I burn wood in my stove. Combustion releases chemical energy from the wood.

Some is absorbed by the CO2, water and other gases created by the combustion itself. Some is radiated away. I suppose some gets conducted away too but I don't suppose it's much...

Now, the hot gases, they go up the chimney and are dumped outside, losing some on the way. But most of that energy is "lost" to the system. Which would be my flat.

The radiated energy though. It's caught by the stove and that's what warms my flat. Am I assuming this right?

How much do I lose by releasing hit gases? More than 50%? Does most of the combustion energy end up in the smoke?

Hello everyone I hope this question is right for this sub.

I like my coffee to stay very hot, when I put the cold plunger into the press and push it into the coffee it obviously takes the heat required to heat the plunger out of the coffee. But I'm wondering if I put the plunger into the top of the coffee press, and leave a head space in-between the coffee and the plunger where the steam from the coffee accumulates, does the cooling of the steam as it meets the plunger transfer over to cooling the coffee below at a equal rate? I hope this is worded clear enough to understand, thanks for the consideration!

My group is trying to experimentally calculate the thermal conductivity of materials, but we're encountering difficulties with our setup. We have a rod made of different materials, with each end submerged in two separate reservoirs: one being an ice bath and the other lukewarm water. We’re using a temperature sensor to measure the temperature change in the lukewarm water due to heat transfer from the rod.

The rod is insulated with cotton and electrical tape to minimize heat loss to the surrounding environment, and both reservoirs are surrounded by foam boxes to reduce heat transfer to/from the ambient air.

Our approach involves using the slope of the temperature change curve in the lukewarm water to estimate the heat transfer, which we then use to calculate thermal conductivity.

Do you have any insights into why this setup might not be working as expected? Is there something crucial that we might be overlooking or a better way to approach this experiment?

Are there any fluids that can be heated and kept at around 500 degrees F without boiling? This would be a closed system so pressure could be added to the system to lower the boiling point.

https://preview.redd.it/282lx4ztkk5e1.png?width=1037&format=png&auto=webp&s=08ecc2c917039f69e1b7f3b2b1fdbcc5d158a2a2

This may be a stupid question but I really don't get it.

In the solution to this problem, you must use the following equation and figure that there is no change in pressure or velocity.

https://preview.redd.it/sv2dfkj5lk5e1.png?width=511&format=png&auto=webp&s=f9da1187e7711bef5819d7fe05a8f8747bc9286f

1. My question is how can I know that there is no change in pressure if I know for a fact there is a change in height? Doesn't pressure increase with depth?

2. Additionally, why do I take the height difference from the surface to the turbine? Wouldn't the turbine be pulling water at its own depth and just pumping it at the same depth to the other side?

I had a final quiz a few days ago, and I made a few basic mistakes leading to a 60%, so i redid the problem on my own and i was wondering if someone could review my work for correctness in procedure.

There are two problems, a basic dew point problem, and a Rankine reheat cycle problem.

Am I correct in assuming the enthalpy chance across turbine 2 is somewhat of a red-herring, or an alternate way to solve the problem by getting the power output of turbine 2, and subtracting it from combined output, then using the leftover output (work out from high pressure turbine), i can work backwards and solve for enthalpy out at 4?

Thank you in advance.

Here are the pictures of my work: https://imgur.com/a/XCd3Ba9

With the data I have from an AC, such as its Btu and flow rate, I want to have some kind of estimation about how hot its outside unit can get when using cooling mode.

What I tried to do is, use Q = m(dot) * c_p * (delta)T
with Q = 12000 Btu/h = 3.599 kW,
flow rate = 22.8 m^3/min = 0.466 kg/s
c_p = 1.005 kJ/kgK

and with this I get a delta T of about 7 degrees. This doesn't sound right to me, would the outside unit really only get 7 degrees hotter than the ambient temperature?

It has been a while since I've done any real engineering so I'm preeety sure I'm doing something (several things) wrong. Please help.

I've tried to understand this, but what should be the specific entropy of a mixture? I'm not talking the entropy of mixture, I'm focusing in a process where the gas is already mixed, so the change in entropy won't take that into account.

I've seen that i should only make a weighted average of the individual entropies and the mass fraction, other sources say that i should subtract Rln(Z) and some other states that i need to plug other terms that depend on the EOS I'm using.

So, what is the rule of thumb to get a good value?

is it possible to calculate the area of heat transfer? For a parallel heat exchanger it was possible to find the area but if I'm asked to compare the percentage of area increase then how do I do it?

I have a tank that I have to get it to -20ºC. The main problem is that it will be in the middle of nowhere, so, I do not have eletricity. Knowing this, I was projecting some kind of a cold sleeve, like they use in the wine industry. I've thought using a brine solution, but I believe it wouldn't get the job done, and using dry ice on itself wouldn't be too reliable, I believe. Does anyone has an idea??

