Thermodyamics Definition and 254 Discussions

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  1. P

    I About the proof of the Carnot theorem given in 'Heat and Thermodynamics'

    But if I would assume that the efficiency of the carnot's engine is greater than the other engine and the carnot engine is driving the other engine backward as a refrigerator ,that would lead to the same contradiction hence disproving carbot's theorem! Is there something wrong I have done...
  2. J

    I Heating gasses in space -- How could we make a greenhouse in space?

    I was thinking the other day about green houses and how they would act in space or on another planet without an atmosphere. I know that green houses work on Earth by stopping convection but could they theoretically trap heat in a non atmospheric environment? I am imagining a material that allows...
  3. S

    I Mining the Universe's expansion?

    There is an article written by astrophysicist Edward Harrison [1] which defends that energy could be extracted from attaching an imaginary cosmologically long string to a receding object from us in an expanding universe. He says that the energy extracted is potentially limited (in decelerating...
  4. S

    I Would infinite entropy break all symmetries?

    If the Universe could somehow reach a state of infinite entropy (or at least a state of extremely high entropy), would all fundamental symmetries of the physical laws (gauge symmetries, Lorentz symmetry, CPT symmetry, symmetries linked to conservation principles...etc) fail to hold or be...
  5. cianfa72

    I About Reversible vs Irreversible Gas Compression and Expansion Work

    Hi, reading the interesting Reversible vs Irreversible Gas Compression and Expansion Work insight by @Chestermiller I would like to ask for clarification on some points. In the second bullet at the beginning my understanding is as follows: consider an ideal gas contained in a cylinder...
  6. T

    Cooling a marine engine while testing

    For my internship I have to test and certify a Marine diesel engine. We are trying to run a few tests in our workshop, but this obviously means we can't use the sea or a river as cooling. We bought an IBC tank, which can hold a 1000 liters of water. The water from the tank will be running...
  7. A

    Calculating specific heat capacity from entropy

    Hey guys! I'm currently struggling with a specific thermodynamics problem. I'm given the entropy of a system (where ##A## is a constant with fitting physical units): $$S(U,V,N)=A(UVN)^{1/3}$$I'm asked to calculate the specific heat capacity at constant pressure ##C_p## and at constant volume...
  8. mcas

    Find change in entropy for a system with a series of reservoirs

    I've calculated the change in the entropy of material after it comes in contact with the reservoir: $$\Delta S_1 = C \int_{T_i+t\Delta T}^{T_i+(t+1)\Delta T} \frac{dT}{T} = C \ln{\frac{T_i+(t+1)\Delta T}{T_i+t\Delta T}}$$ Now I would like to calculate the change in the entropy of the...
  9. mcas

    Find the change in entropy for an ideal gas undergoing a reversible process

    We know that $$dU=\delta Q + \delta W$$ $$dU = TdS - pdV$$ So from this: $$dS = \frac{1}{T}dU + \frac{1}{T}pdV \ (*)$$ For an ideal gas: $$dU = \frac{3}{2}nkdT$$ Plugging that into (*) and also from ##p=\frac{nRT}{V}## we get: $$S = \frac{3}{2}nk \int^{T_2}_{T_1} \frac{1}{T}dT +...
  10. P

    Problem on thermal radiation and lenses

    I know that the Sun is at a very far distance from the lens, so I assume the rays are parallel and the image is formed at the focus (500mm away from the centre of the lens). How do I calculate the diameter of the image? The hint to solving this problem says that "The angular diameters of...
  11. E

    Work in thermodynamics

    i can't manage to grasp the concept of PV work in thermodynamics, for example we all know that W= integral(F*dx) like here but this says that, at the end, W doesn't really depend on the gas temperature or reversible process crap at the end W is simply a constant, atmospheric pressure is...
  12. C

    CO2 Sequestration and Cave Pressure Problem

    I've made it through the first 2 parts, it's just that part C has me stumped. I don't know how to manipulate the information I already know to figure out the total work energy required by the compressor, ##W_{compressor}##, during the process.
  13. J

