Thermodynamics

17–154 Air is flowing in a wind tunnel at 12°C and 66 kPaat a velocity of 230 m/s. The Mach number of the flow is(a) 0.54 m/s (b) 0.87 m/s (c) 3.3 m/s(d) 0.36 m/s (e) 0.68 m/s17–155 Consider a converging nozzle with a low velocity atthe inlet and sonic velocity at the exit plane. Now the nozzleexit diameter is reduced by half while the nozzle inlet temperatureand pressure are maintained the same. The nozzleexit velocity will(a) remain the same (b) double (c) quadruple(d) go down by half (e) go down to one-fourth17–156 Air is approaching a converging–diverging nozzlewith a low velocity at 20°C and 300 kPa, and it leaves thenozzle at a supersonic velocity. The velocity of air at thethroat of the nozzle is(a) 290 m/s (b) 98 m/s (c) 313 m/s(d) 343 m/s (e) 412 m/s17–157 Argon gas is approaching a converging–divergingnozzle with a low velocity at 20°C and 120 kPa, and it leavesthe nozzle at a supersonic velocity. If the cross-sectional areaof the throat is 0.015 m 2 , the mass flow rate of argon throughthe nozzle is(a) 0.41 kg/s (b) 3.4 kg/s (c) 5.3 kg/s(d) 17 kg/s (e) 22 kg/s17–158 Carbon dioxide enters a converging–diverging nozzleat 60 m/s, 310°C, and 300 kPa, and it leaves the nozzle ata supersonic velocity. The velocity of carbon dioxide at thethroat of the nozzle is(a) 125 m/s (b) 225 m/s (c) 312 m/s(d) 353 m/s (e) 377 m/s17–159 Consider gas flow through a converging–divergingnozzle. Of the five following statements, select the one that isincorrect:(a) The fluid velocity at the throat can never exceed thespeed of sound.(b) If the fluid velocity at the throat is below the speed ofsound, the diversion section will act like a diffuser.(c) If the fluid enters the diverging section with a Machnumber greater than one, the flow at the nozzle exit willbe supersonic.Chapter 17 | 881(d) There will be no flow through the nozzle if the backpressure equals the stagnation pressure.(e) The fluid velocity decreases, the entropy increases, andstagnation enthalpy remains constant during flowthrough a normal shock.17–160 Combustion gases with k 1.33 enter a convergingnozzle at stagnation temperature and pressure of 400°C and800 kPa, and are discharged into the atmospheric air at 20°Cand 100 kPa. The lowest pressure that will occur within thenozzle is(a) 26 kPa (b) 100 kPa (c) 321 kPa(d) 432 kPa (e) 272 kPaDesign and Essay Problems17–161 Find out if there is a supersonic wind tunnel onyour campus. If there is, obtain the dimensions of the windtunnel and the temperatures and pressures as well as theMach number at several locations during operation. For whattypical experiments is the wind tunnel used?17–162 Assuming you have a thermometer and a device tomeasure the speed of sound in a gas, explain how you candetermine the mole fraction of helium in a mixture of heliumgas and air.17–163 Design a 1-m-long cylindrical wind tunnel whosediameter is 25 cm operating at a Mach number of 1.8.Atmospheric air enters the wind tunnel through a converging–diverging nozzle where it is accelerated to supersonic velocities.Air leaves the tunnel through a converging–divergingdiffuser where it is decelerated to a very low velocity beforeentering the fan section. Disregard any irreversibilities. Specifythe temperatures and pressures at several locations as well asthe mass flow rate of air at steady-flow conditions. Why is itoften necessary to dehumidify the air before it enters the windtunnel?P 0Ma 1.8 D 25 cmT 0FIGURE P17–163