Thermodynamics-and-Heat-Transfer-in BOARD REVIEW MECHANICAL ENGINEERING PDF

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ME REVIEW IN THERMODYNAMICS 1. To accelerate a body at 5 m/s2 in a horizontal plane, 10 kg force is applied against a coefficient of 0.2. What is the mass of the body? a. 12 kg c. 13 kg b. 14 kg d. 15 kg

By the law of conservation of mass

3. The weight of a 100 kg mass body at a given elevation is 0.9804 kN. If the variation from the standard gravitational acceleration is 0.004 m/s2 per 1000 m, determine the elevation at this point. a. 550 m c. 560 m d. 650 m b. 660 m At a given location:

2. At a certain location, the weight of a metal is 100 N. Its weight was reduced to 16% when brought to a location where g=1.67 m/s 2. What is the local acceleration on the first location in m/s2? a. 10.8 c. 10.6 d. 10.2 b. 10.4 For location 1: For location 2:

4. A 500 kg mass is dropped from an elevation of 20 m. If the corresponding weight of the body is ½ kN, find the velocity as it hits the ground.

Thermodynamics and Heat Transfer| Dr. Rexmelle F. Decapia Jr.

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a. 20 m/s c. 22 m/s b. 24 m/s d. 26 m/s Law of Conservation of energy

6. Convert a vacuum pressure of 110mmHg into absolute pressure. Atmospheric pressure is 10.5 m of water. a. 3.7 m of water c. 45.6 m of water b. 9.1 m of water d. 99.5 m of water

7. An object weighs 1350 g in water, 1600 g in air and 1450 g in an unknown liquid. Determine the SG of the object. a. 6.7 c. 6.6 b. 6.5 d. 6.4

5. A body having a mass of 100 kg is lifted from rest by an external force of 1.5 kN. Determine the time when the body gains a velocity of 21 m/s if the local g at this point is 9.75 m/s2. a. 2 s c. 4 s b. 3 s d. 5 s

8. From the previous problem, determine the SG of the unknown liquid. c. 0.7 a. 0.6 b. 0.8 d. 0.9

9. How much power is there in the kinetic energy of the atmosphere (density = 1.217 kg/m3) at 56 kph wind velocity? Consider the section that passes through a 3-diameter circular area normal to the velocity. a. 10.21 kW c. 15.21 kW d. 17.21 kW b. 16.21 kW

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10.Calculate the quantity of heat to be transferred to 2.25 kg of iron to raise its temperature from 20o C to 240o C taking the specific heat of the iron as 0.46 kJ/kg-K a. 227.7 kJ c. 338.76 kJ b. 246.46 kJ d. 198.55 kJ 11.Determine the average cp value in kJ/kg K of a gas if 522 kJ/kg of heat is necessary to raise the temperature from 300 K to 800 K making the pressure constant. a. 1.44 c. 1.044 b. 1.038 d. 1.026

12.A steam turbine receives 1630 kg of steam per hour at 340 m/s velocity and 3550 kJ/kg enthalpy. The steam leaves at 259 m/s and 3020 kJ/kg. Which of the following most nearly equal the power output? c. 251 kW a. 242 kW b. 260kW d. 269 kW

13.What mass of nitrogen is contained in a 57m 3 tank if the pressure and temperature are 1 atm and 21oC respectively? c. 56.3 kg a. 66.1 kg b. 70.4 kg d. 41.69 kg

14.A 0.71 m3 tank contains 4.5 kg of an ideal gas. The gas has a molecular weight of 44 and is at 21oC. What is the pressure of the gas? c. 325.2 kPa a. 352.2 kPa b. 532.2kPa d. 523.2 kPa

15.A volume of 450 cm3 of air is measures at a pressure of 740 mmHg absolute and a temp of 20oC. What is the volume in cm3 at 760 mmHg absolute and 0oC? a. 516.12 c. 408.25 b. 620.76 d. 375.85 Mixed Gas Law

16.A closed vessel contains air at a pressure of 160 kN/m2 gauge and temperature of 30o C. The air

