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##### عضو جدید

**Review Questions for steam table**

Which of the following statements are true and which are false?

1. The heat content of liquid water is sensible heat.

2. The enthalpy change accompanying the phase change of liquid water at constant temperature is the latent heat.

3. Saturated steam is at equilibrium with liquid water at the same temperature.

4. Absolute values of enthalpy are known from thermodynamic tables, but for convenience the enthalpy values in steam tables are relative values.

5. The enthalpy of liquid water at 273.16 K in equilibrium with its vapor has been arbitrarily defined as a datum for the calculation of enthalpy values in the steam tables.

6. The latent heat of vaporization of water is higher than the enthalpy of saturated steam.

7. The enthalpy of saturated steam includes the sensible heat of liquid water.

8. The enthalpy of superheated steam includes the sensible heat of vapor.

9. Condensation of superheated steam is possible only after the steam has lost its sensible heat.

10. The latent heat of vaporization of water increases with temperature.

11. The boiling point of water at certain pressure can be determined from steam tables.

12. Specific volume of saturated steam increases with pressure.

13. The enthalpy of liquid water is greatly affected by pressure.

14. The latent heat of vaporization at a certain pressure is equal to the latent heat of condensation at the same pressure.

15. When steam is condensing, it gives off its latent heat of vaporization.

16. Themain reason steam is used as a heatingmedium is its high latent heat value.

17. About 5.4 times more energy is needed to evaporate 1 kg of water at 100 oC than to heat 1 kg of water from 0 8C to 100 oC.

18. The latent heat of vaporization becomes zero at the critical point.

19. Superheated steam is preferred to saturated steam as a heating medium in the food industry.

20. Steam in the food industry is usually produced in ‘‘water in tube’’ boilers.

21. Water boils at 08C when the absolute pressure is 611.3 Pa

22. Water boils at 1008C when the absolute pressure is 101325 Pa.

23. Steam quality expresses the fraction or percentage of vapor phase to liquid phase of a vapor-liquid mixture.

24. A Steam quality of 70% means that 70% of the vapor-liquid mixture is in the liquid phase (liquid droplets) and 30% in the vapor phase.

25. The quality of superheated steam is always 100%.

Review Questions on mass balance

Which of the following statements are true and which are false?

1. The mass balance is based on the law of conservation of mass.

2. Mass balance may refer to total mass balance or component mass balance.

3. Control volume is a region in space surrounded by a control surface through which the fluid flows.

4. Only streams that cross the control surface take part in the mass balance.

5. At steady state, mass is accumulated in the control volume.

6. In a component mass balance, the component generation term has the same sign as the output streams.

7. It is helpful to write a mass balance on a component that goes through the process without any change.

8. Generation or depletion terms are included in a component mass balance if the component undergoes chemical reaction.

9. The degrees of freedom of a system is equal to the difference between the number of unknown variables and the number of independent equations.

10. In a properly specified problem of mass balance, the degrees of freedom must not be equal to zero.

__Review Questions on energy balance__

Which of the following statements are true and which are false?

1. The energy in a system can be categorize as internal energy, potential energy, and kinetic energy.

2. A fluid stream carries internal energy, potential energy, and kinetic energy.

3. A fluid stream entering or exiting a control volume is doing PV work.

4. The internal energy and the PV work of a stream of fluid make up the enthalpy of the stream.

5. Heat and shaft work may be transferred through the control surface to or from the control volume.

6. Heat transferred from the control volume to the surroundings is considered positive by convention.

7. For an adiabatic process, the heat transferred to the system is zero.

8. Shaft work supplied to the system is considered positive by convention.

9. The shaft work supplied by a pump in a system is considered negative.

10. If energy is not accumulated in or depleted from the system, the system is at steady state.

**Review Questions on fluid flow**Which of the following statements are true and which are false?

1. TheReynolds number represents the ratio of the inertia forces to viscous forces.

2. If the Reynolds number in a straight circular pipe is less than 2100, the flow is laminar.

3. The velocity at which the flow changes from laminar to turbulent is called critical velocity.

4. The Reynolds number in non-Newtonian fluids is called the Generalized Reynolds number

5. The velocity profile of Newtonian fluids in laminar flow inside a circular pipe is parabolic.

6. The velocity profile of Newtonian fluids in laminar flow is flatter than in turbulent flow.

7. The maximum velocity of Newtonian fluids in laminar flow inside a circular pipe is twice the bulk average velocity.

8. The average velocity of Newtonian fluids in turbulent flow inside a circular pipe is around 80% of the maximum velocity.

9. The maximum velocity of pseudoplastic fluids in laminar flow inside a circular pipe is more than twice the bulk average velocity.

10. The Hagen-Poiseuille equation gives the pressure drop as a function of the average velocity for turbulent flow in a horizontal pipe.

11. The pressure drop in laminar flow is proportional to the volumetric flow rate.

12. The pressure drop in turbulent flow is approximately proportional to the 7/4 power of the volumetric flow rate.

13. In a fluid flowing in contact with a solid surface, the region close to the solid surface where the fluid velocity is affected by the solid surface is called boundary layer.

