Question

Question 2. Estimate the heat flux as well as con- Boiling& Condensation Correlations vection ooefickent for the bottom of a pot of boiling Nucleate Pool Boiling. Between onset of riucleate water if the surface in contact with the water appears boiing (ONB) and the critical to be at 382 K. C, 0.0080. The properties of wa- all properties at T, ter at punl.-96.8 kPa are: Tsae = 371.8 K; hfg 2260 kJ/kg: pe0.5568 kg/m p 959 kg/m ç = 0.05915 N/m: G,.-2024 J/kg-K; cpl = 4216 J/kg-K;んー0.02468 W/urK; 0.6796 w/in-ls; Critical Heat Flux (CHF). The maximinhea flux, with all properties at Tsot: AT 30 deg C): Pr =0.98 aand Prt#1 777; A = 0.002689 K 1, and B-0.0007412 K-1 where C /24 for long horizontal cylinders and spheres and C 0.149 for large horizontal plates (as- suming Le Duile). The Leidenfrost Point. The minimum heat lux in the film boiling regime (ATe 120 deg C; all prop- erties at saturation temperature): Film Boiling. Beyond the Leidenfrost point, with a counbination of conduction and radiation: Here vapor properties are taken at T-(T,+T)/2 and the rest at Tsat with C 0.62 for long horizontal cylinders and 0.67 for a sphere; the corrected latent heat of vaporization is approximated as If T, 300°C, assurning hrnd < hearr, radiation may be accounted for using: where hed eo(TT)T, +Tost) Film Condensation. In the following, the charac- teristic length Lc is the height for a vertical plate or the diameter for a cylinder or sphere: Here liquid properties are taken at Ty and the rest at Tst, with C- 0.943 for a plate; 0.826 for a sphere and 0.729 for a long horizontal tube. The corrected latent heat is:

Answer 1

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