Questions tagged [thermodynamics]
Questions relating to the various laws of thermodynamics, transformation or movement of a form of energy to another form, primarily but not limited to heating or cooling of a fluid.
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Steam turbine powered by hydrogen movement
Steam turbines already exist that generate power from the heat generated by the combustion of gases. Gas turbines and combustion engines also exist that can generate electricity from the combustion of ...
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How to Link between Stoichiometry, Energy Content of a Fuel, Combustion in a Cylinder-Piston, and Otto-Cycle, Compression Ratio, & Thermal Efficiency?
Picture 2, source:
I would like to do a real calculation of a piston. Below is data of my Toyota car engine 2NR-VE's geometry, 4 cylinder but in this case I take only one cylinder:
Total cylinder ...
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What is the correct way to calculate the efficiency of a heat exchanger?
I want to evaluate the efficiency of a heat exchanger. From measurements I know all four temperatures $T_1$, $T_2$, $t_1$ and $t_2$ as well as the mass flows of both fluids $m_1$ and $m_2$ and if ...
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Electricity generation from sand particles in airstream hitting surface [closed]
I read an experiment which demonstrated that metal filings fired at a surface using air blasts charges the particles, surface and airstream. I understand this is triboelectricity, resulting from ...
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Volume of air going through a hole with a temperature difference, and kWh of energy
Let's say we have a square hole of 2cm x 2cm in a wall.
The inside temperature is 20°C, the outside temperature is 10°C, so $\Delta T = 10$.
This creates a flow of air. Let's say the velocity is $1\ ...
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How to interpret the Otto Cycle PV diagram?
AFAIU this is the practical Otto cycle with the added isobaric stroke for when the piston intakes and expells through the valves.
However, there's one thing I don't understand: AFAIK, PV diagrams ...
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Should I put the peltier module at the bottom of the aluminum block?
I'm new to this project. We have an ice chest with a cooling and warming system attached on its lid. The switches etc. were corroded because the lid is very old. It has been sitting around for years ...
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Stress Strain Analysis In Wall
I have a 20mm thick and 10m long wall. On one side of this wall (inner) is 80 degree celcius water, the outer side is air at an ambient temp of 20 degrees celcius. My coeff of thermal expansion is 15e-...
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How to estimate air velocity at turbine in turbojet?
I am designing a small turbojet. I wanted to know how to calculate the air volume expansion to predict the outlet velocity of air towards the turbine. Theoretically, I wouldn't know the flame ...
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Heat needed to prevent freezing of valve expanding compressed air
I am designing a system that is constantly flowing compressed air through a valve which is open to the atmosphere. I would like to size a heater to keep the valve at a constant temperature and prevent ...
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Will hot object near ceiling vent create more draft?
As in the picture, we have a room with vents at the bottom to let cold air in and at the top to let hot air out. Normally the air flow is limited by the temperature gradient (correct me if I'm wrong). ...
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Using the electrolysis of water to cool a room
Browsing the internet yesterday I came across this very esoteric paper which purports to describe the construction of a device which uses the electrolysis of water into hydrogen and oxygen (a highly ...
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Nusselt number equations for external flow over a single finned tube heat exchanger
I am designing a heat exchanger that will utilize a singular finned tube of around 2" diameter with 4 fins per inch that are 3/4" tall and .03" thick. I am looking at finding the ...
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Practical application: questioning the value of insulating a car battery
Living in the north, I am wondering if a sitting car battery's chemical reactions give off enough heat to justify insulating it. That is, will it result in significantly more power available to start ...
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Question About Dimensions and Figures Surrounding A Pressurised Nitrogen Canister
I need a nitrogen gas canister that will nitrogenate a beverage much like how SodaStream carbonates. Here are some approximate numbers:
The beverage to nitrogenate is 600 - 1000 mL
I want to be able ...
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Whats the advantage of variable speed furnace blowers?
I'm in the market for a new heating and air conditioning unit for my home. Most offer variable speed blowers and the more expensive models are equipped with BLDC motors, which seem overkill. I am ...
