EXPERIMENTAL DETERMINATION OF THERMOPHYSICAL PROPERTIES IN SUPERCRITICAL HEAT EXCHANGERS
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Date
2023-12-07
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Authors
Trapani, Michael J
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East Carolina University
Abstract
An ECU team designed, built, and is testing a pilot-scale supercritical water desalination (SWD) system that processed brine discharge from conventional desalination systems. The system completely separates the solid salts from brine wastes. However, SWD is energy intensive. This work presents the design and testing of two heat exchangers (HEXs) used to recover and reuse the waste heat produced during the SWD process to minimize the overall energy requirement. The HEXs have been instrumented with temperature, pressure and flow control components. The collected data is then used to estimate dimensionless numbers (such as Prandtl, Reynolds and Nusselt) using thermophysical properties from the NIST REFPROP database. The dimensionless numbers are useful for HEXs design and are scarce in the literature for supercritical fluids. Brine was also used as a cooling fluid to simulate three different concentrations (3.5%, 7.5% and 14%) of salt which simulate sea water and double the brine waste discharge concentration from conventional desalination processes. The dimensionless numbers are then used to calculate the convective heat transfer coefficients, thermal resistance, and the overall heat transfer coefficient (OHTC). The results show that the Nusselt number for a supercritical HEX in laminar flow conditions is 20 to 30 times greater than that of a conventional counterpart which translates to an order of magnitude higher rate of heat transfer. The heat recovery system saves significant energy with a payback period of around 5 years.