Automobile Engineering in ME
The heat transfer from coolant to air in the radiator of an automobile engine takes place by

Radiation only
Convention only
Conduction, convection and radiation
Convection and radiation

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Automobile Engineering in ME
The function of a second ring is that it is a

Cushion ring which prevents piston slap and knock
Compression ring and aids the top ring in sealing and cooling
Back up oil control ring which will work in place of the bottom ring when it is broken
Back up compression ring which will work in place of the top ring when it is broken

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