4349 Experimental study of influence of mass velocity and heat flux on carbon dioxide flow boiling heat transfer coefficient in horizontal smooth tube

Investigation of Heat Transfer and Pressure Drop for R744 in a Horizontal Smooth Tube of R744/R404A Hybrid Cascade Refrigeration System—Part 1: Intermediate Temperature Region

“…Here, ∆P static is zero because the pressure drop of the two-phase flow through the horizontal tube ignores the gravitational component, and Equation ( 10) is simplified as Equation (11).…”

“…∆P tot = ∆P mom + ∆P frict (11) Pressure drop correlation formulas can be analyzed by assuming homogeneous and separate flows. The homogeneous flow model presumes that the gas and liquid velocities are the same at thermodynamical equilibrium.…”

“…The pressure drop increases with an increasing vapor quality in the low vapor quality range. This means that in the dry-out range (x = 0.7762-0.8337), the liquid enters the vapor core in the form of liquid droplets transferred by the The pressure drop measured under the experimental conditions is the sum of the pressure drop owing to friction and that owing to momentum, as shown in Equation (11). As the pressure drop due to momentum in a short section is negligible, the pressure drop by experiment in this study represents only the frictional pressure drop.…”

“…Wu et al [10] performed experiments on the R744 evaporating heat transfer in a horizontal smooth copper tube at mass fluxes of 100-300 kg/(m 2 •s), heat fluxes of 2-18 kW/m 2 , saturation temperatures of 1-15 • C, and vapor qualities of 0.1-0.9. Hashimoto et al [11] reported on the boiling heat transfer in a smooth horizontal copper tube at mass fluxes of 150-630 kg/(m 2 •s), heat fluxes of 10-40 kW/m 2 , and saturation temperatures of 0-10 • C. Mastrullo et al (2009) [12] evaluated the flow boiling heat transfer in a smooth horizontal Type 304 stainless steel tube at mass fluxes of 200-349 kg/(m 2 •s), saturation temperatures of −7.8-5.8 • C, heat fluxes of 10.0-20.6 kW/m 2 , and vapor qualities of 0.02-0.98. Mastrullo et al (2010) [13] also compared the experimental data obtained by Mastrullo et al (2009) [12] with the existing correlation formulas for evaporative pressure drop and heat transfer.…”