S.D. Joshi
Published: 1978
Total Pages: 0
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An analytical study of laminar flow heat transfer to pseudo -plastic fluids inside a tube subjected to a uniform wall heat flux is reported. Most pseudo plastic fluids are highly viscous and exhibit a strong temperature -dependence of the consistency index, K. Heat transfer is thus affected by heating rate. The objective of this study was to evaluate the effects of non -Newtonian behavior and K -variation on heat transfer coefficients. An explicit, stable numerical scheme, using the Dufort-Frankel finite -difference method, was devised to solve the set of governing partial differential equations. In the constant -property solutions, some increase in heat transfer coefficient above the Newtonian prediction is noticed. This increase is accounted for by employing a non -Newtonian correction, 01/3, for both entrance and fully developed regions. The variable property predictions were obtained for n = 0.75and 0.5, and, for completeness, predictions were also obtained for the Newtonian case, n = 1.0. A new consistency parameter, yAT, was developed to account for the effect of temperature -dependent K on heat transfer coefficient. In the thermal entrance region, for a given n, the increase in heat transfer coefficient above the constant property prediction is a log -linear function of (K/KNJ). However, in the fully developed region, this increase is a complex function of n and yAT. A two-step consistency correction was developed, one for the thermal entrance region and the other for the fully developed region. The analytical predictions, as correlated using non -Newtonian and variable consistency corrections, are in excellent agreement with experimental data of Mahalingam taken in the thermal entrance region.