Heat Transfer Past Paper PDF

SECTION 1 500 times. The acceleration due to gravity is 9.8 ms-2. Neglecting the heat 1. Crystal size in a continuous crystalliser depends upon the capacity of agitator, the temperature of water (in °C)...

SECTION 1 500 times. The acceleration due to gravity is 9.8 ms-2. Neglecting the heat 1. Crystal size in a continuous crystalliser depends upon the capacity of agitator, the temperature of water (in °C) is a. rate of heat transfer. a. 40.5 b. degree of turbulence. b. 34.4 c. degree of supersaturation. c. 26.8 d. all (a), (b) and (c). d. 25 2. Heat waves 16. Fouling factor a. can not pass through vacuum. a. is a dimensionless quantity. b. travel in straight line. b. does not provide a safety factor for design. c. can be reflected by a mirror. c. accounts for additional resistances to heat flow. d. both (b) and (c). d. none of these. 3. Air is best heated with steam in a heat exchanger of 17. In case of vertical tube evaporator, with increase in liquor level, the overall a. plate type. heat transfer co-efficient b. double pipe type with fin on steam side. a. increases c. double pipe type with fin on air side. b. decreases d. shell and tube type. c. is not affected d. may increase or decrease; depends on the feed 4. Which of the following is generally considered as opaque surface towards radiations? 18. The steam ejector is used to a. Gases a. remove condensate from the steam pipelines. b. Solids b. create vacuum. c. Liquids c. superheat the steam. d. Both (b) and (c) d. none of these. 5. Black liquor generated during paper manufacture is concentrated in a 19. For shell and tube heat exchanger, with increasing heat transfer area, the a. single effect evaporator. purchased cost per unit heat transfer area b. single effect evaporator followed by a crystalliser. a. increases c. multiple effect evaporator. b. decreases d. multiple effect evaporators followed by a crystalliser. c. remains constant d. passes through a maxima 6. When vaporisation takes place directly at the heating surface, it is called a. film boiling 20. The thermal efficiency of a reversible heat engine operating between two b. nucleate boiling given thermal reservoirs is 0.4. The device is used either as a refrigerator or as c. vapour binding a heat pump between the same reservoirs. Then the coefficient of d. none of these performance as a refrigerator (COP)R and the co-efficient of performance as a heat pump (COP)HP are 7. Steam consumption in kg/hr in case of an evaporator is given by a. (COP)R = (COP)HP = 0.6 (where, C & E are capacity the economy of the evaporator respectively) b. (COP)R = 2.5; (COP)HP = 1.5 a. C/E c. (COP)R = 1.5; (COP)HP = 2.5 b. E/C d. (COP)R = (COP)HP = 2.5 c. CE 21. Hot water (0.01 m3 /min) enters the tube side of a counter current shell and tube heat exchanger at 80°C and leaves at 50°C. Cold oil (0.05 m 3/min) of density 800 kg/m3 and specific heat of 2 kJ/kg.K enters at 20°C. The log mean d. temperature difference in °C is approximately a. 32 8. Reynold's analogy states that b. 37 a. Nst α f c. 45 b. Nst α NRe d. 50 c. NNu α f d. NRe α f 22. In a heat exchanger, floating head is provided to a. facilitate cleaning of the exchanger. 9. With increase in temperature, the thermal conductivity of non-metallic b. increase the heat transfer area. amorphous solids c. relieve stresses caused by thermal expansion. a. decreases d. increase log mean temperature gradient. b. increases c. remains constant 23. Leidenfrost point is a term concerned with the d. first decreases upto certain temperature and then increases a. condensation of the saturated vapor on a cold surface. b. concentration of a corrosive solution by evaporation. 10. Fourier's law applies to the heat transfer by c. heat transfer between two highly viscous liquids. a. convection d. boiling of a liquid on a hot surface. b. radiation c. conduction 24. A process stream of dilute aqueous solution flowing at the rate of10 Kg.s - d. all (a), (b) & (c) 1 is to be heated. Steam condensate at 95°C is available for heating purpose, also at a rate of 10 Kg.s-1. A 1 - 1 shell and tube heat exchanger is available. 11. Shell side pressure drop in a shell and tube heat exchanger does not The best arrangement is depend upon the a. counter flow with process stream on shell side. a. baffle spacing & shell diameter. b. counter flow with process stream on tube side. b. tube diameter & pitch. c. parallel flow with process stream on shell side. c. viscosity, density & mass velocity of shell side fluid. d. parallel flow with process stream on tube side. d. none of these. 25. Heat produced when a steady state current, I passes through an electrical 12. In the equation Q = UAΔt; Δt is conductor having resistance, 'R' is a. geometric mean temperature difference. a. IR b. arithmetic mean temperature difference. b. I2R c. logarithmic mean temperature difference. c. IR2 d. the difference of average bulk temperatures of hot and cold fluids. d. I2R2 13. With increase in porosity, the thermal conductivity of a solid substance 27. Convective heat transfer co-efficient in case of fluid flowing in tubes is not a. increases affected by the tube length/diameter ratio, if the flow is in the __________ b. decreases zone. c. remains unchanged a. laminar d. may increase or decrease; depends on the solid b. transition c. both 'a' & 'b' 14. For an ideal black body d. highly turbulent a. absorptivity = 1 b. reflectivity = 1 28. The actual temperature drop across the heating surface in an evaporator c. emissivity = 0 depends on the d. transmissivity = 1 a. feed. b. depth of liquid over heating surface. 