sonntag, borgnakke, van wylen. solution manual chapters 1-9 for classical mechanics and thermodynamics

2.14 A vertical hydraulic cylinder has a 125-mm diameter piston with hydraulic fluidinside the cylinder and an ambient pressure of 1 bar.. 2.22 A 5-kg piston in a cylinder with diameter

CHAPTER 2

The correspondence between the problem set in this fifth edition versus the

problem set in the 4'th edition text Problems that are new are marked new andthose that are only slightly altered are marked as modified (mod)

2.1 The “standard” acceleration (at sea level and 45° latitude) due to gravity is 9.80665

m/s2 What is the force needed to hold a mass of 2 kg at rest in this gravitationalfield ? How much mass can a force of 1 N support ?

Solution:

ma = 0 = ∑ F = F - mg

F = mg = 2 × 9.80665 = 19.613 N

F = mg => m = F/g = 1 / 9.80665 = 0.102 kg

2.2 A model car rolls down an incline with a slope so the gravitational “pull” in the

direction of motion is one third of the standard gravitational force (see Problem2.1) If the car has a mass of 0.45 kg Find the acceleration

Solution:

ma = ∑ F = mg / 3

a = mg / 3m = g/3 = 9.80665 / 3 = 3.27 m/s 2

2.3 A car drives at 60 km/h and is brought to a full stop with constant deceleration in 5

seconds If the total car and driver mass is 1075 kg Find the necessary force.Solution:

Acceleration is the time rate of change of velocity

ma = ∑ F ; a = dV / dt = (60 × 1000) / (3600 × 5) = 3.33 m/s2

Fnet = ma = 1075 × 3.333 = 3583 N

2.4 A washing machine has 2 kg of clothes spinning at a rate that generates an

acceleration of 24 m/s2 What is the force needed to hold the clothes?

Solution:

F = ma = 2 kg × 24 m/s2 = 48 N

2.5 A 1200-kg car moving at 20 km/h is accelerated at a constant rate of 4 m/s2 up to a

speed of 75 km/h What are the force and total time required?

Solution:

a = dV / dt => ∆t = dV/a = [ ( 75 − 20 ) / 4 ] × ( 1000 / 3600 )

∆t = 3.82 sec ; F = ma = 1200 × 4 = 4800 N

2.6 A steel plate of 950 kg accelerates from rest with 3 m/s2 for a period of 10s What

force is needed and what is the final velocity?

Solution:

Constant acceleration can be integrated to get velocity

a = dV / dt => ∫ dV = ∫ a dt => ∆V = a ∆t = 3 × 10 = 30 m/s

V = 30 m/s ; F = ma = 950 × 3 = 2850 N

2.7 A 15 kg steel container has 1.75 kilomoles of liquid propane inside A force of 2

kN now accelerates this system What is the acceleration?

Solution:

ma = ∑ F ⇒ a = ∑ F / m

m = msteel + mpropane = 15 + (1.75 × 44.094) = 92.165 kg

a = 2000 / 92.165 = 21.7 m/s 2

2.8 A rope hangs over a pulley with the two equally long ends down On one end you

attach a mass of 5 kg and on the other end you attach 10 kg Assuming standardgravitation and no friction in the pulley what is the acceleration of the 10 kg masswhen released?

Solution:

Do the equation of motion for the mass m2 along the

downwards direction, in that case the mass m1 moves

up (i.e has -a for the acceleration)

2.9 A bucket of concrete of total mass 200 kg is raised by a crane with an acceleration

of 2 m/s2 relative to the ground at a location where the local gravitational

acceleration is 9.5 m/s2 Find the required force

Solution:

F = ma = Fup − mg

Fup = ma + mg = 200 ( 2 + 9.5 ) = 2300 N

2.10 On the moon the gravitational acceleration is approximately one-sixth that on the

surface of the earth A 5-kg mass is “weighed” with a beam balance on the surface

on the moon What is the expected reading? If this mass is weighed with a springscale that reads correctly for standard gravity on earth (see Problem 2.1), what isthe reading?

Solution:

Moon gravitation is: g = gearth/6

m

Beam Balance Reading is 5 kg

This is mass comparison Spring Balance Reading is in kg units length ∝ F ∝ g

Reading will be 5

6 kg

This is force comparison

2.11 One kilogram of diatomic oxygen (O2 molecular weight 32) is contained in a

500-L tank Find the specific volume on both a mass and mole basis (v and v)

Solution:

v = V/m = 0.5/1 = 0.5 m 3 /kg

v = V/n = V

m/M = Mv = 32 × 0.5 = 16 m3 /kmol

2.12 A 5 m3 container is filled with 900 kg of granite (density 2400 kg/m3 ) and the rest

of the volume is air with density 1.15 kg/m3 Find the mass of air and the overall(average) specific volume

Solution:

mair = ρ V = ρair ( Vtot − mgranite / ρ ) = 1.15 [ 5 - (900 / 2400) ] = 1.15 × 4.625 = 5.32 kg

v = V / m = 5 / (900 + 5.32) = 0.00552 m 3 /kg 2.13 A 15-kg steel gas tank holds 300 L of liquid gasoline, having a density of 800

kg/m3 If the system is decelerated with 6 m/s2what is the needed force?

Solution:

m = mtank + mgasoline = 15 + 0.3 × 800 = 255 kg

F = ma = 255 × 6 = 1530 N

2.14 A vertical hydraulic cylinder has a 125-mm diameter piston with hydraulic fluid

inside the cylinder and an ambient pressure of 1 bar Assuming standard gravity,find the piston mass that will create a pressure inside of 1500 kPa

2.15 A barometer to measure absolute pressure shows a mercury column height of 725

mm The temperature is such that the density of the mercury is 13550 kg/m3 Findthe ambient pressure

Solution:

Hg : ∆l = 725 mm = 0.725 m; ρ = 13550 kg/m3

P = ρ g∆l = 13550 × 9.80665 × 0.725 × 10-3 = 96.34 kPa

2.16 A cannon-ball of 5 kg acts as a piston in a cylinder of 0.15 m diameter As the

gun-powder is burned a pressure of 7 MPa is created in the gas behind the ball What isthe acceleration of the ball if the cylinder (cannon) is pointing horizontally?

