Exergy - Science topic

need to know if an energy and exergy analysis for a heat pump was done in a Net Zero Energy building environment

Hello everyone,

I am currently working on calculating the exergy efficiency in a shell and tube unit for thermal energy storage. In this system, the heat transfer fluid (HTF) circulates through the tubes, while the phase change material (PCM) is contained in the shell.

I am using ANSYS Fluent for this analysis. However, I am encountering a challenge regarding the calculation of the exergy stored in the PCM. Specifically, I am uncertain about the appropriate temperature to use in the calculation. I have replaced the temperature (T) with the average temperature of the PCM, but I am unsure if this is the correct approach.

Attached below is a picture showing the expressio used to calculate the exergy stored in the PCM during the melting/solidification process. If anyone has experience with this type of calculation or can offer some advice, I would greatly appreciate your input.

Thank you in advance for your help.

Best regards.

Can energy management and its conversion through electromagnetic conversion into electricity reduce and benefit from its environmental risks and impacts?

The global community has a responsibility to address the environmental concerns for energy purposes by replacing existing coal and hydrocarbon methods with sustainable and efficient energy systems. Hence, current power generation systems are constrained by physical laws that reduce performance by converting more energy into heat. Similarly, the revolution and widespread implementation of renewable energies worldwide have shown that electromagnetic transfer is a viable option for harnessing the induced mechanical energy provided by wind or water into exergy. Exergy focuses on the efficiency of the second law of thermodynamics with the aim of ensuring the availability and quality of energy in energy management systems. Therefore, it is necessary to reduce energy demand by building highly efficient electrical appliances and increasing the quality of energy with the output power generation systems. This chapter provides a single diagram for developing new models and designs for power generation with the aim of developing variable efficiency power systems. In addition, an analysis of magnetism, electromagnetic induction, and magnetic materials will be conducted for design, optimization, and implementation in current power cycles.

The cryogenic system is a liquefaction system.

Dears

I am working on single-effect absorption chiller. In the refrigerant leg where pure water (as refrigerant) exits the evaporator, its exergy decreases because its temperature is under ambient temperature. Is this right? Why does this happen?

Consider a heat exchanger with two streams A & B. Going by Fuel-Product definition for exergy analysis, suppose stream A is the fuel stream and stream B is the product stream. My question is whether the following can be possible.

Exergy @ A_in > Exergy @ A_out &

Exergy @ B_in > Exergy @ B_out.

If this will be true then Exergy destruction = Exergy of Fuel - Exergy of Product will become more than exergy of fuel and thus make the exergetic efficiency of that heat exchanger to be negative.

How to write the fuel and product exergy balances in the cascade heat exchanger in the cascade refrigeration system?

While performing second law analysis of plants (sometimes also regarded as exergy analysis by some researchers) what could be the most suitable definition/relation for Second Law efficiency.

Is there any difference between exergy efficiency and Second Law Efficiency?

In many studies, exergy destruction and exergy loss occurred simultaneously. When describing them, it is usually explained that they are caused by irreversibility, such as temperature difference, friction or adiabatic throttling. What is the essential difference between exergy damage and exergy loss?

Is it possible to ignore chemical exergy when there is no reaction? Let's say there is a separation process of a feed into liquid and gas stream or another example would be when two streams are combined together in a mixer. Is it possible to calculate exergy destruction only based on physical exergy and assume that there is no change in the chemical exergy?

Thanks in advance for your contribution.

Hello,

How can we determine the exergy by Ansys Fluent program? or any another program to solve the exergy equations by simple method?

I am conducting an exergoeconomic analysis of HVAC system energy consumption in a classroom, considering three parametric cases: air conditioning only, air conditioning with mechanical ventilation, and air conditioning with a membrane heat exchanger. I am struggling to determine the specific processes I should follow and employ for my research. Should I perform the analysis using software or manual calculations? This study is an extension of a previous study conducted by my senior, and he has provided me with the electricity consumption data for the three cases. Could you please provide some guidance?

I prefer studying in Textbook so I read along the textbook named: "Thermodynamics: An Engineering Approach by Cengel" and there are chapters about Exergy and Gibbs energy. But the problem is my professor didn't teach or even mention it in the class. The book then utilizes tons of Exergy analysis in the succeeding chapter while I was taught only simple entropy analysis. Now the course is coming to an end and I will have a month break before the next semester starts. Should I study the chapters by myself or should I just skip them and pay attention to the subjects of the next semester?

