Thermodynamics: An Engineering Approach

Problem 1

What is the difference between dry air and atmospheric air?

Keshav Singh

Numerade Educator

00:15

Problem 2

What is the difference between the specific humidity and the relative humidity?

Keshav Singh

Numerade Educator

Problem 3

Can the water vapor in air be treated as an ideal gas? Explain.

Keshav Singh

Numerade Educator

00:14

Problem 4

Is the relative humidity of saturated air necessarily 100 percent?

Keshav Singh

Numerade Educator

Problem 5

Is it possible to obtain saturated air from unsaturated air without adding any moisture? Explain.

Keshav Singh

Numerade Educator

Problem 6

Moist air is passed through a cooling section where it is cooled and dehumidified. How do $(a)$ the specific humidity and ( $b$ ) the relative humidity of air change during this process?

Keshav Singh

Numerade Educator

01:01

Problem 7

How will (a) the specific humidity and (b) the relative humidity of the air contained in a well-sealed room change as it is heated?

Keshav Singh

Numerade Educator

Problem 8

How will (a) the specific humidity and }(b)relative humidity of the air contained in a well-sealed room change as it is cooled?

Keshav Singh

Numerade Educator

00:15

Consider a tank that contains moist air at 3 atm and whose walls are permeable to water vapor. The surrounding air at 1 atm pressure also contains some moisture. Is it possible for the water vapor to flow into the tank from surroundings? Explain.

Keshav Singh

Numerade Educator

00:21

Problem 10

Why are the chilled water lines always wrapped with vapor barrier jackets?

Keshav Singh

Numerade Educator

06:57

Problem 11

A tank contains 15 kg of dry air and 0.17 kg of water vapor at $30^{\circ} \mathrm{C}$ and $100 \mathrm{kPa}$ total pressure. Determine (a) the specific humidity, ( $b$ ) the relative humidity, and (c) the volume of the tank.

Jincy M Saji

Numerade Educator

05:26

Problem 12

Repeat Prob. $14-11$ for a temperature of $20^{\circ} \mathrm{C}.$

Jincy M Saji

Numerade Educator

05:09

Problem 13

A room contains air at $20^{\circ} \mathrm{C}$ and $98 \mathrm{kPa}$ at a relative humidity of 85 percent. Determine $(a)$ the partial pressure of dry air, $(b)$ the specific humidity of the air, and $(c)$ the enthalpy per unit mass of dry air.

Jincy M Saji

Numerade Educator

04:10

Problem 14

Repeat Prob. $14-13$ for a pressure of $85 \mathrm{kPa}$

Jincy M Saji

Numerade Educator

04:29

Problem 15

A room contains air at $85^{\circ} \mathrm{F}$ and 13.5 psia at a relative humidity of 60 percent. Determine $(a)$ the partial pressure of dry air, $(b)$ the specific humidity, and $(c)$ the enthalpy per unit mass of dry air. Answers: (a) 13.1 psia,
(b) 0.0169 lbm $\mathrm{H}_{2} \mathrm{O} / \mathrm{lbm}$ dry air
(c) 39.0 Btu/lbm dry air

Jincy M Saji

Numerade Educator

06:27

Problem 16

An $8 m^{3}-$ tank contains saturated air at $30^{\circ} \mathrm{C}, 105 \mathrm{kPa}$ Determine $(a)$ the mass of dry air, $(b)$ the specific humidity, and $(c)$ the enthalpy of the air per unit mass of the dry air.

Jincy M Saji

Numerade Educator

03:34

Problem 17

Determine the masses of dry air and the water vapor contained in a $90-\mathrm{m}^{3}$ room at $93 \mathrm{kPa}, 26^{\circ} \mathrm{C},$ and 50 percent relative humidity. Answers: $95.8 \mathrm{kg}, 1.10 \mathrm{kg}.$

Jincy M Saji

Numerade Educator

07:30

Problem 18

Humid air at $100 \mathrm{kPa}, 20^{\circ} \mathrm{C},$ and 90 percent relative humidity is compressed in a steady-flow, isentropic compressor to 800 kPa. What is the relative humidity of the air at the compressor outlet?

Jincy M Saji

Numerade Educator

Problem 19

What is the dew-point temperature?

Keshav Singh

Numerade Educator

00:12

Problem 20

Andy and Wendy both wear glasses. On a cold winter day, Andy comes from the cold outside and enters the warm house while Wendy leaves the house and goes outside. Whose glasses are more likely to be fogged? Explain.

Keshav Singh

Numerade Educator

00:14

Problem 21

In summer, the outer surface of a glass filled with iced water frequently "sweats." How can you explain this sweating?

Keshav Singh

Numerade Educator

00:17

Problem 22

In some climates, cleaning the ice off the windshield of a car is a common chore on winter mornings. Explain how ice forms on the windshield during some nights even when there is no rain or snow.

Keshav Singh

Numerade Educator

Problem 23

When are the dry-bulb and dew-point temperatures identical?

Keshav Singh

Numerade Educator

Problem 24

When are the adiabatic saturation and wet-bulb temperatures equivalent for atmospheric air?

Keshav Singh

Numerade Educator

03:50

Problem 25

After a long walk in the $12^{\circ} \mathrm{C}$ outdoors, a person wearing glasses enters a room at $25^{\circ} \mathrm{C}$ and 55 percent relative humidity. Determine whether the glasses will become fogged.

Jincy M Saji

Numerade Educator

02:48

Problem 26

Repeat Prob. $14-25$ for a relative humidity of 30 percent .

Jincy M Saji

Numerade Educator

03:21

Problem 27

A thirsty woman opens the refrigerator and picks up a cool canned drink at $40^{\circ} \mathrm{F}$. Do you think the can will "sweat" as she enjoys the drink in a room at $70^{\circ} \mathrm{F}$ and 38 percent relative humidity?

Jincy M Saji

Numerade Educator

05:39

Problem 28

The dry- and wet-bulb temperatures of atmospheric air at 95 kPa are 25 and $17^{\circ} \mathrm{C},$ respectively. Determine (a) the specific humidity, ( $b$ ) the relative humidity, and ( $c$ ) the enthalpy of the air, in $\mathrm{kJ} / \mathrm{kg}$ dry air.