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Implementing convective boundary conditions for 1-dimensional finite difference computation of heat equation
I am simulating heat transfer through a 1-dimensional wall with convection on both sides. For the wall, I implemented a finite difference model like this:
$$
u(x, t + ∆t) ≈ u(x, t) + c [u(x + ∆x, t) − ...
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How is flow energy different from kinetic energy of a flowing fluid in a control volume?
While I am studying about Mass and Energy analysis in Control volumes in Cengel and Boles I came a across a term called flow energy. The textbook definition that was given is as follows - "The ...
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Heat losses of warm fluid in a cold pipe
I'm looking for a way to calculate/estimate heat loss in a fluid flowing trough a pipe for a length (l) and travel time for the fluid (t). The flow is intermittent and the initial pipe temperature (...
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Any real heat engines based on the Carnot cycle? (or an equally efficient cycle)
Most practical heat engines are based on ideal cycles whose processes are different from the Carnot cycle (eg; constant pressure or constant volume heat addition instead of isothermal). I understand ...
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Understanding chiller performance curves
Recently I was tasked with some chiller-related tasks and I need to understand the performance model. More specifically, I am interested in the EIR EnergyPlus chiller model.
The chiller's performance ...
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Optimal blade/paddle design for low-budget Friction Heater (Joule Machine)
Generating heat by stirring fluids
I am interested in the direct conversion of mechanical energy into thermal energy as it was done by James Prescott Joule. For context: I was inspired by the danish ...
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Vacuum Tank Emptying Transient Equation
I am trying to derive the differential equation for pulling vacuum on an air tank.
The solution to the ODE:
$$P(t)=P_2 \cdot exp(\frac{dV}{dt} \cdot \frac{t}{V_s})$$
Where $\frac{dV}{dt}$=
flow rate ...
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Process engineer dairy
For a project I really need to know some number I can't seem to produce myself.
We are flashing water at 75°C. The water after flash-cooling is 67°C. Constant pressure is 0.27 bar (absolute) flow ...
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Determine the temperature required for expanding or bending?
Is there any possible way to calculate the temperature required for a metal to expand or bend with dimensions?
For example, take Mild steel with a length of 100mm, width of 150mm, and thickness of 2....
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How to find work done by compressors
Which one is correct method to find work done by a isentropic compressor?
Method-1:
Compressor power = mCpdT
Where m = mass flow rate
Cp = specific heat at constant pressure
dT = Temperature ...
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How to solve this thermal equilibrium
I was studying and came across a problem that I'm not sure how to solve. In fact, I think it gives me 1 degree of freedom. In the problem, I am asked to calculate the time and temperature required to ...
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Would this work as a solid fuel heat engine that didn't need to boil water?
Would this engine design work. Is it already a known design.What would be the upsides and downsides? What else would you do?
Air gets compressed by some mechanical compression like a rotary compressor....
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Calculating time to heat up a flowing fluid. Units not matching up
I have an electric heater that can output 915.4 kW of power. I have fluid (isobutane) flowing through the heater around 1 kg/sec. The starting temp is 172.5 °C and the required temp is 343 °C. The ...
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Why is pressure not considered in calculation of 'Maximum achievable velocity of a gas'?
While reviewing the basics of Gas dynamics, I came across the eq for the maximum achievable velocity by gas.
Ref from Wikipedia
This is the velocity that is achievable by the gas by converting the ...
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About a "Tech Ingredients" jet engine explanation: it doesn't describe the Brayton cycle, so what is it?
This question is about a thought experiment described in this YouTube video: https://youtu.be/JzwfzgfJiJ4?t=1139
The video is attempting to explain how a jet engine works, specifically, the importance ...
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Stirling Engine - Geometery, Timing, Compression Ratio, Seals
Inspired by this video: Making the World's Smallest Beam Stirling Engine, I wish to make a small Stirling engine like the one shown in the video.
Based off that video, I have modelled all the parts in ...
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I want to transfer heat from a solar concentrator to be stored in a sand battery , which heat transfer fluid is more viable , cheap and easy to use?
