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The density of liquid water can be correlated as \(\rho(T)=1000-0.0736 T-0.00355 T^{2}\) where \(\rho\) and \(T\) are in \(\mathrm{kg} / \mathrm{m}\) and \({ }^{\circ} \mathrm{C}\), respectively. Determine the volume expansion coefficient at \(70^{\circ} \mathrm{C}\). Compare the result with the value tabulated in Table A-9.

Short Answer

Expert verified
Answer: The calculated volume expansion coefficient of water at \(70^{\circ}\mathrm{C}\) is \(3.318\times10^{-4}\;\mathrm{C}^{\circ -1}\). The difference between the calculated value and the tabulated value is approximately \(2.44\%\).

Step by step solution

01

Calculate the derivative of density with respect to temperature

To calculate the volume expansion coefficient, we need the derivative of \(\rho(T)\) with respect to \(T\). The given expression for \(\rho(T)\) is: \(\rho(T)=1000-0.0736T-0.00355T^{2}\) Taking the derivative with respect to T, we get: \(\frac{d\rho}{dT}=-0.0736-2(0.00355)T\)
02

Calculate the Volume Expansion Coefficient

The volume expansion coefficient, denoted by \(\beta\), is defined as: \(\beta=-\frac{1}{V}\frac{dV}{dT}=-\frac{1}{\rho}\frac{d\rho}{dT}\) Now plug in the values of \(\frac{d\rho}{dT}\) and \(\rho(T)\) at \(T=70^{\circ}\mathrm{C}\): \(\rho(70)=1000-0.0736\times70-0.00355\times70^2=963.24\;\mathrm{kg}/\mathrm{m}^3 \) \(\frac{d\rho}{dT}(70)=-0.0736-2(0.00355)(70)=-0.3196\;\mathrm{kg}/\mathrm{m}^3\mathrm{C}^\circ \) Then, calculate \(\beta\): \(\beta=-\frac{1}{963.24}\times(-0.3196)=3.318\times10^{-4}\;\mathrm{C}^{\circ -1} \)
03

Compare with the tabulated value in Table A-9

The given tabulated value of volume expansion coefficient of water at \(70^{\circ}\mathrm{C}\) is: \(\beta_{\text{tabulated}} = 3.401\times10^{-4}\;\mathrm{C}^{\circ -1} \) Now, we can compare our calculated value with the tabulated one: \(\frac{|\beta-\beta_{\text{tabulated}}|}{\beta_{\text{tabulated}}} \times 100 =\frac{|3.318\times10^{-4}-3.401\times10^{-4}|}{3.401\times10^{-4}}\times 100\approx 2.44\%\) The calculated value of the volume expansion coefficient is approximately \(2.44\%\) different from the tabulated value. Depending on the level of accuracy needed, this difference may or may not be significant.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Density of Liquid Water
Density is a measure of how much mass is packed into a given volume. For liquid water, this varies with temperature, which influences the calculation of other thermodynamic properties.

In the context of the exercise, the density of liquid water is represented as a function of temperature: \(\rho(T) = 1000 - 0.0736T - 0.00355T^2\). It is essential to understand that this mathematical representation portrays how density changes as temperature changes.

As temperature increases, density usually decreases. This is due to the thermal expansion of water, meaning the molecules move apart as temperature rises. At specific points, such as at 4°C for pure water, density reaches a maximum.

When considering volume, realize that an increase in temperature often results in an increase in volume and a corresponding decrease in density. This is critical in calculating the volume expansion coefficient, which measures how much a substance's volume changes in response to a temperature change.
Thermodynamic Properties
Thermodynamic properties help us understand how substances behave under different conditions, such as changes in temperature or pressure. In the case of liquid water, properties like density and the volume expansion coefficient are closely analyzed.

The volume expansion coefficient (\(\beta\)) is a significant property in thermodynamics. It represents the fractional change in volume per degree change in temperature. The equation used in the solution is \(\beta = -\frac{1}{\rho}\frac{d\rho}{dT}\). This equation links density changes to volume changes, emphasizing that for most liquids, an increase in temperature leads to a volume increase and thus affects density.

Understanding these properties aids in predicting how water will behave in various environmental and industrial processes, such as heating and cooling systems.
Derivative Calculations
Derivatives are mathematical tools used extensively in calculus to compute rates of change. In this exercise, derivatives are utilized to determine how quickly density changes with respect to temperature.

The derivative of the given density function \(\rho(T) = 1000 - 0.0736T - 0.00355T^2\) with respect to temperature \(T\) is \(\frac{d\rho}{dT} = -0.0736 - 2(0.00355)T\). Through derivative calculations, we derive an expression that quantifies the rate at which density decreases as temperature rises.

Accurate derivative calculations are crucial because they directly influence the determination of the volume expansion coefficient (\(\beta\)). The precision of these calculations ensures engineers and scientists can predict and mitigate potential issues that arise from temperature-induced density changes. This is particularly significant in applications where small changes in density could have large effects, like material design or climate studies.

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Most popular questions from this chapter

A 10 -cm-diameter and 10 -m-long cylinder with a surface temperature of \(10^{\circ} \mathrm{C}\) is placed horizontally in air at \(40^{\circ} \mathrm{C}\). Calculate the steady rate of heat transfer for the cases of (a) free-stream air velocity of \(10 \mathrm{~m} / \mathrm{s}\) due to normal winds and (b) no winds and thus a free stream velocity of zero.

Consider a 1.2-m-high and 2-m-wide glass window with a thickness of \(6 \mathrm{~mm}\), thermal conductivity \(k=0.78 \mathrm{~W} / \mathrm{m} \cdot \mathrm{K}\), and emissivity \(\varepsilon=0.9\). The room and the walls that face the window are maintained at \(25^{\circ} \mathrm{C}\), and the average temperature of the inner surface of the window is measured to be \(5^{\circ} \mathrm{C}\). If the temperature of the outdoors is \(-5^{\circ} \mathrm{C}\), determine \((a)\) the convection heat transfer coefficient on the inner surface of the window, \((b)\) the rate of total heat transfer through the window, and \((c)\) the combined natural convection and radiation heat transfer coefficient on the outer surface of the window. Is it reasonable to neglect the thermal resistance of the glass in this case?

Physically, what does the Grashof number represent? How does the Grashof number differ from the Reynolds number?

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

Consider a \(1.2\)-m-high and 2-m-wide double-pane window consisting of two 3-mm-thick layers of glass \((k=\) \(0.78 \mathrm{~W} / \mathrm{m} \cdot \mathrm{K})\) separated by a \(3-\mathrm{cm}\)-wide air space. Determine the steady rate of heat transfer through this window and the temperature of its inner surface for a day during which the room is maintained at \(20^{\circ} \mathrm{C}\) while the temperature of the outdoors is \(0^{\circ} \mathrm{C}\). Take the heat transfer coefficients on the inner and outer surfaces of the window to be \(h_{1}=10 \mathrm{~W} / \mathrm{m}^{2} \cdot \mathrm{K}\) and \(h_{2}=25 \mathrm{~W} / \mathrm{m}^{2} \cdot \mathrm{K}\) and disregard any heat transfer by radiation. Evaluate air properties at a film temperature of \(10^{\circ} \mathrm{C}\) and \(1 \mathrm{~atm}\) pressure. Is this a good assumption?

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