Concept explainers
Use the coefficient of volume expansion to estimate the density of water as it is heated from 60°F to 130°F at 1 atm. Compare your result with the actual density (from the appendices).

The density of water.
Answer to Problem 39P
The density calculated is 986.78 kg/m3.
The density calculated and the actual density from appendix is nearly same.
Explanation of Solution
Given information:
The water is heated from 60°F to 130°F at 1 atm.
Write the expression for the average temperature.
Tavg=T1+T22....... (I)
Here, initial temperature is T1. Final temperature is T2 and the average temperature is Tavg.
Write the expression for the density of water.
Δρ=−ρβΔT....... (II)
Here, the change in density is Δρ, coefficient of volume expansion is β, the temperature difference is ΔT, and the initial density is ρ.
Write the expression for temperature difference.
ΔT=T2−T1....... (III)
Here, initial temperature is T1. Final temperature is T2 and the average temperature is Tavg.
Write the expression for final density.
Δρ=ρ2−ρρ2=Δρ+ρ....... (IV)
Write the formula for interpolation of two variables.
ρ2′=(x2−x1)(y3−y1)(x3−x1)+y1....... (V)
Here, the temperature is denoted by variables x, density is denoted by variables y, and the unknown density is ρ2′.
Calculation:
Substitute 60°F for T1 and 130°F for T2 in Equation (I).
Tavg=60°F+130°F2=(60 °F−321.8)°C+(130 °F−321.8)°C2=15.56°C+54.44°C2=35°C
Refer to Table A-3, "Properties of saturated water" to obtain the value of β as 0.00034 K−1 at 35°C.
Substitute 60°F for T1 and 130°F for T2 in Equation (III).
ΔT=130°F−60°F=(130°F−321.8)°C−(60°F−321.8)°C=(54.44°C+273) K−(15.56°C+273) K=38.88 K
Substitute 1000 kg/m3 for ρ, 0.00034 K−1 for β and 38.88 K for ΔT in Equation (II).
Δρ=−(1000 kg/m3)(0.00034 K−1)(38.88 K)=−(13.219 kg/m3)
Substitute 1000 kg/m3 for ρ, −(13.219 kg/m3) for Δρ in Equation (IV).
ρ2=−13.219 kg/m3+1000 kg/m3=986.78 kg/m3
Refer to Table A-3, "Properties of saturated water" to obtain the values of x2 as 54.44°C, x1 as 50°C, x3 as 55°C.
Refer to Table A-3, "Properties of saturated water" to obtain the values of y1 as 988.1 kg/m3, y3 as 985.2 kg/m3.
Prepare the table for temperature and density of water.
Temperature, °F | Density, kg/m3 |
50 (x1) | 988.1 (y1) |
54.44 (x2) | ? (ρ2′) |
55 (x3) | 985.2 (y3) |
Substitute 50°C for x1, 54.44°C for x2, 55°C for x3, 988.1 kg/m3 for y1 and 985.2 kg/m3 for y3in Equation (V).
ρ2′=(985.2 kg/m3−988.1 kg/m3)(54.44°C−50°C)(55°C−50°C)+988.1 kg/m3=((−2.9 kg/m3)4.5°C5°C)+988.1 kg/m3=−2.61 kg/m3+988.1 kg/m3=985.49 kg/m3
Conclusion:
The density calculated is 986.78 kg/m3.
The density calculated and the actual density from appendix is nearly same.
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Chapter 2 Solutions
FLUID MECHANICS:FUND.+APPL. LL + ACCESS
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- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning
