Chapter 14: Problem 70
What are the adverse effects of excess moisture on the wood and metal components of a house and the paint on the walls?
Chapter 14: Problem 70
What are the adverse effects of excess moisture on the wood and metal components of a house and the paint on the walls?
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Get started for freeThe average heat transfer coefficient for airflow over an odd-shaped body is to be determined by mass transfer measurements and using the Chilton-Colburn analogy between heat and mass transfer. The experiment is conducted by blowing dry air at \(1 \mathrm{~atm}\) at a free-stream velocity of $2 \mathrm{~m} / \mathrm{s}$ over a body covered with a layer of naphthalene. The surface area of the body is \(0.75 \mathrm{~m}^{2}\), and it is observed that $100 \mathrm{~g}\( of naphthalene has sublimated in \)45 \mathrm{~min}$. During the experiment, both the body and the air were kept at \(25^{\circ} \mathrm{C}\), at which the vapor pressure and mass diffusivity of naphthalene are $11 \mathrm{~Pa}\( and \)D_{A B}=0.61 \times 10^{-5} \mathrm{~m}^{2} / \mathrm{s}$, respectively. Determine the heat transfer coefficient under the same flow conditions over the same geometry.
A researcher is using a \(5-\mathrm{cm}\)-diameter Stefan tube to measure the mass diffusivity of chloroform in air at \(25^{\circ} \mathrm{C}\) and $1 \mathrm{~atm}\(. Initially, the liquid chloroform surface was \)7.00 \mathrm{~cm}\( from the top of the tube; after \)10 \mathrm{~h}$ elapsed, the liquid chloroform surface was \(7.44 \mathrm{~cm}\) from the top of the tube, which corresponds to \(222 \mathrm{~g}\) of chloroform being diffused. At \(25^{\circ} \mathrm{C}\), the chloroform vapor pressure is $0.263 \mathrm{~atm}$, and the concentration of chloroform is zero at the top of the tube. If the molar mass of chloroform is $119.39 \mathrm{~kg} / \mathrm{kmol}$, determine the mass diffusivity of chloroform in air.
What is the relation \((f / 2) \operatorname{Re}=\mathrm{Nu}=\) Sh known as? Under what conditions is it valid? What is the practical importance of it?
Define the following terms: mass-average velocity, diffusion velocity, stationary medium, and moving medium.
The roof of a house is \(15 \mathrm{~m} \times 8 \mathrm{~m}\) and is made of a 30 -cm-thick concrete layer. The interior of the house is maintained at \(25^{\circ} \mathrm{C}\) and 50 percent relative humidity and the local atmospheric pressure is \(100 \mathrm{kPa}\). Determine the amount of water vapor that will migrate through the roof in \(24 \mathrm{~h}\) if the average outside conditions during that period are \(3^{\circ} \mathrm{C}\) and 30 percent relative humidity. The permeability of concrete to water vapor is $24.7 \times 10^{-12} \mathrm{~kg} / \mathrm{s} \cdot \mathrm{m} \cdot \mathrm{Pa}$.
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