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Chapter 19: Problem 5

Name some irreversible processes that occur in a real engine.

Short Answer

Expert verified
Some of the irreversible processes in a real engine include internal friction, heat transfer to the surroundings, combustion of fuel, and heat loss through exhaust.

Step by step solution

01

Internal Friction

The first irreversible process to be discussed is internal friction. This includes friction between moving parts, such as the pistons and cylinders in a combustion engine. This friction converts mechanical energy into heat, which is then lost to the environment. The energy used to overcome this friction cannot be recovered, making this an irreversible process.
02

Heat Transfer

The second irreversible process is heat transfer. When the engine is running, it generates heat. Some of this heat is transferred to the surrounding environment, reducing the overall energy efficiency of the engine. Once this heat energy is lost to the surroundings, it cannot be reclaimed.
03

Combustion Process

The third irreversible process is the combustion process. In a spark-ignition engine, the fuel-air mixture's burning is an irreversible process, because once the fuel is burned, it cannot be transformed back into its original state.
04

Exhaust Heat Loss

Lastly, exhaust heat loss is another irreversible process. After combustion, the exhaust gases are discharged from the engine at high temperatures. The heat carried away by these exhaust gases is a loss to the engine system and cannot be recovered back under normal conditions.

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Most popular questions from this chapter

Refrigerators remain among the greatest consumers of electrical energy in most homes, although mandated efficiency standards have decreased their energy consumption by some \(80 \%\) in the past four decades. In the course of a day, one kitchen refrigerator removes \(30 \mathrm{MJ}\) of energy from its contents, in the process consuming \(10 \mathrm{MJ}\) of electrical energy. The electricity comes from a \(40 \%\) efficient coal-fired power plant. The fuel energy consumed at the power plant to run this refrigerator for the day is a. \(12 \mathrm{MJ}\) b. \(25 \mathrm{MJ}\) c. \(40 \mathrm{MJ}\) d. \(75 \mathrm{MJ}\)

How much energy becomes unavailable for work in an isothermal process at \(440 \mathrm{K},\) if the entropy increase is \(25 \mathrm{J} / \mathrm{K} ?\)

In an alternative universe, you've got the impossible: an infinite heat reservoir, containing infinite energy at temperature \(T_{\mathrm{b}} .\) But you've only got a finite cool reservoir, with initial temperature \(T_{c 0}\) and heat capacity \(C .\) Find an expression for the maximum work you can extract if you operate an engine between these two reservoirs.

A refrigerator maintains an interior temperature of \(4^{\circ} \mathrm{C}\) while its exhaust temperature is \(30^{\circ} \mathrm{C}\). The refrigerator's insulation is imperfect, and heat leaks in at the rate of 340 W. Assuming the refrigerator is reversible, at what rate must it consume electrical energy to maintain a constant \(4^{\circ} \mathrm{C}\) interior?

A Carnot engine extracts heat from a block of mass \(m\) and specific heat \(c\) initially at temperature \(T_{\mathrm{b} 0}\) but without a heat source to maintain that temperature. The engine rejects heat to a reservoir at constant temperature \(T_{c} .\) The engine is operated so its mechanical power output is proportional to the temperature difference \(T_{\mathrm{h}}-T_{\mathrm{c}}\) $$P=P_{0} \frac{T_{\mathrm{h}}-T_{\mathrm{c}}}{T_{\mathrm{h} 0}-T_{\mathrm{c}}}$$ where \(T_{\mathrm{h}}\) is the instantancous temperature of the hot block and \(P_{0}\) is the initial power. (a) Find an expression for \(T_{\mathrm{h}}\) as a function of time, and (b) determine how long it takes for the engine's power output to reach zero.
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