15. In Joule's experiment, an insulated container contains 20 kg of water c. pressure difference between steam chest and vapour space. initially at 25°C. It is stirred by an agitator, which is made to turn by a slowly d. all (a), (b) and (c). falling body weighing 40 kg through a height of 4 m. The process is repeated 29. Which of the following is not used as a medium for high temperature d. lower heating ? a. Dowtherm 43. The heat flux (from outside to inside) across an insulating wall with thermal b. mercury conductivity, K= 0.04 W/m.°K and thickness 0.16m is 10 W/m2. The c. liquid metal (e.g. molten sodium) temperature of the inside wall is - 5°C. The outside wall temperature is d. fused salts (e.g., an eutectic mixture of 53% KNO3, 40% a. 25°C NaNO2and 7% NaNO3) b. 30°C c. 35°C 30. Presence of a non-condensing gas in a condensing vapour d. 40°C a. increases the rate of condensation. b. decreases thermal resistance. 44. Thermal conductivity of a conducting solid material depends upon its c. is desirable to increase the film co-efficient. a. temperature d. none of these. b. porosity c. both (a) & (b) 31. Kirchoff s law applies to __________ radiation. d. neither (a) nor (b) a. total b. monochromatic 45. Pick out the wrong statement. c. both (a) & (b) a. The controlling resistance in case of heating of air by condensing d. neither (a) nor (b) steam is in the air film. b. The log mean temperature difference (LMTD) for counter flow and 32. With the increase of temperature, the Col-burn jH factor parallel flow can be theoretically same when any one of the fluids a. increases. (hot or cold fluid) passes through the heat exchanger at constant b. decreases. temperature. c. remains unchanged. c. In case of a 1 - 2 shell and tube heat exchanger, the LMTD d. may increase or decrease ; depending on temperature. correction factor value increases sharply, when a temperature cross occurs. 33. In case of evaporators, liquid entrainment results primarily due to d. Phase change in case of a pure fluid at a given pressure from a. high vacuum in the evaporator. liquid to vapor or vice-versa occurs at saturation temperature. b. high evaporation rate. c. foaming of the solution. 46. The average heat transfer co-efficient for laminar film condensation on d. high heat transfer rate. vertical surface is inversely proportional to (where, ΔT = Temperature drop across condensate film ) 34. Baffles in the shell side of a shell and tube heat exchanger a. (ΔT)2 a. increase the cross-section of the shell side liquid. b. ΔT b. force the liquid to flow parallel to the bank. c. (ΔT)1/4 c. increase the shell side heat transfer co-efficient. d. (ΔT)3/2 d. decrease the shell side heat transfer co-efficient. 47. Bulk of the convective heat transfer resistance from a hot tube surface to 35. Air is to be heated by condensing steam. Two heat exchangers are the fluid flowing in it, is available (i) a shell and tube heat exchanger and (ii) a finned tube heat a. in the central core of the fluid. exchanger. Tube side heat transfer area are equal in both the cases. The b. uniformly distributed throughout the fluid. recommended arrangement is c. mainly confined to a thin film of fluid near the surface. a. finned tube heat exchanger with air inside and steam outside. d. none of these. b. finned tube heat exchanger with air outside and steam inside. c. shell and tube heat exchanger with air inside tubes and steam on 48. Which of the following is concerned with both heat and mass transfer ? shell side. a. Lewis relationship d. shell and tube heat exchanger with air on shell side and steam b. Nusselt number inside tubes. c. Kutateladze number d. Froude number 36. The unit of heat transfer co-efficient in SI unit is a. J/M2°K 49. A backward feed multiple effect evaporator is better than forward feed for b. W/m2°K concentrating cold feed, because it provides c. W/m°K a. higher economy d. J/m°K b. lower capacity c. both (a) & (b) 37. The number of kg vaporised per kg of steam fed to the evaporator is d. lower economy defined as a. capacity 50. A 10 cm dia steam pipe, carrying steam at 180°C, is covered with an b. rate of evaporation insulation (conductivity = 0.6 W/m.°C). It losses heat to the surroundings at c. economy 30°C. Assume a heat transfer co-efficient of 0.8 W/m2.°C for heat transfer from d. rate of vaporisation surface to the surroundings. Neglect wall resistance of the pipe and film resistance of steam. If the insulation thickness is 2 cms, the rate of heat loss 38. Pick out the wrong statement. from this insulated pipe will be a. In case of heat transfer by purely forced convection, GR/Re2 ≤ 1. a. greater than that for uninsulated steam pipe. b. The equivalent diameter of heat transfer for a duct of square cross- b. less than that of the uninsulated steam pipe. section (having each side as 'x') is equal to 4x. c. equal to that of the uninsulated steam pipe. c. Distillation process is not the same as evaporation. d. less than the steam pipe with 5 cms insulation. d. The effectiveness of nucleate boiling depends basically on the ease with which the bubbles are formed and detached from the SECTION 2 heating surface. 