Thermodynamics 1- Sept 2017 Presentation Rev 1

THERMODYNAMICS

“Design is not just what it looks like and feels like. Design is how it works.” - Steve Jobs

PROPERTIES

PROBLEM 1

ME Board Problem The temperature of a solution is 31°C. What is this temperature in °R? A. 560.8 C. 520.8 B. 575.5 D. 547.8

Answer: 547.8

PROPERTIES

PROBLEM 2

ME Board Problem Two thermometers, one Celsius and the other Fahrenheit, are both at the same temperature, but the reading on the Fahrenheit thermometer is exactly twice that on the Celsius thermometer, what is the temperature? A. 160 °C C. 40 °C B. 80 °C D. 320 °C Answer: 160 °C

PROPERTIES

PROBLEM 3

Supposing two liquids of different densities  = 1500 kg/m3 and  = 500 kg/m3 were poured together inside a 100 L tank, filling it. If the resulting density of the mixture is 800 kg/m3, find the respective quantities of liquids used. A. 35 kg and 45 kg C. 25 kg and 55 kg B. 30 kg and 50kg D. 20 kg and 60 kg Answer: 35 kg and 45 kg

PROPERTIES

PROBLEM 4

A fluid moves in a steady flow manner between two sections in the same flowline. At section 1: A1 = 0.10 m2 , V1 = 6 m/s, 1 = 0.33 m3 /kg. At section 2: A2 = 0.2 m2 , 2 = 0.27 kg/m3 . Calculate for the velocity of flow of section 2. A. 37.63 m/s C. 40.62 m/s B. 33.67 m/s D. 46.02 m/s Answer: 33.67 m/s

PROPERTIES

PROBLEM 5

ME Board Problem A tank contains water. What is the intensity of pressure at a depth of 6 m? A.68.5 kPa C. 78 kPa B. 58.8 kPa D. 48.7 kPa

Answer: 58.8 kPa

PROPERTIES

PROBLEM 6

ME Board Problem Convert a vacuum pressure of 110 mm of mercury into absolute pressure. Atmospheric pressure is 10.5 m of H2O. A. 3.7 m of H2O C. 9.1 m of H2O B. 45.6 m of H2O D. 99.5 m of H2O Answer: 9.01 m of H2O

ENERGY

PROBLEM 7

Which of the following is equivalent to 1 chu ? A. 1400.4 ft-lb C. 9/5 Btu B. 1.899 kJ D. all of these

Answer: 1.8 Btu = 1400.4 ft-lbf = 1.899 kJ

ENERGY

PROBLEM 8

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. 16.21 kW B. 15.21 kW D. 17.21 kW Answer: 16.21 kW

ENERGY

PROBLEM 9

ME Board Problem Calculate the quantity of heat to be transferred to 2.25 kg of iron to raise its temperature from 20 C to 240 C taking the specific heat of the iron as 0.46 kJ/kgK. A. 227.7 kJ C. 246.46 kJ B. 338.76 kJ D. 198.55 kJ Answer: 227.7 kJ

ENERGY

PROBLEM 10

ME Board Problem Determine the average Cp value in kJ/kgK of a gas if 522 kJ of heat is necessary to raise the temperature from 300 K to 800 K making the pressure constant. A. 1.44 C. 1.038 B. 1.044 D. 1.026 Answer: 1.044

ENERGY

PROBLEM 11

ME Board Problem A steam turbine receives 1,630 kg of steam per hour at 340 km/s velocity and 3550 kJ/kg enthalpy. The steam leaves at 259 m/s and 3020 kJ/kg. Which of the following most nearly equals the power output? A. 242 kW C. 260 kW B. 251 kW D. 269 kW Answer: 251 kW

IDEAL GAS

PROBLEM 12

ME Board Problem What mass of nitrogen is contained in a 57 m3 tank if the pressure and temperature are 1 atm and 21 C respectively? A. 66.1 kg C. 70.4 kg B. 56.3 kg D. 41.69 kg Answer: 66.1 kg

