INFLUENCE OF VARIOUS FACTORS ON THE HEAT TRANSFER CHARACTERISTICS OF MINIATURE TWO-PHASE THERMOSYPHONS WITH NANOFLUIDS

Abstract

Currently, various types of nanofluids are of increasing interest as heat carriers for heat transfer in thermosiphons and other evaporative-condensation devices. This paper presents and analyzes experimental data on heat transfer characteristics (total thermal resistances, maximum transferable heat fluxes and equivalent thermal conductivity) of two-phase miniature thermosyphons with nanofluids. Geometric parameters of thermosiphons for all experimental samples were identical and were: total length 700 mm, inner diameter 5 mm. The length of the heating zone was changed stepwise from 45 mm to 200 mm. The length of the condensation zone was 200 mm for all investigated thermosyphons. The amount of coolant in the thermosiphons was the same, and its height in the heating zone before the start of the study was 88 mm. Distilled water and aqueous nanofluids with nanoparticles of carbon nanotubes, synthetic diamond, and carbon black were used as heat carriers. The main attention is paid to the study of the influence of the filling factor and the angle of inclination of the thermosyphon, the value of the transferred heat flux and the chemical nature of the coolant (nanofluid) on the heat transfer characteristics of thermosyphons. The strong influence of these factors on the efficiency of a miniature closed two-phase thermosyphon has been demonstrated. A more than twofold increase in the heat transfer characteristics of thermosyphons (the maximal transferred heat flux) was obtained with a sharp decrease in their thermal resistance. It is assumed that the significantly higher heat transfer capacity of such thermosiphons compared to those filled with water is explained not only by the higher thermal conductivity of the coolant, but also by the appearance of a peculiar porous structure that prevents the appearance of a vapor film and promotes the intensification of heat transfer processes during boiling. Bibl. 16, Fig. 10, Tab. 2.