Thermo Definition and 299 Threads

  1. N

    Thermo Q RE:isentropic efficiency through nozzles

    Homework Statement Exhaust gas expands through a nozzle whose isentropic efficiency is 88%. The inlet pressure and temperature are 1.6 bar and 400c respectively. At outlet the pressure has fallen to an ambient level of 1.013 bar. Given that the inlet velocity is negligible, and Cp and...
  2. A

    Thermo Radiation and Temperature

    Hi Here is the question. Suppose someone build a thin spherical shield just above the Earth's atmosphere, and it would absorb all the radiation passing through from the sun. What would the average temperature of the Earth's surface be? (Assuming the avg temperature of the Earth is initially 300K)
  3. P

    Solving Thermo Problem: $\Delta U$, $\Delta K_{cm}$, $\Delta I$, $W_{ext}$, $Q$

    we know that $\Delta U$ $=$ $\Delta K_{cm}$ $+$ $\Delta I$ where $\Delta K_{cm}$ is the kinetic energy from cm frame of refrence and the other part is the change in change in potential energy due to various conservative forces. also by first law of thermodynamics $\Delta U$ $=$ $W_{ext} + Q$...
  4. A

    Is Internal Energy Always Dependent Only on Temperature in an Ideal Gas?

    Does the internal energy always depend only on temperature in an ideal gas? Would the equation U=\frac{3}{2}nRT tell us that? are there any other equations? I'm also confused with the area within a cyclic curve on a PV graph. Does the area within the curve represent the work done ON the...
  5. J

    Troubleshooting Mass Flow Rates for CH4 Reaction with Air and Fuel

    I have this reaction: CH4+4(O2+3.76) --> CO2+2H2O+2O2+15.04N2 Through other calculations and given information I have found that the mass flow rate of the air (the O2+3.76N2) is 25kg/s and the mass flow rate of the fuel is .87 kg/s. I am having the hardest time finding, using these mass...
  6. I

    Thermo - Gibbs Free Energy & Entropy

    Homework Statement Consider fuel cell using methane as fuel. Reaction is CH^4 + 2O_2 -> 2H2O+CO_2 Assume room temperature and atmospheric temperature Determine values of delta H (Helmholtz) and delta G (Gibbs) for this reaction for one mole of methane. Question instructed the use of...
  7. S

    How Do You Calculate Properties of a Gas After Adiabatic Compression?

    Hoping someone can help me here quickly. Trying to get this one question. a perfect gas is compressed adiabatically from 100 kPa and 17C to a final pressure of 500 kPa and final temp of 77C. The work done during the compression is 45 kJ/kg. Calculate the values of gamma, Cv, R and the...
  8. G

    Thermo question - final mass/entropy generation

    I think I may have posted this in the wrong forum earlier :\ Homework Statement An insulated and initially empty 0.7m^3 tank is connected by a valve to a line flowing air at 50degreesC and 200kPa. The valve is opened until the tank is filled, and then the valve is closed. The insulation is...
  9. G

    Thermo question - final mass/entropy generation

    Homework Statement An insulated and initially empty 0.7m^3 tank is connected by a valve to a line flowing air at 50degreesC and 200kPa. The valve is opened until the tank is filled, and then the valve is closed. The insulation is then removed from the tank, and a 20degreeC heat sink cools the...
  10. S

    Find Work Done in Thermo Question | Monatomic Gas | Calculation Help

    Homework Statement See Attachment The Attempt at a Solution Well to start off I know the gas is monatomic I can find the work done by finding the area under each curve/line: W_{AB} = p_0(2v_0-v_0) = p_0v_0 W_{CD} = (p_0/32)(8v_0-16v_0) = \frac{-p_0v_0}{4} I can't think...
  11. S

    Answer Processes in T-V Diagram: A, E, C Explained

    An Ideal monatomic gas at initial temperature T_0 (in Kelvins) expands from initial volume V_0 to volume 2V_0 by each of the 5 processes indicated in the T-V diagram. In which process is the expansion a.)isothermal, b.) isobaric or c.)adiabatic? Explain your answers. d.) In which process...
  12. H

    What Is the Final Temperature and Total Work of a Finite Carnot Cycle?