2.17 Repeat the previous problem for a cylinder (cannon) pointing 40 degrees up relative

to the horizontal direction

Solution:

ma = F = ( P1 - P0 ) A - mg sin 400

ma = ( 7000 - 101 ) × π × ( 0.152 / 4 ) - 5 × 9.80665 × 0.6428 = 121.9 - 31.52 = 90.4 N

a = 90.4 / 5 = 18.08 m/s 2

2.18 A piston/cylinder with cross sectional area of 0.01 m2 has a piston mass of 100 kg

resting on the stops, as shown in Fig P2.18 With an outside atmospheric pressure

of 100 kPa, what should the water pressure be to lift the piston?

Solution:

Force balance: F↑ = F↓ = PA = mpg + P0A

P = P0 + mpg/A = 100 kPa + (100 × 9.80665) / (0.01 × 1000) = 100 kPa + 98.07 = 198 kPa

2.19 The hydraulic lift in an auto-repair shop has a cylinder diameter of 0.2 m To what

pressure should the hydraulic fluid be pumped to lift 40 kg of piston/arms and 700

kg of a car?

Solution:

F↓ = ma = mg = 740 × 9.80665 = 7256.9 NForce balance: F↑ = ( P - P0 ) A = F↓ => P = P0 + F↓ / A

A = π D2 (1 / 4) = 0.031416 m2

P = 101 + 7256.9 / (0.031416 × 1000) = 332 kPa

2.20 A differential pressure gauge mounted on a vessel shows 1.25 MPa and a local

barometer gives atmospheric pressure as 0.96 bar Find the absolute pressure insidethe vessel

Solution:

Pgauge = 1.25 MPa = 1250 kPa; P0 = 0.96 bar = 96 kPa

P = Pgauge + P0 = 1250 + 96 = 1346 kPa

2.21 The absolute pressure in a tank is 85 kPa and the local ambient absolute pressure is

97 kPa If a U-tube with mercury, density 13550 kg/m3, is attached to the tank tomeasure the vacuum, what column height difference would it show?

Solution:

∆P = P0 - Ptank = ρg∆l

∆l = ( P0 - Ptank ) / ρg = [(97 - 85 ) × 1000 ] / (13550 × 9.80665)

= 0.090 m = 90 mm

2.22 A 5-kg piston in a cylinder with diameter of 100 mm is loaded with a linear spring

and the outside atmospheric pressure of 100 kPa The spring exerts no force on thepiston when it is at the bottom of the cylinder and for the state shown, the pressure

is 400 kPa with volume 0.4 L The valve is opened to let some air in, causing thepiston to rise 2 cm Find the new pressure

Solution:

A linear spring has a force linear proportional to displacement F = k x, sothe equilibrium pressure then varies linearly with volume: P = a + bV, with anintersect a and a slope b = dP/dV Look at the balancing pressure at zero volume (V-> 0) when there is no spring force F = PA = PoA + mpg and the initial state.These two points determine the straight line shown in the P-V diagram

V

2 = 0.4 + 0.00785 × 20 = 0.557 L

P2 = P1 + dP

dV ∆V = 400 + (400-106.2)

0.4 - 0 (0.557 - 0.4)

= 515.3 kPa

2.23 A U-tube manometer filled with water, density 1000 kg/m3, shows a height

difference of 25 cm What is the gauge pressure? If the right branch is tilted tomake an angle of 30° with the horizontal, as shown in Fig P2.23, what should thelength of the column in the tilted tube be relative to the U-tube?

2.24 The difference in height between the columns of a manometer is 200 mm with a

fluid of density 900 kg/m3 What is the pressure difference? What is the heightdifference if the same pressure difference is measured using mercury, density

13600 kg/ m3, as manometer fluid?

Solution:

∆P = ρ1gh1 = 900 × 9.807 × 0.2 = 1765.26 Pa = 1.77 kPahhg = ∆P/ (ρhg g) = (ρ1gh1) / (ρhg g) = 900

13600 ×0.2 = 0.0132 m= 13.2 mm

2.25 Two reservoirs, A and B, open to the atmosphere, are connected with a mercury

manometer Reservoir A is moved up/down so the two top surfaces are level at h3

as shown in Fig P2.25 Assuming that you know ρA, ρHg and measure the

3 - h

1

2.26 Two vertical cylindrical storage tanks are full of liquid water, density 1000 kg/m3,

the top open to the atmoshere One is 10 m tall, 2 m diameter, the other is 2.5 m tallwith diameter 4m What is the total force from the bottom of each tank to the waterand what is the pressure at the bottom of each tank?

Pbot,A = 101 + (1000 × 10 × 9.80665 / 1000) = 199 kPaPbot,B = 101 + (1000 × 2.5 × 9.80665 / 1000) = 125.5 kPa

2.27 The density of mercury changes approximately linearly with temperature as

ρHg = 13595 - 2.5 T kg/ m3 T in Celsius

so the same pressure difference will result in a manometer reading that is

influenced by temperature If a pressure difference of 100 kPa is measured in thesummer at 35°C and in the winter at -15°C, what is the difference in column heightbetween the two measurements?

Solution:

∆P = ρgh ⇒ h = ∆P/ρg ; ρsu = 13507.5 ; ρw = 13632.5hsu = 100×103/(13507.5 × 9.807) = 0.7549 m

hw = 100×103/(13632.5 × 9.807) = 0.7480 m

∆h = hsu - hw = 0.0069 m = 6.9 mm

2.28 Liquid water with density ρ is filled on top of a thin piston in a cylinder with

cross-sectional area A and total height H Air is let in under the piston so it pushes up,

spilling the water over the edge Deduce the formula for the air pressure as a

function of the piston elevation from the bottom, h.

2.29 A piston, mp= 5 kg, is fitted in a cylinder, A = 15 cm2, that contains a gas The

setup is in a centrifuge that creates an acceleration of 25 m/s2 in the direction ofpiston motion towards the gas Assuming standard atmospheric pressure outsidethe cylinder, find the gas pressure

2.30 A piece of experimental apparatus is located where g = 9.5 m/s2 and the

temperature is 5°C An air flow inside the apparatus is determined by measuringthe pressure drop across an orifice with a mercury manometer (see Problem 2.27for density) showing a height difference of 200 mm What is the pressure drop inkPa?

