Abstract
In order to study the heat transfer of the falling film evaporator with phase change on both sides, in this paper we built the mathematical model and the physical model where the liquid film inside the tube is laminar and turbulent. The film thickness of the condensate at different axial positions, total condensate volume and velocity distribution, and temperature distribution of condensate outside the tube can be obtained by calculating the proposed model. Meanwhile, the liquid film thickness, velocity distribution and temperature distribution inside the tube were obtained by numerical simulation by considering the influence of the liquid film with different compositions on the heat transfer during fluid flow. With ethanol–water as the system, the overall heat transfer coefficient and heat transfer quantity of the falling film evaporator were obtained by the calculation of the model. The accuracy of the proposed model was confirmed by experiments. The model and the calculation of heat transfer proposed in this paper have enormous significance for the basic data and theoretical guidance of the heat transfer performance prediction and operational optimization of the evaporator.
Highlights
The falling film evaporation has widely concerned various scholars for its short residence time, small temperature difference and high heat transfer coefficient
The numerical solution of the local heat transfer coefficient is obtained by the liquid film velocity distribution, temperature distribution and film thickness
The heat transfer coefficient correlation of the multiphase transformation inside and outside the tube is fitted by numerical simulation and verified by experiments
Summary
The falling film evaporation has widely concerned various scholars for its short residence time, small temperature difference and high heat transfer coefficient. Struve [12] studied the liquid film in the steam heating tube and obtained the correlation under the corresponding conditions. Herbert & Sterns [13] experimentally studied the falling film evaporation on the resistance wire heating inner tube liquid film and obtained the analogous correlation. Chun & Seban [14] and Fujita & Ueda [15] conducted experimental studies on the liquid film heated by the electric heating tube and corresponding correlation, respectively. Schnabel & Schlunder [16] analysed the experimental data of several researchers to obtain the heat transfer coefficient correlation. Most studies focus only on unilateral heat transfer of the vertical tube, while the falling film evaporation is bilateral heat transfer. The calculation formula of the overall heat transfer coefficient of the falling film evaporator was obtained and verified by experiments
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