Heat engines Definition and 51 Threads

Hi, i have this question and don't understand it. can somebody explain what i have to do. i know a ideal engine is a engine running on carnot cycle i what the cycles are i don't know what relative efficiency is and what there looking for (Q) Review the relative efficiency of ideal heat engines...

Just to clarify, I'm aware of the two equivalent expressions of the first law ##\Delta U = Q + W## and ##\Delta U = Q - W## when applied to a certain system, though my question is primarily about ##Q## - for which, as far as I am aware, the convention is almost universally that ##Q > 0## if heat...

For the heat engine: First I converted all the temperatures to Kelvin, ηmax=1-(333)/(1000)=0.667 ηclaim=(1*10^3)/(1.75*10^3)=0.5714 So the heat engine seems to be less efficient than a Carnot heat engine which means it can exist. For the refrigerator: COPmax=(253)/(363-253)=2.3...

Hi, I posted a similar question recently and gained some insight on these types of problems. However, I am slightly stumped on how to approach this variation of the problem. So I know that: - there is no net change in enthalpy of the blocks and the engine as the processes are reversible -...

Hi, I was revisiting my (high school level) understanding of thermodynamic cycles and I think I still have some doubts. Last year and more recently I posted a few questions which surely helped me, but I think I need more clarifications. In a nutshell, what I'd like to know is the following...

Homework Statement An office with a volume of 52.5 m^3 uses a heat engine that outputs 1200 W. Suppose that, initially, the office has a pressure of 1 atm and 20 degrees Celsius before the heater is turned on. After 10 minutes (6000 seconds), what is the final air temperature? Homework...

Hello, I am reviewing some thermodynamics and heat engines. Heat engines are cyclical machines able to convert a portion (just a portion) of the thermal energy extracted from a hot reservoir into mechanical work. The residual thermal energy must dump into a lower temperature reservoir...

I have been researching the Rankine cycle. I know that it consists of two adiabatic and two isobaric processes. However, I'm not entirely sure why we ignore the work done during the isobaric processes (this seems to be the case in the analysis I'm looking at). Is that because the work done there...

Homework Statement Two identical bodies of constant heat capacity ##C_p## at temperatures ##T_1## and ##T_2## respectively are used as reservoirs for a heat engine. If the bodies remain at constant pressure, show that the amount of work obtainable is ##W = C_p (T_1 + T_2 − 2T_f)##, where...

I bought the drinking bird toy, and I want to get a better understanding of it, (https://en.wikipedia.org/wiki/Drinking_bird) I understand the basic way it works and that it is a simple heat engine, but I can't seem to find any information that helps me answer the following - I notice all...

My question is: according to Carnot cycle, the maximum efficiency of a heat engine is given by 1 - T2/T1, where T2 is the temperature of the cold source and T1 the temperature of the hot source. So, accordingly, as higher T2 is for a same T1, lowest is the efficiency of the engine. But, the...

Homework Statement Two identical tanks of water are at absolute temperatures ##T_A## and ##T_B## respectively, where ##T_{A} > T_{B}##. The tanks each have a heat capacity ##C##, and they are thermally isolated from their environment. Suppose that a heat engine is installed in contact with the...

Homework Statement I have a question regarding heat engines that cropped up whilst I was doing a practice question. I will summarise the results I obtained for the previous parts of the question so as to save your time. The highlighted parts of the image are where I am having some issues. I...

Homework Statement Suppose that 282 moles of a monatomic ideal gas is initially contained in a piston with a volume of 0.81 m^3 at a temperature of 574 K. The piston is connected to a hot reservoir with a temperature of 1365 K and a cold reservoir with a temperature of 574 K. The gas undergoes...

Noting that ice expands by about 9%, why isn't it possible ot build a heat engine from this natural process?

I tried to calculate the efficiency of a engine using the formula : Efficiency = (Net Work Done) / (Heat absorbed) And then I tried to calculate the efficiency of respective Carnot engine by two ways : 1) Efficiency = (Net Work Done) / (Heat absorbed) 2) Efficiency = 1 - (Temperature Lowest /...

