Dalgalı Yüzeyli Levhalar Arasındaki Isı Geçişi

Abstract

Plakalı ısı değiştiricilerindeki sinüzoidal dalgalı levhalar arasındaki ısı taşınım katsayısının ve basınç düşüşünün incelendiği bu çalışmada, çeşitli parametrelere göre önceden yapılmış deney sonuçları veri olarak kullanılmış ve sayısal yöntemler yardımıyla incelenmiştir. Elde edilen değerler tablo ve grafiklerle ortaya konulmuştur. Veriler değerlendirilerek levhalar üzerindeki yerel ısı geçişinin, ele alınan geometri üzerindeki değişimi grafikler halinde verilmiştir. Sonuçların irdelendiği bölümde, daha önce yapılan çalışmalarda bulunan değerler elde edilen sonuçlarla karşılaştırılmış ve uyum içerisinde oldukları görülmüştür. Ayrıca, bu çalışma sırasında dikkate alınan ve ihmal edilen diğer noktalar üzerinde durulmuş ve bunların etkisinin ne yönde sisteme ne yönde etki edeceğine ilişkin değerlendirmeler yapılmış ve bundan sonra yapılacak çalışmalar yönünde fikir verilmiştir.

This study primarily centers the effect of various physical parameters on the heat transfer rate and heat transfer coefficient of the fluids which flow between horizontal wavy walls. Heat exchangers are used to heat recovery in industry and to obtain different temperatures which is needed in process. Plate heat exchangers is used commonly because of various usage possibilities and their compact structures. A plate exchanger consist of pack of rectangular pressed plates, suspended vertically, and clamped together in a frame by tie bars or screws. The plates are corrugated to increase strength and to improve heat transfer, and are fitted with peripheral sealing gaskets. Four corner ports, which communicate with appropriate connections mounted on the frame, are arranged so that the two liquids flow through alternate passages between adjent plates, usually in countercurrent flow, with heat transfer taking place across the plate surfaces. Plate heat exchangers find their main applications in liquid-liquid heat transfer duties. They are most common in the dairy, beverage, general food processing, and pharmaceutical industries where their ease of cleaning and the thermal control required for sterilization/pasteurization makes themideal. They are also used in synthetic rubber industry, paper mills and petrochemical plants, and in process heaters, coolers and closed-circuit cooling systems. Over 60 different plate patterns have been developed worldwide. Since the geometry of present study has not been studied previously in literature, firsly two adjacent flat walls channels were analyzed and then two adjacent sunizoidal wavy walls channels were analyzed. In the further researches can be also employed to examine graphically dimensionless numbers with mass transfer and velocity distribution. Besides this.various channel geometries can be analyzed. In this study, numerical method was chosen due to limited time and possibility of easy apply. The problem has been modeled and solved using finite difference scheme. Present results are compared to previous experimental studies and industrial usage. In the first step, the finite difference scheme model is arranged 400 grid in the x direction and 24 grid in the y direction. Boundary conditions in the entrance and exit areas can be velocity and pressure for the flow analyses and temperature, heat flux for the heat transfer analyses. The boundary conditions for the geometries in figure 8. 1 can be express as below: > Entrance velocity is constant and horizontal and vertical velocity component is zero. > The velocity on the channel wall is zero. > Gravitational effects are neglected. xii > The physical properties of fluid in the channel such as density, viscosity, specific heat are assumed constant. > Fluid is assumed as isotropic. > The pressure gradian in the exit is zero. > The temperatures in the entrance and exit of the channel are zero. > The entrance and exit effects and secondary flows are neglected. if ""v.iA ?Wrt. (a) (b) Figure 1 The grid domain of the problem. (c) These analyses are compared to the each other and the results of the previous research, [4], and the results of the present study are showed using tables and graphics. The heat transfer rate between flowing fluids in two paralel horizontal sinuzoidal wavy wall is examined and the results are analyzed The results shows that heat transfer coefficient primarily depends upon fluid flux and channel geometry. It is determined minumum and maximum values at certain points on sunizoidal wave using graphical results. Fig. 2 Numax-Re corelation at case (a) Especially, as shown Fig. 2 when the fluid flux is high, this stuation can be seen clearly. The results of the problem for various Reynolds numbers are as below: It can be seen that the higher Reynolds number cause the higher Nusselt number and the higher heat transfer coefficient. On the other hand, when Reynolds number increase, the pressure drop between entrance and exit also increase. It could be seen clearly at Fig. 3. In the high Reynolds number values, there is a big difference between minumum and maximum local heat transfer coefficients on the wavy channel. (see Fig. 4) XUl .7""". ı;" i Kanal geometrisi H_3.8rrs p/h2 hs H_38rre p/h2 ta H_19ms p/h2 te 0.78 Kanal Boyu Fig 3. Pressure distribution along a sinusoidal wavy channel Kanal Geometrisi Pres_3.8ms p/h2 hava Pres_19ms p/h2 hava Pres_38ms p/h2 hava Kanal boyu Fig 4. Local heat transfer coefficient in a sinusoidal wavy channel