sTEm–at-Work (Puzzle #14): Technician double tube heat exchanger installation test

A double tube heat exchanger has an inlet and outlet for each of its tubes. In most cases, one tube is inserted inside the other and the hot fluid to be cooled is allowed to pass through the inside tube. After any maintenance or installation operation, the technician conducts a system test by monitoring the temperature response as each of the two fluids pass through its corresponding tube for a fixed time period at a fixed fluid flow rate. In this specific test result's report the outside tube temperature is reported as line (a), the blue line.

This double tube heat exchanger is operating correctly. (yes or no).Submit your answers at