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# Engineering Thermodynamics - Science topic

Engineering Thermodynamics are exchange information on technical thermodynamics research
Questions related to Engineering Thermodynamics
Question
I have implemented in Matlab a code that calculates the excess Gibbs energy for a given compound in a mixture.
The goal would be to compute the binodal curve for an ATPS system, by equaling the chemical potential of each component (3 in total) in the hypothetical top and bottom phases.
I did this by using fmincon. I fixed the polymer (PEG) concentration on the top phase and then 5 equations were solved to obtain the other 5 variables:
Sum of volume fraction top phase = Sum of volume fraction bottom phase = 1
Chemical potential i top = Chemical potential i bottom
However, every time the algorithm is run, different solutions are obtained and I think it's due to the high nonlinearity of this problem. Could you provide me a better strategy to obtain the binodal curve?
Hello
You must use fsolve not fmincon. The former is used to solve nonlinear equations, but the latter is used for optimization.
Question
I have a 750 ml reactor and working volume is 300 ml. my working temperature is 350 C. By using ideal gas law i found at the pressure to be around 2 bar. But  I need final pressure build up @ 350 C to be around 25Mpa in order to keep my solvent in liquid phase. So, how should i calculate the initial  head space pressure required. I'm planing to use Ngas for pressure build up
I have the same issue, what i have noticed is the free volume of reactor that should be considered for supplying the initial pressure.
Question
Hello,
My reseacrh area is absorbtion refrigeration system with nanofluid. I know how can I calculate the performance parameters of NH3-WATER and LiBr-WATER as a base fluid. But the thing is, how can I integrate the nanoparticles to basefluid to calculate the performance parameters theoretically using Engineering Equation Solver ? I found some articles but they were useless. After adding nanoparticles to base fluid to make a nanofluid, how can I calculate entalphy, entropy, mass flow rate, COP, circulation ratio, variation of rich and poor concentrations, condenser and absorber capacity ?
Question
In what case would a reaction rate always show direct relation with activation energy or would it always be an inverse relation? Is it a indirect relation, inverse relation or both case can hold? (Please provide supporting resource, thank you).
Toyese Oyegoke when we are talking about your question and particularly the catalyst which always lowers the energy of the transition state for the reaction - in this case any reaction you can assume.The difference between the transition state energy and the other part that is the reactant energy is the main ACTIVATION ENERGY and this is very important to understand, Lowering of this energy which means lowering of transition state energy also ensures and lowers the activation energy for sure
Question
Hello dear friends
Kindly I am studying cost variations versus entropy generation for a CCHP system including prime mover, absorption chiller and borehole. There are entropy generation for chiller and entropy generation number(non-dimensional form of entropy generation(EGN)) for borehole. These two criteria are positive and independent each other. Can I study cost variations (vertical axis) versus S+EGN (horizontal axis) in which "S" is chiller entropy generation? Or the S and EGN should be in a same dimension.
regards
Regards
Question
I want to have these components in a hybrid renewable energy system (energy storage (thermal energy storage or CAES), solar collector or solar PV, solar reactor, wind turbine, CCHP plant, biomass boiler, etc.) Exergy and energy analysis is going to be performed in my project, Thanks for your participation.
EES
Question
I am doing   CFD analysis of  waste heat recovery from flue gas to remove moisture content from coal particle. I think This  is problem regarding Discrete Particle Method In fluent. But Hoe to add Moisture content in in coal particle which is 50% . ?
Hi sir
I have the same problem but i have solid silica gel with 5 mm diameter in 30 cm cylinder and high is 20 cm
and it 100%saturated with humidity and i need to dry it by using hot air with temp 70 c with velocity 20 m/s
My question is
How i can add this wetted silica gel in ansys and using hot air
Question
Can I be suggested with good books on Fluid mechanics and Heat Transfer (separate or even same book), preferably in relation with CO2 sequestration? Even the basic books would be fine.
• Heat and Mass Transfer: Fundamentals and Applications (by Yunus Cengel and Afshin Ghajar)
• Heat and Mass Transfer (by PK Nag)
• Textbook of Fluid Mechanics (by Er. R K Rajput)
• Fluid Mechanics (Frank M White)
Question
I would like to create my own TYM2 file to run TRNSYS simulation with my own meteorological data. How should I create my weather data file?
You need to safe in notepad fast then convert.
Question
Is it possible to calculate entalphy of LiBr/H2O or another solution if we know correlation of specific heat without using any software?
If you want to solve your problem as it appears in the image, I recommend using an equation of state for the enthalpy departure.
I also recommend the following articles:
-A computationally effective formulation of the thermodynamic properties of LiBr-H2O solutions from 273 to 500 K over full composition range
- Exergy calculation of lithium bromide-water solution and its application in the exergetic evaluation of absorption refrigeration systems LiBr-H2O
-Thermodynamic Evaluation of LiCl-H2O and LiBr-H2O Absorption Refrigeration Systems Based on a Novel Model and Algorithm
-Mathematical Model of a Lithium-Bromide/Water Absorption Refrigeration System Equipped with an Adiabatic Absorber
Question
I have completed uncertainty analysis for my heat exchanger calorimetric lab.but I am not sure the calculation of enthalpy ( it is required for Q=mr*deltaH) due to ref.prop program. Normally my main equation is U=cv*dT+P*v and I have calculated  uncertainity according to temperature and pressure sensor and I admitted constant the value of specific heat and specific weight but these values have a uncertainty due to Refprop uncertanities. I am not sure whether to add this uncertainty. I would like to learn your opinions and advices.

Question
Looking forward to any research work/ mathematical equations.
Exhaust gas temperature is a function of many variables.
Engines with lower BSFC values typically have lower exhaust gas temperatures because more of the fuels energy is used in the cylinder.
Another important factor is the air/fuel ratio. If excess oxygen is in the exhaust the temperature will be higher.
