Using Henry’s law, show that the dissolved gases in a liquid can be driven off by heating the liquid.

Air is to be cooled in the evaporator section of a refrigerator by passing it over a bank of 0.8-cm-outer-diameter and 0.4-m-long tubes inside which the refrigerant is evaporating at $− 20^\circ C.$ Air approaches the tube bank in the normal direction at $0^\circ C$ and 1 atm with a mean velocity of 4 m/s. The tubes are arranged in-line with longitudinal and transverse pitches of $S_L = S_T = 1.5 cm.$ There are 30 rows in the flow direction with 15 tubes in each row. Determine (a) the refrigeration capacity of this system and (b) pressure drop across the tube bank. Evaluate the air properties at an assumed mean temperature of $—5^\circ C$ and 1 atm. Is this a good assumption?

Determine the mole fraction of the water vapor at the surface of a lake whose temperature is $15^\circ C$ and compare it to the mole fraction of water in the lake. Take the atmospheric pressure at lake level to be 92 kPa.

How does the wavelength distribution of radiation emitted by a gas differ from that of a surface at the same temperature?

How does the presence of a noncondensable gas in a vapor influence the condensation heat transfer?

During a cold winter day, wind at 55 km/h is blowing parallel to a 4-m-high and 10-m-long wall of a house. If the air outside is at $5^\circ C$ and the surface temperature of the wall is $12^\circ C,$ determine the rate of heat loss from that wall by convection. What would your answer be if the wind velocity was doubled?

Determine the convection heat transfer coefficient for the flow of (a) air and (b) water at a velocity of 2 m/s in an 8-cm-diameter and 7-m-long tube when the tube is subjected to uniform heat flux from all surfaces. Use fluid properties at $25^\circ C.$

Consider a large plane wall of thickness L= 0.3 m, thermal conductivity $k= 2.5 W/m \cdot K,$ and surface area $A= 12 m^2.$ The leftside ofthe wall at x = 0 is subjected to a net heat flux of $\dot{q}_{0}=700 \mathrm{W} / \mathrm{m}^{2}$ while the temperature at that surface is measured to be $T_1= 80 ^\circ C.$ Assuming constant thermal conductivity and noheat generation in the wall, (a) express the differential equation and the boundary conditions for steady onedimensional heat conduction through the wall, (b) obtain a relation for the variation of temperature in thewall bysolving the differential equation, and (c) evaluate the temperature of the right surface ofthewall at x = L.

A 6-m-internal-diameter spherical tank made of 1.5-cm-thick stainless steel $(k = 15 W/m \cdot K)$ is used to store iced water at $0^\circ C$ in a room at $20^\circ C.$ The walls of the room are also at $20^\circ C.$ The outer surface of the tank is black (emissivity $\varepsilon = 1),$ and heat transfer between the outer surface of the tank and the surroundings is by natural convection and radiation. Assuming the entire steel tank to be at $0^\circ C$ and thus the thermal resistance of the tank to be negligible, determine (a) the rate of heat transfer to the iced water in the tank and (b) the amount of ice at $0^\circ C$ that melts during a 24-h period. The heat of fusion of water is 333.7 kJ/kg.

Heat is generated in a 3-cm-diameter spherical radioactive material uniformly at a rate of $15 W/cm^3.$ Heat is dissipated to the surrounding medium at $25^\circ C$ with a heat transfer coefficient of $120 W/m^2 \cdot K,$ The surface temperature of the material in steady operation is (a) $56^\circ C$ (b) $84^\circ C,$ (c) $494^\circ C$ (d) $650^\circ C$ (e) $108^\circ C$

Multiple Choice. The limit as x approaches c of a function f is written symbolically as [(a) $\lim f(x)$ (b) $\lim _{c \rightarrow x} f(x)$ (c) $\lim _{x \rightarrow c} f(x)$]

Consider the flow of mercury (a liquid metal) in a tube. How will the hydrodynamic and thermal entry lengths compare if the flow is laminar? How would they compare if the flow were turbulent?

A 1-mm diameter nickel wire with electrical resistance of $0.129 \Omega / \mathrm{m}$ is submerged horizontally in water at atmospheric pressure. Determine the electrical current at which the wire would be in danger of burnout in nucleate boiling.

Under what conditions does natural convection enhance forced convection, and under what conditions does it hurt forced convection?