Chapter 1

Chapter 1: Chapter 1 Heat Transfer 1. Past ME board Problem Calculate the energy transfer rate across 6 in. Wall of firebrick with a temperature diffrence acros s the firewall of 50°C. The thermal conductivity of the firebrick is 0.65 Btu/hr -ft°F at the temperature interest. : 1. Past ME board Problem Calculate the energy transfer rate across 6 in. Wall of firebrick with a temperature diffrence across the firewal l of 50°C. The thermal conductivity of the firebrick is 0.65 Btu/hr -ft°F at the temperature interest. A. 285 W/m² B. 369W/m² C. 112W/m² D. 429W/m² S lide 3: 2. Past ME board Problem At an average temperature of 100°C, hot air flows through a 2.5 m long tube with an inside diameter of 50 mm. The temperature of the tube is 20°C along its entire length. Convective film coefficient is 2 0.1 W/m²-K. Determine the convective heat transfer from air to the tube. 900 W 909 W 624 W 632 W S lide 4: 3. Past ME board Problem Stream, initially saturated at 2.05 Mpa, passes through a 10.10 cm standard steel pipe for a total d istance of 152 m. The stream line is insulated with 5.08 cm thickness of 85% magnesia. For an ambient tempreature of 22°C , what is the quality of t he stream which arises at its destination if the mass flow rate is 0.125 kg stream per second ? Note : k for 85% magnesia is 0.069 W/m-K and h˳ for still air is 9.36 W/m²-K 93% 98% 84% 76% S lide 5: 4. Past ME board Problem The sun generates 1 kW/m² when used as a source for solar collectors. A collector with an area of 1 m² heat water. The flow rate is 3.0 liters per minute. What is the tempera- ture rise in the water ? The specific heat of water is 4,200 J/Kg°C. 4.8°C 0.48°C 0.50°C 0.84°C S lide 6: 5. Past ME board Problem The hot combustion gases of a furnace are separated from the ambient air and its surrounding which a re at 25°C, by a brick wall 0.15 m thick. The brick has a thermal conductivity 0f 1.2 W/m -K and a surface emissivity of 0.80. Under steady state conditions and outer surface temperature of 100°C is measured. Free convection heat transfer to the air adjoining this su rface is characterized by a convection coefficient of 20 W/m²-K. What is the inner temperature in °C ? 623.7 352 461.4 265.3 S lide 7: 6. Past ME board Problem A 6 in. X 20 ft uninsulated B.I. pipe conveys steam at 385°F with an average ambient temperatur e of 85°F. If the cost of the fuel is P 250.00 per 10⁶ Btu with the net energy conversion efficiency of 75%, what is the annual cost of the heat lost ? P 60,482.00 P 65,482.00 P 70,482.00 P 75,482.00 S lide 8: 7. Past ME board Problem What is the external heating surface area in square feet of a tube with the following dimensions : tube inside diameter = 5 in. Wall thickness = ½ in. Length =18 ft. 26.5 24.25 19.25 28.26 S lide 9: 8. Past ME board Problem Determine the vacuum efficiency of a surface condenser which operates at a vacuum of 635 mm Hg and e xhaust steam enters the condenser at 45.81°C . The barometric pressure is 760 mmHg and the saturation pressure at 45.81°C is 0.010 Mpa. 80.4% 85.2% 92.7% 98.3% S lide 10: 9. Past ME board Problem A heat exchanger was installed purposely to cool 0.50 kg of gas per second. Molecular weigth is 28 a nd k- 1.32. The gas is cooled from 150°C to 80°C . Water is available at the rate of 0.30 kg/s and at a temperature of 12°C. Calculate the exit temperature of the water. 48 42 46 44 S lide 11: 10. Past ME board Problem An uninsulated steam pipe passes through a room in which the air and walls are at 25°C. The outside diameter of the pipe is 70 mm, and its surface temperature and emissivity are 200°C and 0.80 repectively. If the coefficient associated with free convec tion heat transfer from the surface to the air is 15 w/ m²-K, what is the rate of heat koss from the surface per unit of length of pipe? 997.84 W/m 897.84 W/m 797.84 W/m 697.84 W/m S lide 12: 11. Past ME board Problem A heat exchanger is used to be designed for the following specifications : Hot gas temperature 1145 °C Cold gas temperature 45°C Unit surface conductance on the hot side 230W/m²-K Unit surface conductance on the cold side 290W/m²-K Thermal thickness of the metal wall 115W/ m²-K Find the maximum thickness of the metal wall between the hot gas and cold gas so that the maximum temperatureof the wall does not exceed 545°C. 10.115 mm 13.115 mm 17.115 mm 20.115 mm S lide 13: 12. Past ME board Problem Calculate the heat transfer per hour through a solid brick wall 6 m long, 2.9 m high, and 225 mm th ick, when the outer surface is at 5°C and the inner surface 17°C , the coefficie nt of the thremal conductivity of the brick being 0.6 W/m -K 2,004.48 Kj 3,004.48 kJ 2,400.48 kJ 3,400,48 kJ S lide 14: 13. Past ME board Problem A vertical furnace wall is made up of an inner wall firebrick20 cm thick followed by insulating bri ck 15 cm thick and an outer wall of steel 1 cm thick, The surface temperature of the wall adjacent to the combustion chamber is 1200° C while that of the outer surface of steel is 50°C. The thermal conductivities of the wall material in W/m -K are : firebrick 10 ; ins ulating brick,0.26 ; and steel, 45. Neglecting the film resistance and contact resistance of joints , determine the heat loss per sq.m. Of wall area. 1.93 W/m² 2.93 W/m² 1.55 W/m² 2.55 W/m²