Camshaft timing, ignition timing, and IN/EX flow ratios during valve overlap are factors too.
I suspect trying to get an accurate exhaust gas temperature will be difficult without having a lot of specific engine parameters.
I have personally experienced exhaust gas temperature variation between cylinders on the same engine of 50C or more.
Question
For a liquid fuel, whose composition is undetermined, given its ultimate analysis as C-x%, H-y% etc., in a temperature and pressure other than the environmental pressure and temperature, How its physical exergy, particularly enthalpy and entropy can be calculated? Any documentation related to the answer would be much beneficial.
Check the exergy book that belongs to Kotas. also you can find similar example that you mentioned it.
Question
I need to calculate exhaust gas temperature at the engine exhaust valve outlet theoretically since I do not have teh luxury to calculate it using EGT thermocouple sensor. Any research references/equations will be helpful.
The thermodynamic two-Zone model can be used to estimate the temperature [Reference: John B. Heywood, internal combustion engine fundamentals]. Other calculation methods are presented in the same reference.
Question
I have start my study about MD simulation of Refrigerant condensation. I am studying the LAMMPS software for my MD simulation. But I am not clear that how I could write a input script in LAMMPS for a particular refrigerant for example R600a in the capillary tube system and how to create the potential file of the Refrigerant?
Researchers can also visit the lammpstube.com
Question
Heat and Mass Transfer, Engineering Thermodynamics, Automotive Engineering, Power plant Engineering
It is lower than Carnot cycle....
Question
How can concentration in terms of rich and poor be affected by adding nanoparticles to LiBr-Water?
Dear Kenkar,
In diffusion absorption coolers regarding to the heat performance of the system, ammonia/water couple with alumina (Al2O3) particles in nano-size can be a better option. It can provide better absorption of heat from the generator and faster evaporation of the cooler from the cooling/absorption fluid. Considering the effect of fluids containing nanoparticles the connection units of the heat transfer in the system operation time of the system might be reduced due to shorter heat transfer periods.
Ashish
Question
What is the thermal conductivity value of graphite in the xy plane? I've seen several papers with different values so is it 100s or 1000s at room T?
The thermal conductivity of graphite depends on the anisotropy of the layers but generally it varies from 25-470 W/Mk.Generally it is “GraphiteTIM(Compressible Type) with thermal conductivity : X-Y direction 390-400W/m∙K, and in Z direction (28W/m∙K).
Why this is different?
However, controlling the orientation of GFs still remains a challenge. The corresponding thermal conductivity is as high as the thermal expansion will be less.
Reason Property
Because of the weak binding and the large lattice spacing in the c-direction, the phonon spectrum of graphite is approximately two-dimensional for frequencies above f c = 4 THz. Thus one can model the a-plane thermal conductivity by a two-dimensional phonon gas. That’s why in XY plane conductivity value is high and it is anisotropic when we compare with Z plane.
Hope it is helpful for you.
Ashish
Question
Hello to all:
I'm trying to think in the following interesting problem:
I have a system which are polycrystals (grains) of Bi2Te3 (actually this compound is a quaternary alloy of Bi, Te, Se and Sb). The grains ended coated with Carbon, in the form of Graphene Nanoplatelets: a stack of several (or could be many) Graphene single Layers.
Does anyone know, have experience or have literature references about the following questions:
1. How an increment in temperature will affect the Chemical Stability of the Bi2Te3-alloy ? for two scenarios:
i. A normal day-to-day working temperature between 10 °C - 37 °C
ii. Or in the scenario reaching the 100°C
And second. The same question but for the aging of the device, rather than the stability in function of the temperature.
or for both conditions for the matter of the subject.
If someone can comment something about, I'll appreciate it !
Best Regards !
The interface between two phases is very important (regarding to Subhasis's answer)
DOI: 10.1016/j.diamond.2019.107561
Question
Dear Colleagues :
Does anyone have literature referencing the diffusion process of Carbon (I mean Carbon atoms) into Bismuth Telluride (Bi2Te3) or into some other compound alike ? E.g. PbTe, (Sb,Se)Bi2Te3, Sb2Te3, etc ... ?
I'll really appreciate if someone can help me out
Kind Regards Sirs !
Question
Maxwell Boltzman distribution is ni/gi =e-(εi−µ)/kT. In quantum mechanical case, +/-1 is added at the end of kT. (+) sign is for Fermi-Dirac distribution and (-) is for Bose-Einstein distribution. I want to know what is the physical significance of these signs and how can we relate this to classical (Boltzman) distribution.
The partition function derived for Boson & Fermion differs in the range of particle including even /odd number distribution - The entropy of B.E / F.D statistics differs - REF : https://demonstrations.wolfram.com/BoseEinsteinFermiDiracAndMaxwellBoltzmannStatistics/
We can calculate delS = f In ( T.P ) . Fermi-dirac Probability is something higher than B.E Stat so expected entropy of F.D is something higher the B.E stat .
Question
After some literature review and from a turbomachinery course I identified the following limiting design parameters,
- Minimum size of last row of high pressure compressor ( about 10 mm ? )
- Maximum temperature that can be tolerated by the machine's disks (about 950 K)
- Maximum temperature allowed for effective turbine blade cooling
Are there any other? Is there a maximum allowable pressure for combustion? Is there a maximum pressure that can be handled by the turbine's outer walls?
Thank you very much in advance
Well the pressure ratio of gas turbine may be in the range (4to 12) but there is an optimum pressure ratio which depend on maximum and minimum cycl tempersture
Question
A mixture of gases 11% CO2 - 89 % N2 (molar) at a temperature of 300 °C and total pressure of 1400 psi. ¿CO2 and N2 at these conditions are in the gas phase or in supercritical state? I mean, ¿what is the pressure to determine the behavior of each component (CO2, N2)?
