Forced Convective Boiling in Channels

Jiji, L. M.,andJ. A. Clark, 1964, Bubble Boundary Layer and Temperature Profiles for Forced Convection Boiling in Channel Flow, Trans. ASME, J. Heat Transfer 56 50 58. (4)... 

Forced convective boiling in channels. Here, evaporation of a liquid occurs in flow in a channel (for instance, a round tube). The vapor generated and the remaining liquid form a two-phase flow within the tube, and there are strong interactions between this two-phase flow (which can occur in a number of different forms) and the boiling process. 

Heat Transfer Below the Critical Heat Flux Limit in Forced Convective Boiling in Channels... 

Mechanisms of CHF in Forced Convective Boiling in Channels. Detailed reviews of critical heat flux mechanisms in forced convective boiling are given by Hewitt [291], Tong and Tang [5], Collier and Thome [3], and Katto [101]. The more commonly accepted mechanisms for the occurrence of critical heat flux in forced convection are as follows ... 

Correlations for CHF in Forced Convective Boiling in Channels. The importance of the critical heat flux phenomenon in nuclear reactor design has led to extensive work on correlation of critical heat flux data. The correlations in the literature have taken two main forms as sketched in Fig. 15.123 ... 

Correlations for Post-CHF Heat Transfer in Forced Convective Boiling in Channels. Despite the complexity of the phenomena involved (as discussed earlier), there have been many attempts at providing general correlations. Here, we give two such correlations that serve as examples of this approach. The previously cited reviews should be consulted for further information. 

Kandlikar SG (2006) Nucleation characteristics and stability considerations during flow boiling in micro-channels. Exp. Thermal and Fluid Science 30 441 47 Katto Y, Ohno H (1984) An improved version of the generalized correlation of critical heat flux for the forced convective boiling in uniformly heated vertical tubes. Int J Heat Mass Transfer 27 1641-1648... 

Kast, W., 1964, Significance of Nucleating and Non-stationary Heat Transfer in the Heat Exchanger during Bubble Vaporization and Droplet Condensation, Chem. Eng. Tech. 36(9) 933-940. (2) Katto, Y., 1981, General Features of CHF of Forced Convection Boiling in Uniformly Heated Rectangular Channels, Ini. J. Heat Mass Transfer 24.14131419. (5)... 

When a liquid is forced through a channel or over a surface maintained at a temperature greater than the saturation temperature of the liquid, forced-convection boiling may result. For forced-convection boiling in smooth tubes Rohsenow and Griffith [6] recommended that the forced-convection effect be computed with the Dittus-Boelter relation of Chap. 6 [Eq. (6-4)] and that this effect be added to the boiling heat flux computed from Eq. (9-33). Thus... 

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). 

Katto Y (1981) General features of CHF of forced convection boiling in uniformly heated rectangular channels. Int J Heat Mass Transf 24 1413-1419... 

The conclusion to be drawn from the above examples and many others is that softness in a boiling system, preceding the boiling channel inlet, may cause flow oscillations of low frequency. It is probably the pressure perturbations arising from the explosive nature of nucleate boiling that initiates the oscillation, and the reduced burn-out flux which follows probably corresponds to the trough of the flow oscillation, as a reduction in flow rate always drops the burn-out flux in forced-convection boiling. 

J6. Jiji, L. M Incipient boiling and the bubble boundary layer formation over a heated plate for forced convection flow in a pressurized rectangular channel, Ph.D. Thesis, Univ. of Michigan, Ann Arbor, 1962. 

The detail experimental study of flow boiling heat transfer in two-phase heat sinks was performed by Qu and Mudawar (2003b). It was shown that the saturated flow boiling heat transfer coefficient in a micro-channel heat sink is a strong function of mass velocity and depends only weakly on the heat flux. This result, as well as the results by Lee and Lee (2001b), indicates that the dominant mechanism for water micro-channel heat sinks is forced convective boiling but not nucleate boiling. 

Number of researchers reports the liquid forced convection inside narrow channels is a most valuable form of heat removal from heat sinks [13-16]. However, the respective key issues are the maximum attainable heat flux by using liquid forced convection, and its value in comparison with the preeminent alternatives of boiling critical heat fluxes. We believe that maximum heat flux could be accomplished by using the inverted meniscus principle of evaporation coupled with excluding of vapor... 

The addition of vapor to the flow leads to the existence of a two-phase vapor-liquid flow in the channel it is the existence of this flow and its interaction with the heat transfer processes that makes forced convective boiling so different from pool boiling. As more and more vapor enters the flow, the two-phase flow patterns or regimes develop in the following succession ... 

CHF in Forced Convective Boiling of Multicomponent Mixtures in Channels. Reviews of critical heat flux data for the forced convective boiling of mixtures are presented by Collier and Thome [3] and by Celata [321], In subcooled boiling and low quality, nucleate boiling predominates and similar effects are observed to those seen with pool boiling. This is exemplified... 

Steam-liquid flow. Two-phase flow maps and heat transfer prediction methods which exist for vaporization in macro-channels and are inapplicable in micro-channels. Due to the predominance of surface tension over the gravity forces, the orientation of micro-channel has a negligible influence on the flow pattern. The models of convection boiling should correlate the frequencies, length and velocities of the bubbles and the coalescence processes, which control the flow pattern transitions, with the heat flux and the mass flux. The vapor bubble size distribution must be taken into account. 

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