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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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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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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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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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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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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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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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How to design a gas fired heater

I am working on a project on how to design a gas fired heater to heat crude oil to a particular temperature before it enters the distillation column. The project is limited to heat balance and ...
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Vapour absorption refrigeration

In vapour absorption refrigeration, why do we mix ammonia vapour coming out from evaporator with weak ammonia solution, why not mix it with just plain water. Is there a specific reason for using weak ...
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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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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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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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empirical or approximate equation in finding enthalpy in superheated state

Is there an empirical or approximate formula for finding enthalpy in the Super-heated state?
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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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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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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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How can we increase the efficiency of external combustion engines?

Many external combustion engines working on the stirling cycle have been designed. Theoritically they have an efficiency equal to the Carnot efficiency but are unable to reach it experimentally. How ...
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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
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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
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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 ...
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Should we protect our AC's outdoor unit from sunlight?Does it increases the durability of an AC and its refrigerant if it is well shaded?

My AC outdoor unit gets direct sunlight (no shading whatsoever) from morning to noon. Temperature normally soars up to 40 degree Celsius (I am from India). I have two questions: Is this bad for the ...
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Formula for “ram rise” that works all the way to orbit

True Airspeed (TAS) is the vehicle speed relative to the surrounding air. My assumption is that if I am in orbit say at 120 km altitude with an instantaneous velocity of 8 km/s my TAS would be fairly ...
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Using a Copper Waterblock or Aluminum Heatsink to Cool Water via Thermo Electric Cooler [closed]

I am attempting to create a ThermoElectric Cooler to Chill Water. I have thought of two options as to how I can cool the water: Some limitations of the design: The water is still, not moving. No "...
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Heat loss from the greenhouse to the soil

I need to find heat loss from the greenhouse. I know how to find heat loss through the walls and roof , but what about soil ? how to find amount heat conductivity loss to the soil ? I would be ...
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Heat of Combustion, Vaporization tables

It's my first time posting on this specific forum. I hope I'm doing this right. I am currently modeling fire spreading through different buildings via FDS, but I lack the properties of the materials ...
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1answer
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Is a Home's Temperature Affected by Solar Gain Through Windows on Cloudy Days?

Do homes increase in temperature due to solar gain with curtains open if it's overcast? In other words, Does having curtains closed reduce the temperature of the home on an overcast day? In other ...
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Question on Phase Change Materials

I am looking at Phase Change Materials as a building fabric option and from reading up on the topic theres something I don’t understand. Hopefully somebody can help explain. I read that when a ...
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1answer
35 views

What are the limiting factors on diesel engine compression ratios?

Higher compression ratios in internal combustion engines generally improve the engine's fuel efficiency. But diesel engines don't seem to go above a ratio of 25 or so. What is the limiting factor for ...
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Operative thermostat influence on heat fluxes

If the heat fluxes in a non-insulated building during the heating period are considered. How these fluxes (Primary energy from the heating system, internal heat gains from people, light and equipment ...
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28 views

Best model to describe this scenario of cooling?

I have a block of CFRP (Carbon Fiber Reinforced Polymer) that has defects (back-drilled holes) in it. This sample was exposed to a source of heat for sometime (say 30 seconds) and the source if ...
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32 views

How to estimate the steam dryness fraction?

I am doing my university graduation project on steam separation and need to find a way to measure the dryness fraction of steam. However, the resources are very low and time is a struggle. Any ...
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Steam separation and improving its quality

I have got my university graduation project on steam separation to hand in next month. My aim is to design, manufacture and test a gas separator to be mainly installed in steam boilers. There are so ...
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How can energy be added at constant temprature?

In the answer to this question: Difference between Saturated Liquid and Saturated Steam How can energy be added with constant temperature? Isn't the energy input itself a change of temperature? ...
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What colour of tarp will let in the least amount of heat?

Source: Low Tunnel Construction: How to Build a Mini Hoop House I have a small greenhouse that I want to keep as cold as possible in the spring. I plan to cover the greenhouse with a polyethylene ...
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Thermodynamics Problem [duplicate]

Air with an initial volume of 0.12m³, pressure 1 bar and temperature 18°C is compressed according to the law pV1.3 = c through an 8:1 compression ratio. It is then allowed to expand isothermally back ...
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What are the differences between Gauge and Absolute pressure?

I am aware that Absolute pressure is zero-referenced to a perfect vacuum and Gauge pressure is zero-referenced to ambient air pressure. So, Absolute pressure is equal to Gauge pressure plus ...
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1answer
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Model of a domestic boiler

I have to design a model of a domestic boiler. I represent the boiler as a heat exchanger (HEX1), as shown in the figure. In many articles I have found that it is schematized with this equation: $$ ...
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Applications of Thermodynamics

I am trying to solve this but I am stuck; I have watched loads of YouTube videos but still don't understand how to complete it: A mass of $m=0.12 kg$ of air has an initial temperature of $T_1=500°C$ ...
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Failure of N.R.T.L method to model Phenol / Methylcyclohexane / Toluene system in AspenPlus. Why?

I have an extractive distillation column set up in AspenPlus. Methylcyclohexane (MCH) is expected to come out from the top (in the distillate stream) and the bottoms stream is mostly Toluene/Phenol, ...
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Energy consumption of a boiler

I have a question that maybe will be very easy for you. I am working on a district heating model using Dymola, and now I have to incorporate a boiler into my model, such as this one. I was asked to ...
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1answer
146 views

estimating the surface area of a steam coil immersed in a tank

I've been tasked to design a steam coil that will be immersed into a tank in order to maintain the fluid temperature above 25C (but not to exceed 40C), and I need to calculate its surface area & ...
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3answers
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What is the best method to generate heat from a compressed air canister?

I want to convert the pressured air exiting a valve to heat. I know that a vortex tube can be used to do this, but I am wondering if I need to make modifications to the vortex tube to make it more ...
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How can I keep a Zippo lighter from losing fluid to evaporation or leaks?

Zippo lighters are notorious for needing regular refilling. The fuel evaporates from the cotton regularly. Some people put a bit of rubber around the seal. What atmospheric conditions keep fuel from ...
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2answers
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Thermal Conductivity? Units On a Data Sheet

I've been trying to find the value of thermal resistivity for some linear disc resistors. I know that Thermal Resistivity is the reciprocal of Thermal Conductivity but the thermal conductivity on the ...
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Room with computer racks, with or without ventilation

I have a room of computer rack that with 2750 watt power needs, which according to this site, I need 9000 BTU/h AC. I'm deciding if I should put a vent in the room or not. When there's a ventilation, ...
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How to work out the size of heat composter required to heat a specific amount of water via heat exchanger?

Am playing around with solutions to turn my brewery into an off grid one (as much as possible anyway). This thread relates specifically to the heating of water. In brief: heat composter with water ...