The subject of fluid behavior is broad and diverse. I cover this at some length in my book, Thermodynamic and Transport Properties of Fluids, which will be free on 3/24/2020. https://www.amazon.com/dp/B07Q5L1CHT The software is always free at http://dudleybenton.altervista.org/software/FluidProperties.zip The fact that these gases are supercritical actually makes your work in this case easier.
Question
Dear all:
I hope this question seems interesting to many. I believe I'm not the only one who is confused with many aspects of the so called physical property 'Entropy'.
This time I want to speak about Thermodynamic Entropy, hopefully a few of us can get more understanding trying to think a little more deeply in questions like these.
The Thermodynamic Entropy is defined as: Delta(S) >= Delta(Q)/(T2-T1) . This property is only properly defined for (macroscopic)systems which are in Thermodynamic Equilibrium (i.e. Thermal eq. + Chemical Eq. + Mechanical Eq.).
So my question is:
In terms of numerical values of S (or perhaps better said, values of Delta(S). Since we know that only changes in Entropy can be computable, but not an absolute Entropy of a system, with the exception of one being at the Absolute Zero (0K) point of temperature):
Is easy, and straightforward to compute the changes in Entropy of, lets say; a chair, or a table, our your car, etc. since all these objects can be considered macroscopic systems which are in Thermodynamic Equilibrium. So, just use the Classical definition of Entropy (the formula above) and the Second Law of Thermodynamics, and that's it.
But, what about Macroscopic objects (or systems), which are not in Thermal Equilibrium ? Maybe, we often are tempted to think about the Entropy of these Macroscopic systems (which from a macroscopic point of view they seem to be in Thermodynamic Equilibrium, but in reality, they have still ongoing physical processes which make them not to be in complete thermal equilibrium) as the definition of the classical thermodynamic Entropy.
what I want to say is: What would be the limits of the classical Thermodynamic definition of Entropy, to be used in calculations for systems that seem to be in Thermodynamic Equilibrium but they aren't really? perhaps this question can also be extended to the so called regime of Near Equilibrium Thermodynamics.
Kind Regards all !
1. At very low temperatures, entropy behaves according to Nernst's theorem
I copy the wiki-web inf. but you also find the same information in Academicians: L. Landau and E. Lifshitz Vol. 5 Vol:
The third law of thermodynamics or Nerst theorem, states that the entropy of a system at zero absolute temperature is a well-defined constant. Other systems have more than one state with the same, lowest energy, and have a non-vanishing "zero-point entropy".
2. Lets try to put Delta Q = m C Delta T, into the expression: Delta(S) >= Delta(Q)/(T2-T1) . What we do obtain? something missing then?
you see, physical chemistry and statistical physics look at entropy in a different subtle way.
3. Delta S = Kb Ln W2/W1 where W is the total number of micro-states of the system, then what is W1 and W2 concerning Delta S?
4. Finally, look at the following paper by Prof. Leo Kadanoff concerning the meaning of entropy in physical kinetics (out of equilibrium systems): https://jfi.uchicago.edu/~leop/SciencePapers/Entropy_is3.pdf
Question
In Convective heat transfer phenomena
to obtain a constant temperature condition, using condensation or evaporation seems the best way. For constant heat flux condition, use of electric heaters is the best way in a laboratory.
Question
Can we use infrared-transmitting materials like silicon (on upward-facing hemisphere of exhaust pipes) to dissipate heat energy from exhaust gases discharged from Generators, vehicles etc, through radiation, that can then be reflected towards space (upward forcing) by using deflectors (like aluminium coated surfaces)?
Mohd,
I either use NIST or HITRAN.
NIST (graphic interface, easy to use)
HITRAN (neither graphic nor easy to use)
Question
I trying to learn fluent and to calculate wall heat transfer coefficient for non circular pipe flow. Pipe has constant heat flux through the wall, flow is turbulent, temperature varies a little with both r and length.
Since i never did it before in fluent, i need community to clarify my thoughts about it.
In such simple case (pipe flow) can we use built-in fluent functions to calculate heat transfer coefficient?
If we can, we interested in surface HTC, not in wall HTC, isn`t it?
If it is so we need to change reference temperature to Tbulk. We culaculate Tbulk as mass average static temperature?
Or it`s better to caculate it "by hand"? In that case how should i extract fluxes and temperatures for 3d case?
Ruben Borrajo Again thank you for your answer. Now the only question remains, you said before that usuale you use "mass weighted average temperature in the inlet and outlet plane, the area average temperature of the wall and the heat transferred". I understand for which reason you need average temperature of the inlet and outlet and transfered heat. So how do you use average temperature of the wall?
Question
In the ejector refrigeration cycle the secondary fluid to primary fluid is called entrainment ratio. Why entrainment ratio is considered secondary the fluid mass flow rate?
The entrainment ratio is a global parameter generally used to evaluate the performance of the ejector system. To calculate the entrainment ratio, the entrained secondary flow required. The secondary flow entrain in suction chamber due to supersonic velocity/low pressure at the exit of nozzle.
Question
Sometimes when I run parametric table of EES (sweep a variable) I have get unstable answer at some rages.
For example for 0, 1, 2, 3 I get 10, 0.005, 9.5, 0.00000014
But when I don't use parametric table and by running them singularly in the main window of EES with F5 key, I get 10, 9.7, 9.5, 9.3 for 0, 1, 2, 3
What's the problem?
I have reduced convergence criteria but the problem is not solved...
For example, I attached a photo. Starting and ending range of the variable are the same, but the results are not. The marked result is the true result.
EES solves your system of equations numerically, and if there are multiple possible solutions, it will only return one of them. I would guess that perhaps your system of equations has multiple solutions and different inputs converge to different solutions. If you know the solution you are looking for is in a particular range you could limit the range of some of your variables, and/or you could change your initial guess.
