You are tasked with selecting a real physical cycle, whether for power, refriger

Question

You are tasked with selecting a real physical cycle, whether for power, refrigeration, or heat exchange, and discussing how you would obtain thermodynamic performance parameters for it (minimally, first and second law efficiencies and heat and work exchanges). You must select a real, existing, tangible, physical, objective thing, not a "Rankine cycle" or a "Carnot vapor-compression cycle". More like a diesel locomotive, your home A/C unit, or a cat. In all cases you must clearly define your inputs and outputs and state what "desirable" outcome is the numerator of a given efficiency. You should only select measurable things, because you also have to describe how you would measure physical variables, like time, distance, mass, temperature, and pressure to obtain the quantities of interest.

Explanation / Answer

A typical real-world cycle is Diesel cycle which is used for generation which propels diesel vehicles.

First law efficiency = Power delivered by the engine at the output shaft / (Rate of Enthalpy supplied by the fuel)
= W_net / (m*H)........where m = Rate of fuel burning, H = Calorific value of fuel = Standard enthalpy of reaction, W_net = Net work done by the engine

Second law efficiency = Power delivered by the engine at the output shaft / (Rate of Free Enthalpy supplied by the fuel)
= W_net / (m*G)........where m = Rate of fuel burning, G = Standard free enthalpy of reaction, W_net = Net work done by the engine

Heat exchanges: There are four processes in which heat is exchanged.
- Compression stroke,
- Constant pressure burning
- Expansion stroke
and Blowdown process.

The work is exchanged in three processes:
- Compression stroke,
- Constant pressure burning
- Expansion stroke.

Work exchange in all 3 processes can be obtained by noting the Pressure and Volume before and after the process. Then obtaining the Work exchanged by Integrating P dV.

From the P, V noted above, we can obtain the internal energy U at each of the states.

Then we can use the relationship Q - W = delta U to get Heat exchange in each process.

Inputs...Presure, Volume, Temperature at each of the states.
Further for efficiency, inputs would be rate of fuel mass burning, and its calorific value.

Also, The speed of the engine will be needed to calculate the power output which is work done per cycle.

Desirable quantity would be Power output from the engine and hence should remain in numerator during efficiency calculations.

Related Questions

Navigate

• Browse (All)
• Browse Y
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.