Thermodynamic Definition and 459 Threads

Hi all, Something has been troubling me. To begin with, I have never been certain about this concept of 'extrinsic' thermodynamic variables. I mean, they don't have to be linear with system size, right? They just need to increase with system size? And also, I have a specific 'example problem'...

I'm looking for some engineering types to have a play around with my thermodynamic model of an internal combustion engine and reply with any thoughts, errors they find, spurious results or anything else which doesn't seem quite right...

Homework Statement Consider relationship for a thermodynamic system: S=A[UVN]^d , where A is a constant and d a real number. I need to explain why d=1/3 is the only allowed value consistent with the postulates of thermodynamics. The Attempt at a Solution I'm having a hard time...

Homework Statement One mole of ideal gas expands isothermally at 20°C against a constant pressure of 1 atm from 20 to 30L. (1 atm = 1.013 x 105Pa; 1 m3 = 1000L Find q, w, ΔE, and ΔH in Joules Homework Equations ΔE = q + w w = -\intPdV H = E + PV The Attempt at a Solution I solved for work...

Prove that $$ \frac{y^x-1}{xy^{x-1}(y-1)}<1$$ where x,y \in ℝ, x>1 and y>1. I was able to prove it using calculus, but am wondering if there was another way of doing so, like exploiting some inequality-theorems which involves real numbers. I'll be glad if anyone can show me a way and...

Homework Statement One mole of ideal gas expands from an initial volume V1,to a final volume V2. Where V1 and P1 correspond to the volume and initial gas pressure, whereas V2 and P2 correspond to the volume and pressure at the end of the process. The process is described by the equation...

The following are Maxwell's Relations right? \left(\frac{\partial s}{\partial v}\right)_{T} = \left(\frac{\partial p}{\partial T}\right)_{v} \left(\frac{\partial s}{\partial p}\right)_{T} = - \left(\frac{\partial v}{\partial T}\right)_{p} Are these all? And BTW, these are derived from the...

I have just watched a video lecture from Robbert Dijkgraaf at Gresham College where he describes gravitation as an emergent entropic thermodynamic force. The video link is listed in reference and the equations are defined at time index 44:00. Emergent entropic thermodynamic force: F \Delta x =...

Homework Statement An ideal gas undergoes the following reversible cycle: (a) an isobaric expansion from (P1, V1) to (P1, V2), (b) an isochoric reduction from (P1, V2) to (P2, V2) (c) an isobaric reduction from (P2, V2) tp (P2, V1) (d) an isochoric expansion from (P2,V1) to (P1, V1). What...

Hi everyone, I would like to program water thermodynamic properties in C, C++ or Matlab in order to model a steam power plant. I'm particularly interested in getting the enthalpy of the fluid by knowing the temperature and the pressure. I recently found out the software Cantera...

hello all. I need some references and problems with soloution of nuclear reactor thermodynamic for practicing and learning better. like presurizer.and exc.

Can someone explain dynamic pressure and the pressure in the outlet of a diffuser nozzle? Its isentropic and follows the Bernoulli energy balance equation. But the pressure in the outlet is close to atmospheric pressure and velocity is significantly less. How can you get thrust from low velocity...

Homework Statement The question is pretty much explained in the picture. The area ABCD is enclosed, i need to find that area. The equation for AB is P=0.8+8.6e^(-0.3V) and the equation for CD is P=1.2+9.6e^-(0.1V) What I did was find the area enclosed by the rectangular shape (C-B)*9. From...

I'm confused about the condition for spontaneity for the Helmholtz energy. My textbook (McQuarrie, "Physical Chemistry") derives the conditions as follows. We start with the combined law of thermodynamics: dU = δq + δw ≤ TdS – PdV since δq/T ≤ dS dU – TdS + PdV ≤ 0 For a process at...

Hi, I've tried several times to get my head around this, but every way I look at it Hawking Radiation doesn't seem to fix the thermodynamic issues it was supposed to solve. People who are a lot smarter than me seem to believe it's real, so can someone please point out where I'm going wrong...

Suppose I have a cylinder with a movable partition inside, separating it into two subsystems. The partition is movable, but will not transmit heat or matter. The same type of gas is contained in each subsystem, but the pressures and temperatures are different. The same amount of mass (M) is in...

