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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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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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64 views

How to determine the time it'll take a mass of aluminum to absorb a specific amount of heat from a gas flowing through an undulating cavity in it

I'll like help with calculating the time it takes a mass of aluminum block with an undulating channel through it to absorb heat from nitrogen gas at 300°C flowing through that channel. On the flip ...
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42 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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41 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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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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32 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 ...
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20 views

How to derive phase equillibrium criteria for more than 2 phases mathematically?

I know the derivation of phase equilibrium criteria derivation for 2 phases. I am not getting how to extend the derivation to more than 2 phases. Please help me out on that. Thank you
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Evaporating temperature of NH3

Considering a flooded evaporator (using plate heat exchanger - PHE). Cold NH3 liquid from a surge drum supplies to the PHE to cool down water from 30 oC to 3 oC. The evaporating temperature of NH3 is -...
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7 views

Deriving Enthalpy in terms of (T,V) and (T,P)

We are being asked to develop thermodynamic expressions for the enthalpy of a system in terms of (T,V) and (T,P). I understand that the Legendre Transform can be used to find H=H(S,P), but I'm getting ...
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Developing a model of rate of cooling of steel tube in air

I am trying to develop an equation to determine the cooling rate of a steel tube in air. I'm using Fourier's Law, Stefan-Boltzman Law, Newton's Law as well as the specific heat capacity equation. The ...
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1answer
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Fit NRTL parameters for an immiscible system

Problem description: I need to know the liquid-liquid eqilibrium behavior of a THF-water-toluene system. I need to use NRTL because UNIFAC does not predict THF-water systems accurately. I have ...
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1answer
25 views

Calculating geothermal heat pump

So I need to calculate how big geothermal heat pumps I need for a building. Heat pump is used for heating and to heat used water. If I know how many kW's are needed for heating the building and the ...
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2answers
94 views

Save money with using a refrigerator correctly - blowing cold air to the back of it?

We are heating up our houses in winter to ex.: 21C to then have an insulated box inside the house, which we cold down to 5 and -15C, and we call it a refrigerator.. :) The situation: we would buy a ...
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1answer
39 views

Working of a fan or propeller

I can roughly understand the working of an axial flow gas turbine i.e. the fluid moves over the blade and gets redirected, its whirl velocity component changes and the blade is pushed in the opposite ...
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36 views

Is using a radiator to warm water inefficient and if so why

I'm currently designing a Hottub for my scouting. This isn't the first time we are doing this. In the past, we build a wood stove around a radiator as shown above. Now I'm wondering if this is ...
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2answers
51 views

Why boiling occurs when vapour pressure equals the local atmospheric pressure

When we increase the temperature of water in an open container, the vapour pressure increases.But boiling (phase transition at constant temperature and pressure) occurs only when the vapour pressure ...
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1answer
44 views

Is this refrigeration cycle thermodynamically possible?

This is a screenshot of a lab where we were experimenting Vapor-Compression Refrig. Systems. I am trying to understand what is happening between points 1-2 because I thought that because of max ...
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Looking for something to reflect ultraviolet light at extremely low wavelengths

I have been working on a product that involves the reflection of low wavelengths of UV light (200-250nm). However, I have not come across many materials that are able to do so and the high-...
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2answers
58 views

which type of casting will give higher cooling rate, casting in thin water-cooled copper mold or casting in thick copper die?

It is will known that increasing cooling of a metal casting will lead to finer micro-structure which mean higher mechanical properties. If I have 2 molds one is thick copper die ,& second is just ...
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1answer
45 views

Connect heated copper tube in PVC tube

I have a copper tube that I'm heating (quite a lot) with a torch, I have to connect a PVC pipe in the entrance of the copper and one in the exit (so water can flow through the copper pipe). The only ...
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30 views

Engine power and torque of a vehicle

Having the Power/Torque-RPM curves of a vehicle, how can we derive the engine power equation and the torque out of these curves with respect to time?
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1answer
21 views

Derivation of specific helmholtz function relationship for an ideal gas

The question is to prove the following form of helmholtz function for an ideal gas $$f=C_v (T-T_0)-C_vT \ln \frac{T}{T_0} -RT \ln \frac{V}{V_0} -s_0(T-T_0) +f_0$$ I tried using $$df=du-Tds-sdT$$ Now ...
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1answer
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Wet bulb temperature in psychrometry

"In a sling psychrometer(with dry and wet bulbs), if the moist air is not saturated(with water vapour) then it evaporates some water on the wet bulb and in turn cools the wet bulb.So the wet bulb ...
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1answer
35 views

Conductive Heat Transfer calculation over time

I am trying to heat the oil in a 1/2 inch thick rectangular steel box by using an Insulated heated blanket covered on all 6 faces of the box, the working conditions of the operation are at -50 Celsius,...
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166 views

Pressure Temperature relation of saturated steam

With the saturation pressure apparatus we did a heating and a colling process. We measured the temperature and afterwards we calculated the specifc volume of saturated vapour. The question 1: What ...
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What factors besides nozzle geometry and propellant's affect engine ISP? How can one optimize ISP?

