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Insulation degrades (experiences an increase in thermal conductivity) if it is subjected to water vapor condensation. The problem may occur in home insulation during cold periods, when vapor in a humidified room diffuses through the drywall (plaster board) and condenses in the adjoining insulation. Estimate the mass diffusion rate for a 3 m× 5 m wall, under conditions for which the vapor pressure is 0.03 bar in the room air and 0.0 bar in the insulation. The drywall is 10 mm thick, and the solubility of water vapor in the wall material is approximately
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Fundamentals of Heat and Mass Transfer
- 6. A sheet of steel 1.5 mm thick has nitrogen atmospheres on both sides at 1200C and is permitted to achieve a steady-state diffusion condition. The diffusion coefficient for nitrogen in steel at this temperature is 6 10-11 m2/s, and the diffusion flux is found to be 1.2 10-7 kg/m2-s. Also, it is known that the concentration of nitrogen in the steel at the high-pressure surface is 4 kg/m3. How far into the sheet from this high-pressure side will the concentration be 2.0 kg/m3? Assume a linear concentration profile.arrow_forward4arrow_forwardAir at 90 0C and 1.00 atm (absolute) contains 10.0 mole% water. A continuous stream of this air enters a compressor–condenser, in which the temperature is lowered to 15.6 0C and the pressure is raised to 3.00 atm. The air leaving the condenser is then heated isobarically to 100 0C. Calculate the fraction of water that is condensed from the air, the relative humidity of the air at 100 0C, and the ratio m3 outlet air at 100 0C/m feed air at 90 0C.arrow_forward
- From an open water surface with air temperature 22°C, relative humidity is 40% and wind speed is 3 m/s, all measured at height 2 m above the water surface. Assume a roughness height of 0.03 cm. The net radiation is 200 W/m^2. Cp = 1005 J/kg-K A. Calculate the latent heat of vaporization (J/kg) B. Calculate the evaporation using Energy Balance Method (mm/day) C. Calculate the saturation deficit of the vapor pressure (Pa) D. Calculate the evaporation using Priestley-Taylor Method (mm/day)arrow_forwardDetermine the binary diffusion coefficient of H₂ in air at 600 K and 3 atm in m²/s. (A) 17.23x10-5 (B) 4.20x10-5 8.58x10-5 (D) 2.43x10-5arrow_forwardi need the answer quicklyarrow_forward
- True or False? Justify your answer. A. In a rectangular drug delivery device that consists of a drug reservoir and a diffusion barrier made of a polymer gel, the steady state diffusion (mass transfer) rate through a barrier of thickness 1 cm was found to be 20 mg/day. If the barrier thickness were to be doubled keeping the reservoir drug concentration the same, the mass transfer rate would be 10 mg/day. B. In a spherical drug delivery device consisting of a core reservoir surrounded by a polymer gel barrier, the steady state diffusion (mass transfer) rate through a barrier of thickness 1 cm was found to be 20 mg/day. If the barrier thickness were to be doubled keeping the reservoir drug concentration the same, the mass transfer rate would be 10 mg/day.arrow_forwardMethane is diffusing at steady state through a 0.5mm diameter and 4mm long tube containing nitrogen gas at 101.32 kPa and 298K. Methane entering the tube is at 2.31x10 Pa and leaving the tube at 1.013x10 Pa. The diffusivity of nitrogen in methane gas is 0.140 x10m/s. Calculate flux of methane. Mention the unit of the flux. Paragraph BIEEarrow_forwardAir at 90°C and 1.00 atm (absolute) contains 10.0 mole% water. A continuous stream of this air enters a compressor-condenser, in which the temperature is lowered to 15.6°C and the pressure is raised to 3.00 atm. The air leaving the condenser is then heated isobarically to 100°C. Calculate: (a) the fraction of water that is condensed from the air (b) the relative humidity of the air at 100°C (c) and the ratio of the volumetric flow of the outlet air to the volumetric flow of the feed air.arrow_forward
- Use the definition of the Sherwood number to calculate the mass transfer coefficient (in cm/s) for a scenario where the characteristic length is 0.034 m, the diffusivity is 0.00099 cm^2/s, and the Sherwood number is 3.5.arrow_forward2. Humid air at 35o C and a pressure of 1 atm and with 98% relative humidity enters a condenser in which the temperature is lowered isobarically (pressure is constant) to 15o C. Part of the water condenses and coexists with the remaining air. The remaining air leaves the condenser flowing through a 20-cm diameter duct at a velocity of 10 m/s. Calculate the rate (moles water/s) at which water condenses.arrow_forwardA dehumidifier brings in saturated wet air (100 percent relative humidity) at 30°C and 1 atm, through an inlet of 8-cm diameter and average velocity 3 m/s. After some of the water vapor condenses and is drained off at the bottom, the somewhat drier air leaves at approximately 30°C, 1 atm, and 50 percent relative humidity. For steady operation, estimate the amount of water drained off in kg/h. (This problem is idealized from a real dehumidifier.) (in kg/hr) Note: Use three decimal places and no need to input the unit.arrow_forward
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