Question
The conditions which I want to know are: -
1. Pressure
2. Temperature
3. Internal Energy of a mixture @ the time of combustion.
4. A function through which we can find different temperature and pressure conditions at which combustion would start.
In order to start combustion, the temperature of mixture is supposed to be higher than ignition temperature.
Question
How to calculate CO/(CO+CO2) from reaction rate constant in the case of Baur-Glaessner diagrams?
I have the Log K values for the reaction at the different temperatures.
You wrote: " I have the reaction constant values, " what reaction rate constants doyou have values for andwhat are the units?
Question
In thermodynamic tables of liquids, S is usually given without mention of constant volume or constant pressure. In solids this makes sense because Cv ~ Cp, so S should be the same. In liquids, Cp > Cv especially as temperature increases, so I'd think that S would depend on constant pressure or constant volume conditions as well.
So my question is: is S the same at constant volume as it is at constant pressure?
To return to your original question: entropy is a function of two independent variables, which we usually take to be temperature and pressure, but we can switch to temperature and volume. If we know the entropy at temperature T1 and volume V, we may calculate it at a different temperature T2 and same volume V along a path of constant V. If have the equation of state we can calculate the pressure P2 at T2, V and report the entropy in the final state as \$S(T_2,V)= S(T2,P2)\$.
Question
Hello all :
I have just got myself interested on the topic of thermal transistors and started to search some readings about the subject, but it has n't come clear for me yet.
Does anyone can give a rough description of the working mechanisms of a thermal transistors ?
Is there a straightforward analogy between an Electric Transistors and a Thermal one ?
Are Thermal transistors and Heat transistors the same thing ?
Are there more than one kind of thermal transistor?
How can we associate the imput DeltaT or imput Heat Flux to the response of a Thermal Transistor.
I hope someone can give base ideas upon we can build a disscution on
Regards ! :)
Dear Franklin,
The basic functioning of thermal and electrical transistors is the same (a transport mechanism that has 2 differentiated states and a way to control that transport in a channel). In a normal transistor the on and off states are pretty much ideal (there are several orders of magnitude in the conductivity of the channel between states) and the control on the switch is almost ideal (ok, I am not talking here about charge trapping, capacitive couplings, etc). In a thermal transistors achieving something similar is rather difficult or
impossible. The heat flow (the equivalent to the current) is not characterised by a single carrier, but by a combination of electron transport, vibrations ( phonons in crystalline materials, propagons/diffusons/locons in amorphous), and finally radiation. The electronic contribution,if any, can be switched off using electromagnetic fields as in normal transistors. However switching off the other two contributions becomes really challenging. The diffusive part (vibrations) requires to somehow control how the atoms interact to each other in the material. A way to do that is by a controlled diffusion of a third material in to the lattice as in the above-mentioned paper. In a "dry" version you will need to look for something triggering a reversible phase change resulting in very different vibrational spectra for each state or something similar. As far as I know there is no easy way to do that, and the concepts proposed by Li in his seminal work have not been properly implemented yet.
Kind regards,
Julian
Question
One principle given in Thermodynamics, Cengel is "The steady flow compression or expansion work is directly proportional to the specific volume of the fluid. Therefore, the specific volume of the working fluid should be as low as possible during a compression process and as high as possible during an expansion process."
Can anybody explain how it is been arrived?
I got to know about the below formula (applicable in some cases) from which we can get partly the answer for the question.
Work = specific volume * change in pressure
Any other conceptual explanation for the above statements known to you?
dq-dw=d(h)=d(u+pv)
Now if we neglected the heat transfer and the change in the internal energy, then
-dw=d(pv) = pdv+vdp
Since dv almost equal zero for liquid (v is almost constant for liquid), then the integration yields to:
w=v*( change in pressure)
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Question
Usually mass transfer is described with the following equation: m = A*U*dc, where dc is the difference in concentration of a component between two phases, or a phase and the interface...
Fick's law of diffusion also uses the difference in concentration.
In reality, the driving force for mass transfer is the difference in chemical potential, which depends not only on the concentration but also on temperature and pressure.
Why then is the difference in concentration usually applied? In which cases can/can't it be applied?
Dear Tom,
thank you very much for all the references, comments and reflexions :)
Here I found a document that relates the cocentration gradient in the Fick law with the chemical potential gradient, but, as you said, I think it is obtained using analogy...
Regards,
Cristina
Question
Hi everybody. For the project that I am working on at the moment I need to have a preliminary estimation of the weight of main engine components of a gas turbine (turbine and compressor, combustion chamber and heat exchangers). I tried to look in the open literature, however not much data are available and the only relations that I have found assume a quite detailed knowledge of design parameters which I do not have at this stage. Do you know if is there any availability of relations that allow a gross estimation of weight based on main characteristics and thermodynamics model of each component?
Thank you very much.
Dear all,
I did a bit of research in my thesis work with component based weight modeling. This is the link to my conference paper ( ), where you can find few relations and related references to estimate individual gas turbine component weight contributions that might be useful to other people. I hope this may help somebody.
Kind regards,
Jacopo
Question
Who can explain this problem for a pure one-component fluid?
Dear Friend,
you probably have no proper backgrounds in thermal sciences and such discussion only based on the mathematical analysis have no sense. Study, please, more deaply the proper topics in advanced thermodynamics and then formulate such 'thesis'. Jan
Question
Hi,
If overall cost is minimized for a system or cycle, does it mean that exergy destruction is minimized?
regards,
Not necessarily...
Refer to the exergoeconomic analysis theory we have two cost source in most thermodynamic systems: 1) The costs that come from exergy destructions and losses because of low exergetic efficiency. or in other case we say the operation and maintenance costs. 2) The costs that are because of high equipment purchase prices. in other case we say the capital costs. by minimizing the exergy destruction you can only decrease operation and maintenance costs of system; while for purchasing high efficiency equipment you should pay high capital cost... so we can not always conclude that minimizing overall cost cause to less exergy destruction.
