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Design, Fabrication, Testing, and Modeling of a High-temperature Printed Circuit Heat Exchanger

出版	Ohio State University, 2015
URL	http://books.google.com.hk/books?id=0vb_jgEACAAJ&hl=&source=gbs_api

註釋One of the very-high-temperature reactor (VHTR) missions is to produce electricity and/or to provide process heat for applications with high efficiency. The electricity generation or process heat applications of these advanced reactors greatly rely on an effective intermediate heat exchanger (IHX) that transfers heat from the primary fluid (i.e., helium) to the secondary fluid, which can be helium, molten salt, water/steam, or supercritical carbon dioxide. The IHX performance is directly related to the efficiency and safety of the overall nuclear system. A printed circuit heat exchanger (PCHE) is one of the leading IHX candidates due to its high effectiveness and compactness, as well as its robustness. In the current study, a scaled-down PCHE was fabricated using Alloy 617 plates and Alloy 800H headers. The PCHE fabrication processes, i.e., photochemical etching, diffusion bonding and brazing, are described. This PCHE has eight hot and eight cold plates with 11 semicircular wavy (zigzag) channels in each plate with the following channel dimensions: 1.2 mm hydraulic diameter, 24.6 mm pitch in the flow (stream-wise) direction, 2.5 mm pitch in the span-wise direction, and 15o wavy pitch angle. The thermal-hydraulic performance of the PCHE is investigated experimentally in the high-temperature helium test facility (HTHF) at The Ohio State University. The PCHE inlet temperatures and pressures are varied up to 350 oC/2 MPa for the cold side and 700 oC/2 MPa for the hot side, respectively, while the maximum mass flow rate of helium reaches 30 kg/h. The corresponding maximum channel Reynolds number for both the hot and cold sides is about 3,000, including the laminar flow and laminar-to-turbulent transitional flow regimes. Comparisons between the obtained experimental data and available empirical correlations in the literature have been carried out. Both hot-side and cold-side friction characteristics of the PCHE with the wavy channels follow the trend established in the empirical model well, while large deviation is presented in the low Reynolds number region. Heat transfer characteristics obtained from model available in the literature show a discrepancy from the experimental results. Large deviation appears in the low Reynolds number region as well. A new heat transfer correlation based on experimental data has been subsequently proposed for the current wavy-channel PCHE. Finally, transients that involve variations of the mass flow rate and temperature on the hot and cold sides of the scaled-down PCHE are investigated by numerical method. A dynamic model has been verified using a commercial software DYNSIM and validated using the experimental data. The model predicts the dynamic trends well and is available for use in the future.