1. Which area is used in case of heat flow by conduction through a cylinder ? a. Logarithmic mean area 39. Economy of a multiple effect evaporator is not influenced much by the b. Arithmetic mean area a. boiling point elevations c. Geometric mean area b. temperature of the feed d. None of these c. rate of heat transfer d. ratio of the weight of the thin liquor to thick liquor 2. Heat transfer by conduction results due to the transfer of free electrons, kinetic energy & vibrational energy from one molecule to another. Conduction 40. Increasing the liquor level in the evaporator results in the heat transfer can not take place a. decreased capacity. a. between two bodies in physical contact with each other. b. increase in liquor film co-efficient. b. between two bodies not in physical contact with each other. c. decreased effect of hydrostatic head. c. from one part of a body to the another part of the same body. d. increased true temperature drop. d. both 'b' & 'c' 41. The equivalent diameter for pressure drop is __________ that for heat 3. The dimensionless group in mass transfer that is equivalent to Prandtl transfer. number in heat transfer is a. smaller than a. Nusselt number. b. greater than b. Sherwood number. c. equal to c. Schmidt number. d. not related with d. Stanton number. 42. Controlling heat transfer film co-efficient is the one, which offers 4. Finned tube heat exchangers __________ resistance to heat transfer. a. give larger area per tube. a. no b. use metal fins of low thermal conductivity. b. the least c. facilitate very large temperature drop through tube wall. c. the largest d. are used for smaller heat load.  c. transition 5. The absorptivity of a grey body at a given temperature __________ with d. film increasing wavelength of radiation. a. increases 18. Minimum recommended baffle spacing in a shell and tube heat exchanger b. decreases is about (where, D = shell diameter) c. remains constant a. 0.2 D d. may increase or decrease ; depends on the material b. 0.5 D c. 0.66 D 6. Which one gives the monochromatic emissive power for black body d. 0.80 D radiation ? a. Planck's law 19. Stefan-Boltzman law which describes the radiation heat transfer states b. Kirchhoffs law that, it is proportional to (where, t = temperature in °C T = absolute c. Wien's law temperature in ° K ) d. Stefan-Boltzman law a. t4 b. T4 7. For what value of Prandtl number, St = f/2? c. 1/t4 a. 1.5 d. 1/T4 b. 1 c. >1 20. The Nusselt number for fully developed (both thermally and d. 1 a. 0.5 d. 2 about __________ kg of steam. d. 1.5 a. 0.4 - 0.6 b. 1-1.3 49. c. 1.8-2 Heat transfer occurs by natural convection because change in temperature causes d. 2 - 2.4 difference in 37. a. viscosity A metal wire of 0.01 m dia and thermal conductivity 200 W/m.K is exposed to a fluid b. density stream with a convective heat transfer coefficient of 100 W/m2.K. The Biot number is c. thermal conductivity a. 5.6 d. heat capacity b. 0.025 e. c. 3.5 50. d. 0.0035 The ratio of kinematic viscosity to thermal diffusivity is called the __________ number. 38. a. Peclet Analogy between mass and heat transfer is not applicable in case of b. Prandtl a. same velocity profile or equal eddy diffusivities. c. Stanton b. thermal or pressure mass diffusion. d. Nusselt c. viscous heating or chemical reaction. d. both (b) and (c). SECTION 4 39. 1. A __________ surface has the maximum thermal emissivity out of the following. The critical radius 'r' of insulation on a pipe is given by a. black & smooth a. r = 2k/h b. black & rough b. r = k/h c. white & smooth c. r = k/2h d. white & rough d. r = h/k 40. Radiant energy received by a body is proportional to (where, d = the distance between 2. the object emitting radiation and that receiving it.) As per Kirchoffs law, the ratio of the total radiating power to the absorptivity of a a. (d)^0.5 body depends on the b. d a. temperature of the body only. c. d2 b. wavelength of monochromatic radiation. d. d1.5 c. both (a) and (b). d. nature of material of body. 41. Mechanical recompression evaporation is used in the production of 3. a. alcohol If the baffle spacing in a shell and tube heat exchanger increases, then the Reynolds b. distilled water number of the shell side fluid c. salt a. remains unchanged. d. fruits jam b. increases. c. increases or decreases depending on number of shell passes. 42. d. decreases. A measure of the extent to which viscous heating is important relative to the heat flow resulting from the impressed temperature difference is represented by the __________ 4. number. The heat transfer by radiation from a mild steel surface is to be reduced by reducing a. Condensation the emissivity of the surface. This can be best achieved by b. Grashoff a. painting the surface black. c. Stantan b. painting the surface white (with aluminium paint). d. Brinkman c. giving the surface a mirror finish. d. roughening the surface. 43. Out of 100 kcal/second of incident radiant energy on the surface of a thermally 5. transparent body, 300 kcal/second is reflected back. If the transmissivity of the body is __________ paint has the maximum absorption coefficient. 0.25, the emissivity of the surface will be a. Black a. 0.35 b. Yellow b. 0.45 c. White d. Grey 16. In a multipass shell and tube heat exchanger, tube side return pressure loss is equal to 6. __________ the velocity head. What is Nusselt number ? a. twice b. four times c. square root of d. square of a. 17. For a given ambient air temperature with increase in the thickness of insulation of a hot cylinderical pipe, the rate of heat loss from the surface would a. decrease b. b. increase c. first decrease and then increase d. first increase and then decrease c. 18. In a parallel flow heat exchanger, if the outlet temperature of hot and cold fluids are the same, then the log mean temperature difference (LMTD) is a. minimum d. b. maximum c. zero 7. d. infinity Steam traps are provided in steam carrying pipelines to a. condense steam. 