Thermalization of a Two-Phase Fluid in Low Gravity: Heat Transferred from Cold to Hot

We present an experimental study of the thermal response to a positive temperature quench in two-phase fluid ${\mathrm{SF}}_6$ in low gravity for temperature ranging from $10.1$ to $0.1$ K from the critical temperature. The temperature was measured simultaneously in the gas, the liquid, and the cell wall by thermistors and the density distribution was observed by interferometry. During the quench the gas temperature considerably exceeded the temperature of the heating walls (overheating up to $23\%$). This striking observation is discussed in the light of the adiabatic heat transfer in this highly compressible fluid while the key role of the localization in low gravity of the gas and liquid phases is revealed.