The main result of thermodynamics is that if you have a place that is hot and another place that is colder, you can operate a heat engine by absorbing heat from the hot place and dumping it in the cold place, extracting some useful work in the process. It gives you a way to calculate the...

1-Is the efficiency of heat engines working in cycles other than Carnot independent of the nature of substance used? Can we still claim that maximum efficiency in converting heat to work is attained during reversible processes for such cycles? For which engines/cycles can we do this? 2- Why is...

(I'm not sure I put this thread in the right sub-forum) If we need to operate a nuclear-powered heat engine in space to run a generator, meaning it can only be cooled by radiation, what kind of system should we go for, if we want the power per unit mass ratio to be as high as possible? I've...

Not sure if this should be posted in the general physics forums or in the hw/coursework section. I'm in my second semester of general physics and have to do a class project. For my project I built an alpha type Stirling engine. In the paper I need to write I need to explain how it works using...

Homework Statement a heat engine draws 200J of heat from the hot reservoir at 400K produces 110J of useful work and dumps 90J into the cold reservoir at 200K could this engine be built why or why not? Homework Equations PV=NkbT The Attempt at a Solution Not Sure on how I would set...

Hello, Homework Statement Engine A receives four times more input heat, produces six times more work, and rejects three times more heat than engine B. Find the efficiency of (a) engine A and (b) engine B. Homework Equations e = |W|/|QH| e = 1 - |Qc|/|QH| The Attempt at a...

Homework Statement There is a heat engine with Th on top at 100 J pointing down, Tc on bottom pointing down with 50 J and the work output is 50 J pointing right out of the engine. (ENGINE 1) a) Draw the diagram for a carnot refrigerator which draws 100 J of heat from the hot reservoir (Th...

So, I'm studying for the MCAT. There..I've said it. :) But, it's not a homework question: I just don't understand the concept. My study book's thermodynamics section includes a very rough sketch of a heat engine to describe the 2nd Law of Thermodynamics. A side note in the text says that if...

In a heat engine we ultimately care about the efficiency of the entire cycle. That is, what percentage of the heat which flows into your system is converted to work. However, you could certainly ask that same question for an individual step in a cycle. Specifically, determine the efficiency of an...

Homework Statement When gasoline(density=.7297 g/cm^3) is burned, it gives off 5.00 times 10^4 J/g(its heat of combustion). If a car's engine is 25% efficient, how much gasoline per hour must it burn in order to develop an output of 50.0hp. 1hp=746 W Homework Equations P=W/t e=W/Qh...

PV diagrams for heat engines are "legitimate"? Hello forum Since my student days i was wondering about how is it possible to represent the cycle of the gas in a heat engine (e.g. otto cycle) in a PV or whatever diagram when it is obvious that the gas is not in equilibrium during the process...

By heating a gas inside a cylinder, you allow it to expand against a piston while maintaining a constant temperature. The energy that you add as heat goes into the PV work of the gas against the piston. To start again, you have to push the piston back to the start point, compress the gas...

I am not a physicist and have no mathematical understanding, but I am very interested in the fact that heat engines need a cold sink, simply by virtue of the Second Law of Thermodynamics. As I understand it, as the temperature of the cold sink rises, its entropy increases at a faster rate than...

even though the thermal efficiency of diesel engine is more than that of gasoline engine , why is it that gasoline is preferred over diesel for cars?

This question has been in the back of my mind for a while. In short, is having a phase change between liquid and vapor more desirable for a heat engine or for a heat pump? Clearly, having a large area enclosed by the loop in a P-V diagram increased the amount of work in the cycle, so...

My question involves heat engines. I understand that a heat engine typically uses energy provided in the form of heat to do work. According to the 2nd law of thermodynamics, however, not all heat energy can be converted into work energy, meaning that heat engines are not perfect. At least some...

The Attempt at a Solution For a) I imagine it is easier to control the temperature of the hot reservoir because you could use a constant heat source e.g. bunsen burner. c) melting/freezing water. d) Entropy of the environment increases and the entropy of the universe always increases...

