Extended Surfaces

Question 1

How do you solve the turbine blade extended Surface?

Answer 1

1. Apply relevant formula depending on tip condition from extended surfaces section

Question 2

What are the area and perimeter in the extended surface equations?

Answer 2

Cross section area and cross section perimeter of fin

Question 3

How do you solve rod system with body conduction and convection?

Answer 3

1. Do energy balance: q in = q convec + q cond
2. Find q conduction using table value of temp. distribution from extended surface and combining it with Fourier law of heat conduction
3. You will find that dT = d(theta/theta b) * theta_b
4. Solve at x = L to find total convection out

Question 4

When do we use the different tip conditions?

Answer 4

Infinitely long fin when tip temperature = t infinity

Prescribed temperature when temperature at L is known

Adiabatic when tip is adiabatic ie. no heat loss at tip

Convection when you have convection heat transfer at fin tip

Question 5

How can you use the corrected length approach and when is it used for fins?

Answer 5

Used when the fin tip is not adiabatic, but we still want to use adiabatic tip condition

We use a corrected length L_corr = L_actual + (A_c)/P