    Homework Statement Specify that the finite reservoirs of a Carnot cycle start at initial temperatures T_h and T_c. Acknowledge the consequence of the finiteness of the reservoirs: the hot reservoir will drop in temperature and the cold reservoir will increase in temperature. The two...
  13. J

    Thermo Question - Fridge cycles

    Consider a 300 kJ/min refrigeration system that operates on an ideal vapor-compression cycle with refrigerant-134a as the working fluid. The refrigerant enters the compressor as saturated vapor at 140 kPa and is compressed to 800 kPa. Determine the (a) quality of the refrigerant at the end of...
  14. D

    Calculating Heat Transfer in a Reversible Isothermal Process with a Slow Leak

    Homework Statement Rigid tank volume .5m^3 initially evacuated. Tiny hole develops, air seeps in @ 1 bar and 21 degrees C. Pressure in tank reaches 1 bar, slow leak so temp remains 21 deg C inside tank. What's amount of heat transfer? Homework Equations Q=T[S(2)-S(1)] Pv=nRT The...
  15. M

    Hard Thermo Question: Find U, S, T For Part B & C

    Well, it's hard to me at least :frown: http://img169.imageshack.us/img169/206/questionzg0.png We are using Schroeders book and this problem was given to us from I assume the book by Reif. We haven't seem to have gotten far enough along in Schroeders book to have gone over this though. I can...
  16. K

    Troubleshooting Nitrogen Gas Storage: Pressure Estimation Methods

    Hey guys, I have been having a really hard time trying to figure out this question. It seems like everything I do, I can not get resonable answers. If you can help me, that would be great. Problem: A 500-L tank stores 100kg of nitrogen gas at 150 degrees K. To design the tank, the pressure...
  17. R

    Solving Basic Thermo Questions: Calculating Velocity and Area in an Open System

    I have question (probably figured that). I have an open system with mass flow rate going into one inlet and going through two outlets. I have all the terms for the two outlets (mass flow, velocity, area, temp, pressure). However for the inlet I'm missing the Velocity and Area. In solving for...
  18. T

    Thermo & Fluids: Student Experiences & Advice

    Hi all. I've heard from students that Thermodynamics and Fluids are really tough classes. I've taken all the physics and the calculus with no problems. What do you guys think about those classes?
  19. I

    How Do You Calculate Cp and Cv for a Specific Fluid?

    Hi, I'm stuck. Can someone help me out? Problem: The properties of a certain fluid are related as follows: u=196+0.718t pv=0.287(t+273) (a)where 'u' is the specific internal energy(Kj kg), t is in degress Celsius, p is pressure(Kn/m2) and v is specific volume (m3 kg).For this...
  20. S

    Help Understanding Thermo Principles

    Okay, I need some help understanding some of the Thermo principles and I found this forum. I hope someone can help. I'm working on Energy Analysis of a closed system. Conservation of energy principle and all that. deltaU = Q-W. Every time I think I know what should be considered work and...
  21. C

    How Much Dry Steam Is Required to Melt Ice in an Open System?

    I need a kick start for the following question. We're studying open/closed systems at the moment. "450kg of ice at -18 degrees C is to be removed from a freezer using a jet of steam. How much dry steam at 100 degrees C is required if the final temp of the effluent is 5 degrees C?" This is...
  22. J

    Statistical Mechanics to Thermo for Isothermal Isobaric Ensemble

    I am trying to make the connection from statistical mechanics to thermodynamics for the isothermal isobaric ensemble. Partition function = (sum of)exp(-BEj-gamma*Vj). I have followed T.L. Hill [Statistical Mechanics, p. 67] but can not understand how he justifies dE=(sum of)EdP, rather than...
  23. C

    Unit of work in mechanics and thermo dynamics

    unit of work and unit of heat When we study dynamics,the unit of work is in joules which is the energy transferred to a mass which in turn is the product of force and the distance along which the force is applied When we study thermodynamics, the unit of work is again in joules. How...
  24. Cyrus

    Thermo -- Airflow Analysis for Heating Ducts in an HVAC system

    2-48) The 60-W fan of a central heating system is to circulate air through the ducts. The analysis of the flow shows that the fan needs to raise the pressure of air by 50Pa to maintain flow. The fan is located in a horizontal flow section where the diameter is 30cm at both inlet and outlet...
  25. Cyrus

    Basic Thermo Help: Work Done by System is Positive?

