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A novel infrared recycler has been proposed for reclaiming the millions of kilograms of waste plastics produced by the dismantling and shredding of auto motive vehicles following their retirement. To address the problem of sorting mixed plastics into components such as polypropylene and polycarbonate, a washed stream of the mixed plastics is routed to an infrared heating system, where it is dried and subsequently heated to a temperature for which one of the components begins to soften, while the others remain rigid. The mixed stream is then routed through steel rollers, to which the softened plastic sticks and is removed from the stream. Heating of the stream is then continued to facilitate removal of a second component, and the heating/removal process is repeated until all of the components are separated.
Consider the initial drying stage for a system comprised of a cylindrical heater aligned coaxially with a rotating drum of diameter
(a) If the flow of dry air through the drum maintains a convection
0.024 m/s on the surface of the pellets, what is the evaporation rate per unit length of the drum?
(b) Neglecting convection heal transfer, determine the temperature Ththat must be maintained by a heater of diameter
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Chapter 13 Solutions
Fundamentals of Heat and Mass Transfer
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- A microwave dinner has the instructions listed below. In this problem, you will explain how following the instructions affect the heat transfer into the meal. (The meal starts off frozen, and is covered with a thin piece of plastic "film" or covering when it is taken out of the box. The vegetables are separate from the beef and potatoes.) Instructions1. Cut slit in film over vegetables.2. Microwave on high 4 minutes3. Turn back film from beef and potatoes. Stir beef and potatoes. Replace film. Return tray to microwave oven4. Microwave on high 3 minutes.5. Let stand 2 minutes in microwave oven., Stir beef and potatoes.a. How does each of the steps above (cut slit in film, stir beef and potatoes, etc) affect the heat transfer to the food? Make sure to consider conduction, convection, and radiation where appropriate. b. The instructions ask you to stir the beef and potatoes, but not the vegetables. From this, what can you tell about how each type of food receives and transfers heat?…arrow_forwardThe extremely high temperatures needed to trigger nuclear fusion are proposed to be generated by laser irradiating a spherical pellet of deuterium and tritium fuel of diameter Dp = 1.8 mm. (a) Determine the maximum fuel temperature that can be achieved by irradiating the pellet with 200 lasers, each producing a power of P = 500 W. The pellet has an absorptivity a = 0.3 and emissivity & = 0.8. (b) The pellet is placed inside a cylindrical enclosure. Two laser entrance holes are located at either end of the enclosure and have a diameter of DLEH = 2.0 mm. Determine the maximum temperature that can be generated within the enclosure. N (a) K Dp Determine the maximum fuel temperature that can be achieved in part (a), in K. Tmax = i K DLEH N #K Determine the maximum fuel temperature that can be achieved in part (b), in K. Tmax i Physical Properties Mathematical Functions (b)arrow_forward4. The filament of a 75 W light bulb may be considered as a black body radiating into a black enclosure at 70° C. the filament diameter is 0.10 mm and length is 5 em. considering the radiation, determine the filament temperature .arrow_forward
- As far as diathermy concern, we use microwaves to deposit its energy in the surface of fatty layers where as the infrared waves most of it energy is deposited in deep area with fatty layers. O true Falsearrow_forwardAn important step in many manufacturing processes is the annealing of a material, particularly of metals. A particular manufacturing requires annealing of a thin metallic sheet at 700°C. To accomplish this task, the sheet is placed in a large furnace, the walls of which are at approximately 730°C. An inert gas circulates through the oven to prevent oxidation of the metal. a) The metallic sheet can be approximated as diffuse, and the absorptivity of the sheet is shown below. Using the fact that a = & for a diffuse surface, determine the emissive power (W/m²) from the sheet when it is at a uniform T = 730°C. 1 0.8 0.3 2.5 λ (μm)arrow_forwardExample 7.9 The filament of a 75 W light bulb may be considered a black body radiating into a black enclosure at 70°C.The filament diameter is 0.10 mm and length is 50 mm. Considering the radiation, determine the filament temperature.arrow_forward
