Falling film heat transfer analysis on a bank of horizontal tube evaporator

Abstract

Heat transfer analysis of falling film evaporation on a bank of horizontal tubes is investigated in this study. Liquid falling from one tube to the next lower one is considered as a thin liquid jet impinging on the top of the tube with a uniform free falling velocity. The hydrodynamic and thermal solutions are obtained by a finite difference method. In these solutions the heat transfer coefficients are modified to account for waviness.Liquid film thickness and local and average heat transfer coefficients are obtained for the constant heat flux and isothermal boundary conditions. Convective heat transfer effects are shown to be dominant as Peclet number increases. Heat transfer coefficients for the tubes in a tube bank decrease from the first tube onwards until the fully developed region is reached. The present predictions agree favorably with the reported heat transfer data.

Flow Structures of a Liquid Film Falling on Horizontal Tubes

“…The processes and conditions of their formation are usually treated on the basis of the Taylor instability, according to which the droplet or column spacing is approximately equal to the so-called most dangerous wavelength 1) k d . This is the wavelength of the most rapidly growing disturbance imposed on an originally smooth but unstable interface.…”

Falling-film evaporation on horizontal tubes—a critical review

“…However, according to Rogers et al [31], this assertion is a flawed, arbitrary assumption. Even modeling that does not consider the flow regime transition exhibits similar behavior [14,39,40]. According to Brumfield and Theofanous [41], the film can be fully turbulent only for Reynolds numbers, Re, higher than 6000.…”

“…A range of turbulence models has been considered by those developing falling-film models. Assuming the effects of waviness at the liquid-vapor interface are similar to those for vertical falling films, Kocamustafaogullari and Chen [40] and Rogers [79] applied corrections for such effects to the empirical correlations that were proposed by Zazuli [40] and Kutateladze and Gogonin [81], respectively. It is interesting to note that Marangoni effect is not typically included, but some cases it might be important (such as for a subcooled film [79]).…”

“…In general, differences between the models are due to how the flow is classified (i.e., the above mentioned regions), the model used for the jet impingement region, initial and boundary conditions, the falling film modes, and the flow regime, either laminar [6,8,13,14,40,75,79] or turbulent [5,75,76,80]. A range of turbulence models has been considered by those developing falling-film models.…”

Characterization of the microscopic mechanics in falling film evaporation outside a horizontal tube

“…The flow and heat transfer of the falling film evaporation along a horizontal tube is classified into different regions where analytical models are proposed [8,13,17]. But their calculations do not agree with each other on the distribution of the fully developed region.…”