0% 0 Chemical Heat Transfer Quiz 9 1 / 50 Which is the best tube arrangement (in a shell and tube heat exchanger) if the fluids are clean and non-fouling ? None of these Square pitch Triangular pitch Diagonal square pitch 2 / 50 When vaporisation takes place directly at the heating surface, it is called_________? None of these Vapour binding Nucleate boiling Film boiling 3 / 50 What is the thermal conductivity of a perfect heat insulator ? ? Zero One Between 0 and ? 4 / 50 To reduce the tube side pressure drop for the same flow rate, the heat exchanger recommended is ________? 1-1 heat exchanger 2-4 heat exchanger 1-2 heat exchanger 3-2 heat exchanger 5 / 50 When the ratio of the Grashoff number and to the square of Reynolds number is one, the dominant mechanism of heat transfer is ________? Forced convection Mixed convection (both free and forced) Entry length problem in laminar forced conduction (developing thermal boundary layer) Free convection 6 / 50 Which characteristic of a fluid is not important in deciding its route in a shell and tube heat exchanger ? Fouling characteristic Corrosiveness Viscosity None of these 7 / 50 Unsteady state heat conduction occurs, when________? Three dimensional heat flow is concerned Temperature distribution is dependent on time Heat flows in one direction only Temperature distribution is independent of time 8 / 50 Which of the following forced convection heat transfer equation accounts for the liquid viscosity effect for viscous liquids ? Nusselt equation Dittus-Boelter equation None of these Sieder-Tate equation 9 / 50 Thermal diffusivity is given by___________? ?/hCp k/?Cp ?Cp/k ?Cp/a 10 / 50 When does the heat generated by fluid friction becomes appreciable compared to the heat transferred between the fluids ? None of these At high fluid velocity When fluid flows past a smooth surface At low velocity 11 / 50 Which is the most suitable for the concert-ration of highly concentrated solution ? Open pan evaporation Long tube vertical evaporator None of these Agitated film evaporator 12 / 50 Walls of a cubical oven are of thickness l, and they are made of material of thermal conductivity k. The temperature inside the oven is 100?C and the inside heat transfer coefficient is ?3k/l?. If the wall temperature on the outside is held at 25?C, what is the inside wall temperature in degree centigrade ? 43.75 81.25 48.25 35.5 13 / 50 Three materials A, B and C of equal thickness and of thermal conductivity of 20, 40 & 60 kcal/hr. m. ?C respectively are joined together. The temperature outside of A and C are 30?C and 100?C respectively. The interface between B and C will be at a temperature of _____ ?C? 70 95 40 50 14 / 50 Which of the following has maximum thermal conductivity ? Nitrogen Tar Iron Coal 15 / 50 The wavelength at which the maximum monochromatic emissive power occurs for a black body, is (where, T = absolute temperature of the black body)? ? ? 1/T ? T4 ?T Independent of T 16 / 50 Three solid objects of the same material and of equal mass-a sphere, a cylinder (length = diameter) and a cube are at 500?C initially. These are dropped in a quenching bath containing a large volume of cooling oil each attaining the bath temperature eventually. The time required for 90% change in temperature is the smallest for__________? Cube Equal for all the three Sphere Cylinder 17 / 50 Thermal conductivity of a gas at low density, ___________ with increase in temperature ? Remains unchanged May increase or decrease; depends on the gas Decreases Increases 18 / 50 What is Nusselt number ? hD/k CP. ?/h CP. ?/k h. CP/? 19 / 50 Trap is used to remove _________ from steam pipe lines? Non-condensable Steam Condensate None of these 20 / 50 Tube pitch is the ________ of tube diameters and the clearances? Difference None of these Ratio Sum 21 / 50 What is the geometric mean of two heat transfer areas A1 and A2 ? 2 ?(A1 . A2) ?(A1 + A2) ? ?(A1 . A2) ?(A1 . A2) 22 / 50 Thermal conductivity of a conducting solid material depends upon its________? Both A. & B. Porosity Neither A. nor B. Temperature 23 / 50 Value of Nusselt number [Nu = (hD/k)] for the heat transfer by conduction from a droplet or a spherical particle to a surrounding stagnant film is___________? 