Transient heat transfer from single circular cylinders and inline tube banks

In the present paper, the fluid flow and heat transfer under transient changes of fluid velocity and thermal boundary conditions are investigated for laminar crossflow over a circular cylinder and a tube bank. Nusselt numbers after step changes of fluid velocity, inlet temperature and wail temperature are calculated by means of a finite element method. The range of Reynolds number investigated is 5 less than or equal to Re less than or equal to 200. The fluid is supposed as incompressible with constant properties. The time responses of Nusselt numbers are approximated by correlations with dimensionless variables. Heat transfer coefficients after step changes of the variables are described as sums of exponential delay functions. The delay times in these correlations are presented as function of the Reynolds number in the range of 5 less than or equal to Re less than or equal to 200. The calculated heat transfer coefficients agree well with experimental and analytical values of other authors, who studied transient heat transfer at a wire after step changes of the wall temperature and the fluid velocity in a smaller range of Reynolds number 1 less than or equal to RE less than or equal to 40. A correlation previously published by others, describing heat transfer after step changes of the wall temperature of a wire for Re = 5 corresponds with our results.