Thermo Definition and 267 Threads

From the solution of my thermodynamics homework, $$ ({\frac{\partial h_{fg}/T}{\partial T}})_P \\ = ({\frac{\partial h_{g}/T}{\partial T}})_P - ({\frac{\partial h_{f}/T}{\partial T}})_P = \frac{1}{T} ({\frac{\partial h_{g}}{\partial T}})_P - \frac {h_g}{T^2} - \frac{1}{T} ({\frac{\partial...

So I found this steam engine on the youtubes: Consider the system not including the candles, only including the can that makes up the boiler shell and the piston, flywheel, etc. The boiler can acts as a hot reservoir; however, the Kelvin-Planck statement of the 2nd law says you can't have an...

i going to do the online HNC mechanical engineering. its has 2 units mechanical principles and thermo. i was wonder how hard is it to learn those units and the maths online or with online tutor. i can do the maths if its inperson in class but learn on line I am not sure.

What I don't understand is why ##dS## is expanded in only the two differentials ##dV## and ##dT.## Why doesn't it look more like: $$dS = \left(\dfrac{\partial S}{\partial V}\right)_{T,P,U} \ dV + \left(\dfrac{\partial S}{\partial T}\right)_{V,P,U} \ dT + \left(\dfrac{\partial S}{\partial...

Hey guys. I have a room which i want to use as a server room. the devices need to work 24/7 and they get pretty hot. so it is imperative to keep the room cool otherwise the devices will be damaged. I have an air vent to bring cold air into the room for the devices so their fans can suck in cold...

##dmL_f= Q \; \; ##,##∆T=\frac{T(v_l-v_s)∆P}{L} \; \;##,##\frac{dmL_f}{T_0}= dS_2 \; \;##,##\frac{dmL_f}{T_1}= dS_1 ##

1- ##\delta P_V =(\frac{\partial P}{\partial T} )_V \delta T_V## 2-##\delta V =(\frac{\partial V}{\partial T})_P \delta T+(\frac{\partial V}{\partial P})_T \delta P## so ##C_v \delta T=-P\delta V=-P((\frac{\partial V}{\partial T})_P \delta T+(\frac{\partial V}{\partial P})_T \delta P)## I can...

Hello. I'm a Senior in high school taking a 200-level thermodynamics course at a local university, and it's turned out to be much more difficult than I had anticipated. I had already taken and done well in quite a few college courses (including double-listed 400/500-level PDEs last year), so I...

Hi PF! I have a tricky problem that I'm trying to model, and none of the typical textbook examples cover this--or they only cover it tangentially--so I was hoping to get some insight here. (Couldn't find a "Thermodynamics" section of the forums so if there's a better place to post this, please...

Ok, I am stuck on understanding when to use a part of an equation and when not to. e = (P/rho) + (Ke/m) + (Pe/m) where P is pressure, Ke and Pe are Kinetic and potential energy divided by mass. Ok, if we look at P/rho and P is defined as rho(g)(h) then the rho's divide out and we are left...

Homework Statement Homework Equations [/B][/B] 3. The Attempt at a Solution Here's my solution attempt: NOTE: Evolution 2 to 3 is really an isothermic process, but in the diagram shows as an politropic process. 4. Further Questions But it isn't giving me logical values of COP...

Hi! As the title suggests, I am searching for some good problem books with really challenging problems for classical physics, more precisely on the topics of electricity and elecromagnetism, geometrical optics and wave optics, thermodynamics and analytical mechanics. When I say challenging I...

Hi everyone. Some years ago I read about the Crower six cycle engine. Always wanted to understand it better. And now is the time to follow up on that desire. I’m trying to calculate what happens during the water injection. The goal is to determine the conditions (pressure, temperature)...

Homework Statement Homework Equations P=F*V, dU=Q-W?, W=m(h1-h2) The Attempt at a Solution I have the initial conditions and final conditions written out. For W=m(h1-h2), I have W=9.48(h1-h2). I am having problems with the h values, which can be found in the steam tables.

I am an new EE with my FE, but my thermo knowledge is lacking in many areas. Its one area where i would like to become an expert. So i try to find ways of applying thermo analysis on my free time to imprve my skills. where here is one and I have no idea where to even start. a youtuber with a...

A very cool new molecular neuro trick Here's some background and a loose summary. Here is the main reference (surprisingly openly available!). In recent years, neurobiologists have been able to get neurons to make particular proteins by various means (such as filling the cells or in someway...

