A. The emissivity of a surface decreases, if it gets corroded by atmospheric environment
B. The emissivity of a surface increases with increase in surface roughness
C. The emissivity of a polished surface is quite low
D. The emissivity of a non-metallic surface decreases with increase in the temperature
Related Mcqs:
- Pick out the wrong statement ?
A. Heat transfer from a hot body to cold body by the emission of heat waves is called radiation
B. Filmwise condensation takes place on non-wettable surfaces
C. The boiling point of a solution is affected by liquid head as well as boiling point elevation
D. None of these - Pick out the wrong statement?
A. Fluid movement under the influence of buoyant forces resulting from change in density takes place in case of natural convection
B. The ratio NNu/NRe . Npr is called the Stanton number
C. The Peclet number is a measure of the ratio of energy transport by convection to that by conduction
D. The Colburn jH factor for heat transfer is given by Nst Npr - Pick out the wrong statement ?
A. Economy of a multiple effect evaporator is not influenced by the boiling point elevation
B. Two identical cubes of iron and copper will have the same heat content under the same
conditions of temperature
C. Double pipe heat exchangers are mostly used in the field of refrigeration
D. Finned tube heat exchangers are suitable for heating air by steam - Pick out the wrong statement ?
A. ‘Solvates’ are chemical compounds formed by solute with their solvents. When water is the
solvent, then it is called a ‘hydrate’
B. In heat exchanger calculations (Δt) weighted is used in place of Δt, when it involves more
than one sequence of heating or cooling i.e., desuperheating & condensation or condensation
& sub-cooling
C. Heat transfer co-efficient during nucleate boiling is not influenced by the agitation imparted
D. In case of short tube vertical evaporators, area of central downtake is about 50 to 100% of the
total tube cross-sectional area - Pick out the wrong statement ?
A. With change in temperature, the radiant energy emitted by a black body remains unchanged
B. Absorptivity of a body approaches unity in case of diffuse reflection
C. Absorptivity of a perfectly black body is unity
D. Value of Stefan-Boltzmann constant is 4.876 × 10-8 KCal/m2.hr.°K4 - Pick out the wrong statement ?
A. The condensing film co-efficient is about 3 times lower for vertical condenser as compared to the equivalent horizontal condenser for identical situation
B. Film co-efficient for vaporisation decreases as a result of vapor binding
C. In industrial practice, sub-cooling of condensate is required, when the condensate is a volatile
liquid and is to be transferred for storage
D. Overall heat transfer co-efficient in a heat exchanger is controlled by the value of the film coefficient,
which is higher - Pick out the wrong statement?
A. Orifice baffles are never used in a shell and tube heat exchanger
B. Pressure drop on the shell side of a heat exchanger depends upon tube pitch also
C. In a horizontal tube evaporator, surface blanketing by air is avoided
D. Split ring type and pull through type floating heads are two commonly used floating heads is
heat exchangers - Pick out the wrong statement?
A. Reciprocal of the resistance to heat flow is called thermal conductance
B. Unit of thermal conductance is W/°K
C. Thermal conductance of a wall of thickness ‘L’, thermal conductivity ‘k’ and heat flow area ‘A’ is kL/A
D. None of these - Pick out the wrong statement ?
A. In case of heat transfer by purely forced convection, GR/Re 2 ≤ 1
B. The equivalent diameter of heat transfer for a duct of square cross-section (having each side as
‘x’) is equal to 4x
C. Distillation process is not the same as evaporation
D. The effectiveness of nucleate boiling depends basically on the ease with which the bubbles are
formed and detached from the heating surface - Pick out the wrong statement?
A. The capacity of an evaporator is reduced by the boiling point elevation
B. Corrosive liquid is normally passed through the tubes in a shell and tube heat exchanger
C. Steam jet ejector is used for vapor compression in a thermal recompression evaporator
D. Heat sensitive materials should be concentrated in high pressure evaporators