S lide 15: 14. Past ME board Problem A composite wall is made up of an external thickness of brickwork 110 mm thick inside which is a layer of fiberglass is faced internally by an insulating board 25 mm thick. The coefficient of thermal conductivity for the three as follows : Brick work 1.5 W/m-K Fiberglass 0.04 W/m-K Insulating board 0.06 w/m -K The surface transfer coefficient of the inside wall is 3.1 W/m²-K while that of the outside wall is 2.5 W/m²-K. Take the internal ambient temperature as 10°C and the external temperature is 27°C. Determine the heat loss through su ch wall 6 m high and 10 m long . 330.10 W 230.10 W 430.10 W 530. 10 W S lide 16: Supplementary Problem One insulated wall of a cold storage compartment is 8 m long 2.5 m high and con - sist of an outer steel plate 18 mm thick. An inner wood wall 22.5 mm and thick, the steel and wood are 90 mm apart to form a cavity ahich filled with cork. If the tempearture drop across extreme faces of the composite wall is 15°C. Calculate the heat transfer per hour through the wall and the temperature drop across th e the thickness of the cork. Take the coefficient of thermal conductivity for steel cork, and wood as 45, 0,045, and 0.18 W/m -K repectively. 408.24 kJ, 12,12°C 708.24 kJ 11.12°C 608.24 kJ 13. 12°C 508.24 kJ 14. 12°C S lide 17: 16. Supplementary Problem A cubical tank of 2 sides is constructed of metal plate 12 mm and contains water at 75°C. The surrounding air temperature is 16°C. Calculate the overall heat transfer from water to air. Take the coeefficient of thermal condcutivity of the metal as 48 W/m-K , the coefficient of thermal conductivity of the metal as 48 W/m -K, the coefficient of thermal conductivity of metal as 48W/m -K, the coefficient of heat trasfer of water is 2.5 kW/m²-K and the coefficient of heat transfer of the air is 16 W/m²-K. 15. 84 W/m²°C 14.84 W/m²°C 16.84 W/m²°C 13.84 W/m²°C S lide 18: 17. Supplementary Problem Calculate the quatity of heat conducted per minute through a duralumin circular disc 127 mm diamete r and 19 mm thick when the temprature drop across the thickness of the plate is 5°C. Take the coefficient of thermal conductivity o f duralumin as 150 W/m -K. 30 kJ 40 kJ 35 kJ 45kJ S lide 19: 18. Supplementary Problem A cold storage compartment is 4.5 m long by 4 m wide by 2.5 m high. The four walls , ceiling and fl oor are covered to a thickness of 150 mm with insulating material which has coefficient of thermal conductivity of 5.8 x 10²W/m -K. Calculate the quantity of heating leaking through the insulation per hour when the outside and inside face temperatures of the material is 15°C and -5°C respctively. 2185.44 kJ 118 5. 44 kJ 3185. 44 kJ 4185. 44 kJ S lide 20: 19. Supplementary Problem A thin square steel plate , 10 cm on a side is heated in a blacksmiths forge to a temperature of 80 0°C. If the emissivity is 0.60, what is the total rate of radiation energy ? 900 Watts 400 Watts 300 Watts 700 Watts S lide 21: 20. Supplementary Problem A furnace wall consist of 35 cm firebrick ( k= 1.55 7 W/m -K ) , 12 cm insulating refractory ( k= 0.346 ) and 20 cm common brick ( k= 0.692 ) covered with 7 cm steel plate ( k= 45 ) . The temperature at hte inner surface of the firebrick is 1,230°C and at the outer face of the steel plate is 60°C. Atmosphere 27°C. What is the value of the combined coefficient for convention and radiation from the out side wall ? 31. 13 W/m²-K 30.13 W/m-K 41.3 W/m²-K 40.13 W/m²-K S lide 22: 21. Supplementary Problem A dry ice storage chest is a wooden box lined with glass fiber insulation 5 cm thick. The wooden bo x ( k = 0.069 ) is 2 cm thick and cubical 60 cm on an edge. The inside surface temperature is -76°C and the outside temperature is 18°C. Use l = 0.035 glass fiber insulation. Determine the heat gain per day 10,211 kJ 11,195 kj 12,211 kJ 9,185 kJ S lide 23: 22. Supplementary Problem One side of refrigerated cold chamber is 6 cm long by 3.7 m high and consists 0f 16 8 mm thickness of cork between outer and inner walls of wood. The outer woll wall is 30 cm thick and its outside face temperature is 20°C, the inner wood wall is 35 mm thick and its inside face temperature is -3°C. Taking the coefficient of thermal conductivity of cork and wood as 0.42 and 0.20 W/m -K respectively , calculate the