Out of the following four assumptions used in the derivation of the equation for LMTD [LMTD = (Δt1 – Δt2)/ln(Δt1/Δt2)], which one is subject to the largest deviation in practice ?

Related Mcqs:

1. In a liquid-liquid heat exchanger, for the same process temperature, the ratio of the LMTD in parallel flow to the LMTD in counter flow is always__________________?

   A. < 1
   B. > 1
   C. 1
   D. ∞

2. LMTD can’t be used as such without a correction factor for the_________________?

   A. Multipass heat exchanger
   B. Baffled heat exchanger
   C. Condensation of mixed vapour in a condenser
   D. All A. B. and C.

3. LMTD for counter-flow and parallel flow heat exchanger will be the same, when the_________________?

   A. Cold fluid is heated to a certain temperature by condensing steam (isothermal fluid)
   B. Outlet temperature of both the hot and cold fluid are same
   C. Outlet temperature of hot fluid is less than the outlet temperature of the cold fluid
   D. None of these

4. LMTD for evaporators & condensers for a given terminal parameters & set of conditions for counter-flow is equal to that for parallel flow. In such heat exchangers, with one of the fluids condensing or evaporating, the surface area required is the least in the ______________ flow?

   A. Parallel
   B. Mixed
   C. Counter flow
   D. Same in either A , B. or C.

5. It is not recommended to use a 1-2 shell and tube heat exchanger for a particular heat duty, whenever the LMTD correction factor is___________________?

   A. > 0.75
   B. < 0.75
   C. < 0.50
   D. < 0.25

6. For a multipass shell and tube heat exchanger, the LMTD correction factor is always________________?

   A. 1
   B. > 1
   C. < 1
   D. Between 1 & 2

7. In a 1-1 concurrent heat exchanger, if the tube side fluid outlet temperature is equal to the shell side fluid outlet temperature, then the LMTD is_________________?

   A. ∞
   B. 0
   C. Equal to the difference between hot and cold fluids inlet temperature
   D. Equal to the difference between hot fluid inlet temperature and cold fluid outlet temperature

8. LMTD correction factor which is to be applied for a cross-flow heat exchanger increases with increase in the number of shell passes. Its value for a single pass cross flow heat exchanger is __________________?

   A. 0
   B. 1
   C. > 1
   D. < 1

9. In a parallel flow heat exchanger, if the outlet temperature of hot and cold fluids are the same, then the log mean temperature difference (LMTD) is_________________?

   A. Minimum
   B. Maximum
   C. Zero
   D. Infinity

10. Log mean temperature difference (LMTD) cannot be used, if ___________________?

    A. Heat transfer co-efficient over the entire heat exchanger is not constant
    B. There exists an unsteady state
    C. The heat capacity is not constant and there is a phase change
    D. None of these