Thermally Driven Flow Unit (TDFU) experiment was performed as a mission of IML-2 Project. TDFU is a thermal accumulator model for Two-Phase Fluid Loop. One of TDFU experiment's purposes was to verify Liquid/Vapor phase-separation and liquid positioning at core section in TDFU vessels, and was satisfactorily achieved in IML-2 Project. Be sides, in NASDA, another vessel experiments abroad airplane was performed as preflight estimation. This paper presents numerical simulation analysis on above exprimenal results basis, and the method of modeling the surface tension and the wall adhesion force in the absence of gravity.