A plate flow reaches Reynolds number of 10,000. Which type of flow is it?

Choose one answer.

	a. Turbulent
	b. Laminar
	c. Transition between turbulent and laminar
	d. None of the above

Question 2

Consider one-dimensional Cartesian steady-state conduction in the y-direction. Assuming no internal heating, what is the general solution for this problem?

Choose one answer.

	a. C1 ∙ y² + C2 ∙ y + C3
	b. C1 ∙ y + C2
	c. C1
	d. C1 ∙ y³ + C2 ∙ y + C3

Question 3

Fill in the blank. It is reasonable to use lumped-capacitance model to analyze transient conduction, if the Biot number (Bi) is _______________.

Choose one answer.

	a. Much larger than 1
	b. Approximately 1
	c. Smaller than 0.1
	d. Larger than 1

Question 4

For a fluid with Pr > 1, which of the following statements is true?

Choose one answer.

	a. The thickness of the thermal boundary layer is less than the thickness of the momentum boundary layer.
	b. The thickness of the thermal boundary layer is greater than the thickness of the momentum boundary layer.
	c. The thickness of the thermal boundary layer is equal to the thickness of the momentum boundary layer.
	d. None of the above

Question 5

For a laminar boundary layer, the Reynolds number at position x is 100. The Prandtl number of the fluid is 1. Estimate the value of the Nusselt number at position x.

Choose one answer.

	a. 33.2
	b. 3.32
	c. 0.332
	d. 1

Question 6

Heat can be transferred from one object to another by which process?

Choose one answer.

	a. Conduction
	b. Convection
	c. Radiation
	d. All of the above

Question 7

Heat conduction is governed by which physical law?

Choose one answer.

	a. Fourier's law
	b. First law of thermodynamics
	c. Newton's second law
	d. None of the above

Question 8

One face of a metal layer has a temperature of 50°C and the other face has a temperature of 30°C. The thickness of the metal layer is 100 mm. The thermal conductivity of the metal is 1W/°C ∙ m. What is the heat transfer per unit face area?

Choose one answer.

	a. 200 W/m²
	b. 500 W/m²
	c. 100 W/m²
	d. 800 W/m²

Question 9

To solve a steady state two-dimensional heat conduction problem, one needs to specify which of the following?

Choose one answer.

	a. Only initial conditions
	b. Both boundary and initial conditions
	c. Only boundary conditions
	d. None of the above

Question 10

To solve a transient two-dimensional heat conduction problem, one needs to specify which of the following?

Choose one answer.

	a. Only initial conditions
	b. Both boundary and initial conditions
	c. Only boundary conditions
	d. None of the above

Question 11

What are the two major forces that govern natural convection?

Choose one answer.

	a. Buoyancy and acceleration
	b. Buoyancy and gravitation
	c. Buoyancy and viscous
	d. Viscous and friction

Question 12

What is a laminar sublayer in a turbulent boundary layer?

Choose one answer.

	a. A layer on top of the turbulent boundary layer
	b. A thin region near the plate surface in which heat and mass transfer are similar to those in a laminar flow
	c. A layer under the wall
	d. None of the above

Question 13

What is a shape factor for heat conduction?

Choose one answer.

	a. A factor used to solve two- and three-dimensional conduction problems with standardized geometries
	b. A factor representing convective heat transfer
	c. A factor used to calculate radiation heat transfer between two black bodies
	d. None of the above

Question 14

What is free convection?

Choose one answer.

	a. Turbulent flow
	b. Bulk movements of the fluid induced by density differences in the fluid occurring due to temperature gradients
	c. Bulk movements of the fluid induced by pressure gradients in the fluid
	d. Forced movements of the fluid induced by external pumps

Question 15

What is the effectiveness of a fin?

