# Questions tagged [heat-engine]

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### Why is it that a Carnot heat engine will reject no heat to a zero temperature sink?

Looking at the equation for Carnot efficiency, I notice that as the temperature of the heat sink approaches zero, the efficiency approaches unity: $$\eta_{rev} = 1 - \frac{0}{T_H} = 1$$ Seeing ...
375 views

### How efficient is the Crookes radiometer?

I remember many years ago, I think at 8th grade, seeing the teacher show us a Crookes radiometer. I remember it being very fascinating. Today I read the wiki article on it, after looking up what it ...
109 views

### Are there actual technical realizations of the Carnot cycle?

The Carnot cycle is composed of four steps: isothermal expansion, adiabatic expansion, isothermal compression and adiabatic compression. In the case of combustion engines, we have the idealized Otto ...
350 views

### What is the problem of this thermodynamic fallacy?

Consider the following (alleged) cycle: Quasi-static adiabatic expansion of a vapor in such a condition that it results in the condensation of part of the mols*; Out of equilibrium adiabatic ...
66 views

### What is the potential energy of a Carnot engine?

Say you've got a closed (but very large) system with a hot and cold reservoir a la the Carnot cycle. You can add up the heat in the two reservoirs and find that the total amount never changes (because ...
522 views

### What variables affect a Heat engine's efficiency? (and more)

I'm writing a Minecraft mod and I'm trying to create the equations for the engines players can build. I'm a highschool sophomore, so my knowledge of physics and mathematics is limited. I asked first a ...
893 views

### What is the best material to use in a solar heater box to convert solar energy into heat energy?

Suppose you want to design a solar heater box with the dimensions: 1 sq meter x 30.48 cm H. 5 sides of the box's interior will be insulated and the interior will be totally black. Ideal glass will be ...
83 views

### Better understanding the Clausius Inequality

My conceptually understanding draws on the section on the Clausius Inequality from Finn's Thermal Physics. Attached is the graphic used for the derivation in the textbook. If I'm to understand ...
32 views

### Does real gas's entropy increase in $T$-$S$ diagram of Brayton Cycle efficiency?

I got T-S diagram for efficiency of Brayton Cycle, which includes ideal cycle (black line), real cycle (red line) and GE's cycle (blue line), can't understand the entropy, whether it increases or ...
109 views

### Does negative absolute temperature imply heat engine efficiency greater than one?

As it is shown in Prove that negative absolute temperatures are actually hotter than positive absolute temperatures, a body with absolute negative temperature is hotter than a body with any absolute ...
179 views

I am trying to learn the derivation of Clausius inequality in the following manner. Consider the following diagram "Reversible cyclic device" is working in Carnot's cycle. The combined system gets ...
6k views

### Formula for the heat input in a heat engine

There's one situation relating to heat engines where there's one equation I never understood completely. The situation is something like: there's a heat engine operating between two systems $A$ and $B$...
68 views

### What does the ratio of reservoir temperatures have to do with the efficiency of a heat engine?

I am having a conceptual difficulty with heat engine efficiency. I do not understand why having a larger difference in temperature between the hot and cold reservoirs have an effect on the thermal ...
234 views

Carnot cycle is a reversible cycle. By definition a reversible cycle must have an infinitesimal temperature difference. That means ($T_{high}-T_{low}$) is very very small. Any finite temperature ...
23 views

### microturbine heat loss

Would the hot combustion gasses in the millimeter-wide turbine in http://thefutureofthings.com/3063-engine-on-a-chip/ lose heat so quickly that the engine efficiency would be low? The velocity of ...
60 views

### Maximum temperature of an elliptical thermodynamic process

Given a heat engine made from the curve $$V(t)=V_0 +A \cos(\omega t); \qquad P(t)=P_0-B \sin(\omega t).$$ What are the hottest and coldest points of this cycle, and what are the temperatures at those ...
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### Water as heat source in a heat pump

Consider we have water flowing in a pipe, which is working as a hot source for a heat pump. We are able to know the temperature of the water in both ends of the pipe, yet we don't have information ...
257 views

### diesel steam engine

Let's imagine a diesel engine's cylinder head would be heated by external means, to some hundred degree celsius, and the fuel would be replaced by water. We've made modifications so that water would'...
206 views

### How Much Heat Is Absorbed/Rejected By The Heat Engine?

If a heat engine undergoes a reversible cycle consisting of two isobaric processes and two adiabatic processes, what methodology is used to determine how much heat is absorbed or rejected by the heat ...