DE-4 HEAT AND MASS TRANSFER 1. Heat conduction in gases occur by All of the above Molecular and atomic interaction in fluids Diffusion of free electrons Elastic molecular collision
2. Two dimension unsteady-state temperature field is t = f(x, ?) t = f(x,y) t = f(x, y, ?) t = f(x, y, z)
3. Which of the following is not the property of ‘Isothermal surface’? Isothermal surfaces are parallel to temperature gradient vectors Isothermal surfaces are locus of equal temperatures Isothermal surfaces form a loop Isothermal surfaces of different temperatures do not intersect
4. Temperature gradient is a It is a scalar quantity Linear combination of vectors Vector parallel to the Isothermal surface Vector normal to the Isothermal surface
5. The relationship q= -? (?t/??) is called Darcy Law Fourier’s Law Henry’s Law Fick’s Law
6. The unit for thermal resistance is: None of the above kcal/m2 °C/kcal/m2-hr kcal/m2–hr-°C
7. Design formula for conduction in a plane wall is given by: q= (a? )/? q= (? )/??t q= (? ?t)/? q= (? ?t)/?
8. Thermal conductivity of liquids range from: 0.08 to 0.6 Less than 0.2 0.02 to 2.5 0.005 to 0.5 kcal/m-hr-°C
9. Thermal conductivity of steel is 45 kcal/m-hr-°C for carbon content 0.1% 1% 1.5% None of the above
10. 70 W/m2 of heat flows through a plane wall of thickness 50 mm, having 70 W/m°C thermal conductivity. The temperature gradient is 100°C/m 1°C/m 0.1°C/m 1000°C/m
11. Temperature curve in a plane homogenous wall is: Hyperbolic Parabolic Logarithmic Linear
12. The relationship between thermal conductivity and temperature in most materials is: None of the above Exponential Quadratic Linear
13. Equivalent thermal resistance depend only on: Thermal resistance Thermal conductance Thickness of individual layers Thermal resistance and thickness finalize dual layers.
14. Hourly loss of heat through a brick wall 4 m long, 2 m high and 250 mm thick, having surface temperatures 20°C and -30°C, ? = 0.6 kcal/m-hr-°C is 1200 kcal/hr 1840 kcal/hr 1440 kcal/hr 1800 kcal/hr
15. If q = 1000 kcal/m2 -hr, ? = 30 mm and t = 30° C, then ? in kcal/m-hr-°C is 0.01 10 0.1 1
16. Surfaces of a flat wall are maintained at 1000°C and 0°C and ? = 1.0 (1 + 0.001 t). Mean thermal conductivity is: 0.8 1.2 1.5 1.0
17. Thermal conductivity of the material of a wall 40 mm thick, maintaining t = 20°C , 2 is 1.5 W/m°C 3 W/m°C 0.29 W/m°C 0.3 W/m°C
18. Temperature distribution curve inside a homogenous cylindrical wall varies along a Logarithmic curve Curvilinear curve Parabolic curve Exponential curve
19. Heat flow through a cylindrical wall is inversely proportional to All of the above Natural logarithm of the ratio of outer radius to inner radius Length of the tube Thermal conductivity of the material
20. The concept of heat flowing through a unit of inner or outer surface area is applicable Heterogeneous composite plane wall Composite cylindrical wall Hollow concentric spheres Composite spherical wall
21. Temperature distribution curve of a composite cylindrical wall can be established only if Adjacent surfaces are at the same temperature Unsteady state conditions exist Thermal conductivities of individual layers are unknown Temperature field is two dimensional
22. Which is not true for convection heat transfer? Conduction is possible only in liquids and gases Heat transfer depends on thermal conductivity and temperature gradient as in heat conduction Heat is transferred by conduction and convection simultaneously Heat is transferred from a liquid or gas to a solid by direct contact
23. The kind and physical properties of fluid play dominating role in: Radiation Conduction and Radiation simultaneous Convection Conduction
24. Which is not true of critical velocity? Fluid velocity exceeding critical velocity leads to turbulent regime It is different for different fluids It depends on the geometry of flow Beyond critical velocity flow is still laminar
25. Friction force per unit contact area between two layers of fluid sliding past one another, is called Velocity gradient Co-efficient of dynamic viscosity Hydrodynamic kinematic viscosity Viscosity factor
26. What is not true? Heat transfer involves both thermal and hydrodynamic phenomena Shape and size of heat transfer surfaces does not affect substantially heat transfer Heat transfer surfaces arrangement depends on specific condition for flow Heat transfer surfaces are composed of plates or tubes
27. The unit of heat transfer co-efficient is: m2/sec kcal/hr kcal/m-hr-°C kcal/m2-hr-°C
28. The concept of overall heat transfer co-efficient is based on Shape and size of heat transfer surface Temperature difference and velocity of fluid flow Newtonian formula Fourier’s law
29. Heat transfer co-efficient is a function of Temperature and fluid flow velocity Physical properties of the fluid All of the above Shape and dimensions of heat transfer surfaces