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is heated at constant volume to 60oC with the atmospheric pressure of 759mmHg. What is the final gauge pressure? a. 174 kPa c. 186 kPa b. 167kPa d. 172 kPa

17.An air bubble rises from the bottom of a well where the temp is 25oC, to the surface where the temp is 27oC. Find the percent increase in the volume of the bubble if the depth of the well is 5m. Patm is 101,528 Pa. c. 56.7 a. 49.3 b. 41.3 d. 38.6

m3 at a constant pressure of 200 kPa. Calculate the work done by the system. a. 8kJ c. 10 kJ b. 12 kJ d. 14 kJ

19.Ammonia weighing 22 kg is confined inside a cylinder equipped with a piston has an initial pressure of 413 kPa at 38o C. If 2900 kJ of heat is added to the ammonia until its pressure and temp are 413 kPa and 100 oC respectively. What is the amount of work done by the fluid in kJ? a. 667 c. 304 b. 420 d. 502 For isobaric process

At the bottom (point 1)

At the surface (point 2)

18.Gas is enclosed in a cylinder with a weighted piston as the top boundary. The gas is heated and expands from a volume of 0.04 m 3 to 0.10

20.Determine the average cp value in kJ/kg-K of a gas if 522 kJ/kg of heat is necessary to raise temp from 300 K to 800K making then pressure constant. a. 1.44 c. 1.044 b. 1.038 d. 1.026 21.Calculate the change in enthalpy as 1 kg of nitrogen is heated from 1000 K to 1500 K, assuming the nitrogen is an ideal gas at a constant pressure. The temperature dependent specific heat of nitrogen is where cp is in kJ/kmol-K, and T is in K.

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a. 600 kJ b. 800 kJ

c. 697.27 kJ d. 897.27kJ 25.The internal energy of a certain ideal gas is given by the expression

22.Find the change in enthalpy of 2kg of a gas heated from 27oC to 227oC if where T is in K and MW is 30 kg/kmol. a. 390.5 kJ c. 398.04 kJ b. 486.5 kJ d. 834.9 kJ

where P is in psia and v ft3/lb. For this gas, determine the specific heat ratio. a. 1.25 c. 1.3 d. 1.4 b. 1.35

23.The following expression relate to a particular gaseous mass: where these units obtain; P in lb/ft2, v in ft3/lb, T in oR ans h in Btu/lb. If the specific heats are temperature dependent only, find cp in Btu/lb-oR. a. 0.3 c. 0.4 b. 0.5 d. 0.6

24.From the previous problem, determine c v in Btu/lb-oR. a. 0.25 c. 0.39 d. 0.74 b. 0.48

26.A closed gaseous system undergoes a reversible process during which 25 Btu are rejected, the volume changing from 5 ft3 to 2 ft 3, and the pressure remains constant at 50 psia. Find the change of internal energy. a. -52.76 Btu c. -2.76 Btu b. 2.76 Btu

d. 52.76 Btu

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27.A rigid tank contains air at 500 kPa and 150 oC. As a result of heat transfer to the surroundings, the temp and pressure inside the tank drop to 65 oC and 400 kPa respectively. Determine the boundary work done during the process. a. 24.3 kJ/kg c. 34.2 kJ/kg b. 44.3 kJ/kg

d. 54.2 kJ/kg

28.There are 1.36 kg of gas for which R = 377 J/kgK and k = 1.25 that undergo a non-flow constant volume process from 551.6 kPa and 60OC to 1655 kPa. During the process the gas is internally stirred and there are also added 105.5 kJ of heat. Determine the change of entropy. a. 2.25 kJ/K c. 22.5 kJ/K b. 32.55 kJ/K d. 222.5 kJ/K 29.A piston cylinder device initially contains 0.4m3 of air at 100 kPa and 800oC. The air is now compressed to 0.1 m3 in such a way that the temp inside the cylinder remains constant. Determine the work done during the process. a. -55.45kJ c. 55.4 kJ b. -35.33 kJ d. 35.33 kJ 30.Air flows steadily thorough the engine at constant temperature of 400 K. Find the work per kg if the exit pressure is 1/3 of the inlet pressure and the inlet pressure is 207 kPa. a. 126.1 kJ/kg c. 12.61 kJ/kg b. 1.26 kJ/kg d. 0.126 kJ/kg