19. b. release excess steam pressure by bleeding steam. For what value of Prandtl number, the Col-burn analogy is valid ? c. remove condensate and inert gases. a. 0.06 to 120 d. none of these. b. 0.6 to 120 c. 1 to 103 8. d. l to 50 The Dietus-Boelter equation for convective leat transfer 20. In a forward feed multiple effect, the pressure build up will be a. least at the inlet of the first effect. b. least at the outlet of the last effect. c. highest at the inlet of the last effect. d. highest at the outlet of the last effect. cannot be used for a. low Reynold's number 21. b. very low Grashoff number Film boiling is usually not desired in commercial equipments, because c. molten metals a. the heat transfer rate is low in view of the large temperature drop. d. all (a), (b) and (c) b. it is difficult to maintain. c. it is not economic. 9. d. none of these. A hot liquid is kept in a big room. The logorithm of the numerical value of the temperature difference between the liquid and the room is plotted against time. The 22. plot will be very nearly a/an For the same heat transfer area and the terminal conditions, the ratio of the capacities a. ellipse of a single effect evaporator to a triple effect evaporator is b. straight line a. 3 c. parabola b. 0.33 d. circular arc c. 1 d. 1.33 10. 23. Radiation heat transfer rates does not depend upon the The variation of thermal conductivity of a metal with temperature is often correlated a. type of absorbing surface. using an expression of the form K = K0 + at. where, K is the thermal conductivity b. distance between the heat source and the object receiving the heat. and T is the temperature (in °K). The units of 'a' in SI system will be c. surface area and temperature of the heat source. a. W/m.k d. none of these. b. W/m c. W/m.k2 1. d. none, 'a' is just a number Which of the following is correct ? a. Rate = Driving force x Resistance 24. b. Driving force = Rate x Resistance Film condensation is promoted on a/an __________ surface. c. Resistance = Driving force x Rate a. oily d. Rate = Resistance/Driving force b. coated c. clean & smooth 12. d. dirty Convective heat transfer, in which heat is transferred by movement of warmed matter is described by 25. a. Fourier's law Dietus-Boelter equation cannot be used for molten metals mainly due to its very low b. Newton's law of cooling a. Prandtl number c. Fick's law b. Grashoff number d. none of these c. thermal conductivity d. viscosity 13. As the difference between the wall temperature and bulk temperature increases, the 26. boiling heat transfer co-efficient If Prandtl number is greater than the Schmidt number, then the a. continues to increase. a. thermal boundary layer lies inside the concentration boundary layer. b. continues to decrease. b. concentration boundary layer lies inside the thermal boundary layer. c. goes through a minimum. c. thermal & concentration boundary layers are of equal thickness. d. goes through a maximum. d. hydrodynamic(i.e., momentum)boundary layer is thicker than the other two. 14. 27. Heat transfer rate per unit area is called Which of the following accessories is provided in the vapor line of an evaporator for a. thermal conductivity removing the entrained liquid ? b. heat flux a. Bleed point c. heat transfer co-efficient b. Vent d. thermal diffusivity c. Catchall d. Baffle 15. Log mean temperature difference (LMTD) cannot be used, if 28. a. heat transfer co-efficient over the entire heat exchanger is not constant. Rate of heat transfer by vaporisation from pools of water is affected by the b. there exists an unsteady state. a. nature of heating surface and distribution of bubbles. c. the heat capacity is not constant and there is a phase change. b. surface tension of water. d. none of these. c. viscosity of water. d. all (a), (b) and (c). b. liquor-film co-efficient c. both (a) and (b) 29. d. neither (a) and (b) Multiple effect evaporators are commonly used in the manufacture of P. Paper Q. Superphosphate 39. R. Sugar S. Fats Electromagnetic radiations propagate in vacuum with a velocity of __________ a. P and Q metre/second. b. P and R a. 3 x l05 c. P and S b. 3 x l08 d. R and S c. 3 x l010 d. 3 x l012 30. Which of the following has the highest thermal conductivity ? 40. a. Brick Heat flux is the time rate of heat transfer per unit b. Air a. length c. Water b. area d. Silver c. volume d. none of these 31. Which of the following is unimportant in forced convection ? 41. a. Reynolds number Film boiling occurs at __________ pressure. b. Prandtl number a. atmospheric c. Grashhoff number b. sub-atmospheric d. none of these c. negative d. very high 32. Steam is to be condensed in a shell and tube heat exchanger, 5 m long with a shell 42. diameter of 1 m. Cooling water is to be used for removing the heat. Heat transfer co- Heat flux through several resistances in series in analogous to the current flowing efficient for the cooling water, whether on shell side or tube side is the same. The best through several arrangement is a. resistances in parallel. a. vertical heat exchanger with steam on tube side. b. capacitors in series. b. vertical heat exchanger with steam on shell side. c. resistances in series. c. horizontal heat exchanger with steam on tube side. d. none of these. d. horizontal heat exchanger with steam on shell side. 43. 