Solution:

∆P = ρgh ; ρHg = 13600

∆P = 13600 × 9.5 × 0.2 = 25840 Pa = 25.84 kPa

2.31 Repeat the previous problem if the flow inside the apparatus is liquid water, ρ ≅

1000 kg/m3, instead of air Find the pressure difference between the two holesflush with the bottom of the channel You cannot neglect the two unequal watercolumns

Solution: Balance forces in the manometer:

2.32 Two piston/cylinder arrangements, A and B, have their gas chambers connected by

a pipe Cross-sectional areas are AA = 75 cm2 and AB = 25 cm2 with the piston

mass in A being mA = 25 kg Outside pressure is 100 kPa and standard gravitation

Find the mass mB so that none of the pistons have to rest on the bottom

A

+ P0 =

mPBgA

B

+ P0 => mPB = mPA AA/ AB = 25 × 25/75 = 8.33 kg

2.33 Two hydraulic piston/cylinders are of same size and setup as in Problem 2.32, but

with neglible piston masses A single point force of 250 N presses down on piston

A Find the needed extra force on piston B so that none of the pistons have tomove

2.34 At the beach, atmospheric pressure is 1025 mbar You dive 15 m down in the

ocean and you later climb a hill up to 250 m elevation Assume the density of water

is about 1000 kg/m3 and the density of air is 1.18 kg/m3 What pressure do youfeel at each place?

Solution:

∆P = ρgh Pocean= P0 + ∆P = 1025 × 100 + 1000 × 9.81 × 15

= 2.4965 × 105 Pa = 250 kPa

Phill = P0 - ∆P = 1025 × 100 - 1.18 × 9.81 × 250

= 0.99606 × 105 Pa = 99.61 kPa

2.35 In the city water tower, water is pumped up to a level 25 m above ground in a

pressurized tank with air at 125 kPa over the water surface This is illustrated inFig P2.35 Assuming the water density is 1000 kg/m3 and standard gravity, findthe pressure required to pump more water in at ground level

Solution:

Pbottom = Ptop + ρgl = 125 + 1000 × 9.807 × 25 × 10-3

= 370 kPa

2.36 Two cylinders are connected by a piston as shown in Fig P2.36 Cylinder A is

used as a hydraulic lift and pumped up to 500 kPa The piston mass is 25 kg andthere is standard gravity What is the gas pressure in cylinder B?

2.37 Two cylinders are filled with liquid water, ρ = 1000 kg/m3

, and connected by a linewith a closed valve A has 100 kg and B has 500 kg of water, their cross-sectional

areas are A

A = 0.1 m2 and AB = 0.25 m2 and the height h is 1 m Find the pressure

on each side of the valve The valve is opened and water flows to an equilibrium.Find the final pressure at the valve location

Solution:

VA = vH2OmA = mA/ρ = 0.1 = AAhA => hA = 1 mV

VA = P

0 + ρghA = 101325 + 1000 × 9.81 × 1 = 111 135 PaEquilibrium: same height over valve in both

Vtot = VA + VB = h2AA + (h2 - H)AB ⇒ h2 =

hAAA + (hB+H)ABA

A + A

B

= 2.43 m

PV2 = P0 + ρgh2 = 101.325 + (1000 × 9.81 × 2.43)/1000 = 125.2 kPa

2.38 Using the freezing and boiling point temperatures for water in both Celsius and

Fahrenheit scales, develop a conversion formula between the scales Find the

conversion formula between Kelvin and Rankine temperature scales

Solution:

TFreezing = 0 oC = 32 F; TBoiling = 100 oC = 212 F

∆T = 100 oC = 180 F ⇒ ToC = (TF - 32)/1.8 or TF = 1.8 ToC + 32For the absolute K & R scales both are zero at absolute zero

TR = 1.8 × TK

English Unit Problems

2.39E A 2500-lbm car moving at 15 mi/h is accelerated at a constant rate of 15 ft/s2 up

to a speed of 50 mi/h What are the force and total time required?

2.40E Two pound moles of diatomic oxygen gas are enclosed in a 20-lbm steel

container A force of 2000 lbf now accelerates this system What is the

acceleration?

Solution:

mO2 = nO2MO2 = 2 × 32 = 64 lbmmtot = mO2 + msteel = 64 + 20 = 84 lbm

a = Fgcmtot = (2000 × 32.174) / 84 = 766 ft/s

2

2.41E A bucket of concrete of total mass 400 lbm is raised by a crane with an

acceleration of 6 ft/s2 relative to the ground at a location where the local

gravitational acceleration is 31 ft/s2 Find the required force

Solution:

F = ma = Fup - mg

Fup = ma + mg = 400 × ( 6 + 31 ) / 32.174 = 460 lbf

2.42E One pound-mass of diatomic oxygen (O

2 molecular weight 32) is contained in a

100-gal tank Find the specific volume on both a mass and mole basis (v and v).Solution:

v = V/m = 15/1 = 15 ft3/lbm

v¯ = V/n = V

m/M = Mv = 32 ×15 = 480 ft3/lbmol

2.43E A 30-lbm steel gas tank holds 10 ft3 of liquid gasoline, having a density of 50

lbm/ft3 What force is needed to accelerate this combined system at a rate of 15ft/s2?

Solution:

m = mtank + mgasoline = 30 + 10 × 50 = 530 lbm

F = ma

gC = (530 × 15) / 32.174 = 247.1 lbf

2.44E A differential pressure gauge mounted on a vessel shows 185 lbf/in.2 and a local

barometer gives atmospheric pressure as 0.96 atm Find the absolute pressureinside the vessel

Solution:

P = Pgauge + P0 = 185 + 0.96 × 14.696 = 199.1 lbf/in2

2.45E A U-tube manometer filled with water, density 62.3 lbm/ft3, shows a height

difference of 10 in What is the gauge pressure? If the right branch is tilted tomake an angle of 30° with the horizontal, as shown in Fig P2.23, what should thelength of the column in the tilted tube be relative to the U-tube?

= Pgauge = 0.36 lbf/in 2

h = H × sin 30°

⇒ H = h/sin 30° = 2h = 20 in = 0.833 ft

2.46E A piston/cylinder with cross-sectional area of 0.1 ft2 has a piston mass of 200 lbm

resting on the stops, as shown in Fig P2.18 With an outside atmospheric pressure

of 1 atm, what should the water pressure be to lift the piston?

