CFD Modelling for flow and heat transfer in a closed Thermosyphon charged with water–A new observation for the two phase interaction

Abstract

A three dimensional transient numerical model is done for a Thermosyphon heat pipe to visualize the steam and condensate flow patterns and interaction. The Computational Fluid Dynamics (CFD) model was arranged using Volume of Fluid solution model (VOF)in Fluent. A copper vertical pipe with 14.2mm inside diameter, 400 mm length, and 0.9mm thickness is selected. The heat input varies from (20-120) Watt. The cooling is made with water jacket heat exchanger around the condenser with outer diameter of 55 mm. Filling ratios of (40,50,60,70 and 100) % are tested. All cases show that the classical known flow pattern where the steam flow upward in the core and the condensate flow downward attached to the inner surface of the pipe do not occurs. The simulation results clear out a behavior that both the rising hot steam and the downward condensate flows near the inner pipe wall. So that, both phases face each other near the wall. The high momentum phase continue it flow in its way and shift the other phase from the wall. This flow behavior leads the steam and condensate to flow in a spatial unstable flow upward and downward respectively. The flow continues even when steady state was achieved and create a secondary mass and heat transfer between the phases.

Thermal and Flow Simulation of Concentric Annular Heat Pipe with Symmetric or Asymmetric Condenser

“…where p 1 and p 2 are the pressures on both sides of the surface, R 1 and R 2 are the curvatures, ρ is the average density for the volume, and σ is the surface tension. As expressed in Equation (19), the surface tension between water and vapor is applied using the equation in the two-phase flow thermosyphon analysis of Fadhl [17]:…”

“…Their Finite element method (FEM) analysis of heat pipe well agreed with experimental results. Temmy et al [19] presented the results from a vertical heat pipe CFD simulation using the VOF model. A vertical copper tube was used as container material, with an inner diameter of 14.2 mm, a length of 400 mm, and a thickness of 0.9 mm.…”

Simulation of Thermosyphon Rankine Engine

“…Temimy [20] performed a CFD modeling study to investigate the flow and heat transfer in a closed thermosyphon heat pipe. The volume of the fluid model (VOF) was implemented in Fluent.…”

“…The ANSYS Fluent CFD solver was used with the Volume-of-Fluid (VOF) approach to describe the complex multiphase flow between gas and liquid. The VOF method [20] is based on the assumption that two or more phases are not interpenetrating, and the volume fraction of each new phase must be included in the computation for each additional phase. The VOF approach benefits from using only one set of momentum equations and tracking the interfaces between fluid phases [22].…”