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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How to work out the kWh required to compress hydrogen gas?
I am trying to work out the kWh/kg of compression of hydrogen. I have used the isentropic compression calculations and get values for the entropy but am unsure how to get this to a kWh value. I might ...
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Does forced convection account for energy transfer in this case?
I have to confess that thermodynamics is not a friend of mine.
My system consists of a volatile droplet sitting on a thermally conductive substrate. The energy balance comprises heat lost due to ...
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DLC wear resistance
I read that a thickness of one micrometer of DLC coating (which, if I understood correctly, shows similar properties to diamond), increases the lifespan of an item plated with it from a week to more ...
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How to calculate the required power to pump out (to vacuum) a container?
Consider I have a cubic container with its volume is 1m cubic as in the simple picture above. It is sealed nicely, it is air proof, no air leaking. I would like to pump out (to vacuum) the container ...
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Do the models of reversible cycles like the Carnot Cycle help engineers in any way to design real Heat engines?
Is there any use in engineering for this kind of very abstract models other than setting an unachievable upper bound on the possible efficiency of heat engines? Can they help in the design of more ...
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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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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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Thermodynamics question
I am looking for help with the following question please.
A piston cylinder device contains 28g of saturated water vapor that is maintained at a constant pressure of 300 kPa. A resistance heater ...
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Derive a heat equation for a shrinking nanoparticle
I consider a spherical nanoparticle (NP) that is shrinking, for instance due to a melting process. I know that the pressure $p$ is proportional to $1/R(t)$, where $R(t)$ is the radius of the NP at ...
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Empirical correlation for low reynolds convective heat transfer coefficient
I am looking for a heat transfer coefficient for a shape (rectangular cross section preferred, could estimate with flow over flat plates) in 2 m/s cross flow.
I have found a few empirical correlations ...
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Why isn't it possible to build a car moved by wind power?
So, first of all, I am a High School student and I wanted you to explain me something (in a more "concrete" way, if you know what I mean): I had an idea the other day to make a car with a wind turbine ...
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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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Does wiring heat elements in parallel vs series at the same power affects the results?
I am designing an electric kiln just for fun and I found myself not knowing how to answer this scenarios.
The main constant is power. The final power must be the same in each case. My question is ...
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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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How to calculate internal convection loss in a sealed container?
Say I have a box with a 1m x 1m x 1m interior wall dimension.
The side walls and the floor are 10cm of styrofoam, with a thermal conductivity of 0.03 W/m K.
The top is 1cm thick opaque plastic with ...
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Rate of heat loss of a block of dry sand over time
I have a rectangular block of dry sand I'm using as passive thermal heater, that's heated by the sun.
Dimensions are 1.0m long, 0.5m wide and 0.5m deep ( 0.25 m3 )
Assume the block of sand is stand ...
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Blower door DIY test
Since in my area there is no way to do a blower door test for a house, I was thinking to do a DIY blower door test. Here is my test scenario:
Preheat the house before testing to have 10 degree ...
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Deviation of Ideal Rankine Cycle from Actual Rankine Cycle
I'd been having difficulty with a problem from Cengel and Boles, Thermodynamics An engineering approach. The problem is about the deviated Rankine cycle from Idealised ones.
The question I would like ...
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Wire heating and heat transfer in a cylindrical pattern
I have a series of copper coils with ¼” cooling plates between each coil. The cooling plates will be manufactured from aluminum and cooled using copper tubing. There are seven in series, and a plate ...
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PV diagram from cubic equation of state
I want to calculate the density of CO2 using a cubic equation of state in order to plot the P-v diagram. From theory I know that I get one real root when the substance is in single-phase region and ...
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Entropy change in a throttling process
In an adiabatic throttling process of ideal gas:
I understand that mathematically lost work is given by Tsurr * entropy generated.
But intuitively I can't understand if there is not heat exchange ...
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Using the Psychrometric Chart to calculate volumetric flow rate
Blockquote
The inside design conditions for a conditioned space are 20.1°C dry-bulb and 15.2°C wet-bulb. The air tem- perature increases 10.6°C as it passes through the conditioned space. The ...
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Isn't the Bernoulli equation just a special case of the Steady-flow equation?
This question is about the following two energy balance equations (assuming no energy input/output):
Bernoulli: $\frac{p}{\rho} +\frac {v^2}{2} + zg = const.$
Steady-flow: $u +\frac {p}{\rho} +\frac{...
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How can a non flowing fluid have kinetic energy?
I am currently studying engineering thermodynamics from Cengel and Boles and there it is given that total energy of non flowing fluid per unit mass basis is given as $e=u+\frac{v^2}{2}+gz$.But if the ...
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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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High thermal conductivity in soft, fleece-like textiles
Fleeces typically exhibit low thermal conductivity, and are often used in winter clothing for their insulating properties.
I am seeking a material for a radiant heat application that is soft to the ...
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In the Rankine Cycle, how does the condenser work without changing the temperature or pressure of the fluid?
