What is Cycle: Definition and 673 Discussions

The urea cycle (also known as the ornithine cycle) is a cycle of biochemical reactions that produces urea (NH2)2CO from ammonia (NH3). This cycle occurs in ureotelic organisms. The urea cycle converts highly toxic ammonia to urea for excretion. This cycle was the first metabolic cycle to be discovered (Hans Krebs and Kurt Henseleit, 1932), five years before the discovery of the TCA cycle. This cycle was described in more detail later on by Ratner and Cohen. The urea cycle takes place primarily in the liver and, to a lesser extent, in the kidneys.

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  1. Y

    Calculate average power in one cycle.

    Homework Statement This is part of a bigger problem, I simplify to just: P=k sin^2 \omega t How do I integrate over one cycle? The Attempt at a Solution \left\langle P \right\rangle = \int_0^T k\; sin^2 (\omega t) d t \;\hbox { where }\; T= \frac c f = \frac {2\pi}{ \omega}...
  2. F

    Why does the Rankine cycle require the condensation of water before reheating?

    In a Rankine cycle such as a steam power plant, why does the liquid (water) have be condensed before being reheated first? Isn't the Q just extracted during the condensation stage, wasted into a nearby reservoir, and then re-added in the boiler? Could this water not be fed straight to the...
  3. O

    Steam plant operates with ideal reheat -regenerative Ranking cycle.

    Question: http://i1179.photobucket.com/albums/x393/mariaschiffer/img017.jpg Can anyone please check whether this answer is right.Thanks in advance Answer: Pressure of the closed feed water heaterP4=1MPa Take the extracted pressure from the second turbine P11=0.3MPa Operating pressure...
  4. O

    Steam plant operates with ideal reheat -regenerative Ranking cycle.

    Question : http://i1179.photobucket.com/albums/x393/mariaschiffer/img017.jpg Can anyone please double check if this answer is right. Thanks in advance. Answer : Pressure of the closed feed water heaterP4=1MPa Take the extracted pressure from the second turbine P11=0.3MPa Operating...
  5. P

    Learning Refrigeration Cycle: Carnot, Real Life & Reversed

    Hi, :smile: So I am learning about how refrigerators work. First I have to show the Carnot cycle and explain why it does not work in reverse - from my understanding, it does not. And then show how it actually works in real life, with the phase transitions, which I am guessing don't exist for...
  6. S

    Why is the Carnot Cycle so Important?

    All reversible cyclic processes (engines) have the same efficiency: 1-T2/T1. And Carnot demostrated this efficiency with the Carnot Cycle and went on to use this to demonstrate that this was the upper limit for efficiency. My question is, why is it that there is such importance placed on...
  7. J

    Work input to a pump in a rankine cycle problem

    If a question asks for the "quantity of work input to the pump" is it acceptable to present the answer as positive. I think so because the direction of energy transfer has been defined in the question itself hence there is no need for a sign on the answer. All that's asked for is the...
  8. D

    Help with Organic Rankine Cycle Project

    Help with Organic Rankine Cycle Project please! Moderator's note: this thread is from May 2011 Hi there everyone, I'm posting here in the hope that someone will be willing to help an engineering layman do some calculations, I'm a plumber not an engineer. Thanks to anyone who decides to help...
  9. D

    How does a PWM duty cycle transform voltage?

    I need to find out how a certain pulse width modulation duty cycle is used in SMPS power supplies (specifically a boost converter). Also, how does the oscillation contribute to a voltage transformation? (step up) Any pointers to some articles are welcome
  10. B

    Carnot's cycle and a-like cycles

    Hello, Lately I encountered thermodynamics. And all that world is very new to me, gas expansion etc etc. I recently learned about Carnot's cycle. IT has 2 isotherms and 2 adiabatic processes. Now, I understand what those processes in separation mean. Adiabatic processes don't...
  11. E

    How to Determine Temperature of Heat and Cold Reservoirs in a Carnot Cycle?