    Relativistic heat conduction

    Are there any known instances of heat transfer via conduction or convection happening at relativistic speeds? Is this even possible or is there a non-relativistic limit to how fast heat can transfer in these ways, like how sound can only move so fast?
  14. N

    Temperature of a Solar panel in space

    Consider two 1 square meter marble slabs each of mass 1 kg floating in space facing the sun such that light from the sun incident perpendicularly on the flat faces. At equilibrium, power received from the sun 'PS' equals the power being lost in the form of radiation 'PR'. PS = PR (at...
  15. Rahulx084

    Joule Thomson expansion

    Wikipedia says, Unlike a free expansion , in Joule Thomson expansion work is done causing the change in internal energy. Whether the internal energy increases or decreases is determined by whether work is done on or by the fluid; that is determined by the initial and final states of the...
  16. StoningTree

    Cooling with Evaporation

    First i calculated the latent heat of vaporation: h_vap(15°C)= 2465.4 kJ/kg In the next step i calculated how much water is already in the air: x=0.622*j*ps/(p-j*ps)=0.00988 kg/kg where: j=50% ps=0.03171 bar p=1.01325 bar Now that i know that i can calculate the enthalpy of humid air: h_hum =...
  17. Rongeet Banerjee

    Thermodynamics in Physics

    In this particular Question according to Meyer's formula,the value of Cp should be (8.314+5) i.e. 13.314 .But that option is missing. There is another approach to this problem by finding the Adiabatic Coefficient and then finding Cp.I have no problem with that approach. But my initial doubt...
  18. cheekyhouidini

    Mass of water given only power and density

    Cannot figure out where to start, apart from maybe something to do with specific heat capacity of water?
  19. Rahulx084

    Irreversible quasi-static processes?

    I read an example where if I go from initial to final state extremely fast (gas inside a piston cylinder assembly) , the gas inside it will be very unhappy, its not going to stay in equilibrium, parts of the system are going to be at different pressure and parts of it at something other...
  20. domingoleung

    Gas in a syringe being compressed - thermodynamic processes

    1. Adiabatic compression (When compressed quickly, there is no heat flow to the environment Q=0) Isochoric with heat loss (The syringe is still compressed, there should be no change in volume) Adiabatic expansion (When the syringe is released, there is work done only) Isochoric with heat gain...
  21. F

    Thermodynamic equation of differentials (and how to work with them)

    Disclaimer: I am not a mathematician, I am a physicist. The thermodynamic identity is usually expressed in the following differential form $$ dU = TdS - PdV + \mu dN, $$ where U , T , S , P , V , \mu and N are the internal energy, temperature, entropy, pressure, volume, chemical...
  22. P

    Entropy and the Helmholtz Free Energy of a Mass-Piston System

    Attempt at a Solution: Heat Absorbed By The System By the first law of thermodynamics, dU = dQ + dW The system is of fixed volume and therefore mechanically isolated. dW = 0 Therefore dQ = dU The change of energy of the system equals the change of energy of the gas plus the change of energy...
  23. J

    Heat transfer through a MultiLayer Cylinder (find the Temperature inside)

    Hello, I am a Mechanical Engineer a little out of practice on Heat transfer. I am trying to solve this problem. It must be solvable but i have yet to find right equations online. I have a multi Layer Cylinder made up of C350 marraging Steel,Zinc Alloy-12 , then 6061 Aluminum T6. All that is...
  24. Robert DeVries

    Trouble with fluid thermodynamics and nuclear thermal rockets

    Summary:: In need of help determining the exhaust velocity of a rocket nozzle given temperature and propellant molar mass Greetings and salutations! My name is Robert DeVries, world builder extraordinaire. I have come with questions in search of answers. So for the last few days I've been...
  25. Aletag

