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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Will a cyclic heat load transform my martensitic steel? How fast?

I have a plunger - that I'm using for glass forming - made out of a martensitic steel. Glass is at 1000°C and since martensite is a metastable phase, should I expect the properties of my plunger to ...
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40 views

Could boiling water inside a semi-enclosed pipe be a low-cost method for a silent marine propulsion system? (redesigned)

I am wondering if boiling water that is trapped inside of a semi-enclosed pipe would be a low-cost method of creating an underwater thruster that would function as a silent marine propulsion system. ...
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43 views

Steam cycle for a boiler / radiator system vs Rankine cycle

Everything I've read on the Rankine cycle indicates that the feedwater pump is necessary for the cycle to work. However the steam cycle used in traditional household boiler / radiator systems seems to ...
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1answer
52 views

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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15 views

How to minimize temperature increase caused by compression of a cryogenic liquid in a multistage high pressure turbopump?

The cryogenic fuel I'm using is methane at 100 K and 300,000 Pa. Based on my calculations, after compression, the pressure is 55 MPa and using the ideal gas equation the temperature is approx. 800 K. ...
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47 views

How is the flow work PV?

I am reading thermodynamivs from cengel and boles.I am currently studying flow work.Following image contains text of the book. (https://i.stack.imgur.com/eCGXR.png) The workdone is calculated by ...
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1answer
16 views

In a warmer/sunnier climate, window (or roller shutters) superior to curtains?

When -on a hot day- the sun is incident on a window covered from the outside by a closed window shutter, the resulting heat is absorbed by the layers of air surrounding the shutter, subsequently ...
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16 views

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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33 views

What pressure is taken as the pressure of liquid

I am learning pure substances in thermodynamics.I read a sentence "Consider a piston cylinder containing liquid at 20 degree celsius and 1 atm pressure."My question is that the pressure of liquid ...
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1answer
25 views

What happens in a cone-shaped nozzle?

So I am learning for thermodynamics now and there is one thing that is bugging me. In the book it shows a laval nozzle (very simplified) and a diffuser. with the formulas: (a is the speed of sound) ...
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45 views

Ideal gas law, theory vs reality

I am trying to get an idea of the amount of hydrogen that I can store in some pressurized steel tanks underground. Based on the ideal gas law PV=nRT I did a simple calculation pressure = 200bar ...
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48 views

Efficiency of TurboJet engines with nozzles

As per Bryton Cycles, most of TurboJet engines' Thermodynamic efficiency should be around 40%. Rest of energy gets rejected as waste heat in exit gases of after the turbine. But if these hot gases ...
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32 views

Effect of Pressure on Combustion efficiency (of hydrogen) in excess air

Can somebody explain relation between combustion efficiency and pressure in lean mixtures using any kind of chart or mathematical equations? At first glance I thought, combustion efficiency increases ...
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29 views

Why doesn't steam/water flow backwards from expansion in power plant feedwater pump/boiler? [duplicate]

I think i understand the mechanics in a steam locomotive: Fill boiler with water Close off boiler Heat boiler until pressure is sufficient Keep boiler hot and use steam pressure until no more water ...
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1answer
13 views

Is there a way to calculate the heat capacity of a solid or volumetric heat capacity of a solid oxide fuel cell?

I am working on a personal project and wanted to use a solid oxide fuel cell to power up a load (I have not decided what yet), so I am trying to find a way to estimate the power I would need to heat ...
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30 views

Does utilizing exhaust energy to supercharge (“turbocharging”) increase the thermal efficiency of a gasoline internal combustion engine?

The work done by a turbocharger increases the inlet charge without much of a burden to the exhaust flow. This increases the amount of air (and fuel) that flows into the engine. How does this affect ...
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23 views

Could I define an isothermal efficiency?

There's an adiabatic efficiency because real processes can't be adiabatic. I want an isothermal compression (yes, I know an adiabatic compression consumes less work, but my pressure differential is ...
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41 views

Search for comprehensive term for plants with heat generation with heat storage and operating states

My master thesis deals with systems with several operating states that generate heat and store it in a heat storage. Thereby I analyze combined heat and power plants with combustion engines, but also ...
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38 views

Difficulty to reach Mach 1 by blowing into a small converging-diverging nozzle?

