Experimental Investigation and CFD Analysis of Heat Transfer in Single Phase Subcooler of a Small Scale Waste Heat Recovery ORC

In the present work, a detailed investigation of the single phase heat transfer mechanism in a novel subcooler of an experimental small scale waste heat recovery Organic Rankine Cycle (ORC) unit is presented. The ORC unit is operating with R134a and is designed to utilize the waste heat from the jacket water of marine diesel auxiliary internal combustion engines (ICEs). The ORC unit produces 3.7 kWel net electrical power at a cycle pressure of 25 bar and an expander inlet temperature of 82 °C. The application of subcooling in such systems is common practice, so as to ensure the cavitation-free operation of the pump.The subcooler is designed to achieve a certain level of subcooling and at the same time minimize the pressure losses on both the refrigerant and the cooling water side. A theoretical CFD model is developed to predict its operation. Based on the experimental results, a new heat transfer correlation is proposed for the single phase heat transfer inside a corrugated tube. The accuracy of the new correlation is compared with existing ones from the literature. Meanwhile, the results of the correlation are validated by the experimental data collected from the respective ORC unit, reducing the theoretical calculations maximum relative error from 2.98% to a 1.88%.