Jincy M Saji

Numerade Educator

05:03

Problem 29

The air in a room has a dry-bulb temperature of $26^{\circ} \mathrm{C}$ and a wet-bulb temperature of $21^{\circ} \mathrm{C} .$ Assuming a pressure of 100 kPa, determine $(a)$ the specific humidity,
(b) the relative humidity, and ( $c$ ) the dew-point temperature. Answers: (a) $0.0138 \mathrm{kg} \mathrm{H}_{2} \mathrm{O} / \mathrm{kg}$ dry air, (b) 64.4 percent, $(c) 18.8^{\circ} \mathrm{C}.$

Jincy M Saji

Numerade Educator

06:30

Problem 30

Reconsider Prob. $14-29 .$ Determine the required properties using EES (or other) software. What would the property values be at a pressure of $300 \mathrm{kPa} ?$

Jincy M Saji

Numerade Educator

05:48

Problem 31

The air a room has a dry-bulb temperature }\end{array}$ of $75 F and a wet-bulb temperature of 65. Assuming a pressure of 14.3 psia, determine $(a)$ the specific humidity, (b) the relative humidity, and ( $c$ ) the dew-point temperature.

Jincy M Saji

Numerade Educator

06:57

Problem 32

Atmospheric air at $35^{\circ} \mathrm{C}$ flows steadily into an adiabatic saturation device and leaves as a saturated mixture at $25^{\circ} \mathrm{C} .$ Makeup water is supplied to the device at $25^{\circ} \mathrm{C}$. Atmospheric pressure is 98 kPa. Determine the relative humidity and specific humidity of the air.

Jincy M Saji

Numerade Educator

Problem 33

How do constant-enthalpy and constant-wet-bulbtemperature lines compare on the psychrometric chart?

Keshav Singh

Numerade Educator

Problem 34

At what states on the psychrometric chart are the dry-bulb, wet-bulb, and dew-point temperatures identical?

Keshav Singh

Numerade Educator

Problem 35

How is the dew-point temperature at a specified state determined on the psychrometric chart?

Keshav Singh

Numerade Educator

00:14

Problem 36

Can the enthalpy values determined from a psychrometric chart at sea level be used at higher elevations?

Keshav Singh

Numerade Educator

01:51

Problem 37

A room contains air at $1 \mathrm{atm}, 82^{\circ} \mathrm{F}$, and 70 percent relative humidity. Using the psychrometric chart, determine $(a)$ the specific humidity, $(b)$ the enthalpy (in $\mathrm{Btu} / \mathrm{lbm}$ dry air) $(c)$ the wet-bulb temperature, $(d)$ the dew-point temperature, and $(e)$ the specific volume of the air (in $\mathrm{ft}^{3} / \mathrm{lbm}$ dry air).

Keshav Singh

Numerade Educator

05:34

Problem 38

Reconsider Prob. $14-37 \mathrm{E}$. Determine the required properties using EES (or other) software instead of the psychrometric chart. What would the property values be at a location at $5000 \mathrm{ft}$ altitude?

Jincy M Saji

Numerade Educator

01:24

Problem 39

The air in a room has a pressure of 1 atm, a dry-bulb temperature of $24^{\circ} \mathrm{C},$ and a wet-bulb temperature of $17^{\circ} \mathrm{C}$ Using the psychrometric chart, determine ( $a$ ) the specific humidity, (b) the enthalpy, in $\mathrm{kJ} / \mathrm{kg}$ dry air, $(c)$ the relative humidity, $(d)$ the dew-point temperature, and $(e)$ the specific volume of the air, in $\mathrm{m}^{3} / \mathrm{kg}$ dry air.

Keshav Singh

Numerade Educator

01:34

Problem 40

Reconsider Prob. $14-39 .$ Determine the required properties using EES (or other) software instead of the psychrometric chart. What would the property values be at a location at $3000 \mathrm{m}$ altitude?

Jincy M Saji

Numerade Educator

02:01

Problem 41

Atmospheric air at a pressure of 1 atm and drybulb temperature of $28^{\circ} \mathrm{C}$ has a wet-bulb temperature of $20^{\circ} \mathrm{C} .$ Using the psychrometric chart, determine $(a)$ the relative humidity, $(b)$ the humidity ratio, $(c)$ the enthalpy, $(d)$ the dew-point temperature, and ( $e$ ) the water vapor pressure.

Keshav Singh

Numerade Educator

04:25

Problem 42

Determine the adiabatic saturation temperature of the humid air in Prob. $14-41 .$

Jincy M Saji

Numerade Educator

02:11

Problem 43

Atmospheric air at a pressure of 1 atm and drybulb temperature of $90^{\circ} \mathrm{F}$ has a dew-point temperature of $75^{\circ} \mathrm{F}$. Using the psychrometric chart, determine $(a)$ the relative humidity, $(b)$ the humidity ratio, $(c)$ the enthalpy, $(d)$ the wet-bulb temperature, and ( $e$ ) the water vapor pressure.

Keshav Singh

Numerade Educator

03:58

Problem 44

Determine the adiabatic saturation temperature of the humid air in Prob. $14-43 \mathrm{E}.$

Jincy M Saji

Numerade Educator

Problem 45

What does a modern air-conditioning system do besides heating or cooling the air?

Keshav Singh

Numerade Educator

00:13

Problem 46

How does the human body respond to $(a)$ hot weather, ( $b$ ) cold weather, and ( $c$ ) hot and humid weather?

Keshav Singh

Numerade Educator

Problem 47

What is the radiation effect? How does it affect human comfort?

Keshav Singh

Numerade Educator

00:55

Problem 48

How does the air motion in the vicinity of the human body affect human comfort?

Keshav Singh

Numerade Educator

Problem 49

Consider a tennis match in cold weather where both players and spectators wear the same clothes. Which group of people will feel colder? Why?

Keshav Singh

Numerade Educator

Problem 50

Why do you think little babies are more susceptible to cold?

Keshav Singh

Numerade Educator

Problem 51

How does humidity affect human comfort?

Keshav Singh

Numerade Educator

Problem 52

What are humidification and dehumidification?

Keshav Singh

Numerade Educator

00:59

Problem 53

What is metabolism? What is the range of metabolic rate for an average man? Why are we interested in the metabolic rate of the occupants of a building when we deal with heating and air-conditioning?

Keshav Singh

Numerade Educator

00:20

Problem 54

What is sensible heat? How is the sensible heat loss from a human body affected by the $(a)$ skin temperature,
(b) environment temperature, and ( $c$ ) air motion?

