Supercritical water flowing through the tubes gets heated by the solar radiation incident on the tubes. The tubes are made of ceramic and have a thermal conductivity of 80 W/m-K. The tubes have an inner radius of 15 mm, and their wall thickness is 3 mm. The outer diameter of the tube has a thin layer of coating whose absorptivity to solar radiation is 0.95. The contact resistance between the coating and the outer diameter of the tube is 𝑅𝑡,𝑐 = 10^-4 𝑚 − 𝑘/𝑊. The amount of solar radiation incident normal to the tube surface depends on the angle to the concentrated solar flux and is given as Q = Qo cos (θ). The range of θ varies from -90 to 90 degrees. The value of q is 100*104 W/m2. On a regular summer day, the ambient air temperature is 40C, and the heat transfer coefficient between the tube and air is 25 W/m2-K. At steady-state, the supercritical water inside the tubes gets heated to a temperature of 600C. The convective heat transfer coefficient between the tube and supercritical water is 1000 W/m2-K.