Thermodynamics

270 | Thermodynamicsis allowed to escape. The spring unwinds as the piston movesdown, and the pressure and volume drop to 0.6 MPa and 0.5m 3 at the end of the process. Determine (a) the amount ofrefrigerant that has escaped and (b) the final temperature ofthe refrigerant.5–143 A 2-m 3 rigid insulated tank initially containing saturatedwater vapor at 1 MPa is connected through a valve to asupply line that carries steam at 400°C. Now the valve isopened, and steam is allowed to flow slowly into the tankuntil the pressure in the tank rises to 2 MPa. At this instantthe tank temperature is measured to be 300°C. Determine themass of the steam that has entered and the pressure of thesteam in the supply line.SteamSat. vapor2 m 31 MPaFIGURE P5–143400°C5–144 A piston–cylinder device initially contains 0.6 kg ofsteam with a volume of 0.1 m 3 . The mass of the piston issuch that it maintains a constant pressure of 800 kPa. Thecylinder is connected through a valve to a supply line thatcarries steam at 5 MPa and 500°C. Now the valve is openedand steam is allowed to flow slowly into the cylinder until thevolume of the cylinder doubles and the temperature in thecylinder reaches 250°C, at which point the valve is closed.Determine (a) the mass of steam that has entered and (b) theamount of heat transfer.to be f 0.015, and the discharge velocity is expressed as2gzV where z is the water height above theB 1.5 fL>Dcenter of the valve. Determine (a) the initial discharge velocityfrom the tank and (b) the time required to empty the tank.The tank can be considered to be empty when the water leveldrops to the center of the valve.5–146 Underground water is being pumped into a poolwhose cross section is 3 m 4 m while water is dischargedthrough a 5-cm-diameter orifice at a constant average velocityof 5 m/s. If the water level in the pool rises at a rate of 1.5cm/min, determine the rate at which water is supplied to thepool, in m 3 /s.5–147 The velocity of a liquid flowing in a circular pipe ofradius R varies from zero at the wall to a maximum at thepipe center. The velocity distribution in the pipe can be representedas V(r), where r is the radial distance from the pipecenter. Based on the definition of mass flow rate m . , obtain arelation for the average velocity in terms of V(r), R, and r.5–148 Air at 4.18 kg/m 3 enters a nozzle that has an inlet-toexitarea ratio of 2:1 with a velocity of 120 m/s and leaveswith a velocity of 380 m/s. Determine the density of air at theexit. Answer: 2.64 kg/m 35–149 The air in a 6-m 5-m 4-m hospital room is tobe completely replaced by conditioned air every 15 min. If theaverage air velocity in the circular air duct leading to the roomis not to exceed 5 m/s, determine the minimum diameter ofthe duct.5–150 A long roll of 1-m-wide and 0.5-cm-thick 1-Mn manganesesteel plate (r 7854 kg/m 3 ) coming off a furnace isto be quenched in an oil bath to a specified temperature. If themetal sheet is moving at a steady velocity of 10 m/min, determinethe mass flow rate of the steel plate through the oil bath.Furnace10 m/minSteelplateQSteam0.6 kg0.1 m 3800 kPaFIGURE P5–144Steam5 kPa500°CReview Problems5–145 A D 0 10-m-diameter tank is initially filled withwater 2 m above the center of a D 10-cm-diameter valvenear the bottom. The tank surface is open to the atmosphere,and the tank drains through a L 100-m-long pipe connectedto the valve. The friction factor of the pipe is givenOil bathFIGURE P5–1505–151E It is well established that indoor air quality (IAQ)has a significant effect on general health and productivity ofemployees at a workplace. A recent study showed thatenhancing IAQ by increasing the building ventilation from 5cfm (cubic feet per minute) to 20 cfm increased the productivityby 0.25 percent, valued at $90 per person per year, anddecreased the respiratory illnesses by 10 percent for an averageannual savings of $39 per person while increasing theannual energy consumption by $6 and the equipment cost by