Solution:

P = P0 + mpg/Agc = 14.696 + (200×32.174) / (0.1 × 144 × 32.174)

= 14.696 + 13.88 = 28.58 lbf/in 2

2.47E The density of mercury changes approximately linearly with temperature as

ρHg = 851.5 - 0.086 T lbm/ft3 T in degrees Fahrenheit

so the same pressure difference will result in a manometer reading that is

influenced by temperature If a pressure difference of 14.7 lbf/in.2 is measured inthe summer at 95 F and in the winter at 5 F, what is the difference in columnheight between the two measurements?

2.49E At the beach, atmospheric pressure is 1025 mbar You dive 30 ft down in the

ocean and you later climb a hill up to 300 ft elevation Assume the density ofwater is about 62.3 lbm/ft3 and the density of air is 0.0735 lbm/ft3 What pressure

do you feel at each place?

CHAPTER 3

The SI set of problems are revised from the 4th edition as:

The english unit problem set is revised from the 4th edition as:

3.1 Water at 27°C can exist in different phases dependent upon the pressure Give the

approximate pressure range in kPa for water being in each one of the three phasesvapor, liquid or solid

Solution:

The phases can be seen in Fig 3.6, a sketch

of which is shown to the right

T =27 °C = 300 ΚFrom Fig 3.6:

PVL ≈ 4 × 10−3 MPa = 4 kPa,

PLS = 103 MPa

ln P

TV

LS

CR.P

P < 4 kPa VAPOR P > 1000 MPa SOLID(ICE) 0.004 MPa < P < 1000 MPa LIQUID

3.2 Find the lowest temperature at which it is possible to have water in the liquid

phase At what pressure must the liquid exist?

Solution:

There is no liquid at lower temperatures than onthe fusion line, see Fig 3.6, saturated ice III toliquid phase boundary is at

T ≈ 263K ≈ - 10°C and P ≈ 2100 MPa

ln P

TV

LS

CR.P

lowest T liquid

3.3 If density of ice is 920 kg/m3, find the pressure at the bottom of a 1000 m thick

ice cap on the north pole What is the melting temperature at that pressure?

Solution: ρICE = 920 kg/m3

∆P = ρgH = 920 × 9.80665 × 1000 = 9022118 Pa

P = Po + ∆P = 101.325 + 9022 = 9123 kPaSee figure 3.6 liquid solid interphase => T LS = -1°C

3.4 A substance is at 2 MPa, 17°C in a rigid tank Using only the critical properties

can the phase of the mass be determined if the substance is nitrogen, water orpropane ?

Solution: Find state relative to critical point properties which are:

a) Nitrogen N2 : 3.39 MPa 126.2 Kb) Water H2O : 22.12 MPa 647.3 Kc) Propane C3H8 : 4.25 MPa 369.8 KState is at 17 °C = 290 K and 2 MPa < Pc

for all cases:

N2 : T >> Tc Superheated vapor P < Pc

H2O : T << Tc ; P << Pc

you cannot say

C3H8 : T < Tc ; P < Pc you cannot say

ln P

TVapor

Liquid Cr.P.

ac

b

3.5 A cylinder fitted with a frictionless piston contains butane at 25°C, 500 kPa Can

the butane reasonably be assumed to behave as an ideal gas at this state ?

Solution Butane 25°C, 500 kPa, Table A.2: Tc = 425 K; Pc = 3.8 MPa

Tr = ( 25 + 273 ) / 425 = 0.701; Pr = 0.5/3.8 = 0.13Look at generalized chart in Figure D.1

Actual Pr > Pr, sat => liquid!! not a gas

3.6 A 1-m3 tank is filled with a gas at room temperature 20°C and pressure 100 kPa

How much mass is there if the gas is a) air, b) neon or c) propane ?

Solution: Table A.2 T= 20 °C = 293.15 K ; P = 100 kPa << Pc for all

Air : T >> TC,N2; TC,O2 = 154.6 K so ideal gas; R= 0.287

Neon : T >> Tc = 44.4 K so ideal gas; R = 0.41195

Propane: T < Tc = 370 K, but P << Pc = 4.25 MPa so gas R = 0.18855

a) m = PV/RT = 100 ×1 / 0.287 × 293.15 = 1.189 kgb) m = 100 × 1/ 0.41195 × 293.15 = 0.828 kg

c) m = 100 × 1 / 0.18855 × 293.15 = 1.809 kg

3.7 A cylinder has a thick piston initially held by a pin as shown in Fig P3.7 The

cylinder contains carbon dioxide at 200 kPa and ambient temperature of 290 K.The metal piston has a density of 8000 kg/m3 and the atmospheric pressure is 101kPa The pin is now removed, allowing the piston to move and after a while thegas returns to ambient temperature Is the piston against the stops?

1 > Pfloat piston moves up, T

2 = To & if piston at stops,then V

⇒ piston is at stops, and P2 = 133 kPa

3.8 A cylindrical gas tank 1 m long, inside diameter of 20 cm, is evacuated and then

filled with carbon dioxide gas at 25°C To what pressure should it be charged if thereshould be 1.2 kg of carbon dioxide?

3.9 A 1-m3 rigid tank with air at 1 MPa, 400 K is connected to an air line as shown in

Fig P3.9 The valve is opened and air flows into the tank until the pressure reaches

5 MPa, at which point the valve is closed and the temperature inside is 450K

a What is the mass of air in the tank before and after the process?

b The tank eventually cools to room temperature, 300 K What is the pressureinside the tank then?

mair2 =

P2VRT

2

= 5000 × 10.287 × 450 = 38.715 kgProcess 2 → 3 is constant V, constant mass cooling to T

3.10 A hollow metal sphere of 150-mm inside diameter is weighed on a precision

beam balance when evacuated and again after being filled to 875 kPa with anunknown gas The difference in mass is 0.0025 kg, and the temperature is 25°C.What is the gas, assuming it is a pure substance listed in Table A.5 ?

PV =

0.0025 × 8.3145 × 298.2

875 × 0.001767 = 4.009 ≈ MHe

=> Helium Gas

3.11 A piston/cylinder arrangement, shown in Fig P3.11, contains air at 250 kPa,

300°C The 50-kg piston has a diameter of 0.1 m and initially pushes against thestops The atmosphere is at 100 kPa and 20°C The cylinder now cools as heat istransferred to the ambient

a At what temperature does the piston begin to move down?

b How far has the piston dropped when the temperature reaches ambient?

