Supercritical heat transfer to refrigerants: advances on a new experimental test rig

In a transcritical Organic Rankine cycle, the working fluid is pressurized above its critical pressure before heat is added in the vapor generator. Insight into supercritical heat transfer is therefore crucial to make an accurate design of the vapor generator. Supercritical heat transfer has already been widely investigated for water and CO2. For these working fluids, the majority of the investigated geometries are vertical tubes. These results are however not generally applicable to the refrigerants used in Organic Rankine cycles due to the differences in operating conditions and fluid properties. So far, a limited number of refrigerants have been examined, nonetheless, there remain areas where further research is required. Therefore, this work provides an overview of the literature on experimental and numerical investigations on supercritical heat transfer to refrigerants. The remaining gaps in literature are highlighted and discussed. Based on this overview, it can be concluded that the main lack of knowledge lies in the large diameter sized geometries and in the low variety of tested refrigerants. To close this gap, a new experimental test rig is designed based on the experience from a previously built test rig. The design and development of this new test rig as well as the selection of the refrigerants that will be tested on the test rig are discussed in the current work. The test rig will be able to examine different low Global Warming Potential refrigerants with a wide range of critical temperatures. The unique data generated will contribute to the understanding of supercritical heat transfer and enable more accurate sizing of vapor generators for their application in transcritical Organic Rankine cycles.      «

In a transcritical Organic Rankine cycle, the working fluid is pressurized above its critical pressure before heat is added in the vapor generator. Insight into supercritical heat transfer is therefore crucial to make an accurate design of the vapor generator. Supercritical heat transfer has already been widely investigated for water and CO2. For these working fluids, the majority of the investigated geometries are vertical tubes. These results are however not generally applicable to the refrige...     »