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A nuclear reactor provides a flow of liquid sodium at \(1500 \mathrm{~F}\), which is used as the energy source in a steam power plant. The condenser cooling water comes from a cooling tower at 60 F. Determine the maximum thermal efficiency of the power plant. Is it misleading to use the temperatures given to calculate this value?

Short Answer

Expert verified
The maximum thermal efficiency is approximately 73.5%. Using given temperatures may be misleading due to ideal assumptions.

Step by step solution

01

Understand the Carnot Efficiency Concept

The maximum efficiency of a power plant is determined by the Carnot efficiency, which depends solely on the temperatures of the heat source and the heat sink. The Carnot efficiency is given by the equation: \( \eta = 1 - \frac{T_{cold}}{T_{hot}} \), where \( T_{hot} \) is the temperature of the heat source and \( T_{cold} \) is the temperature of the heat sink.
02

Convert Temperatures to Absolute Scale

To use the Carnot efficiency formula, we need the temperatures in an absolute scale (Kelvin or Rankine). The temperatures are given in Fahrenheit, so we'll convert them to Rankine using the formula: \( T_{R} = T_{F} + 459.67 \). Therefore, \( T_{hot} = 1500 + 459.67 = 1959.67 \) Rankine, and \( T_{cold} = 60 + 459.67 = 519.67 \) Rankine.
03

Calculate the Carnot Efficiency

Substitute the values of \( T_{hot} \) and \( T_{cold} \) into the Carnot efficiency equation: \( \eta = 1 - \frac{519.67}{1959.67} \). Calculating this gives us \( \eta \approx 0.735 \), or 73.5%.
04

Evaluate the Realistic Application of These Temperatures

The efficiency calculated using the given temperatures assumes ideal conditions without any losses, which is not realistic. Real-world efficiencies are always lower due to various practical process losses that are not accounted for in the ideal Carnot cycle. Additionally, the given temperatures may not precisely reflect the actual working conditions of the power plant.

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Key Concepts

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

Steam Power Plant
A steam power plant is a type of power station where heat energy is converted into electricity. These plants rely on steam-driven turbines that are connected to electrical generators. The steam is produced by heating water in boilers using various fuel sources, such as coal, natural gas, or nuclear reactors.
In a typical operation cycle:
  • Water is heated in a boiler to create steam.
  • This high-pressure steam is then directed to spin turbines.
  • The spinning turbines drive generators, which convert mechanical energy into electrical energy.
  • After passing through the turbines, the steam is cooled down in condensers and converted back to water.
  • This water is pumped back into the boiler to be heated again, continuing the cycle.
Steam power plants have been pivotal since the industrial revolution, playing a crucial role in electricity production. The efficiency of these plants can be highly influenced by the temperature of the heat source and the cooling water.
Temperature Conversion
Temperature conversion is an essential step in calculating the Carnot efficiency of any power plant. To accurately determine the efficiency, temperatures must be converted to an absolute scale, such as Kelvin or Rankine, because the Carnot equation relies on these units.
For instance, in the problem, temperatures are initially provided in Fahrenheit, necessitating conversion to Rankine using: \[T_{R} = T_{F} + 459.67\]
  • For a liquid sodium source at 1500°F, the Rankine equivalent is 1959.67°R.
  • For the cooling water at 60°F, this converts to 519.67°R.
Understanding temperature scales and conversions is vital in fields involving thermodynamics, as they ensure accurate calculations and comparisons involving efficiency and energy metrics.
Heat Source and Heat Sink
In thermodynamic systems such as power plants, the heat source and heat sink are critical components that dictate maximum efficiency. The heat source is the zone where thermal energy is introduced for powering the engine. In the given problem, this energy originates from liquid sodium heated to 1500°F.
The heat sink, on the other hand, acts as a cooling component where excess thermal energy is discarded, allowing the system to regain initial conditions and continue work cyclically. Typically, in power plants, the heat sink can be ambient water or cooling towers. Here, it uses cooling water at 60°F. A fundamental principle is that the wider the temperature difference between the heat source and sink, the greater the potential efficiency of the engine, up to an ideal maximum defined by the Carnot efficiency. However, real systems experience practical inefficiencies such as heat losses and friction, making the actual operational efficiency lower than theoretical expectations. Understanding these components and their temperatures is crucial for optimizing energy production and environmental impact in power industries.

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Most popular questions from this chapter

An ideal gas Carnot cycle with air in a piston cylinder has a high temperature of \(1000 \mathrm{~K}\) and heat rejection at \(400 \mathrm{~K}\). During heat addition the volume triples. Find the two specific heat transfers \((q)\) in the cycle and the overall cycle efficiency.

In a remote location, you run a heat engine to provide the power to run a refrigerator. The input to the heat engine is \(1450 \mathrm{R}\) and the low \(T\) is \(700 \mathrm{R}\) it has an actual efficiency equal to half that of the corresponding Carnot unit. The refrigerator has \(T_{L}=15 \mathrm{~F}\) and \(T_{H}=95 \mathrm{~F}\) with a COP that is one-third that of the corresponding Carnot unit. Assume a cooling capacity of \(7000 \mathrm{Btu} / \mathrm{h}\) is needed and find the rate of heat input to the heat engine.

A refrigerator maintaining a \(5^{\circ} \mathrm{C}\) inside temperature is located in a \(30^{\circ} \mathrm{C}\) room. It must have a high temperature \(\Delta T\) above room temperature and a low temperature \(\Delta T\) below the refrigerated space in the cycle to actually transfer the heat. For a \(\Delta T\) of \(0^{\circ}\) \(5^{\circ},\) and \(10^{\circ} \mathrm{C},\) respectively, calculate the \(\mathrm{COP},\) assuming a Carnot cycle.

A farmer runs a heat pump with a \(2-\mathrm{kW}\) motor. It should keep a chicken hatchery at \(90 \mathrm{~F}\); the hatchery loses energy at a rate of \(10 \mathrm{Btu} / \mathrm{s}\) to the colder ambient \(T_{\mathrm{amb}}\). What is the minimum COP that will be acceptable for the heat pump?

An industrial machine is being cooled by 0.8 \(\mathrm{lbm} / \mathrm{s}\) water at \(60 \mathrm{~F}\) that is chilled from \(95 \mathrm{~F}\) by \(\mathrm{a}\) refrigeration unit with a COP of \(3 .\) Find the rate of cooling required and the power input to the unit.

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