Hello, new to these forums I'm trying to complete a basic thermodynamics problem, calculating the thermodynamic temperature of a gas immersed in water at triple point. The problem begins with a table of pressures at varying temperatures of a gas under pressure P, and pressure P(tp) -...

I am trying to figure out the temperature of steam when it is only dry saturated, it has the follwoing properties Mass = 0.05kg pressure = 15bar volume = 0.0076m^3 temperature = 250°C Thanks

Homework Statement What is the definition for first law of thermodynamic? I was confused and which one is correct? (a) The CHANGE in internal energy of a closed system is equal to the heat that enters a system and the workdone on the system OR (b)...

[b]1. A 2.5GWth nuclear power plant operates at a high temperature of 570°K. In the winter the average low temperature at which it dumps waste heat is 268°K; in the summer it’s 295°K. Determine the thermodynamic efficiency of the plant in each season, and then derive from it the maximum possible...

Homework Statement An amount of saturated steam at a pressure of 10 Bar, undergoes an isentropic (constant entropy) expansion. The final temperature is 30C. Find the final specific enthalpy and specific volume. Homework Equations Saturated Steam tables, Linear Interpolation methods? No...

I am completely lost with this problem. How would I go about breaking it up into manageable components that so I won't get lost in the problem? Homework Statement A 2 m3 rigid storage tank containing 10 kg of steam is heated from 300 to 400 C by transferring heat from a hot reservoir at...

Hi! I have trouble understanding this: Given Temperature: If pressure < saturation pressure => Overheated Vapor If pressure > saturation pressure =>Compressed Liquid Why does this happen?? Thanks in advance!

As the title says, why diesel engines produce less CO2 than gasoline engines and how is this related to the more torque and less power in diesel engines? PLEASE only a fluid dynamics or thermodynamics approach. Spent hours on searching to find why petrol engines produce more CO2 emissions...

http://img842.imageshack.us/img842/7200/img0103iu.jpg Mainly concerned with the first half of the page. You'll see that it derives for a system in contact with a constant-temperature, constant-pressure heat bath that the change in Gibbs entropy is always less than or equal to zero. Equality...

Homework Statement A cylinder has a base area of 0.016 m2 and is fitted with a piston that can freely move. Below the piston, the cylinder is filled with gas that has a pressure P1 = 106000 Pa, a volume V1 = 0.0014 m3, and a temperature of T1 = 0 ° C when in state 1. The gas is then...

Hello guys, I'm studying Thermodynamics and I don't totally see how you introduce the potencials using Legendre transformations. I have seen a non formal explanation showing how you can interpret them, but not a rigorous demonstration of how you get them via the Legendre transformations...

Hello experts! This is my very first post on PF. I have read the rules, and I am hoping that I post this in the right section. Also, I did some research on existing threads, and found quite a few interesting discussions. However, none of them specifically addressed this difference. If I have...

Can someone tell me how I can derive Wien's law, i.e., \lambda_{max} T = constant where \lambda_{max} is the peak wavelength and T is the absolute temperature of the black body, using the equation, P=\frac{U^{*}}{3} where U^{*} is the energy density. Note: I'm not looking for...

Homework Statement How many grams of steam at 100 deg. Celcius would be required to raise the temperature of 35.8 g solid benzene from 5.5 deg Celcius to 45.0 deg Celcius? Assume that heat is only transferred from the steam (not the liquid water) and that the steam/water and benzene are...

Homework Statement Show that for an isentropic compression/expansion process that Pv^k=constant Homework Equations The usual thermodynamic potentials, maxwell relations The Attempt at a Solution The solution I am arriving at follows that of the solutions manual, but there is...

An inventor proposes to make a heat engine using water/ice as the working substance inside a cylindrical piston and taking advantage of the fact that water expands as it freezes and can therefore lift a piston supporting some mass m. The engine process consists of four steps as shown in the...

Homework Statement The question c) I have attached. Capture th.PNG (27.7 KB) Capture th2.PNG (14.8 KB) Homework Equations The Attempt at a Solution Use U=f(T,V) and H=f(T,P), then get Cp and Cv, so I can get gamma. then k=(1/v)(dv/dt) but I still can't prove it.

