Questions tagged [heat-engine]

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Why does adiabatic expansion occur in the carnot process?

(Spoiler: Why adiabatic expansion happens in Carnot cycle doesn't really answer the question for me.) In the Carno cycle, the open system is first brought into contact with the warm reservoir, which ...
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Is this a good, credible design for dyson sphere using stirling engine? If not what should I revisit? This design wouldn't require any active cooling [closed]

Is this a good, credible design for dyson sphere using stirling engine? If not what should I revisit? This design wouldn't require any active cooling with the radiation shield, inspied from james webb....
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Question on Thermodynamics and Heat Engines

Suppose we have a heat pump with 1 mol of some sort of fuel that goes through an isochoric process that takes the pressure of the gas from $P_2$ to $P_1$ while staying at $V_1$, an isobaric ...
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What law of thermodynamics is broken here? [closed]

This question came in the Dhaka university admission exam 18-19. A heat engine in each cycle does positive work and loses energy as heat with no heat energy input. Which law of thermodynamics does the ...
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What exactly is the limiting factor of the efficiency of a heat engine?

In an imagined scenario, $n$ moles of steam at a temperature $T_h$ and pressure $p$ enter an engine. The steam leaving the engine is at a temperature $T_c$ and pressure $p$. In this scenario, the heat ...
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Why do internal combustion engines use adiabatic expansion and combustion?

In the gasoline engine, the gasoline mixture is heated at constant volume, followed by adiabatic expansion. In the diesel engine, the mixture is heated at constant pressure, and this is followed by ...
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Will the heat generated from solar panel electricity eventually generate wind energy?

I'm curious about limits for extracting solar energy, but I never studied this stuff so I'm going to speculate a lot. My first question deals with the things like wind energy. I assume this energy is ...
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How was adiabatic expansion conceived from the caloric theory perspective? [closed]

Nowadays we say that during the adiabatic expansion stage of the Carnot Cycle the internal energy due to the temperature of the gas gets transformed into work, but Carnot himself supported the caloric ...
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How is a Carnot engine in quasi-equilibrium?

If the reversible isothermal expansion and adiabatic expansion both yield positive work (as the pv diagram indicates), it means that the gas inside the cylinder was compressed before those stages ...
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How was Enrico Fermi able to predict a power output from his uranium and graphite Chicago Pile 1 (CP-1) reactor?

Uranium and graphite heat engine physics - early detection methods I've been inspired by the early developments in fission heat engines which happened even before uranium enrichment methods were ...
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2 answers
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How to prove the efficiency of Carnot engine is bigger than Otto engine [closed]

I know the Carnot engine has maximum efficiency among all engines from Clausius statement, but how to prove the relationship of these two engines in equation? Thanks. More specifically, the ...
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Does this system violate the second law of thermodynamics?

Consider a system (Blundell and Blundell 2nd edition, page 135) where a cycle consists of connecting each point to a reservoir at temperature $T_i$ and a heat amount $\delta Q_i$ enters that point. A ...
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Origin of the thrust force in jet engine

I am reading a lot about the jet engine operation and I meet mostly explenation that the thrust is generated thanks to the exhaust nozzle that "accelerates" the air. However the nozzle ...
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Comparing a gas turbine (Joule cycle) to the Carnot cycle?

My understanding of gas turbines is as follows: When you spin an impeller, you can compress air (this requires work) and when compressed air is expanded, it can be used to spin a turbine (this ...
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2 answers
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Alternatives to Steam Engines [closed]

Since the 18th century, humankind relied on steam engines to convert heat into electricity on mass scale even in fission and fusion (in the future) power plants. However, this process involves several ...
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Why are the pressures in the Joule-Thompson effect the same before and after?

I understand the Joule-Thompson effect and the mathematics behind it that results in the Enthalpy, $H$, remaining constant. However, one thing I conceptually fail to grasp is why the pressure on gases ...
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Sign problem with Thomson 1848 definition of temperature

It can be shown that for every reversible process $$\frac{Q_1}{T_1}+\frac{Q_2}{T_2}=0,$$ and we can exploit this for a definition of temperature, ok, but shouldn't we add a minus sign? Is it ...
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Rayleigh Benard Convection analyzed as heat engine?

