Heat Transfer

261. LMTD can't be used as such without a correction factor for the

1. Multipass heat exchanger
2. Baffled heat exchanger
3. Condensation of mixed vapour in a condenser
4. All (A) (B) and (C)

262. 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

1. 0
2. 1
3. > 1
4. < 1

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

1. Cold fluid is heated to a certain temperature by condensing steam (isothermal fluid)
2. Outlet temperature of both the hot and cold fluid are same
3. Outlet temperature of hot fluid is less than the outlet temperature of the cold fluid
4. None of these

264. 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.

1. Parallel
2. Mixed
3. Counter flow
4. Same in either 'a', b' or 'c'

265. Log mean temperature difference (LMTD) cannot be used, if

1. Heat transfer co-efficient over the entire heat exchanger is not constant
2. There exists an unsteady state
3. The heat capacity is not constant and there is a phase change
4. None of these

266. Loss of heat from untagged steam pipe to the ambient air is by

1. Conduction
2. Convection
3. Radiation
4. All (A), (B) & (C)

267. Low thermal conductivity of heat insulating materials is due to its

1. Dense structure
2. High proportion of air space
3. High specific heat
4. None of these

268. Maximum heat transfer rate is achieved in _________ flow.

1. Co-current
2. Counter-current
3. Turbulent
4. Laminar

269. Maximum heat transfer rate is obtained in _________ flow.

1. Laminar
2. Turbulent
3. Creeping
4. Transition region

270. Maximum water velocity in tubes of a 1-2 shell and tube heat exchanger may be around _________ metres/second.

1. 1
2. 10
3. 20
4. 30