What is Thermodynamic: Definition and 499 Discussions

Thermodynamics is a branch of physics that deals with heat, work, and temperature, and their relation to energy, radiation, and physical properties of matter. The behavior of these quantities is governed by the four laws of thermodynamics which convey a quantitative description using measurable macroscopic physical quantities, but may be explained in terms of microscopic constituents by statistical mechanics. Thermodynamics applies to a wide variety of topics in science and engineering, especially physical chemistry, biochemistry, chemical engineering and mechanical engineering, but also in other complex fields such as meteorology.
Historically, thermodynamics developed out of a desire to increase the efficiency of early steam engines, particularly through the work of French physicist Nicolas Léonard Sadi Carnot (1824) who believed that engine efficiency was the key that could help France win the Napoleonic Wars. Scots-Irish physicist Lord Kelvin was the first to formulate a concise definition of thermodynamics in 1854 which stated, "Thermo-dynamics is the subject of the relation of heat to forces acting between contiguous parts of bodies, and the relation of heat to electrical agency."
The initial application of thermodynamics to mechanical heat engines was quickly extended to the study of chemical compounds and chemical reactions. Chemical thermodynamics studies the nature of the role of entropy in the process of chemical reactions and has provided the bulk of expansion and knowledge of the field. Other formulations of thermodynamics emerged. Statistical thermodynamics, or statistical mechanics, concerns itself with statistical predictions of the collective motion of particles from their microscopic behavior. In 1909, Constantin Carathéodory presented a purely mathematical approach in an axiomatic formulation, a description often referred to as geometrical thermodynamics.

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  1. H

    A refrigerator in a hospital removes 40 kW of heat from a sp

    A refrigerator in a hospital removes 40 kW of heat from a space used for blood storage. The coefficient of performance of the refrigerator is 8. What is the work (kJ) required to operate the refrigerator continuously for one day? What I attempted to do: W in = Qin/COP therefore, Win =...
  2. R

    Thermodynamic Steam Trap; Pressure needed to Drive

    How much of a differential pressure does a typical thermodynamic steam trap need to discharge condensate? i.e. Say one needs to drain condensate from a shell under vacuum 310 mmHg abs, would a thermodynamic steam trap work correctly if I connected the discharge pipe to a vessel maintained at...
  3. Mnemonic

    Thermodynamics relating to temperature and phase changes V.2

    Homework Statement Suppose a room with 75 m3 of air also contains 80 kg of glycerol and the initial temperature in the morning is 16 °C. If 1.2 kWh of heat is added to the room between morning and afternoon, calculate the final temperature of the air in the room in the afternoon. Use 18 °C for...
  4. Nantes

    If the air temperature were the same as the human body's....

    Damn title character limits. I just had the weirdest thought while rearranging my computer's case fans. I put my hand in front of one of them and felt a light breeze of air, telling me it was working. This is due to the local cooling produced where the fan's airstream comes in contact with the...
  5. M

    Extracting Ambient Thermal Energy Without Gradients

    It seems possible to extract energy from the ambient air without temperature gradients (or at least with very small local gradients that will always be available). Being curious about this, I checked out some other threads and did not really find the specific question. (I did find some...
  6. @PinkGeology

    Why would hot fluid retain more % heat at lower flow rates?

    Homework Statement Hot magma (1500 K) is flowing into the Earth at rates of 0.05 meters/year, 0.5 meters per years and 1 meter per year. Although more total volume of magma will retain a temperature at or above 1150 K at higher rates of flow for any given time (say, at 1000 years), a higher...
  7. A

    I want to know the differences about isothermal process.

    I'm sorry for bad english. I wonder what is the differences between reversible-isothermal-expansion and irreversible-isothermal-expansion. Is their entropy same?
  8. J

    What Are the Thermodynamic Processes Involved in This Gas Cycle?

    if anyone could answer these questions it would be much appreciated Pump 3 Q1. A gas, with mass of 2.3 kg, undergoes a thermodynamic cycle which consists of the following processes, 1→2 Isobaric expansion, =2.3 bar , 1=4.1 m3 and 2=7.9 m3 2→3 Isothermal compression (=constant) where...
  9. andrewkirk

    Thermodynamic systems: spot the invalid fundamental equation

    Homework Statement In Herbert Callen's text 'Thermodynamics and an introduction to thermostatistics', 2nd edition, Problem 1.10-1 on page 32 presents ten potential fundamental equations of thermo systems, labelled (a) - (j), and asks the reader to identify the five that are invalid because they...
  10. M

