Ünal AKDAĞ, A. Feridun ÖZGÜÇ, Mustafa ÖZDEMİR

Hareketli sıvı kolonunda ısı geçişinin incelenmesi

Bu çalışmada, halkasal zorlanmış salınımlı akışta ısı geçişi deneysel ve sayısal olarak incelenmektedir. Halkasal kesit içinde akışkan bir piston-silindir düzeneği ile farklı frekans, genlik ve ısı yükünde titreştirilmektedir. Deneyler farklı ısı akıları ve frekanslar için yapılmış olup bu frekanslara karşılık gelen Nusselt sayıları bulunarak, boyutsuz sayılar cinsinden bir korelasyon eşitliği ile verilmektedir. Ayrıca sonlu hacimler ayrıklaştırma yöntemine göre çözüm yapan FLUENT yazılımı kullanılarak Hareketli Sıvı Kolonunda ısı geçişi sayısal olarak da incelenmektedir. Yapılan incelemelerde, sıvı içerisindeki hız ve sıcaklık dağılımı elde edilerek ısı geçiş mekanizması açıklanmaktadır. Isı geçişinde etkili olan mekanizmanın akışın merkezini takip edemeyen hidrodinamik sınır tabakadan kaynaklandığı ve bunun ısı geçişini artırdığı anlaşılmıştır. Sayısal çözüm içinde bir çevrimde suya geçen ısı için Nusselt sayıları bulunarak deneysel sonuçlarla karşılaştırılmaktadır.

Investigation of heat transfer in moving liquid column

In this study, the heat transfer from a surface heated with constant heat flux to an oscillating vertical annular liquid column having an interface with the atmosphere is investigated experimentally and numerically. The reciprocating motion of water column is created using a piston cylinder mechanism. The space-cycle heat transfer rate from heater to water was calculated by using experimental measurements. The analysis was carried out for the case of different oscillation frequencies while the displacement amplitude remains constant. Based on the experimental data a correlation equation was obtained for the cycle-averaged Nusselt number as a function of kinetic Reynolds number. Heat transfer in the moving liquid column was also investigated numerically using the FLUENT program. Fluent uses a control-volume-based technique to convert the governing equations to algebraic equations that can be solved numerically. This control volume technique consists of integrating the governing equations about each control volume, yielding discrete equations that conserve each quantity on a control-volume basis. It is clear that heat transfer rate depends on velocity and temperature profile. The numerical results reveal that there is a phase difference between hydrodynamic boundary layer and core flow, which improves the heat transfer. The averaged heat transfer rate is found to increase with the frequency. The space-cycle averaged Nusselt number was found numerically and. compared with experimental results. The numerical solution is in good agreement with the experimental data.

PDF

___

Akhavan, R., Kamm, R. D., and Shapiro, A. H., (1991). An investigation of the transition to turbulence in bounded oscillatory stokes flows, part 1: Experiments. Journal of Fluid Mechanics, 225, 423-444.
Bouvier P., Stouffs, P. and Bardon, J.P., (2005). Experimental study of heat transfer in oscillating flow. International Journal of Heat Mass Transfer, 48, 2473-2482.
FLUENT 6.1.22., (2001). Fluent incorperated, centerra reource park, 10, Cavendish Court, Lebanon, NH 03766, USA.
Hino, M., Savamato, M. ve Takasu, S., (1976). Experiments on Transition to Turbulence in an Oscillatory Pipe Flow, Journal of Fluid Mechanics, 75, 2, 193-207.
Kurzweg, U. H. ve Zhao, L. D., (1984). Heat transfer by high-frequency oscillations: a new hydrodynamic technique for achieving large effective thermal conductivities, Physics of Fluids, 27, 11, 2624-2627.
Kurzweg, U.H. ve Zhang, J.G., (1990). Numerical simulation of time-dependent heat transfer in oscillating pipe flow, International Journal of Thermophysic, 5, 401-406.
Nishio, S., Shi, X.H. and Zhang,W.M., (1995). Oscillation- induced heat transport: heat transport characteristics along liquid-columns of oscillation- controlled heat transport tubes, Int. J. Heat Mass Transfer, 38, 13, 2457-2470.
Pecock, J. A. ve Stairmand, J. W., (1983). Film Gauge Calibration in Oscillatory Pipe Flow, J. Physics, E: Scientific Instruments, 16, 571-576,
Siegel, R., (1987). Influence of Oscillation-Induced Diffusion on Heat Transfer in a Uniformly Heated Channel, Journal of Heat Transfer, 109, 244-247.
Uchida , S., (1950). The pulsating viscous flow superposed on the steady laminar motion of an incompressible fluid in a circular pipe, ZAMP, 7, 403-422.
Zhao,T.S. ve Cheng, P., (1995). A numerical solution of laminar forced convection in a heated pipe subjected to a reciprocating flow, International Journal of Heat Mass Transfer, 38, 16, 3011- 3022.
Zhao T.S. ve Cheng, P., (1996). Oscillatory heat transfer in a pipe subjected a periodically reversing flow, Journal of Heat Transfer, 118, 592-598.
Zhao,T.S. ve Cheng, P., (1998). A numerical study of laminer reciprocating flow in a pipe of finite length, Applied Scientific Research, 59, 11-25.
Watson, E.J., (1983). Diffusion in Oscillatory Pipe Flow, Journal of Fluid Mechanics, 133, 233-244.
Womersley, J.R., (1950). Method for the calculation of velocity, rate of the flow and viscous drag in arteries when the pressure gradient is known, Journal of Physiology, 127, 553-563.