heat transfer per second per sq. M of surface area. 5.138 J 4.138 J 6.318 3.318 J S lide 24: 23. Supplementary Problem Hot gases at 280°C flow on one side of a metal plate of 10mm thickness and air at 35°C flows on the other side. The heat ransfer coefficient of the gases is 31.5 W/m²-K and that of the air is 32 W/m²-K. Calculate the over-all transfer coefficient A. 15.82 W/m²-K B. 16.82 W/m²-K C. 14.82 W/m²-k D. 17.82 W/m²-K S lide 25: 24. Supplementary Problem The surface temperature of the hot side of the furnace wall is 1200°C. It is desired to mainttain t he outside of the wall at 38°C. A 152 mm of refractory silica is used adjacent to the combustion chamber and 10 mm of steel c overs the outside. What thickness of insulating bricks is necessary between refractory and steel , if the heat loss should be kept at 788 W/m² ? Use k = 13.84 W/m -K for refractory silica ; 0.15 for insulating brick, and 45 for steel. 220 mm 240 mm 260 mm 2 80 mm S lide 26: 25. Supplementary Problem How much heat will flow has an outside flow in 24 hours through a palster wall that is 0.51 in thic k 8 ft x 14 ft ina area if the temperature is 80°F on one side and 40°F on the other. Use k = 3.25 Btu – in/ hr - ft² -°F 5.99 x 10⁵ Btu 6.99 x 10⁵ Btu 7.99 x 10⁵ Btu 4.99 x 10⁵ Btu S lide 27: 26. Supplementary Problem A hollow sphere has an outside radius of 1 m and is made of polystyrene foam with a thickness of 1 cm. A heat source inside keeps the inner surface 5.20°C hotter than the outside surface. How much power is produced by the heat source The thermal conductivity of polytrene foam os 0.033 W/m°C 200 W 216 W 300 W 316 W

S lide 28: 27. Supplementary Problem A glass window has an area of 1.60m² and a thickness of 4 mm. If one side is at a temperature of 6.80°C and the other is at -5°C, how much thermal energy flows through the window in a time of 24 hours ? The thermal conductivity of glass is 1.89 x 10ˉ ⁴ kCal/m-s-°C. 26,200 kCal 58,000 kCal 40,700 kCal 77,100 kCal S lide 29: 28. Supplementary Problem The wall of a cold room consist of a layer of cork sandwiched between outer and inner walls of wood , the wood walls being each 30 mm thicj. The inside atmosphere of the room is maintained at -20°C when the external atmospheric temperature is 25°C, and the heat loss through the wall is 42 W/m². Taking the thermal conductibity of wood and cork as 0.20 W.m -K and 0.05 W/m-K respectively , and the rate of heat transfer between each exposed wood surface and their respective atmospheres as 15W/m²-K , calculate the thickness of the cork. 31.90 mm 21.90 mm 41.90 mm 51.90 mm S lide 30: 29. Supplementary Problem A slab of material has an area of 2m² and is 1 mm thick. Ine side is maintained at a temperature of 0°C while the other is at 12°C. It is determined that 6820 J of heat flows through the material in a time of 10 minutes. What is the thermal conductivity of the material ? A. 4.74 x 10ˉ⁴ W/m°C B. 5.74 x 10ˉ⁴ W/m°C C. 2.66 x 10ˉ⁴ W/m°C D. 9.79 x 10ˉ² W/m°C S lide 31: 30. Supplementary Problem An insulated steam piece located where the ambient temperature is 32°C, has an inside diameter of 5 0 mm with 10 mm thick wall. The outside diameter of the corrugated asbestos insulation is 125 mm and the surface coeffiecient of st ill air, h˳ = 12 W/m²-K. Inside the pipe is steam having a temperature of 150 °C with film coefficient h ₁ = 6000 W/m²-K. Thermal conductivity of pipe and asbestos insulation are 45 and 0.12 W/m-K respectively. Determine the heat loss per unit length of pip e. 110 W 120 W 130 W 140 W S lide 32: 31. Supplementary Problem A pipe 200 mm outside diameter and 20 m length is covered with a later, 70 mm thick of insulation h aving a thermal conductivity of 0.05 W/m -K and a thermal conductance of 10 W/m² at the outer surface. If the temperature of the pipe is 350 °C and the ambient temperature 15 °C, calculate the external surface temperature of the lagging. A. 32.6 °C B. 22.6 °C C. 42.6 °C D. 53.5 °C S lide 33: 32. Supplementary Problem Dry and saturated steam at 6 Mpa abs. Enters a 40 m length of 11.5 cm O.D. Steel pipe at a flow rate of 0.12 kg/s. The pipe is covered with a 5 cm thick asbestos imsulation ( k = 0.022 W/m -K ). The pipe is located in a tunnel with stagnant air temperature of 27 °C. The unit outside convective coefficient is 10 W/m²-K. Neglecting steam film and pipe wall resistances, determine the mass of steam. 4.86 kg/hr 3.86 kg/hr 5.86 kg/hr 6.86 kg/hr S lide 34: 33. Supplementary Problem Calculate the heat loss per linear ft. From 2 in. Nominal pipe ( 2.375 in. Outside diameter ) cover ed with 1 in. of an insulating material having an average thermal conductivity of 0.0375 Btu/hr-ft °F. Assume that the inner and outer surface temperatures of the insulation are 380 °F and 80 °F respectively. 