I'm learning about the basics of converging/diverging nozzles in my thermodynamics class, and it has me curious. Could you theoretically blow into a tiny converging/diverging nozzle and break the ...
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22 views

How to build multiple large scale fish tanks with water at different temperatures

I am wondering at a high level what are the material components that might be used in building several large scale fish tanks that are temperature regulated like on a fishing farm. For example, what ...
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2answers
51 views

Cooling Down Fridge Encased in wooden box

I'm currently working on a project which involves a small fridge encased in a wooden box. It's designed for hotels and the boxes vary slightly, but one common trait is that the box has an open vent ...
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How do you calculate the temperature after methane combustion if liquid H2O is sprayed into the combustor?

Calculating adiabatic flame temperature is pretty clear in thermo books, but how would you determine the temperature if liquid H20 was sprayed into the combustion chamber simultaneously? Thanks
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Solar Heat Gain/Outside Temperature Effects on a House

I'm currently a sophomore Mechanical engineering student and need some help with an equation for my project. I am coding a simulation in Matlab and have been given a very short time frame to do it. I ...
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41 views

Steam at 1 MPa, 300°C flows through a 30 cm diameter pipe with an average velocity of 10 m/s. The mass flow rate of this steam is:

Steam at 1 MPa, 300°C flows through a 30 cm diameter pipe with an average velocity of 10 m/s. The mass flow rate of this steam is: A) 0.731 kg/s B) 2.74 kg/s C) 3.18 kg/s D) 3.78 kg/s Can anyone ...
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14 views

Efficiency of a sterling engine

What is meant by thermodynamic efficiency of a sterling engine? and what are the factors that affect the thermodynamic efficiency of a sterling engine? Similair to other questions i know despite ...
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1answer
26 views

Doubt in proof of condition dG<=0

I tried proving the condition dG<=0 where G is Gibb's free energy and instead ended up proving dB<=0 where B is exergy. Can someone please explain what went wrong with my derivation. I have ...
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6 views

Is there a formula to relate the axial length of a nozzle expander with its radius?

I know the inlet, throat and outlet areas for a nozzle expander. Is there a formula to know its axial length? Something like L= f(A) = f(D).
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19 views

Gasturbine energy balance

I have a question regarding gasturbine energy balance, the total energy that flows into the gasturbine is given 12 MW and the power needed for the compressor is 4.4 MW and the turbine power is 9.3 MW....
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17 views

Is it feasible/possbile to do regenerative cooling of ScramJet or Ram jet powered aircraft surface?

Thinking of ScramJet/RamJet powered aircraft for unmanned vehicle. One of the challenges in designing such an aircraft is surface heating. Just like Rocket nozzles are cooled regeneratively with fuel(...
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1answer
32 views

What's the minimum area ratio required to achieve choking in Converging nozzle?

Is there any equation for minimum area ratio (Throat area (At)/ Combustion Chamber area (Ac) ) required for choked flow in convergent nozzle (just like equations for minimum Pressure ratio and ...
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Feasability of melting through ice crust with radiocative heater

I'm pretty interested in space exploration. Here I'm interested in a moon of Jupiter (Encealadus) which is covered by a thick ice crust, but apparently has at some depth a liquid water ocean which ...
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1answer
100 views

What is the meaning of dew point -20 or -40 or -70 deg.C? Since below zero centigrade, water cannot dew (already freeze)?

I saw these specifications listed for a compressed air dryer (desiccant type). I also wonder, can we extract moisture without make it liquid (dew) first when in it is in a vapor state? How would we do ...
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36 views

equivalent deduction of Non-mechanical thermodynamic work

"Work (as in Thermodynamics) is said to be done by a system if sole effect on the surroundings could be the raising of a weight." So, how is non mechanical work like : Chemical work, Magnetization ...
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31 views

Minimum distance between long curtains and radiator for good air flow?

