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physics
thermodynamics

Questions and Answers of Thermodynamics

Repeat Problem 13–20, assuming a fouling factor Rf, i = 0.0005 m2 ( (C/W on the inner surface of the tube.Water at an average temperature of 107(C and an average velocity of 3.5 m/s flows through a
A double-pipe parallel-flow heat exchanger is to heat water (Cp = 4180 J/kg ( (C) from 25(C to 60(C at a rate of 0.2 kg/s. The heating is to be accomplished by geothermal water (Cp = 4310 J/kg ( (C)
A shell-and-tube heat exchanger with 2-shell passes and 12-tube passes is used to heat water (Cp = 4180 J/kg ( (C) in the tubes from 20(C to 70(C at a rate of 4.5 kg/s. Heat is supplied by hot oil
A double-pane window consists of two 3-mm thick layers of glass separated by a 12-mm wide stagnant air space. For specified indoors and outdoors temperatures, the rate of heat loss through the window
A composite wall consists of several horizontal and vertical layers. The left and right surfaces of the wall are maintained at uniform temperatures. The rate of heat transfer through the wall, the
A 50-m long section of a steam pipe passes through an open space at 15SYMBOL 176 \f "Symbol"C. The rate of heat loss from the steam pipe, the annual cost of this heat loss, and the thickness of
Circular aluminum fins are to be attached to the tubes of a heating system. The increase in heat transfer from the tubes per unit length as a result of adding fins is to be determined.
Two cast iron steam pipes are connected to each other through two 1-cm thick flanges exposed to cold ambient air. The average outer surface temperature of the pipe, the fin efficiency, the rate of
A) If the number of molecules in an ideal gas is doubled, by how much does the pressure change if the volume and temperature are held constant?B) If the volume of an ideal gas is halved, by how much
If the number of molecules in an ideal gas is doubled and the volume is doubled, by how much does the pressure change if the temperature is held constant?
If the number of molecules in an ideal gas is doubled, and the absolute temperature is doubled and the pressure is halved, by how much does the volume change? (Absolute temperature is simply the
What happens to the internal energy of water vapor in the air that condenses on the outside of a cold glass of water? Is work done or heat exchanged? Explain.
Use the conservation of energy to explain why the temperature of a gas increases when it is quickly compressed, whereas the temperature decreases when the gas expands.
In a isothermal process, 3700J of work is done by an ideal gas. Is this enough information to tell how much heat has been added to the system If so, how much?
Is it possible for the temperature of a system to remain constant ever though heat flows into or out of it? If so, give one or two examples.
Explain why the temperature of a gas increases when it is adiabatically compressed.
Can mechanical energy ever be transformed completely into heat or internal energy? Can the reverse happen? In each case, if you answer is no, explain why not; if yes, give one or two examples.
Can you warm a kitchen in winter by leaving the oven door open? Can you cool the kitchen on a hot summer day by leaving the refrigerator door open? Explain.
Would a definition of heat engine efficiency as e = W/QL is useful? Explain.
What plays the role of high-temperature and low-temperature areas in?(a) An internal combustion engine, and (b) A steam engine?
Which will give the greater improvement in the efficiency of a Carnot engine, a 10Co increase in the high-temperature reservoir, or a 10Co decrease in the low-temperature reservoir? Explain.
The oceans contain a tremendous amount of thermal (internal) energy. Why, in general, is it not possible to put this energy to useful work?
A gas is allowed to expand(a) Adiabatically and (b) Isothermally. In each process, does the entropy increase, decrease, or stay the same? Explain.
A gas can expand to twice its original volume either adiabatically or isothermally. Which process would result in a greater change in entropy? Explain.
Give three examples, other than those mentioned in this Chapter, of naturally occurring processes in which order goes to disorder. Discuss the absorbability of the reverse process.
Which do you think has the greater entropy, 1 kg of solid iron or 1 kg of liquid iron? Why?
