Related Questions

Heat transfer by radiation from a hot body will be most rapid, if its surface is __________ because of its higher emissivity.
A White & rough
B Black & rough
C White & polished
D Black & polished
Extended heat transfer surface like fins are used to increase the heat transfer rate. Fin efficiency is defined as the ratio of heat transferred across the fin surface to the theoretical heat transfer across an equal area held at the
A Surrounding temperature
B Average temperature of the fin
C Temperature of the fin end
D Constant temperature equal to that of the base
The heat transfer by radiation from a mild steel surface is to be reduced by reducing the emissivity of the surface. This can be best achieved by
A Painting the surface black
B Painting the surface white (with aluminium paint)
C Giving the surface a mirror finish
D Roughening the surface
An insulating refractory brick should have high porosity and low thermal conductivity. Which of the following is not used for inducing porosity in the insulating refractory bricks during its manufacture?
A Cork
B Saw dust
C Sand
D Chemically prepared foam
The scales form in heat exchanges after a period of operation and provide additional resistance to heat transfer with some heat transfer coefficient . The reciprocal of this scale heat transfer coefficient is called .
A scaling factor
B forming factor
C resisting factor
D fouling factor
Dry mix hydraulic compositions of refractory aggregates with suitable bonding materials are called refractory
A Mortars
B Cements
C Castables
D None of these
If a refractory contains high content of silicon, it means refractory is
A Acidic
B Basic
C Neutral
D Brittle
With increase in the distance between the heat source and the object receiving the heat, the radiation heat transfer
A Decreases
B Increases
C Increases exponentially
D Remains unaffected
Ceramic recuperators used for waste heat recovery from high temperature flue gas going out of the furnace is made of
A Fireclay
B Silicon carbide
C Corrundum
D Siliceous fireclay
In thermal radiation for a black body (where, ε is emissivity and α is absorptivity)
A α = 1; ε ≠ 1
B α ≠ 1, ε = 1
C α ≠ 1, ε ≠ 1
D α = 1; ε = 1

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