- 13.75 Coated metallic disks are cured by placing them at the top of a cylindrical furnace whose bottom surface is electrically heated and whose sidewall may be approximated as a reradiating surface. Curing is accomplished by maintaining a disk at T, = 400 K for an extended period. The electrically heated surface is maintained at T, = 800 K and is mounted on a ceramic base material of thermal conductivity k = 20 W/m · K. The bottom of the base material, as well as the ambient air and large surroundings above the disk, are maintained at a temperature of 300 K. Emissivities of the heater and the disk inner and outer surfaces are ɛ, = 0.9, E2 j= 0.5, and ɛ2 o = 0.9, respectively. sur = 300 K T, h -T2, E2.i E2,0 L. = 200 mm -T1, Ɛ1 L, = 25 mm k, = 20 W/m •K D = -T, = 300 K +120 mm-►| Assuming steady-state operation and neglecting convection within the cylindrical cavity, determine the electrical power that must be supplied to the heater and the convection coefficient h that must be…arrow_forwardA water-cooled spherical object of diameter 10 mm and emissivity 0.9 is maintained at 4000 C. What is the net transfer rate from the oven walls to the object? A surface of area 0.5 m² , emissivity 0.8 and temperature 150 °C is placed in a large, evacuated chamber whose walls are maintained at 25°C. What is the rate at which radiation is emitted by the surface? What is the net rate at which radiation is exchanged between the surface and the chamber walls?arrow_forwardA thin, disk-shaped silicon wafer of diameter D=20 cm on a production line must be maintained at a temperature of 100 deg C. The wafer loses heat to the room by convection and radiation from its upper surface, while heat is supplied at a constant flux from below. The surrounding air is at 20 deg C, while all surrounding surfaces (which can be treated as blackbodies) can be approximated to be isothermal at a temperature of 15 deg C. The wafer-to-air heat transfer coefficient is 30 W/m2-K and the emissivity of the wafer’s surface (which can be approximated to be gray) is 0.85. How much heat (in W) must be supplied to the wafer?arrow_forward
- 13.48 An electronic device dissipating 50 W is attached to the inner surface of an isothermal cubical container that is 120 mm on a side. The container is located in the much larger service bay of the space shuttle, which is evacuated and whose walls are at 150 K. If the outer surface of the container has an emissivity of 0.8 and the thermal resistance between the surface and the device is 0.1 K/W, what are the temperatures of the surface and the device? All surfaces of the con- tainer may be assumed to exchange radiation with the service bay, and heat transfer through the container restraint may be neglected.arrow_forwardcorrect answer otherwise dislikearrow_forwardGive step-by-step calculation and explanation Consider a person sitting nude on a beach in Florida. On a sunny day, visible radiation energy from the sun is absorbed by the person at a rate of 30 kcal/h or 34.9 W. The air temperature is a warm 30 °C and the individual’s skin temperature is 32 °C. The effective body surface exposed to the sun is 0.9 m². (Assume this same area for sun absorption, radiative transfer, and convective loss. Is this a good assumption?) a. Find the net energy gain or loss from thermal radiation each hour. (Assume thermal radiative gain and loss according to the equation 6.51 in Herman and an emissivity of 1.) -(4). Equalion (6.51) - (40Tin)Eskin Aşkin (Tskin – Troom) dt = (4 x 5.67 x 10¬8 w/m²–K* x (307 K)')€skin Askin (Tskin – Troom). (6.52) b. If there is a 4 m/s breeze, find the energy lost by convection each hour. (Use Eq. 6.61 with eq. 6.63.) 1 Equation he(Tskin – Tair), (6.61) A dt he 10.45 – w + 10w0.5 (6.63) - c. If the individual’s metabolic rate is…arrow_forward
Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning