Heat Transfer
In regenerative air preheater (as practised in heating of coke ovens), the heat is transferred

None of these
By heating an intermediate material (like chequor bricks) and then heating the air from this hot material
Through a metallic wall
By direct contact of hot flue gas with air

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Heat Transfer
Vacuum is generally maintained in the vapour space of an evaporator mainly to

Facilitate forward feeding in multiple effect evaporation
Get economical temperature difference by using moderate pressure steam
Concentrate heat sensitive materials
Achieve very high concentration of the final product

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Heat Transfer
In a gas-liquid shell and tube heat exchanger, the

Presence of a non-condensible gas decreases the condensing film co-efficient
Gases to be heated/cooled is normally routed through the shell side, because the corrosion caused by the cooling water or steam condensate remain localised to the tubes
Gases under high pressure are routed through the tube side, because high pressure gases are corrosive in nature
All of these

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