In the design of a Rocket engines, it is understandably desirable to have a more efficient engine. Ensuring the gasses coming out of the engine comes out straight, and the chemistry of the ...
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1answer
56 views

Contradictory result for mass balance

I solved this problem by doing a mass balance for the mixing chamber and an energy balance for the water heater and the mixing chamber as follows: $\dot{m}_{\text{mix}}=\dot{m}_{\text{Tank}}+\dot{m}_{...
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32 views

Does a closed loop biomass-fired cogeneration/CHP make sense?

I'm working on a project concerning electricity production using biomass, and we have seen that making use of cogeneration is very attractive in order to increase the efficiency of the installation. ...
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1answer
48 views

A question on non-destructive testing and evaluation

In most geometry inverse problem, information like the temperature measurement on the surface is use to detect the shape and location of a defect. My question is: is it possible to measure the ...
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1answer
149 views

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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32 views

How much can a double Peltier stack cool to -30 C?

I need a -30 C freezer. Inside volume 5-30 l. I've seen videos of double Peltier stacks reaching -50 C with one Peltier running at 12V and the other at 5 or 7 V. How big a freezer could such a stack ...
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Adiabatic paths

Can two adiabatic process paths intersect on a plot? This question is for 2 cases- 1.) Can two irreversible adiabatic curves intersect. 2.) Can a reversible & an irreversible adiabatic curve ...
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83 views

How do external irreversibilities decrease the efficiency of thermodynamic cycles?

In gas power cycles, one mentioned that: The Carnot cycle is both externally and internally reversible. Therefore making the Carnot cycles more efficient than other practical cycles. Question: ...
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3answers
71 views

Why not drive an air source heat pump domestic heating system with an auto engine?

Theses are my thoughts on the question. I can't find an answer to "why not?". It there something I am missing, or are auto manufacturers simply too focussed on cars only? The automotive industry has ...
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67 views

Calculation for heat transfer rate / cooling capacity for air cooled solid

I have a pipe which is channeling air flow from a compressor with a known mass flow rate and temperature. I can adjust the mass flow rate (power setting) and measure the delta T for the temp of air ...
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1answer
19 views

How To Find Reheat Parameters In an ideal rankine system

So I was trying To Solve a problem on reheat Rankine cycle . I can Solve for everything Aside The part of The Reheat That has Entropy constant With the Main boiler entropy.. I don't know if when ...
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1answer
56 views

How cold for lack of heat?

I know that on the moon, while the daytime surface temperature can be above 270° F, in the shade but a few feet above the surface temperature can get quite low. Wondering whether a similar phenomenon ...
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2answers
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Why is the saturation pressure of the refrigerant desired to be slightly greater than atmospheric pressure in an evaporator?

I read that it "is a positive pressure against the environment". But I am not too sure what that means.
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Peltier Calculation Conundrum

I have a peltier (TEC) device capable of 400W Qmax, a 160W thermal load that I'd like to keep at ambient, and this water block running at about 1.5 gpm w/ room temp water. I think this system is right ...
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1answer
74 views

how would one calculate the % of heat not absorbed by a heat sink?

I'm planning on building a plant growth chamber inside a sealed/insulated 55 g rain barrel, and I'm trying to figure out how much of the heat from my lights will enter the chamber, and how much ...
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125 views

what's the best shape for inducing condensation?

What would be the best ceiling shape for inducing condensation? I'm guessing it would a curve ︶ or V shape, but those are just guesses. (I don't have any background on thermal physics)
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37 views

Learn thermodynamics before beginning with control engineering ? [closed]

I'm about to start learning about control engineering. But am I advised to learn first Thermodynamics? (Since control engineering has applications in Thermodynamics)
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Equation for temperature of gas at Joule-Thompson Inversion State

Assume that a gas obeys the following equation of state: $\nu = {\frac{RT}{P}}-{\frac{a}{T}} + b$ Where $a , b $ are constant. Derive an equation for the temperature at the Joule-Thompson ...
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What are typical efficiencies of thermocompressors acting on air?

Thermocompressors use a high pressure gas to draw in low pressure gas, resulting in a larger volume of medium pressure gas. Some googling showed mainly thermocompressors using steam, but I suppose it ...
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1answer
37 views

How to use consumer electronics for industrial application on high temperature

I need to measure the width of a bar made out of glowing red steel (900-1200 degrees Celsius) using computer vision. In order to ensure resolution of a 0.5 millimeters/px, the camera is needed to ...
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2answers
343 views

How do solar balloons work at high altitudes?

I am interested in the challenges that Solar Balloons face when flying. For example, the high altitude could cause drastic changes in: Wind speed Temperature Moisture How does the unique design of ...
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2answers
53 views

What methods are used to extract energy from low energy heat sources?

Most of what I was able to find pointed towards thermoelectric generators which are very inefficient, stirling engines which have a low torque output at low temperatures, or generators that use the ...
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2answers
55 views

What is the practical application of Rayleigh number to heat sinks?

I understand that there is such a metric as the Rayleigh number which governs convective cooling in a medium. Assume for example, a fist sized heatsink like that below in free air:- Does the ...