14. The velocity gradients and the shear stresses are larger in the region outside the boundary layer than in the boundary layer.

15. Boundary layer thickness is defined as the distance from the solid surface where the velocity reaches 99% of the free stream velocity.

16. The viscosity of a liquid can be calculated if the pressure drop of the liquid flowing in a horizontal pipe in laminar flow is known.

17. The viscosity of non-Newtonian liquids is independent of the shear rate.

18. The flow behavior index in pseudoplastic liquids is less than one.

19. In liquids that follow the power-law equation, the relationship between average velocity and maximumvelocity is independent of the flow behavior index.

20. The apparent viscosity of a pseudoplastic liquid flowing in a pipe decreases as the flow rate increases.

__Review Questions on pumps__

Which of the following statements are true and which are false?

1. Mechanical energy includes kinetic energy, potential energy, shaft work, and the flow work term of enthalpy.

2. Mechanical energy cannot be completely converted to work.

3. The fluid pressure drop due to friction in a straight pipe is proportional to the velocity of the fluid.

4. The pressure drop due to skin friction in a pipe can be calculated from the Fanning equation.

5. The friction factor f in laminar flow depends on the Reynolds number and the surface roughness of the pipe.

6. The friction factor f in turbulent flow can be obtained from the Moody chart.

7. In turbulent flow, the higher the surface roughness of the pipe the higher the influence of the Reynolds number on the friction factor f.

8. A sudden change of the fluid velocity in direction or magnitude causes friction losses.

9. Equation 6.1 gives the energy added to a fluid by a pump.

10. The energy added to a fluid by a pump is often called the developed head of the pump and is expressed in m.

11. The required power for a pump is independent of the liquid flow rate.

12. The brake power of a pump depends on the efficiency of the pump.

13. If the pressure in the suction of a pump becomes equal to the vapor pressure of the liquid, cavitation occurs.

14. Under cavitation conditions, boiling of the liquid takes place in the pump.

15. The difference between the sum of the velocity head and the pressure head in the suction of the pump and the vapor pressure of the liquid is called available net positive suction head (NPSH).

16. To avoid cavitation, the available NPSH must be greater than the required NPSH provided by the pump manufacturer.

17. The higher the temperature of the liquid, the lower the available NPSH.

18. It is impossible to pump a liquid at its boiling point unless the pump is below the liquid level in the suction tank.

19. Centrifugal pumps are usually self-primed pumps.

20. Positive displacement pumps are usually self-primed pumps.

21. Positive displacement pumps develop higher discharge pressures than centrifugal pumps.

22. The discharge line of a positive displacement pump can be closed without damaging the pump.

23. The discharge line of a centrifugal pump can be completely closed without damaging the pump.

24. The flow rate in a positive displacement pump is usually adjusted by varying the speed of the pump.

25. The flow rate in a positive displacement pump decreases significantly as the head increases.

26. Centrifugal pumps are used as metering pumps.

27. Liquid ring pumps are usually used as vacuum pumps.

28. The capacity of a centrifugal pump is proportional to the rotational speed of the impeller.

29. The head developed by a centrifugal pump is proportional to the speed of the impeller.

30. The power consumed by a centrifugal pump is proportional to the cube of the speed of the impeller.

**Review Questions on conduction**

Which of the following statements are true and which are false?

1. Heat is conducted in solids, liquids, and gases by the transfer of the energy of motion from one more energetic molecule to an adjacent less energetic one.

2. Fourier’s law is the basic relationship for heat transfer by conduction.

3. Resistance to heat transfer is proportional to thermal conductivity.

4. Air has low thermal conductivity.

5. Metals have higher thermal conductivity than non-metals.

6. Ice has a thermal conductivity much higher than water.

7. The thermal conductivity of gases is higher than the thermal conductivity of solids.

8. Thermal conductivity is a weak function of temperature.

9. In all cases, thermal conductivity varies with temperature gradient.

10. At steady state, the rate of heat transfer is always zero.

11. At steady state, the temperature at various points in a system does not change with time

12. At steady state, the temperature at various points in a system may change with position.

13. The temperature gradient is positive.

14. For the same heat transfer rate, the slope of the temperature gradient in insulating materials is smaller than in non-insulating materials.

15. The temperature distribution in a plane wall varies linearly with distance in the wall if there is no heat generation in the wall and the thermal conductivity is constant.

16. The temperature distribution in a cylindrical wall varies logarithmically with the distance in the wall if there is no heat generation in the wall and the thermal conductivity is constant.

17. The arithmetic mean area differs from the logarithmic mean area by less than 1.4% if A2/A1 < 1.5.

18. In a composite wall at steady state, the heat transfer rate in each layer depends on the thermal conductivity of the layer.

19. The temperature drop in a plane wall is inversely proportional to the resistance.

20. The slope of the temperature gradient in each layer of a composite plane wall depends on the thermal conductivity of the laye