110 Btu/hr-ft 116 Btu/hr-ft 120 Btu/hr-ft 126 Btu/hr-ft S lide 35: 34. Supplementary Problem Calculate the heat loss per linear foot from a 10 in. Nominal pipe ( outside diamete r = 10.75 in. ) covered with a composite pipe insulation consisting of 1½ in. Of insulation I placed next to the pipe and 2 in. Of insulation II placed upon insulatio n I. Assume that the inner and outer surface temperatures of the composite insulation aree 700 °F and 100 °F respectively, and that the thermal conductivity of material I is 0.05 Btu/hr-ft- °F and for material II is 0.039 Btu/hr-ft- °F. 3 23.13 Btu/hr-ft 123.13 Btu/hr-ft 120 Btu/hr-ft 126 Btu/hr-ft S lide 36: 35. Supplementary Problem A steam pipe carrying steam at 380 kPa pressure for a pressure for a distance of 120 m in a chemical plan is not insulated. Estimate the saving in steam cost that would be made per year if this 8 cm steam line were covered with 85% magnesia pipe covering 5 cm thick. Take room temperature to be 25 °C, the cost of steam is 65 cents per 1000 kg. Thermal conductivity of magnesia k = 0.0745 W/m -k\K, unit convective coefficient of room air, h˳ = 12 W/m²-K. $ 305 $ 405 $ 505 $ 605 S lide 37: 36. Supplementary Problem A liquid to liquid counterflow heat exchanger is used to heat a cold fluid from 120 °F to 310 °F. Assuming that the hot fluid enters at 500 °F and leaves at 400 °F, calculate the log mean temperature difference fot the heat exchanger. 132 °F 232 °F 33 2 °F 432 °F S lide 38: 37. Supplementary Problem A turbo-generator, 16 cylinder, Vee type diesel engine has an air consumption of 3000 kg/hr per cylinder at rated load and speed. This air is drawn in thru a filter by a centrifugal compressor direct connected to the exhaust gas turbine. The temperature Of the aircon from the compressor is 145°C and a counterflow air cooler reduces the air temperature to 45°C before it goes to the engine suction hea der. Cooling water aur cooler at 30°C and leaves at 38°C. Calculates the arithmetic mean temprature difference. 41°C 51°C 61°C 71°C S lide 39: 38. Supplementary Problem A pond is covered by a sheet of ice 2 cm thick ( thermal conductivity 1.68 W/m°C ). The temperature of the lower surface of the ice is 0°C and that of the upper surface is -10°C. At what rate is heat conducted through each square meter of the ice? 840 W 740 W 940 W 640 W S lide 40: 39. Supplementary Problem How much heat is conducted through a sheet of plates glass , k = 0.0024 Cal/s -cm-°C which is 2 m by 3 m and 5 mm thick , when the temperatures of the surfaces are 20°C and -10°C. 318,400 Cal/min 418,400 Cal/min 518,400 Cal/min 618,400 Cal/min S lide 41:

40. Supplementary Problem A copper rod whose diameter is 2 cm and length 50 cm has one end in boiling water , the other end in a jacket cooledd by a flowing water which enters at 10°C . The thermal conductivity of the copper is 0.102 kCal/m -s°C. . If 0.20 kg of water flows through the jacket in 6 min , by how much does the temperature of the water increas e ? A. 10.38°C B . 9.38°C C. 11.38°C D . 12.38°C S lide 42: 41. Supplementary Problem The thermal insulation of a wollen glove may be regarded as being essentially a layer og quiescent air 3 cm thick , of conductivity 5.7 x 10ˉ⁶ kcal/m-s-°C . How much heat does a person lose per minute from his hand of area 200 cm² and skin temperature 35°C on a winter day at -5°C ? A. 6.12°C B. 7.12°C C. 9.12°C D. 8.12 S lide 43: 42. Supplementary Problem The temperature directly beneath a 3 in. Concrete road is 5°F and the air temperature os 20°F . Cal culate the steady flow per square foot through the concrete . The thermal conductivity of the concrete is 0.50 Btu/ft-hr-°F 30 Btu/ft-hr² 40 Btu/ft-hr² 50 Btu/ft-hr² 60 Btu/ft-hr² S lide 44: 43. Supplementary Problem At what rate does to sun lose energy by radiation ? The temperature of the sun is about 6000 K and its radius is 6.95 x 10⁵ km. 3.48 x 10²⁶ W 4.48 x 10²⁶ W 5.48 x 10²⁶ W 6.48 x 10²⁶ W S lide 45: 44. Supplementary Problem How many watts will be radiated from a spherical black body 15 cm in diameter at a temperature of 8 00°C ? 