INFLUENCE OF CRITICAL PHENOMENA ON THE HEAT-TRANSFER TO BINARY-MIXTURES

Free convective heat transfer to mixtures of ethane and n-heptane are studied experimentally. A horizontal platinum wire is used in the investigations. During the measurements the pressure is kept above the critical pressure, and the bulk temperature below the critical temperature of the mixture. For pressures below the maximum pressure of the phase envelope, i.e. in the region where retrograde condensation could occur, a strong increase of the heat transfer coefficient is observed coinciding with the onset of retrograde condensation. Visual observations show highly turbulent boiling-like behaviour of the flow pattern at the wire during this mode of heat transfer. For high-temperature differences the heat transfer mechanism is found to be similar to film boiling for pressures not too close to the critical point. If the pressure is close to the critical point the heat transfer mechanism for high-temperature differences changes and resembles turbulent free convective heat transfer.