Solution:

Piston Ap = π

4 × 0.12 = 0.00785 m2Balance forces when piston floats:

Pfloat = Po + mpgAp = 100 + 50 × 9.807

0.00785 × 1000 = 162.5 kPa = P2 = P3

To find temperature at 2 assume ideal gas:

21P

V

P 2

Vstop3

T2 = T1 × P2

P1 = 573.15 × 162.5

250 = 372.5 Kb) Process 2 -> 3 is constant pressure as piston floats to T3 = To = 293.15 K

3.12 Air in a tank is at 1 MPa and room temperature of 20°C It is used to fill an

initially empty balloon to a pressure of 200 kPa, at which point the diameter is 2

m and the temperature is 20°C Assume the pressure in the balloon is linearlyproportional to its diameter and that the air in the tank also remains at 20°Cthroughout the process Find the mass of air in the balloon and the minimumrequired volume of the tank

Solution: Assume air is an ideal gas

Balloon final state: V2 = (4/3) π r3 = (4/3) π 23

= 33.51 m3

m2bal= P2 V2 / RT2 = 200× 33.51 / 0.287 × 293.15 = 79.66 kgTank must have P2 ≥ 200 kPa => m2 tank ≥ P2 VTANK /RT2

Initial mass must be enough: m1 = m2bal + m2 tank = P

3.13 A vacuum pump is used to evacuate a chamber where some specimens are dried at

50°C The pump rate of volume displacement is 0.5 m3/s with an inlet pressure of0.1 kPa and temperature 50°C How much water vapor has been removed over a 30-min period?

Solution:

Use ideal gas P << lowest P in steam tables R is from table A.5

m = m. ∆t with mass flow rate as: m.= V./v = PV./RT (ideal gas)

⇒ m = PV.∆t/RT = (0.46152 × 323.15)0.1 × 0.5 × 30×60 = 0.603 kg

3.14 An initially deflated and flat balloon is connected by a valve to a 12 m3 storage

tank containing helium gas at 2 MPa and ambient temperature, 20°C The valve is

opened and the balloon is inflated at constant pressure, Po = 100 kPa, equal to ambient pressure, until it becomes spherical at D

1 = 1 m If the balloon is largerthan this, the balloon material is stretched giving a pressure inside as

D1DThe balloon is inflated to a final diameter of 4 m, at which point the pressure

inside is 400 kPa The temperature remains constant at 20°C What is the

maximum pressure inside the balloon at any time during this inflation process?What is the pressure inside the helium storage tank at this time?

3.15 The helium balloon described in Problem 3.14 is released into the atmosphere and

rises to an elevation of 5000 m, with a local ambient pressure of Po = 50 kPa and

temperature of −20°C What is then the diameter of the balloon?

Solution:

Balloon of Problem 3.14, where now after filling D = 4 m, we have :

m1 = P1V1/RT1 = 400 (π/6) 43 /2.077 × 293.15 = 22.015 kg

P1 = 400 = 100 + C(1 - 0.25)0.25 => C = 1600For final state we have : P0 = 50 kPa, T2 = T0 = -20°C = 253.15 K

State 2: T2 and on process line for balloon, i.e the P-V relation:

By trial and error D* = 3.98 so D = D*D1 = 3.98 m

3.16 A cylinder is fitted with a 10-cm-diameter piston that is restrained by a linear spring

(force proportional to distance) as shown in Fig P3.16 The spring force constant is

80 kN/m and the piston initially rests on the stops, with a cylinder volume of 1 L.The valve to the air line is opened and the piston begins to rise when the cylinderpressure is 150 kPa When the valve is closed, the cylinder volume is 1.5 L and thetemperature is 80°C What mass of air is inside the cylinder?

Solution:

Fs = ks∆x = ks ∆V/Ap ; V1 = 1 L = 0.001 m3, Ap = π

4 0.1

2 = 0.007854 m2State 2: V

3 = 1.5 L = 0.0015 m3; T

3 = 80°C = 353.15 KThe pressure varies linearly with volume seen from a force balance as:

PAp = P0 Ap + mp g + ks(V - V0)/Ap Between the states 1 and 2 only volume varies so:

P3 = P2 + ks(V3-V2)

Ap2 = 150 +

80×103(0.0015 - 0.001)0.0078542 × 1000 = 798.5 kPa

m =

P3V3

RT3 =

798.5 × 0.00150.287 × 353.15 = 0.012 kg

3.17 Air in a tire is initially at −10°C, 190 kPa After driving awhile, the temperature goes

up to 10°C Find the new pressure You must make one assumption on your own.Solution:

Assume constant volume and that air is an ideal gas

P2 = P1 × T2/T1 = 190 × 283.15/263.15 = 204.4 kPa

3.18 A substance is at 2 MPa, 17°C in a 0.25-m3 rigid tank Estimate the mass from the

compressibility factor if the substance is a) air, b) butane or c) propane

Solution: Figure D.1 for compressibility Z and table A.2 for critical properties.Nitrogen Pr = 2/3.39 = 0.59; Tr = 290/126.2 = 2.3; Z ≈ 0.98

m = PV/ZRT = 2000 × 0.25/(0.98 × 0.2968 × 290) = 5.928 kgButane Pr = 2/3.80 = 0.526; Tr = 290/425.2 = 0.682; Z ≈ 0.085

m = PV/ZRT = 2000 × 0.25/(0.085 × 0.14304 × 290) = 141.8 kgPropane Pr = 2/4.25 = 0.47; Tr= 290/369.8 = 0.784; Z ≈ 0.08

m = PV/ZRT = 2000 × 0.25/(0.08 × 0.18855 × 290) = 114.3 kg

ln Pr

Z

T = 2.0ra

bc

T = 0.7r

T = 0.7r

3.19 Argon is kept in a rigid 5 m3 tank at −30°C, 3 MPa Determine the mass using the

compressibility factor What is the error (%) if the ideal gas model is used?