The condenser changes the state of the fluid from a saturated mixture to a saturated liquid by rejecting heat, yet the process occurs isothermally and isobarically. How then does it manage to perform ...
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Doubt regarding meta-stable and labile region of a supersaturated solution
I have read in a paper that the for formation of new crystals in a solution the energy released due to formation of solid from solution should be more than the energy needed to overcome solid-liquid ...
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Would stillsuits as in the Dune movie actually work?
Could the stillsuits worn by the Fremen of Dune actually work? Stillsuit
Ever since I first read Dune, when I was much younger, I have wondered about the efficacy of these stillsuits. A person sweats,...
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Assumption of specific enthalpy
Given an adiabat turbine with state 1 fluid data as:
$$h_1 = a$$
$$p_1 = b$$
$$t_1 = c$$
and state 2 data fluid data as:
$$h_2 = unknown$$
$$p_2 = e << b$$
$$t_2 = f < c$$
$$h_2' = g$$
$$h_2''...
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Enthalpy of Fuels
I am running some analysis on an engine cycle through matlab using TMATS with Cantera. I am looking to change the fuel from the default to a blend of ammonia and hydrogen. In order to do this I have ...
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What is a thermodynamic process that is not polytropic?
In discussion under another question, it was pointed out: "Not every process is polytropic; that is just a special case when $pV^n$ is constant" Must have missed that in school.
What is a ...
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Recommendations for accessible thermodynamics textbooks?
I've recently started a new job where my very, very limited thermodynamics background (intro + intermediate, 10+ yrs ago in undergrad) is starting to be an issue. I am looking for recommendations for ...
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Why does a compressed gas duster get cold?
I have a compressed gas duster with difluoroethane as the gas. When I shake the bottle, I feel sloshing, so I assume that it is a vapor liquid mixture inside.
When I expel the gas, the can gets cold ...
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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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How does humidity, specifically using a humidifier, affect the filtration of PM2.5 particles from a room?
I live in a very smokey and dry area where people are advised to use air purifiers. Since it's also dry I'm curious what affects, if any, adding a humidifier to a room with an air purifier would have?
...
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Why is the compression considered as isentropic in Otto cycle?
We know the ideal Otto cycle is modeled by the two ideal processes isentropic (compression and expansion) and isochoric (heat addition and heat rejection). But why the compression and expansion ...
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Help needed understanding atmospheric tank vent physics principals
I try not to be a complete moron but am not an engineer so please bear with me. I have this LP record ultrasonic cleaner system that uses a solution stored in a "tank" which is a simple ...
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Is it possible to use two sets of stator blades after each set of rotor blades in an axial compressor?
I am currently designing an axial air compressor for a project, and I require the stator blades to reduce the velocity from 50m/s to 2.5 m/s in each stage of the stator. This requires a ratio of the ...
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Consumption modeling of wood in a boiler
I know very little about thermodynamics, and I need it to do my master's dissertation in Operations Research. I don't know if what I did is correct, and if it is, I don't know how to model the amount ...
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Why air cannot be used as a cooling medium in CO2 refrigeration system?
Can anyone please explain the reason for above question?
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Heat convenction through double pipe
I have a realistic scenario which involves a double contained PP plastic pipe which a section of the pipeline is placed outdoor. What I want to determine if insulation is required at all. The media is ...
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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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What is the behaviour of water at a pressure reducing valve (PRV)?
Suppose I pass water through a pressure reducing valve, which can lower the pressure enough for the water to boil, will the water fully boil? If so, what would happen if that vapour passed to a tube, ...
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What effect does airflow rate have on heat dissipation if the initial heat varies proportionally to the airflow rate?
If I have a server rack consuming 10 kW of power in an empty room with A/C, what effect does the rate of airflow from the rack's exhaust have on the temperature in the room and the load on the HVAC?
I ...
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Is it possible to find heat flux without emissivity value?
In this question there is a value given for absorptivity of infrared radiation however in order to work out a value for heat flux emitted from the solar panel in order to answer part (a) surely I'd ...
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R value of a hole?
Suppose I have a room, 10x10x10m with insulated walls (R-value: 4) and a single double-pane window 1x1m (R-value: 0.35).
Now the total thermal power required to keep the room at a desired temperature ...
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Heat added per unit mass in a cylindrical pipe
I have a question, which seems simple, but for the life of me I cannot figure out.
So, let's say I have a very thin cylinder (consider an interface), between two fluid with different temperatures. The ...
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Thermodynamics Adiabatic process
This is the question please:
1 kg of steam is at 100 bar and 375 °C expands reversible in a perfectly thermally insulated cylinder behind a piston until the pressure is 38 bar and then steam is dry ...
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Can $R$ value be estimated by change in temperature over time?
Suppose a closed sphere with a hull and an $R$-value of $10$ m2 K/W and a radius of $1$ m. Suppose the temperature inside of the sphere is Ti, the temperature outside is To. The inside temperature is ...
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