    Homework Statement All i want to know is how do i find the temperature of my heat and cold reservoir, given that they have a 90 degree celsius/kelvin differential and a 28% efficency. Homework Equations Efficency= Work out/ Work in = 1- Q out/Q in The Attempt at a Solution I been...
  12. B

    Ideal gas undergoes cycle process

    Hi, An amount of ideal gas undergoes the folowing cycle process in the following graph: This process can be presented by the following PV-graph : The answer has to be the upper graph but why can't it be the lower graph ? Thank you!
  13. B

    Milankovitch 100,000 years cycle problem

    According to the Milankovitch 100,000 years cycles, there is a problem. The orbit of the Earth will change to a gradually more ecliptic orbit, and it will be a bit colder when this happen. But the problem is that this is not enough to explain ice ages. How much is missing. I mean how much...
  14. A

    Calculating Core Nuclear Reaction Rates for Stars Undergoing the CNO Cycle

    Problem: Two stars with identical core composition and density are undergoing nuclear fusion by the CNO cycle. Star A has a core temperature of 10% higher than star B. What is the ratio of their core nuclear reaction rates? My solution: as the energy generation rate q is proportional...
  15. J

    Help needed understanding the Vapour-Compression Cycle in refrigeration

    So I can follow the sequence of operations: the refrigerant enters the compression stage as a saturated vapour(a gas?) and it's compressed raising the temperature of the refrigerant, it gives off some of this heat to the surrounding ambient air, causing a decrease in temperature and an according...
  16. S

    Brayton Cycle with Supercritical CO2

    Researchers at Sandia have found the Brayton cycle with supercritical CO2 to be 50% more efficient than existing steam turbine technology used with nuclear reactors: http://www.eurekalert.org/pub_releases/2011-03/dnl-scd030311.php I suppose it's safer too, since the CO2 would help to...
  17. K

    Help! Rankine Cycle Turbine: Finding Low Cost Feed Pump Advice

    Hello! first time user, in desperate need of advice: My company (start up) has built a 5 hp Rankine cycle generator with a thermal efficiency of about 33%, it works fantastic in an open cycle, however 6 engineers and many pump specialists later, and i am still at a loss... My system uses...
  18. M

    Calculating Efficiency of Otto Cycle

    My team has recorded information on a single cylinder Otto cycle from a lab we have done. We are supposed to compare the theoretical efficiency of the cycle to the experimental efficiency. Using a given compression ratio of 3 and the ratio of specific heats for the fuels we used we were able to...
  19. A

    Brayton Cycle modelling - optimum system design

    Hi I am trying to model the Brayton cycle in a gas turbine that is used for electricity generation. My main aim is to be able to fully power the x amount of daily electricity load of a building using this machine. In order to do this, is it correct to do a backwards model and find what...
  20. S

    Beta or Alpha emitter nuclear fuel cycle?

    Do exist some proposed nuclear fuel cycle in which uranium or thorium whoud be first converted in some beta or alpha emitting isotope and after energy whould be harnessed with direct energy conversion methods?Possibly, it could reduce size of power plant and make steam turbine unnecessary.
  21. C

    Zero Crossing Point of ac cycle

    How can equipments work in ac current even it is oscillating from +ve to -ve and to zero? Alternating current is alternation of positive and negative values.If we consider the sinusoidal case,the current value becomes zero,negative,positive in a cycle.In that case,how can electrical equipment...
  22. J

    Efficiency of a heat engine in a reversible cycle

    Homework Statement A heat engine operates in a reversible cycle with the following steps: (i) An ideal gas characterized by γ = 1.4 expands adiabatically, so that it cools from an initial temperature of 330°C to 30°C. (ii) It is compressed isothermally until it reaches its initial volume...
  23. U

    Reheat and Regeneration in Brayton cycle.