Choose one answer.

	a. The ratio of the fin heat transfer rate to the heat transfer rate of the object if it had no fin
	b. The ratio of the actual heat loss to the heat loss if the fin was at the base temperature
	c. The ratio of fin area to the base area
	d. The ratio of the fin heat transfer rate to the heat transfer by convection

Question 16

What is the efficiency of a fin?

Choose one answer.

	a. The ratio of the fin heat transfer rate to the heat transfer rate of the object if it had no fin
	b. The ratio of the actual heat loss to the heat loss if the fin was at the base temperature
	c. The ratio of fin area to the base area
	d. The ratio of the fin heat transfer rate to the heat transfer by convection

Question 17

What is the Grashof number?

Choose one answer.

	a. The ratio of viscous forces and inertia forces
	b. The ratio of gravitation forces and forced convection
	c. The ratio of buoyant forces to acceleration forces acting on a fluid
	d. The ratio of buoyant forces to viscous forces acting on a fluid

Question 18

What is the Nusselt number?

Choose one answer.

	a. The ratio of momentum diffusivity to thermal diffusivity
	b. The ratio of convective to conductive heat transfer across a boundary
	c. The ratio of convective heat transfer coefficient to conduction heat transfer coefficient
	d. The ratio of momentum transfer to heat transfer

Question 19

What is the range of heat transfer coefficient for natural convection in liquids?

Choose one answer.

	a. 50-1000 W/m²K
	b. 1-5 W/m²K
	c. 0.1-1 W/m²K
	d. 104-105 W/m²K

Question 20

What is the range of heat transfer coefficient for forced convection in liquids?

Choose one answer.

	a. 50-10⁴ W/m²K
	b. 1-5 W/m²K
	c. 0.1-1 W/m²K
	d. 10⁴-10⁵ W/m²K

Question 21

What is the range of heat transfer coefficient for forced convective boiling?

Choose one answer.

	a. 5-10 W/m²K
	b. 1-5 W/m²K
	c. 0.1-1 W/m²K
	d. 10³-10⁵ W/m²K

Question 22

What is the relationship between thermal resistance R, conduction shape factor S, and thermal conductivity k?

Choose one answer.

	a. R = 1/k + 1/S
	b. R = k ∙ S
	c. R = 1/(k + S)
	d. R ∙ S ∙ k = 1

Question 23

What is the thermal resistance of a 1-cm thick layer of rubber? The thermal conductivity of rubber is 0.2 W/m ∙ K. The total surface area is 10^-2 m².

Choose one answer.

	a. 15 K/W
	b. 50 K/W
	c. 5 K/W
	d. 1 K/W

Question 24

What is the thermal resistance per unit area of heat convection with a heat transfer coefficient h?

Choose one answer.

	a. 1/h²
	b. 1/h
	c. L/k
	d. k/L

Question 25

Which of the following equations is the mathematical expression of method of separation of variables for two-dimensional steady-state conduction?

Choose one answer.

	a. T(x, y) = U(x) ∙ V(y)
	b. T(x, y) = U(x) + V(y)
	c. T(x, y) = U(x/y)
	d. T(x, y) = U(x) - V(y)

Question 26

Which of the following equations represents Newton's law of cooling?

Choose one answer.

	a. q'' = h (T_s - T_∞)
	b. q'' = -k dT/dx
	c. E_b = σ T_s⁴
	d. None of the above

Question 27

Which of the following heat transfer regimes does NOT belong to the boiling curve?

Choose one answer.

	a. Conduction
	b. Film boiling
	c. Nucleate boiling
	d. Natural convection

Question 28

Which of the following statements about a poor heat insulator is true?

Choose one answer.

	a. A poor heat insulator is a good heat conductor.
	b. A poor heat insulator is a poor heat conductor.
	c. A poor heat insulator is a good heat conductor.
	d. None of the above

Question 29

Which of the following statements about radiation is false?

Choose one answer.

	a. All forms of matter emit radiation.
	b. Transport of thermal radiation energy requires matter.
	c. Temperature is the driving force for thermal radiation.
	d. Radiation energy varies continuously with wavelength.