(a) What happens if you remove the lid of a bottle containing chlorine gas? (b) Does the reverse process ever happen? Why or why not?(c) Can you think or two other examples of irreversibility?
You are asked to test a machine that the inventor calls an “in-room air conditioner”, a big box, standing in the middle of the room, with a cable that plugs into a power outlet. When the machine
Think up several processes (other than those already mentioned) that would obey the first law of thermodynamics but, if they actually occurred, would violate the second law.
Suppose a lot of papers are strewn all over the floor; then you stack them neatly. Does this violate the second law of thermodynamics? Explain.
The first law of thermodynamics is sometimes whimsically stated as, “You can’t get something for nothing”, and the second law as, “You can’t even break even”. Explain how these statements
Entropy is often called “time’s arrow” because it tells us in which direction natural processes occur. If a movie were run backward, name some processes that you might see that would tell you
Living organisms, as they grow, convert relatively simple food molecules into a complex structure. Is this a violation of the second law of thermodynamics?
An ideal gas expands isothermally, performing 3.40 X 103 J of work in the process. Calculate (a) The change in internal energy of the gas, and (b) The heat absorbed during this expansion.
A gas is enclosed in a cylinder fitted with a light frictionless piston and maintained at atmospheric pressure. When 1400 keal of heat is added to the gas, the volume is observed to increase slowly
One liter of air is cooled at constant pressure until its volume is halved, and then it is allowed to expand isothermally back to its original volume. Draw the process on a PV diagram.
Sketch a PV diagram of the following process::2.0L of ideal gas at atmospheric pressure are cooled at constant pressure to a volume of 1.0L, and then expanded isothermally back to 2.0L, whereupon the
A 1.0-L volume of air initially at 4.5 atm of (absolute) pressure is allowed to expand isothermally until the pressure is 1.0atm. It is then compressed at constant pressure to its initial volume, and
The pressure in an ideal gas is cut in half slowly, while being kept in a container with rigid walls. In the process, 265kJ of heat left the gas.(a) How much work was done during this process? (b)
In an engine, an almost ideal gas is compressed adiabatically to half its volume, In doing so, 1850J of work is done on the gas.(a) How much heat flows into or out of the gas?(b) What is the change
(An ideal gas expands at a constant total pressure of 3.0atm from 400mL to 660mL. Heat then flows out of the gas at constant volume, and the pressure and temperature are allowed to drop until the
One and one-half moles of an ideal monatomic gas expand adiabatically, performing 7500K of work in the process, what is the change in temperature of the gas during this expansion?
Consider the following two-step process. Heat is allowed to flow out of an ideal gas at constant volume so that its pressure drops from 2.2atm to 1.4atm. Then the gas expands at constant pressure,
The PV diagram in Fig. 15-23 shows two possible states of a system containing 1.35 moles of a monatomic ideal gas, (P1 = P2 = 455 N/m2, V1 = 2.00 m3, V2 = 8.00m3.)(a) Draw the process which depicts
When a gas in taken from a to c along the curved path in Fig. 15-24, the work done by the gas is W = €“ 35J and the heat added to the gas is Q = €“ 63 J. Along path abc, the work
In the process of taking a gas from state a to state c along the curved path shown in Fig. 15 €“ 24, 80 J of heat leaves the system and 55 J of work is done on the system.(a) Determine the
How much energy would the person of Example 15-8 transform if instead of working 11.0 h she took a noon-time break and ran for 1.0h?
Calculate the average metabolic rate or a person who sleeps 8.0h, sits at a desk 8.0h, engages in light activity 4.0h, watches television 2.0h, plays tennis 1.5 h, and runs 0.5h daily.
A person decided to lose weight by sleeping one hour less per day, using the time for light activity. How much weight (or mass) can this person expect to lose in 1 year, assuming no change in food
A hear engine exhausts 8200J of heat while performing 32000 J of useful work. What is the efficiency of this engine?
A heat engine does 9200 J of work per cycle while absorbing 22.0 keal of heat from a high-temperature reservoir. What is the efficiency of this engine?
