Improving the Heat Transfer Performance of the Tower Molten Salt Solar Receiver With the Novel Folded Flow Tubes

The molten salt has been widely used in concentrated solar power generation as an effective high-temperature heat transfer and heat storage working fluid. However, due to the concentrating characteristic of the tower receiver, the solar flux distribution of the molten salt receiver is extremely non-uniform, and thus the circumferential non-uniform heat flux has a prominent effect on the heat transfer performance and reliability of the traditional solar molten salt receiver tube (TRT). In this contribution, in order to solve above problems, we propose some novel folded flow tubes (NFTs), which add a partition in the tube and seal the top with end cap so that the inflow and outflow of the fluid can only proceed from the same cross section. Then, we apply the binary nitrate (solar salt) as a heat transfer fluid, which is a mixture of 60% sodium nitrate and 40% potassium nitrate. First, we analyze some effects such as flow parameters, structure, and heat flux loading direction on the convective heat transfer performance of the NFTs. The results show that the circumferential temperature difference of NFTs is about 17–92 K lower than that of TRT, and the molten salt temperature distribution is more uniform accordingly. Moreover, the heat transfer coefficient is increased about 88.37–122.85%, which can provide a guidance for the structural optimization of practical solar molten salt receivers to improve the heat transfer performance and reliability.