A new heat balance for flow boiling

Abstract

Recently, one of the authors suggested calculating void fraction, an essential element in thermal‐hydraulics, working with the “thermodynamic” quality instead of the usual “flow” quality. However, the standard heat balance is currently stated as a function of the “flow” quality. Therefore, we should search a new energy balance between the mixture enthalpy, based on “thermodynamic” quality, and the absorbed heat. This work presents the results of such analysis based on accurate measurements of the axial profile of the cross‐sectional average void fraction in the region of boiling with subcooling for water at medium and high pressures taken by Moscow Power Institute (MPI) and Argonne National Laboratory (ANL). As main results, we find that, under uniform heat flux, the mixture enthalpy suffers an abrupt reduction of its slope upon passing saturation point, and a new slip ratio could balance heat with such mixture enthalpy. © 2007 American Institute of Chemical Engineers AIChE J, 2007

Void fraction thermo-kinematics for subcooled flow boiling

“…For subcooled flow boiling tests measured by Bartolomei et al 14 from Moscow Power Institute (MPI) in 1980s, the author has already published 12 good fittings of the slip ratio profile varying only two key slip ratio values, namely, the slip ratio just at saturation point, S 1;sat , and a constant slip along the saturation zone, S 2 . The location of the point of Net Vapor Generation (NVG) [1][2][3]5,14 was also varied in the fitting.…”

“…The starting point of the new void fraction model presented here was suggested by the author some years ago, i.e., to work with the well-known static or thermodynamic quality, x, which is the third quality, suggested in Ref. 4, to pose a new heat balance [9][10][11][12] from which the void fraction could be derived. x is defined as follows: 4…”

“…In order to search a new heat balance based on x, mixture properties based on such quality have been already formulated; [9][10][11][12] in particular, the mixture density q m , which is defined in Eq. ( 7), and the mixture enthalpy, h m , which is given by…”

“…A brand new heat balance, including the above mixture enthalpy, has been already presented elsewhere [9][10][11][12]…”

“…These new mass and heat balances have been already checked against accurate void fraction data several times. [9][10][11][12] Such comparisons have merely calculated the mixture enthalpy profiles, Eq. ( 8), which include the void fraction data, Eq.…”