    Peltier cooler- thermodynamics

    Im working on a project for fun using a peltier cooler. A tec1-12706. If i am operating the peltier at 9v, 6.4 amps of current and dt =45ºC (from datasheet) and bring its cold side in contact with a body at 33ºC for 10 seconds. Keeping hot side at 27ºC(cold side =-18) using sink, what will be...
  11. shrutiphysics

    Thermodynamic Query: Calculating Heat Transfer for Monoatomic Gas at S.T.P.

    one gram molecule of monoatomic gas is taken at s.t.p. keeping its volume constant,its temperature is raised by 1k. one gram molecule of the gas is added isothermally to this.the mixture is now cooled by 1k at constant volume to return to s.t.p. if [c][/v] be gram molecular specific heat of gas...
  12. PinkGeologist

    How Does Magma Injection Rate and Sill Height Affect Crustal Heating?

    Imagine you inject a 16km high stack of magma in the Earth's crust continuously over X years and then analyze the size and shape of the final "hot zone" as your "result" ... let's say you want to quantify the volume of crust at a temperature (T) greater than 1000 Kelvin (K). In case 1, that...
  13. S

    Question about derivations of thermodynamic properties

    I don't understand how some terms are derived. How did the last term of 3-47 originate? How did 3-49 get so many terms from just one term in 3-41? Why integrate from V to infinite? That is not intuitive. Thas a functions are unusual because the absolute values of U,H,S cannot be computed...
  14. mooncrater

    Thermodynamic Problem: Ideal Gas Expansion and Work Calculation

    Homework Statement Two moles of an ideal mono atomic gas (C2=12. 55 JK-1mol-1) expands irreversibly and adiabatically from an initial pressure of 10 atm against a constant external pressure of 1 atm until the temperature drops from the initial value of 325 K to a final temperature of 275 K...
  15. P

    How to derive U(S(V,T),V) from U(S,V,N)?

    Homework Statement My question is how can one derive U(S(V,T),V) from the relation U(S,V,N).This is the beginning of a given solution which is not explained in more detail. Homework EquationsThe Attempt at a Solution I can understand U(S,V,N) as dU=TdS-pdV+μdN but not the transition...
  16. S

    Thermodynamic question: first law

    Estimate the kilowatt pump you would need to pump 450 L/min of liquid water at 20c through a rise in elevation of 100m. Assume the water is pumped adiabatically and with negligible changes changes in temperature and kinetic energy. answer given to us is -7.35kw.. Question.. what formula should...
  17. K

    Thermodynamic Cycles & Formulas: A Summary

    This is not a homework question, but more of a information seeking question. I'm currently enrolled in Fundamentals of Thermodynamics where we studied many different cycles (Carnot, Rankine, Otto, Brayton, etc.) and their respective components (compressors, turbines, heat exchangers, pumps...
  18. D

    Can a thermodynamic heat engine include all these processes?

    Homework Statement Hi, I'm a new user and got this problem. Sorry to bother, but I couldn't find any relevant information from my Physics books.. The problem states: Build a heat engine using these processes: adiabatic, isothermal, isochoric and isothermal. The work-cycle of the engine must...
  19. S

    Brayton Cycle Thermodynamic Analysis

    Hi! I'd appreciate some help solving the thermodynamic's problem. I am sorry if the problem statement isn't 100% clear, as I've translated it from my native language. I'd really like if you could help me check my equations/procedure/results. In the following link both my attempted solutions...
  20. davidbenari

    Understanding Thermodynamic Efficiency: Debunking Myths

    The thermodynamic efficiency ##\eta## is calculated by ##\eta= \frac{W_{out}}{Q_{in}}## Using the first law of thermodynamics we usually say that ##W_{out}## is ##Q_c+Q_h##, where ##Q_c## is the heat dissipated into a cold reservoir, and ##Q_h## is the heat absorbed by the system because of a...
  21. SalfordPhysics

    Derive Internal Energy from Thermodynamic Identity

    Homework Statement For a single molecule, derive the internal energy U = 3/2kBT In terms of the partition function Z, F = -kBTlnZ Where Z = V(aT)3/2 Homework Equations Thermodynamic identity: δF = -SδT - pδV p = kBT/V S = kB[ln(Z) + 3/2]The Attempt at a Solution U = F + TS δU = δF +...
  22. kelvin490

    Thermodynamic temperature derivation

    In deriving thermodynamic temperature scale, it uses the concept that heat transfer between two reservoirs is the function of the reservoirs' temperatures. i.e. Q1/Q2=Φ(T1,T2). And then further express that Φ(T1,T2)=ψ(T1)/ψ(T2). I have two questions, 1. Is it a hidden assumption that the...
  23. R