10 2 100 0.5 24 / 50 Which is the most suitable for the concentration of foamy & frothy liquors ? Agitated film evaporator None of these Open pan evaporator Long tube vertical evaporator 25 / 50 What is the absorptivity of a black body? 0.95 0 0.78 1 26 / 50 Value of Prandtl number for water ranges from__________? 5 to 10 1 to 2 1000 to 2000 100 to 500 27 / 50 Viscous & heat sensitive liquids are concentrated in ______ evaporators? Long tube None of these Agitated film Open pan 28 / 50 Water is normally used as a coolant in the heat exchange equipments mainly because of its_____? Low density Low viscosity Abundance & high heat capacity High fluidity 29 / 50 Thermal conductivities of most of the liquids ________ with rise in temperature? Increases May increase or decrease; depends on the liquid Remains unchanged Decreases 30 / 50 Thickness of thermal boundary layer is more compared to that of hydrodynamic boundary layer, when the value of Prandtl number is__________? > 1 < 1 > 5 1 31 / 50 What is the steam economy in case of a single effect evaporator system ? 0.1 > 1 1 < 1 32 / 50 What is the logarithmic mean of r1 and r2 ? (r1 ? r2)/-ln(r1/r2) (r2 ? r1)/ln(r1/r2) (r1 ? r2)/ln(r1/r2) (r1 ? r2)/ln(r2/r1) 33 / 50 What is the emissivity of a black body ? 0.5 1 0 0.9 34 / 50 Use of transverse baffles in a shell and tube heat exchanger is done to increase the_____? Turbulence of shell side fluid Rate of heat transfer All A., B. and C. Flow velocity 35 / 50 When warm and cold liquids are mixed, the heat transfer is mainly by________? Convection Conduction Both A. & C. Radiation 36 / 50 Vent pipes are provided in a condenser to _________? None of these Facilitate easy cleaning of tubes Purge the condenser Remove non-condensable gases 37 / 50 Vacuum is generally maintained in the vapour space of an evaporator mainly to___________? Concentrate heat sensitive materials Facilitate forward feeding in multiple effect evaporation Achieve very high concentration of the final product Get economical temperature difference by using moderate pressure steam 38 / 50 Viscosity of gases _______ with increase in temperature? Increase slowly Increase very rapidly Decrease slowly Remain unaffected 39 / 50 What is the unit of thermal conductivity ? Kcal/hr.m.?C Kcal/hr. ?C Kcal/hr. m2 ?C Kcal/hr.m 40 / 50 Thermal diffusivity of a material ___________? All A., B. and C. Has the unit m2 /sec Is the ratio of thermal conductivity to thermal capacity Is defined as K/? . Cp 41 / 50 When vaporisation takes place through a blanketting film of gas, the phenomenon is termed as _____ boiling? Transition Nucleate Pool Film 42 / 50 Which area is used in case of heat flow by conduction through a cylinder ? Geometric mean area None of these Logarithmic mean area Arithmetic mean area 43 / 50 Vibrations in the tubes of a shell and tube heat exchanger is induced due to the __________? Oscillations in the flow of shell/tube sides fluid Flow of fluid on the tube and shell sides Vibrations transmitted through piping and/or supports due to external reasons All A., B. and C. 44 / 50 Tubes are held between top and bottom tube sheets in Calandria type evaporator by keeping__________? Both the tube sheets floating The top tube sheet fixed and the bottom tube-sheet floating Both the tube sheets fixed The top tube sheet floating and bottom tube sheet fixed 45 / 50 Tube expansion allowances exist in ______ heat exchanger? Single pass fixed tube sheet Multipass fixed tube sheet None of these U-tube 46 / 50 Which of the following accessories is provided in the vapor line of an evaporator for removing the entrained liquid ? Vent Catchall Bleed point Baffle 47 / 50 Which has the lowest Prandtl number ? Liquid metal Water Lube oil Aqueous solution 48 / 50 Thermal diffusivity is the most important in heat transfer by___________? Natural convection Radiation Conduction Condensation 49 / 50 View factor is important in heat transfer by_______? Natural convection Radiation Steady state conduction Forced convection 50 / 50 Wavelength corresponding to the maximum energy is inversely proportional to the absolute temperature. This is _________ law? Wien?s Stefan?s Kirchoff?s Dalton?s Provide Your Information Your score is The average score is 0% LinkedIn Facebook Twitter 0% Restart quiz Send feedback Share on facebook Facebook Share on twitter Twitter Share on whatsapp WhatsApp PrevChemical Heat Transfer Quiz 8 Chemical Heat Transfer Quiz 10Next