I’m currently taking a class called Advanced Thermodynamics, and we’re using M. Scott Shell’s Thermodynamics and Statistical Mechanics book. One area I’m having significant difficulty with is the differences between partition functions and ensembles, both between each other and between different types of each (e.g. difference between microcanonical and canonical, classical partition function and grand canonical partition function). I can complete problems that are presented but it feels more due to rote memorization than true understanding. I’ve re-read the chapters multiple times but it still feels like something isn’t clicking. Can anyone share a way of thinking that helped it click better for them? Thank you in advance.

Why does energy have a direct proportionality with temperature, and whereas the temperature has various application based relations with different fundamental physical units,
like for example the Q/t=kA(∆T/d), and Q=k_b*∆T , and E=σT^4 , KE=3(k_b*T)/2 ,
also for entropy etc,
what i am really trying to learn is how is energy different , one such answer i got from
the internet is "Temperature is a measure of the average kinetic energy of particles in a substance, while heat refers to the total energy transferred between systems due to a temperature difference. Heat flows from a hotter object to a cooler one until thermal equilibrium is reached ." and the distinguishing factor between these has confused me,
"

1. Nature of Quantity:
   • Temperature is an intensive property: It does not depend on the amount of substance. For example, a small and large pot of boiling water can both have the same temperature.
   • Heat is an extensive property: It depends on the amount of substance. The total heat energy in a larger pot of boiling water is greater than that in a smaller pot.
2. Energy Transfer:
   • Heat flows spontaneously from a higher temperature body to a lower temperature body until thermal equilibrium is reached. The flow of heat can be described by Fourier's law of heat conduction, which states:

• Q=−k⋅A⋅ΔT/d,
• Temperature is an intensive property: It does not depend on the amount of substance. For example, a small and large pot of boiling water can both have the same temperature. by this do you mean , that the temperature does not depend on number of particles, rather , the particle's nature, and the heat contributes due to all existing particles and and their properties...
• if it were particle nature then would it be this way?,
• "Particle Nature: The temperature of a substance reflects the average kinetic energy of its particles. It is a measure of how fast the particles are moving, regardless of how many particles are present."
• "Heat Contribution:
• While temperature does not change with the number of particles, the total heat energy in a system does depend on the number of particles and their specific properties (like mass and specific heat capacity).
• The heat energy of the system is the sum of the kinetic energies of all the particles, but the temperature remains constant for a given state of matter."

my simple question is are these all analogies correct ,
if yes then, then
would it mean the 'Temperature' is an intensive property due to average KE of particles,
and their nature , by this i also mean system's nature, or rather an intrinsic property of
energy of the system,
and heat is total KE of the system contributed by the particles and their particle nature,
and other properties of system which add up to be energy ,
is my understanding or explanation correct on this,
please guide me further because i am new to this field and enthusiastic about
these fascinating things, it would be great help if somebody could explain me these things in a proper format, so i could learn and understand it better,...

Hello, I have a Bubble T - VLE problem where I need to implement the UNIFAC model to determine the activity coefficients and find values of T and Y as I vary the values of X and keep the pressure constant. My system is the binary mixture (1) ETHANOL + (2) CYCLOHEXANE, and I must account for ALL the non-idealities in both phases (liquid and vapor), meaning I need to calculate the fugacity coefficients (using the Virial equation truncated at the second term), POY, and activity coefficients (gamma). I am doing all of this in Excel. I have already implemented the entire UNIFAC method in the spreadsheet, but the issue is that I cannot find an objective function to solve the vapor-liquid equilibrium problem (I cannot find consistent values for Y and T using Solver). plss, if anyone can help me

Say you got state 1 before the compressor, and state 2 after the compressor. The work W is then given as:

W = m(h_1 - h_2)?

I see sometimes my professor switches it up and says h_2 - h_1.

For example I had an exact problem in an exam where I knew the W in kW, h_1 and needed to find h_2. Again:

W= m(h_1 - h_2), solved for h_2:

h_2 = h_1 - W/m. But my professor got h_1 + W/m.

(I did the same for the turbine on the other side of the cycle, and got correct)

Can someone explain?

I work with large industrial engines and we often do cogeneration for heat and electricity. On our larger units we can have up to 871 m3/min of exhaust at 475C which is a lot of waste heat/energy.

On some sites they do not have the need for the excess heat so we dump to atmosphere. Specific to these sites, if we were to use a heat exchanger and run the resultant steam through a turbine attached to a generator, what kind of losses in energy would we be looking at aka how much electricity could we produce?

I’m assuming we’d be in the 500ekW to 1000ekW range but I’m having a hard time finding steam turbines small enough to get some efficiency data on.

Thoughts, recommendations, advice?

Hi everybody. I hope I can reach someone with this post. I am currentky working on a thesis about the cooling systems used by space suits for my bachelor degree in aerospace engineering. At the end I need to calculate the diameter of a collection of square pipelines to exchange approximately 800W. The pipelines have to stay inside a square plate which is 0.24 x 0.24 square meters. The fact is that when I try to calculate the diameters (which for sure have to be less than 0.24 meters I obtain a diameter of 3 meters). I am adding my calculus papers. Can someone help me?