The treatment I've seen for Benard convection in a textbook is to derive approximate equations of motion and then show that there is a periodic solution matching the boundary conditions. This is ...
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Does $W_{out}$ in gas turbines refer to the shaft or the blades?

I was studying the Bryton cycle for a gas turbine and a question came to my mind about the turbine work output. That is, are we talking about the work output for the turbine blades or about the work ...
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1 answer
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Will fuel consumption be the same at constant speed between two engines of different power?

We have two same cars,same weights,just with two petrol engines, one has 200hp and second has 400hp.engines have same efficiency factor. In theory at same constant speed at highway of 140km/h cars ...
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Clausius inequality leading to absurd result

Background: After deriving Clausius inequality, the author of this book derives the following relation: Consider the cycle shown in the figure in which leg $A \rightarrow B$ is irreversible. In the ...
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Temperature rise in IC engine without heat flow

In an IC engine, the air fuel mixture is ignited in a cylinder resulting in temperature rise of the mixture. However, there is no heat flowing into the engine cylinder from some heat reservoir. Yet, ...
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Definition of heat when the temperature is changing in stochastic thermodynamics

I am currently studying stochastic thermodynamics, where the heat for a Brownian particle is defined by $$ dQ = -\gamma \dot{x} dx +\eta(t)dx, $$ where $\eta(t)$ is a white noise, with correlation $\...
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Generally will the power output from a heat engine increase as the work from this engine increases?

Generally speaking, does increasing a heat engine's work will essentially increase the power output? Whether this heat engine was a turbine, vechile or whatever.
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Reaction entropy in internal combustion engines

In air-standard analysis of internal combustion engines, the combustion phase is modeled as a heat input providing an energy corresponding to the reaction enthalpy. The entropy variation is calculated ...
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In Isothermal expansion of Carnot Cycle, Energy of the system should be constant, Since Temperature is constant. How does the system absorb energy?

In Carnot cycle's Isothermal phase, Heat is said to be absorbed. Energy of the Carnot Engine in Isothermal phase as per Ideal Gas equation should be: $$E=\frac32nRT$$ Since the amount of Gas($n$) and ...
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1 answer
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Relation between reversible and irreversible nature of engine and its entropy [closed]

please someone tell me about the relationship of the reversible and irreversible nature of an engine and how is it related to its change in entropy
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1 answer
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Work done on system and surroundings in an irreversible adiabatic compression

In an adiabatic irreversible compression process, suppose the pressure $P_{ext}$ compresses the piston and does some work say 50J. (50J of energy is lost by surrounding). Since the pressure $P_{int}$ ...
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2 answers
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Energy to counteract gravity without doing work? [duplicate]

Say I wanted to keep a body of 10kg at a certain altitude above the ground. If I elevate it 1m with my own arms or by any other means (with a drone, pulley system...) I'm spending energy in the form ...
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2 answers
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Efficiency of an heat engine with finite hot reservoir

I'm working on a problem that asks me the efficiency of a heat engine exchanging heat with an infinite cold reservoir and a finite hot reservoir of capacity $C$ that operates between the temperatures $...
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1 answer
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Thermodynamics Otto cycle

I have a conceptual question regarding the Otto cycle. In a piston-cylinder when using the otto cycle at compression since the piston applies work on to the system (the gas), is the sign convention ...
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How do we use $Δh=v(Δp)$ in pumps assuming $ΔT=0$ while the temperature can increase for the fluid such as in rankine cycle?

In incompressible fluids, for liquids & Constant-temperature processes, as in pumps $(ΔT=0)$ then $Δh=v(Δp)$ . But for a pump in Rankine cycle it will increase the temperature.So, how will we ...
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1 answer
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Will the moisture content in steam turbine power plant decrease the work expansion of the turbine?

In a steam turbine power plant. If the moisture content is increased during the expansion of turbine stages. Will Wturbine decrease because of some of the steam has been converted from gas to water?
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Is $Q=TS$ valid for externally reversible process or internally reversible process?

