Convection ovens operate on the principle of inducing forced convection inside the oven chamber with a fan.A small cake is to be baked in an oven when the convection feature is disabled. For this situation, the freeconvection coefficient associated with the cake and its panis
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Fundamentals of Heat and Mass Transfer
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- A pipe 30 m long with an outer diameter of 75 mm is used to deliver steam at a rate of 2000 kg / hour. The vapor pressure is 198.53 kPa entering the pipe with a quality of 98%. The pipe needs to be insulated with a thermal conductivity of 0.2 W / (m K) so that the quality of the steam will only slightly decrease to 95%. The outer surface temperature of the insulation is assumed to be 25 ° C. Ignore resistance conductive of the pipe material and it is assumed that there is no pressure drop in the pipe. a. Determine the enthalpy of incoming vapor = AnswerkJ / kg. b. Determine the enthalpy of steam coming out = AnswerkJ / kg. c. Determine the vapor heat change / loss along the flow = Answerwatt. d. Specify the minimum required insulation thickness = Answercm.arrow_forwardA pipe 30 m long with an outer diameter of 75 mm is used to deliver steam at a rate of 1500 kg / hour. The vapor pressure is 198.53 kPa entering the pipe with a quality of 98%. The pipe needs to be insulated with a thermal conductivity of 0.2 W / (m K) so that the quality of the steam will only slightly decrease to 95%. The outer surface temperature of the insulation is assumed to be 25 ° C. Ignore resistance conductive of the pipe material and it is assumed that there is no pressure drop in the pipe. a. Determine the enthalpy of incoming vapor = Answer kJ / kg. b. Determine the enthalpy of steam coming out = Answer kJ / kg. c. Determine the vapor heat change / loss along the flow = Answer watt. d. Specify the minimum required insulation thickness = Answer cm.arrow_forwardThe temperature of a tank in the form of liquid nitrogen is -10 ° C. Tank diameter is 16 cm. The amount of heat lost by convection and radiation from the tank to the environment is 65.5 W / m. Calculate the temperature of the environment where the tank is located .h = 4.35 W / m2K, e= 1.arrow_forward
- 5. Consider a carton of milk that is refrigerated at a temperature of Tm = 5 °C. The kitchen temperature on a hot summer day is T- -30 °C. If the four sides of the carton are of height and width L = 200 mm and w= 100 mm, respectively, determine the heat transferred to the milk carton as it sits on the kitchen counter for durations of t=10 s, 60 s, and 300 s before it is returned to the refrigerator. The convection coefficient associated with natural convection on the sides of the carton is h = 10 W/m²K. The surface emissivity is 0.90. Assume the milk carton temperature remains at 5 °C during the process. Your parents have taught you the importance of refrigerating certain foods from the food safety perspective. Comment on the importance of quickly returning the milk carton to the refrigerator from an energy conservation point of view.arrow_forwardA thick-walled cylindrical tubing of hard rubber (k=0.151 W/m*K) having an inside radius of 5 mm and an outside radius of 20 mm is being used as a temporary cooling coil in a bath. Ice water is flowing rapidly inside, and the inside wall temperature is 275 K. The outside surface temperature is 300 K. A total of 20 W must be removed from the bath by the cooling coil. How many meter of tubing are needed?arrow_forwardSteam at 350 °C flows through the stainless steel pipe with k=26 W/m.°C. The inner and outer diameters of the stainless steel pipe are 6.0 cm and 7.0 cm, respectively. The pipe is insulated from the outside with a 4.0 cm thick glass wool (k= 0.038 W/m.°C) and then a 3.0 cm thick k=0.25 W/m.K material. The insulated pipe is in the environment at 20 °C. The heat loss from the pipe occurs only by [natural convection+radiation]. Film heat transfer coefficient including the effects of [natural convection+radiation] in the insulated pipe is 30 W/m². is C. Calculate the heat transferred per unit pipe length since the film heat transfer coefficient defined according to the inner area of the pipe is 110 W/m².°C.arrow_forward
- Design a solar chimney to cover 80% of total heating losses in February, where U value for the chimney=D0.4 W/m2.K and the total wall area of the spaces equal 60m² and the temperature outside are 30C at night and 8°C at day and the temperature for the interior is 23 Ос.arrow_forwardA thermometric well is placed in a pipe having diameter of 55 mm. Pipe wall temperature is 100°C and heat transfer coefficient inside the pipe is 300 W/m² K. Thickness of thermowell is 1.2 mm and its length is 50 mm. Thermal conductivity of thermowell material. Is 30 W/mK. If the temperature of the gas flowing through the pipe is recorded by thermometer as 200°C, determine the true temperature of gas. If the error in gas temperature is to be reduced by 80% by increasing the length of thermowell, determine the new length of thermowell. Draw a sketch of this thermowell. Take perimeter to area ratio for thermowell as 1/T (T= thickness).arrow_forwardThe temperature of a cylindrical tank containing liquid nitrogen is -10 ° C. Tank diameter is 16 cm. The amount of heat lost by convection and radiation from the tank to the environment is 65.5 W / m. Calculate the temperature of the environment where the tank is located: h = 4.35 W / m2K, ∈ = 1.arrow_forward
- A Pressurized Water Reactor fuel rod is 12 ft long and 0.374 inches in diameter (outer) on a 0.496 inch square pitch. The fuel pellet diameter is 0.3225 inches. The fuel rod gap is constant with a width of 0.0065 inches. The system pressure is 2250 psia and can be assumed to be constant. The rod operates at linear heat rate of 12.1 kW/ft. At the elevation of interest, the coolant temperature is 575 °F with a convective heat transfer coefficient of 6200- For this elevation determine the temperature BTU hr ft²F margin to boiling according to Jens-Lottes. Also assume constant fluid properties given as: p=46.39 Ibm = ,c. 1.261- BTU Ibm-F BTU -,k=0.334- hr-ft-F Ibm ft-hr M=0.222- -, Tsat 652.7F =arrow_forwardGround turkey was made into me at balls and refrigerated at 2 ° C before being deep fried. The diameter of each meat ball is 9cm. To make sure that the meat balls are safe to be consumed, they must be cooked over 70 ° C. Assume that the cooking oil is at a constant temperature of 180 ° C and has a heat transfer coefficient of 50 W/(m 2 ∙ K). The conductivity and specific heat of the ground turkey are approximated at 2 W/( m∙K ) and 4 kJ/( kg ∙ K) respectively. The density of the ground turkey is 500kg/ m 3 . a) During the deep- frying process, do you anticipate that each meat ball has a uniform temperature distribution throughout its volume? Please show calculation to support your answer (5 pts) . b) Please calculate the minimum time required for cooking (1 5 p ts). c) When served, what are the surface and center temperatures of each meat ball ( 15 pts).arrow_forwardA pipe 30 m long with an outer diameter of 75 mm is used to carry steam at a rate of 1000 kg / hour. The vapor pressure is 198.53 kPa entering the pipe with a quality of 98%. The pipe needs to be insulated with a thermal conductivity of 0.2 W / (m K) so that the quality of the steam will only slightly decrease to 95%. The outer surface temperature of the insulation is assumed to be 25 ° C. Ignore resistance conductive of the pipe material and it is assumed that there is no pressure drop in the pipe. a. Determine the enthalpy of incoming vapor = Answer kJ / kg. b. Determine the enthalpy of steam coming out = Answer kJ / kg. c. Determine the vapor heat change / loss along the flow = Answer watt. d. Specify the minimum required insulation thickness = Answer cm.arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning