Thermodynamics: An Engineering Approach
8th Edition
ISBN: 9780073398174
Author: Yunus A. Cengel Dr., Michael A. Boles
Publisher: McGraw-Hill Education
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Chapter 14.7, Problem 21P
In summer, the outer surface of a glass filled with iced water often “sweats.” How can you explain this sweating?
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A conditioned space receives warm, humidified air during winter air conditioning in order to maintain 20 °C and 30% relative humidity. The space experiences an infiltration rate of 0.3 kg/s of outdoor air and an additional sensible heat loss of 25 kW. The outdoor air is saturated at a temperature of –20 °C (see the table of properties of saturated air at atmospheric pressure of 101.325 kPa). If conditioned air is supplied at 40 °C dry-bulb temperature, what must the wetbulb temperature of supply air be in o
The air in a room has a dry-bulb temperature of 90 F and a wet-bulb temperature of 60 F. Assume a pressure of 1 atm
total pressure.
In the question that follows, select the answer that is closest to the true value.
What is the dew point temperature in units of F ?
Define the range of permissible values for the barometric pressure, relative humidity, and temperature in your environment.
Chapter 14 Solutions
Thermodynamics: An Engineering Approach
Ch. 14.7 - What is the difference between dry air and...Ch. 14.7 - What is the difference between the specific...Ch. 14.7 - Can the water vapor in air be treated as an ideal...Ch. 14.7 - Is the relative humidity of saturated air...Ch. 14.7 - Is it possible to obtain saturated air from...Ch. 14.7 - Moist air is passed through a cooling section...Ch. 14.7 - How will (a) the specific humidity and (b) the...Ch. 14.7 - Prob. 8PCh. 14.7 - Consider a tank that contains moist air at 3 atm...Ch. 14.7 - Why are the chilled water lines always wrapped...
Ch. 14.7 - A tank contains 15 kg of dry air and 0.17 kg of...Ch. 14.7 - Prob. 12PCh. 14.7 - Prob. 13PCh. 14.7 - 14–13 A room contains air at 20°C and 98 kPa at a...Ch. 14.7 - A room contains air at 85F and 13.5 psia at a...Ch. 14.7 - An 8-m3 tank contains saturated air at 30C, 105...Ch. 14.7 - Prob. 17PCh. 14.7 - Prob. 18PCh. 14.7 - Prob. 19PCh. 14.7 - Andy and Wendy both wear glasses. On a cold winter...Ch. 14.7 - In summer, the outer surface of a glass filled...Ch. 14.7 - In some climates, cleaning the ice off the...Ch. 14.7 - Prob. 23PCh. 14.7 - Prob. 24PCh. 14.7 - Prob. 25PCh. 14.7 - Prob. 26PCh. 14.7 - A thirsty woman opens the refrigerator and picks...Ch. 14.7 - Prob. 28PCh. 14.7 - The air in a room has a dry-bulb temperature of...Ch. 14.7 - Prob. 31PCh. 14.7 - Prob. 32PCh. 14.7 - How do constant-enthalpy and...Ch. 14.7 - At what states on the psychrometric chart are the...Ch. 14.7 - How is the dew-point temperature at a specified...Ch. 14.7 - Can the enthalpy values determined from a...Ch. 14.7 - Prob. 37PCh. 14.7 - Prob. 39PCh. 14.7 - Prob. 41PCh. 14.7 - Prob. 42PCh. 14.7 - Prob. 43PCh. 14.7 - Prob. 44PCh. 14.7 - What does a modern air-conditioning system do...Ch. 14.7 - How does the human body respond to (a) hot...Ch. 14.7 - Prob. 47PCh. 14.7 - How does the air motion in the vicinity of the...Ch. 14.7 - Consider a tennis match in cold