Problem 168
A gas mixture in a tank at \(550 \mathrm{R}\) and 25 psia consists of $1 \mathrm{lbm}\( of \)\mathrm{CO}_{2}\( and \)3 \mathrm{lbm}\( of \)\mathrm{CH}_{4}$. Determine the volume of the tank and the partial pressure of each gas.
Problem 171
Consider a 30 -cm-diameter pan filled with water at \(15^{\circ} \mathrm{C}\) in a room at \(20^{\circ} \mathrm{C}, 1 \mathrm{~atm}\), and 30 percent relative humidity. Determine \((a)\) the rate of heat transfer by convection, (b) the rate of evaporation of water, and \((c)\) the rate of heat transfer to the water needed to maintain its temperature at \(15^{\circ} \mathrm{C}\). Disregard any radiation effects.
Problem 173
Using Henry's law, show that the dissolved gases in a liquid can be driven off by heating the liquid.
Problem 174
Consider a glass of water in a room at \(20^{\circ} \mathrm{C}\) and $100 \mathrm{kPa}$. If the relative humidity in the room is 70 percent and the water and the air are at the same temperature, determine \((a)\) the mole fraction of the water vapor in the room air, (b) the mole fraction of the water vapor in the air adjacent to the water surface, and \((c)\) the mole fraction of air in the water near the surface. Answers: (a) \(1.64\) percent, (b) \(2.34\) percent, (c) \(0.0015\) percent
Problem 176
Consider a brick house that is maintained at \(20^{\circ} \mathrm{C}\) and 60 percent relative humidity at a location where the atmospheric pressure is $85 \mathrm{kPa}$. The walls of the house are made of 20 -cm-thick brick whose permeance is \(23 \times 10^{-12} \mathrm{~kg} / \mathrm{s}\) - $\mathrm{m}^{2} \cdot \mathrm{Pa}$. Taking the vapor pressure at the outer side of the wallboard to be zero, determine the maximum amount of water vapor that will diffuse through a \(3-\mathrm{m} \times 5-\mathrm{m}\) section of a wall during a 24-h period.
Problem 179
Oxygen gas is forced into an aquarium at \(1 \mathrm{~atm}\) and $25^{\circ} \mathrm{C}$, and the oxygen bubbles are observed to rise to the free surface in \(4 \mathrm{~s}\). Determine the penetration depth of oxygen into water from a bubble during this time period.
Problem 180
In an experiment, a sphere of crystalline sodium chloride \((\mathrm{NaCl})\) was suspended in a stirred tank filled with water at \(20^{\circ} \mathrm{C}\). Its initial mass was \(100 \mathrm{~g}\). In 10 minutes, the mass of the sphere was found to have decreased by 10 percent. The density of \(\mathrm{NaCl}\) is \(2160 \mathrm{~kg} / \mathrm{m}^{3}\). Its solubility in water at $20^{\circ} \mathrm{C}\( is \)320 \mathrm{~kg} / \mathrm{m}^{3}$. Use these results to obatin an average value for the mass transfer coefficient.
Problem 182
Liquid methanol is accidentally spilled on a $1-\mathrm{m} \times 1-\mathrm{m}$ laboratory bench and covers the entire bench surface. A fan is providing a \(20 \mathrm{~m} / \mathrm{s}\) airflow parallel over the bench surface. The air is maintained at \(25^{\circ} \mathrm{C}\) and $1 \mathrm{~atm}$, and the concentration of methanol in the free stream is negligible. If the methanol vapor at the air-methanol interface has a pressure of \(4000 \mathrm{~Pa}\) and a temperature of \(25^{\circ} \mathrm{C}\), determine the evaporation rate of methanol on a molar basis.
Problem 183
The top section of an 8-ft-deep, 100-ft \(\times 100-\mathrm{ft}\) heated solar pond is maintained at a constant temperature of \(80^{\circ} \mathrm{F}\) at a location where the atmospheric pressure is \(1 \mathrm{~atm}\). If the ambient air is at \(70^{\circ} \mathrm{F}\) and 100 percent relative humidity and wind is blowing at an average velocity of \(40 \mathrm{mph}\), determine the rate of heat loss from the top surface of the pond by \((a)\) forced convection, \((b)\) radiation, and (c) evaporation. Take the average temperature of the surrounding surfaces to be \(60^{\circ} \mathrm{F}\).
Problem 186
A sphere of ice, \(5 \mathrm{~cm}\) in diameter, is exposed to $65 \mathrm{~km} / \mathrm{h}$ wind with 15 percent relative humidity. Both the ice sphere and air are at \(-1^{\circ} \mathrm{C}\) and \(90 \mathrm{kPa}\). Predict the rate of evaporation of the ice in \(\mathrm{g} / \mathrm{h}\) by use of the following correlation for single spheres: $\mathrm{Sh}=\left[4.0+1.21(\mathrm{ReSc})^{2 / 3}\right]^{0.5}\(. Data at \)-1^{\circ} \mathrm{C}\( and \)90 \mathrm{kPa}: D_{\text {ais } \mathrm{H}, \mathrm{O}}=2.5 \times 10^{-5} \mathrm{~m}^{2} / \mathrm{s}^{3}\(, kinematic viscosity (air) \)=1.32 \times 10^{-7} \mathrm{~m}^{2} / \mathrm{s}\(, vapor pressure \)\left(\mathrm{H}_{2} \mathrm{O}\right)=0.56 \mathrm{kPa}\( and density (ice) \)=915 \mathrm{~kg} / \mathrm{m}^{3}$.