33. Extended heat transfer surface like fins are used to increase the heat transfer rate. Fin In a multiple effect evaporator, the effect of boiling point elevation is to efficiency is defined as the ratio of heat transferred across the fin surface to the a. reduce the capacity theoretical heat transfer across an equal area held at the b. reduce the economy a. surrounding temperature. c. increase the economy b. average temperature of the fin. d. none of these c. temperature of the fin end. d. constant temperature equal to that of the base 34. The rate of heat transfer through a pipe wall is given 44. by,. For cylinder of very thin wall, q can be Vacuum is generally maintained in the vapour space of an evaporator mainly to a. get economical temperature difference by using moderate pressure steam. b. facilitate forward feeding in multiple effect evaporation. c. concentrate heat sensitive materials. d. achieve very high concentration of the final product. approximated by 45. Double pipe heat exchangers are used a. when heat transfer area required is very high. b. when heat transfer area required is very low, i.e (100-200 ft2). a. c. because it occupies less floor area. d. because it is less costly. 46. Nusselt number (for forced convection heat transfer) is a function of the __________ b. number. a. Prandtl b. Reynolds c. both (a) & (b) d. neither (a) nor (b) c. 47. Pick out the wrong statement. a. Heat transfer by radiation can not occur across an absolute volume. d. b. In case of a shell and tube heat exchanger, the pressure drop through the shell is proportional to the number of times the fluid crosses the bundle between baffles. 35. c. Propagation velocity for travel of heat radiation through vacuum is equal to the Dropwise condensation occurs on __________ surfaces. velocity of the light. a. clean and dirt free d. The amount of heat involved in the condensation or vaporisation of 1 kg of a fluid is b. smooth clean the same. c. contaminated cooling d. polished 48. Which type of heat exchanger is preferred for heavy heat loads ? 36. a. Double pipe For specified tube outside diameter, higher BWG means higher b. Plate fine a. tube thickness c. Series and parallel set of shell and tube b. cross-sectional area d. None of these c. weight per unit length d. none of these 49. Pick out the wrong statement. 37. a. Reciprocal of the resistance to heat flow is called thermal conductance. Pick out the wrong statement. b. Unit of thermal conductance is W/°K. a. Swenson-Walker crystalliser is a batch crystalliser. c. Thermal conductance of a wall of thickness 'L', thermal conductivity 'k' and heat flow b. Super saturation of the solution is the driving potential for a crystal growth. area 'A' is kL/A. c. The liquor left after the removal of crystals from a solution is called mother liquor. d. none of these. d. The first stage of crystal formation is called nucleation. 50. 38. While the total emissivity of a perfect black body is unity, the same for a real body is In case of a vertical tube evaporator, with increase in the liquor level, the __________ a. 0 is increased. b. 1 a. velocity of circulation c. >1 d. between 0 and 1 13. In forced convection, the Nusselt number is a function of a. Re and Pr SECTION 5 b. Re and Gr c. Pr and Gr. d. Re and Sc 1. The Grashoff number is defined as the ratio of the a. buoyancy to inertial forces. 14. b. buoyancy to viscous forces. At what value of Prandtl number, the hydrodynamic and thermal boundary layers are c. inertial to viscous forces. identical ? d. buoyancy to surface tension forces. a. 0.5 b. 1 2. c. 1.5 According to Reynolds analogy, Stanton number is equal to (where, f = Fanning d. 80 friction factor) a. 2f 15. b. f A dilute aqueous solution is to be concentrated in an evaporator system. High pressure c. f/2 steam is available. Multiple effect evaporator system is employed, because d. f/4 a. total heat transfer area of all the effects is -less than that in a single effect evaporator system. 3. b. total amount of vapor produced per Kg of feed steam in a multiple effect system is The absorptivity of a body is equal to its emissivity much higher than in a single effect. a. at a particular temperature. c. boiling point elevation in a single effect system is much higher than that in any effect b. for circular bodies. in a multieffect system. c. under thermal equilibrium. d. heat transfer co-efficient in a single effect is much lower than that in any effect in a d. none of these. multieffect system. 4. Absorptivity and refletivity of a perfect black body are respectively 16. a. 1 and 0 Heat transfer efficiency leading of energy conservation in a heat exchanger can be b. 0 and 1 achieved by c. 1 and ∞ a. keeping the heat transfer surface clean. d. 0 and 0.5 b. enhancing the fluid pumping rate. c. increasing the tube length. 5. d. none of these. In thermal radiation for a black body (where, ε is emissivity and α is absorptivity) a. α = 1; ε ≠ 1 17. b. α ≠ 1, ε = 1 Trap is used to remove __________ from steam pipe lines. c. α ≠ 1, ε ≠ 1 a. steam d. α = 1; ε = 1 b. condensate c. non-condensables 6. d. none of these Pick out the wrong statement. a. Superheated steam is preferably not used for process heating because of its low heat 18. transfer film co-efficient. A composite flat wall of a furnace is made of two materials 'A' and 'B'. The thermal b. In a shell and tube heat exchanger, the shell pressure drop is maximum for orifice conductivity of 'A' is twice of that of material 'B', while the thickness of layer of 'A' is baffles. half that of B. If the temperature at the two sides of the wall are 400 and 1200°K, then c. S.I. unit of fouling factor is Watt/m2.