A \(10-\mathrm{cm}\) thick aluminum plate \(\left(\rho=2702 \mathrm{~kg} / \mathrm{m}^{3}, c_{p}=\right.\) \(903 \mathrm{~J} / \mathrm{kg} \cdot \mathrm{K}, k=237 \mathrm{~W} / \mathrm{m} \cdot \mathrm{K}\), and \(\left.\alpha=97.1 \times 10^{-6} \mathrm{~m}^{2} / \mathrm{s}\right)\) is being heated in liquid with temperature of \(500^{\circ} \mathrm{C}\). The aluminum plate has a uniform initial temperature of \(25^{\circ} \mathrm{C}\). If the surface temperature of the aluminum plate is approximately the liquid temperature, determine the temperature at the center plane of the aluminum plate after 15 seconds of heating. Solve this problem using analytical one- term approximation method (not the Heisler charts).

Short Answer

Expert verified
Fo ≈ 0.5826 #tag_title#Step 2: Calculate the temperature difference#tag_content# In order to find the temperature at the center plane, we will also need to calculate the temperature difference between the initial uniform temperature and the heated liquid temperature. The temperature difference (ΔT) is given by: ΔT = T_liquid - T_initial Where: T_liquid = 500 degrees Celsius (heated liquid temperature) T_initial = 25 degrees Celsius (initial uniform temperature) Now, we can calculate the temperature difference: ΔT = 500 - 25 ΔT = 475 degrees Celsius #tag_title#Step 3: Use one-term approximation method#tag_content# The one-term approximation method allows us to estimate the temperature at the center plane of the aluminum plate. According to this method: T_center ≈ T_initial + (ΔT * (1 - 2 * Fo)) We already have the values for ΔT and Fo, so we can plug them into the equation: T_center ≈ 25 + (475 * (1 - 2 * 0.5826)) #tag_title#Step 4: Calculate the temperature at the center plane#tag_content# Now we can find the temperature at the center plane of the aluminum plate: T_center ≈ 25 + (475 * (1 - 1.1652)) T_center ≈ 25 - (475 * 0.1652) T_center ≈ 25 - 78.46 T_center ≈ -53.46 degrees Celsius However, the calculated temperature is below the minimum possible temperature (25°C) in this scenario, which means the analytical one-term approximation method is not an accurate solution in this case. An alternative method, such as numerical methods or transient heat conduction analysis, should be employed for a more accurate result. #SolutionSummary#The calculated center plane temperature using the one-term approximation method is approximately -53.46 degrees Celsius, which is not possible since the minimum temperature was given as 25 degrees Celsius. The analytical one-term approximation method is proven inaccurate in this case, and an alternative method such as numerical methods or transient heat conduction analysis should be used for a more accurate result.

Step by step solution

01

Calculate the Fourier number (Fo)

The Fourier number (Fo) is a dimensionless parameter that describes the ratio of diffusive heat conduction to the rate of thermal energy storage in a given material. It is defined as: Fo = \(\frac{\alpha t}{L^2}\) Where: α = thermal diffusivity of the material (\(97.1 \times 10^{-6} m^2/s\)) t = heating time (15 seconds) L = half-thickness of the plate (0.05 meters) Now, we can calculate the Fourier number: Fo = \(\frac{97.1 \times 10^{-6} m^2/s * 15 s}{(0.05 m)^2}\)

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Most popular questions from this chapter

A 30 -cm-diameter, 4-m-high cylindrical column of a house made of concrete \(\left(k=0.79 \mathrm{~W} / \mathrm{m} \cdot \mathrm{K}, \alpha=5.94 \times 10^{-7} \mathrm{~m}^{2} / \mathrm{s}\right.\), \(\rho=1600 \mathrm{~kg} / \mathrm{m}^{3}\), and \(\left.c_{p}=0.84 \mathrm{~kJ} / \mathrm{kg} \cdot \mathrm{K}\right)\) cooled to \(14^{\circ} \mathrm{C}\) during a cold night is heated again during the day by being exposed to ambient air at an average temperature of \(28^{\circ} \mathrm{C}\) with an average heat transfer coefficient of \(14 \mathrm{~W} / \mathrm{m}^{2} \cdot \mathrm{K}\). Using analytical one-term approximation method (not the Heisler charts), determine \((a)\) how long it will take for the column surface temperature to rise to \(27^{\circ} \mathrm{C},(b)\) the amount of heat transfer until the center temperature reaches to \(28^{\circ} \mathrm{C}\), and (c) the amount of heat transfer until the surface temperature reaches to \(27^{\circ} \mathrm{C}\).

