An air heater consists of a steel tube, with inner and outer radii ofr1= 12 mmandr2= 15 mm, respectively, length of tube L= 2 m, and eight integrally machined longitudinal fins, each of thicknesst= 2 mm. The fins extend to a concentric tube, which is of radiusr3= 50 mmand insulated on its outer surface. Water at a temperatureT8,i= 95°Cflows through the inner tube with inner heat transfer coefficient hi = 10 W/m2·K, while air atT8,o= 25°Cflows through the annular region formed by the larger concentric tube at the speed of 10 m/s in the axial direction. Assume the 8 fins are the rectangular straight fins; and the air flow is a parallel flow over the 8 plates. What is the total heat transfer rate from water to air?
Hints:
Drawing diagrams of thermal circuit, heat transfer rates or heat fluxes, temperatures, etc.
Stating that which equations, figures and tables you are using at each step.
Compute the flow over a plate problem.
Is it Laminar or turbulent flow?
Solve the total heat transfer rate for the entire structure.
Will the two sides of every fin be considered?