EXPERIMENTAL STUDY ON HEAT TRANSFER AND PRESSURE DROP IN RECTANGULAR NARROW CHANNEL AT LOW PRESSURE

Abstract

The specificity of the new Jules Horowitz research Reactor (RJH) core geometry and operating conditions required an experimental program to validate the friction factor and heat transfer correlations currently used for single-phase flow in rectangular channels. A specific facility was built to provide known thermal-hydraulic conditions for a simulated fulllength coolant channel of the RJH reactor, allowing the experimental determination of the instability threshold leading to a flow excursion and, possibly, to the critical heat flux. The facility was also designed to examine other thermal-hydraulics phenomena, including the onset of incipient boiling, the single-phase heat transfer coefficients and friction factors, and the pressure drop characteristics. The test section simulates a single vertical rectangular channel of the RJH core with a 50 mm width and a 600 mm heated length. Two flow channel gaps were tested: 1.5 mm and 2.1 mm. The heater plates are made of 1 mm thick Inconel−600 and are uniformly heated by a DC power supply. Tests with water flowing vertically upward covered heat fluxes from 0 to 7 MW/m2, velocities from 0.6 to 18 m/s, exit pressures from 0.2 to 1.0 MPa and inlet temperatures from 25 to 180 °C. The dry side of each heater plate was instrumented with 20 thermocouples on the center line of each plate. Differential pressure measurements were taken axially along the test section. The temperature of the wetted wall was determined from the dry wall temperature measurement, taking into account the temperature dependent thermal conductivity of Inconel−600. Experimental friction factors and heat transfer coefficients were compared to correlations available in the literature. Because the experimental heat transfer coefficients were greater than those given by these correlations, additional studies were conducted first to validate the measurement techniques and data processing (especially for determining Inconel−600 thermal conductivity as a function of temperature), and second to determine a general correlation accounting for the specificities of both the geometry and the thermal hydraulic conditions. This new correlation for forced convection heat transfer in narrow rectangular channels is shown to be in good agreement with experimental data.