Recent content by nightingale

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    Refrigeration: Coefficient of Performance (Carnot & Lorenz)

    Homework Statement Cooling of a food from 293K (20 ⁰C), freezing it at 272K (-1⁰C), and further cooling to 253K (-20 ⁰C); using cooling water rising in temperature from 293K (20 ⁰C) to 303K (30 ⁰C) to accept heat. The specific heat of the unfrozen food is taken as 3.2 kJ/kg K, that of the...
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    Is Turbulence at Point A Isotropic? Calculation Help

    I understand, I will continue to read about the topic. Thank you very much for the patience and the guidance all this time Chet! You are a wonderful teacher!
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    Is Turbulence at Point A Isotropic? Calculation Help

    Thank you, Sir. I take the unit of the eddy viscosity as Pa.s. I attempt to do the last question, which asked me to determine the production of the turbulence energy at B. I found that the corresponding formula is: Production = -2 u'v'*(dU/dy) and thus the production is: Production = -2...
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    Is Turbulence at Point A Isotropic? Calculation Help

    Thank you Sir. I have borrowed the book you recommend and read chapter 5 and chapter 1 which talk about kronecker delta. I really helps me to understand turbulence better. I'm still intrigued on why Pope (2000) simply said VT as 'eddy viscosity' when it is, I think, 'kinematic eddy viscosity'...
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    Is Turbulence at Point A Isotropic? Calculation Help

    The viscous shear stress is thus: τ = 1.8 * 10-5 * 0.4219. I was wondering, for the turbulent shear stress, I consider both the fluctuations in the radial and axial direction. But for the viscous shear stress I only consider the fluctuations at the axial direction. Why and when do I have to only...
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    Is Turbulence at Point A Isotropic? Calculation Help

    Ah, I see, thank you very much Sir! How clueless of me!
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    Is Turbulence at Point A Isotropic? Calculation Help

    I plot the average velocity at A (7.525), where I take A as the origin (0,0). Then I plot average velocity at B (7.5375) which is 0.4mm from A (0.4, 7..5375). Then I plot the average velocity at C (7.8625) at 0.8mm from A (0.8, 7.8625). I then asked ms excel to generate the equation of the...
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    Is Turbulence at Point A Isotropic? Calculation Help

    I tried searching about the difference between the 'average of products' and the 'product of averages'. But I still don't quite get it yet. Do you mean I should reduce the each velocity components with each other and find the fluctuations? At B: u' =u1 - u2 = 7.6 - 8 = -0.4 u' =u2 - u3 = 8 -...
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    Is Turbulence at Point A Isotropic? Calculation Help

    Thank you, Sir. I found that the average fluctuations u' and v' are both zero. Thus the shear stress is zero. τ = -ρu'v' τ = -1.2 * 0 * 0 τ = 0 Will this be acceptable? I found the average velocities at A, B and C respectively are: A= 7.525 B= 7.5375 C =7.8625 I was thinking that the...
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    Is Turbulence at Point A Isotropic? Calculation Help

    Chet, would it be alright if I ask you about the subsequent questions? I'm worried that I might be making mistakes, like the ones I did with the fluctuations. The next question asks me to calculate the magnitude of shear stress at B, and I read from a book that the total stress for turbulent...
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    Is Turbulence at Point A Isotropic? Calculation Help

    Thank you for clearing that up Chet! Unfortunately I don't have a textbook or lecture slides on this, but I have borrowed some books from the library. I learned that: U(x,t) =U (x,t) + u(x,t) Where U is the velocity, U is the time averaged velocity, u is the fluctuations. I read that: U (x,t)...
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    Is Turbulence at Point A Isotropic? Calculation Help

    Chet, here is the full picture of the problem. Question a asks me to calculate rms values of fluctuations at B and whether it is isotropic, to which I answer (with your help, thank you very much): First rms fluctuations= 7.55 Second rms fluctuations= 0.3352 There are two different rms values...
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    Is Turbulence at Point A Isotropic? Calculation Help

    I'm really sorry Chet, but I couldn't seem to grasp on why yet. I see, I'm sorry for writing velocity components, I meant the fluctuations in the velocity components. My questions still stands however, why do I have to take 0.335 three times? "where u1 is the velocity fluctuations parallel...
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    Is Turbulence at Point A Isotropic? Calculation Help

    I'm really sorry, Chet, but I don't quite understand. If turbulent kinetic energy = 0.5 * (rms u12+rms u22+rmsu32) where u1 is the velocity component parallel to the pipe axis (axial) u2 is the velocity component along the radius (radial) u3 is the velocity component in the circumferential...
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    Is Turbulence at Point A Isotropic? Calculation Help

    The question says that 'assuming the rms fluctuations in the circumferential (i.e. tangential) direction to be similar to that of the fluctuations in the radial direction, estimate the turbulent energy at A'. Thus I assume that the rms fluctuations in the circumferential direction = rms...
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