Experimental study on pressure and temperature distribution characteristics of subcritical and supercritical water in vertical flow channel

To enhance knowledge about efficiency improvement and reactor optimization in supercritical water gasification, an experimental system was designed to study the pressure and temperature distribution of subcritical and supercritical water in a channel, representing a simplified continuous reactor. The pressure drop and temperature distribution along and perpendicular to the forced flow are studied by the measure points inserted inside the test section. Experimental results show that the pressure drop in the test section is linearly negatively correlated with the average enthalpy of the inlet and outlet, eventually reaching negative values (-0.177 MPa) at high average enthalpy (2300 kJ kg-1). Temperature and specific enthalpy along the flow direction match theoretical estimates, except near the pseudocritical region. In subcritical cases, horizontal temperature differences are positively correlated with enthalpy differences and mass flow rates but remain nearly constant in supercritical cases. However, with fluid temperature rising from the pseudocritical point, the horizontal temperature difference first increases, then decreases, and reaching a peak of 4.29 K at a fluid temperature of 664 K. Analysis of the obtained data reveals that the negative correlation and values of the pressure drop are caused by fluid volume expansion. Additionally, fluid volume expansion, near-wall natural convection, and turbulent forced flow fluctuations contribute to horizontal temperature non-uniformity.