    Work done BY the gas in a cyclic thermodynamic process

    Since the assignment asks the work done by the gas, that should be equal to P1*(V2-V1) aka the area under the P1 line. Do I have to subtract the work done to the system or is this the solution already? If so, why do I need P2?
  26. patric44

    Question in Bose-Einstein statistics

    iam not getting why in bose statistics the number of ways to arrange ni particles in gi degenerate states is = (gi+ni-1) ? and why do we divide by ni factorial , and gi factorial .
  27. Baibhab Bose

    Final temperature of an adiabatic process between two reservoirs

    *Here, no mention of these reservoirs being a gas, so I'm not sure if I can use the PV=nRT or the P*V^(gamma)=K equation. SO I am left with only the 1st law. If I can write dQ1( going out from object 1)= Cp (indep of T)*(Tf-T1) dQ2(coming into the object 2)= Cp*(T2-Tf)...
  28. M

    How is it possible to use only 1000 W to transfer 10,000 BTU/h?

    Hi, I was reading a newspaper article on the energy efficiency of commonly used air conditioners in homes. Then a doubt arose when the article informed me that there are air conditioners that have an energy efficiency of 10 BTU/watt. That means a classic 10,000 BTU/h air conditioning machine...
  29. M

    Ending global warming with Maxwell's demon

    As a start for discussion I'd like to make the following bold claim: Both the problems of enough usable energy and global warming can be resolved by implementing Maxwell's demon on a large scale. To justify this bold statement somewhat, I'd like to point to a (relatively) recent...
  30. C

    Could somebody please explain the vapor compression cycle?

    Heat is taken from food in the refrigerated space to the evaporator which has evaporated (I am assuming saturated vapor) refrigerant flowing through it. My first stumble would be, if this is true, why doesn't the temperature increase for the fluid coming out of the evaporator (unless it is...
  31. Harperchisari

    Thermodynamics in an ion beam?

    Hi there, I'm trying to design an ion beam source, but having some issues with the thermodynamics of it. I'm no expert in thermodynamics, but I do understand some. I'm trying to find an equation which I can use to find the amount of energy I need to put into a set mass of a set material in order...
  32. Zeynaz

    Could you help me with this thermodynamics question?

    So, I converted the V (milk) to m3 and found 1.8E-4 m3 and i already know the density so i found the mass of the milk in the bottle. Mmilk= 1.9E-7 kg Normally i would try to connect it with the formulas above but i don't know temperature. I am not sure how i can connect the dots. Can...
  33. C

    For a throttling valve, why is it that temperature remains the same?

    For a throttling valve C.V analysis, I am wondering why is it known that temperature remains the same for ideal gases. I understand that using the energy balance equation, I end up with h1=h2. Pretty simple so far. By breaking down enthalpy into its components u1+P1v1 = u2+P2v2 I realized that...
  34. QuasarBoy543298

    The zeroth law of thermodynamics

    let's assume I have 2 systems A and B. the surface that describes when the 2 systems are in equilibrium is given by F(a1,a1,...,b1,b2,...) = 0. assuming we can write this surface as A(a1,a2,..)=B(b1,b2,...) why do A and B describes the temperature function of the systems? in class, we...
  35. K

    Compressed Air Engine Calculations

    Hi, I am designing a compressed air engine for a project. A little stuck with calculations. I need to work out how long the engine will run at its top speed using a air pressure which is supplied from a compressed air tank. Compressed air pushed down a piston which is connected to a...
  36. C

    What is the difference between flow energy and boundary work?

    What is the difference between the two? Also, as another question, for enthalpy, is it correct to define it to be the sum of internal energy and flow energy or is there another understanding for it? Thanks in advance
  37. C

    How does specific volume play its role in the phase diagram?

    So, I am casually sifting through a chapter in a thermodynamics textbook talking about the multiphase process that pure substances go through. I understand how the P-v and T-v diagram works and that out of the three properties (specific volume, temperature and pressure), two of them are...
  38. C

    Does temperature increase when water is boiling at 100C......

