Experimental correlation of falling film absorption heat transfer in micro-scale hatched tubes

The objectives of this paper are to investigate the effect of surface roughness of micro-hatching tubes on the absorption performance and to develop an experimental correlation of Nusselt number as a function of the roughness. Two different micro-scale hatched tubes and a bare tube are tested to quantify the effect of the surface roughness on the absorption performance. The roughness of the micro-scale hatched tubes ranges 0.386-11.359 μm. The working fluid is H₂O/LiBr solution with inlet concentration of 55, 58 and 61 wt.% of LiBr. The absorber heat exchanger consists of 24 horizontal tubes in a column, liquid distributor at the liquid inlet and the liquid reservoir at the bottom of the absorber. It was found that absorption performance of micro-hatching tubes was improved up to two times compared with the bare tube. An experimental correlation of Nusselt number was developed as a function of the film Reynolds number and the roughness with an error band of ±25%.