Hot air duct

Dow developed an experimental moderate-temperature resin, XV-71794, which is claimed to offer incredibly high toughness and low moisture absorption. Baltimore Aerospace has used Nextel and graphite fibers in a bismaleimide matrix for a hot air duct in a jet engine. The duct is 75% lighter than one made of metal. 

The application of very high-permeability dryer fabrics in the paper industry made it possible to introduce air through the fabrics. Therefore, the above-mentioned blowing rolls and the hot air ducts below (or above) the felt rolls between the cylinders became very popular. These systems provide better crossflow ventilation, which in turn results in more uniform and higher mass-transfer rates. 

Ducted radomes are used that are hemispherical domes mounted on a cylindrical base. These consist of several orange peel side panels connected by a spherical cap panel. Such an RP structure can include hot-air ducts between the inner and outer skins of the side panels for anti-icing purposes. 

Aircraft applications include exhaust-pipe shrouds, fireproof bulkheads, gas-turbine bypass ducts, hot-air ducts, engine cowlings, formed brackets and skins for hot areas. Other aircraft applications include galley equipment, chemical toilets and... 

Because of its small size and portabiHty, the hot-wire anemometer is ideally suited to measure gas velocities either continuously or on a troubleshooting basis in systems where excess pressure drop cannot be tolerated. Furnaces, smokestacks, electrostatic precipitators, and air ducts are typical areas of appHcation. Its fast response to velocity or temperature fluctuations in the surrounding gas makes it particularly useful in studying the turbulence characteristics and rapidity of mixing in gas streams. The constant current mode of operation has a wide frequency response and relatively lower noise level, provided a sufficiently small wire can be used. Where a more mgged wire is required, the constant temperature mode is employed because of its insensitivity to sensor heat capacity. In Hquids, hot-film sensors are employed instead of wires. The sensor consists of a thin metallic film mounted on the surface of a thermally and electrically insulated probe. 

Blowing hot air A typical arrangement is shown in Figure 31.9. The bus duct enclosure is provided with inlet and outlet valves at suitable locations. Hot air is supplied through the inlet valve until the interior of the enclosure is completely dry. The blowing equipment comprises an axial flow fan. a heater unit, an inlet air filter unit, pressure... 

Alloys of nonferrous metals, primarily the brasses (copper and zinc) and the bronzes (copper and tin), can cause an air pollution problem during melting and casting. The type and degree of emissions depend on the furnace and the alloy. Control systems consist of hoods over the furnaces and pouring stahons to collect the hot gases, ducts and fans, and baghouses or ESPs. 

Drying. The drying step for large shapes is critical. Extremely large fireclay and silica shapes are sometimes allowed to dry on a temperature-controlled floor heated by steam or air ducts embedded in the concrete. Smaller shapes are generally dried in a tunnel dryer. The ware is placed on cars that enter the cold end and exit at the hot end. 

A 600-ft-long duct having a diameter of I ft serves as a space heater in a warehouse area. Hot air enters the duct at 800°F, and the emissivity of the outside duct surface is 0.6. Determine duct air temperature, wall temperature, and outside heat flux along the duct for flow rates of 0.3. 1.0, and 1.5 lb ,/s. Take into account variations in air properties. The room temperature for both convection and radiation is 70°F. 

Applications for BMs are used to contain many different products that include foodstuffs, beverages, household products (appliances, air conditioners, furniture at home/office/hospital/sports arenas, etc.), personal care products, medicine/pharmaceutical products, automotive parts [bumpers, spoilers, air ducts, seat backs, etc.], construction panels, tote boxes, trays, leisure items (toys, floatation, marine buoys, canoes, sailboards, sports goods, etc.), industrial parts (business machines, tool boxes, trash containers, hot water tanks, etc.), and so on.215-217... 

A 5-m-long section of an air beating system of a house passes through an unheated space in the basement Fig. ] 20). The cross section of the rectangular duct of the heating system is 20 cm X 25 cm. Hot air enters the duct at 100 kPa and 60 C at an average velocity of 5 m/s. The temperature of the air in the duct drops to 54°C as a result of heat loss to the cool space in the basement. Determine the rate of heat loss from the air in the duct to the basement under steady conditions Also, determine the cost of this heat loss per hour if the house is heated by a natural gas furnace that has an efficiency of 80 percent. and the cost of the natural gas in that area is 1.60Aherm (1 therm = 105,500 kJ). 

SOLUTION The temperature of the air in the heating duct of a house drops as a result of heat loss to the cool space in the basement. The rate of heat loss from the hot air and its cost are to be determined. 

Hot air at atmospheric pressure and SOX enters an 8-m-long uninsulated square duct of cross section 0.2 m x 0.2 m that passes through the attic of a house at a rate of 0.15 m /s (Fig. 8-31). The duct is observed to be nearly Isolhermal at 60°C. Determine the exit temperature of the air and the rale of heat loss from the duct to the attic space. 

An 8-m long, uninsulated square duel of cross section 0.2 m X 0.2 m and relative roughness 10 passes through the attic space of a house. Hot air emers the duct at 1 atm and 80°C at a volume flow rale of 0.15 mVs. The duct surface is nearly isothermal at 60°C. Determine the rate of heat loss from the duct to the attic space and the pressure difference between the inlet and outlet sections of the duct. 

Hot au at 60 C leaving the furnace of a house enters a 12-m-long section of a sheet metal duct of rectangular cross section 20 cm X 20 cm at an average velocity of 4 m/s. The thermal resistance of the duct is negligible, and the outer surface of the duct, whose einissivity is 0.3, is exposed to the cold air at 10°C in the basement, with a convection heal transfer coefficient of 10 W/m °C. Taking the walls of the basement to be at 10°C also, determine (a) the temperature at which the hot air will leave the basement and (ft) the rale of heat loss from llie hot air in the duct to ihe basement. 

A thermocouple used to measure the temperature of hot air flowing in a duct whose walls are maintained at T = 400 K shows a temperature reading of fu, = 650 K (Fig. 13-33). Assuming the emissivity of the thermocouple junction to be 8 - 0,6 and the convection heat transfer coefficient tobe/r-F 80 W/m K, determine the actual temperature of the air. 

Application Examples Room, office Domestic refrigerator Large refrigerators Hot air furnaces Air-conditioning ducts... 

---