# Tagged Questions

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### Application of Carnot's theorem to calculate efficiency of thermal engine

I understood Carnot's theorem in theory, but I still have some doubt on the practical use of it. In particular I would like to know: if I have any reversible cycle followed by a gas, then the thermal ...
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### Does the thermal efficiency depend on the reversibility of the engine when isochoric or isobaric processes are involved?

I'm confused on the efficiency of a thermal engine (with an ideal gas) in the case in which it is reversible or not reversible, in particular where the ideal gas follows isochoric or isobaric ...
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### Heat Pumps and COP?

Heat Pump COP (Coefficient of Performance) $$COP=1-\frac{T_c}{T_H}$$ With Heat Pumps is the efficiency/COP more dependent on the hot or the cold reservoir and why?
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### Why is the efficiency of human cells less than the efficiency of an Otto engine?

I always used to think (I don’t know why!) that the efficiency of human (and animal and plant) cells should be equal to or near the efficiency of a Carnot engine or at least should be the highest ...
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### Entropy and Clausius inequality

From the Clausius inequality we can derive that the efficiency of a Carnot (reversible) cycle is given by: $$e= 1 - \frac{T_c}{T_h}$$ Is this true for every reversible cycle? Is the efficiency of all ...
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### Isochoric Kelvin Plank - Clausius Equivalence

As the Clausius statement is underpinned by the assumption that W=P.∆V Therefore ∆V=0 , W=0 Can anyone restate the Kelvin Plank-Clausius Equivalence Proof considering a solely Isochoric process ...
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### 2nd law of thermodynamics' violation?

According to 2nd law of thermodynamics, it is not possible to convert heat 100% into work. Well, investigating about the Carnot Cycle, I have found out that in the first step, the process is to heat ...
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### Carnot engine basics?

A line in my textbook says.. ' if we employ any other process that is not adiabatic, say an isochoric process, to take the system from one temperature to another, we shall need a series of ...
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### A system with temp T is in contact with a reservoir of temp T. Would the system ever take in energy and expand (do work) in this situation?

The context is explain a Carnot cycle and how to get work from a system. Its starts by saying the system is in equilibrium with its surroundings, but then it take in some energy Qin. How does ...
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### Example of a Carnot machine made of a different physical system than a ideal gas?

Anybody knows an example of a Carnot machine made with any different thing than a gas? For example wire or a magnet. I was wondering that since I read the Kardar's book on Statistical Mechanics. He ...
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### Efficiency of a Carnot refrigerator without knowledge of the temperatures

We know that in a Carnot refrigerator we can express the efficiency as $$\eta = \dfrac{Q_1}{Q_2-Q_1}=\dfrac{T_1}{T_2-T_1},$$ where $T_1$ and $T_2$ are temperatures of the reservoirs between which ...
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### Carnot Engine- Cold Reservoir is a black body [closed]

My question: A satellite powered by a Carnot engine uses heat from a nuclear reactor at a fixed temperature T0. Heat is released into outer space via thermal radiation emitted by a set of fins at ...
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### Why is entropy of system same for reversible and irreversible processes? [closed]

I read that entropy change of universe is zero in a reversible process but positive in a irreversible process,then doesn't it mean that entropy change of system of both the processes must be ...
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### Relation between Pressure and volume in adiabatic process?

Why in adiabatic compression and expansion small volumetric change occurs while in isothermic compression or expansion very small pressure is applied and volume changes very significantly i am ...
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### Adiabatic compression and expansion and isothermal expansion? [closed]

Please help me in understanding the concepts Why in adiabatic compression and expansion small volumetric change occurs while in isothermic compression or expansion very small pressure is applied ...
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first time poster in this site. I am trying to create a small program to make a graph of the Carnot cycle. For isothermals I am simply trying to look for points where P*V would give the same ...
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### Ways to increase efficiency of carnot refrigerator and a four stroke engine? [closed]

What are ways to increase the efficiency of a Carnot refrigerator. I remember something about decreasing the temperature but also about something about the flow rate, and fins? Also, for four stroke ...
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### Heating up water with a heat pump

Suppose we wish to heat 1 litre of 0°C water up to 50°C during wintertime by using an ideal heat pump (Carnot cycle in "reverse"). We will place this water amount in an initally empty container, in ...
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### Proving the following cycle is equivalent to Carnot cycle

I want to investigate whether the following cycle I'm about to describe is equivalent to Carnot cycle or not. By equivalent I mean, giving two reservoirs($A$,$B$) with temperature $T_1$ and $T_2$ with ...
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### How is isothermal expansion/compression physically possible when it assumes heat flow between equally hot bodies?

An ideal Carnot engine is composed of two reservoirs and a working fluid. The hot Reservoir and the cold one have temperatures $T_1$ and $T_2$ respectively, with $T_1>T_2$. The working fluid is in ...
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### Why can't the Carnot cycle be used to operate automobiles, if its the most efficient?

Since the cycle proposed by Carnot (consisting of two isothermal and two adiabatic processes) is the most efficient one on which to run a heat engine, why do we use other, less efficient ones (like ...
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### Otto and Carnot efficiency comparison

Lets say both engines operate between same temperature limits. Carnot eff: $$e_\text{Carnot} = 1-\frac{T_L}{T_H}$$ Otto eff: $$e_\text{Otto} = 1-\frac{T_4-T_1}{T_3-T_2}$$ assuming ...
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### Questions on Carnot's theorem

This article on Carnot's theorem states that All heat engines between two heat reservoirs are less efficient than a Carnot heat engine operating between the same reservoirs. However, it only ...
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### Understanding the Carnot cycle

My textbook explains the Carnot cycle as follows: Heat is added to the boiler, where the steam inside expands isothermally at high temperature (T(High))--(both valves closed). The intake valve is ...
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### Entropy change in a reversible carnot cycle with 2 beakers

Consider 2 beakers each containing 1kg of water. One beaker has initial temperature of 25 degrees celsius and the other at 100 degrees celsius. The beaker are now mixed. Assuming no heat exchanged is ...
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### COP of Stirling engine

If we consider the theoretical maximum of COP for a heat pump, we will see that it is possible to make it infinite by approaching the temperatures of each source to each other. Yet, in a real engine ...
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### Efficiency of reversible engines

I'm a little confused about something. All reversible engines have the same efficiency, or one could drive the other to move more heat in the reverse direction. Also, no engine has an efficiency ...
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### How to define the thermodynamic temperature

I've been reading derivations of the thermodynamic temperature scale. I'm assuming these are using Kelvin's method. I follow the math and the conclusion of the argument, but I don't understand how it ...
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### Energy density and Carnot cycle

For example, diesel has about 40 MJ/kg, what does it mean? Is that if we burn it we will get 40 MJ of energy per kg, but we can not get all of it to mechanical work? If that is the case, then why can'...
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### Irreversible heat engines strictly less efficient than reversible ones

I understand how Carnot's theorem implies that irreversible heat engines must be no more efficient than reversible one's, but it is less clear why they need to be less efficient, as I have seen stated ...
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### Inequality of Clausius

I'm having some trouble understanding the inequality of Clausius. My treatment of the inequality applies to an engine operating in a cycle between two temperatures (i.e. like a Carnot engine). The ...