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Thermodynamics Power Cycle Energy Balance
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[QUOTE="AGiantGolden49er, post: 5812129, member: 617294"] [h2]Homework Statement [/h2] As shown in Fig. P5.39, a system undergoing a power cycle develops a net power output of 1 MW while receiving energy by heat transfer from steam condensing from saturated vapor to saturated liquid at a pressure of 100 kPa. Energy is discharged from the cycle by heat transfer to a nearby lake at 17°C. These are the only significant heat transfers. Kinetic and potential energy effects can be ignored. For operation at steady state, determine the minimum theoretical steam mass flow rate, in kg/s, required by any such cycle. Fig. 5.39: [URL]https://gyazo.com/49a3ca702a5fa239633f8f054618345e[/URL] (Can't get it to embed) [h2]Homework Equations[/h2] η = W[SUB]cycle[/SUB] / Q[SUB]H[/SUB] = 1 - T[SUB]C[/SUB] / T[SUB]H[/SUB] W[SUB]cycle[/SUB] = Q[SUB]H[/SUB] - Q[SUB]C[/SUB] mass flow: dm[SUB]cv[/SUB] / dt = ∑ m[SUB]i[/SUB] - ∑ m[SUB]e[/SUB] energy balance: dEcv / dt = Q - W + ∑ m[SUB]i[/SUB](h[SUB]i[/SUB] + V[SUB]i[/SUB][SUP]2[/SUP] / 2 + gz[SUB]i[/SUB])- ∑ m[SUB]e[/SUB](h[SUB]e[/SUB] + V[SUB]e[/SUB][SUP]2[/SUP] / 2 + gz[SUB]e[/SUB]) [h2]The Attempt at a Solution[/h2] Knowing that the system operates at steady state, I know that the entry mass flow and exit mass flow are the same. I also know that since kinetic energy and potential energy can be ignored, the energy balance equation simplifies to: 0 = Q - W + ∑ m[SUB]i[/SUB](h[SUB]i[/SUB])- ∑ m[SUB]e[/SUB](h[SUB]e[/SUB]) => W = Q + m(h[SUB]i[/SUB] - h[SUB]e[/SUB]) Knowing that the initial and final states are at saturated vapor and saturated liquid, respectively, using the tables in the back of the book, I found the specific enthalpy values to be: h[SUB]1[/SUB] = 2675.5 kJ/kg h[SUB]2[/SUB] = 417.46 kJ/kg I know that I can use the thermal efficiency relation to find the Q[SUB]H[/SUB] value, but I don't know how exactly to find the thermal efficiency since there's no listed T[SUB]H[/SUB] value, unless I'm missing something in the problem statement. I feel that the energy balance equation will be cake once the heat transfer value is found, but I just can't figure out how to get it. If anyone could steer me in the right direction, that would be appreciated. Edit: The temperature of the lake is 17°C, not 178C. Copy-and-paste didn't recognize the degree symbol. [/QUOTE]
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Thermodynamics Power Cycle Energy Balance
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