This simulation calculates temperatures and the rate of heat transfer in a concentric tube heat exchanger. The cold fluid is liquid water, which flows through the center of the heat exchanger. Select the hot fluid (air, liquid water, liquid sodium), which flows through the annular region, from the drop-down menu. Use the drop-down menu to select either parallel or counterflow. Set the length of the heat exchanger and the mass flow rates of the hot and cold fluids with sliders. Arrows indicate the direction of flow.