Keshav Singh

Numerade Educator

00:33

Problem 55

What is latent heat? How is the latent heat loss from the human body affected by the $(a)$ skin wettedness and $(b)$ relative humidity of the environment? How is the rate of evaporation from the body related to the rate of latent heat loss?

Keshav Singh

Numerade Educator

02:29

Problem 56

A department store expects to have 225 customers and 20 employees at peak times in summer. Determine the contribution of people to the total cooling load of the store.

Keshav Singh

Numerade Educator

01:41

Problem 57

In a movie theater in winter, 500 people, each gen erating sensible heat at a rate of $70 \mathrm{W}$, are watching a movie. The heat losses through the walls, windows, and the roof are estimated to be 130,000 Btu/h. Determine if the theater needs to be heated or cooled.

Keshav Singh

Numerade Educator

10:23

Problem 58

For an infiltration rate of 1.2 air changes per hour (ACH), determine sensible, latent, and total infiltration heat load of a building at sea level, in $\mathrm{kW}$, that is $20 \mathrm{m}$ long, $13 \mathrm{m}$ wide, and $3 \mathrm{m}$ high when the outdoor air is at $32^{\circ} \mathrm{C}$ and 35 percent relative humidity. The building is maintained at $24^{\circ} \mathrm{C}$ and 55 percent relative humidity at all times.

Jincy M Saji

Numerade Educator

03:31

Problem 59

Repeat Prob. $14-58$ for an infiltration rate of $1.8 \mathrm{ACH}$

Jincy M Saji

Numerade Educator

02:02

Problem 60

An average person produces 0.25 kg of moisture while taking a shower and $0.05 \mathrm{kg}$ while bathing in a tub. Consider a family of four who each shower once a day in a bathroom that is not ventilated. Taking the heat of vaporization of water to be $2450 \mathrm{kJ} / \mathrm{kg}$, determine the contribution of showers to the latent heat load of the air conditioner per day in summer.

Keshav Singh

Numerade Educator

04:06

Problem 61

An average $(1.82 \mathrm{kg} \text { or } 4.0 \mathrm{lbm})$ chicken has a basal metabolic rate of $5.47 \mathrm{W}$ and an average metabolic rate of $10.2 \mathrm{W}(3.78 \mathrm{W} \text { sensible and } 6.42 \mathrm{W}$ latent) during normal activity. If there are 100 chickens in a breeding room, determine the rate of total heat generation and the rate of moisture production in the room. Take the heat of vaporization of water to be $2430 \mathrm{kJ} / \mathrm{kg}.$

Jincy M Saji

Numerade Educator

00:13

Problem 62

How do relative and specific humidities change during a simple heating process? Answer the same question for a simple cooling process.

Keshav Singh

Numerade Educator

00:17

Problem 63

Why does a simple heating or cooling process appear as a horizontal line on the psychrometric chart?

Keshav Singh

Numerade Educator

09:12

Problem 64

Air enters a heating section at $95 \mathrm{kPa}, 12^{\circ} \mathrm{C},$ and 30 percent relative humidity at a rate of $6 \mathrm{m}^{3} / \mathrm{min},$ and it leaves at $25^{\circ} \mathrm{C}$. Determine $(a)$ the rate of heat transfer in the heating section and $(b)$ the relative humidity of the air at the exit.

Jincy M Saji

Numerade Educator

04:33

Problem 65

Humid air at 1 atm, $35^{\circ} \mathrm{C},$ and 45 percent relative humidity is cooled at constant pressure to the dew-point temperature. Determine the cooling, in $\mathrm{kJ} / \mathrm{kg}$ dry air, required for this process.

Jincy M Saji

Numerade Educator

06:39

Problem 66

Humid air at 40 psia, 50^ $\mathrm{F}$, and 90 percent relative humidity is heated in a pipe at constant pressure to $120^{\circ} \mathrm{F}$ Calculate the relative humidity at the pipe outlet and the amount of heat, in Btu/lbm dry air, required.

Jincy M Saji

Numerade Educator

06:21

Problem 67

Air enters a 30 -cm-diameter cooling section at $1 \mathrm{atm}$ $35^{\circ} \mathrm{C},$ and 45 percent relative humidity at $18 \mathrm{m} / \mathrm{s}$. Heat is removed from the air at a rate of $750 \mathrm{kJ} / \mathrm{min}$. Determine $(a)$ the exit temperature, $(b)$ the exit relative humidity of the air, and $\begin{array}{ll}\text { (b) } 73.1 & \text { percent, }\end{array}$
(c) the exit velocity. Answers: (a) $26.5^{\circ} \mathrm{C}$,
(c) $17.5 \mathrm{m} / \mathrm{s}$

Jincy M Saji

Numerade Educator

02:52

Problem 68

Repeat Prob. $14-67$ for a heat removal rate of $950 \mathrm{kJ} / \mathrm{min}$.

Jincy M Saji

Numerade Educator

07:23

Problem 69

A heating section consists of a 15-in-diameter duct that houses a $4-\mathrm{kW}$ electric resistance heater. Air enters the heating section at 14.7 psia, $50^{\circ} \mathrm{F}$, and 40 percent relative humidity at a velocity of $25 \mathrm{ft} / \mathrm{s}$. Determine $(a)$ the exit temperature, (b) the exit relative humidity of the air, and $(c)$ the exit velocity.

Jincy M Saji

Numerade Educator

00:12

Problem 70

Why is heated air sometimes humidified?

Keshav Singh

Numerade Educator

04:08

Problem 71

Air at $1 \mathrm{atm}, 15^{\circ} \mathrm{C},$ and 60 percent relative humidity is first heated to $20^{\circ} \mathrm{C}$ in a heating section and then humidified by introducing water vapor. The air leaves the humidifying section at $25^{\circ} \mathrm{C}$ and 65 percent relative humidity. Determine $(a)$ the amount of steam added to the air, and $(b)$ the amount of heat transfer to the air in the heating section.

