LAUSR

Abstract The effect of radiative heat transfer on the thermocapillary flow of a high-Prandtl-number (high-Pr) liquid is studied. The flow geometry is a long liquid bridge (long LB) suspended between coaxial disks in microgravity (μg). Experimental data taken on the International Space Station are used, and the numerical simulations for the two-phase flow in the chamber containing the LB and the ambient gas (AG) are carried out. The local radiative heat transfer from the LB to its surroundings is incorporated into this two-phase flow simulation. The two-phase flow simulation allows for the evaluation of QHD, QCD and QLB, which are the heat transfer from the hot disk to the LB, from the LB to the cold disk and from the LB free surface to the surroundings, respectively. It is shown that the radiative heat transfer Qr contributes more to QLB than the convective heat transfer Qc. This relationship applies when the temperatures involved in the flow system are near room temperature. The heat balance changes depending on the directions and the magnitudes of QHD, QCD and QLB, and a dimensionless parameter called the “modified heat transfer ratio”, defined as χ = Q LB / max ( Q HD , Q CD ) to distinguish four conditions: a large heat-gain, a moderate heat-gain, a moderate heat-loss and a large heat-loss, which correspond to χ - 1 , - 1 ⩽ χ 0 , 0 ⩽ χ ⩽ 1 and 1 χ , respectively. It is found that a large heat-loss condition and a large heat-gain condition generate a secondary roll in the flow pattern near the cold disk and near the hot disk, respectively. The effect of radiative heat transfer on the flow pattern in the LB is examined in terms of χ r = Q r / max ( Q HD , Q CD ) to conclude that approximately 84% of the heat transfer from the LB to its surroundings is undertaken, under the present LB conditions, by radiative heat transfer in large heat gain and loss conditions where the secondary roll appears.