A Printed Circuit Heat Exchanger (PCHE) was tested using air and carbon dioxide as working fluids to determine the temperature behavior of the fluid in the PCHE.These tests are conducted and analyzed to pave way for testing the heat exchanger with supercritical carbon dioxide (S − CO 2 ), to obtain data on its performance for use in S − CO 2 Brayton cycles.The tests have been conducted at thermal steady state where a total of 18 data sets have been tested. Air inlet temperature has been varied from 70 o C to 100 o C to 140 o C where both air and CO 2 were both kept at a pressure of either 5 bars or 10 bars while varying the flow from 5 LPM to 10 LPM. Results pertaining to the heat rate and pressure drop were analyzed and discussed. A 3D COMSOL model was created to simulate the PCHE's performance and the results obtained from the simulations have been analyzed and compared to the results obtained experimentally. The results show an average percentage error of 5.65% and 5.73% when comparing the outlet temperatures of air and CO 2 respectively. Further improvements to the test loop is required to remove limitations constricting the range of operation of the loop allowing us to obtain more data in wider ranges of temperatures, pressures and flow rates.ii