31.Work done by a substance in reversible nonflow manner in accordance with

where P is in psia. Evaluate the work done on or by the substance as the pressure increases from 10 psia to 100 psia. a. 33,157.22 ft lb c. -33,157.22 ft lb b. 43,157.22 ft lb d. -43,157.22 ft lb

32.Air having an initial pressure of 6,516 kPa and an initial volume of 0.113 m3 is compressed adiabatically to a final volume of 0.057 m3. Calculate the pressure at the end of compression. a. 16985.02 kPa c. 18726.82 kPa b. 286472.98 kPa d. 7648 kPa

33.How much work is necessary to compress air in an insulated cylinder from 0.20 m 3 to 0.01 m3. Use t1= 20oC and P1 = 100 kPa c. 115.75 kJ a. -115.75 kJ b. -145.75 kJ d. 145.75 kJ

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A Carnot engine working between 400 oC and 40oC produces 130 kJ of work. 34.Determine the cycle thermal efficiency. a. 90% c. 63.25% b. 53.49% d. 82.35%

35.Find heat rejected. a. 144.44 kJ b. 243.04 kJ

38.An air standard engine has a compression ratio of 20 and cut-off ratio of 5. If the intake air pressure and temperature are 100 kPa and 27 o C. Find the work in kJ/kg. c. 3458 a. 2165 b. 27521 d. 4563

c. 14.44 kJ d. 113.04 kJ

36.What is the change in entropy during the heat addition process? a. 0.325 kJ/K c. 0.3611 kJ/K b. 0.4615 kJ/K d. 0.2826 kJ/K

37.An Otto engine has a clearance vol of 7%. It produces 300 kW of power. What is the amount of heat rejected in kW? c. 170 a. 152 b. 160 d. 140

39.In an air standard Otto cycle, the clearance volume is 18% of the displacement volume. Find the thermal efficiency. a. 0.52 c. 0.55 d. 0.60 b. 0.53 40.In an air standard Diesel cycle, compression starts at 100 kPa and 300 K. The compression ratio is 16:1. The maximum cycle temperature is 2031 K. determine the thermal efficiency. c. 62.27 a. 60.287 b. 63.27 d. 64.27

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41.The compression ratio of an Otto cycle is 9. If the initial pressure is 150 kPa, determine the final pressure a. 1251.10 kPa c. 4251.10 kPa d. 3251.10 kPa b. 2251.10 kPa

2-3: polytropic compression from 202.65 kPa to 405.30 kPa 3-1: Isentropic expansion from 405.30 kPa to initial condition. Calculate the heat transfer from process 1 to 2 Use R=0.287kJ/kg K and k=1.4 c..-30.21kJ a. -57.29 kJ b. 70.30kJ d.100.30kJ

42.What is the final temperature after compression of a Diesel cycle if the initial temp is 32 oC and the clearance is 8%? a. 863.84 K c. 763.84 K b. 963.84 K d. 663.84 K

43.The compression ratio of petrol engine working on the constant volume cycle is 8.5. The pressure and temp at the beginning of compression are 101.325kPa and 40 oC. and the maximum pressure of the cycle is 3141.08K. taking the compression to follow the law PV1.35=C. calculate the temp at the end of compression. c. 288.97 oC a. 388.97 oC b. 355.65 oC d. 255.65 oC

45.What is the thermal efficiency of an ideal Otto cycle if the heat transferred to air during heat addition process is 600 kJ/kg and the heat rejected is 250 kJ/kg? a. 65.02% c. 76.21% d.58.33% b. 45.62%

44.One kilogram of air at pressure and temperature of 101.325 kPa and 15 oC. Initially, undergoes the following processes in the cycle. 1-2: isothermal compression to 202.65kPa

47.An Otto engine has a clearance volume of 7%. It produces 300 kW of power. What is the amount of heat rejected in kW? a. 170 c. 160 .