weather where both...Ch. 14.7 - Prob. 50PCh. 14.7 - Prob. 51PCh. 14.7 - Prob. 52PCh. 14.7 - What is metabolism? What is the range of metabolic...Ch. 14.7 - What is sensible heat? How is the sensible heat...Ch. 14.7 - Prob. 55PCh. 14.7 - Prob. 56PCh. 14.7 - Prob. 57PCh. 14.7 - Prob. 58PCh. 14.7 - Repeat Prob. 1459 for an infiltration rate of 1.8...Ch. 14.7 - An average person produces 0.25 kg of moisture...Ch. 14.7 - An average (1.82 kg or 4.0 lbm) chicken has a...Ch. 14.7 - How do relative and specific humidities change...Ch. 14.7 - Prob. 63PCh. 14.7 - Prob. 64PCh. 14.7 - Prob. 65PCh. 14.7 - Humid air at 40 psia, 50F, and 90 percent relative...Ch. 14.7 - Air enters a 30-cm-diameter cooling section at 1...Ch. 14.7 - Prob. 68PCh. 14.7 - Prob. 69PCh. 14.7 - Why is heated air sometimes humidified?Ch. 14.7 - Air at 1 atm, 15C, and 60 percent relative...Ch. 14.7 - Prob. 72PCh. 14.7 - An air-conditioning system operates at a total...Ch. 14.7 - Prob. 74PCh. 14.7 - Why is cooled air sometimes reheated in summer...Ch. 14.7 - Prob. 76PCh. 14.7 - Prob. 77PCh. 14.7 - Air enters a 40-cm-diameter cooling section at 1...Ch. 14.7 - Repeat Prob. 1479 for a total pressure of 88 kPa...Ch. 14.7 - Prob. 81PCh. 14.7 - Prob. 83PCh. 14.7 - Prob. 84PCh. 14.7 - Prob. 85PCh. 14.7 - Atmospheric air at 1 atm, 32C, and 95 percent...Ch. 14.7 - Prob. 88PCh. 14.7 - Prob. 89PCh. 14.7 - Does an evaporation process have to involve heat...Ch. 14.7 - Prob. 93PCh. 14.7 - Prob. 94PCh. 14.7 - Air at 1 atm, 20C, and 70 percent relative...Ch. 14.7 - Two unsaturated airstreams are mixed...Ch. 14.7 - Consider the adiabatic mixing of two airstreams....Ch. 14.7 - Prob. 98PCh. 14.7 - Two airstreams are mixed steadily and...Ch. 14.7 - A stream of warm air with a dry-bulb temperature...Ch. 14.7 - Prob. 104PCh. 14.7 - How does a natural-draft wet cooling tower work?Ch. 14.7 - What is a spray pond? How does its performance...Ch. 14.7 - The cooling water from the condenser of a power...Ch. 14.7 - Prob. 108PCh. 14.7 - A wet cooling tower is to cool 60 kg/s of water...Ch. 14.7 - Prob. 110PCh. 14.7 - Prob. 111PCh. 14.7 - Prob. 112PCh. 14.7 - Prob. 113RPCh. 14.7 - Prob. 114RPCh. 14.7 - Prob. 115RPCh. 14.7 - Prob. 116RPCh. 14.7 - Prob. 117RPCh. 14.7 - Prob. 118RPCh. 14.7 - Prob. 119RPCh. 14.7 - Prob. 120RPCh. 14.7 - 14–121 The relative humidity inside dacha of Prob....Ch. 14.7 - Prob. 122RPCh. 14.7 - Prob. 124RPCh. 14.7 - 14–126E Air at 15 psia, 60°F, and 70 percent...Ch. 14.7 - Prob. 127RPCh. 14.7 - Air enters a cooling section at 97 kPa, 35C, and...Ch. 14.7 - Prob. 129RPCh. 14.7 - Humid air at 101.3 kPa, 36C dry bulb and 65...Ch. 14.7 - 14–131 Air enters an air-conditioning system that...Ch. 14.7 - Prob. 132RPCh. 14.7 - Prob. 133RPCh. 14.7 - Conditioned air at 13C and 90 percent relative...Ch. 14.7 - Prob. 138RPCh. 14.7 - A room is filled with saturated moist air at 25C...Ch. 14.7 - Prob. 141FEPCh. 14.7 - A 40-m3 room contains air at 30C and a total...Ch. 14.7 - Prob. 143FEPCh. 14.7 - The air in a house is at 25C and 65 percent...Ch. 14.7 - On the psychrometric chart, a cooling and...Ch. 14.7 - On the psychrometric chart, a heating and...Ch. 14.7 - An airstream at a specified temperature and...Ch. 14.7 - Prob. 148FEPCh. 14.7 - Air at a total pressure of 90 kPa, 15C, and 75...