°K. the temperature drop (in °K) across the layer of material 'A' is d. Longitudinal fins are used in extended surface heat exchangers, when the direction of a. 125 fluid flow is parallel to the axis of the tube. b. 133 c. 150 7. d. 160 When warm and cold liquids are mixed, the heat transfer is mainly by a. conduction 19. b. convection Tube pitch is the __________ of tube diameters and the clearances. c. radiation a. sum d. both(a) & (c) b. difference 8. c. ratio A cube, sphere & a thin circular plate (all having same mass and made of same d. none of these material) are all heated to 300°C and allowed to cool in natural air. Which one will cool the slowest ? 20. a. Cube With increase in the distance between the heat source and the object receiving the heat, b. Plate the radiation heat transfer c. Sphere a. decreases d. All will cool at the same rate b. increases c. increases exponentially 9. d. remains unaffected Vent pipes are provided in a condenser to a. remove non-condensable gases. 21. The equivalent diameter for the annulus of a double pipe heat exchanger, whose b. purge the condenser. inner pipe has fins on the outside is __________ compared to the same size pipes c. facilitate easy cleaning of tubes. without fins. d. none of these. a. more b. less 10. c. same Heat transfer by natural convection is enhanced in system with d. unpredictable a. high viscosity. b. high co-efficient of thermal expansion. 22. c. low temperature gradients. Natural convection is characterised by d. low density change with temperature. a. Grashhoff number b. Peclet number 11. c. Reynolds number In case of __________ boiling, the bubbles formed on a submerged hot surface get d. Prandtl number absorbed in the mass of the liquid. a. nucleate 23. b. pool Nusselt number for full developed, laminar, constant property flow in a pipe at c. low pressure uniform heat flux is d. none of these a. 0.72 12. b. 4.364 A body cools down from 75°C to 70°C in 10 minutes. It will cool down from 70° C to c. 18 65° C in __________ minutes. d. 83 a. 10 b. >10 24. c. 5 Economy of an evaporator is influenced by the a. steam pressure 25. b. feed temperature The critical radius of insulation for cylindrical pipe is (where, hi = heat transfer c. number of effect coefficient at inside of the pipe ) d. both(b) & (c) a. K/h0 b. 2K/h0 c. hi/K 36. If the thermal conductivity of a wall material is independent of temperature, the d. 2hi/K steady state temperature distribution in the very large thin plane wall having steady, uniform surface temperature follows __________ law. 26. a. hyperbolic The heat flux in the nucleate boiling regimes is proportional to (where, ΔT = excess b. parabolic temperature) c. linear a. (ΔT)2 d. logarithmic b. (ΔT)4 c. (ΔT)3 37. d. (ΔT)^0.5 In regenerative air preheater (as practised in heating of coke ovens), the heat is transferred 27. a. through a metallic wall. In a 1-1 cocurrent heat exchanger, if the tube side fluid outlet temperature is equal to b. by direct contact of hot flue gas with air. the shell side fluid outlet temperature, then the LMTD is c. by heating an intermediate material (like chequor bricks) and then heating the air from a. ∞ this hot material. b. 0 d. none of these. c. equal to the difference between hot and cold fluids inlet temperature. d. equal to the difference between hot fluid inlet temperature and cold fluid outlet 38. temperature. __________ equation relates the thermal conductivity of a solid to its temperature. a. Antonie 28. b. Kopp's A body is called grey if the monochromatic emissivity of the body is c. Lee's a. zero d. Kistyakowski b. unity c. same for all wavelengths 39. d. different for all wavelengths For small temperature difference, the heat transfer rate as per Newton's law of cooling is proportional to (where, Δt = excess temperature) 29. a. Δt In an extended surface heat exchanger, fluid having lower co-efficient b. Δt2 a. flows through the tube. c. Δt3 b. flows outside the tubes. d. Δt^0.5 c. can flow either inside or outside the tubes. d. should not be used as it gives very high pressure drop. 40. Pick out the wrong statement. 30. a. The condensing film co-efficient is about 3 times lower for vertical condenser as In a shell and tube heat exchanger, the tube side heat transfer co-efficient just at the compared to the equivalent horizontal condenser for identical situation. entrance of the tube is b. Film co-efficient for vaporisation decreases as a result of vapor binding. a. infinity. c. In industrial practice, sub-cooling of condensate is required, when the condensate is a b. zero. volatile liquid and is to be transferred for storage. c. same as average heat transfer co-efficient for tube side. d. Overall heat transfer co-efficient in a heat exchanger is controlled by the value of the d. none of these. film co-efficient, which is higher.. 31. Grashoff number, which is defined as g. β(Ts - T∞) ρ2. L3/μ2, is proportional to the 41. Viscous & heat sensitive liquids are concentrated in __________ evaporators. ratio of buoyancy force to __________ force. a. open pan a. viscous b. long tube b. elastic c. agitated film c. inertial d. none of these d. none of these 42. 32. 1 BTU/hr.ft.°F is equal to __________ kcal/hr. m.°C. Pick out the wrong statement. a. 1.49 a. By increasing the number of shell passes, the temperature cross in a shell and tube heat b. 1 exchanger can be prevented. c. 4.88 b. An underdesigned steam trap will back up the condensate instead of discharging it out. d. none of these c. Steam condensate is corrosive because of the presence of dissolved oxygen in it. d. Film boiling is desirable in commercial equipments due to high heat transfer rate at 43. low temperature drop. Heat transfer by radiation between two bodies at T1 & T2 and in an ambient temperature of Ta°C depends on 33. a. T1 - T2 Graetz number is given by b. T1 - Ta c. T2 - Ta d. none of these 44. a. The ratio of momentum diffusivity to thermal diffusivity is the __________ number. a. Prandtl b. Nusselt c. Stanton b. d. Grashoff 45. For a perfectly transparent surface (like gases), the c. a. absorptivity = 0 b. transmissivity = 1 c. reflectivity = 0 d. all (a), (b) & (c) d. 46. 