Improvement of thermal-hydraulic efficiency of mining power equipment through the application of porous freon steam generators with high heat conductivity

Abstract

In the article, various areas of technical application of porous freon steam generators in mining power equipment are described, and explanations why freon coolants can provide a positive energy effect in such facilities are given. The paper presents results of calculations of thermal-hydraulic efficiency of the porous once-through tubular steam generators with freon-12 as a model working fluid in the the laminar flow area and with boundary conditions of the first kind. The smooth-wall cylindrical channels with different diameters were used as the reference surfaces to be compared. The following mode and design parameters were taken as a calculation base: the liquid temperature and pressure on the saturation line at the entry into the channel were: Ts0= 110 °С; P0s = 39,9·105 N/m2.; temperature heads, i.e. a difference between the wall temperature and temperature of the liquid at the entry into the channel were: ΔT=Tw-Ts0 = 1 °C; 2 °C; 3 °C; 4 °C; 5 °C; the Reynolds numbers at the entry into the channel were: Reo = 100; 200; 500; 1000; 2000; 2300; the channel porosities were: θ = 0.7; 0.75; 0.8; 0.85; 0.9. The porous material was metal felt with the copper fiber diameter of 200 microns. The channel diameters were: d =3·10-3 m; 4·10-3 m; 5·10-3 m; 6·10-3 m; 7·10-3 m. On the basis of the performed computational studies, it was concluded that for the conditions of the same mass flow rates of the coolant, with laminar flow, and the same channel diameters, it is possible to achieve a significant reduction in the length of the porous once-through steam generator in comparison with the length of the smooth-wall once-through steam generator. Due to the significantly shorter length, differential pressure for pumping the coolant can be several tens of percent less in porous evaporation channels than in the similar smooth-walled channels. This computational study also made it possible to establish main regularities in dynamics of the energy efficiency coefficients and their dependence on the model mode and design parameters. It was shown, that positive dynamics of the efficiency coefficients of porous steam generators occurs with decrease of the channel diameter and temperature head, as well as with increase of the Reynolds number in the investigated region of coolant laminar flow.