Abstract
Flow boiling heat transfer is routinely encountered in nuclear reactors, steam engines and other engineering applications. Although several researchers have carried out different numerical and experimental investigations on flow boiling, the underlying physics of the interfacial interaction is still a complex phenomenon to understand in detail. Hence, the numerical simulation and optimisation regarding the adoption of engineering flow boiling parameters have been conducted in this study using the Modified Eulerian-Eulerian Model (MEEM) and Wall Heat Balance Model (WHBM). To predict interpenetrating flow fields and to provide detailed relevant information on the flow behaviour, this study considered a uniform axial heating profile for a cylindrical flow channel. The Raynolds Average Navier Stokes (RANS) equation with an appropriate turbulence model are used to predict the effect of turbulence on the mean flow field, while the MEEM multiphase sub-models are employed to predict the temperature distribution along the wall, the average void fraction, tracking of the single bubble detachment diameter, heat balance at the wall, effect of surface roughness on heat transfer, the effect of aspect ratio, and the critical heat flux. The results obtained from this study are compared with the selected numerical investigation and experimental data presented in the open literature. The present study shows a better approximate prediction (with minimal uncertainties) of both the subcooled boiling heat transfer and the saturated boiling heat transfer. In summary, this study agrees with extant theories and experimental predictions. Thus, it has provided more profound insights into flow boiling heat transfer particularly for flow in a vertical pipe.
Highlights
Flow boiling occurs when a fluid circulates over a heated surface by external means such as a pump or due to the natural buoyancy effect [1]
The results show that the number of grid points has an overriding on the entry length and the void fraction at the outlet
This adiabatic entry length accounts for a single-phase flow region where there is no transfer of heat between the thermodynamic system and the environment, neither there is a change in the temperature of the subcooled liquid flowing along this region
Summary
Flow boiling occurs when a fluid circulates over a heated surface by external means such as a pump or due to the natural buoyancy effect [1]. The non-boiling height is the singlephase height in which the subcooled liquid entering the channel receives a quantity of sensible heat This sensible heat causes a change in subcooled temperature, resulting in subcooled boiling without any significant effects on the pressure drops and fluid density. Flow boiling heat transfer is primarily affected by factors such as the inertia forces, viscous forces, pressure forces, interfacial tension forces, liquid-surface contact angle, exchange of mass, momentum, and energy between the interacting interface between the liquid and vapour phases. These interfaces are bubbles in a continuous liquid flow, a droplet in continuous vapour flow, a vapour film in continuous liquid flow and a liquid film in continuous vapour flow [3]. Buoyancy and the frictional (drag) forces are responsible for the bubble detachment from a heated surface in a low subcooled region [2]
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