    Does temperature increase when water is boiling at 100C in a closed system? I am picturing a scenario where I am boiling water in a pot to make pasta. However, I decide to close the pot as the water is still boiling. By doing this I am sealing away the system of study from the environment. Thus...
  39. babaliaris

    Thermodynamics simple problem.

    I'm new to thermodynamics and after some reading I tried to solve the problem below but I have stuck (I think this problem assumes you know only the first law of thermodynamics) You have a piston resting on some stops inside a container filled with water and you want to find out after heating...
  40. EastWindBreaks

    Heat exchanger - efficiency of the cycle

    Homework Statement Homework Equations The Attempt at a Solution Since we want the fluid to be in liquid state before entering a boiler, and super-heated water can only reach 374°C before entering super-critical state, suppose after the expansion, the temperature at point 3 is still higher...
  41. U

    Are all arrows of time special cases of the thermodynamic one?

    Are all arrows of time special cases of the thermodynamic one? The arrows of time I am referring to are the psychological arrow of time and the cosmological arrow of time. Thanks.
  42. hnnhcmmngs

    Minimum heat removed from gas to restore its state

    Homework Statement After a free expansion to quadruple its volume, a mole of ideal diatomic gas is compressed back to its original volume isobarically and then cooled down to its original temperature. What is the minimum heat removed from the gas in the final step to restoring its state...
  43. CrosisBH

    Mass of Ice required to achieve a certain final Temperature

    Homework Statement An insulated beaker with negligible mass contains a mass of 0.350 kg of water at a temperature of 76.5 °C. How many kilograms of ice at a temperature of − 23.9 ∘C must be dropped in the water to make the final temperature of the system 40.0 ∘C? Take the specific heat for...
  44. E

    I Derivation of the Onsager symmetry

    Derivation of the Onsager symmetry in many textbooks and papers is as follows: First, assume that the correlation function of two state variables,##a_i## and ##a_j## satifsies for sufficiently small time interval ##t## that $$\langle a_i(t) a_j(0) \rangle = \langle a_i(-t) a_j(0) \rangle =...
  45. jybe

    Work on a compressed gas

    Homework Statement What is w when a gas is compressed from 42.1 L to 25.1 L using a constant external pressure of 739 Torr? Remember to include a "+" or "−" sign as appropriate. Homework Equations W = -P(dV) The Attempt at a Solution Pressure = (739 Torr / 760 Torr)*(101.325 kPa) W =...
  46. P

    Creating steam efficiently

    Hello! new here. recently I've developed an interest in the way electricity is produced, I've seen some mechanisms, most of them are steam turbine based. i have a few questions about the topic, mainly about thermodynamics. if i want to create enough energy to move a steam turbine that requires...
  47. Q

    Thermal Expansion (Area Expansion) problem help

    Homework Statement A steel ring with a hole having area of 3.990 cm2 is to be placed on an aluminum rod with crosssectional area of 4.000 cm2. Both rod and ring are initially at a temperature of 35.0°C. At what common temperature can the steel ring be slipped onto one end of the aluminum rod...
  48. C

    B Could steam be expanded through a nozzle to get 0°C gas?

    Obviously expanding the gas cools it down. I'm interested if you could boil water and then expand the high pressure steam to cool it down to 0°C. Or are there subtler thermodynamics that would prevent this?
  49. DLeuPel

    What is temperature?

    The understanding that I have of temperature is that it is defined as the vibration of particles. Now, does this mean that in a vacuum where there are no particles the temperature is the absolute 0 ?
  50. EastWindBreaks

    Are theses approaches correct? (entropy change of water turning into steam)

    Homework Statement An insulated piston-cylinder device contains 5 L of saturated liquid water at a constant pressure of 150 kPa. An electric resistance heater inside the cylinder is now turned on, and 2200 kJ of energy is transferred to the steam. Determine the entropy change of the water...