from the errors in the numerical schemes used. These errors include truncation and round off errors, approximations in the numerical differentiation for interfacial fluxes at the vapor-liquid interface, constant properties assumption and approximations in the initial profiles. Mixing and re-circulation in the steam-air mixture at the lower tubes may be the other reasons for these deviations.


Numerical analysis of natural convective heat transfer through porous medium
Aylangan, Benan; Yüncü, Hafit; Department of Mechanical Engineering (2006)
In this thesis, natural convective heat transfer through an impermeable and fluid saturated porous medium is investigated numerically. A FORTRAN based code is developed and used in order to present the outputs of the applied model and the assumptions. The solutions of flow fields and temperature fields are presented within the medium. Moreover, Nusselt number variations for different values of Darcy, Prandtl, and Rayleigh numbers, and some other thermodynamic properties are investigated and presented. Compa...
Numerical investigation of incompressible flow in grooved channels-heat transfer enhancement by self sustained oscillations
Gürer, Türker; Yüncü, Hafit; Department of Mechanical Engineering (2004)
In this study, forced convection cooling of package of 2-D parallel boards with heat generating chips is investigated. The main objective of this study is to determine the optimal board-to-board spacing to maintain the temperature of the components below the allowable temperature limit and maximize the rate of heat transfer from parallel heat generating boards cooled by forced convection under constant pressure drop across the package. Constant heat flux and constant wall temperature boundary conditions on ...
Numerical simulation and analytical optimization of microchannel heat sinks
Türkakar, Göker; Okutucu Özyurt, Hanife Tuba; Department of Mechanical Engineering (2010)
This study has two main objectives: The performance evaluation of existing microchannel heat sinks using a CFD model, and the dimensional optimization of various heat sinks by minimizing the total thermal resistance. For the analyses, the geometric modeling is performed using the software GAMBIT while the thermal analysis is performed with FLUENT. The developed model compares very well with those available in the literature. Eight different metal-polymer microchannel heat sinks are analyzed using the model ...
Analysis of single phase convective heat transfer in microtubes and microchannels
Çetin, Barbaros; Yüncü, Hafit; Department of Mechanical Engineering (2005)
Heat transfer analysis of two-dimensional, incompressible, constant property, hydrodynamically developed, thermally developing, single phase laminar flow in microtubes and microchannels between parallel plates with negligible axial conduction is performed for constant wall temperature and constant wall heat flux thermal boundary conditions for slip flow regime. Fully developed velocity profile is determined analytically, and energy equation is solved by using finite difference method for both of the geometr...
Numerical analysis of ablation process on a two dimensional external surface
Aykan, Fatma Serap; Dursunkaya, Zafer; Department of Mechanical Engineering (2005)
The thermal response analysis of an ablative material on a two dimensional external surface is performed. The method is applied to both rectangular and cylindrical coordinate systems, where rectangular coordinate system is used for comparison with results available in literature. The current study solves the decomposition of the material at high temperatures by using the nth order Arrhenius equation but excludes the removal of char from the surface due to mechanical erosion or phase change and considers tha...
Citation Formats
A.-G. M. Ramadan, “Numerical and experimental investigation of forced filmwise condensation over bundle of tubes in the presence of noncondensable gases,” Ph.D. - Doctoral Program, Middle East Technical University, 2006.