5.34 W 4.34 W 6.34 W 3.34 W S lide 46: 45. Supplementary Problem Calculate the radiation in watts per square centimeter from a block of copper at 200°C and at 1000°C . The oxidized copper surface radiates at 0.60 the rate of a black body. 0.17 0.27 0.37 0.07 S lide 47: 46. Supplementary Problem A surface condenser serving a 50,000 kW steam turbo -generator unit receives exhaust steam at the rate of 196,000 kg/hr . Vacuum in condenser is 702 mm Hg. Sea water for cooling enters at 29.5°C and leaves at 37.5°C . For steam turbine condenser , manufacturers consider 950 Btu/lb of steam turbine condensed as heat given up to cooling water . Calculate the logarithmic mean temperautre difference . A. 4.57°C B. 5.57°C C. 6.57°C D. 7.57°C S lide 48: 47. Supplementary Problem The stack gas from a chemical operation contains noxiuos vapors that must be condensed by lowering its temperautre from 315°C to 35°C . The gas flow rate is 0.70 m³/s . Water is available at 10°C at 1.26 kg/s . A two shell and a 4 tube pass a , counterflow heat exchanger will be used with a water flowing through the tubes . The gas has specific heat of 1.10 kJ/kg-K and a gaas constant of 0.26 kJ/kg-K . Calculate the logarithmic mean temperature difference . A. 102.8°C B. 110.9°C C. 120.8°C D. 118.9°C S lide 49: 48. Supplementary Problem Exhaust steam at 7 kPa at the rate of 75 kg/s enters a sin gle pass condenser containing 5,780 pcs copper tubes with a total surface area of 2950 m² . The steam has a moisture content of 10% and the condensate leaves saturated liquid at steam t emperature . The cooling water flow rate is 4,413 liters per second entering at 20°C . Size of tubes , 25 mm O.D. By 3 mm thick wall . Find the overall heat transfer coefficient . 5275 W/m²-K 2275 W/m²-K 4274 W/m²-K 3225 W/m²-K S lide 50: 49. Supplementary Problem What is the heat flow per hour through a brick and mortar wal l 9 in. Thick if the coefficient of thermal conductivity has been determined as 0.40 Btu/fr-hr-°F and the wall is 10 ft high by 6 ft wide , the temperature on one side of the surface being 330°F and on the other 130°F. 6400 Btu/hr 7400 Btu/hr 5400 Btu/hr 8400 Btu/hr S lide 51: 50. Supplementary Problem Water is flowing in a pipe with radius of 25.4 cm at a velocity of 5 m/s at the temperature in the pipe . The density and viscosity of the water are as follows : density = 997.9 kg/m³ and viscosity = 1.131 Pa -s . What is the Reynolds number for this situation ? 2241 96.2 3100 1140 S lide 52: 51. Supplementary Problem A heat exchanger has an over – all coefficient of heat transfer of 900 W/m²-K. The mean temperature diffrence is 20°C and heat loss is 15, 000 W. Calculate the heat transfer area. 0.833 m² 0.733 m² 0.933 m² 0.633 m² S lide 53: 52. Supplementary Problem A composite furnace wall is made up of a 12 in. l ining of magnesite refractory brick, a 5 in. t hi ckness of 85% magnesia, and a steel casing 0.10 in. thick. Flue gas temperature is 2200°F and the boiler room is at 80°F. Gas side film coefficient is 15 Btu/hr -ft²-°F and air side is 4. Determine the thermal current Q/A. A .187.41 Btu/hr-ft² B .197.41 Btu/hr-ft² C. 200.62 Btu/hr-ft² D. 250.46 Btu/hr-ft² S lide 54: 53. Supplementary Problem The wall of a furnace is made up of 9 in. Firebrick ( k= 0.72 Btu/hr -ft-°F 5 in. Of insulating brick ( k= 0.08 ) and 7.5 in. Of red brick ( k= 0.5 ). The inner and outer surface temperature t₁ and t₄ of the wall are 1500°F and 150°F respectively. Neglecting the resistance of the mortar joints, compute the rate of heat flow through 1ft ² of the wall. 80 Btu/hr 180 Btu/hr 100 Btu/hr 200 Btu/hr S lide 55: 54. . Past ME board Problem What is the heat transfer in the glass surface area of 0.7 0 m² having an inside tem - perature of 25°C and 13°C outside temperature. The thickness of the glass surface is 0.007 m. The thermal conductivity is 1.8 W/ m -K. 4.16 Kw 3.16 kW 2.16 kW 1.16 kW

S lide 56: 55. Suplemmentary Problem The interior of an oven is maintained at a temperature of 1500° F by means of suitable control apparatus. The walls of the oven are 9 in. thick and constructed from a material having a thermal conductivity of 0.18 btu/hr -ft-°F. Calculate the heat loss for each square foot of a wall surface per hour. Assume that the inside and outside wall temperatures are 1500°F and 400°F respectively. 264 Btu/hr -ft² 364 Btu/hr-ft² 164 Btu/hrft² 64 Btu/hr-ft² S lide 57: 56. Past ME board Problem Compute the amount condensate formed during 10 minu tes warm-up of 150 m pipe conveys saturated steam with enthalpy of vaporation hfg = 1,947. 8 kJ/kg. The minimum external temperature of pipe is 2°C and the final temperature is 195°C. The s pecific heat of pipe material is 0.6 kJ/kg-K and the specific weigth is 28 kg/m. 249.69 kg 499.38 kg 124.85 kg 62.42 kg S lide 58: 57. Suplemmentary Problem A high pressure steam generator is to be fitted with convection type superheater having 72 elements in parallel. Steam at rate og 70,000 kg/hr from the boiler drum enters the superheater inlet header at 8.3 Mpa absolute 98% quality, and leaves the the same at 8 Mpa and 485°C. Combustion products at 980°C enters the superheater proper at the rate of 160,000 kg/hr. Superheater elements are made of 60mm O.D. By 8 mm thick tubing of 30 m length. Assume that the flue gas has the same thermal properties pf air. Calcuilate the heat transferred to the superheated tubes. 