30. Which differential equation describes heating and cooling at the boundaries of the substance Equation of conduction Continuity equation Equation of heat transfer Equation of flow
31. Temperature distribution in the field can be obtained form Differential equation of continuity Differential equation of conduction Differential equation of heat transfer Differential equation of flow
32. Differential equation of conduction is based on Mass conservation law Bernoulli’s law Newton’s second law Energy conservation law
33. Which is not true for convection heat transfer? Conduction is possible only in liquids and gases Heat transfer depends on thermal conductivity and temperature gradient as in heat conduction Heat is transferred by conduction and convection simultaneously Heat is transferred from a liquid or gas to a solid by direct contact
34. The kind and physical properties of fluid play dominating role in: Radiation All of the above Convection Conduction
35. Which is not true of critical velocity? Fluid velocity exceeding critical velocity leads to turbulent regime Beyond critical velocity flow is still laminar It is different for different fluids It depends on the geometry of flow
36. Frictional force per unit contact area between two layers of fluid sliding past one another, is called Hydrodynamic kinematic viscosity Co-efficient of dynamic viscosity Velocity gradient Viscosity factor
37. Which is not the condition of unambiguity? Chemical conditions Boundary conditions Time conditions Geometric conditions
38. Factor of similarity transformation depends on Neither on co-ordinates nor time Time Both space co-ordinates and time Space co-ordinates
39. Hydromechanical similarity involves Both (b) and (c) Equation of flow Continuity equation Differential equation of conduction
40. Grashoff number is identical to Gallilian number All of the above Froude number Archimedes number
41. Criteria equation for steady state forced flow is Nu = f (Fo, Re) Nu = f (Re, Pr) Nu = f (Re) Nu = f (Gr, Pr)
43. Reference temperature in a heat transfer process is Temperature at the wall Temperature at which physical properties are determined Average temperature Inlet fluid temperature
44. Which is not true of empirical formulas? These relations are validated by experiments These are used within the limits of independent variables These can be extra polated for larger or smaller values of the argument Empirical relationships between dimensionless groups are usually power functions
45. If A = 1, R = 0, D = 0, then body is defined as Ather manous Diather manous Black body White body
46. Solids and liquids which are practically non transparent to heat rays, in such cases: R = 0 A + R = 1 R+ D = 1 A + D = 1
47. Emission of the body proper depends on: All of the above Incident Radiation from surroundings Physical properties of the body Temperature of the body only
48. 2.9 mm-°C 2.9 m-°K 2.9 cm-°K 2.9 mm-°K
49. Energy emitted by a body in all directions is determined by: Kirchoff’s Law Stefan-Boltzmann Law Plank’s Law Lamert’s Law
50. The relationship between emissivity and absorptivity of a body is given by Kirchoff’s Law Plank’s Law Lambert’s Law Wien’s Law
51. Steam boiler is a heat exchange of the type None of the above Direct contact Regenerative Recuperative
52. Heat exchange in which one and the same heating surface is alternately exposed to the hot and cold fluids is: None of the above Direct contact Recuperative Regenerative
53. Water-cooling towers are heat exchangers of the type Direct-contact Recuperative Regenerative Surface exchangers
54. Water equivalent of heat carrier is given by: All of the above GCp VrCp WrfCp
55. Heat exchanges in which two liquids are directed at right angles to each other are called Multi-pass cross flow Parallel flow Cross flow Counter flow
56. 250 litres of hot fluid of gravity 100 kg/m3 and heat capacity 0.727 kcal/kg-o C, will have its water equivalent 25 kcal/hr-degree celcius 2000 kcal/hr-degree celcius 200 kcal/hr-degree celcius 250 kcal/hr-degree celcius
57. Which is not true for fins? Fins are also used in many refrigerating systems. Commonly used on small pores machines, scooters, motorcycles Widely used where temperature difference between the surface and surrounding fluids can be increased Fins are commonly used for increasing the heat transfer rates.
58. An extended surface attached circumferentially to a cylindrical surface is an example of Pin fin Spine fin Annular fin Straight fin
59. The circumferential fins used on the engine cylinder of scooters and motorcycles are of Triangular profile only Rectangular profile only Conical shape Rectangular or triangular profile
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