Question
Comprehensive Thesis/Project, Exergy, Second law, Thermodynamics
Following
Question
Working on Zn-Al-Ni solder alloy system. What is the best possible way to determine thermodynamic stability at different composition of the solder system ?
These articles may be helpful for you.
Question
Generally pre-heating, humidification , re-heat used in Winter A/C. Whereas cooling coils in Summer A/C i.e. a single de-humidification process
This is because winter air-conditioning demands heating and humidification.
Dr DB JANI
Question
I want to know that in an exist steam power plant, what aspects (such as heat exchanging aria, level of condensate or etc) of the steam feed water heaters can improve?
The modifications can improve efficiency or decrease the flow rate of steam to the condenser.
By increasing the feed water temperature, the feed water heater increases the overall efficiency of the steam power plant. Feed water heater increases the feed water temperature near to the boiling point. So, the interning water of the boiler can easily transfer into steam and improve the efficiency of the plant.
Question
Dear Researchers,
I am working on simulating shell and tube heat exchangers using ANSYS Fluent. I have the huge number of tubes and it is not recommended to model it. Therefore, I am trying with alternative approaches like porous medium and heat exchanger models.
*In the porous medium approach, the non-equilibrium thermal model is recommended for heat exchanger type of problems.
*In heat exchanger model, dual cell method is used to simulate shell side and tube side flow and heat transfer.
I request you guys to help me in this regard.
Question
A simple problem confused me:
suppose a constant amount of heat Q and a solid body with heat capacity C and initial temperature T1.
I want to calculate the final temperature of the body when heat Q transferred to the body at the following conditions:
1- irreversible heat transfer
2- reversible heat transfer
3- quasi static heat transfer
???
Hallo,
as a matter of fact, not in the way you pose the problem. If a given amount Q of thermal energy is exchanged, the final temperature will be as the colleague said T2=T1+Q/(M*C); you can realize this if you apply the energy balance to your system and express the variation of internal energy as the product of the specific thermal capacity times mass times temperature difference. As a matter of fact, the first-pricniple (energy balance) does not discern between reversible and irreversible processes (and heat and work would seem indistinguishable in this regard), you need to apply second-law balance equation to find out that non-reversible thermal exchanges introduce a term called entropy production (rate) which is absent in reversible processes. If you need a rather broad but accurate insight into the matter, I suggest (I take it German is your native tongue) you have a look at chapter 3 (for 2nd law) and 2 (first law) of the excellent "Thermodynamik - Grundlagen und technische Anwendungen" by Baher and Kabelac, published by Springer.
Marco
Question
I want the specific heat at constant pressure values of all metals at different temperature in all phases.
There are a few very useful sources that are publically available:
1. NIST Chem Webbook (http://webbook.nist.gov/chemistry/)
2. The data files from the NASA Lewis chemical equilibrium program (attached)
3. Several commercial/fee-based databases (DIPPR, DECHEMA, etc.)
I find all of these quite reliable for common chemical compounds.
Question
I would like to calculate the boiling point for propylene carbonate:acetone and propylene carbonate:ethanol:acetone. May i know what formula can be used for the calculation? Thanks
Dear Lee,
We can use an Ebulliometer, a device to accurately measure the boiling point of pure solvents or mixture of solvents.
We can use Joback method. This method is an estimation of normal boiling points from molecular structure.
Simulation is also a tool to calculate boiling point (Himmelblau).
With my best regards!
Question
In the RE-FUEL POWER projects, we are considering a number of conventional power cycles, such as supercritical reheated steam cycle, and advanced power cycles, such as supercritical CO2, ethane, helium or HAT cycles. Based on your experience, what other cycles can compete with these in terms of techno-economic performance?
#powercycle #thermodynamic #economic #feasibility #cleanenergy #refuelpower
The superiority of any power plant from a techno-economic point of view depends on several economic parameters that vary from a country to another namely: fuel cost, C&M cost, electricity selling price... Then, we can not say that a power plant is better than another absolutely. Each case study has its own results. However, I suggest you to add the combined cycle in the set of your power plants since it has shown interesting results in a large range of economic and thermodynamic parameters.
Question
I want simulate numerically heat transfer of nanofluid in a cavity with magnetic field . I need electrical conductivity of water- Al2O3 nanofluid.
Question
I calculated Activity coefficient of components of binary solution at infinite dilution and need to have experimental data to compare my results. I would like to know references for activity coefficient of components at infinite dilutionboth.
Dear Dr Tahery,
My colleagues and I have gathered some data (IL+Organic) from http://ilthermo.boulder.nist.gov/ but I have trouble with that.
I would be grateful if you could answer my question too.
Yours sincerely,
A. Abbasi
Question
Suppose a high temperature sphere where is located in a stationary fluid. Is it possible the fluid surrounding the sphere moves?
If you use ANSYS CFX or FLUENT, you have to select 'density ' analysis to inform the effect of the density as a function of temperature. This will get the buoyancy force effect appear through the investigation.
Good Luck
Question
Dear all,
Does anybody knows what the vapor thermal conductivity of FC-72 is?
Regards, Alireza
According to http://multimedia.3m.com/mws/media/64892O/fluorinert-electronic-liquid-fc-72.pdf, the thermal conductivity of liquid FC-72 varies with temperature according to
0.060 – 0.00011 (T, °C)
However, you may have already had that. I do not have information on the vapor
Question
What is the effect of inlet Mach No. on centrifugal compressors performance? I mean for Mc<1 i.e. without shock effects. Is it better to have lesser or higher inlet Mach Number? And why?
I understand D.G. Shepard had treated this topic in his book 'Principles of Turbomachinery' published in 1956. M# of 0.7 was treated as a design target but he went on to say that there were common applications that operated at 0.85 and higher with no catastrophic effects.
His interpretation was that mach number was purely an aerodynamic issue and did not adversely affect the mechanical operation in any way. Compressor OEMs have had a better understanding of these parameters since the time when these books were written.
