Extended surfaces

In some cases, increasing heat transfer can be done by increasing surface area (As) rather than increasing convective heat transfer coefficient (h). Is this statement true?

• Yes

• No

Extended surfaces or fins are made of

• highly conductive material

• low conductivity

What are the assumptions that can be made in order to solve the problem for extended surfaces?

• Heat is generated

• No heat generation

• k and h not constant

• k and h are constant

• steady state

For actual operation, the value of h is usually

• much lower at the fin base than it is at the fin tip

• much higher at the fin base than it is at the fin tip

• constant

If the temperature of base is higher than surronding, the temperature profile for a long fin

• increase with its length

• decrease with its length

• constant

If very long fin is attached to the base, it is _______ because_______

• more efficient, higher resistant

• less efficient, temperature at the fin tip closer to surrounding temperature

• good, company makes more profit

If too many fins are attached to the base, it may_______, because_______

• increase the overall heat transfer, many fins

• decrease the overall heat transfer, fluid motion is hindered

• increase cost, less optimize design

Which of the following types of fins have uniform cross section area

• a, b, c, d

• a,e,g

• e,f,g

Which of the followings have parallel fluid to the fins

• a,b,d,e,g

• ab,c,d

• a,b,d,g

• f,c

Calculate ratio of A_base (in mm²) to perimeter (in mm) for the pin fin . Given that d= 3 mm