Phase change boiling

Kawahara A, Chung PM, Kawaji M (2002) Investigation of two-phase flow pattern, void fraction and pressure drop in a micro-channel. Int J Multiphase Plow 28 1411-1435 Kawaji M (1999) Fluid mechanics aspects of two-phase flow Flow in other geometries. In Kand-likar SG, Shoji M, Dhir VK (eds) Handbook of phase change boiling and condensation. Taylor and Francis, Washington, DC, pp 205-259... 

If the coolant undergoes a phase change (boiling), a different approach must be used since the design limit is clad heat flux, not clad temperature. The CHF is used as the limit to prevent film boiling and fuel rod failure. Figure 22.29 shows the heat balance. 

If the fluid is at its boiling point, then volume is generated through the phase change that occurs upon vaporization ... 

Carey van P (1992) Liquid-vapor phase-change phenomena. An introduction to the thermophysics of vaporization and condensation processes in heat transfer equipment. Hemisphere, New York Celata GP, Cumo M, Mariani A (1997) Experimental evaluation of the onset of subcooled flow boiling at high liquid velocity and subcoohng. Int J Heat Mass Transfer 40 2979-2885 Celata GP, Cumo M, Mariani A (1993) Burnout in highly subcooled water flow boiling in small diameter tubes. Int J Heat Mass Transfer 36 1269-1285 Chen JC (1966) Correlation for boiling heat transfer to saturated fluids in convective flow. Ind Eng Chem Process Des Develop 5 322-329... 

Carey VP (1992) Liquid-vapour phase-change phenomena. Hemisphere, Washington, DC Collier SP (1981) Convective boiling and condensation. McGraw-Hill, New York Ha JM, Peterson GP (1998) Capillary performance of evaporation flow in micro grooves an analytical approach for very small tilt angles. ASME J Heat Transfer 120 452 57 Hetsroni G, Yarin LP, Pogrebnyak E (2004) Onset of flow instability in a heated capillary tube. Int J Multiphase Flow 30 1424-1449... 

Table 11-4 lists values of A, A / vap, melting points, and boiling points for different chemical substances. Example provides practice in using enthalpies of phase changes. 

Phase diagrams are constructed by measuring the temperatures and pressures at which phase changes occur. Approximate phase diagrams such as those shown in Figures 11-39 and 11-40 can be constmcted from the triple point, normal melting point, and normal boiling point of a substance. Example illustrates this procedure. 

What is unique about these three properties of water boiling point, specific heat capacity, and density change over phase change ... 

Carey, Van P., 1992, Convective Boiling in Tubes and Channels, in Liquid-Vapor Phase Change Phenomena, chap. 12, Hemisphere, Washington, DC. (5)... 

Kandlikar, S. G., 1989b, Development of a Flow Boiling Map for Subcooled and Saturated Flow Boiling of Different Fluids Inside Circular Tubes, Heat Transfer with Phase Change, ASME HTD Vol. 114, pp. 51-62, Winter Annual Meeting, San Francisco, CA. (4)... 

Martinelli and Nelson (M7) developed a procedure for calculating the pressure drop in tubular systems with forced-circulation boiling. The procedure, which includes the accelerative effects due to phase change while assuming each phase is an incompressible fluid, is an extrapolation of the Lockhart and Martinelli x parameter correlation. Other pressure drop calculation procedures have been proposed for forced-circulation phase-change systems however, these suffer severe shortcomings, and have not proved more accurate than the Martinelli and Nelson method. 

The metastable liquid form boils at 44°C, the more stable solid alpha form melts at 62°C and has 25-30 J/g heat of fusion. This permits pressure generation when proceeding in either direction through the phase change. 

We see this phenomenon in a different way when we look back at the phase diagram in Figure 5.6. The stable phase is liquid before applying a vacuum. After turning on the water pump, to decrease the applied pressure, the s.v.p. exceeds P(appiied)> and the solvent boils at a lower pressure. The bold arrow again indicates how a phase change occurs during a depression of the external pressure. 

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