Nowadays, OEMs test over a wide range of mach numbers and there is a greater degree of confidence in performance curves for individual stages. It is also inevitable since industrial process conditions and the duties that compressors are asked to perform are more or less pushing the boundaries. I agree with some other comments - it is not advisable to give a blanket statement about mach number without looking at the specific context of the case.
Question
Which theoretical and thermodynamic equation or group of expressions and equations can be used for calculation of water loss due to evaporation and wind when it is being flown over evenly using a spraying unit or nozzle system over a smooth glass surface of the Photovoltaic panel forming a thin water film layer as part of the PV cooling system built outdoors at a desert location in North Africa? Can the Penman equation be useful in this scenario for this calculation? Suggestions and sources required from you please?
Sambit,
I'm using 'Evaporation from free water surface' by Lurie and Michailoff (1936).
Tractable, robust, and short equations to model water vapour uptake into an airstream from a saturated surface.
Question
I am trying to simulate a specific type of an Absorption machine under Trnsys, the machine is a Yazaki 17.6 kWcool.
My question is how can I create a parametric file of the Type 107 to meet the performance of my AB machine ?
I'm having the same problem, the external performance data for modeling the absorption chiller using Type 107 requires:
- Part load fraction to chiller
- inlet hot water temperature
- Inlet water temperature to the evaporator
- Inlet cooling water temperature
I think the absorption chiller you mentioned above is the Yazaki WFC SC5, for this and other size, the manufacturer defines the performance of the chiller using the last three parameters, nothing about the part load fraction chiller.
To be more specific in the manufacturer datasheet is shown the effect of water inlet temperature and hot water generator inler temperature on the design heat input and chilling power factor, giving the fraction of design heat input and the values of fraction of related chilling capacity.
What I'm trying to create is a simple model that allows to predict Yazaki's performance using the equations for the absorption chiller heat balance.
Question
i made Qin= m cp delta T, with delta T outlet inlet solar colletor, where the salty water is heated, and mass flowrate of the salty water. GOR is lower than 0.1.. Seems to low..
Dear Hanna
I already calculated the GOR for our unit. Please read the last part of the attached paper
Regards,
Question
Say 2 fluids are water and superheated steam.
Dear Ashok Singh,
I am not getting how with increase in pressure mass flow rate increases
Question
for u-bundle heat exchanger oder any other heat exchange device
Question
Also calculate Heat release and cumulative heat release.
The data obtained from the experiments conducted were collected from relevant sensing setup using the instrumentation automation software package (LabView). Data batches collected were migrated to (Matlab) in order to process the data to obtain related values for peak pressure and the accompanying angle at which peak pressure occurred, the angle between start of combustion (SOC) and peak pressure, and to estimate the amount of apparent heat release rate (AHRR). The mathematical processing was carried out using an elementary methodology using the conventional first law heat release model assuming a constant specific heat ratio of 1.35 without any accompanying modeling of heat transfer or crevice effects. While this method was very elementary but was found to be adequate for conducting comparisons.  For the purpose of ensuring that a constant value cp/cv could represent both fuels satisfactorily, an approximation of the cp/cv values made from the charts of logarithm of pressure / logarithm of volume were used in the conducted calculations.
Figure (2) demonstrates the definitions upon which the AHHR parameters calculations were based. For the purpose of reducing noise effect on the obtained results and maintaining the crucial characteristics of combustion, each pressure point on the trace was calculated from averaging every 100 cycle pressure data. The data acquisition system logged pressure data once for every degree of crank angle, but these data were interpolated to one decimal place by a program written to run under (Matlab) .The combustion criteria parameters listed in the points after the following paragraph were calculated using the AHRR curve of figure (2) without any filtering or averaging except for the end of combustion value and the end of premixed burn. The end of combustion value was outlined using the moving average of the AHRR for the purpose of improving its consistency. The end of premixed burn was calculated from the second derivative of the AHRR. The following points list the combustion criteria calculated from the AHRR curve:
1. Start of injection (SOI): this factor was defined from the instructed SOI set within the engine management software. Any impending difference between the instructed and actual SOI is possible due to solenoid delay and should be uniform in conducted measurements as the engine speed was maintained constant.
2. Ignition delay (ID): the value of ID is defined as the difference between the instructed SOI and calculated SOC.
3. Start of combustion (SOC): the start of combustion is defined as the point at which the heat release rate becomes positive. On the AHRR curve, it is defined as the point where the curve crosses the x-axis.
4. Premixed burn Fraction (PMBF): the value for this factor is calculated from dividing the Integral of the AHRR curve between SOC and EOPMB by the Integral of the AHRR curve between SOC and EOC.
5. End of premix burn (EOPMB): the end of premix burn is defined as the first point at which the second derivative of the AHRR reaches a local maximum following a global minimum. In most conditions, the value of this factor approximates the one that corresponds to the position at which the AHRR curve reaches its first local minimum after a global maximum. But in this study, the second differential was used instead due to the reason of unclear local minimum in the AHRR curve under low load conditions which can be observed in figure ( ).
6. End of combustion (EOC): this point can be defined as the first point at which the moving average of heat release rate drops below zero. The moving average was used to minimize the noise impact on the results accuracy while keeping its representative consistency with the general tendencies of collected data. Additional characteristic values can be calculated from the in-cylinder pressure data, these include: the total
apparent heat release, peak AHRR, angle of peak AHRR, angle between SOC and peak AHRR, PMBF, 10 – 90% burn fraction intervals, duration of partial burn fraction intervals, and average burn rates through partial intervals. Emissions data averaged over 180 s durations were recorded.
you can see my paper
An Investigation of the Relation Between Combustion Phase and Emissions of ULSD & RME Biodiesel with a Common-Rail HSDI Diesel Engine
Question
significance of calculating the mass heat flux in flow boiling experimentation.