Jincy M Saji

Numerade Educator

03:23

Problem 72

Air at 14.7 psia, $35^{\circ} \mathrm{F}$, and 50 percent relative humidity is first heated to $65^{\circ} \mathrm{F}$ in a heating section and then humidified by introducing water vapor. The air leaves the humidifying section at $75^{\circ} \mathrm{F}$ and 55 percent relative humidity. Determine $(a)$ the amount of steam added to the air, in $1 \mathrm{bm} \mathrm{H}_{2} \mathrm{O} / \mathrm{lbm}$ dry air, and $(b)$ the amount of heat transfer to the air in the heating section, in $\mathrm{Btu} / \mathrm{lbm}$ dry air.

Jincy M Saji

Numerade Educator

07:32

Problem 73

An air-conditioning system operates at a total pressure of 1 atm and consists of a heating section and a humidifier that supplies wet steam (saturated water vapor) at $100^{\circ} \mathrm{C}$. Air enters the heating section at $10^{\circ} \mathrm{C}$ and 70 percent relative humidity at a rate of $35 \mathrm{m}^{3} / \mathrm{min}$, and it leaves the humidifying section at $20^{\circ} \mathrm{C}$ and 60 percent relative humidity. Deter mine $(a)$ the temperature and relative humidity of air when it leaves the heating section, $(b)$ the rate of heat transfer in the heating section, and ( $c$ ) the rate at which water is added to the air in the humidifying section.

Jincy M Saji

Numerade Educator

08:18

Problem 74

$\begin{array}{lllllll}14-74 & \text { Repeat } & \text { Prob. } & 14-73 & \text { for } & \text { a } & \text { total } & \text { pressure } & \text { of }\end{array}$ 95 kPa for the airstream.

Jincy M Saji

Numerade Educator

Problem 75

Why is cooled air sometimes reheated in summer before it is discharged to a room?

Keshav Singh

Numerade Educator

02:19

Problem 76

Air enters a window air conditioner at $1 \mathrm{atm}, 32^{\circ} \mathrm{C}$ and 70 percent relative humidity at a rate of $2 \mathrm{m}^{3} / \mathrm{min}$, and it leaves as saturated air at $15^{\circ} \mathrm{C}$. Part of the moisture in the air that condenses during the process is also removed at $15^{\circ} \mathrm{C}$. Determine the rates of heat and moisture removal from the air. Answers: 97.7 kJ/min, 0.023 kg/min.

Anand Jangid

Numerade Educator

04:28

Problem 77

Humid atmospheric air at 1 atm, $90^{\circ} \mathrm{F}$, and 90 percent relative humidity is cooled to $50^{\circ} \mathrm{F}$ while the mixture pressure remains constant. Calculate the amount of water in lbm/lbm dry air, removed from the air and the cooling requirement, in Btu/lbm dry air, when the liquid water leaves the system at $60^{\circ} \mathrm{F}.$

Jincy M Saji

Numerade Educator

08:04

Problem 78

Air enters a 40 -cm-diameter cooling section at (tes) 1 atm, $32^{\circ} \mathrm{C}$, and 70 percent relative humidity at $120 \mathrm{m} / \mathrm{min}$. The air is cooled by passing it over a cooling coil through which cold water flows. The water experiences a temperature rise of $6^{\circ} \mathrm{C}$. The air leaves the cooling section saturated at $20^{\circ} \mathrm{C}$. Determine $(a)$ the rate of heat transfer, (b) the mass flow rate of the water, and ( $c$ ) the exit velocity of the air stream.

Mohammad Mehran

Numerade Educator

03:07

Problem 79

Reconsider Prob. $14-78 .$ Using EES (or other) software, develop a general solution of the problem in which the input variables may be supplied and parametric studies performed. For each set of input variables for which the pressure is atmospheric, show the process on the psychrometric chart.

Hariprasad Annamalai

Numerade Educator

11:47

Problem 80

Repeat Prob. $14-78$ for a total pressure of 95 kPa for air.

Mohammad Mehran

Numerade Educator

08:04

Problem 81

Air enters a 1-ft-diameter cooling section at 14.7 psia, $90^{\circ} \mathrm{F},$ and 60 percent relative humidity at $600 \mathrm{ft} / \mathrm{min} .$ The air is cooled by passing it over a cooling coil through which cold water flows. The water experiences a temperature rise of $14^{\circ} \mathrm{F}$ The air leaves the cooling section saturated at $70^{\circ} \mathrm{F}$. Determine (a) the rate of heat transfer, ( $b$ ) the mass flow rate of the water and $(c)$ the exit velocity of the airstream.

Mohammad Mehran

Numerade Educator

11:02

Problem 82

Reconsider Prob. 14-81E. Using EES (or other) software, study the effect of the total pressure of the air over the range 14.3 to 15.2 psia on the required results. Plot the required results as functions of air total pressure.

Khoobchandra Agrawal

Numerade Educator

11:47

Problem 83

Repeat Prob. $14-81 \mathrm{E}$ for a total pressure of 14.4 psia for air.

Mohammad Mehran

Numerade Educator

00:46

Problem 84

Air from a workspace enters an air conditioner unit at $30^{\circ} \mathrm{C}$ dry bulb and $20^{\circ} \mathrm{C}$ wet bulb. The air leaves the air conditioner and returns to the space at $20^{\circ} \mathrm{C}$ dry-bulb and $6.5^{\circ} \mathrm{C}$ dew-point temperature. If there is any, the condensate leaves the air conditioner at the temperature of the air leaving the cooling coils. The volume flow rate of the air returned to the workspace is $800 \mathrm{m}^{3} / \mathrm{min}$. Atmospheric pressure is $101 \mathrm{kPa}$ Determine the heat transfer rate from the air, in $\mathrm{kW},$ and the mass flow rate of condensate water, if any, in $\mathrm{kg} / \mathrm{h}$.