IDEAL GAS

PROBLEM 13

ME Board Problem A 0.71 m3 tank contains 4.5 kg of an ideal gas. The gas has a molecular weight of 44 and is at 21C. What is the pressure of the gas? A. 352.2 kPa C. 532.2 kPa B. 325.2 kPa D. 523.2 kPa Answer: 352.2 kPa

IDEAL GAS

PROBLEM 14

A volume of 450 cm3 of air is measured at a pressure of 740 mm Hg absolute and a temperature of 20 C. What is the volume in cm3 at 760 mm Hg absolute and 0 C? A. 516.12 C. 620.76 B. 408.25 D. 375.85 Answer: 408.25

IDEAL GAS

PROBLEM 15

An air bubble rises from the bottom of a well where the temperature is 25 C, to the surface where the temperature is 27 C. Find the percent increase in the volume of the bubble if the depth of the well is 5 m. Atmospheric pressure is 101,528 Pa. A. 49.3 C. 41.3 B. 56.7 D. 38.6 Answer: 49.3%

ISOBARIC PROCESS

PROBLEM 16

ME Board Problem 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 m3 to 0.10 m3 at a constant pressure of 200 kPa. Calculate the work done by the system. A. 8 kJ C. 12 kJ B. 10 kJ D. 14 kJ Answer: 12 kJ

ISOBARIC PROCESS

PROBLEM 17

ME Board Problem Ammonia weighing 22 kg is confined inside a cylinder equipped with a piston has an initial pressure of 413 kPa at 38 C. If 2900 kJ of heat is added to the ammonia until its pressure and temperature are 413 kPa and 100 C respectively. What is the amount of work done by the fluid in kJ? A. 667 C. 420 B. 304 D. 502 Answer: 667

ISOBARIC PROCESS

PROBLEM 18

ME Board Problem 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 Cp = 39.06 – 512.79 T-1.5 + 1072.7 T-2 – 820.4T-3

where Cp is in kJ/kg-mol, and T is in K. A. 600 kJ C. 800 kJ B. 697.27 kJ D. 897.27 kJ Answer: 697.27 kJ

ISOMETRIC PROCESS

PROBLEM 19

A rigid tank contains air at 500 kPa and 150 degree C. As a result of heat transfer to the surroundings, the temperature and pressure inside the tank drop to 65 degree C and 400 kPa respectively. Determine the boundary work done during the process. Answer: 0

ISOMETRIC PROCESS

PROBLEM 20

There are 1.36 kg of gas for which R = 377 J/kg K and k = 1.25 that undergo a nonflow constant volume process from 551.6 kPa and 60 deg C 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. Answer: +2.25 kJ

ISOTHERMAL PROCESS

PROBLEM 21

ME Board Problem A piston cylinder device initially contains 0.4 m3 of air at 100 kPa and 80 deg C. The air is now compressed to 0.1 m3 in such a way that the temperature inside the cylinder remains constant. Determine the work done during the process. Answer: -55.45 kJ

ISOTHERMAL PROCESS

PROBLEM 22

ME Board Problem Air flows steadily through an engine at constant temperature of 400 K. Find the work per kg if the exit pressure is one – third of the inlet pressure and the inlet pressure is 207 kPa. Answer: +126.12 kJ/kg

ISENTROPIC PROCESS

PROBLEM 23

ME Board Problem 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.

Answer: 16,985.02 kPa

ISENTROPIC PROCESS

PROBLEM 24

ME Board Problem How much work is necessary to compress air in an insulated cylinder from 0.20 m3 to 0.01 m3. Use t1 = 20C and P1= 100 kPa A. 113.4 kJ C. 110.1 kJ B. 121.4 kJ D. 115.7 kJ Answer: 115.7 kJ

POLYTROPIC PROCESS

PROBLEM 25

ME Board Problem During the polytropic process of an ideal gas, the state changes from 138 kPa and 5C to 827 kPa and 171C. Find the value of n . A. 1.354 C. 1.345 B. 1.253 D. 1.234 Answer: 1.354

POLYTROPIC PROCESS

PROBLEM 26

A gas at 1 atmosphere pressure originally occupies a volume of 20 ft3. The gas is polytropically compressed with n = 1.15 until the pressure is 48.51 psia. What work is required for this compression?

Answer: -47, 560.13 ft-lbf

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