A small edtion,
Thank you. In any boiling process exit heat flux (q in J.m^-2.s^-1) and mass flux "of evaporated fluid" (N in kg.m^-2.s^-1). The heat flux provides the energy requirements for phase change form liquid to vapor. Now, like any liquid in its boiling point (the temperature at which the liquid vapor pressure is equal to surrounding pressure) transform the total of the energy supplied in latent heat its temperature remains constant. Therefore in any boiling experiment the mass flux "of evaporated fluid" (N) indicates the heat flux (q) through the liquid evaporation latent heat (DHv in J.kg^-1): N=q/(DHv)
Question
Heat transfer in brazed plates exchanger
Dear Mohamed,
I invite to take a look at Ph.D. thesis that can be found in the following link (it is in french) :
or at the article :
I have studied single phase flow and two-phase flow (condensation) inside BPHE. In general there is no single value for "critical" Reynolds number. I prefer not to call it critical because it is not a transition between laminar and turbulent flow. it is in fact a transition between helical flow and zig-zag (cross-flow). this Reynolds number represents the transition between a dominant helical flow for Re < Re_cr and a dominant zig-zag flow for Re> Re_cr.
the value of this Reynolds number depends on the geometry (inclinaison angle, corrugation pitch, plate spacing). In my Ph.D. , the first part is about single phase flow where you can find all the previous informations.
I hope this will be helpful for you.
Kind regards,
Kifah SARRAF
Question
How to do geothermal power plant optimization by using EES software with turbine and condenser pressure parameters
Dear Alimuddin Muchtar
after finishing the system modeling by the EES, I mean calculating each states thermal properties, you can comment each parameter that you want to see the effects of its variation like optimization, then yo can use min/max icon at the EES as the optimization tool. Just remember it is needed to fix the min and max value of variable and also, initial value of function is important.
Question
IN THE NAME OF GOD
I want to calculate the temperature after a stage of orifice plate in which we drop pressure from P1 to P2. (So temperature drops from T1 to T2.) (For example for Methane)
I studied somewhere we can consider gas flow through an orifice as an adiabatic process.
On the other hand we have PV^k=constant for reversible-adiabatic process in which k=Cp/Cv . But I think my process is not reversible.
Can we use polytropic formula for it? If it is ok, How I can find the power of V in PV^n=constant ? (n=?)
Can I calculate it by formula or find it by using gas property tables?
What's your suggestion for calculating T2 after orifice plate?
In an orifice plate, the total enthalpy should stay constant. At which pressure is the methane? If your fluid is an ideal and perfect gas (pressure not too high) and the cross-section after the plate is the same as in front of the plate, you can then assume that also the temperature remains constant (dh = cp*dT,  therefore with dh = 0, dT = 0). It depends a bit on whether you can assume ideal gas conditions or not.
Question
In FSAE events we need to use a restrictor of 20mm diameter in the upstream of intake manifold. it is to restrict the intake mass flow rate. my question is how it affects the engine power output? any mathematical formula is welcomed.
Thank you.
The output power is m_dot*g*h_flow. m_dot is the mass flow rate, g=9.81 m/s^2 the gravitational acceleration and h_flow is the head of flow. By using the restrictor, the h_flow (can be converted to pressure) is reduced. The mass flow rate is already reduced therefore you should expect lower power (and not constant power) output.
Question
A Carnot engine running between two temperatures Tc and Th has the efficiency 1-Tc/Th. According to Carnot’s theorem all reversible engines running between Tc and Th would have the same efficiency. However if I calculate the efficiency for an engine with two isotherms at Tc and Th which are connected by either isobars or isochors I get an efficiency lower than that of the Carnot process unless I let the compression ratio become infinite. How do I resolve this contradiction.
Hi Philip
First of all, there should be no controversy about efficiency: it's work out (what you get) over heat in (what you pay for). Heat exchange with regenerators is free (internal exchange, you don't have to provide the heat from, say, burning a fuel), hence is not considered in the efficiency.
From all I know, the Stirling cycle, that is the ideal cycle as well as all real life approximations in Stirling engines, always include the regenerator. The ideal cycle has no irreversibilities, exchanges heat externally only with the reservoirs, at reservoir temperature, hence has Carnot efficiency.
When you consider a cycle of isotherms and isochors without regenerator (I would not call it Stirling), then you have two options:
(a) you still exchange heat only with the two reservoirs at TH, TL, which leads to heat transfer over temperature differences. Hence, the cycle is irreversible (entropy generation in heat transfer), and, quite naturally, the efficiency is lower than that of the--fully reversible--Carnot cycle running between the same two temperatures.
(b) You use, as you suggest, an infinite series of reservoirs at different temperatures during the isochoric heating and cooling process. Then, the process can still assumed to be reversible. But this cycle cannot be compared to the Carnot engine, because the set-up is different: Carnot exchanges heat only with two reservoirs, while this cycle uses a (infinite?) number of reservoirs at different temperatures. It should be possible, indeed, to slice this process with many reservoirs into pieces, and consider it as a combination of Carnot cycles, each between a different pair of temperatures.
The Carnot engine is a rather limited model, since it assumes a process just between TWO reservoirs, nothing else. If there are more reservoirs to consider, or heat exchange with a gradually cooling flow, etc, the analysis of cycles based on first and second law becomes more involved, since all reservoirs have to be included (you get a taste in Chap 11 of my book, as linked before).
Question
This can be attained by evaporative cooling by fog or cooling wet pads.
We need to compare between  added cos and the energy benefit.
The efficiency of any heat engine is maximized by raising the inlet temperature Thot and lowering the outlet temperature Tcold. For example the Carnot efficiency is 1 - Tcold/Thot and for the Curzon-Ahlborn efficiency is 1 - (Tcold/Thot)^1/2.
Question
In refrigerators and air conditioners to increase the refrigeration effect, the capillary tube and suction line are placed in contact with each other to make a suction line heat exchanger usually available in two configurations.
