A small oven consists of a cubical box of dimension
(a) Find the following view factors: F12, F13, F21, F31, F23, F32, F33.
(b) Determine the temperature of the floor and the net rate of heat transfer leaving the sphere due to radiation. Is the sphere under steady-state conditions?
Want to see the full answer?
Check out a sample textbook solutionChapter 13 Solutions
Fundamentals of Heat and Mass Transfer
- 3.4 Estimate the rate of heat loss due to radiation from a covered pot of water at 95 ° C. How does this compare with the 60 W that is lost due only to convection and conduction losses? What amount of energy input would be needed to maintain the water at its boiling point for 30 minutes? The polished stainless steel pot is cylindrical, 20 cm in diameter and 14 cm high, with a tight-fitting flat cover. The air temperature in the kitchen is about 25 ° C. State any assumptions you make in deriving your estimatesarrow_forwardA box made of copper plate with outside dimensions of 5 ft by 5 ft by 6-in.is suspended horizontally in a large room where the air and wall temperaturesare 80°F. The box contains a heating coil which maintains a temperature of500 °F on all external surfaces. What is the total heat loss from the box inBtu/hr.arrow_forwardQuestion 5: Z=62 a. An iron sphere of mass (Z + 300)g is kept in a container having boiling water (100 °C). If the temperature of the sphere is 25.5°C, how much heat energy is absorbed by the iron sphere? Consider the specific heat of iron as 452J/kg. b. The wall of an industrial furnace is constructed from (Z + 3) cm thick fireclay brick having a thermal conductivity of 1.7 W/mK. Measurements made during steady-state operation reveal temperatures of 530°C and 375°C at the inner and outer surfaces, respectively. Find the rate of heat loss through a wall which is (Z + 5) cm by (Z + 3) m on a side.arrow_forward
- A machine element as seen in the figure is made of pure copper. It has an inner diameter of D;=2.9 cm, outer diameter of Do=5.9 cm, and height of H=19 cm. The initial temperature of the element is 749 K, and then suddenly placed in an environment which has a temperature of Too=300O K. The temperature of the element is measured as 489 K, 4.8 minutes after the cooling process. If the lumped system method is applicable, determine the heat transfer coefficient of the environment, in W/(m²K). Note: All the surfaces should be considered to calculate the surface area. Not: Yüzey alanı hesaplamak için tüm yüzeyler dikkate alınmalıdır. Properties of pure copper: k=370 W/(mK), C=920 J/(kg°C), p=8933 kg/m³ H Dịarrow_forwardThe 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 polystyrene is 0.033 W/m°C.arrow_forward4. Two aluminum blocks with different dimensions, but the same mass are shown in the figure. The dimensions of block 1 are 0.25 cm in thickness, 3 cm in width, and 36 cm in length. The dimensions of block 2 are 3 cm for each side of the cube. Aluminum has a density of 2700 kg/m³ and a specific heat capacity of 900 J/kg-°C. The value of the heat transfer coefficient to the surrounding air is 10 W/m²-°C. 0.25 cm 36 cm 3 cm 3 cm Block 1 3 cm Block 2 3 cm Complete the following. (a) Calculate thermal time constant (in min) for both blocks. (b) Each block is heated to an initial temperature 120 °C and then allowed to cool in the surrounding air which is at 20 °C. Write a script file in MATLAB® that plots the temperature as a function of time, T(t), for both blocks on the same graph. Plot the temperature of block 1 using a solid black line and the temperature of block 2 using a dotted black line. Plot for a duration equal to four of the longer time constant between blocks 1 and 2. The time…arrow_forward
- Sipho’s mother is making a fire in the stove inside a shack using coal. A fan is used to extract the flue gasfrom the fire via a chimney made of zinc material. The wall thickness of Chimney is L=4mm and the walltemperature of the chimney on the flue gas side is T_si=60˚C. Sipho, playing outside next to the chimneyexperiences an ambient temperature of 20˚C. The surrounding temperature is T_sur=35˚C and the emissivityis ε=0.95. Assume the convection coefficient is 20W/m2K and the chimney is grey material.Under these conditions determine the outer surface (air side) temperature T_so=? of the chimney.arrow_forwardOn a mild Saturday morning while people are working inside, the furnace keeps the temperature inside the building at 23°C. At noon the furnace is turned off, and the people go home. The temperature outside is a constant 14°C for the rest of the afternoon. If the time constant for the building is 3 hr, when will the temperature inside the building reach 19°C? If some windows are left open and the time constant drops to 2 hr, when will the temperature inside reach 19°C? If the time constant for the building is 3 hr, the temperature inside the building will reach 19°C about hr after noon. (Round to the nearest tenth as needed.) If the time constant for the building drops to 2 hr, the temperature inside the building will reach 19°C about (Round to the nearest tenth as needed.) hr after noon. Carrow_forwardCalculate the heat transferred from the cube-shaped iron mass (a = 30 cm) to the environment at 20 ° C with all surfaces at a temperature of 100 ° C. (Assume that the heat is only from the surfaces, the inner parts of the surfaces are insulated.)arrow_forward
- The inside wall of a furnace is at 2100oF and the outside wall is at 300oF. The wall of a furnace must be designed to transmit no more than 220 Btu/hr-ft2. Two types of bricks are available for construction:TYPE A: k = 0.38 Btu/ hr-ft-R with an allowable maximum temperature of 1400oFTYPE B: k = 0.98 Btu/ hr-ft-R with an allowable maximum temperature of 2300oF Both types of bricks have the same dimensions (9” x 4.5” x 3”) but the cost for Type B brick is twice the cost of Type A brick. Illustrate the order of arrangement of bricks A and B in the furnace wall (with thickness, estimated temperatures at the interface between walls A and B and at the interior and exterior surface, the transport area and direction of transfer included)arrow_forwardThe inside wall of a furnace is at 2100oF and the outside wall is at 300oF. The wall of a furnace must be designed to transmit no more than 220 Btu/hr-ft2. Two types of bricks are available for construction:TYPE A: k = 0.38 Btu/ hr-ft-R with an allowable maximum temperature of 1400oFTYPE B: k = 0.98 Btu/ hr-ft-R with an allowable maximum temperature of 2300oF Both types of bricks have the same dimensions (9” x 4.5” x 3”) but the cost for Type B brick is twice the cost of Type A brick. Model the wall as one-dimensional and determine the most economical arrangement of the bricks. Include:a drawing labeled with all given informationthe variables used in the appropriate places on the drawing (along with values and units, if provided)a thermal circuit showing the paths for heat transmissionequations and calculationsCalculations that show that the maximum temperature for Type A brick does not exceed 1400oFA recommendation for the number and orientation of the bricks. The inside temp is 2100f…arrow_forwardThe inside wall of a furnace is at 2100oF and the outside wall is at 300oF. The wall of a furnace must be designed to transmit no more than 220 Btu/hr-ft2. Two types of bricks are available for construction:TYPE A: k = 0.38 Btu/ hr-ft-R with an allowable maximum temperature of 1400oFTYPE B: k = 0.98 Btu/ hr-ft-R with an allowable maximum temperature of 2300oF Both types of bricks have the same dimensions (9” x 4.5” x 3”) but the cost for Type B brick is twice the cost of Type A brick. What is the rate of heat conduction through wall A? If a 15 ft2 wall is to be constructed, how many bricks will be used? how many brick A and how many brick B?arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning