Heat Transfer Surprise Quizz

Which one of the following will have least value of thermal conductivity

• (A) aluminium

• (B) copper

• (C) water

• (D) silver

The unit of overall coefficient of heat transfer is

• W/m²K

• W/m²

• W/mK

• W/m

Heat flows from one body to other when they have

• Different heat contents

• Different specific heat

• Different atomic structure

• Different temperatures

The logarithmic mean temperature difference (t_m) is given by (where Δt₁ and Δt₂ are temperature differences between the hot and cold fluids at entrance and exit)

• t_m = (Δt₁ - Δt₂)/ log_e (Δt₁/Δt₂)

• t_m = log_e (Δt₁/Δt₂)/ (Δt₁ - Δt₂)

• t_m = tm = (Δt₁ - Δt₂) log_e (Δt₁/Δt₂)

• t_m = log_e (Δt₁ - Δt₂)/ Δt₁/Δt₂

The rate of energy transferred by convection to that by conduction is called

• Fourier Number

• Stanton Number

• Nusselt Number

• Biot Number

• Peclet Number

The natural convection air cooled condensers are used in

• Domestic Refrigerator

• Water Cooler

• Room Air Conditioner

• Washing Machine

Heat is transferred by all three modes of transfer, viz. conduction, convection and radiation in

• Electric Heater

• Steam Condenser

• Boiler

• Refrigerator Condenser Coil

In liquids and gases, heat transmission is primarily caused by

• a) Convection

• b) Radiation

• c) Conduction

• d) Conduction as well as convection

What is the rate of heat transfer from the fin in case of fin insulated at the tip?

• a) (h P k)^1/2 (t ₀ – t _a) tan h ml

• b) (h P A)^1/2 (t ₀ – t _a) tan h ml

• c) (h P k A)^1/2 (t ₀ – t _a) tan h ml

• d) (h k A)^1/2 (t ₀ – t _a) tan h ml

For laminar film condensation on a vertical plate, the local heat transfer coefficient at the lower edge of the plate is given by

• a) [k ³ p ² g h _{f g} /4 δ l (t _sat – t _s)] ^0.125

• b) [k ³ p ² g h _{f g} /4 δ l (t _sat – t _s)] ^0.

• ¹c) [k ³ p ² g h _{f g} /4 δ l (t _sat – t _s)] ^0.25

• d) [k ³ p ² g h _{f g} /4 δ l (t _sat – t _s)] ^0.5