Heat Transfer

161. Heat flux, as defined in heat flow is analogous to _________ in electricity flow.

1. Current
2. Voltage
3. Resistance
4. None of these

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162. Heat produced when a steady state current, I passes through an electrical conductor having resistance, 'R' is

1. IR
2. I2R
3. Ir₂
4. I2r₂

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163. Heat sensitive materials can be concentrated in an evaporator employing

1. Vacuum
2. High pressure
3. High residence time
4. None of these

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164. Heat transfer by _________ may not necessarily require the presence of a medium.

1. Conduction
2. Natural convection
3. Forced convection
4. Radiation

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165. Heat transfer by conduction in the turbulent core of a fluid flowing through a heated pipe is negligible, if the value of Prandtl number is

1. 0.2
2. 0.4
3. 0.6
4. 0.8

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166. Heat transfer by conduction results due to the transfer of free electrons, kinetic energy & vibrational energy from one molecule to another. Conduction heat transfer cannot take place

1. Between two bodies in physical contact with each other
2. Between two bodies not in physical contact with each other
3. From one part of a body to the another part of the same body
4. Both 'b' & 'c'

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167. Heat transfer by natural convection is enhanced in system with

1. High viscosity
2. High co-efficient of thermal expansion
3. Low temperature gradients
4. Low density change with temperature

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168. Heat transfer by radiation between two bodies at t₁ & t₂ and in an ambient temperature of Ta°C depends on

1. t₁ - t₂
2. t₁ - Ta
3. t₂ - Ta
4. None of these

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169. Heat transfer co-efficient (h) for a fluid flowing inside a clean pipe is given by h = 0.023 (K/D) (DVρ/μ)^0.8 (CP.μ/k)^0.4. This is valid for the value of N_Re equal to

1. < 2100
2. 2100-4000
3. > 4000
4. > 10000

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170. Heat transfer co-efficient (h₁) for liquids increases with

1. Increasing temperature
2. Decreasing temperature
3. Decreasing Reynolds number
4. None of these

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