    Difference between the absolute thermodynamic temperature scale and ITS-90

    Homework Statement What is the difference between the absolute thermodynamic temperature scale and the practical temperature scale: ITS-90? Homework EquationsThe Attempt at a Solution
  24. D

    Stirling Approximation for a thermodynamic system

    Homework Statement The stirling approximation, J! = √JJ+1/2e-J, is very handy when dealing with numbers larger than about 100. consider the following ratio: the number of ways N particles can be evenly divided between two halves of a room to the number of ways they can be divided with 60% on...
  25. G

    Thermodynamic cycle p-v to T-s

    Homework Statement I have been given a description of a thermodynamic cycle that looks like this. I have two polytropic processes (n1=1.2, n2=1.9), and one isochoric. The known data are: p1 = 1 bar T1 = 15 °C p2 = 15 bar Homework Equations p v^(1.2) = 0.7958 p v^(1.9) = 0.69657 The Attempt...
  26. B

    Zeroth law of thermodynamic and definition of temperature

    Hello everybody, I am a new member and do not know what is the best way to asking question. in "Statical physics of particle , m.kardar" . how he derived eq1.6 ? he said that we can eliminate "C" from eq1.4, but how? http://libgen.org/book/index.php?md5=BC07A3BDB70689E0E612DED12C96CC78 the book...
  27. H

    Curie's Symmetry Principle and Heterogeneous Thermodynamic Systems

    I am trying to understand the (possible) couplings between scalar chemical reaction phenomena and vectorial phenomena such as heat conduction and mass diffusion. It is argued in the literature that I have read that the usual assumption of cross coefficients for scalar+vectorial phenomena only...
  28. M

    Thermodynamic equilibrium of ideal gas and mechanical system

    Homework Statement Hi I am new to Physics Forums and desperately need some help! This is my first class back since undergrad and my math skills have gotten a little rusty. I think that's where I am failing. Okay here goes: http://tinypic.com/r/2zqf04k/8 There is a 4 subsystem...
  29. M

    Understanding Thermodynamic Functions: H, G, and A in Simple Terms

    What are the purposes of defining the Thermodynamic functions such as H (enthalpy), G (Gibbs function), A (Helmholtz function) in Thermodynamics. I just know the expressions for this functions but unable to understand the physical significance of these functions and also haven't understand what...
  30. V

    Relap thermodynamic property error

    Hi I am using relap to study a blowdown transient. If I let it run it with actual heat fluxes, the program terminates with error message saying thermodynamic property error with maximum time step. Reducing the time step delays the onset of the error by a fraction of a second. Runs much longer...
  31. M

    Thermodynamic state entirely determined by only two quantities?

    I am trying to understand why I can specify the specific volume v of a fluid element as a function of the equilibrium pressure, p, and the equilibrium entropy, s. This is for example done in this article http://www.sno.phy.queensu.ca/sno/str/SNO-STR-95-051.pdf , on this website...
  32. D

    Is Gasification More Thermodynamically Efficient Than Direct Combustion?

    Hi there, I have been thinking about attempting to quantify the statement that: "Gasification is more efficient thermodynamically than direct combustion of the fuel source as the gas can be combusted at higher temperatures, resulting in higher thermodynamic efficiencies as defined by...
  33. kelvin490

    Questions about thermodynamic relations

    We know that for constant pressure thermodynamic processes which only expansion work is possible, dH=dQp. My question is, is it necessary that both work W and Qv be reversible to arrive this relation? What if the heat transfer is irreversible? Similar question for dU=dQv, does the heat...
  34. Runei

    Integrating a differential (Problem in thermodynamic derivation)

    Hi, I'm looking at a derivation of the thermodynamics of black-body radiation. My question is in regards to the math of the derivation. Using the first law of thermodynamics and considering an adiabatic expansion of the cavity, it can be stated that dU = -\frac{u}{3}dV Here small u...
  35. kelvin490

    Question about thermodynamic quantities

    We know that for constant pressure thermodynamic processes, dH=dqp. My question is, does it implies that only reversible work is possible in this processes so that dw=0 because dv is zero? In addition, does qv necessarily be reversible heat transfer in this case? What if the heat transfer is...
  36. A

    Entropy in Information theory vs thermodynamic

    We Now From Information Theory That Entropy Of Functions Of A Random Variable X Is Less Than Or Equal To The Entropy Of X. Does It Break The Second Law Of Thermodynamic?
  37. T

