Combined Effect of Bubble Size and Gas Volume Fraction on Natural Convective Heat Transfer Enhancement in Homogeneous Bubbly Flow: Eulerian–Eulerian Numerical Simulations

Abstract

Abstract Natural convective heat transfer can be enhanced through either fins or riblets, wall roughness elements, or the injection of bubbles in the flow. Bubble injections in a quiescent (pseudo-turbulent) liquid phase or an already turbulent liquid phase had been shown to enhance the natural convective heat transfer from literature. However, study of the combined effect of bubble size and gas volume fraction rather than individual effect on natural convective heat transfer enhancement for homogeneous bubbly flow is lacking. The present work intends to fill in that data gap through conducting numerical simulations to study the combined effect of bubble size and gas volume fraction on natural convective heat transfer enhancement. The present numerical work employs the validated interphase force models and the Eulerian–Eulerian model. ansysfluent is used to simulate a bubbly flow in a three-dimensional rectangular channel with a natural convective heat transfer. Bubbles ranging from microto millimeter diameter with inlet gas volume fraction varied in the range of 0.351–3.725% are injected upward to a quiescent liquid phase in a rectangular channel with a heated left wall and a cooled right wall. The flow regime is homogeneous without bubble coalescence and breakup effect. Validated computational models are employed to study the combined effect of bubble size and gas volume fraction on heat transfer enhancement. A relation between Nusselt number, bubble Reynolds number, Rayleigh number, nondimensional bubble size, and inlet gas volume fraction is constructed using the power regression method.