Hast Aggarwal

Numerade Educator

05:20

Problem 85

Atmospheric air from the inside of an automobile enters the evaporator section of the air conditioner at $1 \mathrm{atm}$ $27^{\circ} \mathrm{C}$ and 50 percent relative humidity. The air returns to the automobile at $10^{\circ} \mathrm{C}$ and 90 percent relative humidity. The passenger compartment has a volume of $2 \mathrm{m}^{3}$ and 5 air changes per minute are required to maintain the inside of the automobile at the desired comfort level. Sketch the psychrometric diagram for the atmospheric air flowing through the air conditioning process. Determine the dew point and wet bulb temperatures at the inlet to the evaporator section, in $^{\circ} \mathrm{C}$. Determine the required heat transfer rate from the atmospheric air to the evaporator fluid, in $\mathrm{kW}$. Determine the rate of condensation of water vapor in the evaporator section, in $\mathrm{kg} / \mathrm{min}.$

Mohammad Mehran

Numerade Educator

03:19

Problem 86

Atmospheric air at 1 atm, $32^{\circ} \mathrm{C}$, and 95 percent relative humidity is cooled to $24^{\circ} \mathrm{C}$ and 60 percent relative humidity. A simple ideal vapor-compression refrigeration system using refrigerant-134a as the working fluid is used to provide the cooling required. It operates its evaporator at $4^{\circ} \mathrm{C}$ and its condenser at a saturation temperature of $39.4^{\circ} \mathrm{C}$. The condenser rejects its heat to the atmospheric air. Calculate the energy destruction, in $\mathrm{kJ},$ in the total system per $1000 \mathrm{m}^{3}$ of dry air processed.

Khoobchandra Agrawal

Numerade Educator

06:13

Problem 87

Humid air is to be conditioned in a constant pressure process at 1 atm from $39^{\circ} \mathrm{C}$ dry bulb and 50 percent relative humidity to $17^{\circ} \mathrm{C}$ dry bulb and $10.8^{\circ} \mathrm{C}$ wet bulb. The air is first passed over cooling coils to remove all of the moisture necessary to achieve the final moisture content and then is passed over heating coils to achieve the final state.
(a) Sketch the psychometric diagram for the process.
(b) Determine the dew point temperature of the mixture at the inlet of the cooling coils and at the inlet of the heating coils.
(c) What is the net heat transfer for the entire process for this process, in $\mathrm{kJ} / \mathrm{kg}$ dry air?

Eric Mockensturm

Numerade Educator

Problem 88

What is evaporative cooling? Will it work in humid climates?

Keshav Singh

Numerade Educator

00:22

Problem 89

During evaporation from a water body to air, under what conditions will the latent heat of vaporization be equal to the heat transfer from the air?

Keshav Singh

Numerade Educator

00:28

Problem 90

Does an evaporation process have to involve heat transfer? Describe a process that involves both heat and mass transfer.

Keshav Singh

Numerade Educator

09:58

Problem 91

Air enters an evaporative cooler at $95 \mathrm{kPa}, 40^{\circ} \mathrm{C},$ and 25 percent relative humidity and exits saturated. Determine the exit temperature of air. Answer: $23.1^{\circ} \mathrm{C}.$

M Hassan Anwar

Numerade Educator

08:22

Problem 92

Air enters an evaporative cooler at 14.5 psia, $93^{\circ} \mathrm{F}$ and 30 percent relative humidity and exits saturated. Determine the exit temperature of air.

M Hassan Anwar

Numerade Educator

06:52

Problem 93

Air enters an evaporative cooler at $1 \mathrm{atm}, 40^{\circ} \mathrm{C}$ and 20 percent relative humidity at a rate of $7 \mathrm{m}^{3} / \mathrm{min},$ and it leaves with a relative humidity of 90 percent. Determine
(a) the exit temperature of the air and ( $b$ ) the required rate of water supply to the evaporative cooler.

M Hassan Anwar

Numerade Educator

03:07

Problem 94

Air enters an evaporative cooler at $1 \mathrm{atm}, 32^{\circ} \mathrm{C},$ and 30 percent relative humidity at a rate of $5 \mathrm{m}^{3} / \mathrm{min}$ and leaves at $22^{\circ} \mathrm{C} .$ Determine $(a)$ the final relative humidity and $(b)$ the amount of water added to air.

Supratim Pal

Numerade Educator

05:03

Problem 95

Air at 1 atm, $20^{8} \mathrm{C},$ and 50 percent relative humidity is first heated to $35^{\circ} \mathrm{C}$ in a heating section and then passed through an evaporative cooler where its temperature drops to $25^{\circ} \mathrm{C}$. Determine $(a)$ the exit relative humidity and $(b)$ the amount of water added to air, in $\mathrm{kg} \mathrm{H}_{2} \mathrm{O} / \mathrm{kg}$ dry air.

M Hassan Anwar

Numerade Educator

Problem 96

Two unsaturated airstreams are mixed adiabatically. It is observed that some moisture condenses during the mixing process. Under what conditions will this be the case?

Keshav Singh

Numerade Educator

Problem 97

Consider the adiabatic mixing of two airstreams. Does the state of the mixture on the psychrometric chart have to be on the straight line connecting the two states?

Keshav Singh

Numerade Educator

07:51

Problem 98

During an air-conditioning process, 900 ft^{3/min } of conditioned air at $65^{\circ} \mathrm{F}$ and 30 percent relative humidity is mixed adiabatically with $300 \mathrm{ft}^{3} / \mathrm{min}$ of outside air at $80^{\circ} \mathrm{F}$ and 90 percent relative humidity at a pressure of 1 atm. Determine ( $a$ ) the temperature, ( $b$ ) the specific humidity, and $(c)$ the relative humidity of the mixture.

M Hassan Anwar

Numerade Educator

07:24

Problem 99

Reconsider Prob. $14-98 \mathrm{E}$. Using EES (or other software, develop a general solution of the problem in which the input variables may be supplied and parametric studies performed. For each set of input variables for which the pressure is atmospheric, show the process on the psychrometric chart.

Eric Mockensturm

Numerade Educator

06:32

Problem 100

Two airstreams are mixed steadily and adiabatically. The first stream enters at $35^{\circ} \mathrm{C}$ and 30 percent relative humidity at a rate of $15 \mathrm{m}^{3} / \mathrm{min}$, while the second stream enters at $12^{\circ} \mathrm{C}$ and 90 percent relative humidity at a rate of $25 \mathrm{m}^{3} / \mathrm{min}$ Assuming that the mixing process occurs at a pressure of 1 atm, determine the specific humidity, the relative humidity, the dry-bulb temperature, and the volume flow rate of the mixture.

Mohammad Mehran

Numerade Educator

13:19

Problem 101

Repeat Prob. 14-100 for a total mixing-chamber pressure of $90 \mathrm{kPa}.$

Mohammad Mehran

Numerade Educator

05:39

Problem 102

A stream of warm air with a dry-bulb temperature of $36^{\circ} \mathrm{C}$ and a wet-bulb temperature of $30^{\circ} \mathrm{C}$ is mixed adiabatically with a stream of saturated cool air at $12^{\circ} \mathrm{C}$. The dry air mass flow rates of the warm and cool airstreams are 8 and $10 \mathrm{kg} / \mathrm{s},$ respectively. Assuming a total pressure of $1 \mathrm{atm}$ determine ( $a$ ) the temperature, ( $b$ ) the specific humidity, and (c) the relative humidity of the mixture.