Hey all, I'm currently studying for my thermo final and it's really kicking my butt. My average has been a C and if I do EXTREMELY well on my final I'll be REALLY pushing for a B. I'm not sure how thermo is taught in other universities, but I'm learning it through statistical mechanics with...

I am enrolling for classes for next semester and I have the option to take either differential Equations or Linear algebra or both next semester. I have completed Calc 1, 2, and I am completing multivariable this semester. I am a physics major and going into thermo and waves next semester so I...

Homework Statement Assume 1.500 mol of a monatomic ideal gas is compressed from 3.00 L to 1.00 L. a. If the initial and final temperature is 10.0 °C, what are the initial and final pressures (in atm)? b. How much work input (in kJ) is required if a reversible isothermal path at 10.0 °C is...

Homework Statement Please consider a mixture of oxygen (1 mole), nitrogen (4 mole), and carbon dioxide (3 mole). The mixture was heated in a well - insulated vessel with 753 kJ. Determine the final temperature if the mixture is composed of real gases behaving ideally as described by Eq. 3.48...

Homework Statement Please consider ethylene at 152oF and 126 atm. Please determine the molar volume (ft3/lbmole) if Z is determined by Corresponding States Theory. Homework Equations Z=PVm/RmT Vm= Molar volume R=Rm/M M= molecular weight Rm=1545(ft*lbf)/(lbmol*oR) Zc=(Pcvc)/(R*Tc) Tc=283 K...

Homework Statement A 3-m3 rigid vessel contains steam at 10 MPa and 500 degC. The mass of the steam is? I know this question involves using a thermo-table, I'm just very confused on how to find mass from the given information. Homework Equations Maybe PV=nRT The Attempt at a Solution I...

Homework Statement The tires on a bicycle require an air pressure of 80 psig. When isothermally pumped up the bicycle tires, the volume of the air (that was originally in the atmosphere) is reduced by a factor of 5.7. Please determine the work that must be done on each lbm of air that is pumped...

This question is related to a project. I have the mass flow rate, RPM, and all other related information regarding a refrigeration cycle, does anyone have an idea on how can I estimate the total amount of working fluid I need to put into the device? In case this comes up: the device is going...

Homework Statement You have 1.0kg of ice at 0.0 deg C in a pot on a stove that produces 900 W of power. Assuming that the pot and the stove are 'perfect' (i.e., no heat lost) and ignoring the heat capacity of the pot, compute the time it will take for this ice to boil away completely...

Homework Statement Two moles of a monatomic ideal gas are at a temperature of 300K. The gas expands reversibly and isothermally to twice its original volume. Calculate the work done by the gas, the heat supplied and the change in internal energy. So: T = 300K; ΔT = 0 n = 2; R = 8.314 J K-1...

Thermodynamics (Yunus Cengel Michael Boles , 8) I'm taking Thermodynamics right now at my community college and if you saw my last post about my physics teacher, you know I have the right to be paranoid about not learning enough in my classes. I've always heard Thermo for mechanical engineers...

Hi guys, I was hoping that someone might be able to help me out with a formal derivation of this common thermodynamic equation regarding the change in entropy during an isothermal change of state. The first equation is what I would like to derive, and the second is where the book tells me to...

Homework Statement Air in an insulated cylinder is separated by a piston into two equal valves. When the pin is removed, the system comes to a new equilibrium position. There is friction between the piston and the cylinder walls but friction does not influence the mechanical equilibrium...

How do you find a value for Z using the compressibility chart when the temperature line you're trying to use ends? For example, if you look at the compressibility chart and try to find a value for z with P_r = .75 and T_r = .96, you will notice that the line for T_r = .95 ends well before the...

A rigid tank with a volume of 2.00m3 contains 5.77 kg of saturated liquid-vapor mixture of water at 75 deg C. Now the water is slowly heated. Determine the temperature at which the liquid in the tank is completely vaporized. Why isn't the temperature just 75C? If it is already a mixture in...

Homework Statement An ideal monatomic gas has initial pressure Po and occupies initial volume Vo. The gas undergoes an adiabatic expansion in which the volume is doubled. Calculate in terms of Po and Vo a) the final pressure of the gas b) the change in its enthalpy during the...

I'm taking mechanical engineering thermodynamics right now and it's awesome. We just got into enthalpy and stuff like that and it's so interesting. It has me thinking that maybe I want to do something that has a lot of thermo or subjects that are similar.

Hi everyone Would like some help here. If I draw a control volume across a valve that I can control the flow area to, and I know the temperature and pressure upstream of the valve, I will know its enthalpy:in. High temperature liquid going through this valve supposedly changes to steam due...

