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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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Calculation of the stored energy for a heat storage tank

There is a heat storage tank that is directly loaded from the top and the heat is also taken from the top. The colder water from the heating circuit return flow enters the heat storage tank at the ...
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Oil pressure inside copper tube?

**Background ** I'm struggling finding how to calculate the pressure that occurs within my system and then once calculated I need to reduce that pressure. My system I have a 1 inch copper pipe ...
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How to calculate the thermodynamics properties of the LiBr/H2O solution?

When modelling an absorption heat pump cycle one would need to calculate the state properties of absorbent, absorber, and the mixture of these two; in order to find out the cycle properties. Is there ...
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2answers
32 views

Can a Peltier's device (i.e.Thermoelectric cooler) achieve cryogenic temperature efficiently?

Does the stacking of peltiers device shows promising results in achieving the cryogenic temperature? I have tried doing the experiment, the overall temperature of the system increased around 80ºC and ...
2
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1answer
43 views

Modelling a refrigeration cycle in Excel

Is it possible to model a heat pump cycle without using tools like EES, but using Excel? I am considering to use Refprop application as an add-in in Excel, and model a heat pump cycle. Another ...
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1answer
39 views

Method for comparing efficiency of heater block designs?

How would I go about comparing the efficiency of different heater block shapes for the outlined system? So, in the attached diagram there is a cylindrical heater cartridge (A) that is used to ...
2
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1answer
43 views

What is the (thermodynamic) explanation for heat/temperature reduction due to wind?

Here is my fan in my office. Sometimes I used it if my air conditioner (AC) has problems, or I my self have problems with my health due to the freon. What I observed is that the heat (or probably ...
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Ignoring Mechanical Material Properties and Design Implications, in a Compressor, does the Thermal Density of the Blades Affect Efficiency?

Consider an ideal adiabatic compressor, ignoring the remainder of the thermodynamic cycle. In this case, the heat flow q into and out of the compressor itself is zero, by definition of adiabatic ...
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27 views

How to calculate heat transfer between two solids in a medium?

If I have a cuboid block of metal and there is a cylindrical source of heat input (A) and I want to determine the heat energy at B (also cylindrical) how would I do this? I understand considerations ...
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3answers
32 views

Why do the fan or blower of the Air Conditioner not facing the coil flowing hot liquid?

I observed the fan on external units of air conditioners does not force air towards the hot coil containing hot liquid to make it cooler. Instead it draws air from from the direction of the coil it ...
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1answer
20 views

Why does combustion happen at constant pressure in jet engines?

Why does combustion happen at constant pressure in gas turbines but at constant volume in pulsejets? I need to ensure my design adds heat at constant volume. Is it because combustion starts from ...
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1answer
22 views

Calculating Entropy from Gibbs Free Energy?

I guess Cp = dH/dT= dq/dT=dS Thus SdT = integral of CpdT. From that ∆H is given and we can calculate ∆G. However, entropy for this reaction should be -7.4J/molK and I am getting like 26J/molK. Also S ...
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Thermodynamics equality question

Can someone help with this question ? it's a thermodynamic question based upon Sonttage book 7th edition (*)the question states :- R-152a with a volume of 15 L and at 36 Celsius degrees with an ...
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1answer
42 views

Effect of bypass valve on flow rate and pressure

I have no background in thermodynamics or fluid dynamics, so please bear with me. Refer to the following figure: A working fluid with a flow rate of $1~kg/s$ enters a heater at a pressure of $1~MPa$ ...
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1answer
23 views

Heat Transfer Rate. Find Outside Temperature

I am required to find the temperature of the outside wall. I have rearranged an equation but it doesn't feel right Ti and To are the inside and outside temperatures. U is the overall heat transfer ...
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38 views

How can we dissipate the heat from a block of 10*10*3 mm with 100 degree Celsius without losing the portability of the block?

I have a Peltier's device of 10*10*3mm and the material is Bismuth Telluride. The hot side is 100 $^oC$ and I want to dissipate the heat, and at the same time, the device should be portable i.e. it ...
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1answer
34 views

How can I establish as much airflow from my house to outdoors as possible?

I live in a small flat with all doors and windows sealed. The temperature outside is moderately cold. I assume the temperature in my flat is hotter because my body and the computer are emitting ...
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1answer
31 views

Recovering mechanical energy from natural gas water boiler

Is there any heat energy lost to the mechanical force of pushing a piston in a combustion engine? In other words, would a natural gas burning as a flame produce more heat than the same amount of ...
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17 views

N2O/Kerosene Rocket Fuel

I am interested in building a small liquid fuel rocket and I have decided to use nitrous oxide and kerosene as the oxidiser and fuel respectively. I would like to know if anyone has any advice ...
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2answers
104 views

Heat transfer coefficient of a cylindrical hot water storage tank depending on its size

I have a simulation model of a cylindrical hot water storage tank. The heat loss is determined by the surface area and the heat transfer coefficient. A configuration of the storage tank with 900 ...
3
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1answer
51 views

What is the thermodynamic consideration so almost all air conditioners are installed on top?