How can I calculate entropy, and exergy efficiency in ANSYS FLUENT?

Doing exergy analysis of steam turbine. However, the exergy balance on boiler (heat exchanger) includes exergy of fuel which is to be determined. The measured data contained the mass flow rate of fuel.

Hello Every one, I am working on steam-water direct contact condensation problem. Can anybody help me how to perform exergy analysis using ANSYS Fluent software.

the

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Dr.Abolfazl Ahmadi

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Dear researchers, is there anyone who know the chemical exergy amount of "Molten salt" (60NaNO3_40KNO3) which use in the solar towers.. .

I designed LiBr/H2O single effect absorption refrigeration system using Aspen Plus. Energy analysis is OK. However, exergy destruction rate of solution expansion valve in absorption refrigeration system is negative. Do you know why it is ? Also, exergy destruction rate of pump is so large.

Please note that the exergy destruction of the flash separator is calculated by taking into account both physical and chemical exergy. the inlet mixture consists of methane, ethane, and propane. The major constituent is methane. whereas no pressure drop is involved and the process is below ambient i.e., -105 C.

Hello,

I designed a single effect absorption cooling system working with LiBr/H2O in Aspen Plus software. But the exergy flow rates don't seem right. For example, when I try to find the exergy destruction of the pump (and other components), the result is negative. What is the reason of this? My reference conditions are 25 oC and 101.325 kPa.

I am looking for help in finding the standard chemical exergy value of a component. For example, in literature, we can find the standard chemical exergy value of nitrogen as 0.72 kJ/mol. How one can calculate this value? Actually, I want to calculate the chemical exergy value of perhydro dibenzyl toluene (C21H38), and dibenzyl toluene (C21H20).

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.

Obtain the following information about a power plant:

1. The net power output.

2. Exergy.

3. The type and amount of fuel used;

4. The power consumed by the pumps, fans, and other auxiliary

equipment; stack gas losses;

5. The rate of heat rejection at the condenser.

Using these and other relevant data, determine the rate of irreversibility

in that power plant.

Dear RG,

I am working on the waste gas from the refinery to electricity production. I propose to utilize Aspen Hysys Model from where conventional exergy will be evaluated. However, I'm unable to make real progress on the part of Advanced Exergy in my initial dry-run following the challenges I'm having to determine the unavoidable exergy of my components. I have the following challenges: (1) Is it possible to use Hysys as a thermodynamic tool to calculate unavoidable exergy (advanced exergy) for my components? If Yes, how is it done? If not what thermodynamic tool can I use?

(2) The mathematical (Graphical) approach for Unavoidable exergy calculation appears to me to be more straightforward from the several journals I have read. But unable to determine the straight-line graph despite defining the ideal operation of each of the components. Therefore, I would appreciate it if you can take out a few minutes of your time to provide me with a clear guide to enable me to unveil the challenge I am experiencing with the concept of Advanced exergy splitting calculation. I appreciate your kind feedback and the wonderful work and contributions you have been making to the engineering world.

O.D. Samuel

Could anyone please share the sample calculation for the inlet and exhaust exergy calculation for simple PEM fuel cell?

somebody, please elaborate on how to calculate exergy destruction in kW units. from Aspen HYSYS I found mass exergy with kJ/kg unit and i don't know how to calculate it by using Aspen HYSYS and if somebody has mathematical calculation with example please share with me. I know how to calculate by aspen plus but I need a mathematical or Aspen HYSYS solution.

thanks in anticipation

I am designing a new system for natural gas liquefaction but I couldn't find how can I calculate its exergy destruction in kilowatt and I also tried to find from previous research on this topic but couldn't help me to find an answer even roundabout to mention in the previous study .. so if anyone knows kindly guide me the right way to solve this problem ..

thanks in anticipation.

Which tool can l use to calculate chemical exergy in Aspen Plus, as far as l am concerned, Aspen Plus does not ccalculatehemical exergy of material streams.

Anyone who know a free tool l can use for calculation of exergy?

Hi, I have a question: I would like to use the enthalpy and exergy values of streams to build a Sankey Diagram of my process. But because of pre-build reference temperature and pressure, the enthalpy and exergy values of streams have mostly negative values. How can I deal with this problem?

