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Heat Pipe Science and Technology, An International Journal

ISSN Print: 2151-7975
ISSN Online: 2151-7991

Heat Pipe Science and Technology, An International Journal

DOI: 10.1615/HeatPipeScieTech.2013006563
pages 97-124

THERMAL TRANSPORT BEHAVIOR OF A LIQUID PLUG MOVING INSIDE A DRY CAPILLARY TUBE

Ashish Kumar Bajpai
Department of Mechanical Engineering, Indian Institute of Technology Kanpur, Kanpur 208016, India
Sameer Khandekar
Department of Mechanical Engineering, Indian Institute of Technology Kanpur, Kanpur, India

ABSTRACT

Computational simulation of flow and heat -transfer characteristics of a single isolated liquid plug (of glycerin and water, respectively) flowing in a round capillary tube (internal diameter, D = 2.0 mm), so as to understand its local thermo-hydrodynamic transport behavior, is reported. Both, constant heat flux and constant-temperature boundary conditions have been considered at the tube wall. 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 dynamic contact angles with the velocity of the liquid plug (i.e., Ca = µU/σ). Simulations are carried out for a range of Capillary numbers and lengths of liquid plugs (L/D ratio). It has been found that variation in dynamic contact angle leads to an enhanced local and average heat-transfer coefficient in the moving liquid plug; the local fluid circulation being affected by menisci deformation. In addition, as the length of the liquid plug is increased, the heat-transfer coefficient decreases and finally shows the asymptotic transport behavior of Poiseuille flow. Other than the flow Capillary number, the fluid Prandtl number and the L/D ratio of the liquid plug, strongly affect the local thermo hydrodynamics.