Heat transfer analysis of preheated turbulent falling films in vertical tube evaporators

Autor: N. M. Al-Najem, K. Y. Ezuddin, M. A. Darwish
Rok vydání: 1998
Předmět:
Zdroj: Desalination. 115:43-55
ISSN: 0011-9164
DOI: 10.1016/s0011-9164(98)00025-3
Popis: A theoretical investigation is conducted to study the hydrodynamics and thermal aspect of preheated turbulent free-falling liquid films in long vertical tube evaporators. A formal analytical solution of the governing energy problem is developed based on a splitting-up procedure. This leads to homogeneous and non-homogeneous simple problems that can be solved to yield a more convenient solution for computational purposes. The eigenvalues associated with the homogeneous problem are efficiently computed by the sign-count algorithm. A new correlation for the local heat transfer coefficient is developed over wide ranges of Reynolds and Prandtl numbers. Also, a correlation for the average heat transfer coefficient is established to include the effect of interfacial shear forces exerted by gas flow at the film surface. This influence is more pronounced in long tube applications such as desalination industries. Furthermore, a correlation for the fully developed heat transfer coefficient is developed as well. The theoretical predictions obtained in the present study compare well with existing experimental results reported in the literature with similar conditions. A sensitivity study is also performed in which the influence of various participating flow parameters are explored for their general effect on velocity and heat transfer of sensibly heated turbulent falling films.
Databáze: OpenAIRE
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