12,152 kW 11,512 kW 10,152 kW 13,152 kW S lide 59: 58. Suplemmentary Problem In a hot water heating system, water heated to 95°C and then is pumped at the rate of 4 L/min throu gh a radiator where it is cooled to 35°C . If the water arrives at the radiator at a temperature of 85°C , how much heat does the r adiator release each hour ? 50,244 kJ/hr 45,422 kJ/hr 55,344 kJ/hr 65,244 kJ/hr S lide 60: 59. Suplemmentary Problem Brine enters a cooler at the rate of 50 m³/hr at 15°C and leaves at 1°C. Specific heat and specific gravity of brine are 1.07 kJ/kg-K and 1.1 repsectively. Calculate the heat transferred in kW. 158.21 kW 228.86 kW 258.21 kW 128.86 kW S lide 61: 60. Suplemmentary Problem A metal rod is 10 cm long and has a diameter of 2 cm one end is in contact with steam at 100°C whil e the other end contacts a block of ice at 0°C. The cylindrical surface of the rod is carefully insulated so heat flows only from end to end. In a time of 20 minutes, 320 grams of ice melts. What is the thermal conductivity of the metal ? A. 0.28266 kJ/kg°C B. 0.18266 kJ/kg°C C. 0.38366 kJ/kg°C D. 0.48266 kJ/kg°C S lide 62: 61. Suplemmentary Problem A wall with an area of 10 m² is made of a 2 cm thickness of white pine (k= 0.113 W/m°C ) followed by 10 cm of brick (k= 0.649 W/m°C). The pine is on the inside where the temperature is 30°C while the outside temperature is 10°C. Assuming equilib rium conditions exist, what is the temperature at the interface between the two metals ? 15.65°C 17.64 0°C 18.21 0°C 19.31 0°C S lide 63: 62. Suplemmentary Problem In a hot air heating system, the furnace heats air from 60°F . If the air is then circulated at the rate of 330 ft³/min by the blower, how much thermal energy is tranffered per hour. Note : The specific heat of air at constant pressure is 0.250 Btu/lb° F , the density of air is 0.0806 lb/ft³ at atmospheric pressure. 39,000 Btu/hr 46,800 Btu/hr 36, 805 Btu/hr 39,900 Btu/hr S lide 64: 63. Suplemmentary Problem if 1000 liters of air at 27°C and pressure of 1 atm has a mass of 1.115 kg and a specific heat at c onstant pressure of 1x10³ J/kg-K, How much heat is required to raise the temperature of this gas from 27°C to 177°C at co nstant pressure? 176. 25 Kj 157 kJ 167.25 kJ 175 kJ S lide 65: 64. Suplemmentary Problem Calculate the amount of energy required ti heat the air in a house 30 by 50 by 40 ft from 10 to 70° F. The density of air is about 0.08 lb/ft³, and its specific heat at constant pressure 0.24 Btu/lb°F. 49,120 Btu 59,120 Btu 69,129 Btu 79,129 Btu S lide 66: 65. Suplemmentary Problem Water enters the condenser at 20°C and leaves at 35°C. What is the log mean temperature difference if the condenser temperature is 40°C. 16.37°C 13,37°C 69.37°C 17.37 °C S lide 67: 66. Suplemmentary Problem When 200 grams of aluminum at 100°C is dropeed into an aluminum calorimeter (k= 0.909 x 10³ J/kg -K) of mass 120 grams and contaning 150 grams of kerosene at 15°C, what is the specific hea t of kerosene ? 1004 J/kg-K 1050 J/kg-K 1110 J/kg-K 1080 J/kg-K S lide 68: 67. Suplemmentary Problem A calorimeter contains 66 kg of turpentine at 10.6°C. Whean 0. 147 kg of alcohol at 75°C is added, the temperature rises to 25.2°C. The specific heat of turpentine is 1.95 x 10³ J/kg-°C and the calorimeter is thermally equivalent to 30 grams of water. Find the specific heat of alcohol. 2.81745 kJ/kg°C 3.81745 kJ/kg°C 0.81745 kJ/kg°C 1.81745 kJ/kg°C S lide 69: 68. Suplemmentary Problem The temperature of a sample of molten lead near its temperature of solidification is falling at t he rate of 6 K/min. If the lead continues to lose heat at this same rate and takes 35 min to solidify completely , what is the heat of fusion of the lead ? T he specific heat of molten lead is 0.126 kJ/kg-K. 16.46 kJ/kg-K 26.46 kJ/kg-K 36.46 kJ/kg-K 46.46 kJ/kg-K S lide 70:

69. Suplemmentary Problem A counterflow heat exchanger is designed to heat fuel oil from 45°C to 100°C while the heating flui d enters at 150°C and leaves at 115°C. Calclulate the arith- metic mean temperature difference. 40°C 50°C 60°C 70°C S lide 71: 70. Suplemmentary Problem A fule oil 20° API is to be heated in a heater which makes two passes thru a heater tubes and the h eating fluids makes one passes but the flow is crossf flow through the heater due to baffles inside the shell. Quan tity of oil to be heated 3000L/hr Temperature of oil entering heater tubes 21°C Temperature of oil leaving heater tubes 95°C Heating fluid, steam enter at 05°C and leaves as condensate at 105°C. Assume specific heat of oil to be 2.093 kJ/kg-K. Find the heating surface area if the over- all coefficient of heat transfer is taken as 140 W/m² °C. 24.76 m² 30.75 m² 23.75 m² 32.54 m² S lide 72: 71. Suplemmentary Problem A 30 cm thick wall has an inside and outside surface temperature of 300°C and 50°C respective ly. If the thermal Conductivity of wall is 8 W/m -K. Calculate the heat transffered in kW/m². ? 