M Hassan Anwar

Numerade Educator

02:02

Problem 103

Reconsider Prob. $14-102 .$ Using EES (or other $)$ software, determine the effect of the mass flow rate of saturated cool air stream on the mixture temperature, specific humidity, and relative humidity. Vary the mass flow rate of saturated cool air from 0 to $16 \mathrm{kg} / \mathrm{s}$ while maintaining the mass flow rate of warm air constant at $8 \mathrm{kg} / \mathrm{s} .$ Plot the mixture temperature, specific humidity, and relative humidity as functions of the mass flow rate of cool air, and discuss the results.

Hariprasad Annamalai

Numerade Educator

06:59

Problem 104

Saturated humid air at 1 atm and $50^{\circ} \mathrm{F}$ is to be mixed with atmospheric air at 1 atm, $90^{\circ} \mathrm{F}$, and 80 percent relative humidity, to form air at $70^{\circ} \mathrm{F}$. Determine the proportions at which these two streams are to be mixed and the relative humidity of the resulting air.

Mahnoor Amin

Numerade Educator

00:16

Problem 105

How does a natural-draft wet cooling tower work?

Keshav Singh

Numerade Educator

Problem 106

What is a spray pond? How does its performance compare to the performance of a wet cooling tower?

Keshav Singh

Numerade Educator

05:34

Problem 107

The cooling water from the condenser of a power plant enters a wet cooling tower at $40^{\circ} \mathrm{C}$ at a rate of $90 \mathrm{kg} / \mathrm{s}.$

Mohammad Mehran

Numerade Educator

05:34

Problem 108

The water is cooled to $25^{\circ} \mathrm{C}$ in the cooling tower by air that enters the tower at 1 atm, $23^{\circ} \mathrm{C}$, and 60 percent relative humidity and leaves saturated at $32^{\circ} \mathrm{C}$. Neglecting the power input to the fan, determine ( $a$ ) the volume flow rate of air into the cooling tower and $(b)$ the mass flow rate of the required makeup water.
The cooling water from the condenser of a power plant enters a wet cooling tower at $110^{\circ} \mathrm{F}$ at a rate of $100 \mathrm{lbm} / \mathrm{s}$. Water is cooled to $80^{\circ} \mathrm{F}$ in the cooling tower by air that enters the tower at 1 atm, $76^{\circ} \mathrm{F}$, and 60 percent relative humidity and leaves saturated at $95^{\circ} \mathrm{F}$. Neglecting the power input to the fan, determine ( $a$ ) the volume flow rate of air into the cooling tower and $(b)$ the mass flow rate of the required makeup water.

Mohammad Mehran

Numerade Educator

05:46

Problem 109

A wet cooling tower is to cool $60 \mathrm{kg} / \mathrm{s}$ of water from 40 to $33^{\circ} \mathrm{C}$. Atmospheric air enters the tower at 1 atm with dryand wet-bulb temperatures of 22 and $16^{\circ} \mathrm{C},$ respectively, and leaves at $30^{\circ} \mathrm{C}$ with a relative humidity of 95 percent. Using the psychrometric chart, determine $(a)$ the volume flow rate of air into the cooling tower and ( $b$ ) the mass flow rate of the
(a) $30.3 \mathrm{m}^{3} / \mathrm{s}$
(b) $0.605 \mathrm{kg} / \mathrm{s}$

Mohammad Mehran

Numerade Educator

09:14

Problem 110

A wet cooling tower is to cool $25 \mathrm{kg} / \mathrm{s}$ of cooling water from 40 to $30^{\circ} \mathrm{C}$ at a location where the atmospheric pressure is 96 kPa. Atmospheric air enters the tower at $20^{\circ} \mathrm{C}$ and 70 percent relative humidity and leaves saturated at $35^{\circ} \mathrm{C}$. Neglecting the power input to the fan, determine
(a) the volume flow rate of air into the cooling tower and
(b) the mass flow rate of the required makeup water.

Mohammad Mehran

Numerade Educator

04:15

Problem 111

Water enters a cooling tower at $95^{\circ} \mathrm{F}$ and at a rate of $3 \mathrm{lbm} / \mathrm{s},$ and leaves at $80^{\circ} \mathrm{F}$. Humid air enters this tower at 1 atm and $65^{\circ} \mathrm{F}$ with a relative humidity of 30 percent and leaves at $75^{\circ} \mathrm{F}$ with relative humidity of 80 percent. Determine the mass flow rate of dry air through this tower.

Mohammad Mehran

Numerade Educator

12:18

Problem 112

How much work potential, in $\mathrm{Btu} / \mathrm{lbm}$ dry air, is lost in the cooling tower of Prob. $14-111 \mathrm{E}$. Take $T_{0}=65^{\circ} \mathrm{F}.$

Mohammad Mehran

Numerade Educator

06:27

Problem 113

Dry air whose molar analysis is 78.1 percent $\mathrm{N}_{2}$ 20.9 percent $\mathrm{O}_{2},$ and 1 percent Ar flows over a water body until it is saturated. If the pressure and temperature of air remain constant at 1 atm and $25^{\circ} \mathrm{C}$ during the process, determine $(a)$ the molar analysis of the saturated air and $(b)$ the density of air before and after the process. What do you conclude from your results?

Mohammad Mehran

Numerade Educator

02:28

Problem 114

The relative humidity of air at $80^{\circ} \mathrm{F}$ and 14.7 psia is increased from 25 to 75 percent during a humidification process at constant temperature and pressure. Determine the percent error involved in assuming the density of air to have remained constant.

M Hassan Anwar

Numerade Educator

03:51

Problem 115

The condensation of the water vapor in compressedair lines is a major concern in industrial facilities, and the compressed air is often dehumidified to avoid the problems associated with condensation. Consider a compressor that compresses ambient air from the local atmospheric pressure of 92 kPa to a pressure of 800 kPa (absolute). The compressed air is then cooled to the ambient temperature as it flows through the compressed-air lines. Disregarding any pressure losses, determine if there will be any condensation in the compressed-air lines on a day when the ambient air is at $20^{\circ} \mathrm{C}$ and 50 percent relative humidity.

