Effects of soluble surfactant on heat transfer in turbulent bubbly channel flow

Understanding of heat transfer in a turbulent bubbly flow is crucially important in numerous natural processes and industrial applications. 

The addition of bubbles in a single-phase turbulent channel flow leads to a significant enhancement in convective heat transfer. The presence of bubbles ‘agitates’ the turbulent flow further and hence the rate of heat transfer is enhanced. 

This role of bubbles greatly depends upon the bubble distribution in the channel and the bubble distribution is critically influenced by the presence of surfactant (surface-active agent) contamination. In the absence of surfactant, the bubble distribution is primarily determined by bubble deformability. 

If the flow conditions are such that the bubbles are less deformable, they accumulate near the channel wall, stir up the viscous layer, reduce the size of the conduction layer and thus increase heat transfer rate. The maximum increase in the rate of heat transfer is achieved in this case. If the bubble deformability is high enough, they accumulate in the core region of the channel. 

The heat transfer rate still increases but remains lesser than the spherical bubbles case. As the presence of surfactant drastically alters the bubble distribution in the flow, the mechanism of heat transfer in such a flow is still an open question. 

This proposed study aims to explore the effects of soluble surfactant contamination on heat transfer in a turbulent bubbly channel flow using our in-house high-fidelity front-tracking code.

As the interface is explicitly represented, the front-tracking method has distinct advantages for the interface-resolved direct numerical simulation (DNS) study of surfactant-contaminated multiphase flows over the interface-capturing approaches such as the volume-of-fluid method.