Category: Mechanical Engineering

Latest multiple choice questions with answers for mechanical engineering students.

Mechanical Engineering MCQs [Quiz 38]

Q1. In convection heat transfer from hot flue gases to water tube, even though flow may be turbulent, a laminar flow region (boundary layer of film) exists close to the tube. The heat transfer through this filmtakes place by
(a) convection
(b) radiation
(c) conduction
(d) both convection and conduction
(e) none of the above.

Q2. Film coefficient is defined as Inside diameter of tube
(a) Equivalent thickness of film
(b) Thermal conductivity Equivalent thickness of film Specific heat x Viscocity
(c) Thermal conductivity Molecular diffusivity of momentum Thermal diffusivity
(d) Film coefficient x Inside diameter Thermalconductivity
(e) none of the above.

Q3. Heat conducted througfi unit area and unit thick face per unit time when temperature difference between opposite faces is unity,is called
(a) thermal resistance
(b) thermal coefficient
(c) temperature gradient
(d) thermal conductivity
(e) heat-transfer.

Q4. The rate of energy emission from unit surface area through unit solid angle, along a normal to the surface, is known as
(a) emissivity
(b) transmissivity
(c) reflectivity
(d) intensity of radiation
(e) absorptivity.

Q5. Emissivity of a white polished body in comparison to a black body is
(a) higher
(b) lower
(c) same
(d) depends upon the shape of body
(e) none of the above.

Q6. A grey body is one whose absorptivity
(a) varies with temperature
(b) varies with wavelength of the incident ray
(c) is equal to its emissivity
(d) does not vary with temperature and. wavelength of the incident ray
(e) none of the above.

Q7. Two balls of same material and finish have their diameters in the ratio of 2 : 1 and both are heated to same temperature and allowed to cool by radiation. Rate of cooling by big ball as compared to smaller one will be in the ratio of
(a) 1 :1
(b) 2: 1
(c) 1 : 2
(d) 4 : 1
(e) 1 : 4

Q8. A non-dimensional number generally associated with natural convection heat transfer is
(a) Grashoff number
(b) Nusselt number
(c) Weber number
(d) Prandtl number
(e) Reynold number.

Q9. LMTD in case of counter flow heat exchanger as compared-to parallel flow heat exchanger is
(a) higher
(b) lower
(c) same
(d) depends on the area of heat exchanger
(e) depends on temperature conditions.

Q10. In heat exchangers, degree of approach is defined as the difference between temperatures of
(a) cold water inlet and outlet
(b) hot medium inlet and outlet
(c) hot medium outlet and cold water inlet
(d) hot medium outlet and cold water outlet
(e) none of the above

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