Experimental Investigations on Pressure Drop for Subcooled Water in a Circular Channel with a Twisted Tape Insert under One-Side Heating Conditions

The pressure drop characteristics of subcooled water were experimentally investigated in a circular cooling channel with and without a twisted tape (TT) under high heat fluxes, which was designed for the water-cooling structure of the divertor target in a tokamak device. The working medium was deionized water, and the main parameters were mass flux G = 3000–8000 kg·m−2·s−1, inlet pressure of the test section p = 3, 4.2, 5 MPa, equivalent one-side heating flux qe = 5~10 MW·m−2. The off-center circular channel is electrically heated to simulate the unilateral radiation heating on the divertor target by high-temperature plasma. The pressure drop experiment of vertical upward circular cooling channels under high and unilateral heat flux is carried out. The influences of the TT and system parameters such as qe, G, and p on the pressure drop of the test section (Δp) were discussed in detail. In the single-phase (SP) flow region, Δp is mainly affected by the TT, G, and qe. The pressure drop with a TT is significantly higher than that without a TT, a higher G and a lower qe lead to a greater Δp. In the subcooled boiling (SB) flow region, Δp is correlated with the TT, qe, G, and p: the influence of the TT and G decreases, while the influence of p increases. The higher the qe, the higher the G, and the lower the p, the larger the Δp. The results show that almost all of the SP pressure drop correlations for heated circular channels overestimate the experimental pressure drop coefficient ratio for a given viscosity ratio. According to the test results, a new correlation of SP pressure drop under high and unilateral heat fluxes has been proposed, the average error (AE) and root mean square error (RMSE) of which are 0.26% and 3.17%, respectively.