46.The compression ratio of an ideal Otto cycle is 6. Under the cold air standard assumption, compute the thermal efficiency of the cycle? a. 48.84% c.51.16% b. 58.29% d.60.4%

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b. 152

d. 145

48.The compression ratio of an air standard gasoline engine is 8. The initial pressure and temperature are 100 kPa and 25oC. If heat added is 1850 kJ/kg. What is the temperature after isentropic expansion? a. 1147 K c. 1399 K d. 1278 K b. 1423 K

51.An air standard Diesel cycle has a compression ratio of 18. at the beginning of the compression process, air is at 100 kPa and 15oC. If the mean effective pressure is 1362 kPa and the heat of combustion is 1800kJ/kg. Find the thermal efficiency. a. 0.496 c. 0.587 b. 0.597 d. 0.496

49.What is the final temperature after compression of a Diesel cycle if the initial temperature is 32oC and the clearance is 8%? a. 863.84 K c. 763 K b. 963.84 K d. 663.84 K

50.The volumes of states 1,2, and 3 of a Diesel cycle are 300 cm3, 30 cm3 and 90 cm3 respectively. What is the power output if the heat input is 120 kW. a. 57.63 kW c.53.67 kW b. 67.53 kW d.63.37kW

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ME REVIEWER IN HEAT TRANSFER 1. The sum for the resistance for outside wall of a house is 8 K-m2/W. For a temperature difference of 25oC across the wall and a total surface area of 150 m2, determine the heat flow through the wall. a. 469 W c. 298 W b. 159 W d. 348 W

2. An experiment is undertaken to determine the thermal conductivity of an unknown material. The material is 5 cm thick and has a diameter of 15 cm. It is placed on a hot plate of equal diameter where the surface temperature is maintained at 60oC. The outer surface temperature is 24oC, and the power used by the hot plate is 45 W. Determine the thermal conductivity of material. c. 5.33 W/m-K a. 3.53 W/m-K b. 7.53 W/m-K d. 2.53 W/m-K

3. Determine the steady state rate of heat transfer per unit area through a 4.0 cm thick homogenous slab with its two faces maintained at uniform temperatures of 38oC and 21oC. The thermal conductivity of the material is 0.19 W/m-K. a. 80.75 W/m2 c. 89.75 W/m2 b. 87.85 W/m2 d. 85.70 W/m2

4. A plane wall 0.15 m thick, of a homogenous material with k=0.40 W/m-K, has steady and uniform temperatures T1=20oC and T2=70oC. Determine the heat transfer rate in the positive x-direction per square meter of surface area. a. -133 W/m2 c. 133 W/m2 2 b. 311 W/m d. 333 W/m2 5. A laboratory furna wall is constructed of 0.2 m thick fireclay brick aving ka=1.0 W/m-K. This is covered on the ou surface with a 0.03 m thick layer of insulatin material having kb=0.07 W/m-K. The furn inner brick surface is at 1250 K and the outer surface of the insulation material is at 310 K. Calculate the steady state heat transfer rate through the wall in W/m2. a. 1495 W/m2 c. 1497 W/m2 b. 1490 W/m2 d. 1459 W/m2

6. A co e ering problem is to determine the insulatio F ickness for a specified heat transfer rate C the maximum allowable heat transfer rate ugh the wall of the furnace in the previous problem is 900 W/m2 how thick must the insulating layer be? The brick is unchanged and the same insulating material is to be used. c. 0.095 m a. 0.059 m b. 0.009 m d. 0.005 m 7. The surface of a furnace wall is at a temperature of 1200oC. The outside wall is 38oC. The furnace wall construction has 15 cm of refractory

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material, k=1.73 W/m-K, and the outside wall is 1-cm steel, k=44 W/m-K. What thickness of refractory brick must be inserted between the refractory material and the wall if the heat loss is not to exceed 0.7 kW/m2? The thermal conductivity of the brick is 0.34 W/m-K. a. 0.535 m c. 0.595 m b. 1.535 m d. 0.333 m