Dear Colleagues

Recently I start the energy, exergy, economic and exergoenvironmental analyses of the configuration system that the configuration is attached. I want to calculate the entropy of the lithium bromide solution for the absorption chiller. But in the external library of EES software only calculate the enthalpy which I need the entropy for exergy calculationof . If anyone has an external library for calculation the properties of the lithium bromide solution please send it to me.

Regards

M.A.Ehyaei

How to calculate exergy efficiency of overall process? The process contains 3 compressors, 3 heat exchangers, 2 distillation columns and 3 pumps.

I have a condenser in my system which cools down Cyclohexane saturated vapor (mass flow rate=13 kg/s) to saturated liquid in 100 kPa using a subcooled CH4 flow in P=4000(kPa) and T=-160.3 (C) (mass flow rate=9 kg/s). Inexplicably the exergy efficiency of the component is greater than 1 whilst the exergy destruction rate is positive. Is it possible or I'm missing something?

Thank you for answers

As we know, every process in physics results in an amount of exergy destruction. Is there any estimation about the exergy destruction rate of the overall world processes? When the exergy of the world will be finished? Is there any estimation?

Exergy analysis of desiccant cooling system.

How to calculate avoidable and unavoidable exergy destruction?

e.g., if compressor have an exergy destruction of 2000 kW at 72% efficiency, and a destruction of 900 kW at 90% efficiency, then what will be unavoidable exergy destruction value?

Procedure required to calculate both forms of exergy destruction. I have simulated a plant on real, unavoidable and theroatical conditions, but unable to do the said exergy destruction..

Hello researchers, I need some suggestions to find out thermal exergy term for any heat transferring process. Hope to hear from you soon. Thanks alot

Do you think that the maximum exergy principle together with other thermodynamical related ecosystem

theories has its roots in the thermodynamical only in laws originally formulated?

Any information in this direction will be useful

Please, What is the value of energy efficiency and exergy efficiency for all lighting devices and how to calculate them?

if a combined cycle (brayton & ORC)coupled with the solar parabolic through collector it means its taking heat from the solar system. Then what is mathematical relation to put in EES which show the variation of exergy and energy efficiency of combined cycle with solar irradiation. another question is that how to calculate exergy destruction in the parabolic through collector.?

How to determine the exergy efficiency of heat integrated distillation columns, during cryogenic air separation. Would appreciate if anyone provide formula for both column`s.

I am unable to find the procedure, of how to calculate the exergy loss profile i.e., tray to tray in the distillation column operation.

FOM is a ratio of actual COP to the ideal COP and Exergy efficiency is a ratio of product exergy (output Exergy) to the fuel exergy (input exergy). The rationale behind the use of FOM and Exergy efficiency is not clear.

how to calculate the exergy destruction in parabolic through collectors. If number of collectors in series an parallel of LS 3?

How to calculate the unavoidable exergy destruction of demethanizer and deethanizer in the attached figure? Some paper said using minimun reflux ratio to calculate unvoidable exergy destruction of columns, but I find it impossible used it in complex demethanizer and deethanizer because infinite stages cannot be achieved in simulation. So I think wether it is right that I just increase the theoretical stages to a certain value and I define it as unavoidable condition.

How to calculate chemical exergy of the species that do not exist as stable components in the reference environment?

For example carbon dioxide (CO2) compressed at 298.15 K and 80 MPa

Standard chemical exergy of CO2 is only existed at gas phase.. so i don't know how to calculate chemical exergy of carbon dioxide in liquid phase

power plant - exergy

Dear researchers

I want to use commercial oils like Thermiol-VP1 as working fluid in solar collectors and insufficient data are available for these oils in the references. How can I calculate exergy and entropy properties?

Dear Researchers,

My researcher group and students are at edge of adopting exergetic tool to determine ineffectiveness in parts of bioreactor and might result in employing Sankey and Grassmann diagrams to depict the results of exergy. How can i explored the diagram?

Utilisation of heat transfer enhancement methods usually comes with undesired results; e.g. increased exergy destruction and/or pressure drop, which impose constraints of thermodynamic or practical nature.

Are there any standards (or otherwise, references which contain such standards) for definition of an optimisation problem for an energy system (heat exchangers, in my case)?