M Hassan Anwar

Numerade Educator

02:17

Problem 116

The capacity of evaporative coolers is usually expressed in terms of the flow rate of air in $\mathrm{ft}^{3} / \mathrm{min}(\text { or } \mathrm{cfm})$ and a practical way of determining the required size of an evaporative cooler for an 8 -ft-high house is to multiply the floor area of the house by 4 (by 3 in dry climates and by 5 in humid climates). For example, the capacity of an evaporative cooler for a 30 -ft-long, 40 -ft-wide house is $1200 \times 4=4800$ cfm. Develop an equivalent rule of thumb for the selection of an evaporative cooler in SI units for 2.4 -m-high houses whose floor areas are given in $\mathrm{m}^{2}.$

Mahnoor Amin

Numerade Educator

04:39

Problem 117

A cooling tower with a cooling capacity of 30 tons $(105 \mathrm{kW})$ is claimed to evaporate $4000 \mathrm{kg}$ of water per day. Is this a reasonable claim?

M Hassan Anwar

Numerade Educator

01:54

Problem 118

The air-conditioning costs of a house can be reduced by up to 10 percent by installing the outdoor unit (the condenser) of the air conditioner at a location shaded by trees and shrubs. If the air-conditioning costs of a house are $\$ 500$ a year, determine how much the trees will save the home owner in the 20 -year life of the system.

Supratim Pal

Numerade Educator

00:57

Problem 119

The thermostat setting of a house can be lowered by $2^{\circ} \mathrm{F}$ by wearing a light long-sleeved sweater, or by $4^{\circ} \mathrm{F}$ by wearing a heavy long-sleeved sweater for the same level of comfort. If each $^{\circ} \mathrm{F}$ reduction in thermostat setting reduces the heating cost of a house by 4 percent at a particular location, determine how much the heating costs of a house can be reduced by wearing heavy sweaters if the annual heating cost of the house is $\$ 600$.

Keshav Singh

Numerade Educator

03:14

Problem 120

A typical winter day in Moscow has a temperature of $0^{\circ} \mathrm{C}$ and a relative humidity of 40 percent. What is the relative humidity inside a dacha that has air that has been heated to $18^{\circ} \mathrm{C} ?$

M Hassan Anwar

Numerade Educator

07:57

Problem 121

The relative humidity inside dacha of Prob. 14-120 is to be brought to 50 percent by evaporating water at $20^{\circ} \mathrm{C}$ How much heat, in $\mathrm{kJ},$ is required for this purpose per $\mathrm{m}^{3}$ of air in the dacha?

M Hassan Anwar

Numerade Educator

08:22

Problem 122

During a summer day in Phoenix, Arizona, the air is at 1 atm, $110^{\circ} \mathrm{F}$, and 15 percent relative humidity. Water at $70^{\circ} \mathrm{F}$ is evaporated into this air to produce air at $75^{\circ} \mathrm{F}$ and 80 percent relative humidity. How much water, in $\mathrm{lbm} / \mathrm{lbm}$ dry air, is required and how much cooling, in Btu/lbm dry air, has been produced?

M Hassan Anwar

Numerade Educator

05:12

Problem 123

If the system of Prob. $14-122 \mathrm{E}$ is operated as an adiabatic system and the air produced by this system has a relative humidity of 70 percent, what is the temperature of the air produced? Answer: $79.6^{\circ} \mathrm{F}.$

Mahnoor Amin

Numerade Educator

05:02

Problem 124

A $1.8-m^{3}$ tank contains saturated air at $20^{\circ} \mathrm{C}$ and 90 kPa. Determine $(a)$ the mass of the dry air, $(b)$ the specific humidity, and $(c)$ the enthalpy of the air per unit mass of the dry air.

M Hassan Anwar

Numerade Educator

01:30

Problem 125

Reconsider Prob. 14-124. Using EES (or other $)$ software, determine the properties of the air at the initial state. Study the effect of heating the air at constant volume until the pressure is 110 kPa. Plot the required heat transfer, in $\mathrm{kJ}$, as a function of pressure.

Manik Pulyani

Numerade Educator

05:08

Problem 126

Air at 15 psia, $60^{\circ} \mathrm{F}$, and 70 percent relative humidity flows in an 6 -in diameter duct at a velocity of 35 ft/s. Determine ( $a$ ) the dew-point temperature, ( $b$ ) the volume flow rate of air, and $(c)$ the mass flow rate of dry air.

M Hassan Anwar

Numerade Educator

04:40

Problem 127

Air flows steadily through an isentropic nozzle. The air enters the nozzle at $35^{\circ} \mathrm{C}, 200 \mathrm{kPa}$ and 50 percent relative humidity. If no condensation is to occur during the expansion process, determine the pressure, temperature, and velocity of the air at the nozzle exit.

M Hassan Anwar

Numerade Educator

09:05

Problem 128

Air enters a cooling section at $97 \mathrm{kPa}, 35^{\circ} \mathrm{C},$ and 30 percent relative humidity at a rate of $6 \mathrm{m}^{3} / \mathrm{min},$ where it is cooled until the moisture in the air starts condensing. Determine $(a)$ the temperature of the air at the exit and $(b)$ the rate of heat transfer in the cooling section.

M Hassan Anwar

Numerade Educator

04:00

Problem 129

Outdoor air enters an air-conditioning system at $10^{\circ} \mathrm{C}$ and 70 percent relative humidity at a steady rate of $26 \mathrm{m}^{3} / \mathrm{min},$ and it leaves at $25^{\circ} \mathrm{C}$ and 55 percent relative humidity. The outdoor air is first heated to $18^{\circ} \mathrm{C}$ in the heating section and then humidified by the injection of hot steam in the humidifying section. Assuming the entire process takes place at a pressure of 1 atm, determine ( $a$ ) the rate of heat supply in the heating section and $(b)$ the mass flow rate of steam required in the humidifying section.

Mohammad Mehran

Numerade Educator

05:13

Problem 130

Humid air at $101.3 \mathrm{kPa}, 36^{\circ} \mathrm{C}$ dry bulb and 65 percent relative humidity is cooled at constant pressure to a temperature $10^{\circ} \mathrm{C}$ below its dew-point temperature. Sketch the psychrometric diagram for the process and determine the heat transfer from the air, in $\mathrm{kJ} / \mathrm{kg}$ dry air.

