Description and Analytical Modeling for a Solid Block Cross-flow High Temperature Heat Exchanger

In this report, the design specifics, and performance modeling results, for a simple, solid metal block, liquid-liquid cross-flow heat exchanger, intended for high temperature applications, are given. The design consists of a solid block of metal, with cylindrical channels providing the cross-flow passageways for two non-mixing liquids. In this design, all flow channels are separated by a certain minimum thickness of the host solid block material. This particular design is limited by the length of pores that can be machined from a solid block. In this study, a simple heat transfer model, appropriate for such an exchanger, was used to estimate what values of effectiveness might be obtainable while keeping the size of the exchanger as compact as possible. The effects of channel length and spacing, liquid specific heat and viscosity and block material conductivity on exchanger effectiveness are considered and results reported. The model predicts that for a cubic exchanger of side length 8.25 cm with 50 channels per side at a diameter of 3.0 mm each, for a particular high temperature situation using molten salts, with an inlet and outlet temperature difference of around 170 K, an effectiveness of 0.4 can be achieved with a total mass flow rate of 0.5 kg.s(-1) along with a Reynolds number of less than 2000.