    Homework Statement 1. In a set-up of Brayton cycle , I know that the turbine has to give a greater magnitude of work output than the magnitude of the work done by the compressor (because the turbine has to run the compressor)...but the turbine and compressor are at the ends of the same shaft...
  24. Astronuc

    What were the highest sustained winds of Tropical Cyclone Yasi at landfall?

    http://www.accuweather.com/blogs/news/story/45263/devastating-tc-yasi-crashing-a-1.asp Landfall between Cairns and Townsville (actually between Innisfail and Cardwell), Queensland, on Feb. 2, 2011 http://www.bom.gov.au/products/IDQ65002.shtml
  25. N

    Solve Otto Cycle Problem: Max Pressure Lambo Murcielago w/r=11.0

    Homework Statement (a.) This was just a log-log plot of the otto cycle (b.) Derive an expression for the ratio of maximum to minimum temperature experienced by the cylinder head during the part of the cycle that contains only isochoric and and adiabatic transitions in terms of the compression...
  26. M

    Carnot Cycle Question: Heat Transfer and Pressure Changes Explained

    Homework Statement Dear All, I have a question regarding the Carnot Cycle: (The image is taken from Wikipedia, I hope that is not a problem... In case it is I will change it.) Points one to two are an isothermal reaction. The gas, kept at constant temperature, is expanding, the...
  27. B

    Sociology: Organizational/Political Cycle

    ……Independence Family Clan Tribe Sovereignty Aristocracy Rebellion…… It seems to me that humans have repeated this same cycle of organization and disorganization throughout history. Would you agree? If so, do you think this cycle has...
  28. B

    Is this Thermodynamic Cycle Possible and Reversible?

    Homework Statement Determine Whether or not this cycle violates the first law and if it is reversible, irreversible, or not possible. 2000kW or power are produced by taking 3000 kW of heat transfer from a 750C reservior and rejecting 1000kW of heat to a 20C reservoir. Homework...
  29. N

    AZING! Understanding the Carnot Cycle: Heat, Work, and Internal Energy

    Homework Statement I don't understand the process between the points in a carnot cycle. Homework Equations Can someone please explain what is going on from point to point in terms of Q (heat), U(thermal energy), and Work? The Attempt at a Solution
  30. P

    Air Conditioners - The Refrigerant Cycle

    I was taking a look at how air conditioners work. After reading some texts in websites I decided to try a video. The concept seems pretty simple but I came across two things I did not quite grasp: 1st. When the refrigerant enters the compressor it is a hot gas because the air in the room lost...
  31. B

    Thermal question: Reversible cycle

    Homework Statement Hi all I'm a little confused about work in gases. I thought I knew it now I'm not so sure. Basically I'm answering a question about work done on the gas in a reversible cycle where a change in temperature (T1 -T2)at constant volume (V1) is followed by a change in volume at...
  32. A

    AC Voltage at Point X on Wire: Positive and Negative Half Cycle

    greetings, consider a wire which is subjected to AC supply.now consider a point X anywhere on wire. now what will be the potential of that point during the positive and negative halfcycle of sinusoidal AC?what will be the direction of current? thanks
  33. V

    Euler's path same as Hamiltonian cycle

    Homework Statement Find (classify) all graphs with n vertices who's Euler's path is the same as their Hamiltonian cycle. The Attempt at a Solution I'd say that any regular graphs with a degree greater than n/2 (Dirac's Theorem) with and n divisible by 2 has both and Euler's path and a...
  34. P

    Preserving cycle structure in transpositions

    Hi all, long time reader first time poster! Just need a hand on this problem I've been stuck on for a few days Homework Statement Let r=(a_1,a_2...a_k) be in S_n. Suppose that ß is in S_n. Show that: ßrß^-1=(ß(a_1), ß(a_2)...ß(a_k)). Homework Equations The Attempt at a...
  35. S

    Material balance- purge cycle help

    I am really struggling to get to grips with this question, ( struggling with material balance overall!) I can do dimple material balance however for things with a recycle stream or purge stream, really confuses me. I have the solution which I will post up, but I still don't get 'why' it...
  36. U

    Why Are Carnot Cycle Calculations So Confusing?

