Answer 1: Real heat engines transferring energy between two reservoirs are less efficient than Carnot heat engines. This is a consequence of the fact that real heat engines undergo irreversible processes , and irreversible processes are less efficient (transfer less heat energy for a given temperature).
Why is thermal efficiency always less than Carnot efficiency?
So if all the heat input was converted to useful work, the engine would have an efficiency of one (100% efficient). Thus, the efficiency is always less than one. Carnot showed that the maximum efficiency of a heat engine depends only on the temperatures between which the engine operates, not on the type of engine.
Can thermal efficiency be greater than Carnot efficiency?
No device converting heat into mechanical energy, regardless of its construction, can exceed this efficiency. , the temperature at which the heat is added to the engine. ... Devices that convert a fuel's chemical energy directly into electrical work , such as fuel cells, can exceed the Carnot efficiency.
Is thermal efficiency the same as Carnot efficiency?
Carnot efficiency represents the maximum possible efficiency which can be obtained by a given thermodynamic cycle. It is calculated based strictly on the maximum and minimum temperatures which occur in the cycle. Broadly speaking, thermal efficiency represents the ratio of work energy output to energy input.
Why is thermal efficiency less than 1?
Figure 1: The amount of work output for a given amount of heat gives a system its thermal efficiency. This is impossible because some waste heat is always produced produced in a heat engine, shown in Figure 1 by the term. ...
Is Carnot engine 100 efficient?
In order to achieve 100% efficiency (η=1), Q 2 must be equal to 0 which means that all the heat form the source is converted to work. The temperature of sink means a negative temperature on the absolute scale at which the temperature is greater than unity.
What is the formula of thermal efficiency?
The thermal efficiency, η th , represents the fraction of heat, Q H , that is converted to work. The air-standard Otto cycle thermal efficiency is a function of compression ratio and κ = c p /c v . The thermal efficiency, η th , represents the fraction of heat, Q H , that is converted to work.
What is the ideal Carnot efficiency?
A Carnot engine operating between two given temperatures has the greatest possible efficiency of any heat engine operating between these two temperatures. ... No real heat engine can do as well as the Carnot efficiency—an actual efficiency of about 0.7 of this maximum is usually the best that can be accomplished.
How do you increase thermal efficiency?
Lower compression ratios need higher degrees of constant volume to improve the thermal efficiency by cooling loss reductions . Therefore, a method that reduces cooling loss without lowering the degree of constant volume will be effective to improve the thermal efficiency of internal combustion engines.
Why is thermal efficiency of SI engine low?
The results showed that the major factors were cooling loss and unburned fuel . Both of these factors increase with smaller swept volume, larger S/V ratio combustion chamber, and lower engine speed and load. These effects explain the observation that thermal efficiency peaks at relatively low compression ratio.
Why Carnot cycle is not possible?
In real engines, the heat transfers at a sudden change in temperature whereas in a Carnot engine, the temperature remains constant . In our day to day lives, reversible processes can't be carried out and there is no such engine with 100 % efficiency. Thus, the Carnot cycle is practically not possible.
What is Carnot efficiency formula?
efficiency =WQH=1−TCTH . These temperatures are of course in degrees Kelvin, so for example the efficiency of a Carnot engine having a hot reservoir of boiling water and a cold reservoir ice cold water will be 1−(273/373)=0.27, just over a quarter of the heat energy is transformed into useful work.
How can I improve the thermal efficiency of my house?
- Reduce your heating or use a secondary heating source.
- Use a new, energy efficient boiler.
- Fit insulation.
- Double or triple glazing.
- Draught proofing.
- Generate your own energy from renewable sources.
- Energy efficient fittings.
Can a machine ever be 100% efficient?
Explanation: No machine is free from the effects of gravity, and even with wonderful lubrication, friction always exists. The energy a machine produces is always less than the energy put into it (energy input). ... That is why 100% efficiency in machines shall not be possible.
Can pump efficiency be greater than 1?
It's Coefficient of Performance (the term used instead of efficiency) is normally greater than 1 and does not violate the laws of thermodynamics. Your first equation is for a heat engine. For the heat pump it is QHW.
What are the factors of thermal efficiency?
The thermal efficiency of a heat engine is expressed as a product of the Carnot efficiency, the external irreversibility factor and the internal irreversibility factor , by which the three factors that affect the thermal efficiency can be clearly distinguished, and the influences of the external and internal ...
