센겔 앤 볼스 열역학 5th 솔루션4-3
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센겔 앤 볼스 열역학 5th 솔루션입니다.
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Review Problems
본문내용
4-110 Heat is transferred to a piston-cylinder device containing air. The expansion work is to be determined.
Assumptions 1 There is no friction between piston and cylinder. 2 Air is an ideal gas.
Q
Air
0.5 kg
ΔT=5°C
Properties The gas contant for air is 0.287 kJ/kg.K (Table A-2a).
Analysis Noting that the gas constant represents the boundary work for a unit mass and a unit temperature change, the expansion work is simply determined from
kJ
4-111 Solar energy is to be stored as sensible heat using phase-change materials, granite rocks, and water. The amount of heat that can be stored in a 5-m3 = 5000 L space using these materials as the storage medium is to be determined.
Assumptions 1 The materials have constant properties at the specified values. 2 No allowance is made for voids, and thus the values calculated are the upper limits.
Analysis The amount of energy stored in a medium is simply equal to the increase in its internal energy, which, for incompressible substances, can be determined from )(12TTmcU−=Δ.
(a) The latent heat of glaubers salts is given to be 329 kJ/L. Disregarding the sensible heat storage in this case, the amount of energy stored is becomes
ΔUsalt = mhif = (5000 L)(329 kJ/L) = 1,645,000 kJ
This value would be even larger if the sensible heat storage due to temperature rise is considered.
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