2. (20 pts) Hot wire anemometers are devices used to measure flow velocity. These devices have a thin heated wire filament in the flow and a second unheated sensor to measure the flow temperature. The flow speed can be determined based on the amount of electrical power required to keep the heated filament at a specific temperature above the bulk flow temperature. 4115 123 Use the following information for this problem: The heated filament is tungsten (electrical resistivity pe = 6.46 10-8 m) with diameter D = 10 m and length L = 7.5 mm. The anemometer is operated such that the filament is always maintained 40C above To = 20C. The filament voltage (E) is measured and mapped to known free-stream velocities. a. (8 pts) Calculate the required filament voltage (E) when the free stream velocity is 5 m s. Tip: At steady state, the filament cooling rate by convection equals the power provided to the anemometer, i.e., q conv=Rel. Also, E = Relc and Re = PeL/Ac where Ac is the cross- sectional area of the anemometer. b. (6 pts) Generate a plot of E vs the free stream velocity from 0.1 to 10 m s. c. (6 pts) Would radiation heat transfer from the filament ever become significant, or can the heat transfer always be modeled as convective?