2. (60 pts) A bot wire anemometer is a very sensitive velocity measurement device. One type consists of a very thin wire with a constant electrical voltage across it. - The wire temperature increases because its electrical resistance dissipates energy. - A steady state temperature is reached when the rate of energy lost by convection at the wire surfice equals the rate of energy dissipated by electrical resistance. - As the fluid velocity increases, the rate of heat transfer also increases, and it is possible to produce an accurate calibration of velocity as a function of beat loss (and ultimately current). The diameter of the thin wire is 0.2mm and its length is 1cm. Air is blown across the wire at a constant velocity. Other data follow. side view of wire, - Wire surfice temperature =600K - Air pressure =1 atm - Air temperature =300K - Air velocity =25m/s direction of air flow (a) (40) Determine the convection coefficient, h, and the rate of heat loss from the wire, q, for this situation. In answering part (b), you may assume that physical properties of air (Ck,,, ctc. ) do not vary with pressure with one exception. Density is directly proportional to pressure as a consequence of the ideal gas law. (b) (10) Repeat part (a), determining h and q, for the situation where the air pressure is 0.5 atm but all other data remain the same. (c) (10) One of the advantages of hot wire anemometers is a quick response time to changes in velocity. Assuming that the wire may be treated as a lumped capacitance, determine its thermal time constant if the wire material is AISI 304 stainless steel, using the data from part (a). MATERIAL DATA FROM TABLE A.1 AT END OF EXAM PHYSICAL PROPERTIES FROM TABLE A.4 AT END OF EXAM PAGE 328 (CHAPTER 7) AT END OF EXAM