Question 30

What is the Prandtl number?

Choose one answer.

	a. The ratio of momentum diffusivity to thermal diffusivity
	b. The ratio of dynamic viscosity to thermal diffusivity
	c. The ratio of convective heat transfer coefficient to conduction heat transfer coefficient
	d. The ratio of momentum diffusivity to heat conduction coefficient

Question 31

A 100 m long pipe is heated to 150°C. The temperature of the surrounding is 20°C. Estimate heat loss due to radiation if the pipe outer diameter is 10 cm. The surface emissivity of the pipe is 0.7.

Choose one answer.

	a. 100 kW
	b. 30 kW
	c. 10 kW
	d. 5 kW

Question 32

A 45 cm wire is used to boil water. The power of the wire is 1.25 kW. Its radius is 2 mm. The thermal conductivity of the wire material is 20 W/(m ∙ K). What is the difference between the temperature at the center of the wire and the temperature on the surface of the wire?

Choose one answer.

	a. 11°C
	b. 9°C
	c. 7°C
	d. 4°C

Question 33

A metal object is initially at a uniform temperature of 400°C. It is then exposed to an environment at 100°C. The Biot number of the system is 0.001. It takes 60 s for the object to cool down to 300°C. Calculate the additional time needed for the object to reach 200°C.

Choose one answer.

	a. 103 s
	b. 283 s
	c. 1043 s
	d. 3 s

Question 34

A plane wall of thickness L has thermal conductivity k. One side of the wall is cooled by a liquid with temperature T₁ and heat transfer coefficient h₁. The other side of the wall is heated by a gas with temperature T₂ and heat transfer coefficient h₂. What is the heat flux through the wall per unit area?

Choose one answer.

	a. q = (T₂ + T₁)/(1/h₁ + 1/h₂ + L/k)
	b. q = (T₂ - T₁)/(1/h₁ + 1/h₂)
	c. q = (T₂ + T₁)/(1/h₁ - 1/h₂ + L/k)
	d. q = (T₂ - T₁)/(1/h₁ + 1/h₂ + L/k)

Question 35

A wire is used to boil water. The length and the diameter of the wire are 1 m and 4 mm, respectively. The thermal conductivity of the wire material is 20 W/(m ∙ K). Heat is generated in the wire uniformly at a rate of q_gen = 10 W/cm³. What is the value of heat flux on the surface of the wire?

Choose one answer.

	a. 50 kW/m²
	b. 20 kW/m²
	c. 10 kW/m²
	d. 100 kW/m²

Question 36

Calculate heat loss due to radiation of a metal horizontal pipe with emissivity of 0.93. The temperature of the outer surface of the pipe is 560ºR. The temperatures of the walls and air in the room are 540ºR. The outer diameter of the pipe is 6 in.

Choose one answer.

	a. 32 Btu/hr
	b. 50 Btu/hr
	c. 12 Btu/hr
	d. 20 Btu/hr

Question 37

Calculate the Biot number for a metal sphere of 6 cm in diameter placed in an air flow. The heat transfer coefficient to air is 30W/(m² °C). The thermal conductivity of the metal is 300 W/m°C.

Choose one answer.

	a. 10^-2
	b. 10^-1
	c. 1
	d. 10^-3

Question 38

Consider one-dimensional Cartesian steady-state conduction in a plane wall of thermal conductivity k. An internal heat source Q uniformly generates heat thorough the plane wall. What is the general solution of the temperature distribution?

Choose one answer.

	a. (Q/2k) ∙ y² + C1 ∙ y + C2
	b. (Q/2k) ∙ y + C2
	c. (Q/2k) ∙ y³ + C2
	d. (Q/2k) ∙ y

Question 39

Choose one answer.

	a. (Q/2k) ∙ y² + C1 ∙ y + C2
	b. (Q/2k) ∙ y + C2
	c. (Q/2k) ∙ y² + C2
	d. (Q/2k) ∙ y

Question 40

Estimate the heat flux emitted from the sun surface, if the sun can be approximated as a black body emitting radiation with a maximum intensity at ⎣ = 0.5 microns ( 5000 Aº). Hint: Use the Stefan Boltzmann law.

