3. A heat engine absorbs 1,000 J of heat per cycle at a temperature of 400 K and

Question

3. A heat engine absorbs 1,000 J of heat per cycle at a temperature of 400 K and deposits 900 J of heat at 4. A Carnot engine absorb 1000 J of heat per cycle at temperature of 400 K and rejects heat at 300 K. How much heat does it reject? ture of 30oC. If 1000 J of heat are deposited into the house every second and if electricity costs 10 cents per kilowatt-hour, then what is the cost of operating this heat pump for 24 h? 6. What is the coefficient of performance of a Carnot refrigerator whose inside temperature is 00C an whose outside temperature is 300C if it takes 500 W of electrical power to operate it? 7. A gasoline engine operates approximately according to the Otto cycle which takes in a gas/air mixture at ambient temperature TA, compresses that mixture adiabatically to a higher temperature TB, ignites the mixture at constant volume to an even higher temperature Tc, expands the gas adiabatically to a cooler temperature TD, reduces the pressure at constant volume back to Ta, and then expels the gas into the atmosphere. The efficiency of an Otto cycle is 1 -TA/TB. Assume TA- 270C, TB 1270C, and Tc 2270C. (a) What is the efficiency of this gasoline engine? (b) What would be the maximum possible efficiency of an ideal heat engine utilizing these same temperatures? (c) What is the efficiency ratio for this gasoline engine (i.e. the ratio of its efficiency to the maximum possible efficiency)?

Explanation / Answer

3)

Efficiency of heat engine is eta = 1-(Tc/Th)

Tc = 300 K

TH = 400 K

then eta = 1-(Tc/Th) = 1-(300/400) = 1-(3/4) = 1/4 = 0.25 = 25 %

4) eta = 1-(Tc/TH) = (1-300/400) =1-(3/4) = 0.25

but eta = W/Qh = (Qh-Qc)/Qh

0.25 = (1000-Qc)/1000

1000-Qc = 250

Qc = 1000-250 = 750 J

Related Questions

Navigate

• Browse (All)
• Browse 3
• Subjects

---

---

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