Critical Heat Flux in a Forced Convective Boiling with an Impinging Jet (Effect of Subcooling)

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Critical heat flux during forced convective boiling on a rectangular heated surface of 40 or 60 mm in length and 7 mm in width, being supplied with subcooled liquids through a small round jet which impinges at the center of the surface has been studied experimentally employing water, R113 and R22 at a pressure from 1 to 25 bar, which is raised by using N_2 gas, to obtain a high subcooling condition up to 115K. The increase in the critical heat flux due to the subcooling liquid depends on the liquid velocity, heated surface length, and the density ratio. A flow model can be proposed based on observation of the change in the flow aspect with increasing the heat flux. The following generalized correlation, which can be analytically derived by using the model, can predict about 82% of the CHF data with an accuracy of * 20%.and c_p: Specific heat of liquid, D:diameter of a disk heater, d:diameter of an impinging jet, g:gravitational acceleration, H_<fg>:latent heat of evaporation, Ja:Jakob number(=(rho_l/rho_v(C_pDELTAT_<sub>/H_<fg>), L:Length of the heated surface, q_<co>:critical heat flux for saturated boiling, q_c:critical heat flux for subcooled boiling, DELTAT_<sub>:subcooling temperature, u:velocity of a liquid jet at the nozzle exit, rho_l:density of saturated liquid,rho_v:density of saturated vapor, sigma:surface tension.