Solution: No Argon table so we use generalized chart Fig D.1

Tr = 243.15/150.8 = 1.612, Pr = 3000/4870 = 0.616 => Z ≅ 0.96

m = PVZRT =

3000 × 50.96 × 0.2081 × 243.2= 308.75 kgIdeal gas Z = 1

m = PV/RT = 296.4 kg 4% error

3.20 A bottle with a volume of 0.1 m3 contains butane with a quality of 75% and a

temperature of 300 K Estimate the total butane mass in the bottle using the

generalized compressibility chart

3.21 A mass of 2 kg of acetylene is in a 0.045 m3 rigid container at a pressure of 4.3

MPa Use the generalized charts to estimate the temperature (This becomes trialand error)

Solution:

Table A.2, A.5: Pr= 4.3/6.14 = 0.70; Tc = 308.3; R= 0.3193

v = V/m = 0.045/2 = 0.0225 m3/kgState given by (P, v) v = ZRT/P

Since Z is a function of the state Fig D.1 and thus T, we have trial and error.Try sat vapor at Pr = 0.7 => Fig D.1: Zg = 0.59; Tr = 0.94

2 at 30°C, 3 MPa Ideal Gas ( T » Tc = 155 K from A.2)

b) Methane, CH4 at 30°C, 3 MPa Ideal Gas ( T » Tc = 190 K from A.2)

c) Water, H

2O at 30°C, 3 MPa NO compressed liquid P > Psat (B.1.1)

d) R-134a at 30°C, 3 MPa NO compressed liquid P > Psat (B.5.1)e) R-134a at 30°C, 100 kPa Ideal Gas P is low < Psat (B.5.1)

ln P

TVapor

Liq

Cr.P

a, b

c, de

3.23 Determine whether water at each of the following states is a compressed liquid, a

superheated vapor, or a mixture of saturated liquid and vapor

Solution: All states start in table B.1.1 (if T given) or B.1.2 (if P given)

a 10 MPa, 0.003 m3/kg

vf = 0.001452; vg = 0.01803 m3/kg, so mixture of liquid and vapor

b 1 MPa, 190°C : T > Tsat = 179.91oC so it is superheated vapor

c 200°C, 0.1 m3/kg: v < vg = 0.12736 m3/kg, so it is two-phase

d 10 kPa, 10°C : P > Pg = 1.2276 kPa so compressed liquid

e 130°C, 200 kPa: P < Pg = 270.1 kPa so superheated vapor

f 70°C, 1 m3/kg

vf = 0.001023; vg = 5.042 m3/kg, so mixture of liquid and vapor

States shown areplaced relative to thetwo-phase region, not

to each other

PC.P

v

TC.P

v

Ta

d

ec

3.24 Determine whether refrigerant R-22 in each of the following states is a

compressed liquid, a superheated vapor, or a mixture of saturated liquid and

vapor

Solution:

All cases are seen in Table B.4.1

a 50°C, 0.05 m3/kg superheated vapor, v > vg =0.01167 at 50°C

b 1.0 MPa, 20°C compressed liquid, P > Pg = 909.9 kPa at 20°C

c 0.1 MPa, 0.1 m3/kg mixture liq & vapor, vf < v < vg at 0.1 MPa

d 50°C, 0.3 m3/kg superheated vapor, v > vg = 0.01167 at 50°C

e −20°C, 200 kPa superheated vapor, P < Pg = 244.8 kPa at -20°C

f 2 MPa, 0.012 m3/kg superheated vapor, v > vg = 0.01132 at 2 MPa

States shown areplaced relative to thetwo-phase region, not

to each other

P C.P

v

TC.P

vT

adec

b

e

dac

b

P = const.f

f

3.25 Verify the accuracy of the ideal gas model when it is used to calculate specific

volume for saturated water vapor as shown in Fig 3.9 Do the calculation for 10kPa and 1 MPa

Table B.1.2: v1 = 14.647 m3/kg so error = 0.3 %

v2 = 0.19444 m3/kg so error = 7.49 %

3.26 Determine the quality (if saturated) or temperature (if superheated) of the

following substances at the given two states:

Solution:

a) Water, H2O, use Table B.1.1 or B.1.2

1) 120°C, 1 m3

/kg => v > vg superheated vapor, T = 120 °C2) 10 MPa, 0.01 m3/kg => two-phase v < vg

x = ( 0.01 – 0.001452 ) / 0.01657 = 0.516b) Nitrogen, N2, table B.6

1) 1 MPa, 0.03 m3/kg => superheated vapor since v > vg

Interpolate between sat vapor and superheated vapor B.6.2:

T ≅ 103.73 + (0.03-0.02416)×(120-103.73)/(0.03117-0.02416) = 117 K2) 100 K, 0.03 m3/kg => sat liquid + vapor as two-phase v < vg

v = 0.03 = 0.001452 + x × 0.029764 ⇒ x = 0.959c) Ammonia, NH3, table B.2

1) 400 kPa, 0.327 m3/kg => v > vg = 0.3094 m3/kg at 400 kPa

Table B.2.2 superheated vapor T ≅ 10 °C2) 1 MPa, 0.1 m3/kg => v < vg 2-phase roughly at 25 °C

x = ( 0.1 – 0.001658 ) / 0.012647 = 0.7776d) R-22, table B.4

1) 130 kPa, 0.1 m3/kg => sat liquid + vapor as v < vg

vf ≅ 0.000716 m3/kg, vg ≅ 0.1684 m3/kg

v = 0.1 = 0.000716 + x × 0.16768 ⇒ x = 0.5922) 150 kPa, 0.17 m3/kg => v > vg superheated vapor, T ≅ 0°C

3.27 Calculate the following specific volumes

3.28 Give the phase and the specific volume.

2 T = 267°C P = 0.5 MPa Table A.5

sup vap assume ideal gas v = RT

P =

0.18892 × 540

500 = 0.204 m

3 /kg

d Air T = 20°C P = 200 kPa Table A.5

sup vap assume ideal gas v = RT

P =

0.287 × 293

200 = 0.420 m

3 /kg

to each other

P C.P

v

TC.P

vT

to each other.

