Calculation of thermohydraulic effectiveness of the porous once-through water steam generators in laminar flow region with boundary conditions of the first kind

Abstract

The paper presents results of calculations of thermohydraulic efficiency of the porous once-through steam generators with water as a model working fluid in the region of the heat-transfer agent laminar motion 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 operating and design parameters were taken as a calculation base: temperature of the liquid on the saturation line at entry into the channel was: Tso = 280 °C, 300 °C, 320 °C, 340 °C, 360 °C. Temperature head, i.e. a difference between the wall temperature and temperature of the liquid at entry into the channel was: ΔT=Tw-To = 1 °C; 2 °C; 3 °C; 4 °C; 5 °C. The Reynolds number at entry into the channel was: Reo = 700; 1000; 1200; 1500; 1700; 2000; 2300. The channel porosity was: 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 diameter was: d =3·10-3 m; 4·10-3 m; 5·10-3 m; 6·10-3 m; 7·10-3m; 10·10-3 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 mode of motion, 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; however, under these conditions it is not possible to reduce pressure drop in the channels and, accordingly, to reduce power consumption needed for heat-transfer agent pumping. This computational study also made it possible to establish main regularities in behavior of the energy efficiency coefficients and their dependence on the model operating and design parameters. Keywords: thermo-hydraulic efficiency; porous steam-generating channels; heat-transfer agent, water; boundary conditions of the first kind; laminar flow regime.