I'm mostly looking for material that can answer questions like the one that follows:

maximise Heat transfer enhancement

subject to Pressure drop increment < Given value

Many researchers have applied the traditional approach to estimating the flows of energy and exergy (Torio and Schmidt), Hepbasli, and Yücer ? I am looking for a new approach. I will be thankful, If anyone can help.

What and what must be in place before I can successfully carry out the energy and exergy analysis of a chosen vessel.

What is needed are those data that are indispensable for a work of this nature. research of this magnitude can be daunting and although Nguyen, Baldi and others have done similar work, what i might perhaps be looking for is the methodology employed and the data used.

I want to represent exergy flows in a system using Grassmann Diagram. I need some suggestions for software, tutorials or anything that may be helpful.

How do I create chemical and physical exergies as user variable in HYSYS and also include calculation procedure to compute them such that they become part of the stream properties that can be displayed or exported to other platforms?

exergy efficiency comparison

Hi,

If overall cost is minimized for a system or cycle, does it mean that exergy destruction is minimized?

regards,

Please let me know if you could introduce any reference

There are two definitions of exergy efficiency. i.e.

1. eff = Wnet/ Exergy In

2. eff= 1- (exergy destruction/ Exergy In )

While analyzing supercritical CO2 power cycles, the exergy efficiency from two definitions comes out to be different. There is almost a difference of 4 to 5%.

Kindly explain this?

I have realized that scientists and engineers in the field of energy and exergy hardly talk about the application of passive methods in their respective researches. But I see passive methods as conventional means of dispelling global warming and more importantly the leeway in achieving greener technology in our today's world.

My question on how to calculate the exergy and efficiency for a flat plate solar collector.......

Dear all,

I am looking for references that explains the steps of Exergy, exergoeconomic and exergoenvironmental analyses of Trigenerator. If there is any software can be used for this purpose that will be helpful as well.

Best,

For the exergy behavior of human body, researchers found that exergy destroyed and exergy efficiency decrease over human body is more efficient and destroys less exergy in lower relative humidities and higher temperatures. These conditions meet in the summer and presented discomfort conditions. Is the exergy efficiency in inversely proportional with the comfort conditions?

Nanofluids widely used to enhance heat transfer because of increase in thermal conductivity, at the same time the pressure drop increases as a result of an increase in viscosity of the new fluid. It is accompanied by smaller temperature gradients within the fluid and larger pressure drops when increasing the nanoparticle concentration. Pressure drop has a large effect on the exergy loss. Why is the exergy efficiency increased when using nanofluids?

In view of second law of thermodynamics, to optimize the performance of any thermal system, it is important to analyze the exergy of this system by making exergy balance between the system and the environment. In some researches, I noticed that the pumping power exists within the exergy balance. What is the relationship between the exergy and the pumping power?

Is there any available literature to calculate Exergy losses of Blast Furnace.

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

???

The enthalpy and mass flow rates of air after compression, mass flow rate of inlet fuel (CH4) and mass flow rates after combustion reaction are known. Complete combustion is assumed in combustion chamber. Kindly tell what is the best way to calculate exergy destruction in combustion chamber.

Exergy / Available energy is being lost in several engineering processes. It is of prime interest in the field of heat transfer. Is there any numerical models (or) some minor numerical works developed based on exergy destruction?

Or produced at an absorber or a condenser.

The exergy destroyed was obtained by balance of exergy at each component at the double-effect LiBr/H2O absorption refrigeration system.

I am evaluating the performance of Sensible Heat TES

 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 ?

How can I apply exergy to fabricated biogas reactor and oil screw expeller?

For Diesel we know HHV is 39,500 kJ/kg; Chemical exergy is 42,265 kJ/kg

Therefore Exergy grade function is 1.07

Can I use the same for HSDO and LDO?

I,m using a ideal gas model in ees and the exergy of stream is cosidered as following :

ex[i]=mf₁(h₁[i]-h₁[0]-T0(s₁[i]-s₁[0]))+mf₂(h[i]-h₂[0]-T0(s₂[i]-s₂[0]))+...

which mf_k  is the mass fraction of species k .

So s_k[0] should be calculated at the partial standard pressure of the species k or in the overall standard pressure?

Exergy, biodiesel, blends, Thermodynamics, diesel