For $q=tds$ is this equation valid for externally reversible process or internally reversible process? Like for example a heat transfer process in Rankine Cycle is internally reversible but not ...
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How does the heat transfer in carnot cycle occur without a temperature difference between the reservoir and the fluid?

If the temperature of reservoir in carnot cycle (Th) is the same of the fluid's temperature (Th also) then how the heat will transfer . I know that heat transfer from a hotter substance to a lower ...
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1 answer
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Why $W_{\rm net, out} = W_{\rm out} - W_{\rm in}$?

Why when we use thermal efficiency the $\text{net work output} = W_{\text{out}}-W_{\text{in}}$ I asked my friend once he told me is that because we need the useful work but I told him an example in ...
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1 answer
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What puts a limit on lowering $\langle T\rangle$ low avg in heat engines?

I have a simple question which is: We know that the thermal effeciency in heat engines increases when we lower the average temperature at which heat is rejected. But the problem is that there is ...
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How will the compression ratio increase thermal effeciency of otto cycle while Win is higher?

Why the ideal otto cycle thermal effeciency increase with compression ratio although that will increase work input? While the temperature difference in the combustion chamber could be low,the overall ...
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Will increasing or decreasing $\langle T\rangle$ improve thermal efficiency for all power cycles?

The statement: Increasing the average temperature, $\langle T\rangle$, at which heat is supplied to a fluid or decreasing the average temperature at which heat is rejected from a fluid increases the ...
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Why lowering the condenser's temperature is limited?

Why is lowering the condensers pressure limited by a 10 °C difference between the fluid and the sink source in cycles like Rankine Cycle?
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Will $Q_{in}$ increase in this case?

When increasing boiler pressure in rankine cycle the efficiency increases, I think this is because $Q_{in}=(\triangle S).(T_{avg})$ and $T_{avg}$ will increase when the boiler pressure increase and So ...
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2 answers
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How does external work move heat from cold reservoir to hot?

From Clausius statement on Wikipedia: "In a refrigerator, heat flows from cold to hot, but only when forced by an external agent, the refrigeration system." How exactly does the external ...
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Otto cycle reversible or not?

In my course it states that the Otto cycle is an irreversible process. I'm not really sure why. I have also found by a quick google search that a lot of people say the cycle is reversible. To my ...
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1 vote
2 answers
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Why don't we turn on the air conditioner instead of the heater during the winters? [closed]

During winters the temperature at my area drops to around $5° \text C$. I feel comfortable around $25° \text C$. To stay warm, we usually turn on the heater instead of air conditioner even tough I ...
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How can the heat absorbed by an engine be measured by "measuring the fall in a weight"?

In Atkin's Introduction to the thermodynamics, he speaks about the definition of the absolute thermodynamic temperature scale and in his discussion he states that the work done by any engine can in ...
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What is the need of adiabatic compression in Carnot cycle?

Why do we need to compress the gas adiabatically after the isothermal compression of gas? What if we just skip this step? What will be the consequences? By "skipping this step",I mean, after ...
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5 answers
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Why is it necessary for a heat engine to work in cycles?

We can make a steam engine just by putting huge amount of water in large tank and heat it and then use the steam to run the wheel. We just have to put huge amount of water and heat then engine will ...
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3 answers
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Why don't we really consider the TOTAL (SYSTEM +SURROUNDINGS) entropy change in Carnot cycle?

During a Carnot cycle, why don't we consider the increase in entropy of surrounding by the energy given to surrounding via work done by gas piston? I mean we want to find the total entropy change then ...
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2 votes
1 answer
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Why is entropy of gas reamains constant during adiabatic expansion?

In adiabatic compression, we add energy to the gas via piston and decrease volume. Now the increase in energy and decrease in volume will cause increase and decrease in entropy respectively, but it ...
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1 answer
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Could we replace pump in Rankine cycle with just a check valve?

Is it possible for a rankine cycle to work without a feed pump? Or if we replace the feed by the check valve? Or maybe if we use gravity only?
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