6.67 5.67 7.67 8.87 S lide 73: 72. Suplemmentary Problem A 4-pass low pressure surface type feedwater heater is designed to heat 92,730 kg/hr of feedwater from 40°C initial to 80°C final temperature using steam bleed at 70 kPa abs. c ontaning 2,645 kJ/kg enthalpy. Assume no subcooling of cindensate, determine the effective length of 19 mm O.D. x 2 mm thick Muntz meatl tubes to be installed, if the water velocity inside the tubes is 1.22 m/s and U= 3000 W/m²K based on the external surface of the tubes. 2 m 4 m 3 m 5 m S lide 74: 73. Suplemmentary Problem Find the thermal conductivity of the 500 cm thick material with an area of 50,000 cm² and a tempera ture difference of 10 K if the heat transmitted during 2 hours test is 2000 kJ. 0.014 W/m -K 0.025 W/m-K 0.126 W/m-K 0.214 W/m-K S lide 75: 74. Suplemmentary Problem A pipe with an outside diameter of 2.5 in. Insulated with a 2 in. layer of asbestos ( Ka = 0.396 Bt u-in/hr-ft²-°F ). If the temperature of the outer surface of the cork is 90°F, calculate the heat loss per 100 ft of insulated pipe. 847.64 Btu/hr 384 7.51 Btu/hr 2847.42 Btu/hr 1847.14 Btu/hr S lide 76: 75. Suplemmentary Problem At $ 0.25 per kW-hr, How much will it cost to maintain a temperature of 96°F for 24 hours in a box 2ft square on each side if the outside temperature is 72°F and the over-all heat transfer coefficient for the box is 0.10 Btu/hr-ft²-°F ? P 0.10 P 0.20 P 0.15 P 0.25 S lide 77: 76. Suplemmentary Problem A steam pipe having a surface temperature of 300°C passes through a room where the temperature is 2 5°C. The outside diameter of pipe is 100 mm and emissivity is 0.60. Determine the ra diated heat loss for a 5 m pipe length 5.34 kW 4.34 kW 3.34 kW 6.34 kW S lide 78: 77. Suplemmentary Problem An air-cooled condenser has an expected U value of 30 w/m²-K based on the air side area. The condenser is to transfer 60 kW with an airflow rate of 15 kg/s entering at 35°C. If the condensing temperature is to be 48°C, what is the required air -side area ? 184 m² 194 m² 174 m² 164 m² S lide 79: 78. Suplemmentary Problem An air-cooled condenser is to reject 70 kW of heat from condensing refrigerant to air. The condenser has an air-side area of 210 m² and a U value basewd on this area of 0.037 kW/m²-K; it is supplied with 6.6 m³/s of air which has a density of 1.15 kg/m³. If the condensing temperature is to be limited to 55°C, what is the maximum allowa ble temperature of the unlet air ? 30.7°C 40. 7°C 50. 7°C 20. 7°C S lide 80: 79. Suplemmentary Problem Two walls are composed of 150 mm thick insulating material at the outer layer ( k=0.139W/m -K ) and 300 mm thick material at the inner layer ( k=1.111W/m -K). Calculate the heat transmitted per m²if the surface temperatures of the cold side and the hot side are 25°C and 300°C respectively. 203.79 W/m² 303.79 W/m² 254.65 W/m² 354.65 W/m² S lide 81: 80. Suplemmentary Problem The temperature of the flame in a frunace is 1277°C and the temperature of its surrounds is 277°C. Calculate the maximum theoretical quantity og the heat energy radiated per minute per square meter to the surrrounding surface area. 19,321 .65 kJ 18 ,321.65 kJ 17 ,321.65 kJ 16 ,321.65 kJ S lide 82: 81. Suplemmentary Problem A small sphere has a radius of 3.50 cm and is maintained at a temperature of 360°C. Assuming it to be a black body surrounded by empty space, how much energy does it radiate each second ? 240.7 J 140.2 J 320.5 J 134.5 J S lide 83: 82. Suplemmentary Problem The inner wall of a thermos bottle is at 0°C while the outer at 37°C. The space between the walls i s evacuated and the walls are silvered so the emissivity is reduced to 0.10. If each wall has an area of 700 cm², how m uch energy is transformed by radiation between the walls each second ? 1.46 J 1.04 J 16.5 J 16.03 J S lide 84: 83. Suplemmentary Problem The hot gas temperature ina a heat exchanger is 350°C h˳= 220 W/m² -K). What is the surface temperature on the wall if the heat transferred is 1500 W/m²? 350°C 338°C 343°C 358°C

S lide 85: 84. ME Board Problem An oil heater heats 100 kg per minute of oil from 35°C to 100°C in a counterflow heat exchanger. The average specific heat of the oil is 2.5 kJ/kg°C. Exhaust gases used for heating enter heater with an average specific heatof 1kJ /kg°C, mass flow rate of 250 kg/min and an initial temperature of 200°C. The over-all heat transfer coefficient is 75 W/m²°C. Determine the heating surface in m². 36.11°C 41. 72°C 32.72°C 25.34 °C S lide 86: 85. Suplemmentary Problem If the total resistance to heat flow of a composite wall is 3.0875 m²-K/W. What is the over-all transfer coefficient of the wall ? 