Chapter 1: Problem 111
Solve this system of three equations with three unknowns using appropriate software: $$ \begin{aligned} 2 x-y+z &=5 \\ 3 x^{2}+2 y &=z+2 \\ x y+2 z &=8 \end{aligned} $$
Chapter 1: Problem 111
Solve this system of three equations with three unknowns using appropriate software: $$ \begin{aligned} 2 x-y+z &=5 \\ 3 x^{2}+2 y &=z+2 \\ x y+2 z &=8 \end{aligned} $$
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Get started for freeWhich expression is used to determine the heat flux for conduction? (a) \(-k A \frac{d T}{d x}\) (b) \(-k \operatorname{grad} T\) (c) \(h\left(T_{2}-T_{1}\right)\) (d) \(\varepsilon \sigma T^{4}\) (e) None of them
Air enters a 12-m-long, \(7-\mathrm{cm}\)-diameter pipe at $50^{\circ} \mathrm{C}\( at a rate of \)0.06 \mathrm{~kg} / \mathrm{s}$. The air is cooled at an average rate of \(400 \mathrm{~W}\) per square meter surface area of the pipe. The air temperature at the exit of the pipe is (a) \(4.3^{\circ} \mathrm{C}\) (b) \(17.5^{\circ} \mathrm{C}\) (c) \(32.5^{\circ} \mathrm{C}\) (d) \(43.4^{\circ} \mathrm{C}\) (e) \(45.8^{\circ} \mathrm{C}\)
Heat is lost through a brick wall $(k=0.72 \mathrm{~W} / \mathrm{m} \cdot \mathrm{K})\(, which is \)4 \mathrm{~m}\( long, \)3 \mathrm{~m}\( wide, and \)25 \mathrm{~cm}\( thick at a rate of \)500 \mathrm{~W}$. If the inner surface of the wall is at \(22^{\circ} \mathrm{C}\), the temperature at the midplane of the wall is (a) \(0^{\circ} \mathrm{C}\) (b) \(7.5^{\circ} \mathrm{C}\) (c) \(11.0^{\circ} \mathrm{C}\) (d) \(14.8^{\circ} \mathrm{C}\) (e) \(22^{\circ} \mathrm{C}\)
A 40-cm-long, 0.4-cm-diameter electric resistance wire submerged in water is used to determine the convection heat transfer coefficient in water during boiling at \(1 \mathrm{~atm}\) pressure. The surface temperature of the wire is measured to be \(114^{\circ} \mathrm{C}\) when a wattmeter indicates the electric power consumption to be \(7.6 \mathrm{~kW}\). The heat transfer coefficient is (a) \(108 \mathrm{~kW} / \mathrm{m}^{2} \cdot \mathrm{K}\) (b) \(13.3 \mathrm{~kW} / \mathrm{m}^{2} \cdot \mathrm{K}\) (c) \(68.1 \mathrm{~kW} / \mathrm{m}^{2} \cdot \mathrm{K}\) (d) \(0.76 \mathrm{~kW} / \mathrm{m}^{2}, \mathrm{~K}\) (e) \(256 \mathrm{~kW} / \mathrm{m}^{2} \cdot \mathrm{K}\)
It is well known that wind makes the cold air feel much colder as a result of the wind-chill effect that is due to the increase in the convection heat transfer coefficient with increasing air velocity. The wind-chill effect is usually expressed in terms of the wind-chill temperature (WCT), which is the apparent temperature felt by exposed skin. For an outdoor air temperature of \(0^{\circ} \mathrm{C}\), for example, the windchill temperature is $-5^{\circ} \mathrm{C}\( with \)20 \mathrm{~km} / \mathrm{h}\( winds and \)-9^{\circ} \mathrm{C}\( with \)60 \mathrm{~km} / \mathrm{h}$ winds. That is, a person exposed to \(0^{\circ} \mathrm{C}\) windy air at \(20 \mathrm{~km} / \mathrm{h}\) will feel as cold as a person exposed to \(-5^{\circ} \mathrm{C}\) calm air (air motion under \(5 \mathrm{~km} / \mathrm{h}\) ). For heat transfer purposes, a standing man can be modeled as a 30 -cm- diameter, 170 -cm-long vertical cylinder with both the top and bottom surfaces insulated and with the side surface at an average temperature of $34^{\circ} \mathrm{C}\(. For a convection heat transfer coefficient of \)15 \mathrm{~W} / \mathrm{m}^{2} \cdot \mathrm{K}$, determine the rate of heat loss from this man by convection in still air at \(20^{\circ} \mathrm{C}\). What would your answer be if the convection heat transfer coefficient is increased to $30 \mathrm{~W} / \mathrm{m}^{2} \cdot \mathrm{K}$ as a result of winds? What is the wind-chill temperature in this case? Answers: $336 \mathrm{~W}, 672 \mathrm{~W}, 6^{\circ} \mathrm{C}$
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