How are heat, internal energy, and thermal energy related to each other?

Define thermal conductivity and explain its significance in heat transfer.

From a heat transfer point of view, what is the difference between isotropic and unisotropic materials?

Write down the one-dimensional transient heat conduction equation for a plane wall with constant thermal conductivity and heat generation in its simplest form, and indicate what each variable represents.

Consider a medium in which the heat conduction equation is given in its simplest form as

$$\frac{\mathbf{1}}{\mathbf{r}^{\mathbf{2}}}\frac{\mathbf{d}}{\mathbf{\text{dr}}}\left( \mathbf{r}^{\mathbf{2}}\frac{\mathbf{\text{dT}}}{\mathbf{\text{dr}}} \right)\mathbf{+}\frac{\mathbf{1}}{\mathbf{r}^{\mathbf{2}}\mathbf{\text{si}}\mathbf{n}^{\mathbf{2}}\mathbf{\theta}}\frac{\mathbf{\text{\ d}}^{\mathbf{2}}\mathbf{T}}{\mathbf{d}\mathbf{\varphi}^{\mathbf{2}}}\mathbf{=}\frac{\mathbf{1}}{\mathbf{\alpha}}\frac{\mathbf{\text{dT}}}{\mathbf{\text{dt}}}\mathbf{\text{\ \ \ }}$$

(a)) Heat transfer is transient, (b) it is two-dimensional, (c) there is no heat generation, and (d) the thermal conductivity is constant.

How is the boundary condition on an insulated surface expressed mathematically?

Explain how the fins enhance heat transfer from a surface. Also, explain how the addition of fins may actually decrease heat transfer from a surface.

Explain how the thermal contact resistance can be minimized?

Consider heat conduction through a wall of thickness L and area A. Under what conditions will the temperature distributions in the wall be a straight line?

What is the critical radius of insulation? How is it defined for a cylindrical layer?

For which solid is the lumped system analysis more likely to be applicable: an actual apple or a golden apple of the same size? Why?

What is the physical significance of the Nusselt number? How is it defined?

What is the physical significance of the Reynolds number? How is it defined for external flow over a plate of length L ?

What is the physical significance of the Prandtl number? Does the value of the Prandtl number depend on the type of flow or the flow geometry? Does the Prandtl number of air change with pressure? Does it change with temperature?

What is the no-slip condition? What causes it?

What is hydraulic diameter? How is it defined? What is it equal to for a circular tube of diameter?

Consider the flow of oil in a tube. How will the hydrodynamic and thermal entry lengths compare if the flow is laminar? How would they compare if the flow were turbulent?

In which mode of heat transfer is the convection heat transfer coefficient usually higher, natural convection or forced convection? Why?

Consider two fluids, one with a large coefficient of volume expansion and the other with a small one. In what fluid will a hot surface initiate stronger natural convection currents? Why? Assume the viscosity of the fluids to be the same.

Physically, what does the Grashof number represent? How does the Grashof number differ from the Reynolds number?

What is the difference between film and dropwise condensation? Which is a more effective mechanism of heat transfer?

Draw the boiling curve and identify the different boiling regimes. Also, explain the characteristics of each regime.

Consider film condensation on a vertical plate. Will the heat flux be higher at the top or at the bottom of the plate? Why?

Classify heat exchangers according to flow type and explain the characteristics of each type.

What is thermal radiation? How does it differ from the other forms of electromagnetic radiation?

Define the properties emissivity and absorptivity. When are these two properties equal to each other?

What does the view factor represent? When is the view factor from a surface to itself not zero?

What is a radiation shield? Why is it used?

Define spectral transmissivity of a medium of thickness L in terms of (a) spectral intensities and (b) the spectral absorption coefficient.

What is heat generation in a solid? Give examples

Write down the one-dimensional transient heat conduction equation for a long cylinder with constant thermal conductivity and heat generation, and indicate what each variable represents.

For steady two-dimensional flow, what are the boundary layer approximations?

Consider turbulent forced convection in a circular tube. Will the heat flux be higher near the inlet of the tube or near the exit? Why?

How is the hydrodynamic entry length defined for flow in a tube? Is the entry length longer in laminar or turbulent flow?

How does the Rayleigh number differ from the Grashof number?

Under what conditions can the overall heat transfer coefficient of a heat exchanger be determined from U= (1/hi +1/h0)^-1 ?

In the heat transfer relation Q=UAsΔTlm for a heat exchanger, what is _Tlm called? How is it calculated for a

parallel-flow and counter-flow heat exchanger?

Explain how the LMTD method can be used to determine the heat transfer surface area of a multipass shell-andtube heat exchanger when all the necessary information, including the outlet temperatures, is given.

The fin efficiency is defined as the ratio of the actual heat transfer from the fin to

a. The heat transfer from the same fin with an adiabatic tip

b. The heat transfer from an equivalent fin which is infinitely long

c. The heat transfer from the same fin if the temperature along the entire length of the fin is the same as base temperature

d. The heat transfer through the base temperature

e. None of the above

What is thermal contact resistance? How it is related to thermal contact conductance?

How does the thermal resistance network associated with a single – layer plane wall differ from the one associated with a five – layer composite wall?

What is lumped system analysis? When is it applicable?

The…………….….Number is a significant dimensionless parameter for forced convection and the…………..….. Number is a significant dimensionless parameter for natural convection

Consider laminar natural convection from a vertical hot plate. Will the heat flux be higher at the top or at the bottom of the plate? Why?

What is a blackbody? Does a blackbody actually exists?