P C.P

v

TC.P

vT

a, c, eb

a, c, eb

P = const.d

c H

2O T = 263 K v = 200 m3/kg Table B.1.5

sat solid + vap., P = 0.26 kPa, x = (200-0.001)/466.756 = 0.4285

d Ne P = 750 kPa v = 0.2 m3/kg; Table A.5

ideal gas, T = Pv

R =

750 × 0.20.41195 = 364.1 K

e NH

3 T = 20°C v = 0.1 m3/kg Table B.2.1

sat liq + vap , P = 857.5 kPa, x = (0.1-0.00164)/0.14758 = 0.666

States shown areplaced relative to thetwo-phase region, not

to each other

P C.P

v

TC.P

vT

3.31 Give the phase and the missing properties of P, T, v and x.

Solution:

a R-22 T = 10°C v = 0.01 m3/kg Table B.4.1

sat liq + vap. P = 680.7 kPa, x = (0.01-0.0008)/0.03391 = 0.2713

b H2O T = 350°C v = 0.2 m3/kg Table B.1.1 v > vg

sup vap. P ≅ 1.40 MPa, x = undefined

c CO2 T = 800 K P = 200 kPa Table A.5

to each other

P C.P

v

TC.P

vT

3.32 Give the phase and the missing properties of P, T, v and x These may be a little

more difficult if the appendix tables are used instead of the software

c) H2O T = 60°C, v = 0.001016 m3/kg: Table B.1.1 v < vf = 0.001017

=> compr liq. see Table B.1.4

v = 0.001015 at 5 MPa so P ≅ 0.5(5000 + 19.9) = 2.51 MPad) NH3 T = 30°C, P = 60 kPa : Table B.2.1 P < Psat

=> sup vapor interpolate in Table B.2.2

An iterpolation gives: T ≅ 68.7°C, P = 2.06 MPa

States shown areplaced relative to thetwo-phase region, not

to each other

P C.P

v

TC.P

vT

a

b, e

a

P = const.d

b, ec

c

d

3.33 What is the percent error in specific volume if the ideal gas model is used to

represent the behavior of superheated ammonia at 40°C, 500 kPa? What if thegeneralized compressibility chart, Fig D.1, is used instead?

v = ZRT/P = 0.2964 m 3 /kg ⇒ 1.4% error

3.34 What is the percent error in pressure if the ideal gas model is used to represent the

behavior of superheated vapor R-22 at 50°C, 0.03082 m3

/kg? What if thegeneralized compressibility chart, Fig D.1, is used instead (iterations needed)?Solution: Real gas behavior: P = 900 kPa from Table B.4.2

Ideal gas constant: R = R

_/M = 8.31451/86.47 = 0.096155

P = RT/v = 0.096155 × (273.15 + 50) / 0.03082

= 1008 kPa which is 12% too high

Generalized chart Fig D.1 and critical properties from A.2:

Tr = 323.2/363.3 = 0.875; Pc = 4970 kPaAssume P = 900 kPa => Pr = 0.181 => Z ≅ 0.905

v = ZRT/P = 0.905 × 0.096155 × 323.15 / 900 = 0.03125 too highAssume P = 950 kPa => Pr = 0.191 => Z ≅ 0.9

v = ZRT/P = 0.9 × 0.096155 × 323.15 / 950 = 0.029473 too low

P ≅ 900 + ( 950 − 900 ) × 0.03082 − 0.0294370.03125 − 0.029437 = 938 kPa 4.2 % high 3.35 Determine the mass of methane gas stored in a 2 m3 tank at −30°C, 3 MPa Estimate

the percent error in the mass determination if the ideal gas model is used

Error: 5.83 kg 10.9% too small

3.36 A water storage tank contains liquid and vapor in equilibrium at 110°C The distance

from the bottom of the tank to the liquid level is 8 m What is the absolute pressure

at the bottom of the tank?

Solution:

Saturated conditions from Table B.1.1: Psat = 143.3 kPa

vf = 0.001052 m3/kg ; ∆P = ghvf = 9.807 × 8

0.001052 = 74578 Pa = 74.578 kPaPbottom = Ptop + ∆P = 143.3 + 74.578 = 217.88 kPa

3.37 A sealed rigid vessel has volume of 1 m3 and contains 2 kg of water at 100°C.

The vessel is now heated If a safety pressure valve is installed, at what pressureshould the valve be set to have a maximum temperature of 200°C?

Solution:

Process: v = V/m = constant

v

1 = 1/2 = 0.5 m3/kg 2-phase200°C, 0.5 m3/kg seen in Table B.1.3 to be

between 400 and 500 kPa so interpolate

3.38 A 500-L tank stores 100 kg of nitrogen gas at 150 K To design the tank the

pressure must be estimated and three different methods are suggested Which isthe most accurate, and how different in percent are the other two?

a Nitrogen tables, Table B.6

b Ideal gas

c Generalized compressibility chart, Fig D.1

Solution:

State 1: 150 K, v = V/m = 0.5/100 = 0.005 m3/kga) Table B.6, interpolate between 3 & 6 MPa with both at 150 K:

3 MPa : v = 0.01194 6 MPa : v = 0.0042485P= 3 + (0.005-0.01194)×(6-3)/(0.0042485-0.01194) = 5.707 MPa

b) Ideal gas table A.5: P = RT

v =

0.2968 × 1500.005 = 8.904 MPac) Table A.2 Tc = 126.2 K, Pc = 3.39 MPa so Tr = 150/126.2 = 1.189

Z is a function of P so it becomes trial and error Start with P = 5.7 MPa

Pr ≅ 1.68 ⇒ Z = 0.60 ⇒ P = ZRTv = 5342 kPa

⇒ Pr = 1.58 ⇒ Z = 0.62 ⇒ P = 5520 kPa OK

ANSWER: a) is the most accurate with others off by b) 60% c) 1%

3.39 A 400-m3 storage tank is being constructed to hold LNG, liquified natural gas,

which may be assumed to be essentially pure methane If the tank is to contain90% liquid and 10% vapor, by volume, at 100 kPa, what mass of LNG (kg) willthe tank hold? What is the quality in the tank?

Vvap

vg =

0.1 × 4000.5726 = 69.9 kg

mtot = 152 612 kg, x = mvap / mtot = 4.58×10-4

(If you use computer table, vf ≅ 0.002366, vg ≅ 0.5567)

3.40 A storage tank holds methane at 120 K, with a quality of 25 %, and it warms up

by 5°C per hour due to a failure in the refrigeration system How long time will ittake before the methane becomes single phase and what is the pressure then?Solution: Use Table B.7.1

Assume rigid tank v = const = v

1= 0.002439 + 0.25×0.30367 = 0.078366All single phase when v = vg => T ≅145 K

∆t = ∆Τ/5°C ≅ (145 – 120 ) / 5 = 5 hours P = Psat= 824 kPa

3.41 Saturated liquid water at 60°C is put under pressure to decrease the volume by 1%

keeping the temperature constant To what pressure should it be compressed?

