Heat Transfer

151. Fruit juice (a heat sensitive material) can be concentrated in a _________ evaporator.

1. Long tube
2. Falling film
3. High pressure
4. None of these

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152. Graetz number is given by

1. mC_p/kL
2. kL/mC_p
3. mC_p/kμ
4. kμ/mC_p

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153. Grashoff number is given by

1. gD³.β.Δtρ²/μ²
2. gD²βΔtρ/μ²
3. gD²βΔtP²μ
4. gD³βΔtP²/μ

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154. Grashoff number, which is defined as g . β (T_s - T∞) ρ². L³/μ², is proportional to the ratio of buoyancy force to _________ force.

1. Viscous
2. Elastic
3. Inertial
4. None of these

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155. Harmonic mean temperature difference is given by

1. √(Δt₁ . Δt₂)
2. 2 (Δt₁ . Δt₂)/(Δt₁ + Δt₂)
3. 2 (Δt₁ . Δt₂)/(Δt₁ - Δt₂)
4. (Δt₁ - Δt₂)/(Δt₁ . Δt₂)

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156. Heat exchanger tubes are never made of

1. Plain carbon steel
2. Stainless steel
3. Lead
4. Copper

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157. Heat exchangers operating, when the asymptotic range is reached,

1. Provide very large heat transfer co-efficient
2. Results in making part of the heating surface inactive
3. Results in abruptly increased velocity
4. None of these

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158. Heat flux increases with temperature drop beyond the Leiden frost point in the plot of heat flux vs. temperature drop for a boiling liquid, because

1. Convection becomes important
2. Conduction becomes important
3. Radiation becomes important
4. Sub-cooled boiling occurs

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159. Heat flux is the time rate of heat transfer per unit

1. Length
2. Area
3. Volume
4. None of these

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160. Heat flux through several resistances in series in analogous to the current flowing through several

1. Resistances in parallel
2. Capacitors in series
3. Resistances in series
4. None of these

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