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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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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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38 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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Confusing portion of class notes regarding Betz's Law

In my class notes I have the following written after a section about Betz's Law: The maximum amount of work obtained from a wind turbine can be approximated as follows: $$W_{max}\simeq\frac{\...
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51 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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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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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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what kind of heat insulation should I provide to a camera mounted externally on a surface facing supersonic flow

i wanted to know if we could estimate the heat of supersonic flow and insulate the external camera accordingly. Are there any transparent materials withstanding stresses similar to CFRP that I can ...
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34 views

Finding the Work done by Nitrogen

I have assumed Nitrogen gas as an ideal gas for solving the problem. But our professor says that don't assume it as ideal gas and calculate the work done by only using thermodynamic tables. But I don'...
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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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58 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
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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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1answer
55 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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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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72 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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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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99 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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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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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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2answers
339 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
52 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
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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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3answers
166 views

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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1answer
41 views

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
65 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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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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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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53 views

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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2answers
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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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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: $$ ...