Critical heat flux, correlation

C-E Report, 1975, C-E Critical Heat Flux Correlation for C-E Fuel Assemblies with Standard Spacer Grids, Part I, Uniform Axial Power Distribution, CENPD-162, Combustion Engineering Co., Winsor, CT. (5)... 

Computational system based on the CHF data bank for testing critical heat flux correlations... 

Carajilescov, P. B.R. Valente (2011). Analysis system of critical heat flux correlations in water-cooled reactors. Proceedings of the International Nuclear Atlantic Conference INAC 2011. (in Portuguese). 

Startup. The critical heat flux correlations should be improved, including the effect of grid-spacers on the boiling transition. 

Katto Y, Ohno H (1984) An improved version of the generalized correlation of critical heat flux for the forced convective boihng in uniformly heated vertical tubes. Int J Heat Mass Transfer 27(9) 1641-1648... 

Qu W, Mudawar 1 (2002a) Experimental and numerical study of pressure drop and heat transfer in a single-phase micro-channel heat sink. Int J Heat Mass Transfer 45 2549-2565 Qu W, Mudawar 1 (2004) Measurement and correlation of critical heat flux in two-phase micro-channel heat sinks. Int J Heat Mass Transfer 47 2045-2059 Qu W, Mudawar 1 (2002b) Prediction and measurement of incipient boiUng heat flux in micro-channel heat sinks. Int J Heat Mass Transfer 45 3933-3945... 

The large heated wall temperature fluctuations are associated with the critical heat flux (CHE). The CHE phenomenon is different from that observed in a single channel of conventional size. A key difference between micro-channel heat sink and a single conventional channel is the amplification of the parallel channel instability prior to CHE. As the heat flux approached CHE, the parallel channel instability, which was moderate over a wide range of heat fluxes, became quite intense and should be associated with a maximum temperature fluctuation of the heated surface. The dimensionless experimental values of the heat transfer coefficient may be correlated using the Eotvos number and boiling number. 

Katto Y (1978) A generalized correlation for critical heat flux for the forced convection boihng in vertical uniformly heated round tubes. Int J Heat Mass Transfer 21 1527-1542 Khrustalev D, Faghri A (1996) Fluid flow effect in evaporation from liquid-vapor meniscus. ASME J Heat Mass Transfer 118 725-747... 

Mostinski16 gives a correlation for the estimation of the critical heat flux for single tubes ... 

S.4.6.2 Critical heat flux in horizontal tubes. Horizontal CHF data are rather meager, so correlations for predicting such cases are less accurate than for vertical flows. Groeneveld et al. (1986) suggested that use be made of a correction factor, K, such that... 

Gaspari, G. P., A. Hassid, and G. Vanoli, 1968, Critical Heat Flux (CHF) Prediction in Complex Geometries (Annuli and Clusters) from a Correlation Developed for Circular Conduits, Rep. CISE-R-276, CISE, Milan, Italy. (5)... 

Macbeth (M5) has recently written a detailed review on the subject of burn-out. The review contains a number of correlations for predicting the maximum heat flux before burn-out occurs. These correlations include a dependence upon the tube geometry, the fluid being heated, the liquid velocity, and numerous other properties, as well as the method of heating. Sil-vestri (S6) has reviewed the fluid mechanics and heat transfer of two-phase annular dispersed flows with particular emphasis on the critical heat flux that leads to burn-out. Silvestri has stated that phenomena responsible for burn-out, due to the formation of a vapor film between the wall and the liquid, are believed to be substantially different from phenomena causing burn-out due to the formation of dry spots that produce the liquid-deficient heat transfer region. It is known that the value of the liquid holdup at which dry spots first appear is dependent on the heat flux qmi. The correlations presented by Silvestri and Macbeth (S6, M5) can be used to estimate the burn-out conditions. 

The minimum (or critical) heat flux required to reach ignition (because temperature and heat flux can be correlated with the Stefan-Boltzmann constant and black-body radiation). 

In this expression, q u is calculated with the correlation of choice, while hiG is the latent heat of vaporization and hsub in the enthalpy change necessary to bring the incoming subcooled liquid to saturation. Thus, from a design point of view, once the critical heat flux is known, the maximum exit vapor quality to avoid CHF can be calculated. It should be pointed out that Xcrit is not often the same value as x, which is the onset of dryout, since the latter can occur from a hydrodynamic effect (vapor shear) at low heat flux. 

Katto, Y. and Ohno, H., An Improved Version of the Generalized Correlation of Critical Heat Flux for the Forced Convective Boiling in Uniformly Heated Vertical Channels,J. Heat Mass Transfer, 27, 1641-1648, (1984). 

Shah, M.M., Improved General Correlation of Critical Heat Flux during Upflow in Uniformly Heated Vertical Tubes, Int. J. Heat Fluid Flow, 8, 326-335, (1987). 

Qu, I. and Mudawar, W., Measurement and Correlation of Critical Heat Flux in Two-Phase Micro-Channel Heat Sinks, Int. J. of Heat and Mass Transfer, 47, 2045-2059, (2004). 

Zhang, W., Hibiki, T., Mishima, K. and Mi, Y., Correlation for Critical Heat Flux for Flow Boiling of Water in Mini-Channels, Int J. Heat Mass Transfer, 49, 1058-1072, (2006). 

Effect of Subcooling. Critical heat flux increases linearly with subcooling, the effect of subcooling decreasing with increasing pressure. The data are well represented by a correlation from Ivey and Morris [148] that relates the critical heat flux q",n to its value (<7"m)Sat for saturated conditions by the expression... 

Correlations for CHF in Pool Boiling. Most correlations for critical heat flux in pool boiling have been of the form indicated in Eq. 15.128. Although this equation was introduced in the context of the hydrodynamic instability model of Zuber [159,160], the form of the equation was derived some years earlier by Kutateladze [166], Thus, the use of the equation is not necessarily associated with any physical model. In the following text, equations will be given for the most usual practical cases of horizontal flat plates and horizontal cylinders relationships for other shapes are discussed by Lienhard and Dhir [155,161],... 

Effects of liquid viscosity are not included in Eq. 15.132, although critical heat flux for viscous liquids is higher than that for those with low viscosity. A more detailed correlation taking viscosity effects into account is given by Dhir and Lienhard [167], To use Eq. 15.132, the viscosity number Vi as defined by... 

The correlations given here are also limited to well-wetting fluids increase in contact angle gives a decrease in critical heat flux as discussed previously. 

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