    Nevermind for now, just redid the whole thing and saw I made a stupid little mistake in computing the first volumes that messed everything else up. A Carnot engineer operating with a perfect gas between 800C and 25C has an operating pressure range between 20kPa and 6000kPa. Determine the work...
  37. P

    Water versus Air for cold reservoir in thermodynamic cycle

    I am wondering why water is used instead of air for the cold temperature source for a thermo cycle. My guess is the higher specific heat, which means the condenser unit can be smaller, and the mass flow rate less, which reduces the overall cost. Are there any other reasons to choose water...
  38. S

    Thermodynamics/Statisical Mechanics: Carnot Cycle

    Homework Statement Consider a Carnot Cycle that absorbs heat from the hot reservoir at Thw and expels to the cold reservoir at Tcw just below Th and above Tc respectively. a.) Derive an equation that relates the four temperatures. b.) Using the first and second law, write down an...
  39. Q

    Good book for studying rankine cycle

    so what book is the best when dealing with rankine cycle? i hope it has tons of problems with solution manual (for self-study purposes) pls. thanks
  40. A

    Split cycle HCCI engine idea

    Just wondering if an idea I've had for a few years would actually work. If I had an engine where compression took place externally and the engine was only used for combustion for example. This engine would be direct injected. The fuel would be injected a very high pressures (common rail)...
  41. M

    Calculating Heat Over a Cycle: Q, dU, W

    Homework Statement How much heat is added over this cycle? During which processes? What is the heat expelled from d to a? Homework Equations http://img838.imageshack.us/img838/6270/29494670.png (Goes clockwise, abcda) The Attempt at a Solution I'm just generally confused...
  42. L

    Combined cycle gas turbines (solar and natural gas)

    Not sure if I've posted it on the correct thread but I don't think this classifies as advanced physics! I'm currently doing a physics assignment where we have to choose an energy source for a town in Australia (Broome). I am choosing to use a combined cycle gas turbine with natural gas as...
  43. W

    Thermodynamics - Brayton Cycle

    Hey all. I'm going through my textbook at the moment and struggling to figure out something. Here is the ideal Brayton cycle (same as in my text). Now I want to find q in, so: The first law of thermodynamics can be written as (neglecting changes in ke and pe): h_in - h_out + q_in - q_out +...
  44. A

    Understanding Condensation in a Rankine Cycle

    I am a 2nd year mech engg student. I have a basic doubt in condensers. The steam from turbine exhaust enters the condenser & gets condensed during which its specific volume decreases resulting in formation of partial vacuum. Now according to rankine cycle the process in a condenser is a isobaric...
  45. R

    Peer-Reviewed Papers on Earth's Magnetic Field & Sun's 11-Year Cycle

    Hey all, i was having a dicussion with a friend of mine and i wanted some evidence to support my position as indicated by the title. I was hoping someone here could help me find some peer reviewed papers published on how long it takes for the Earth's magnetic field to flip, what happens to...
  46. Q

    Energy vs. entropy plot for a Carnot cycle

    Homework Statement I'm trying to understand how one would plot this. Homework Equations dS = dQ/T dU = dQ-dW (W is work done by the system, Q is heat absorbed by system, U is energy) For a closed cycle, dU = 0. Carnot Cycle: 1- isothermal expansion at Th 2- adiabatic expansion to Tc...
  47. J

    Efficiency of an ideal-gas cycle.

    Homework Statement A possible ideal-gas cycle operates as follows: (i) from an initial state (p1,V1) the gas is cooled at constant pressure to (p1,V2); (ii) the gas is heated at constant volume to (p2,V2); (iii) the gas expands adiabatically back to (p1,V1). Assuming constant heat...
  48. A

    Rankine Cycle with Reheat+Regen

    Hello, I'm working on designing a rankine cycle steam power plant for a class and am trying to incorporate both reheat and a direct contact feedwater heater for regen. I've attempted to read up on this online but beyond some basic information it's hard to find anything. My question is should I...
  49. C

    Prove G contains a cycle of length at least k+1

    This is a graph theory related question. Let G be a simple graph with min. degree k, where k>=2. Prove that G contains a cycle of length at least k+1. Am I suppose to use induction to prove G has a path length at least k first, then try to prove that G has a cycle of length at least k+1...
  50. K

    Reversible(Carnot) Cycle Temperature Equilibrium Problem

    Homework Statement A reversible hear engine, operating in a cycle, withdraws heat from a high temperature reservoir (temperature consequently decreases). It performs work w, and rejects heat into a low-temperature reservoir(temperature consequently increases). The 2 reservoirs are...
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