Consider a sphere of diameter 5 cm, a cube of side length 5 cm, and a rectangular prism of dimension
Now all three of these geometries are exposed to ambient air at 33°C on all of their surfaces with a heat transfer coefficient of 12 W/m2 K. Determine how long it will take for the temperature of each geometry to rise to 25°C.
Want to see the full answer?
Check out a sample textbook solutionChapter 4 Solutions
Heat and Mass Transfer: Fundamentals and Applications
- Q2/ A 4-m-internal-diameter spherical tank made of 1.75-cm-thick stainless steel (k 15 W/m °C) is used to store iced water at 0°C. The tank is located in a room whose temperature is 35°C. The walls of the room are also at 35°C. The outer surface of the tank is black, and heat transfer between the outer surface of the tank and the surroundings is by natural convection and radiation. The convection heat transfer coefficients at the inner and the outer surfaces of the tank are 80 W/m2 °C and 10 W/m2· °C, respectively. Determine (a) the rate of heat transfer to the iced water in the tank and (b) the amount of ice at 0°C that melts during a l-h period. The heat of fusion of water at atmospheric pressure is hif 334 kJ/kg.arrow_forwardA USB-powered coffee cup warmer advertised on Amazon claims to have a heating plate that reaches 85°C when there is no cup placed on it. What is the electrical power required for this? Assume the device is 100% efficient at converting electrical power to heat in the plate and that heat from the plate is lost to air from the top surface of the heating plate only. Take ambient temperature to be 20.0°C, the diameter of the plate to be 10.0 cm, the convection coefficient from the plate to air to be 7.1 W/(m2.K), and take the emissivity of the plate to be 1.0. 7.0 W 9.8 W 12 W 3.6 W 7.7 W 5.5 Warrow_forwardA thin board of 0.5 cm thickness is exposed to a fluid of T, = 22°C and h = 30 W/m².K from one side with an emissivity of 0.7 where it faces a surrounding whose temperature is Tsur = 30°C. A heat flux of q" = 3500 W/m? is applied to the other side. Each side has an area of 12cm×12cm. Tsur (a) If the board has the following properties: k = 15.1 W/m.K, c, = 480 J/kg.K and p = 8055 kg/m², express an equation for the variation of temperature with respect to time. (b) Find the initial time rate of change of the board temperature if the initial board temperature is q" h 50°C.arrow_forward
- A square thermal window is constructed of two sheets of flat glass, each 4.00 mm thick, separated by 5.00 mm of stationary air. If the inside of the window is at 20.0 oC, the external one at -30.0 oC and the cross-sectional area of the window is 6.00 m2, determine for the steady state: kglass= 0,80 W/(m*K); kair= 0,024 W(m*K) a) The temperatures between the air layer ?1 and ?2 indicated in the figure.b) The flow of heat through the windowarrow_forwardConsider a sphere of diameter 5 cm, a cube of side length 5 cm, and a rectangular prism of dimension 4 cm × 5 cm × 6 cm, all initially at 0°C and all made of silver (k = 429 W/m2·K, ρ = 10,500 kg/m3 , Cp = 0.235 kJ/kg·K). Now all three of these geometries are exposed to ambient air at 33°C on all of their surfaces with a heat transfer coefficient of 12 W/m2 ·K. Determine how long it will take for the temperature of each geometry to rise to 25°C.arrow_forwardA wall made of concrete 0.305 m thick is insulated on the rear side. The wall at a uniform temperature of l0°C (283.2 K) is exposed on the front side to a gas at 843°C (1116.2 K). The convection coefficient is 28.4 W/m2-K, the thermal diffusivity is 1.74 x 10–3m2/h, and the thermal conductivity is 0.935 W/m-K.a. Calculate the time for the temperature at the insulated face to reach 232°C (505.2 K).b. Calculate the temperature at a point 0.152m below the surface at this same timearrow_forward
