Sai K. Mylavarapu

Investigation of High-Temperature Printed Circuit Heat Exchangers for Very High Temperature Reactors

Very high-temperature reactors require high-temperature (900-950°C) and high-integrity heat exchangers with high effectiveness during normal and off-normal conditions. A class of compact heat exchangers, namely the printed circuit heat exchangers (PCHEs), made of high-temperature materials and found to have these above characteristics, are being increasingly pursued for heavy duty applications. A high-temperature helium test facility, primarily aimed at investigating the heat transfer and pressure drop characteristics of the PCHEs, was designed and is being built at Ohio State University. The test facility was designed to facilitate operation at temperatures and pressures up to 900°C and 3 MPa, respectively. Owing to the high operating conditions, a detailed investigation on various high-temperature materials was carried out to aid in the design of the test facility and the heat exchangers. The study showed that alloys 617 and 230 are the leading candidate materials for high-temperature heat exchangers. Two PCHEs, each having 10 hot plates and 10 cold plates, with 12 channels in each plate, were fabricated from alloy 617 plates and will be tested once the test facility is constructed. Simultaneously computational fluid dynamics calculations have been performed on a simplified PCHE model, and the results for three flow rate cases of 15, 40, and 80 kg/h at a system pressure of 3 MPa are discussed. In summary, this paper focuses on the study of the high-temperature materials, the design of the helium test facility, the design and fabrication of the PCHEs, and the computational modeling of a simplified PCHE model.

Hydrodynamically Developing and Fully Developed Laminar Flows in a Semicircular Duct: Analytical and Computational Analyses

Abstract Hydrodynamically developing and fully developed laminar flows in a semicircular duct are numerically and analytically investigated, respectively. As part of the analytical approach, scale analysis is used to develop order-of-magnitude estimates for the friction factor–Reynolds number product for developing and fully developed laminar flows in a semicircular duct. Dimensionless axial velocity distribution is determined and presented in terms of the dimensionless pressure drop constant for hydrodynamically fully developed laminar flow. Fully developed laminar frictional characteristics for flow through a semicircular duct are then deduced from the dimensionless axial velocity distribution, from which the location of maximum axial velocity and the ratio of maximum axial velocity to the mean axial velocity are determined. In addition, hydrodynamically developing laminar flow in a semicircular duct is numerically analyzed. Various developing flow region parameters, such as the apparent Fanning friction factor and incremental pressure drop number, for laminar flows in a semicircular duct are determined from the numerical analysis. Furthermore, the fully developed laminar flow results obtained from the numerical analysis are compared with the analytical solution, and good agreement is observed between them.

Investigation of Printed Circuit Heat Exchangers for VHTRs

Very High Temperature Reactors (VHTRs) require high temperature (900–950 °C), high integrity, and high efficiency heat exchangers during normal and off-normal conditions. A class of compact heat exchangers, namely, the Printed Circuit Heat Exchangers (PCHEs), made of high temperature materials, found to have the above characteristics, are being increasingly pursued for heavy duty applications. A high-temperature helium experimental test facility, primarily aimed at investigating the heat transfer and pressure drop characteristics of the PCHEs, was designed and is being built at the Ohio State University. The test facility was designed for a maximum operating temperature and pressure of 900 °C and 3 MPa, respectively. Owing to the high operating conditions, a detailed investigation on various high temperature materials was carried out to aid in the design of the test facility and the heat exchangers. The study showed that alloy 617 is the leading candidate material for high temperature heat exchangers. Two PCHEs, each having 10 hot and 10 cold plates with 12 channels in each plate, are currently being fabricated from alloy 617 plates and will be tested once the test facility is constructed. To supplement the experiments, computational fluid dynamics modeling of a simplified PCHE model is being performed and the results for three flow rate cases of 15, 40, and 90 kg/h and a system pressure of 3 MPa are discussed. In summary, this paper focuses on the study of the high-temperature materials, the design of the helium test facility, the design and fabrication of the PCHEs, and the computational modeling of a simplified PCHE model.Copyright