# Questions tagged [heat-engine]

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### Why does intercooling improve the efficiency of a Brayton Cycle?

I've read in numerous sources that intercooling improves the efficiency of a Brayton cycle. The explanation given is that it decreases the compression work by minimizing the temperature during the ...
4k views

### 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 ...
226 views

### Brayton Cycle Efficiency

Hi, I'm trying to calculate the efficiency for the Brayton Cycle. The end result is supposed to be: $$\eta = \frac{C_p(T_3-T_4) - C_p(T_2-T_1)}{C_p(T_3-T_2)}$$ Where the denominator is from $Q_h$. ...
45 views

### Work done by a heat engine given thermodynamic cycle

A heat engine uses an ideal gas as its working substance, and is described by the following thermodynamic cycle; Isobaric expansion at $4 \text{ atm}$ from a volume of $4~\text L$ to $8~\text L$. ...
34 views

### Frequency of refrigeration cycle

How often does the refrigeration cycle repeat itself? I have read that the compressor runs at about 1000 rpm. Does that mean that the frequency of the cycle is 1000/60=17 Hz?
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 $B$...
139 views

### About the 2nd Carnot Corollary

I have a question about the 2nd Carnot Corollary. According to Moran, Fundamentals of Engineering Thermodynamics, the 2nd Carnot Corollary stated that "all reversible power cycles operating between ...
191 views

### Is a Curie pendulum an example of a heat engine?

By definition, a heat engine absorbs energy and uses that energy to do work. A Curie pendulum doesn't seem to do work when absorbing that energy. Instead, the magnet is heated and loses it's magnetic ...
214 views

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### Carnot's Engine Proof flawed?

https://www.youtube.com/watch?v=LUoUb4hGMH8 I was looking at the reason as to why a Carnot Engine and watched this video on KhanAcademy. He used a very clever method of proving this by using the ...
59 views

### Thermodynamic cycles

Consider a system that takes excess air (assume it to be an ideal gas, $Cp = \frac{7}{2} R$) from a power plant stack at $370 \rm K$ (typo in figure) and $2$ bar and compresses it to 20 bar ...
125 views

### Clarification on Clausius Inequality

Consider a heat reservoir which gains heat $Q$ irreversibly at temperature $T$ from the surroundings which is at temperature $T_0$. The entropy change of reservoir is then given by $\frac{Q}{T}$, ...
380 views

### Work obtained from Rankine cycle vs Carnot cycle

In this diagram, We can say that the work obtained from Carnot cycle is greater than the work obtained from the Rankine cycle because the area enclosed by the curve is greater. However, if we try ...
666 views

### Seebeck effect or Peltier effect for optimal thermoelectric effect?

I am building an experimental thermopile, and I'm getting confused with the definitions for the Seebeck effect and Pettier effects. From Wikipedia: The Seebeck effect: The Seebeck effect is the ...
2k views

### Does chaining Carnot heat engines make them more efficient?

Since the efficiency of a Carnot cycle depends on the difference between the hot and cold sides of the engine, could you put multiple heat engines in a series to maximize overall efficiency? A \$3000 \,...
234 views

### Lowering of temperature in expansion valve of refrigerator

We know that the high pressure liquid refrigerant (comming from condenser) passes through the expansion valve and lowers the temperature (due to decrease in pressure). My Question: From the formula ...
144 views

### Why does taking work from a system not reduce its entropy?

In Daniel Schroeder's book Thermal Physics, he makes the point that as energy is put into a system it's entropy goes up (there are some exceptions to this generally, but for this question we can ...
102 views

### Carnot cycle with varying reservoirs

I was thinking what will happen to the standard Carnot cycle, if instead of - say - the usual cold reservoir, we adopt a smaller refrigerator, whose temperature in fact changes after the heat release ...