Hi, i found this statement in a book "The efficiency of the Carnot cycle is greatly affected by the temperature T1 at which heat is transferred to the working fluid. Since the critical temperature for steam is only 374°C, therefore, if the cycle is to be operated in the wet region, the maximum possible temperature is severely limited." What does this mean? Isn't the critical point of water is 374 C only at 220 bar pressure? Why is this a constraint to Carnot's cycle if it usually operates way below this pressure?

If we have a hot solid metal sphere in open air, it will cool by natural convection. In this case we can find the heat transfer rate Q' by 1) estimating the Rayleigh and Prandtl numbers at the film temperature, 2) using a correlation to find the Nusselt number, 3) finding the surface heat transfer coefficient h, 4) Q' = hA * (T_surface - T_env).

Now, if the sphere is a good thermal conductor, as you would expect of a metal, its Biot number will be very small, and its temperature will change uniformly. So you could then say that T_surface = T (of the sphere), and say mc dT/dt = hA * (T_env - T) to find the temperature evolution. The thermal time constant will be mc/hA.

However, what if the sphere cannot be assumed to cool uniformly? The thermal resistance of a solid sphere from the centre to the surface is undefined so we can't use steady state analysis. The only way I can think of then is to solve the heat equation in spherical coordinates (only the radial part is needed though). But then, the boundary condition seems tricky. It would be a Robin-type boundary condition: -Q'/A = |∇T| -> dT/dr = h/λ * (T - T_env) at r = r_surface. I'm not sure if there is any analytic solution.

What I'm really interested in is the temperature at the centre of the sphere. Is there any better way to do this?

I have an electric dirt bike with a very large plastic wrapped lithium-ion battery. Would getting a winter insulated cover (similar to winter coat material) be sufficient to keep the bike above 40°F in as low as 5°F weather for long term winter storage? Or will the temperature outside eventually equalize with the insulated bike? Help would be greatly appreciated. I'm very new to thermodynamics.

Container 1 has volume V1​, and inside that container there is a number of moles n1​, temperature T1. Container 2 has volume V2​, and inside the container there is a number of moles n2, temperature T2. The gases in Container 2 are transferred adiabatically to Container 1 mixing both gases. What is the pressure and temperature​ inside Container 1 after the mix of those two gases?

Hello! I'm stuck on a calculation that requires me to determine C*pm (Dimensionless heat capacity). I know that I need to use the formula:

(T2/T1)=(1/π)^(n/C*pm)

and somehow iterate to find T2s by guessing and testing its value. The correct C*pm​ should be about 3.55 (according to the lecture material), but I keep getting 3.687.

Initial values:

• T1=616  (air temperature before the turbine compressor)
• P1=1 bar (air pressure before compression)
• P2=12.4 bar (air pressure after compression)
• η_isentrop=0.89 (isentropic efficiency)
• m_flow=120 kg/s (air mass flow rate through the compressor)

ChatGPT gave me some integral methods (which I tested and got the same Cpm=3.687), but the correct method should involve guessing T2s​ and iterating until reaching a consistent value. I'm a bit lost here because the lecture materials don't explain the iterative method clearly. Any tips?

Edit: T2s refers to the temperature under the same entropy but with a different enthalpy.

Edit2: Correcting my bad grammar

Hail mary but figured worth a shot.

Situation: creating a small water chiller system.

Issue: may have gotten in over my head - been entirely self-taught and been constantly learning, hopefully someone more knowledgable can help me out.

Details: sort of replicating a water chiller system with my own parts, but ran into issues when charging.

My system: a LBP/MBP R134a compressor, mini tube fin condenser, 1/8” OD capillary tubing as metering device, 40 plate BPHE, and 3/8” suction line. Using a freon scale to monitor freon charge.

Was advised I needed to get: suction saturation, liquid saturation, superheat, subcooling, water temp approach, and metering device type.

How can I obtain this data and calculate how to charge system with freon?

Hopefully looking for an engineer or expert that can help, even better if any in my area. Thank you so much for your time!

This is a compressor power formula.

https://preview.redd.it/lrokfia0mq2e1.png?width=980&format=png&auto=webp&s=686a91dd9305f73af0074bd3241fb4554ec16521

I think that T1 should be P1

Q is volume flow through compressor m^3/h or whatever units are used here.

PV=wRT (2.7)

V=(wRT)/P

This is from a different source:

https://preview.redd.it/p41x7ptbmq2e1.png?width=693&format=png&auto=webp&s=781ac84ea83b89727e410bb2db00b2215c0415f5

What confuses me is that the first equation is in imperial units and is supposed to be a real compressor formula. Other 2 formulas are soposed to be thermodynamic and theoretical.

I can't figure out which textbook this was taken from. Anybody recognize it? Thanks.

https://preview.redd.it/2wadum8pih2e1.png?width=1566&format=png&auto=webp&s=8f0e9ef85c76d3264b9c23707f6368255d9f9526