Choose one answer.

	a. 2.0 x 10⁷Btu / hr. ft²
	b. 5.0 x 10⁷Btu / hr. ft²
	c. 7.0 x 10⁷Btu / hr. ft²
	d. 2.0 x 10⁷Btu / hr. ft²

Question 41

Estimate the length of the thermal entrance region for water flow in a pipe. The diameter of the pipe is 10 cm. The Reynolds number of the flow is 500.

Choose one answer.

	a. 2.5 m
	b. 1.5 m
	c. 0.5 m
	d. 0.1 m

Question 42

Estimate the temperature of the sun, if it can be approximated as a black body emitting radiation with a maximum intensity at ⎣ = 0.5 microns ( 5000 Aº).

Choose one answer.

	a. 1230 K
	b. 4500 K
	c. 5760 K
	d. 4200 K

Question 43

Heat loss due to radiation for a pipe is 30 kW. The temperature of the surrounding is 20°C. Estimate the temperature of the pipe. The pipe is 100 m long and its outer diameter is 10 cm. The surface emissivity of the pipe is 0.7.

Choose one answer.

	a. 50°C
	b. 250°C
	c. 150°C
	d. 100°C

Question 44

Hot air at 50°C flows over a 15 cm long turbine blade, with velocity of 10 m/s. The same air flows over a 30 cm long turbine blade with velocity of 5 m/s. The average heat transfer coefficient for the first blade is 100 W/m²K. What is the average heat transfer coefficient for the second blade?

Choose one answer.

	a. 100 W/(m²K)
	b. 225 W/(m²K)
	c. 50 W/(m²K)
	d. 355 W/(m²K)

Question 45

The Peclet (Pe) number can be calculated from the Prandtl (Pr) and the Reynold (Re) number as follows:

Choose one answer.

	a. Pe= Pr²Re
	b. Pe = Pr.Re
	c. Pe = Re/Pr
	d. Pe = Pr/Re

Question 46

The Raleigh (Ra) number can be calculated from the Prandtl (Pr) and the Grashof (Gr) number as follows:

Choose one answer.

	a. Ra = Pr²Gr
	b. Ra = Gr .Pr
	c. Ra = Gr/Pr
	d. Ra = Pr/Gr

Question 47

The total surface area of a house 300 m². The average thickness of the wall is 0.1 m. The thermal conductivity of the wall is 5 10^-4 kW/(m ∙ K). Estimate the amount of energy needs to supplied to the house in a day to keep its temperature 10°C higher than outside.

Choose one answer.

	a. 0.3 10⁶ J
	b. 1.3 10⁹ J
	c. 5.3 10⁶ J
	d. 2.3 10⁹ J

Question 48

What is the shape factor for conduction through wall of a thick cylinder with inner radius r_i and outer radius r_o?

Choose one answer.

	a. 2π/[ln(r_o) + ln(r_i)]
	b. 2π/[ln(r_o) - ln(r_i)]
	c. π/[ln(r_o/r_i)]
	d. 2π(r_o/r_i)

Question 49

Which of the following boiling regime is characterized by a thin layer of vapor insulating the surface?

Choose one answer.

	a. Nucleate boiling
	b. Film boiling
	c. Transition boiling
	d. Natural convection

Question 50

The thermal conductivity of a brick is 1 W/(m ∙ K). The thickness of the brick is 10 cm. What is the heat flux q through the brick if a temperature difference of 100°K is applied across it?

Choose one answer.

	a. 1 W/m²
	b. 0.1 kW/m²
	c. 100 kW/m²
	d. 1 kW/m²