Homework Statement Consider the heating curve for H2O. a. As heat is added to melt ice, does the the temperature change? Explain what happens to the heat that is added. b. For the same amount of H2O, does it take more to melt ice or vaporize water? Explain why. c. Is the fusion of ice...

We are using Sandler's Chemical, Biochemical, and Engineering Thermodynamics, and Smith & van Ness for our third year thermodyamics course. What is a good book to study power, heat and refrigeration cycles? Sandler's has a chapter dedicated to that, but it's not enough.

Homework Statement 1kg air with the pressure 10^6 Pa and temperature 398K expands until the volume is 5 times its' initial value. The expansion occurs so that in every moment the absorbed heat energy (dQ) is 1/4 of the work done by the gas. Find the final pressure. 1kmol of air has the mass...

Adiabatic process: a process where no heat is gained or lost. it is my understanding, however, that this is a hypothetical system. There is no insulator on Earth good enough to allow this system to exist, except to approximations. So, what happens is you have a system where whatever is...

Homework Statement In a constant-volume process, 208 J of energy is transferred by heat to 0.99 mol of an ideal monatomic gas initially at 290 K. (a) Find the work done on the gas. (b) Find the increase in internal energy of the gas. (c) Find its final temperature. I just don't...

Does anyone have a good source of saturation data for nitrogen at low pressures? By low pressures, I mean something along the lines of 0.01 atm. Thanks,

I have recently developed a multi-computer networked simulation of a turbofan jet engine test cell control room, including a real-time simulated jet engine "model", PLC control logic, video playback of a engine at various states, and a throttle for maneuvering. I currently calculate all...

I have to calculate the thermodynamic efficiency of a power station. I have to assume the cooling towers maintain 70 degrees C and hence the amount of electrical energy (in J) from one mole of methan. I've been given the enthalpy of combustion of Methane. I know the thermo efficiency is (sum of...

Hi, everyone ! I am a new member to PF but I find it helpful as people will give ideas and suggestions for me :) Recently,I come across something called as a magnetic motor. From the design, a few permanent magnets are placed on the edge of a circular disk. Then, as another magnet approaches...

Thermodynamic Cosmic Problem ! Ill start with the third law of thermodynamics which denies the existence of zero kelvin (as stated by my lecturer). Also i found out that the temperature of vacuum is 3k due to the radiations left over from the Big Bang. However the space(or the absolute vacuum)...

Homework Statement This question is about entropy of magnetic salts. I got up to the point of finding H1, the final applied field. The Attempt at a Solution But instead of doing integration I used this: dS = (∂S/∂H)*dH = (M0/4α)(ln 4)2 I removed the negative...

In a lot of practical situations it is simply assumed the canonical and microcanonical ensemble give the same predictions, and that's fine, but I'm interested in a more exact statement of when they are indeed equivalent (in the thermodynamic limit). First of all, a thermodynamic limit must...

This is about the basic thermodynamic cycle of the gas turbine (i.e. Brayton or Joule cycle), consisting of adiabatic compression, heat addition at constant pressure, adiabatic expansion, and heat rejection at constant pressure, and the standard ways of analysing this through Pressure-Volume...

dE = TdS - PdV, or equivalently \Delta E = \int T \mathrm d S - \int P \mathrm d V In general this is said to be derivable in the reversible case, however since S and V are state variables, it's also true for the irreversible case. But it can't be true for any irreversible case, since the...

dE = dQ + dW = dQrev + dWrev = dQirev + dWirev. We have for an reversible process, dQrev = TdS and dWrev = -PdV. So; dE = TdS - PdV So this relation is for all changes (irreversible or reversible) since dS and dV are state functions. What doesn't make sense to me is the next part when...

Homework Statement a gas turbine is designed to produce 3000hp when using air at a maximum inlet temperature of 650k and assuming a heat loss of 70 kj/s. if the exhaust temperature is desired to be no greater than 200 degrees celsius, determine the mass flow rate of air required. Homework...

The following comes from Landau's Statistical Physics, chapter 32. Using a Hamiltonian \hat{H} = \hat{H}_0 + \hat{V} we get the following expression for the energy levels of a perturbed system, up to second order: E_n = E_0^{(0)} + V_{nn} + \sideset{}{'}{\sum}_m \frac{\lvert...