1) When a thermocouple is moved from one medium to another medium at a different temperature, the thermocouple must be given sufficient time to come to thermal equilibrium with the new conditions before a reading is taken. Consider a 0.1 cm diameter copper thermocouple wire originally at 150 oC. Determine the temperature response (temperature variation with time) when this wire is suddenly immersed in a) water at 40 oC (h= 80 W/m2 K) and b) air at 40 oC (h=10 W/m2.K). Given that for copper k=391 W/m K, c=383 J/kg K and ??=8930 kg/m3. Please comment on the results.
2) A heating contractor must heat 0.2 kg/s of water from 15 oC to 35 oC using hot gases in cross flow over a thin walled tube.
Your assignment is to develop a series of design graphs that can be used to demonstrate acceptable combinations of tubes dimensions (D and L) and plot gas conditions (T∞ and V) that satisfy this requirement. In your analysis, consider the following parameter ranges: D= 20, 30, and 40 mm; L=3, 4. Or 6 m; T∞=250, 375, or 500 oC; and 20 <= V<= 40 m/s.