- Q2/ A 3-m internal diameter spherical tank made of 2-cm-thick stataless steel (k= 15 W/m 0°C. The tank is located in a room whose %3D C) is used to store iced water at Te temperature is T-22°C. The walls of the room are also at 22°C. The outer surface of the tank is black and heat transfer between the outer surface of the tank and the surroundings is by natural convection and radiation. The convection heat transfer coefficients at the inner and the outer surfaces of the tank are h-80 W/m2 C and h 10 W/m2 C, respectively. Determine (a) the rate of heat transfer to the iced water in the tank and (b) the amount of ice at 0°C that melts during a 24-h period.arrow_forwardTwo long rods of the same diameter, one of brass(k= 85 W/mK) and the other of copper (k=375 W/mK) have one of their ends inserted in a furnace and the other ends exposed to the same atmosphere. At a distance of 105mm away from the furnace, the temperature of the brass rod is 120 C. Find the distance form the furnace in which the copper rod have the same temperaturearrow_forward1. A 1000-W iron is left on the iron board with its base exposed to the air at 20°C. The convection heat transfer coefficient between the base surface and the surrounding air is 35 W/m². °C. If the base has an emissivity of 0.6 and a surface area of 0.02 m², determine the temperature of the base of the iron. 2. The inner and outer surfaces of a 5-m x 6-m brick wall of thickness 30 cm and thermal conductivity 0.69 W/m °C are maintained at temperatures of 20°C and 5°C, respectively. Determine the rate of heat transfer through the wall, in W.arrow_forward
- Two parallel back disks are positioned coaxially with a distance of 0.25 m apart. The lower disk is 0.2 m in diameter and the upper disk is 0.4 m in diameter. If the lower disk is heated electrically at 20 W to maintain a uniform temperature of 500 K, determine the temperature of the upper disk.arrow_forwardConsider steady heat transfer between two large parallel plates at constant temperatures of T1=300 K and T2=200 K that are L= 2cm apart. Assuming surfaces to be black (emissivity = 1), determine the rate of heat transfer between the plates per unit surface area assuming the gaps in between the plates are filled with atmospheric air (k=0.0219 W/m.C).arrow_forwardTwo nested spherical tanks with the internal and outer diameters of the 100 cm by 104 cm and 114 cm by 118 cm is used to store hot water at 100 C. Both tanks are made of boron fiber epoxy with different composite compositions. The thermal conductivity of the inner tank is 1.5 W/m K while the outer tank has a thermal conductivity of 0.5 W/m K. The gap between the tanks is filled with air (use properties of air at 50°C). The tank is located in an open environment at 0'C. The outer surface of the tank is white painted and heat transfer between the outer surface of the tank and the surrounding is by natural covection and radiation. The convection heat transfer coefficient at the inner and the outer surface of the pipe is h 20 W/m' K and h 10 W/m K. Determine; a. the rate of heat loss from the tank b. the inside, outside and intermediate surface temperatures. Hint: Take the outer surface temperature as 3°C for radiation calculations.arrow_forward
- Elements Of ElectromagneticsMechanical EngineeringISBN:9780190698614Author:Sadiku, Matthew N. O.Publisher:Oxford University PressMechanics of Materials (10th Edition)Mechanical EngineeringISBN:9780134319650Author:Russell C. HibbelerPublisher:PEARSONThermodynamics: An Engineering ApproachMechanical EngineeringISBN:9781259822674Author:Yunus A. Cengel Dr., Michael A. BolesPublisher:McGraw-Hill Education
- Control Systems EngineeringMechanical EngineeringISBN:9781118170519Author:Norman S. NisePublisher:WILEYMechanics of Materials (MindTap Course List)Mechanical EngineeringISBN:9781337093347Author:Barry J. Goodno, James M. GerePublisher:Cengage LearningEngineering Mechanics: StaticsMechanical EngineeringISBN:9781118807330Author:James L. Meriam, L. G. Kraige, J. N. BoltonPublisher:WILEY