34. For a fluid flowing in an annulus space, the wetted perimeter for heat transfer and For a cold dilute feed to produce thick viscous liquor, backward feeding as compared pressure drop are to forward feeding results in a. same a. increased economy b. different b. decreased economy c. never different c. lower capacity d. linearly related d. no effect on economy 47.  During crystallisation, formation of crystal can occur in __________ solution only. d. transition region a. saturated b. supersaturated 10. c. undersaturated In case of __________ boiling, the liquid temperature is below the saturation d. all (a), (b) and (c) temperature and the boiling takes place in the vicinity of the heated surface. e. a. nucleate 48. b. local An evaporator while concentrating an aqueous solution from 10 to 40% solids c. pool evaporates 30000 kg of water. The amount of solids handled by the system in kg is d. saturated a. 4000 b. 9000 c. 4600 11. The ratio of velocity head to tube side return loss in case of a multipass shell and d. 3000 tube heat exchanger is e. a. 2 49. b. 1/2 An insulator should have c. 4 a. low thermal conductivity. d. 1/4 b. high thermal conductivity. c. less resistance to heat flow. 12. d. a porous structure. Terminal point temperature differences between fluids in case of a heat exchanger is termed as 50. a. approach. In a backward feed multiple effect evaporator b. log mean temperature difference. a. feed is introduced in the first effect. c. arithmetic mean temperature difference. b. feed flows from low pressure to high pressure. d. geometric mean temperature difference. c. no pumps are required between successive effects. d. none of these. 13. LMTD can't be used as such without a correction factor for the a. multipass heat exchanger. SECTION 6 b. baffled heat exchanger. c. condensation of mixed vapour in a condenser..1. d. all (a) (b) and (c). Choose the correct equation. a. Nu = (Re) (Pr) (Gz) 14. b. Nu = (Re) (Pr) (St) Fqra cold viscous feed, backward feed gives __________ than forward feed. c. Nu = (Re)(Pr) a. a higher capacity d. Nu = (Pr)(St) b. a lower capacity c. lower economy 2. d. none of these In a forward feed multiple effect evaporator unit a. viscosity of liquid is highest in first effect. 15. b. transfer from effect to effect is done by pumps. Walls of a cubical oven are of thickness l, and they are made of material of thermal c. no pump is required to withdraw the product from the last effect. conductivity k. The temperature inside the oven is 100°C and the inside heat transfer d. none of these. co-efficient is 3k/l. If the wall temperature on the outside is held at 25°C, what is the inside wall temperature in degree centigrade ? 3. a. 35.5 In case of heat flow by conduction for a cylindrical body with an internal heat source, b. 43.75 the nature of temperature distribution is c. 81.25 a. linear d. 48.25 b. hyperbolic c. parabolic d. none of these 16. Overall heat transfer co-efficient of a particular tube is U1. If the same tube with some dirt deposited on either side has coefficient U2, then 4. a. U1 = U2 For heat flow through very thick walled cylinder, use____mean radius. b. U2 > U1 a. arithmetic c. U1 > U2 b. logarithmic d. U1 = dirt factor - U2 c. geometric d. either (a) or (c) 17. ADABB In SI units, thermal conductivity is expressed in 5. a. Watt/m.°K Indirect contact heat exchangers are preferred over direct contact heat exchangers, b. Watt/m2. °K because c. Watt/m2. °K a. heat transfer co-efficient are high. d. Watt/m4. °K b. there is no risk of contamination. c. there is no mist formation. 18. d. cost of equipment is lower. Boiling point of a solution according to Duhring's rule is a linear function of the __________ of water. 6. a. boiling point (at the same pressure) Water is normally used as a coolant in the heat exchange equipments mainly because b. viscosity ofits c. density a. abundance & high heat capacity d. thermal conductivity b. low density c. low viscosity 19. d. high fluidity The overall resistance for heat transfer through a series of flat resistance, is the __________ of the resistances. 7. a. average The rate of emission of radiation by a body does not depend upon the b. geometric mean a. wavelength of radiation. c. product b. surface temperature of the body. d. sum c. nature of the surface. d. shape and porosity of the body. 20. At what value of Prandtl number, conduction is negligible in the turbulent core of a 8. fluid flowing through a heated pipe ? Which of the following has maximum thermal conductivity at the same temperature? a. 0.5 a. Steel b. < 0.5 b. Petrol c. >0.6 c. Air d. < 0.1 d. All have the same conductivity 9. 