What is the maximum efficiency of a heat engine whose operating temperature are 580oC and 380oC?
The exhaust temperature of a heat engine is 230oC. What must be the high temperature if the Carnot efficiency is to be 28%?
A nuclear power plant operates at 75% of its maximum theoretical (Carnot) efficiency between temperature of 625oC and 35oC. If the plant produces electric energy at the rate of 1.3 GW, how much
It is not necessary that a heat engine€™s hot environment be hotter than ambient temperature. Liquid nitrogen (77K) is about as cheap as bottled water. What would be the efficiency of an
A Carnot engine performs work at the rate of 440 kW while using 680 kcal of heat per second. If the temperature of the heat source is 570oC, at what temperature is the waste heat exhausted?
A Carnot engine’s operating temperatures are 210oC and 45oC. The engine’s power output is 950W. Calculate the rate of heat output.
A certain power plant puts out 550MW of electric power. Estimate the heat discharged per second, assuming that the plant has an efficiency of 38%.
A heat engine utilizes a heat source at 550oC and has an ideal (Carnot) efficiency of 28%. To increase the ideal efficiency to 35%, what must be the temperature of the heat sources?
A heat engine exhausts its heat a t35oC and has a Carnot efficiency of 39%. What exhaust temperature would enable it to achieve a Carnot efficiency of 49%?
At a steam power plant, steam engines work in pairs the output of heat from one being the approximate heat input of the second. The operating temperatures of the first are 670oC and 440oC, and of the
The low temperature of freezer cooling coli is – 15oC, and the discharge temperature is 30oC, what is the maximum theoretical coefficient of performance?
An ideal refrigerator-freezer operates with a COP = 7.0 in a 24oC room. What is the temperature inside the freezer?
A restaurant refrigerator has a coefficient of performance of 5.0. If the temperature in the kitchen outside the refrigerator is 29oC, what is the lowest temperature that could be obtained inside the
A heat pump is used to keep a house warm at 22oC. How much work is required of the pump to deliver 2800 J of heat into the house if the outdoor temperature is?(a) 0oC,(b) –15oC? Assume ideal
What volume of water at 0oC can a freezer make into ice cubes in 1.0 hour, if the coefficient of performance of the cooling unit is 7.0 and the power input is 1.0 kilowatt?
An ideal (Carnot) engine has an efficiency of 35%. If it were possible to run it backward as a heat pump, what would be its coefficient of performance?
What is the change in entropy of 250g of steam at 100oC when it is condensed to water at 100oC?
One kilogram of water is heated from 0oC to 100oC. Estimate the change in entropy of the water.
What is the change in entropy of 1.00m3 of water at 0oC when it is frozen to ice at 0oC?
If 1.00m3 of water at 0oC is frozen and cooled to -10oC by being in contact with a great deal of ice at -10oC, what would be the total change in entropy of the process?
A 10.0-kg box having an initial speed of 3.0m/s slides along a rough table and comes to rest. Estimate the total change in entropy of the universe. Assume all object are at room temperature (293K).
A falling rock has kinetic energy KE just before striking the ground and coming rest. What is the total change in entropy of the rock plus environment as a result of this collision?
An aluminum rod conducts 7.50cal/s from a heat source maintained at 240oC to a large body of water at 27oC. Calculate the rate entropy increases per unit time in this process.
1.0 kg of water at 30oC is mixed with 1.0 kg of water at 60oC in a well-insulated container. Estimate the net change in entropy of the system.
A 3.8-kg piece of aluminum at 30oC is placed in 1.0 Kg of water in s Styrofoam container at room temperature (20oC). Calculate the approximate net change in entropy of the system.
A real heat engine working between heat reservoirs at 970K and 650K produces 550J of work per cycle for a heat input of 2200 J.(a) Compare the efficiency of this real engine to that of an ideal
Calculate the probabilities, when you throw two dice, of obtaining (a) A 5, and(b) An 11.
