P21_056 - nRT ln 8 3 which yields (for T = 300 K and T =...

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56. (a) Processes 1 and 2 both require the input of heat, which is denoted Q H . Noting that rotational degrees of freedom are not involved, then, from the discussion in Chapter 20, C V = 3 2 R , C p = 5 2 R , and γ = 5 3 . We further note that since the working substance is an ideal gas, process 2 (being isothermal) implies Q 2 = W 2 . Finally, we note that the volume ratio in process 2 is simply 8 / 3. Therefore, Q H = Q 1 + Q 2 = nC V ( T 0 T )+
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Unformatted text preview: nRT ln 8 3 which yields (for T = 300 K and T = 800 K) the result Q H = 25 . 5 10 3 J. (b) The net work is the net heat ( Q 1 + Q 2 + Q 3 ). We nd Q 3 from nC p ( T T ) = 20 . 8 10 3 J. Thus, W = 4 . 73 10 3 J. (c) Using Eq. 21-9, we nd that the eciency is = | W | | Q H | = 4 . 73 10 3 25 . 5 10 3 = 0 . 185 ....
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