51. Dietus-Boelter equation used for the determination of heat transfer co-efficient is valid
52. The equation, , corrosponds to __________ analogy.
53. For large heat transfer area requirement, shell and tube heat exchanger is preferred, because it
54. Out of the following four assumptions used in the derivation of the equation for LMTD , which one is subject to the largest deviation in practice ?
55. Heat flux increases with temperature drop beyond the Leiden frost point in the plot of heat flux vs. temperature drop for a boiling liquid, because
56. Resistance to heat flow by conduction is proportional to (where, t & ρ are thickness & density of the material respectively and A = area normal to the direction of heat flow. )
57. Temperature profile in steady state heat transfer is
58. For the same heat load and mass flow rate in the tube side of a shell and tube heat exchanger, one may use multipass on the tube side, because it
59. When vaporisation takes place through a blanketting film of gas, the phenomenon is termed as __________ boiling.
60. Minimum recommended baffle spacing in a shell and tube heat exchanger is about (where, D = shell diameter)
61. Stefan-Boltzman law which describes the radiation heat transfer states that, it is proportional to (where, t = temperature in °C T = absolute temperature in ° K )
62. The Nusselt number for fully developed (both thermally and hydrodynamically) laminar flow through a circular pipe, where the wall heat flux is constant, is
63. What is the unit of thermal conductivity ?
64. The thermal radiation emitted by a body is proportional to Tn, where T is its absolute temperature. The value of 'n' is exactly 4 for
65. It is not preferable to use superheated steam in evaporators, because of its very
66. It is desired to concentrate a 20% salt solution (20 kg of salt in 100 kg of solution) to a 30% salt solution in an evaporator. Consider a feed of 300 kg/min at 30°C. The boiling point of the solution is 110°C, the latent heat of vaporisation is 2100 kJ/kg and the specific heat of the solution is 4 kJ/kg.K. The rate at which the heat has to be supplied in (kJ/min) to the evaporator is
67. LMTD for counterflow and prallel flow heat exchanger will be the same, when the
68. For flow over a flat plate, the ratio of thermal boundary layer thickness, 'xt' and hydrodynamic boundary layer thickness 'x' is equal to (where, NPr = Prandtl number)
69. The range of electromagnetic spectrum important in heat transfer by radiation is __________ microns.
70. Use of transverse baffles in a shell and tube heat exchanger is done to increase the
71. The actual temperature drop across the heating surface of an evaporator depends on the
72. Economy of a multiple effect evaporator depends upon the
73. The Graetz number is concerned with the
74. Solid angle subtended by the finite surface at the radiating element is
75. In forced convection, the heat transfer depends on