1. Latent (Capillary having a line contact with the outer diameter of the suction line)
2. Co-axial/ Concentric (Capillary inside the suction line)
Thank you, Andre.
Assuming that both models operate under same conditions (LBP ASHRAE), and have same mass flow rates.
If I compare the heat transfer areas of the two heat exchanger configurations,
The lateral type configuration only has two tubes the capillary and the suction line in line-contact with each other. Here the heat transfer area is only limited to the contact area between the two tubes.
whereas the Coaxial type configuration has one tube inside another and thus seems to have far more surface area available for heat transfer.
So I am wondering if the coaxial type configuration would be a better choice of the two, heat transfer wise.
I know that I would have to eventually do the numerical analysis and experimental trails. But I was hoping to find some literature or some basic information from someone who might have studied this earlier.
Question
properties of condensing operators
thanks the chapter 2 of this book is good.
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is it the diameter size, the angle or the length of the nozzle?
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I have a cylindrical combustion chamber cookstove. The feed rate of the cook stove is 1 kg/h (CV of fuel 18.5 MJ/kg). I would like to determine the temperature distribution over the inner surface of the combustion chamber analytically. How do i determine this?
Dear Rupam,
a realistic result implies the use of 3-D models and as mentioned previously a finite volume approach (using a software) is appropriate. however, if you want to consider simple case of homogeneous surface temperature at steady state you can apply the energy balance at the inner surface and use an energy balance at the outer surface in order to determine the temperature of the inner surface. in your case, once can assume that the temperature (in cylindrical coordinates) doesn't depend on teta (angle) nor the radius because normally you have a thin wall. the only variable is z ( the vertical distance). thus if the cookstove height isn't much, you can look then for a (one) temperature of the interior wall. I repeat, this is only due to previous assumptions and to simplify the equations.
next step would be to determine the flame temperature (assumed adiabatic flame temperature) by using the chemical reaction between the fuel and air and determining the combustion products compositions. then the flame temperature will be used for the radiation part in the energy balance at the interface where you need to add the convection part. the convection part is determined based on Nusselt correlations for internal convection, you have the mass flow rate and the cross-section of the cylindrical combustion chamber, thus you can calculate Re and based the thermo-physical properties of the exhaust gas (for simplicity, it might be assumed as air), you can deduce the average heat transfer coefficient.
It is interesting to compare the results of 1-D simple model with the finite volume (3D-model). Good luck.
Kind regards,
Kfiah SARRAF
Question
For instance, 4 inline 2.0 litre engine with V6 2.0 litre engine. Do they produce same output in terms of power and torque? One engine built with 4 piston and the other with 6. Would that effect the performance? Open for discussion.
The V-6 will be a much sweeter engine, whether or not it gets more power than an equal displacement 4 inline. And a straight 6 would be even nicer, in terms of vibration-free operation.
At equal displacement, and let's assume (to reduce the variables) that both are naturally aspirated, power and torque would depend on many factors. Generally speaking, the engines would be similar in performance. But for example, increasing the stroke, and consequently reducing the bore, will typically give you more torque but less maximum horsepower. The maximum revs are reduced, when you have long stroke, because the pistons have a longer distance to travel for each revolution. However in order to create the greater stroke, the crankpins have to be offset more from the crankshaft itself, resulting in greater leverage from piston connecting rods to the crankshaft. That greater leverage creates more torque.
So you get more low end torque, but not enough revs to create that high horsepower, which requires high revs.
But again, the number of cylinders per se doesn't make a huge difference to performance. On the positive side, more cylinders will mean greater total piston area, for a given displacement. So that would improve efficiency. (Same calculation that makes 4 valves per cylinder better than two.) On the negative side, you have more frictional losses with more cylinders, so that reduces efficiency.
Automakers seem to have discovered that the best fuel efficiency, in practice, is achieved with turbocharged 4 cylinder engines. That might be true, but 4 cylinder engines, even with balance shafts, simply do not feel as nice as V-6s or inline 6s. Give me a small displacement 6 in favor of a 4 any day.
Question
The main function of the expansion valve in a refrigeration system is to reduce the pressure of a fluid by controlling the flow rate of the fluid. When the pressure of the fluid decrease, so thus the temperature of the fluid (according to the properties of the fluid, the pressure reduces and the enthalpy might remain unchanged, the temperature will drops). So, is it correct if I say I use expansion valve to reduce the temperature of the fluid/ refrigerant.
You have to be clear on the system's objective. If the objective is cold production, then by using EV reducing the pressure will meet the objective by the consequent reducing temperature. I believe in not fixing a specific strict function on an instrument but rather on fulfilling the objective of the system. Thus you may have also capillary tube, throttling valve, or any forced convection 'tool' to reduce the working fluid temperature.
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Hi to all,
Does anybody know any reference book or articles about modeling and control of heat recovery steam generator (HRSG) and boiler ?
Thanks.
I think it is an excellent  book
Industrial Boilers and Heat Recovery Steam Generators : Design, Applications, and Calculations.
V. Ganapathy
ABCO Industries
Abilene, Texas, U.S.A.
sincerly
Question
there are some research groups who are working with new refrigerants properties using vapor compression system.
Thank you very much. Actually we have our own experimental set up to study the cycle performance of new refrigerants. I just wanted to know how the other group study new refrigerant.
Question
LiBr-H2O  Solution single effect absorption chiller Refrigeration System
1) The specific exergy is the sum on the physical exergy and chemical exergy.
a- Physical exergy : (h-h0)-To(s-so)
b- Chemical exergy: Standard exergy + Dissolution Exergy
If the chemical exergy shall be evalueted, how should I calculated the activities for H2O and LiBr ?
Can anyone provide a sample calculation ?
Do EES can provide the evaluation of the chemical exergy ? What is the function that shall be used ?