Conference Proceedings Paper
MODELING A DIRECT CONTACT HEAT EXCHANGER FOR A SUPERCRITICAL WATER LOOP
34th Annual CNS Conference - 2013 June 09-12
Franco Cascella (École Polytechnique de Montréal)
Alberto Teyssedou (École Polytechnique de Montréal)
In the last thirty years, Direct Contact Heat Exchangers (DCHX) have found a great success in different power engineering applications. In fact, due to the direct contact of hot and cold working fluids, it is possible to reach very high mass and energy transfer efficiencies. Despite their high performance, it is still quite difficult to predict the correct heat transfer as a function of plant operation conditions, which constitutes a fundamental parameter to correctly operate heat exchangers. Therefore, in this work, a DCHX used in the Thermo-Hydraulic Laboratory of École Polytechnique de Montréal, has been studied. It consists of a vessel where superheated steam is cooled by mixing it with sub-cooled water via a nozzle that sprays the water under the form of tiny droplets (i.e., of about 200 μm in diameter). A thermodynamic model that takes into account the statistical distribution of droplets and their temperature evolution is developed. To this aim, the Droplet Distribution Function (DDF) based on Rosin-Rammler’s equation is used. In the proposed model, the thermal energy exchange between liquid and steam takes into account both convection and evaporation heat transfer mechanisms. A comparison of model’s predictions with experimental data shows very good agreement for steam pressures of 1.6 and 2.1 MPa, however at higher pressures the model over predicts the experimental trends.
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