Homework Statement A heat engine operates between 40°C and 380°C. Being a real engine, its efficiency is only 60% of that theoretically possible for a Carnot engine at these temperatures. If it absorbs heat at a rate of 60 kW, at what rate does it exhaust heat? Homework...

So I wrote my Thermodynamics final today and one of the questions were as follows: A reversible heat engine supplies a reversible heat pump. Both draw off of a temperature reservoir T (can't remember the exact value, but there was one). The heat engine discharges heat into TL, and the heat...

1. What is the thermal efficiency for the heat engine shown in the figure? What is the heat extracted from the hot reservoir for the heat engine shown in the figure?t Figure shown here: 2.Wout = 1/2 B*H Also, Qc=Qh-Wout, efficiency: Wout/Qh 3. Wout = .5 * 200KPA*...

Hey all, This is a simple question: Lets say we have a solid hot-body in outer-space that's emitting thermal radiation. Assuming that it doesn't sublimate, will it simply radiate black-body radiation until it reaches absolute zero? This doesn't sound right. Thanks

Homework Statement An aircraft engine akes in 9000 Joules of heat and discards 6400 J each cycles a) What is the mechanical work output of the engine during one cycle? b) What is the thermal efficiency of the engine? Homework Equations e=W/Qh The Attempt at a Solution A) Qh =...

I am having trouble with this question...It is from "applied thermodynamics for engineering technologists" by Eastop (Q5.2 if anyone has it)... The Question: Two reversible heat engines operate in series between a source at 527°C and a sink at 17°C. If the engines have equal efficiencies and...

I'm having trouble trying to get my head around the role entropy plays in a heat engine. When the energy from a hot reservoir enters the engine, it brings a certain amount of entropy with it. Then, the "waste heat" (which is energy) gets rid of the entropy. But, why does it take less energy to...

[SOLVED] Heat Engines and the Carnot Cycle Homework Statement The operating temperatures for a Carnot engine are Tc and Th= Tc + 55K. The efficiency of the engine is 15%. How do i find Tc?

we are learning about heat engines and the 2nd law of thermodynamics...and i don't know how to relate torque to these concepts... the question is... a multicylinder gasoline engine in an airplane, operating at 2500rev/min, takes in energy at 7.89E3 J and exhausts 4.58E3 J for each revolution...

Homework Statement Suppose that two heat engines are connected in a series, such that the heat exhaust of the first engine is used as the heat input of the second (attached diagram below). The efficiencies of the engines are e1 and e2, respectively. Show that the net efficiency of the...

Could someone explain to me how heat engines and refrigerators and air conditioners work. I'm very confused about the process and if they are isothermic, isovolumetric, or adiabatic. ~Kitty

Hello, If anybody could answer this question for me that would be great. I have been wondering about it all morning. In the Diesel cycle for heat engines, on the second stage of operation, the Volume increases while pressure stays the same. I understand how this can be accomplished by raising...

Hello, If anybody could answer this question for me that would be great. I have been wondering about it all morning. In the Diesel cycle for heat engines, on the second stage of operation, the Volume increases while pressure stays the same. I understand how this can be accomplished by raising...

Could anyone suggest a book on heat engines at undergraduate level?

As a future engineer, my proffessors teach us to be concerned about pollutant emissions. I always hear about NOx production inside heat engines and turbomachinery. But little is explained about the true nature of this problem. Usually, we are told that NOx is produced at high temperatures...

In class, we're being introduced to thermodynamics, and one of the topics is heat engines. Steam engines were also mentioned. Carot engines also entered the pic. They are described as ideal systems. Exactly why are Carnot engines not "real" engines, or are not possible? I'm sorry if...

A 20% efficient real engine is used to speed up a train from rest to 5 m/s. It is known that an ideal (Carnot) engine using the same cold and hot reservoirs would accelerate the same train from rest to a speed of 6.5 m/s using the same amount of fuel. The engines use air at 300 K as a cold...