# Overall Heat Transfer Coefficient and Fouling Factor - MCQs with Answers

## Overall Heat Transfer Coefficient and Fouling Factor – MCQs with Answers

1. How can the total thermal resistance of a heat exchanger, in which two fluids are separated by a plane wall of surface area A, thickness t and thermal conductivity k, be calculated?
h1 and h2 are the convection heat transfer coefficients on each side of wall.

a. (t / h1 A) + (t / h2 A)
b. (1 / h1 A) + (1 / h2 A)
c. (1 / h1 A) + (1 / h2 A) + (1 / k A)
d. (1 / h1 A) + (1 / h2 A) + (t / k A)

ANSWER: d. (1 / h1 A) + (1 / h2 A) + (t / k A)

2. Which side is suitable to provide fins on to enhance heat transfer, when heat exchanges between gas and liquid?

a. Gas side
b. Liquid side
c. None of the sides

3. How is the effective surface area of finned tube surface calculated?

a. A = Aunfinned + Afin
b. A = ηfin (Aunfinned + Afin)
c. A = Aunfinned + (ηfin x Afin)
d. A = (ηfin x Afin)

Where,
Afin = the area of tube surface on which fines are provided
Aunfinned = the area of tube surface on which fines are not provided
ηfin = fin efficiency

ANSWER: c. A = Aunfinned + (ηfin x Afin)

4. The scales form in heat exchangers after a period of operation and provide additional resistance to heat transfer with some heat transfer coefficient. The reciprocal of this scale heat transfer coefficient is called as

a. scaling factor
b. fouling factor
c. forming factor
d. resisting factor

5. Fouling factor of a heat exchanger can be calculated by

a. [Thermal resistance of heat exchanger without scaling] – [Thermal resistance of heat exchanger with scaling]
b. [Thermal resistance of heat exchanger with scaling] – [Thermal resistance of heat exchanger without scaling]
c. [Thermal resistance of heat exchanger without scaling] x [Thermal resistance of heat exchanger with scaling]
d. none of the above