Xiaojing Zhu

Numerical investigation on characteristics of falling film in horizontal-tube falling film evaporator

AbstractHorizontal-tube falling film technology is widely used in multi-effect desalination plant. The film characteristics of falling water film outside the tubes in horizontal-tube falling film evaporator were simulated. The numerical result was compared with the experimental result and they were proven with good agreement. The film thickness distribution at different Reynolds number and different circular angle had been investigated. Also, the effects of liquid flow rate and tube diameter on the film thickness distribution were discussed in detail. Numerical simulation result shows that, with the increase in Reynolds number, the falling film thickness at a certain circumferential angle increases with almost linear growth rate, and the thinnest film at the surface of the tube appears at the angle of about 120°. The result also indicates that the local dry out spot on the surface of the tube would occur when the fluid flow rate decreases to a certain value. In addition, the film thickness decreases with ...

An investigation on the falling film thickness of sheet flow over a completely wetted horizontal round tube surface

AbstractAn investigation was performed to analyze the liquid film distributions of sheet flow on the surface of a horizontal round tube in a falling film evaporator using the commercial computational fluid dynamic code Fluent 6.3.26. A two-dimensional multi-phase flow model was developed under adiabatic condition. The temporal variation of flowing process of sheet flow and the steady film thickness distribution in the circumferential direction were analyzed in detail. The main objective has focused on the effects of multiple factors on the film thickness distribution. It was found that the whole process of liquid film flowing along the horizontal tube surface includes the transient sub-process and steady-state sub-process, and the former can be divided into five stages to be analyzed. The obviously asymmetric distribution of film thickness, which is contradictory to the Nusselt theory, is captured by the simulation results. Multiple factors have effects on the film thickness distribution. The film thickne...

The analysis of the fluxion and heat transfer in the liquid film during the process of horizontal tube falling film

: In this paper, a fixed three-dimensional model was applied to simulate liquid film spreading process and heat transfer process. The so-called volume of fluid (VOF) method was used to deal with the interface between the liquid and gas phase by using Fluent 14.5. It was found that two adjacent columns both spread along the axial direction and collide with each other at the midpoint between two columns and a crest is formed. The composition and heat is mixed in the liquid film fully at the crest, which broke the velocity and temperature boundary layers, promoting the heat transfer between liquid film and tube wall. Besides, the temperature of liquid film is increased with the circumferential direction and reaching the maximum temperature at the bottom of the tube.: In this paper, a fixed three-dimensional model was applied to simulate liquid film spreading process and heat transfer process. The so-called volume of fluid (VOF) method was used to deal with the interface between the liquid and gas phase by using Fluent 14.5. It was found that two adjacent columns both spread along the axial direction and collide with each other at the midpoint between two columns and a crest is formed. The composition and heat is mixed in the liquid film fully at the crest, which broke the velocity and temperature boundary layers, promoting the heat transfer between liquid film and tube wall. Besides, the temperature of liquid film is increased with the circumferential direction and reaching the maximum temperature at the bottom of the tube.