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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 powerful would a laser need to be to melt through an iron girder from a distance of ~260m?

Merely a curious fool contemplating how plausible it would be to cut the Eiffel Tower in half with a massive laser (you know, for fun). What kind of laser would it take to cut an iron girder from ...
Ariadne's user avatar
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Help Needed: Looking for Sample Phase Change Material (PCM) Calculations

I am working on implementing a Phase Change Material (PCM) system for a cold storage facility. While I'm familiar with traditional refrigeration systems, I'm relatively new to PCM technology and would ...
Neo Mech Eng's user avatar
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Parameters to characterize heat dispersion

I'm working in a team to model some production machinery in a factory. They ask me to find a way to describe and quantify the heat loss to be able to make an initial and approximate comparison between ...
M4rc0txt's user avatar
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How to derive the relation of a and b according to critical points (including compressibility factor) from Peng Robinson EoS

I've been trying to prove the relation of a and b according to critical points of PR EoS: prove that a and b are: a = 0.457 (R^2T_c^2)/p_c , b=0.0778(RT_c)/p_c I tried to prove it by doing the partial ...
roee danan's user avatar
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Mass flow rate through a turbine in order to produce a 852 kWh

Over a $30$-day period, $852$ kWh of energy is produced by an electric generator, which has an efficiency of $80$%. The generator is spun by an ideal turbine. What is the mass flow rate, in $\frac{kg}{...
Eric Brown's user avatar
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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 ...
Metadani's user avatar
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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 ...
user47337's user avatar
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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 ...
blair's user avatar
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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 ...
Patrick12341's user avatar
2 votes
4 answers
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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,...
Rich's user avatar
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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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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 ...
Synchronicity's user avatar
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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 ...
DaleCloudman's user avatar
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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 ...
Julian Leland Bell's user avatar
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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 ...
Milos Radojevic's user avatar
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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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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 ...
wasbo's user avatar
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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 ...
Manish S's user avatar
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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 ...
Dfhaa_DK's user avatar
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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 ...
Chris's user avatar
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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 ...
divB's user avatar
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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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How estimate the error of chemkin 2.55 results?

I've been using chemkin 2.55 for preliminary calculations of premixed laminar H_2 and CH_4 combustion and in some of the calculations, the solver fails. There is a way to hypothesize the calculation ...
gcomp4's user avatar
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Behaviour of a mixture of ideal gases

If we have a mixture of ideal gases can we consider the mixture also an ideal gas? This holds true in air for example where we consider it an ideal gas, when oxygen and nitrogen are considered ideal. ...
Youssef Mohamed's user avatar
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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 ...
Josa Ferreira's user avatar
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How do I derive the expression of boundary work in relation to a polytropic index?

I don't understand how to derive the formula, How do I derive the expression of boundary work in relation to a polytropic index? I used the Definition of boundary work for a polytropic index, the ...
AxeNoQuestions_ DrawNoLines Sh's user avatar
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2 answers
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How to calculate the optimum heat absorption rate of an object?

Consider I want to heat 1L water in a 1L aluminum container. That container I put on my stove that I heat with gas. I want to know, what is the optimum energy I can deliver to cook that water ...
AirCraft Lover's user avatar
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Suggestions for estimating Heat Load (watts) in an evaporator (antifreeze - hot fluid, R744 - cold fluid)

I am working on simulating an evaporator for an R744 refrigeration cycle. Here, I have inlet conditions of R744 with low pressure (around 30 bar) and low temperature(-8°C) and that of antifreeze (35% ...
ascruine's user avatar
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Designing a microwave based vacuum dehydration system

I am designing a Microwave based vacuum dehydration system for waste management sector and food dehydration. Currently I'm using a 3kw output 2.45GHz magnetron as heating element. My vacuum pump is an ...
Rohan Abraham Mathews's user avatar
1 vote
2 answers
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How does an expansion valve cool fluid?

How does fluid loose temperature after leaving an expansion valve in a refrigeration cycle? Where does this heat go?
leoJ's user avatar
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Calculating heat loss over a maple syrup pan evaporator

I am working on a final project for my thermo-fluids design course, and I am designing a maple syrup steam evaporator. The sap enters the evaporator through a 1.2 meter wide channel at ambient ...
remusconnor's user avatar
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1 answer
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Need advice on building small incubator

I need to build an incubator that can vary temperature between 32 degrees and 36 degrees Celsius with discreet or continuous control. It needs to be made with perspex. It needs to be a two chamber ...
Iskander's user avatar
-1 votes
1 answer
53 views

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 ...
AirCraft Lover's user avatar
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1 answer
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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 ...
Axel's user avatar
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2 answers
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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 ...
El Flea's user avatar
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1 answer
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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\ ...
Basj's user avatar
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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 ...
popeye's user avatar
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2 answers
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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 ...
Rudolph's user avatar
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2 answers
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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-...
jude's user avatar
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0 answers
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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 ...
user43461's user avatar
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1 answer
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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 ...
charlp's user avatar
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1 answer
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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). ...
El Flea's user avatar
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2 answers
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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 ...
Hadi Khan's user avatar
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1 answer
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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 ...
Brad Lasley's user avatar
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2 answers
26 views

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 ...
empleadozera's user avatar
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2 answers
27 views

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 ...
user148298's user avatar
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1 answer
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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) − ...
Dave's user avatar
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2 answers
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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 ...
Prasanna B's user avatar
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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 (...
mephisto73's user avatar

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