scholarly journals Discussion: “A Pressure Pulse Model for Two-Phase Critical Flow and Sonic Velocity” (Moody, F. J., 1969, ASME J. Heat Transfer, 91, pp. 371–381)

1969 ◽  
Vol 91 (3) ◽  
pp. 381-382
Author(s):  
H. K. Fauske ◽  
M. A. Grolmes
Keyword(s):  
Heat Transfer ◽  
Pressure Pulse ◽  
Critical Flow ◽  
Sonic Velocity ◽  
Two Phase

A Pressure Pulse Model for Two-Phase Critical Flow and Sonic Velocity

1969 ◽  
Vol 91 (3) ◽  
pp. 371-381 ◽  
Author(s):  
F. J. Moody
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Present Model ◽  
Pressure Pulse ◽  
Critical Flow ◽  
Sonic Velocity ◽  
Phase Pattern ◽  
Two Phase ◽  
Theoretical Formulation ◽  
Pulse Transmission

Pressure pulse transmission in a flowing mixture provides the basis for a theoretical formulation of two-phase critical flow and sonic velocity. Homogeneous and separated phases are considered, showing that phase pattern plays an important role in pulse transmission. Graphs are presented for critical flow and sonic velocity of steam-water mixtures, based on no phase change or heat transfer across the pulse. The present model predicts most available data with homogeneous and separated phase patterns and suggests quality ranges for which each pattern applies.

Some Experiments on Sonic Velocity in Two-Phase One-Component Mixtures and Some Thoughts on the Nature of Two-Phase Critical Flow

1969 ◽  
Vol 184 (3) ◽  
pp. 185-194
Author(s):  
F. J. Barclay ◽  
T. J. Ledwidge ◽  
G. C. Cornfield
Keyword(s):  
Thermodynamic Equilibrium ◽  
Equilibrium Theory ◽  
Critical Flow ◽  
Sonic Velocity ◽  
Rarefaction Waves ◽  
Local Pressure ◽  
Two Phase ◽  
Flowing Liquid ◽  
Flow Experiment ◽  
Velocity Of Propagation

The pressure drop characteristics and flow rates encountered in measurements of flashing water flow in parallel-sided pipes cannot be simply related to the thermodynamic equilibrium theory of the velocity of sound in homogeneous two-phase one-component mixtures. It is shown in the paper that the velocity of propagation through such a mixture is different in magnitude, both to the thermodynamic equilibrium theory and to the theory postulating no phase change. Measurements of the velocity of propagation of compression and rarefaction waves in atmospheric pressure stagnant boiling water are described and interpreted. Some aspects of bubble motion in a pressure gradient are discussed. Measurements in stagnant water are not precisely relevant to the case of flowing liquid in which the vapour component is slipping positively with respect to the liquid. The effect of slip is discussed. It seems to the authors that some relationship between the sonic velocity obtained from their tests and the critical velocity correctly defined in terms of local pressure slip and void fraction should exist. The data which should be extracted from a critical flow experiment are suggested.

THE MECHANISM OF RAISING AND QUANTIFICATION OF SPECIFIC HEAT FLUX AT BOILING OF NANOFLUIDS IN FREE CONVECTION CONDITIONS

2017 ◽  
pp. 25-34
Author(s):  
V.N. Moraru
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Capacity ◽  
Specific Heat ◽  
Chemical Properties ◽  
Heating Surface ◽  
Physical Models ◽  
Superheated Liquid ◽  
Two Phase ◽  
Boiling Process

The results of our work and a number of foreign studies indicate that the sharp increase in the heat transfer parameters (specific heat flux q and heat transfer coefficient _) at the boiling of nanofluids as compared to the base liquid (water) is due not only and not so much to the increase of the thermal conductivity of the nanofluids, but an intensification of the boiling process caused by a change in the state of the heating surface, its topological and chemical properties (porosity, roughness, wettability). The latter leads to a change in the internal characteristics of the boiling process and the average temperature of the superheated liquid layer. This circumstance makes it possible, on the basis of physical models of the liquids boiling and taking into account the parameters of the surface state (temperature, pressure) and properties of the coolant (the density and heat capacity of the liquid, the specific heat of vaporization and the heat capacity of the vapor), and also the internal characteristics of the boiling of liquids, to calculate the value of specific heat flux q. In this paper, the difference in the mechanisms of heat transfer during the boiling of single-phase (water) and two-phase nanofluids has been studied and a quantitative estimate of the q values for the boiling of the nanofluid is carried out based on the internal characteristics of the boiling process. The satisfactory agreement of the calculated values with the experimental data is a confirmation that the key factor in the growth of the heat transfer intensity at the boiling of nanofluids is indeed a change in the nature and microrelief of the heating surface. Bibl. 20, Fig. 9, Tab. 2.

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