Rank the following five-card hands in order of increasing probability;(a) Four aces and a king;(b) Six of hearts, eight of diamonds, queen of clubs, three of hearts, jack of spades;(c) Two jacks, two
Suppose that you repeatedly shake six coins in you hand and drop them on the floor. Construct a table showing the number of microstates that correspond to each microstate what is the probability of
Solar cells (Fig 15-26) can produce about 40 W of electricity per square meter of surface area of directly facing the Sun. How large an area is required to supply the needs of a house that requires
Energy may be stored for use during peak demand by pumping water to a high reservoir when demand is low and then releasing it to drive turbines when needed. Suppose water is pumped to a lake 135m
Water is stored in an artificial lake created by a dam (Fig. 15-27). The water depth is 45m at the dam, and a steady flow rate of 35m3/s is maintained through hydroelectric turbines installed near
An inventor claims to have designed and built and engine that produces 1.50MW of usable work while taking in 3.00MW of thermal energy at 425K, and rejecting 1.50MW of thermal energy at 215K. Is there
When 5.30 X 105 J of heat is added to a gas enclosed in a cylinder fitted with a light frictionless piston maintained at atmospheric pressure, the volume is observed to increase from 1.9m3 to 4.1m3.
A 4-cylinder gasoline engine has an efficiency of 0.25 and delivers 220 J of work per cycle per second,(a) What is the work done per second?(b) What is the total heat input per second from the
A “Carnot” refrigerator (the reverse of a Carnot engine) absorbs heat from the freezer compartment at a temperature of –17oC and exhausts it into the room at 25oC.(a) How much work must be done
It has been suggested that a heat engine could be developed that made use of the temperature difference between water at the surface of the ocean and that several hundred meters deep. In the tropics,
Two 1100-kg cars are traveling 95Km/h in opposite directions when they collide and are brought to rest. Estimate the change in entropy of the universe as a result of this collision. Assume T = 20oC.
A 120-g insulated aluminum cup at 15oC is filled with 140g of water at 50oC. After a few minutes, equilibrium is reached. (a) Determine the final temperature, and (b) Estimate the total change in
(a) What is the coefficient of performance of an ideal heat pump that extracts heat from 6oC air outside and deposits heat inside you house at 24oC?(b) If this heat pump operates on 1200W of
The burning of gasoline in a car releases about 3.0 X 104 kcal/gal if a car averages 41km/gal when driving 90 km/h, which requires 25 hp, what is the efficiency of the engine under those conditions?
A Carnot engine has a lower operating temperature TL = 20o C and an efficiency of 30%. By how many kelvins should the high operating temperature TH be increased to achieve an efficiency of 40%?
Calculate the work done by an ideal gas in going from state A to state C in Fig.15-28 for each of the following processes;(a) ADC,(b) ABC, and(c) AC directly
A 33% efficient power plant puts out 850MW of electrical power. Cooling towers are used to take away the exhaust heat.(a) If the air temperature is allowed to rise 7.0Co, estimate what volume of air
Suppose a power plant delivers energy at 980 MW using steam turbines. The steam goes into the turbines superheated at 625 K and deposits its unused heat in river water at 285 K. Assume that the
A 100-hp car engine operates at about 15% efficiency. Assume the engine’s water temperature of 85oC is its cold-temperature (exhaust) reservoir and 495oC is its thermal “intake” temperature
An ideal gas is placed in a tall cylindrical jar of cross-sectional area 0.080m2. A frictionless 0.10-kg movable piston is placed vertically into the jar such that the pistons weight is supported by
Metabolizing 1.0 kg of fat results in about 3.7 X 107 J of internal energy in the body. (a) In one day, how much fat does the body burn to maintain the body temperature of a person staying in bed and
An ideal air conditioner keeps the temperature inside a room at 21oC when the outside temperature is 32oC. If 5.3kW of power enters a room through the windows in the form of direct radiation from the

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