Experimental study of a straight channel printed circuit heat exchanger on supercritical CO2 near the critical point with water cooling

The study presents an experimental examination of heat transfer of straight printed circuit heat exchanger (PCHE) for a precooler of supercritical carbon dioxide (sCO2) Brayton cycle. To perform heat transfer experiment, experimental loop for thermal hydraulic of CO2 in supercritical (ETHICS) was constructed at POSTECH. The straight PCHE was independently manufactured by photochemical etching and diffusion bonding process. An experiment for CO2 cooling with water was conducted via the ETHICS. We focused on heat transfer and flow characteristics of CO2 in the printed circuit heat exchanger. The experiments were conducted at three operating conditions for CO2 cooling, namely the trans-critical case (cooling from supercritical state to subcooled liquid), near the critical case (cooling from gas-like supercritical state to liquid-like supercritical state), and far critical case (cooling just in gas-like supercritical state). Nusselt numbers for different pressure and different operating conditions were compared by following typical analysis used in previous which is using averaged enthalpy based on inlet and outlet data but we conclude that the method of average value using inlet and outlet data is not appropriate for data reduction due to significant changes in the properties of CO2 near the critical point. Instead of that, we propose to use discretization method in data reduction of experimental data of CO2 near the critical point. It is difficult to predict heat transfer performance near the critical point of CO2 in PCHE. Hence, the data from this experiments and discretization method for data reduction are useful in designing a precooler for the sCO2 Brayton cycle.