Heat transfer of supercritical mixtures of water, ethanol and nitrogen in a bluff body annular flow

Hydrothermal spallation drilling is a promising drilling technique that could prove economically advantageous over rotary techniques for deep wells, where hydrothermal flames can provide the required heat to spall the rock. Assisted ignition of hydrothermal flames must be understood prior to the field implementation of the technology. The convective heat transfer in a burner setup has been therefore investigated, where the flow conditions are similar to those of a bluff body wake flow in annular geometry. Various ternary mixtures of water, ethanol and nitrogen were used as model working fluids to simulate the combustion conditions of water–ethanol mixtures with oxygen. Water ethanol mixtures were pre-heated between 350 °C and 420 °C, and nitrogen was pre-heated up to 400 °C, while the working pressure was set at 260 bar. The convective heat transfer coefficient from an electrically heated surface to the mixtures is presented.

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► Heat transfer coefficients of supercritical ternary mixtures (water, ethanol, nitrogen) were measured.
► A bluff body flow heat transfer was directly measured.
► The influence of the heat flux on the heat transfer coefficient of the ternary mixtures was investigated.
► The influence of the composition of the ternary mixtures on their heat transfer coefficient was investigated.