    Im having trouble finding the reasoning here. Work done by the system is called positive? For example, a gas pushing up on a piston and causing the piston to rise. Well, it seems to me that as the gas pushes up on the piston, the gas does work on the piston, so the gas should LOOSE...
  26. Q_Goest

    Will Air Inside the Cylinder and Tank B Have the Same Temperature Upon Arrival?

    Imagine two infinitely large air tanks connected by a long, straight pipe. Tank A is at a higher pressure than tank B, so air is flowing from one to the other. For the sake of argument, we will say there is no heat flux or work into or out of the pipe. Now we put a perfectly insulated...
  27. T

    How is Work Done in an Adiabatic Process of an Ideal Gas Calculated?

    hello the problem is as stated: a cylinder containing n moles of an ideal gas undergoes an adiabatic process. using W=-\int Pdv and using the condition PV^\gamma=constant, show that the work done is: W=(\frac{1}{\gamma - 1}(PfVf - PiVi) where Pf is final pressure, Pi is initial pressure... I...
  28. P

    Solving Thermo Difficulties: Calculating Entropy Change

    Hello; I'm having some difficulties with a thermo question of mine. at low density water vapor conforms well to the ideal gas equation provided the temp is higher than about 320K, but the heat capacity is a function of temperature. The following formula gives the specific heat capacity at...
  29. O

    Solve Thermo Questions: Gas Equation, Work, Refrigerator Cooling & Heat Capacity

    There are a couple of questions on my practice exam I am stuck on. If you could point me in the right direction I'd appreciate it. 1. A gas is described by the equation PV= RT+aT^2 where a is some gas specific constant. Find (dU/dV)@constant T And provide an expression for the...
  30. P

    How to Determine Final Temperature and Enthalpy Change During Vaporization?

    OK, I have a piston-cylinder with water. V = 50L = 0.05 m^3 T = 25 C P = 300 kPa m = 49.85 kg specific volume @ 25 C = 0.001003 m^3/kg The water is heated to vaporization with pressure held constant. I need to determine the final temperature and the enthalpy change. I know what the...
  31. C

    Calculating Properties of Helium Gas Under Isothermal Compression

    a 2.00 mol sample of helium gas at 300K and 0.400atm pressure is compressed isothermally to 1.20atm Find the volume of the gas, work done on the gas and the energy transferred by heat just wondering how to approach this question, and what formulae i hould use where?
  32. C

    How Much Steam is Needed to Raise Water Temperature from 20°C to 50°C?

    hi guys, i have the following question to answer: a 40g copper calorimeter contains 200g of water at 20 degrees celsius, it asks how much stam must be condensed in order to achieve a final temperature of 50 degrees celsius. I was just wondering what formula to use?, and do i need to know the...
  33. C

    Calculating Final Temperature of Iron Object Dropped in Water

    hi guys, i have a thermodynamics question. a 2.50 kg iron object is initially at 650 degrees celsius and dropped into a bucket containing 20kg of water at 25 degrees celsius, what is the final temperature? As always it just a matter of applying the formula, but i don't seem to be applying...
  34. B

    Thermo Exam Question: Estimate Temp & Pressure After Compression

    Hello. I have a thermodynamics exam tomorrow. This is a past exam question and I'm not doing very well with it. If anyone has any ideas please help! A charge enters a spark ignition engine at 330K and 1 bar, and is isentropically compressed through a ratio of 7:1. Estimate the temp and...
  35. N

    Solving for Minimum Duct Diameter in a Hospital Room Air Exchange System

    Q. The air in a 6m x 5m x 4m hospital room is to be completed replaced by conditioned air every 20 min. If the average air velocity in the circular air duct leading to the room is not to exceed 5 m/s, determine the minimum diameter of the duct. We can figure out the volume of the room...
  36. F

    Having problems with a thermo. cycle

    Having problems with a thermo. cycle! OK, so in the problem A->B is isobaric, B->C is adiabatic, C->D is isothermal, D->A is isochoric. Pa = 2atm, Va = 2 m^3, n = 1mole, Vb = 1/2Va, Pa = 2Pd (That is all the information that is given.) I always end up with the temperatures of B and C...
  37. N

    Diesel Cycle - Heat Engines - Thermo.