Almost all air conditioners (AC) are installed on top. For house small office use, will be like the picture. For office with central air conditioner, the blowing come from the ceiling through duct. ...
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1answer
71 views

Storage losses of a heat storage tank

Suppose I have a heat generator with a connected heat storage tank. If the heat generator remains the same and the heat storage tank is dimensioned larger, the running time of the heat generator ...
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1answer
17 views

Given a known relation between the saturation pressure and temperature of an unspecified metal, how can we determine the following properties?

This problem contains multiple parts, and I will write my initial attempts at solving the problem under it's corresponding section If we're given that the vapor pressures (described in Atm) of both ...
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1answer
30 views

Are there steam tables for subsaturated steam?

By Googling I can find basically two types of steam tables for water. They are either saturated steam tables, which I understand are for steam in saturated state. Here pressure are temperature are ...
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8 views

Tg and vitrification

If the particular reaction temperature is lower than the value of Tg at full conversion, Tg∞ = Tg(x = 1), a conversion will be reached where Tg(x) equals T(reaction temperature) and vitrification of ...
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Conceiving a wind turbine as a thermodynamic machine

Traditionally, and continuing till the present day, wind turbines are conceived/presented as power plants which harvest the (macroscopic) kinetic energy carried by an externally available airflow, ...
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35 views

When does the minimum temperature in a four-stroke cycle occur inside the engine cylinder?

I've checked on quite a few places on the net and some say it occurs at the beginning of suction stroke and others say at the end of suction stroke. I believe it to be at the end of suction stroke ...
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16 views

Difference between RK and SRK equations of state in molar volume calculations

I'm doing a simple paper for my postgrad course in Chem. Eng. In this study, I'm just comparing equations of state and the data found in PH diagrams. For Methane, at 263.15 K and 20000 kPa, the molar ...
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1answer
35 views

How many heaters needed

A room 10"x10"x17" lxbxh respectively to be heated 397F if a heater is placed inside the room (2 kw) how many heater are to be required to heat the room from room temperature to 397 F in 1 hour.
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64 views

1 Ton of Refrigeration

"1 TR is equivalent to the rate of heat transfer needed to produce 1 U.S. ton (2000 lbs) of ice at 32F from water at 32F in one day, i.e., 24 hours." While defining 1 Ton of Refrigeration (TR), why ...
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Final temperature of an isolated vessel - Thermodynamics

8) Consider an inextensible tank of 10 m3 of volume, isolated by an adiabatic wrap. The tank contains nitrogen at 2 bar and 300 K. This tank is connected to a piping by which more N2 (at 300 K) is ...
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2answers
110 views

From a mechanical point of view(Physics/Engineering) why are Front-Load washers said to clean/wash better than Top-Load washers on average?

Which cleans better? Is it just marketing or do they really clean/wash better due to some physical property or the way they work, I am asking how do they if they do? N.B I do not intend to indicate ...
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37 views

Confusion about throttling process

A throttling process is defined as an isenthalpic process. But in certain cases, the throttling process is defined with the stagnation enthalpy being constant (ref: http://web.mit.edu/16.unified/www/...
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1answer
32 views

Is there something called the stagnation volume?

When discussing the stagnation flow properties we always discuss stagnation temperature, stagnation pressure, and stagnation enthalpy. Is there also a stagnation property called the stagnation volume ...
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20 views

In a throttling process do we consider static pressure or stagnation pressure and is there a reverse throttling process?

In a throttling process, the 'pressures' decreases whereas the enthalpy and so the 'temperature' remains constant. Are these pressures and temperatures static values or the stagnation values? I am ...
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2answers
44 views

Time to change temperature inside the box

I have an interesting problem here. I have a box of certain dimensions. Inside of the box is some insulation and another box, from the same material as the outer box. I know everything possible about ...
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1answer
67 views

How do I determine the temperature inside a transformer vault?

I am trying to determine the temperature of an underground concrete vault buried 10m underground. The vault has the following dimensions: 2640mm x 5995mm x 2640mm with a wall thickness of 250mm. The ...
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0answers
17 views

Question with regard to spacex raptor engineand other full flow staged combustion engines

The diagram linked is unofficial but I've looked at other diagrams which are similar. The coolant is pumped in at a high pressure much higher than the maximum chamber pressure of the rocket the ...
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1answer
66 views

How can a non flowing fluid have kinetic energy?

I am currently studying engineering thermodynamics from Cengel and Boles and there it is given that total energy of non flowing fluid per unit mass basis is given as $e=u+\frac{v^2}{2}+gz$.But if the ...
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1answer
31 views

Carefully attaching Pt-wire to mild/carbon steel surface

Problem: I have a near 100% Pt wire (25 AWG / D ≈ 0.45mm) that I would like to attatch to a cold rolled steel (E235 / EN 1.0308) surface. Assume this surface is flat. Goal: Keep wire attached to ...
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21 views

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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1answer
75 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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3answers
54 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
63 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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0answers
16 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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2answers
79 views

How is flow work calculated?

I am reading thermodynamics from Cengel and Boles. I am currently studying flow work. The following image contains text of the book: The work done is calculated by considering the pressure of ...
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1answer
23 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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1answer
27 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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2answers
34 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
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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) ...