PLEASE ANSWER ALL Which of the following conditions would be necessary for the t

Question

PLEASE ANSWER ALL

Which of the following conditions would be necessary for the thermal circuit approach to be applicable? 2. (a) Thermal conductivity varies with temperature (b) Heat generation exists in the mediunm (c) Steady state condition (d) None of the above 3. An opaque plate has an emissivity of 0.3 and an absorptivity of 0.3, its reflectivity would be (a) 0.3 (b) 0.4 (c) 0.7 (d) Not enough information to determine 4. Which of the following statements is coret about compact heat exchangers? (a) They depend on high flow rates to achieve high heat transfer rates (b) They have high heat-transfer-area density (c) They have large flow passages (d) None of the above 5. Two very long fins (fin A & fin B) are identical, except that the convection heat transfer coefficient for fin A is thrice that for fin B. Which statement below is inaccurate about the efficiency and effectiveness of fin A relative to fin B? (a) Fin A has higher efficiency and higher effectiveness (b) Fin A has higher efficiency but lower effectiveness (c) Both fins have equal efficiency and equal effectiveness (d) All of the above

Explanation / Answer

2. Thermal circuit aproach is applicable when system reaches steady state conduction. Hence, the correct option is (c).

3. Reflectiity=1-emissivity-absorptivity

Reflectivity=1-0.3-0.3

=0.4

Hence, the correct option is (b).

4. Option (b) is correct. Compact heat exchangers has high rate of heat transfer with low area.

5. FIns are effective at lower heat transfer coefficients but efficiency is high at higher value of heat transfer coefficients. Hence, the coorect option is (b).

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