21. A sphere of radius 'R1' is enclosed in a sphere of radius 'R2'. The view (or shape) Maximum heat transfer rate is obtained in __________ flow. factor for radiative heat transfer of the outer sphere with respect to the inner sphere is a. laminar a. 0 b. turbulent b. R2/(R1+R2) c. creeping c. 1 d. (R1/R2)2 The capacity of double-effect evaporator is less than half of the capacity of two single effects, each of which is operating over same terminal temperature difference, when 22. the For a laminar flow of fluid in a circular tube, 'h1' is the convective heat transfer co- a. solution has an elevation of boiling point. efficient at velocity 'V1'. If the velocity is reduced by half and assuming the fluid b. evaporators operate under vacuum. properties are constant, the new convective heat transfer co-efficient is c. evaporators opreate at atmospheric pressure. a. 1.26 h1 d. none of these. b. 0.794 h1 c. 0.574 h1 35. d. 1.741 h1 Peclet number (Pe) is given by a. Pe = Re.Pr 23. b. Pe = Re/Pr The main purpose of providing fins on heat transfer surface is to increase the c. Pe = Pr/Re a. temperature gradient. d. Pe = Nu.Re b. mechanical strength of the equipment. c. heat transfer area. 36. d. heat transfer co-efficient. Nusselt number is the ratio of the a. temperature gradient of the wall to that across the entire pipe. 24. b. temperature difference to the temperature gradient at the wall. A BTU/hr.ft.2 °F is equal to c. heat flux at the wall to that across the entire pipe. a. 1 kcal/hr. m2°C. d. none of these b. 4.88 kcal/hr. m.2°C. c. 1 kcal/hr. m2.°K. 37. d. none of these. Prandtl number is the ratio of a. momentum diffusivity to mass diffusivity. 25. b. momentum diffusivity to thermal diffusivity. Which of the following has the lowest Prandtl number ? c. thermal diffusivity to mass diffusivity. a. Molten sodium (a coolant used in fast breeder reactor) d. thermal diffusivity to momentum diffusivity. b. Water c. Transformer oil 38. d. Dilute H2SO4 Which of the following parameters is increased by use of finned tube in a multipass shell and tube heat exchanger ? a. Tube side pressure drop and the heat transfer rate. 26. b. Convective heat transfer co-efficient. In SI units, fouling factor is expressed in c. Effective tube surface area for convective heat transfer. a. m2°K/W d. All (a) (b) and (c). b. W/m2°K c. m2°K 39. d. m°K/W Forced circulation evaporators are useful for the concentration of viscous, salting and scale forming liquors. Which of the following is a forced circulation evaporator? 27. a. Long vertical evaporator An ejector is used to b. Horizontal tube evaporator a. increase pressure c. Agitated film evaporator b. increase temperature d. Calenderia vertical tube evaporator c. remove condensate d. none of these 40. "The ratio of the total emissive power to the absorptivity for all bodies is same at ther- 28. mal equilibrium". This is __________ law. Extremely large or small volumes of fluids are generally best routed through the shell a. Kirchoffs side of a shell and tube heat exchanger, because of the b. Planck's a. less corrosion problems. c. Wien's displacement b. flexibility possible in the baffle arrangement. d. Stefan-Boltzman c. low pressure drop. d. high heat transfer co-efficient. 41. View factor is important in heat transfer by 29. a. steady state conduction All analogy equations connecting friction factor and heat transfer co-efficient apply b. natural convection only to c. forced convection a. wall or skin friction d. radiation b. form friction c. both (a) and (b) 42. d. turbulent flow The advantage of using a 1 - 2 shell and tube heat exchanger over a 1 - 1 shell and tube heat exchanger is 30. a. lower tube side pressure drop. Electro-magnetic spectrum range, which is important for radiation varies from b. lower shell side pressure drop. __________ microns. c. higher tube side heat transfer co-efficient. a. 1 to 100 d. higher shell side heat transfer co-efficient. b. 0.5 to 50 c. 10 to 100 43. d. 100 to 1000 For a multipass shell and tube heat exchanger, the LMTD correction factor is always a. 1 b. >1 31. The characteristic dimensionless groups for heat transfer to a fluid flowing through c. wall temperature. c. suspended solids content b. exit fluid temperature < wall temperature. d. all (a), (b) and(c) c. exit fluid temperature = wall temperature. 20.At steady state the temperature variation in a plane wall, made of two different solids I & II is shown below : d. Graetz number > 100. 29.1000 kg of wet solids are to be dried from 60% to 20% moisture (by weight). The mass of moisture removed in kg is a. 520 b. 200 c. 400 d. 500 30.Which is the most suitable for the con-certration of highly concentrated solution? a. Open pan evaporation b. Long tube vertical evaporator The thermal conductivity of material I a. is smaller than that of II. c. Agitated film evaporator b. is greater than that of II. d. None of these c. is equal to that of II. 31.Unsteady state heat conduction occurs, when d. can be greater than or smaller than that of II. a. temperature distribution is independent of time. b. temperature distribution is dependent on time. 21. Duhring rule is important in solving problems on a. distillation c. heat flows in one direction only. b. crystallisation d. three dimensional heat flow is concerned. c. evaporation 32.What is the absorptivity of a black body ? a. 1 d. humidification b. 0 22. In a shell and tube heat exchanger, the height of 25 percent cut baffles is equal to (where, D = inside diameter of shell) c. 0.78 a. 0.25 D d. 0.95 b. 0.75 D 33.Mode of heat transfer in which the fluid moves under the influence of c. 0.50 D changes in fluid pressure produced by external work is called a. radiation d. none of these b. natural convection 23. Multiple effect evaporation is generally recommended, when the a. large scale evaporation of liquor is needed. c. forced convection d. conduction a. maximum resistance in the series. b. sum of all resistances. c. average of all resistances. 34.Baffle spacing a. is not the same as baffle pitch. d. minimum resistance presents in the series. b. should be less than one fifth the diameter of the shell. 44.Double pipe heat exchangers are preferably useful, when c. should be less than the inside diameter of the shell. a. high viscosity liquid is to be cooled. d. none of these.