0.324 W/m²-K 0.423 W/m²-K 0.243 W/m²-K 0.234 W/m²-K S lide 87: 86. Suplemmentary Problem In a composite vertical surface wall, the resistance due to insulating brick is 0.5769 °C/W. What i s the total resistance to heat flow if the percent of the total resistance due to insulating brick is 96.80%. A. 0.597 °C/W B. 0.795 ° C/W C. 0.975 ° C /W D. 0.957 °C/W S lide 88: 87. Suplemmentary Problem A counterflow bank of boiler tubes has a total area o f 900 ft² and its over-all efficiency of heat transfer is 13 Btu/hr-ft²-°F. Calculate the heat transferred if the log mean temperature difference is 1380°F 16,146,000 Btu/hr 17,147, 000 Btu/hr 18,148, 000 Btu/hr 15,145, 000 Btu/hr S lide 89: 88. Suplemmentary Problem Calculate the quantity of heat to be transferred to 3.25 kg of brass to raise its temperature from 30°C to 250°C taking the specific heat of the brass as 0.394 kJ/kg-K. 182 Kj 282 kJ 151 kJ 251 kJ S lide 90: 89. Suplemmentary Problem The mass of copper calorimeter is 0.28 kg and it contains 0.4 kg of water at 15°C. Taking the speci fic heat of copper as 0.39 kJ/kg-K , Calculatethe heat required to raise the temperature to 20°C 6.92 kJ 7.92 kJ 8.92 kJ 9.92 kJ S lide 91: 90. Suplemmentary Problem In an experiment to find the specific heat of lead, a 0.50 kg of lead shot at a temperature of 51°C is poured into an insulated calorimeter containing 0.25 kg of water at 13.5°C and the resultant temperature of the mixtu re is 15.5°C. If the water equivalent of the calorimeter is 0.020 kg, find the specific heat of the lead. 0.1278 kJ/kg -K 0.0278 kJ/kg-k 0.01389 kJ/kg-K 0.0389 kJ/kg-K S lide 92: 91. Suplemmentary Problem A casting of mass 5 kg is pulled a distance of 10 m along a horizontal floor, the coefficient of friction between the surfaces of the casting and floor being 0.40. Calculate the heat generated at the surfaces. 196. 2 J 186. 2 J 176. 2 J 166. 2 J S lide 93: 92. Suplemmentary Problem A water brake couped to an engine on test absorbs 70 kW of power. Find the heat generated at the br ake per minute and mass of flow of fresh water through the brake in kg/min if the temperature increase of the water is 10°C. Assume all the heat generated is carried away by the cooling water. 4200 kJ, 100 kg/min 4100 kJ, 500 kg/min 4200 kJ, 500 kg/min 4100 kJ, 100 kg/min S lide 94: 93. Suplemmentary Problem With three different quantities x,y, and z of the same kind of liquid of tem peratures 9,21 and 38°C respectively, it is found that when x and y are mixed together the resultant temperature is 17°C and when y and z are mixed together the resultant temp erature is 28°C. Find the resultant temperature if x and z were mixed. 29.87°C 25.92°C 20.85°C 24.86 °C S lide 95: 94. Suplemmentary Problem A 2.5 of brass of specific heat of 0.39 kJ/kg -K at a temperature of 176°C is dropped into 1.2 liters of water at 14°C. Find the resultant temperature of the mixture 40.26°C 35.25°C 45. 25°C 36. 2 6°C S lide 96: 95. Suplemmentary Problem The journals of a shaft are 380 mm diameter, it runs at 105 rpm and the coefficient of friction bet ween journals and bearinfs is 0.02. If the average load on the bearing is 200 kN, find the heat generated per minute at the bearings. 501.375 kJ 505.575 kJ 401.375 kJ 501.575 kJ S lide 97: 96. Suplemmentary Problem To ascertain the temperature of flue gases, 1.8 of copper of specific heat 0.395 kJ /kg -K was suspended on the flue gas until it attained the temperature of the gases, and then dropped into 2.27 kg of water at 20°C. If the resultant temperature of hte copper and water was 37.2°C, find the temperature of the flue gases. A.165.6°C B. 167.9°C C. 267.9°C D.265.6°C S lide 98: 97. Suplemmentary Problem In an experiment to find the specific heat of iron, 2.15 kg of iron cuttings at 100°C are dropped into a vessel containing 2.3 liters of water at 17°C and the resultant temperature of the mixture is 24.4°C. If the water equivalent of the vessel os 0.18 kg determine the specific heat of the iron. 0.47 kJ/kg 0.37 kJ/kg 0.27 kJ/kg 0.17 kJ/kg S lide 99: 98. Suplemmentary Problem The effective radius of the pads in a single collar thrust block is 230 mm and the total load on th e thrust block is 240 kN, when the shaft is running at 93rpm. Taking the coefficient of friction between thrust and collar pads as 0.025, find the heat generated per hou r. 48.40 MJ 45.40 MJ 50.50 MJ 55.50 MJ S lide 100:

99. Suplemmentary Problem Calculate the Reynolds number for water at 80°F flowi ng through a tube 2 in. i n diameter, if the average water velocity and specific weight is 10ft/s and 62.4 lb/ft³ repsectively. Use a value of the viscosity as 0.0648 slug/ft-hr. 189,400 179,434 160,500 180,500 S lide 101: 100. Suplemmentary Problem If the mass velocity for water at 80°F flowing through a 1 in. d iameter tube is 30,000 slug/hr -ft². What is the Reynolds number. Take a viscosity value of 0.0648 slug.ft-hr. 35,100.42 35,560.34 38,500.64 38,580.25