Numerical simulation of time-dependent heat and fluid flows inside and around single rising bubbles using a moving axisymmetric boundary-fitted mesh system

Purpose - This paper aims to develop a numerical method for analysing the time-dependent conjugate heat and fluid flows inside and around single bubbles rising in a hot liquid. Design/methodology/approach - The procedure combines the moving mesh method for flows in time-dependent geometries and the zoned calculation algorithm for conjugate viscous flows. A moving axisymmetric boundary-fitted mesh is used to track the deformable gas-liquid interface, while conjugate flows in both gas and liquid sides are calculated by a two-block zoned method. The interfacial stresses are employed to calculate the velocity value and to decide the time-dependent bubble shape simultaneously. Governing equations for the rising velocity and acceleration of the bubble are derived according to the forces acting on the bubble. Findings - A calculating procedure for time-dependent conjugate heat and fluid flows inside and around a rising single bubble has been developed. The algorithm has been verified, and can be employed for further analysing heat, mass and momentum transfer phenomena and their relevant mechanisms. Originality/value - The paper developed a method to obtain high fidelity results for the heat and fluid flow details in the vicinity of a time-dependent moderately deformable rising bubble; the physically zero-thickness of a gas-liquid interface is guaranteed. The governing equations for the time-dependent rising velocity and acceleration are derived.