Variation Of Critical Heat Flux Research Articles

Experimental investigation of the CHF of HFE-7100 under pool boiling conditions on differently roughened surfaces

Nucleate pool boiling experiments with HFE-7100 under saturated conditions are reported. An accurate quasi-steady procedure was introduced to raise boiling curves and attain the Critical Heat Flux condition. The results include boiling curves and Critical Heat Flux data (CHF) for four different surfaces of Brass CuZn39Pb3 at four different pressures, ranging from 25 to 200 kPa. The boiling surfaces were characterized by means of confocal microscopy. Mean roughness of the surface varied from 0.023 μm to 1.878 μm. Contact angles of liquid HFE-7100 with the boiling surfaces were also measured. Critical Heat Flux results were compared with well-known correlations, displaying a general trend agreement with some of them. Critical Heat Flux increases with pressure, and its variation with roughness is more pronounced when pressure is increased. Critical Heat Flux variations with surface topography revealed an increment with roughness up to a certain limit, diminishing for the higher roughness. The dimensionless Critical Heat Flux, designated by K, is solely independent of pressure in the case of the polished surface. This trend suggests the occurrence of a “smooth“ surface characterised by pressure independence Critical Heat Flux.

Study on boiling heat transfer of water–TiO2 and water–MWCNT nanofluids based laminar jet impingement on heated steel surface

Abstract The present study aims at investigating the boiling heat transfer aspect of water–TiO2 and water- multi-walled carbon nanotubes (water–MWCNT) nanofluids based laminar jet cooling of heated horizontal steel surface. Experimental results show that cooling rate is enhanced by using nanofluids when compared to water. A one-dimensional finite volume inverse heat transfer model is developed to predict the total heat flux removal rate from the hot steel surface. It is also observed in the present case that the shift from “film boiling” to “transition boiling” regime occurs earlier for nanofluid than that of water jet cooled surface. An order of magnitude analysis shows that the shift may be attributed to the vapor film instability in presence of nanoparticle deposition. However, only marginal variation of critical heat flux (CHF) is observed in case of nanofluid jet when compared to water jet.

Effect of heater diameter on the critical heat flux from horizontal cylinders in pool boiling

AbstractThe characteristic variation of critical heat flux (CHF) with heater diameter in the pool‐boiling of horizontal cylinders is discussed. Critical heat flux expressions have been obtained based on hydrodynamic considerations for saturated pool‐boiling of cylinders and are compared with existing and new data. Experimental studies are reported which verify the postulated mechanics of the boiling process at CHF over a range of cylinder diameters.

The critical heat flux for electrically heated wires in saturated pool boiling

An experimental and analytical investigation of the variation of critical heat flux with wire diameter and wire material in saturated pool boiling of water and mixtures of water-methyl ethyl ketone is presented and compared with the results of other investigators. Water data are presented for electrically heated wires of tungsten, Tophet A, copper and constantan with diameters ranging from 0.0005 to 0.051 inch. Measurements are also presented for 0.0035, 0.010 and 0.051 inch Tophet A wires in mixtures of water-methyl ethyl ketone with concentrations of 0–17 per cent by weight of the ketone. A simplified model is proposed for the critical flux phenomenon with small wires. An analysis based on this model agrees qualitatively with the experimental results. There is little variation of the critical flux with wire properties over the entire range of diameters tested, although the thermal coefficient of resistivity appears to have some effect, especially for very small wires.