RM

B

S

8. A 6-in thick concrete wall having thermal conductivity k=0.50 Btu/hr-ft-oF, is exposed to air at 70oF on one side and air at 20oF on the opposite side. The heat transfer coefficients are h1=2.0 Btu/hr-ft2-oF on the 70oF and ho=10 Btu/hr-ft2-oF on the 20oF side. Determine the heat transfer rate. a. 31.25 Bt/hr-ft2 c. 33.52 Btu/hr-ft2 b. 38.23 Btu/hr-ft2 d. 42.89 Btu/hr-ft2

9. It is desired that no more than 1892 W/m 2 be conducted through a 30-cm thick wall whose average thermal conductivity is k=0.865 W/m-K; the conducted heat will be controlled by insulating one side. Find the least thickness of insulating material is k=0.346 W/m-K that will assure the heat constraint if the surfaces temperatures of the composite wall are 1150oC and 40oC.

a. 8.3 cm b. 8.8 cm

c. 1.8 cm d. 8.7 cm

10.A hollow steel sphere contains a 100 W electrical filament, and these data are known: ri=9 in, ro=12 in. The film coefficient for the inner and outer surfaces are hi=6, ho=2 Btu/hrft2-oF; the environmental temperature is 80oF. Assuming the steady state, compute the temperature inside air is a. 101.9oF c. 102.4oF o b. 110.8 F d. 101.8oF

11.A blackbody filament is heated to 2300 K. What is the maximum radiative heat flux from the filament? c. 1,654,938 W/m2 a. 1,586,698 W/m2 b. 2,586,397 W/m2 d. 3,548,798 W/m2

12.A large blackbody filament has a small opening area of 1 cm2. The radiative energy emitted by the opening is 5.67 W. Determine the temperature of the blackbody enclosure. a. 1000 K c. 1500 K b. 700 K d. 2000 K 13.After sunset, radiant energy can be sensed by a person standing near a brick wall. Such walls frequently have surface temperatures around 44oC, and typical brick emissivity values are on

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the order of 0.92. What would be the radiant thermal flux per square foot from a brick wall at this temperature? a. 527 W/m2 c. 627 W/m2 2 b. 528 W/m d. 529 W/m2

14.Asphalt pavements on hot summer days exhibit surface temperatures of approximately 50oC. Consider such a surface to emit as a blackbody and calculate the emitted radiant energy per unit square area. a. 617 W/m2 c. 716 W/m2 b. 167 W/m2 d. 761 W/m2 15.The total incident radiant energy upon a body which partially reflects, absorbs, transmits radiant energy is 2200 W/m2. Of this amount, 450 W/m2 is reflected and 900 W/m2 is absorbed by the body. Find the transmissivity. a. 0.386 c. 0.486 b. 0.287 d. 0.832

16.The filament of a 75-W light bulb may be considered a blackbody radiating into a black enclosure at 70oC. The filament diameter is 0.10 mm and length is 5 cm. Considering only radiation, determine the filament temperature. a. 3029 K c. 4029 K b. 2030 K d. 3025 K

17.What surface area must be provided by the filament of a 100-W evacuated light globe where t=2482oC and ε=0.38 for the filament? Assume the ambient temperature to be 25.6oC. a. 0.806 cm2 c. 0.803 cm2 2 b. 9.088 cm d. 0.190 cm2 18.Saturated steam at 500 K flows in a 20 cm ID , 21 cm OD pipe. The pipe is covered with 8 cm of insulation that has a thermal conductivity of 0.1 W/m-K. The pipe’s conductivity is 52 W/m-K. The ambient temperature is 300 K. The unit convective coefficient on the inside is 18 000 W/m2-K and on the outside is 12 W/m2-K. Determine the heat loss from 4 m pipe. c. 1023 W a. 821 W b. 987 W d. 432 W

19.At an average temperature of 100oC, hot air flows through a 2.5 m long tube with an inside diameter of 50 mm. The temperature of the tube is 20oC along its entire length. Convective film coefficient is 20.1 W/m2-K. a. 631.5 W c. 235.1 W b. 345.2 W d. 897.4 W

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