    'Relation between the psychological and thermodynamic arrows of time'

    I recently came across the paper 'Relation between the psychological and thermodynamic arrows of time' (arXiv). Their argument makes sense to me, however their concept doesn't seem to address what 'now' is. If each person exists in an unchanging state in the block universe, and the flow of...
  38. U

    Find equation for thermodynamic process

    Homework Statement Find the equation of the thermodynamic process in which specific heat of the gas is given by C=\dfrac{R}{\gamma -1} + \alpha P The Attempt at a Solution I can write C=C_v + \alpha P But I don't know how to proceed ahead. What does C mean here? Is it specific heat...
  39. A

    Why is a condenser necessary in a thermodynamic Rankine cycle?

    hi guys , I am studying thermodynamic cycles in my thermodynamic course , I have a question about the power cycles like Rankine , in these systems v use superheated steam to produce work from turbine, so y there must be condenser to cool it first and then heat it , y can't v use turbine - boiler...
  40. P

    Two questions on retrieving thermodynamic properties

    Homework Statement ''A rigid insulated container fitted with a paddle wheel contains 5lb of water, initially at 260F and a quality of 60%. The water is stirred until the temperature is 350F. For the water, determine the work.'' How do we know whether the state of the water at 350F is...
  41. V

    Pressure-Time relation for polytropic thermodynamic process

    Dear Friends, I carried out an experiment of sudden release of oxygen (open nozzle) from an oxygen cylinder used for medical college and hospitals. I found that pressure drops quite rapidly and cylinder surface cools from outside such that water droplets accumulate on its surface. This...
  42. M

    This thermodynamic quantity equals what?

    I am trying to use thermodynamics manipulations in order to find \partialP/\partialV (at constant entropy) I tried replacing P by T(\partialS/\partialV)(at constant Energy) and then differentiated that by V but didn't help me. Do you have any idea where I can get around with this? Just throw in...
  43. N

    Thermodynamic PV-diagram: Why does a critical point =inflection point?

    http://en.wikipedia.org/wiki/Critical_point_%28thermodynamics%29 Look here please. Why is the first and 2nd order derivatives of pressure with regards to volume equal zero at the critical point for an isotherm phase curve? Why/how is it possible to expand a fluid at its critical point...
  44. gfd43tg

    Troubleshooting Mathcad Functions for Thermodynamic Calculations

    Hello, I am trying to use some functions in MathCad given in my thermodynamics textbook to calculate thermodynamic properties. I attached the functions below. I try using them and then I get an error saying too many commas I just type in: MCPH(T1,T2;A,B,C,D)= of course with numerical...
  45. A

    Understanding Thermodynamic Variables: Fixing Confusion and Clarifying Relations

    So I have had related questions over the past month, but I would like to ask this question to clarify my understanding. In thermodynamics you work with certain potentials, which are a function of the thermodynamic variables, i.e.: U(S,T,V,N,P) Now for U one has the identity: dU=...
  46. A

    What are the Three Main Types of Connections in Thermodynamics?

    It seems to me that for some thermodynamic variables it makes sense to talk of systems in contact with different values of these variables. An example is temperature. We can the problem of two systems in contact with different temperatures. However, I am not sure if this is the case for all...
  47. R

    Work in a thermodynamic process

    Hello, could someone please let me know if I have worked this problem out correctly, or if I need to try again? Thank you. Homework Statement A 40.0 g projectile is launched by the expansion of hot gas in an arrangement showing in Figure P12.4a (attached file). The cross-sectional area of...
  48. N

    Differentiating thermodynamic coefficients

    Homework Statement In oppgave 1 a) I am supposed to show that the given equality is true (namely that the isoterm compressibility coefficient partial-differentiated with regards to temperature = isobar coefficient differentiated with regards to pressure multiplied by minus one)...
  49. U

    Calculating work done in this thermodynamic cycle

    Homework Statement In the thermodynamic cycle as shown, a) What is the direction that the cycle is executed-clockwise or anticlockwise? b) What is the work done? Homework Equations First law of thermodynamics for a cycle E2-E1= Q-W= Tds-Pdv=0 The Attempt at a Solution a) I...
  50. Pythagorean

    A new thermodynamic theory of life

    A "new" thermodynamic theory of life Interesting idea... https://www.simonsfoundation.org/quanta/20140122-a-new-physics-theory-of-life/ The peer-reviewed paper, published in AIP: Journal of Chemical Physics: Statistical physics of self-replication...
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