Heat transfer of water layer on a heated structured wall has been studied. Experimental data have been compared with a smooth wall. It is shown that evaporation rate J on the structured wall is quasi-constant for most part of the evaporation time and increases sharply when the drop height becomes <0.5–0.8 mm. The evaporation rate on the structured wall (in the form of a rectangular profile) is 15–20% higher than on the smooth one. Experimental data for the structured wall show the maximum excess by about 20–30% for the heat transfer coefficient compared to the smooth wall. Previously, it was thought that heat transfer can be calculated for thin layers and films without taking into account characteristic scales of convection in liquid. In this paper, the free convection of liquid is shown to play a key role. For the first time, a simple calculation method linking the Peclet and Marangoni numbers, as well as the wall roughness with liquid convection is proposed. For correct simulation of heat and mass transfer, it is necessary to take into account local data on thermal and velocity fields inside the water layer, as well as to determine the characteristic scales of circulation. There are several types of characteristic scales, the role of which depends on the thickness and diameter of the layer. The strong influence of free convection in a thin layer, located on the heated structured wall, is extremely important for accurate modeling of a wide range of modern technologies. Heat transfer enhancement due to the structured wall may be applied in heat exchangers.
|Журнал||International Communications in Heat and Mass Transfer|
|Состояние||Опубликовано - 1 мар 2019|
ASJC Scopus subject areas
- Atomic and Molecular Physics, and Optics
- Chemical Engineering(all)
- Condensed Matter Physics