Heat

Condensation refers to a change from the

• Solid to liquid phase

• Vapor to liquid phase

• Liquid to solid phase

• Liquid to vapor phase

A perfectly black body

• Absorbs all the incident radiation

• Allow all the incident radiation to pass through it

• Reflects all the incident radiation

• Has its surface coated with lamp black or graphite

A body is called gray body if the monochromatic emissivity of the body is

• Zero

• One

• Same for all wavelengths

• Different for all wavelengths

In double-pipe heat exchangers, for chilling oil to be dewaxed, there are scrapers inside the pipe to keep the walls of pipe clean and to increase the mixing of the warmer oil with the cooler oil thus increasing the rate of heat transfer by

• Conduction

• Convection

• Radiation

• By all means

Absorptivity of the perfact black body is

• 1

• 0

• 0.5

• All of these

The hydrodynamic & thermal boundary layer are identical when

• N_pr = 0.7

• N_pr = 1

• N_pr = 1.5

• N_pr = 120

A cold fluid is heated from 40 °C to 130 °C by steam at 150 °C. The LMTD in parallel flow is

• lower than the LMTD in counter flow

• greater than the LMTD in counter flow

• equal to the LMTD in counter flow

• zero

Baffles used on the shell side of a heat exchanger will

• Decrease heat transfer rate

• Increase heat transfer rate

• Not affect heat transfer rate

• Decrease pressure drop on shell side

Forced convection in a liquid bath is caused by

• Intense stirring by an external agency

• Density difference brought about by temperature gradients

• Molecular energy interactions

• Flow of electrons in a random fashion

Steam condensate is highly corrosive mainly due to

• Presence of CO₂

• Presence of dissolved O₂

• Presence of both dissolved CO₂ and O₂

• Other reason than the presence of either dissolved CO₂ or O₂