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- A fixed mass of air has a volume of 2.2 m3 and a pressure of 98 kPa. The dry-bulb temperature and degree of saturation of the air are 28°C and 55% respectively. -Calculate the relative humidity in %-The partial pressure of dry air in kPa-The partial pressure of water vapor in kPa-The mass of dry air in kg-The mass of water vapor in kgarrow_forwardAn air-conditioned classroom in Texas is maintained at 72ºF in the summer. The students attend classes in shorts, sandals, and tee shirts and are quite comfortable. In the same classroom during the winter, the same students wear wool slacks, long-sleeve shirts, and sweaters, and are equally comfortable with the room temperature maintained at 75ºF. Assuming that humidity is not a factor, explain this apparent anomaly in "temperature comfort."arrow_forward3. What is the percent moisture of saturated water at 70 psia and h = 1026.4264 BTU/lb?arrow_forward
- Proper indoor ventilation is important to lower the risk of infection from the SARS-CoV-2 virus. The air in a room (28.0°C and 30% humidity) with a volume of 96.6 m3 must be replaced every 5 minutes. Outside air at 38.0°C and 70% humidity is chilled to remove some of its water content and then dehumidified to the required temperature. What is the volumetric flow rate (in m3/min) of the humid air entering the chiller? How many kg of water per kg of dry air is removed from the dehumidification process? To what temperature (in °C) should the outside air be chilled?arrow_forwardcan u explain and be fast pleasearrow_forwardAir at 30 ºC with a dew point of 14ºC enters a textile dryer at a rate of 15.3 m3/min and leaves saturated. The dryer operates adiabatically. Use the psychrometric chart to determine the absolute humidity and humid volume of the entering air, and then use the results to determine the flow rate of dry air (kg/min) through the dryer, thefinal temperature of the air, and the rate (kg/min) at which water is evaporated in the dryer.arrow_forward
- 1. In the process of air conditioning in a humidifier, the air at a dry bulb temperature of 20 °C and 25% RH increases its RH to 40%. Determine the amount of moisture added in the humidifier per kg of dry air. = (kg water/kg air). 2. The air has a dry bulb temperature of 34 °C and a wet bulb temperature of 22°C. The liquid is heated in a heater so that the dry bulb temperature increases to 80 °C. Then the air is passed through the corn kernels to dry. The air coming out of the corn kernels is at bulb temperature. dry 55 °C Then this air is passed to the dehumidifier to reduce its RH to 10%. Draw the course of the air change process on a psychrometric diagram. The rate of air flow through the corn kernels and dehumidifier is 4.0 m/s and the cross-sectional diameter of the pile is 0.7 m. a) Determine the amount of water content lost from the pile of corn kernels (in grams of water/second) b) Determine the amount of water content lost from the air when passing through the…arrow_forwardAir at a temperature of 26.7C and a total pressure of 200 kPa contains water vapor with a partial pressure of 2.8 kPa. Determine: (a) the percentage humidity, (b) relative humidity, (c) absolute humidity (d) humid heat in kJ/kg-K (e) wet bulb temperature, and (f) humid volume. Ans: (a) 79.7% (b) 80% (c) 0.00881 (d) 1.0215 (e) 21.2C (f) 0.4435 m3/kg d.a.arrow_forwardAtmospheric air at a pressure of 1 atm and dry-bulb temperature of 28°C has a dew-point temperature of 20°C. Using the psychrometric chart, determine the adiabatic saturation temperature of the humid air. 1 atm 28°C To=20°C Air Water Humidifier 100% The adiabatic saturation temperature of the humid air is °C.arrow_forward
- For Questions 6 and 7 The dry-bulb temperature and wet-bulb temperature of a sample of air are 23°C and 18°C, respectively. The pressure of the air is 97 kPa. If the air was adiabatically saturated: Question 6 Calculate the humidity ratio in kg of vapor per kg of dry air. Round your answer to 5 decimal places. Add your answer Question 7 What is its degree of saturation in %? Round your answer to 0 decimal places. Add your answerarrow_forwardOn a summer day, in Phoenix, Arizona, the inside room temperature is maintained at 20° C while the outdoor air temperature is a sizzling 43.3° C . What is the outdoor-indoor temperature difference in (a) degrees Celsius, and (b) kelvins? Is a 1° temperature difference in Celsius equal to a 1° temperature difference in kelvins If so, why?arrow_forwardIn your own words, answer the following questions: 1. What is the dew-point temperature? 2. How does the air motion in the vicinity of the human body affect human comfort? 3. What is the difference between dry air and atmospheric air? 4. Describe the difference between mass fraction and mole fractionarrow_forward
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