Study on local thermal–hydraulic performance and optimization of zigzag-type printed circuit heat exchanger at high temperature

• Flow and temperature at high temperature cannot be fully-developed.
• Non-dimensional velocity and temperature are proposed to evaluate performances.
• Local Nusselt number and friction factor at high and low temperature are similar.
• Bigger inclined angle should be used in cold region when using hybrid channels.
• Optimal inclined angles are depended on operating conditions.

High temperature heat exchanger is one of the most important components to transfer heat from the first loop to the second loop in the very high temperature reactor in nuclear energy application. In order to enhance the heat transfer performance, a mini-channel heat exchanger called printed circuit heat exchanger has attracted more attention in recent years. In this paper, the thermal–hydraulic performance of zigzag-type printed circuit heat exchanger with helium as the working fluid operating at the typical temperature of 900 °C in the very high temperature reactor is studied. It is found that the flow and temperature at high temperature cannot achieve a fully-developed condition due to the significant variation of thermal physical properties arisen from the large temperature difference. However, the non-dimensional velocity and temperature can become steady after the second pitch and is similar to the fluid flow behaviors at low temperature. Therefore the local Nusselt number and friction factor at high temperature can match well with those at low temperature when the Reynolds number is bigger than 900. With the increase of inclined angle, the heat transfer and pressure drop increase. It is recommended to put the channel with a larger inclined angle to the cold region when using the hybrid channels. The heat transfer enhancement method with inclined angles completely depends on the operating conditions.