Homework Statement A sample consisting of 1 mol of a diatomic perfect gas with Cv,m = 3/2 R is heated from 100 ºC to 300 ºC at constant pressure. Calculate ∆S for the system. Homework Equations Cv,m = 3/2 R The Attempt at a Solution Cpm=Cvm +r because we want cp right isobaric ∆S= Cp ln...

Homework Statement Here is the problem: An inventor claims to have developed a heat pump that provides a 180 kW heating effect for a 293 K household while only consuming 70 kW of power and using a heat source at 273 K. Can this claim be possible? Homework Equations COP of heat pump = Qh/W COP...

Entropy has units of kJ/kg K and energy has units of kJ. So my question is if entropy is not conserved how is energy conserved when there is a unit of energy within entropy?

Homework Statement n moles of a diatomic gas with CV =5/2 R has initial pressure pi and volume Vi. The gas undergoes a process in which the pressure is directly proportional to the volume until the rms speed of the molecules has doubled. a. Show this process on a pV diagram. b. How much heat...

Homework Statement A gas in equilibrium has distribution function: f(p,r) = C0*(1+y*x)(2*pi*m*k*T)-3/2*exp(-p2/(2*m*k*T)) where x is the distance along an axis with fixed origin, and y is a constant. What's the nature of the force acting on this gas? Homework Equations Maxwell bolztmann...

Homework Statement A cylinder having a piston restrained by a linear spring (of spring constant 15 kN/m) contains 0.5 kg of saturated vapor water at 120ºC. Heat is transferred to the water causing piston to rise. If the piston’s cross sectional area is 0.05 m2 and the pressure varies linearly...

Homework Statement Hellooo, so this is the question that i have: A 0.5-m3 rigid tank initially contained a saturated liquid-vapor mixture of water at 140 °C is now heated until the mixture reaches the critical state. Determine the mass and the volume of liquid before the heating process...

Homework Statement Atmospheric air at 300K and 100kPa is to be delivered to a line at 600K, 200kPa. Two possible schemes for doing this are suggested. The first scheme involves reversible adiabatic compression and then internally reversible isobaric heating. .The second scheme involves...

http://phys.org/news/2015-02-big-quantum-equation-universe.html Some people claim that universe has existed for eternity to get around the Big Bang theory. However wouldn't this violate either the 1st of 2nd laws of Thermodynamics which forbid perpetual motion of the 1st and 2nd kind...

1. Homework Statement We want to heat up 200 liters of water in a bathtub from 15 ◦C to 30 ◦C. The temperature is increased by adding marble stones to the water. The initial temperature of the marble stones is 773, 15 K. Assume that the marble is rigid, with the heat capacity cm = 0.88 J ·K−1...

Homework Statement U = u(T)V; P=u(T)/3 a. Find (ds/dt)v and (ds/dv)T in terms of u. Ans. (ds/dt)v = 1/T[du/dt] and (ds/dv)T = 1/T[du/dv + P]...Correct b. Show that u(T) = Const*T^4 equate partials above and integrate...Correct c. Find a Relation between V and T during adiabatic compression or...

Hello, PF! Days ago, while playing Batman: Arkham Origins, I was wandering through the Batcave when I noticed something that caught my eye immediately. There's a nice, cozy lab in there which includes a blackboard where Bruce Wayne apparently did some kind of thermodynamic calculations, which...

Homework Statement Show that the internal energy at constant entropy and volume decrease for a spontaneous process Homework Equations F = U-TS The Attempt at a Solution Use Clausius: dS-dQ/dT > 0 Assume constant volume: TdS > dU assume constant entropy this becomes 0>dU Since dU is...

Homework Statement You have 0.50 mol of steam which has been supercooled to 95˚C at 1 atm. Since the steam is below the boiling/condensation point, it proceeds to partially condense into liquid water. This happens in a thermally-insulated vessel at constant pressure. (a) When the system...

Homework Statement One m3 of an ideal gas expands in an isothermal process from 760 to 350 kPa. Determine the specific work done by the gas. Homework Equations ω=W/m 1W2=mRTln(P1/P2) = P1V1ln(P1/P2) P1V1=P2V2 The Attempt at a Solution P1V1ln(P1/P2) = (760)(1)ln(760/350) = 589.29kJ...

Homework Statement Find the equation of state given that k = aT^(3) / P^2 (compressibility) and B = bT^(2) / P (expansivity) and the ratio, a/b? Homework Equations B = 1/v (DV /DT)Pressure constant ; k = -1/v (DV /DP)Temperature constant D= Partial derivative dV = BVdT -kVdP (1) ANSWER is...