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1、1-11 A barometer is used to measure the height of a build ing by record ing read ing at the bottom and atthe top of the build ing. The height of the build ing is to be determ ined.Assumptions The variation of air density with altitude is n egligible.730 mmHg3Properties The density of air is given to

2、 beP = 1.18 kg/m . The3den sity of mercury is 13,600 kg/m .Analysis Atmospheric pressures at the top and at the bottom of the build ing areRop =( Pgh)top=(13,600 kg/m3 )(9.807 m/s2 )(0.730 m)1 kPa7.55. .mmHg=97.36 kPaPbottom =( gh)bottom=(13,600 kg/m3)(9.807 m/s2 )(0.755 m)=100.70 kPa1N,1kg m/s21 kP

3、a2XJ000 N/mTaking an air colu mn betwee n the top and the bottom of the buildi ng and writi ng a force bala nee per un it base area, we obta inWair / A = Pbottom - Rop (;gh) air = Pbottom Ptop(1.18kg/m3)(9.807 m/s2)(h)Y1 kg -m/s2 j1000 N/m2 丿1 kPa=(100.70-97.36) kPaIt yieldsh = 288.6 mwhich is also

4、the height of the buildi ng.1-21 The air pressure in a duct is measured by an in cli ned mano meter. For a give n vertical level differe nee, the gage pressure in the duct and the len gth of the differe ntial fluid colum n are to bedeterm ined.AssumptionsThe mano meter fluid is an in compressible su

5、bsta nee.Properties The den sity of the liquid is give n to be = 0.81 kg/L = 810 kg/m 3.Analysis The gage pressure in the duct is determ ined fromPgage二 Pabs Patm =动32= (810 kg/m )(9.81 m/s )(0.08 m)=636 Pa1 NQ kg m/s 21 Pa21 N/mThe len gth of the differe ntial fluid colu mn isL 二h/sin j-(8cm)/sin 3

6、5 =13.9 cmDiscussion Note that the length of the differential fluid column is extended considerably by inclining the mano meter arm for better readability.2-4 No. This is the case for adiabatic systems on ly.2-6 A classroom is to be air-c on diti oned using win dow air-c on diti oning un its. The co

7、oli ng load is due to people, lights, and heat tra nsfer through the walls and the win dows. The n umber of 5-kW win dow air con diti oning un its required is to be determ in ed.AssumptionsThere are no heat dissipat ing equipme nt (such as computers, TVs, or ran ges) in the room.Analysis The total c

8、ooling load of the room is determined fromQcooling QlightsQaeopleOneatgainwhereQlights =10 100 W =1 kWQpeople =40 360kJ/h =4kWQheatgain = 15,000 kJ / h = 4.17 kWSubstitut ing,Qcooling =14 417 =9.17kWThus the n umber of air-c on diti oning un its required is9.17 kW1.83 '2 units5 kW/unit2-18 The f

9、low of air through a flow cha nnel is con sidered. The diameter of the wind cha nnel dow nstream from the rotor and the power produced by the wi ndmill are to be determ in ed.Analysis The specific volume of the air isRT(0.287 kPa m3/kg K)(293 K)-1 0 k P a3=0.8 4 0m / k gThe diameter of the wi nd cha

10、 nnel dow nstream from the rotor is2 2A1VA2V2 C -D12/4)VC ：D2/4)V2 D2= (7m)10m/s- 9 m/s= 7.38 mThe mass flow rate through the wind mill is2= 457.7 kg/s-A1V1n(7 m) (10 m/s)m3v 4(0.8409 m /kg)The power produced is the nW=m字=(457.7kg/s)22(10 m/s)2 -(9 m/s)21 ""g 2=4.35 kW1000 m2/s22-19 The av

11、ailable head, flow rate, and efficiency of a hydroelectric turbine are given. The electric power output is to be determ in ed.Assumptionsl The flow is steady. 2 Water levels at the reservoir and the discharge site remaincon sta nt. 3 Fricti on al losses in pip ing are n egligible.Properties We take