Mohammad Mehran

Numerade Educator

08:13

Problem 131

Air enters an air-conditioning system that uses refrigerant-134a at $30^{\circ} \mathrm{C}$ and 70 percent relative humidity at a rate of $4 \mathrm{m}^{3} / \mathrm{min}$. The refrigerant enters the cooling section at $700 \mathrm{kPa}$ with a quality of 20 percent and leaves as saturated vapor. The air is cooled to $20^{\circ} \mathrm{C}$ at a pressure of 1 atm. Determine $(a)$ the rate of dehumidification, $(b)$ the rate of heat transfer, and $(c)$ the mass flow rate of the refrigerant.

Dading Chen

Numerade Educator

11:47

Problem 132

Repeat Prob. $14-131$ for a total pressure of $90 \mathrm{kPa}$ for air.

Mohammad Mehran

Numerade Educator

07:53

Problem 133

An air-conditioning system operates at a total pressure of 1 atm and consists of a heating section and an evaporative cooler. Air enters the heating section at $15^{\circ} \mathrm{C}$ and 55 percent relative humidity at a rate of $30 \mathrm{m}^{3} / \mathrm{min},$ and it leaves the evaporative cooler at $25^{\circ} \mathrm{C}$ and 45 percent relatively humidity. Determine ( $a$ ) the temperature and relative humidity of the air when it leaves the heating section, $(b)$ the rate of heat transfer in the heating section, and $(c)$ the rate of water added to air in the evaporative cooler.

M Hassan Anwar

Numerade Educator

03:19

Problem 134

Reconsider Prob. $14-133 .$ Using EES (or other) software, study the effect of total pressure in the range 94 to $100 \mathrm{kPa}$ on the results required in the problem. Plot the results as functions of total pressure.

Naman Kumar

Numerade Educator

11:55

Problem 135

Repeat Prob. $14-133$ for a total pressure of $96 \mathrm{kPa}.$

Mohammad Mehran

Numerade Educator

04:50

Problem 136

Conditioned air at $13^{\circ} \mathrm{C}$ and 90 percent relative humidity is to be mixed with outside air at $34^{\circ} \mathrm{C}$ and 40 percent relative humidity at 1 atm. If it is desired that the mixture have a relative humidity of 60 percent, determine ( $a$ ) the ratio of the dry air mass flow rates of the conditioned air to the outside air and $(b)$ the temperature of the mixture.

M Hassan Anwar

Numerade Educator

06:30

Problem 137

Reconsider Prob. 14-136. Determine the desired quantities using EES (or other) software instead of the psychrometric chart. What would the answers be at a location at an atmospheric pressure of $80 \mathrm{kPa} ?$

Jincy M Saji

Numerade Educator

09:14

Problem 138

A natural-draft cooling tower is to remove $70 \mathrm{MW}$ of waste heat from the cooling water that enters the tower at $42^{\circ} \mathrm{C}$ and leaves at $30^{\circ} \mathrm{C}$. Atmospheric air enters the tower at 1 atm with dry- and wet-bulb temperatures of 23 and $16^{\circ} \mathrm{C},$ respectively, and leaves saturated at $32^{\circ} \mathrm{C} .$ Determine $(a)$ the mass flow rate of the cooling water
(b) the volume flow rate of air into the cooling tower, and $(c)$ the mass flow rate of the required makeup water.

Mohammad Mehran

Numerade Educator

03:07

Problem 139

Reconsider Prob. $14-138 .$ Using EES $($ or other software, investigate the effect of air inlet wet-bulb temperature on the required air volume flow rate and the makeup water flow rate when the other input data are the stated values. Plot the results as functions of wet- bulb temperature.

Hariprasad Annamalai

Numerade Educator

03:40

Problem 140

A room is filled with saturated moist air at $25^{\circ} \mathrm{C}$ and a total pressure of $100 \mathrm{kPa}$. If the mass of dry air in the room is $100 \mathrm{kg},$ the mass of water vapor is
$(a) 0.52 \mathrm{kg}$
$(b) 1.97 \mathrm{kg}$
$(c) 2.96 \mathrm{kg}$
$(d) 2.04 \mathrm{kg}$
$(e) 3.17 \mathrm{kg}$

Sanu Kumar

Numerade Educator

02:53

Problem 141

A room contains 65 kg of dry air and 0.6 kg of water vapor at $25^{\circ} \mathrm{C}$ and $90 \mathrm{kPa}$ total pressure. The relative humidity of air in the room is
$(a) 3.5 \%$
$(b) 41.5 \%$
$(c) 55.2 \%$
$(d) 60.9 \%$
$(e) 73.0 \%$

M Hassan Anwar

Numerade Educator

03:11

Problem 142

A $40-m^{3}$ room contains air at $30^{\circ} \mathrm{C}$ and a total pressure of $90 \mathrm{kPa}$ with a relative humidity of 75 percent. The mass of dry air in the room is
$(a) 24.7 \mathrm{kg}$
$(b) 29.9 \mathrm{kg}$
$(c) 39.9 \mathrm{kg}$
$(d) 41.4 \mathrm{kg}$
$(e) 52.3 \mathrm{kg}$

M Hassan Anwar

Numerade Educator

02:10

Problem 143

A room contains air at $30^{\circ} \mathrm{C}$ and a total pressure of $96.0 \mathrm{kPa}$ with a relative humidity of 75 percent. The partial pressure of dry air is
$(a) 82.0 \mathrm{kPa}$
$(b) 85.8 \mathrm{kPa}$
$(c) 92.8 \mathrm{kPa}$
$(d) 90.6 \mathrm{kPa}$
$(e) 72.0 \mathrm{kPa}$

M Hassan Anwar

Numerade Educator

02:27

Problem 144

The air in a house is at $25^{\circ} \mathrm{C}$ and 65 percent relative humidity. Now the air is cooled at constant pressure. The temperature at which the moisture in the air will start condensing is
$(a) 7.4^{\circ} \mathrm{C}$
$(b) 16.3^{\circ} \mathrm{C}$
$(c) 18.0^{\circ} \mathrm{C}$
$(d) 11.3^{\circ} \mathrm{C}$
$(e) 20.2^{\circ} \mathrm{C}$

Mahnoor Amin

Numerade Educator