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Chapter 5: Problem 9

Does a reversible heat engine burning coal (which in practice cannot be done reversibly) have impacts on our world other than depletion of the coal reserve?

Short Answer

Expert verified
Yes, burning coal has environmental impacts, such as pollution and climate change, beyond just resource depletion.

Step by step solution

01

Understanding the Basics of a Reversible Heat Engine

A reversible heat engine is an idealized engine that operates in a cycle and follows the laws of thermodynamics perfectly without any energy losses or entropy changes. It is important to remember that in reality, no heat engine can be completely reversible due to friction, energy dissipation, and other losses.
02

Identify the Effects of Burning Coal

When coal is burned, it releases carbon dioxide (CO2), sulfur dioxide (SO2), nitrogen oxides (NOx), and other pollutants. These emissions contribute to air pollution, acid rain, and global warming by enhancing the greenhouse effect.
03

Connect the Heat Engine to Environmental Impacts

Even an ideal reversible engine still requires an external energy source, which, in this case, is coal. The burning of coal for fuel involves these emissions just mentioned, contributing dramatically to environmental issues despite the engine being reversible.
04

Consider Additional Environmental Consequences

Apart from atmospheric pollution, coal mining causes habitat destruction, soil erosion, and water pollution due to runoff. This means that even with a reversible heat engine, if coal is mined and burned as the energy source, several environmental impacts are unavoidable.
05

Combining Knowledge for the Final Impact Assessment

A reversible heat engine doesn't mitigate the environmental impacts associated with acquiring and burning coal. These impacts include pollution, climate change, and ecological damage beyond just the depletion of the coal reserve.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Environmental Impact
The environmental impact of using a reversible heat engine with coal is significant. While the concept of a reversible heat engine is theoretically efficient, in practice, the energy source still holds environmental consequences. Burning coal contributes to various environmental problems:
  • Pollution: Emissions from coal combustion include harmful pollutants like sulfur dioxide and nitrogen oxides.
  • Climate Change: Carbon dioxide released from coal burning is a major greenhouse gas contributing to global warming.
  • Habitat Destruction: Coal mining often leads to the destruction of ecosystems and loss of biodiversity.
Despite the engine's potential energy efficiency, the source of that energy significantly influences environmental health.
Coal Combustion
Coal combustion is the process of burning coal to release energy. It is a primary method to fuel heat engines, including theoretical reversible ones. However, burning coal releases a combination of harmful substances:
  • Carbon Dioxide (CO鈧�): A potent greenhouse gas contributing to the Earth's temperature rise.
  • Sulfur Dioxide (SO鈧�): Causes acid rain, which damages soils, waters, and vegetation.
  • Nitrogen Oxides (NOx): Prompt the formation of smog and respiratory issues in humans.
The process is inherently inefficient due to energy loss and the unavoidable release of these harmful emissions, making it crucial to consider alternatives.
Greenhouse Gases
Greenhouse gases (GHGs) play a significant role in the Earth's climate system by trapping heat in the atmosphere. Coal combustion is a major source of GHGs, particularly carbon dioxide (CO鈧�). This process enhances the "greenhouse effect," which can significantly amplify global warming.
Although other pollutants, like methane (CH鈧�) and nitrous oxide (N鈧侽), also act as GHGs, CO鈧� from coal is the most abundant due to the sheer volume produced. Its impact includes:
  • Climate Alteration: Rising global temperatures and changes in weather patterns.
  • Ice Cap Melting: Leads to rising sea levels affecting coastal communities.
The critical challenge is reducing GHG emissions to mitigate these substantial impacts on both the environment and society.
Sustainability
Sustainability focuses on meeting the needs of the present without compromising the ability of future generations to meet their own needs. In the context of energy production, burning coal is not sustainable. It creates several barriers:
  • Resource Depletion: Coal is a finite resource, and excessive use threatens its availability for the future.
  • Environmental Damage: Mining and combustion leave long-term ecological and health impacts.
  • Alternative Solutions: To achieve sustainability, transitioning to renewable energy sources such as wind, solar, and hydro is vital.
Fostering sustainable energy practices ensures environmental protection and resource preservation, promoting a healthy planet for future generations.

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Most popular questions from this chapter

A refrigerator operates at steady state using \(500 \mathrm{~W}\) of electric power with a COP of \(2.5 .\) What is the net effect on the kitchen air?

A window air conditioner cools a room at \(T_{L}=\) \(22^{\circ} \mathrm{C}\), with a maximum of \(1.2 \mathrm{~kW}\) power input possible. The room gains \(0.6 \mathrm{~kW}\) per degree temperature difference to the ambient, and the refrigeration COP is \(\beta=0.6 \beta_{\text {Carnot }}\). Find the actual power required on a day when the temperature is \(30^{\circ} \mathrm{C}\) outside.

A small house that is kept at \(20^{\circ} \mathrm{C}\) inside loses \(12 \mathrm{~kW}\) to the outside ambient at \(0^{\circ} \mathrm{C}\). A heat pump is used to help heat the house together with possible electric heat. The heat pump is driven by a \(2.5-\mathrm{kW}\) motor, and it has a COP that is one- fourth that of a Carnot heat pump unit. Find the actual COP for the heat pump and the amount of electric heat that must be used (if any) to maintain the house temperature.

A Carnot heat engine operating between a high \(T_{H}\) and low \(T_{L}\) energy reservoirs has an efficiency given by the temperatures. Compare this to two combined heat engines, one operating between \(T_{H}\) and an intermediate temperature \(T_{M}\) giving out work \(W_{A}\) and the other operating between \(T_{M}\) and \(T_{L}\) giving out work \(W_{B}\). The combination must have the same efficiency as the single heat engine, so the heat transfer ratio \(Q_{H} / Q_{L}=\psi\left(T_{H}, T_{L}\right)=\left[Q_{H} / Q_{M}\right]\left[Q_{M} / Q_{L}\right]\) The last two heat transfer ratios can be expressed by the same function \(\psi()\) also involving the temperature \(T_{M}\). Use this to show a condition that the function \(\psi\) () must satisfy.

A power plant with a thermal efficiency of \(40 \%\) is located on a river similar to the arrangement in Fig. P5.61. With a total river mass flow rate of \(1 \times 10^{5} \mathrm{~kg} / \mathrm{s}\) at \(15^{\circ} \mathrm{C},\) find the maximum power production allowed if the river water should not be heated more than 1 degree.
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