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Question 6 (a) Explain the physical interpretation of the following dimensionless numbers; (i) Reynold Number (Re) (ii) Prandlt Number (Pr) (iii) Nusselt Number (Nu) (b) A cartridge electrical heater is shaped as a cylinder of length L = 200 mm and outer diameter D = 20 mm as shown in below diagram. Under normal operating conditions the heater dissipates 2 kW while submerged in a water flow that is at 20°C and provides a convection heat transfer coefficient of h = 5000 W/m²K. Neglecting heat transfer from the ends of the heater, determine its surface temperature Ts. D=20mm L=200mm 个个个 -P=2000W -Ts Too=20°C [h=5000 W/m².K (water) h=50W/m².K (air) If the water flow is inadvertently terminated while the heater continues to operate, the heater surface is exposed to air that is also at 20°C but for which h = 50 W/m²K. What is the corresponding surface temperature?