Heat transfer performance of liquid film outside horizontal sintered tube evaporator.

Sintered tubes as heat transfer elements have a porous surface structure enabling them to transfer heat better than smooth tubes. Sintered tubes are prepared by sintering aluminium alloy powder with particle diameters of 20–40 μm on the outer surface of smooth round tubes. In this study, the heat transfer performance of a liquid film located outside horizontal sintering tube evaporators with annular flow is investigated using numerical simulations and experiments. The influence of porosity (n = 45.9%, 55.8%, 60.2%, and 65.0%) and sintered layer thickness (t = 0.1, 0.2, and 0.3 mm) on the local heat transfer coefficient of sintered tubes is analysed. The study findings indicate the following. (1) Under columnar flow, alternating column and crest sections exist in the flow around the tube. (2) For different porosities and sintered layer thicknesses, the local heat transfer coefficient decreases as the circumferential angle, θ, varies from 0° to 180°. (3) At the column and crest sections, the experimental value of the heat transfer ratio coefficients are 1.16–1.34 and 1.04–1.28, respectively; the experimental value of heat transfer enhancements are 1.27–4.79 and 2.25–4.78 times, respectively. Results show that the average local heat transfer coefficient is maximum when the porosity, n , is 55.8% or the sintered layer thickness is t = 0.1 mm. Finally, the study summarises the Nu equations for the column and crest sections of the sintered tube based on experimental data. [ABSTRACT FROM AUTHOR]