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Chapter 21: Q.18 (page 595)

At what pressure ratio tyyuudoes a Brayton cycle using a monatomic gas have an efficiency of 50 ?

Short Answer

Expert verified

rytiu

Step by step solution

01

 Introduction

We know that for a refrigerator, the heat added to the environment is equal to the sum of the work done and the heat extracted from the cold reservoir. That is,

Qh=W+Qc Q+ W

where W is the total work. This work will therefore be

$$

W=119-78=\underline{41 . J}

$$

Knowing the heat released in the heat reservoir, we can find the heat extracted as

$$

Q_{c}=Q_{h}-W

$$

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Most popular questions from this chapter

The engine that powers a crane burns fuel at a flame temperature of 2000°C. It is cooled by 20°C air. The crane lifts a 2000 kg steel girder 30 m upward. How much heat energy is transferred to the engine by burning fuel if the engine is 40% as efficient as a Carnot engine?

A heat engine extracts 55KJof heat from the hot reservoir each cycle and exhausts 40KJof heat. What are (a) the thermal efficiency and (b) the work done per cycle?

In going fromito localid="1648790171714" fin each of the three processes of FIGURE Q21.1, is work done by the system localid="1648790168795" W<0,Ws>0is work done on the system , or is no net work done on the system localid="1648790176001" W>0,Ws<0or is no net work done?

A refrigerator requires 200Jof work and exhausts 600Jof heat per cycle. What is the refrigerator’s coefficient of performance?

The FIGURE shows the Diesel cycle. It is similar to the Otto cycle (see Problem), but there are two important differences. First, the fuel is not admitted until the air is fully compressed at point 2. Because of the high temperature at the end of adiabatic compression, the fuel begins to burn spontaneously. (There are no spark plugs in a diesel engine!) Second, combustion takes place more slowly, with fuel continuing to be injected. This makes the ignition stage a constant-pressure process. The cycle shown, for one cylinder of a diesel engine, has a displacement localid="1650278379201" Vmax-Vminof localid="1650278390412" 1000cm3and a compression ratio localid="1650278397535" r=Vmax/Vmin=21These are typical values for a diesel truck. The engine operates with intake air localid="1650278425123" (γ=1.40)at localid="1650278430754" 25°Cand localid="1650278435051" 1.0atmpressure. The quantity of fuel injected into the cylinder has a heat of combustion of localid="1650278440305" 1000J.

a. Find p, V, and Tat each of the four corners of the cycle. Display your results in a table.

b. What is the network done by the cylinder during one full cycle?

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