    Hello, If anybody could answer this question for me that would be great. I have been wondering about it all morning. In the Diesel cycle for heat engines, on the second stage of operation, the Volume increases while pressure stays the same. I understand how this can be accomplished by raising...
  38. N

    Diesel Cycle - Heat Engines - Thermo.

    Hello, If anybody could answer this question for me that would be great. I have been wondering about it all morning. In the Diesel cycle for heat engines, on the second stage of operation, the Volume increases while pressure stays the same. I understand how this can be accomplished by raising...
  39. B

    Thermo Heat Transfer: Water Boiling at 1 Atm Pressure

    Hello all, I am a little confused on this problem and want to be clear on it. Given: Water is boiled at 1 atm pressure in a 20-cm i.d. pan. Water level in pan drops by 10cm in 30 min, determine the rate of heat transfer to the pan. Now correct me if I'm wrong but water boils at 100...
  40. B

    1D Thermo problem, something is wrong

    A startled armadillo leaps upwards so that it rises to .56 m in a time .21 s. Note: I use a web-submitting thing for my answers. So it tells me what is right and wrong. A: What was the armadillo's initial speed when it left the ground? 3.70 m/s - this part is correct. B: What is its...
  41. F

    Theorem of maximum work (Thermo)

    How would you guys explain "qualitatively" the theorem of maximum work based on this diagram. (that is when a process is reversible and no entropy change in the universe) I don't really know what the graph means. Let's say it's an ideal gas, (S=LnU+...). The diagram divides the plane in two...
  42. E

    Thermo Q: S2-S1=0? Why Doesn't Equation Yield 0?

    For a device operating at steady state, is the change in entropy (S2-S1) equal to 0? If it is equal to 0, then why doesn't the s2-s1=s(degree)(T2)-s(degree)(T1) - R ln (p2/p1) equation yield 0? I'm confused on this point... Any help greatly appreciated!
  43. E

    Need help with thermo problems

    Need urgent help with thermo problems... Here are my problems: 1) A rigid tank contains 5 lb of a two-phase liquid vapor mixture of water, initially at 260 F with a quality of .6 Heat transfer to the contents of the tank occurs until the temperature is 320 F. Determine the initial mass of...
  44. E

    Thermo Problem: Analyzing Work Done by Gases in an Internal Combustion Engine

    Here's my problem: Measured data for pressure versus volume during the expansion of gases within the cylinder of an internal combustion engine are given in the table below. Data Point p (bar) V (cubic cm) 1 15...
  45. M

    Solve 1st Law of Thermo P20.38: Net Work & Energy

    An ideal gas initially at Pi, Vi, and Ti is taken through a cycle as in Figure P20.38 (n = 2.6). Figure P20.38 (see attachment) (a) Find the net work done on the gas per cycle. PiVi (b) What is the net energy added by heat to the system per cycle? PiVi (c) Obtain a numerical value...
  46. R

    Thermo Dynamics Help: Solving for Final Temperature and Total Mass of Ice Melted

    A single 50g ice cube is dropped into a thermally insulated container holding 200g of water. The water is initially at 25oC and the ice is initially at -15oC. ********** a) What is the final temperature of the system after is has come to thermal equilibrium ? b) Now let's drop a second...
  47. P

    Discover the Heat Transfer in a Thermo-Aluminum Calorimeter with Metallic Blocks

    An aluminum calorimeter of mass 100 g contains 250 g of water. The calorimeter and water are in thermal equilibrium at 12.0°C. Two metallic blocks are placed into the water. One is a 40.0 g piece of copper at 80.0°C; the other block has a mass of 13.0 g and is originally at a temperature of...
  48. P

    How Much Ice Melts When a Hot Bullet Hits It?

    A 1.0 g lead bullet at 33°C is fired at a speed of 250 m/s into a large block of ice at 0°C, in which it becomes embedded. What quantity of ice melts? Heres what I have: From ΔQ = mcΔT, mA = dQ/[c(dT)] And from ΔQA = -ΔQB ... Further cogitations are in...
  49. M

    How Does Pressure Change with Volume in an Ideal Gas Expansion Scenario?

    An unknown number of Helium atoms are in a 1 liter container at an unknown temperature. The gas is made to expand such that it's final volume is 4 liters and pressure rises 'in direct proportion to its volume'. 1. does 'in direct proportion to it volume' mean Pf = Pi * Vf/Vi or should there...
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