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.