Simulation of Heat Transfer in Liquid Plugs Moving Inside Dry Capillary Tubes

The present work numerically simulates the flow of a single isolated liquid plug (of glycerine and water, respectively) flowing in a round capillary tube (ID = 2.0 mm), to understand its local thermal transport behavior. When an isolated liquid plug moves in a capillary tube there is a difference in the advancing and receding dynamic contact angles of the two menisci, respectively. This has been considered in the simulations. The linearized simplification of Hoffman-Tanner’s law is used to model the variation in the two respective apparent contact angles, with the velocity of the liquid plug (i.e. Ca = μU/σ). Simulations are carried out for a range of Capillary number and length of liquid plugs. It has been found that variation in dynamic contact angle leads to enhanced local and average heat transfer coefficient in the moving liquid plug; the local fluid circulation being affected by meniscus deformations. In addition, as the length of the liquid plug is increased, heat transfer coefficient decreases and finally shows the asymptotic transport behavior of Poiseuille flow. Other than Capillary number, the fluid Prandtl number strongly affects the local thermo-hydrodynamics.