I am searching about connecting a solar concentrating system to a sand battery so I need a viable ,cheap and practical heat transfer fluid to distribute and store solar heat into the sand layers up to ...
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Advice needed on how to cool 50 ml liquid from 60 °C to 30 °C
In Short: I'm working on a project where we need to cool 50 ml of liquid from 60 °C to 30 °C or 20 °C. The liquid will be in a 150 ml copper container with an open top.
Due to the lack of skills in ...
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Phase diagram for 1,3 butadiene + acetonitrile binary mixture
Acetonitrile (82 deg C b.p) is used to absorb 1,3 butadiene (-4.4 deg C b.p) in several manufacturing processes. I am looking for a binary phase diagram at 1 atm. The only thing I could find was ...
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Can water in a small container increase the humidity of the surrounding area?
I have been instructed to keep a liquid drug in a cool and dry place (away from humidity), at temperature not exceeding $25^\circ$ C, but also to avoid freezing it, as it may crystallize. On a very ...
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Entropy change in particle electric dipole alignment
Suppose a bunch of micron sized particles are charged positively on one half of their surface, and negative on the other. If they are arranged randomly, I understand they will have high entropy, as ...
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Why is there a MIN and MAX marking on a car coolant bottle?
This question was initially posted in physics stack exchange, then the mechanics stack exchange but I think it's more appropriate for engineering section instead.
I've always thought the minimum and ...
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What is the theoretical explanation of flow work/energy?
Given the following definition of flow work:
Reading and following the derivations I understand that in theory, this is only accurate when the fluid accelerates from rest. However, if we consider ...
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My question is thermodynamic
What can I use to cover a mirror that is a backsplash at my stove which protect it from shattering with high heat? 44x28 inches
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Pin Forest Heat Sink Design and Optimization
I am trying to design a heat sink as part of a broader system and determine two things:
Given the size constraints of the system, commercially available fans, and heat dissipation requirements, is it ...
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Would steam locomotives be more efficient if the working fluid had a lower latent heat?
This is a cross post from physics where this question didn't get an answer - it seems relevant here too.
People often express an idea that steam engines would be more efficient if they used a working ...
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Trying to calculate heat transfer into an insulated rectangular box in the sun
I am trying to calculate the BTU/hr of cooling needed for an RV. I am willing to assume it is an 8'x16'x8' box with no windows with uniform insulation (lets say R15 if it matters) on all surfaces. ...
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When fluid hits a surface or object, why doesn't its energy decrease?
In turbojet (gas turbine engines), we analyze fluid in terms of pressure. We say that when fluid/air hits stator of compressor, its velocity decreases but static pressure increases due to Bernoulli ...
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Plotting Muzzle velocity vs Pressure graph
I am trying to replicate the following plot between projectile muzzle velocity and initial gas pressure. The equations are as follows:
$$u_p(t)=\frac{2 c_0}{\gamma-1}\left\{1-\left[1+\frac{\gamma+1}{2 ...
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Is thermal expansion of water a consideration in steam power plants? If so, how is it managed?
I understand in residential plumbing, that a thermal expansion tank is needed before the hot water tank. From my understanding this is to allow for the water in the hot water tank to expand, instead ...
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Would injecting water in a turboshaft engine avoid turbine material meltdown?
For the little I know about turbine engines, I know that these run at enormous high temperatures and thus, need nickel based superalloys.
From what I know, jet engines use a smart use of air flow ...
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What is the impact of energy control in an AC in terms of cooling and power consumption?
Nowadays many inverter ACs come with energy saver modes claiming to run at 80% 60% etc…
In this case wouldnt the cooling capacity also decrease? For eg if the AC is running at 60%, the AC compressor ...
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Why modern diesel engines have low compression ratio?
Modern diesel engines have low compression ratio (some only 14:1, old diesel has 23:1), if compression ratio is directly connected to thermal efficency, how this engines achieve good efficency?
Can ...
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Work done in an Adiabatic Process
My question is, where did they get the equation of work done? So far I know only one equation: $W=\dfrac{mR\left(T_1-T_2\right)}{\gamma-1}$
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