When water, as in a pond or lake, is heated by warm air above it, it remains stable, does not move, and forms a warm layer of water on top of a cold layer. Consider a deep lake \(\left(k=0.6 \mathrm{~W} / \mathrm{m} \cdot \mathrm{K}, c_{p}=4.179 \mathrm{~kJ} / \mathrm{kg} \cdot \mathrm{K}\right)\) that is initially at a uniform temperature of \(2^{\circ} \mathrm{C}\) and has its surface temperature suddenly increased to \(20^{\circ} \mathrm{C}\) by a spring weather front. The temperature of the water \(1 \mathrm{~m}\) below the surface 400 hours after this change is (a) \(2.1^{\circ} \mathrm{C}\) (b) \(4.2^{\circ} \mathrm{C}\) (c) \(6.3^{\circ} \mathrm{C}\) (d) \(8.4^{\circ} \mathrm{C}\) (e) \(10.2^{\circ} \mathrm{C}\)

For heat transfer purposes, an egg can be considered to be a \(5.5-\mathrm{cm}\)-diameter sphere having the properties of water. An egg that is initially at \(8^{\circ} \mathrm{C}\) is dropped into the boiling water at \(100^{\circ} \mathrm{C}\). The heat transfer coefficient at the surface of the egg is estimated to be \(800 \mathrm{~W} / \mathrm{m}^{2} \cdot \mathrm{K}\). If the egg is considered cooked when its center temperature reaches \(60^{\circ} \mathrm{C}\), determine how long the egg should be kept in the boiling water. Solve this problem using analytical one-term approximation method (not the Heisler charts).

An electronic device dissipating \(20 \mathrm{~W}\) has a mass of \(20 \mathrm{~g}\), a specific heat of \(850 \mathrm{~J} / \mathrm{kg} \cdot \mathrm{K}\), and a surface area of \(4 \mathrm{~cm}^{2}\). The device is lightly used, and it is on for \(5 \mathrm{~min}\) and then off for several hours, during which it cools to the ambient temperature of \(25^{\circ} \mathrm{C}\). Taking the heat transfer coefficient to be \(12 \mathrm{~W} / \mathrm{m}^{2} \cdot \mathrm{K}\), determine the temperature of the device at the end of the 5 -min operating period. What would your answer be if the device were attached to an aluminum heat sink having a mass of \(200 \mathrm{~g}\) and a surface area of \(80 \mathrm{~cm}^{2}\) ? Assume the device and the heat sink to be nearly isothermal.

A small chicken \(\left(k=0.45 \mathrm{~W} / \mathrm{m} \cdot \mathrm{K}, \alpha=0.15 \times 10^{-6} \mathrm{~m}^{2} / \mathrm{s}\right)\) can be approximated as an \(11.25\)-cm-diameter solid sphere. The chicken is initially at a uniform temperature of \(8^{\circ} \mathrm{C}\) and is to be cooked in an oven maintained at \(220^{\circ} \mathrm{C}\) with a heat transfer coefficient of \(80 \mathrm{~W} / \mathrm{m}^{2} \cdot \mathrm{K}\). With this idealization, the temperature at the center of the chicken after a 90 -min period is (a) \(25^{\circ} \mathrm{C}\) (b) \(61^{\circ} \mathrm{C}\) (c) \(89^{\circ} \mathrm{C}\) (d) \(122^{\circ} \mathrm{C}\) (e) \(168^{\circ} \mathrm{C}\)

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