It's a known fact that you cannot place a curtain near a radiator because it will trap hot air behind the curtain and also block cold air from going through the radiator from bellow. But obviously ...
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1answer
53 views

Calculating the Surface Temperature of a Cable with known heat flow

I have a cable which dissipates $\dot Q_{total}$ and I need to determine the surface temperature of the insulation $T_{ins}$ and the surface temperature of the conductor $T_{cond}$. There is an ...
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1answer
46 views

Fluid Mechanic Buoyancy problem. How to determine the height?

I tried to solve it but I don't know how to bring the Area A in this equation. I used the area of the small vessel, but this one shouldn't be in the equation. Thanks a lot
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1answer
48 views

Air conditioner using liquid nitrogen and a cryogenic heat exchanger

I have been trying to understand if compressor-based systems in air conditioners can be replaced to make something more economical and energy efficient. From what I understand, the compressors ...
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1answer
35 views

calculating the efficiency of a microwave oven

If I want to calculate the efficiency of a microwave oven, I have the input Energy (= power (watts) x time (s)) and the output which I measured using temperature difference (q=mct). So do I divide ...
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43 views

Enthalpy vs Heat

If we have a closed cylinder filled with a gas and we heat it, by $1^{st}$ law we have: $\Delta q=\Delta U$ (?) since $\Delta V$ = 0. But $\Delta H= \Delta U+ V. \Delta P$. What does that difference ...
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36 views

Industrial scale heat pumps

I've read (1) that the efficiency (COP) of a heat pump does not change much with size. If that is true, why don't power companies employ them to produce yet more power from fossil fuels or renewables? ...
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32 views

How to calculate adiabatic air temperature loss caused by increase of humidity?

I'm searching for an approach on how to calculate the adiabatic temperature loss of air when increasing its humidity by a humidifier. Assumed we have the following setup: Air measuring position 1 (...
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1answer
73 views

Practical Application of Adiabatic processes

The concept of Adiabatic is basically the isolation of a system in a realm where energy doesn't flow either way. Adiabatic compression and expansion is a common phenomenon harnessed in equipments and ...
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Designing a submersible cooling system for rapid flow hot nitrogen gas [duplicate]

I'm trying to design a cooling system for cooling nitrogen at 300°C. My original design (which is very open to modifications) is an aluminum ring block with exterior fins and vertical holes through ...
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1answer
38 views

Is thermodynamic data of fresh water a good approximation for saline water?

I am currently working on desalination project for my final year. The design is based on flashing of hot liquid in low pressure vessel and then condensing the extracted the steam to produce pure water....
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Would an afterburner on a turbine drastically improve acceleration lag?

A little bit of context. My friends and I were watching the "Dark Knight Rises" and a discussion about the Batmobiles ensued. I, being a former ME student, said it was stupid that batman has a turbine ...
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172 views

Cooling Hot Nitrogen with an aluminum block

I'm designing a cooling system to cool nitrogen gas stream at 300°C with a mass flow rate of 15.6 g/s moving through an undulating channel in a cylindrical aluminum ring block with external fins. How ...
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68 views

How can I calculate the amount of heat my copper water trap can dissipate?

My small (1.5hp) air compressor is connected to a water trap made of 8mm copper of about 4 metres length. The idea is that you push the compressed air through the piping which cools it, condensing the ...
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47 views

Does a tank of liquid nitrogen increase in total internal energy after emptying?

Suppose there's a 10 liter perfectly-insulated sealed tank of saturated liquid nitrogen at 4 bar. Therefore the fluid has properties, $\rho=740 \,\frac{\text{kg}}{\text{m}^3}$, $m=7.4 \,\text{kg}$, $\...
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16 views

Why can we extend the derivation of delta(S mix) to ideal solution from ideal gas behavior?

The formula for change in enthalpy for ideal gas is derived using ideal-gas law which cannot be extended to ideal solutions (my intuition). Then why can we extend the formula of delta S mix to ideal ...
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47 views

Classic Thermodynamics: Ideal gas question

The question is in the attached picture. I know how to solve the first part of the problem, but the second part confused me a lot. Now when the oven (system) is unsealed, doesn’t make that an open ...