DESIGN OF A SUPERCRITICAL HEAT EXCHANGER FOR AN INTEGRATED CPV/T-RANKINE CYCLE

asme-orc2015 Tracking Number 198

The worldwide interest for low grade heat utilization by using Organic Rankine Cycle (ORC) technologies has increased significantly. An Organic Rankine Cycle can be combined with several renewable sources, such as solar energy. Concentrating solar power is a well proven technology and it can be efficiently combined with ORC technology for electricity generation. The goal was achieved by utilizing the excess heat source from PV collectors through a low temperature supercritical heat exchanger in the Organic Rankine Cycle. The motivation for working at supercritical state in the heat exchanger is the better thermal match between the heat source and the working fluid, leading to better overall cycle efficiency. In this paper measurements on the supercritical heat exchanger prototype are reported. It is a helical coil heat exchanger with R404a as working fluid flowing in the coil and the heat source fluid in the shell. The design of this heat exchanger was done using heat transfer and pressure drop correlations available from literature. There exists a large uncertainty on these correlations for the considered application because they were derived for working fluids water and CO2, more than ten years ago. In order to have good performance and heat transfer rate the heat exchanger was oversized by 20%. Next, the prototype was built and installed in a test set-up. The measurements on the prototype show that the heat exchanger is indeed oversized. Based on the measurements, a new heat transfer correlation is suggested. In future design this correlation can be used to make a less oversized (and thus cheaper) heat exchanger.