CH 6-2 Solution [PDF]

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GAZİANTEP ÜNİVERSİTESİ HAVACILIK VE UZAY BİLİMLERİ FAKÜLTESİ



UÇAK VE UZAY MÜHENDİSLİĞİ BÖLÜMÜ



Dr.Öğr.Üyesi MOHAMMAD MUNIR ALHAMWI



AE 301 Heat transfer 6 CHAPTER Empirical and Practical Relations for Forced-Convection Heat Transfer



Empirical and Practical Relations for Forced-Convection Heat Transfer



EMPIRICAL RELATIONS FOR PIPE AND TUBE FLOW



A traditional expression for calculation of heat transfer in fully developed turbulent flow in smooth tubes is that recommended by Dittus and Boelter



𝑇𝑏



Prandtl numbers ranging from about 0.6 to 100 and with moderate temperature differences



More recent information by Gnielinski [45] suggests that better results for turbulent flow in smooth tubes may be obtained from the following:



𝑇𝑏



𝑇𝑏



A power function for each of these parameters is a simple type of relation to use, so we assume



𝑇𝑏 where C, m, and n are constants to be determined from the experimental data



the fact that the viscosity of gases increases with an increase in temperature, while the viscosities of liquids decrease with an increase in temperature.



take into account the property variations, Sieder and Tate [2] recommend the following relation:



𝑇𝑏



𝑇𝑤



All properties are evaluated at bulk-temperature conditions, except μ , which is evaluated at the wall temperature w



In the entrance region the flow is not developed, and Nusselt [3] recommended the following equation: 𝑇𝑏



where L is the length of the tube and d is the tube diameter. The properties in Equation (6-6) are evaluated at the mean bulk temperature.



Petukhov [42] has developed a more accurate, although more complicated, expression for fully developed turbulent flow in smooth tubes:



𝑇𝑏



𝑇ഥ𝑓



𝑇𝑤 where n=0.11 for T >T , n=0.25 for T