Solution: H

2O T = 60°C , x = 0.0; Table B.1.1

v = 0.99 × vf (60°C) = 0.99×0.001017 = 0.0010068 m3/kgBetween 20 & 30 MPa in Table B.1.4, P ≅ 23.8 MPa

3.42 Saturated water vapor at 60°C has its pressure decreased to increase the volume

by 10% keeping the temperature constant To what pressure should it be

expanded?

Solution:

From initial state: v = 1.10 × vg = 1.1 × 7.6707 = 8.4378 m3/kg

Interpolate at 60°C between saturated (P = 19.94 kPa) and superheated vapor

P = 10 kPa in Tables B.1.1 and B.1.3

P ≅ 19.941 + (8.4378 − 7.6707)(10-19.941)/(15.3345-7.6707) = 18.9 kPaComment: T,v ⇒ P = 18 kPa (software) v is not linear in P, more like 1/P,

so the linear interpolation in P is not very accurate

3.43 A boiler feed pump delivers 0.05 m3/s of water at 240°C, 20 MPa What is the mass

flowrate (kg/s)? What would be the percent error if the properties of saturated liquid

at 240°C were used in the calculation? What if the properties of saturated liquid at

20 MPa were used?

3.44 A glass jar is filled with saturated water at 500 kPa, quality 25%, and a tight lid is

put on Now it is cooled to −10°C What is the mass fraction of solid at this

temperature?

Solution:

Constant volume and mass ⇒ v1 = v

2 From Table B.1.2 and B.1.5:

3.45 A cylinder/piston arrangement contains water at 105°C, 85% quality with a

volume of 1 L The system is heated, causing the piston to rise and encounter alinear spring as shown in Fig P3.45 At this point the volume is 1.5 L, piston

diameter is 150 mm, and the spring constant is 100 N/mm The heating continues,

so the piston compresses the spring What is the cylinder temperature when thepressure reaches 200 kPa?

3.46 Saturated (liquid + vapor) ammonia at 60°C is contained in a rigid steel tank It is

used in an experiment, where it should pass through the critical point when thesystem is heated What should the initial mass fraction of liquid be?

1

3.47 For a certain experiment, R-22 vapor is contained in a sealed glass tube at 20°C It is

desired to know the pressure at this condition, but there is no means of measuring it,since the tube is sealed However, if the tube is cooled to −20°C small droplets ofliquid are observed on the glass walls What is the initial pressure?

Solution: R-22 fixed volume (V) & mass (m) at 20°C cool to -20°C ~ sat vapor

T

v

v = const = v

g at -20 ° C = 0.092843 m3/kg State 1: 20°C, 0.092843 m3/kg

interpolate between 250 and 300 kPa inTable B.4.2

=> P = 291 kPa

3.48 A steel tank contains 6 kg of propane (liquid + vapor) at 20°C with a volume of

0.015 m3 The tank is now slowly heated Will the liquid level inside eventually rise

to the top or drop to the bottom of the tank? What if the initial mass is 1 kg instead

V c

vc = 0.203/44.094 = 0.004604 > v1

eventually reaches sat liq

⇒ level rises to top

If m = 1 kg ⇒ v1 = 0.015 > vc then it will reach sat vap

⇒ level falls

3.49 A cylinder containing ammonia is fitted with a piston restrained by an external force

that is proportional to cylinder volume squared Initial conditions are 10°C, 90%quality and a volume of 5 L A valve on the cylinder is opened and additional

ammonia flows into the cylinder until the mass inside has doubled If at this point thepressure is 1.2 MPa, what is the final temperature?

Solution:

State 1 Table B.2.1: v

1 = 0.0016 + 0.9(0.205525 - 0.0016) = 0.18513 m3/kg

P1 = 615 kPa; V1 = 5 L = 0.005 m3m

1 = V/v = 0.005/0.18513 = 0.027 kgState 2: P2 = 1.2 MPa, Flow in so: m2 = 2 m1 = 0.054 kg

Process: Piston Fext = KV2 = PA => P = CV2 => P2 = P1 (V2/V1)2

From the process equation we then get:

3.50 A container with liquid nitrogen at 100 K has a cross sectional area of 0.5 m2.

Due to heat transfer, some of the liquid evaporates and in one hour the liquid leveldrops 30 mm The vapor leaving the container passes through a valve and a heaterand exits at 500 kPa, 260 K Calculate the volume rate of flow of nitrogen gasexiting the heater

Solution:

Properties from table B.6.1 for volume change, exit flow from table B.6.2:

∆V = A × ∆h = 0.5 × 0.03 = 0.015 m3

∆mliq = -∆V/vf = -0.015/0.001452 = -10.3306 kg ∆mvap = ∆V/vg = 0.015/0.0312 = 0.4808 kg mout = 10.3306 - 0.4808 = 9.85 kg

vexit = 0.15385 m3/kg

V. = m.vexit = (9.85 / 1h)× 0.15385 = 1.5015 m3/h = 0.02526 m 3 /min

3.51 A pressure cooker (closed tank) contains water at 100°C with the liquid volume

being 1/10 of the vapor volume It is heated until the pressure reaches 2.0 MPa.Find the final temperature Has the final state more or less vapor than the initialstate?

1 = 0.001044 + 0.0062×1.67185 = 0.01141 = v2 < vg(2MPa) so two-phase0.01141 = 0.001177 + x

2 × 0.09845 => x2 = 0.104 More vapor

T2 = Tsat(2MPa) = 212.4°C

3.52 Ammonia in a piston/cylinder arrangement is at 700 kPa, 80°C It is now cooled at

constant pressure to saturated vapor (state 2) at which point the piston is locked with

a pin The cooling continues to −10°C (state 3) Show the processes 1 to 2 and 2 to 3

on both a P–v and T–v diagram.

14

-10

3.53 A piston/cylinder arrangement is loaded with a linear spring and the outside

atmosphere It contains water at 5 MPa, 400°C with the volume being 0.1 m3 If the

piston is at the bottom, the spring exerts a force such that P

lift = 200 kPa Thesystem now cools until the pressure reaches 1200 kPa Find the mass of water, the