scholarly journals Self-similarity of fluid residence time statistics in a turbulent round jet

2017 ◽  
Vol 823 ◽  
pp. 1-25 ◽  
Author(s):  
Dong-hyuk Shin ◽  
R. D. Sandberg ◽  
E. S. Richardson
Keyword(s):  
Reynolds Number ◽  
Probability Density ◽  
Residence Time ◽  
Time Distribution ◽  
Residence Time Distribution ◽  
Mass Fraction ◽  
The Self ◽  
Similar Profile ◽  
Self Similar ◽  
The Mean

Fluid residence time is a key concept in the understanding and design of chemically reacting flows. In order to investigate how turbulent mixing affects the residence time distribution within a flow, this study examines statistics of fluid residence time from a direct numerical simulation (DNS) of a statistically stationary turbulent round jet with a jet Reynolds number of 7290. The residence time distribution in the flow is characterised by solving transport equations for the residence time of the jet fluid and for the jet fluid mass fraction. The product of the jet fluid residence time and the jet fluid mass fraction, referred to as the mass-weighted stream age, gives a quantity that has stationary statistics in the turbulent jet. Based on the observation that the statistics of the mass fraction and velocity are self-similar downstream of an initial development region, the transport equation for the jet fluid residence time is used to derive a model describing a self-similar profile for the mean of the mass-weighted stream age. The self-similar profile predicted is dependent on, but different from, the self-similar profiles for the mass fraction and the axial velocity. The DNS data confirm that the first four moments and the shape of the one-point probability density function of mass-weighted stream age are indeed self-similar, and that the model derived for the mean mass-weighted stream-age profile provides a useful approximation. Using the self-similar form of the moments and probability density functions presented it is therefore possible to estimate the local residence time distribution in a wide range of practical situations in which fluid is introduced by a high-Reynolds-number jet of fluid.

Quantitative Analysis of Residence Time Distribution in Kenics Static Mixer

2012 ◽  
Vol 499 ◽  
pp. 198-202 ◽  
Author(s):  
Dan Jin ◽  
Hai Ling Fu ◽  
Jian Hua Wu ◽  
Dan Sun
Keyword(s):  
Quantitative Analysis ◽  
Residence Time ◽  
Time Distribution ◽  
Residence Time Distribution ◽  
Plug Flow ◽  
Axial Direction ◽  
Static Mixer ◽  
Mixing Quality ◽  
Experimental Approaches ◽  
The Mean

The residence time distribution in Kenics static mixer is investigated using experimental approaches. Experimentally, RTD measure in SK with pulse tracer technology was used to characterize flow and mixing quality. The effect of velocity on the RTD was investigated for all sections. The results show that the flow in SK mixer tends to the plug flow along the axial direction when the velocity increases. The quantization analysis, the effect of factors on the mean residence time, is done by using the power function considering the numbers of mixer element, diameter, element aspect radio, and velocity. The validity of this function is testified by other experiments.

scholarly journals Determination of the residence-time distribution in industrial dryer for the production of recycled polyester

2020 ◽  
pp. 47-47
Author(s):  
Felipe Zauli da Silva ◽  
Izabella Bastos ◽  
Rafael Perna ◽  
Sergio Villalba Morales
Keyword(s):  
Intrinsic Viscosity ◽  
Residence Time ◽  
Time Distribution ◽  
Residence Time Distribution ◽  
Industrial Processes ◽  
Polyester Fibers ◽  
Pulse Type ◽  
The Mean

The study proposes the evaluation of the residence-time distribution (RTD) in-situ in an industrial dryer for the production of recycled polyester fibers (PES) from colorless polyethylene terephthalate (PET) flakes without interruption of the production. A disturbance of the pulse type was employed, in which the tracer (blue PET flakes) had previously been crystalized and its concentration was obtained according to the time at the dryer outlet. Additionally, analyses of intrinsic viscosity and crystallization percentage of the PET flakes (colorless and blue) and PES intrinsic viscosity and color force were performed. By RTD, the mean residence time (322.8 min), the variance (1305.4 min2), the standard deviation (36.1 min) and the relative error (1.5%) were obtained when compared to the theoretical residence time, indicating the absence of preferred paths or flake agglomerates in the equipment. Finally, the characterization demonstrated that there was no alteration in the parameters of product quality during RTD evaluation, confirming the potential of application of this methodology for diagnoses of continuous industrial processes.

scholarly journals Correction of residence time distribution measurements for short holding times in pasteurization processes

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Nilo H. M. Fortes ◽  
Jorge A. W. Gut
Keyword(s):  
Residence Time ◽  
Time Domain ◽  
Time Distribution ◽  
Residence Time Distribution ◽  
Pilot Scale ◽  
Signal Distortion ◽  
Process Step ◽  
The Mean ◽  
The Time Domain ◽  
Mean Time

AbstractWhen in-line cells are used for obtaining residence time distribution (RTD) data from systems with short residence time, the signal distortion caused by the cell can compromise the results. A procedure to correct such distortion using convolution of signals in the time domain is proposed. First, the RTD of the cell is characterized, and then the E-curve of an RTD model is convoluted with the cell curve. The convoluted E-curve is fitted to the experimental data by adjusting the mean time and the model parameter. The procedure is demonstrated using a pilot scale pasteurization unit with two heaters, one cooler and six options of holding tube. Pulse experiments were performed, E-curves were obtained for each process step and five RTD models were tested. The convolution procedure was successful in removing the distortion caused by the detection cell, which was very significant for the holding tubes.

scholarly journals Effect of oscillation amplitude on the residence time distribution for the mesoscale oscillatory baffled reactor

2017 ◽  
Vol 19 ◽  
pp. 111
Author(s):  
HW Yussof ◽  
SS Bahri ◽  
AN Phan ◽  
AP Harvey
Keyword(s):  
Reynolds Number ◽  
Residence Time ◽  
Oscillation Frequency ◽  
Time Distribution ◽  
Residence Time Distribution ◽  
Chemical Engineering ◽  
Continuous Production ◽  
Velocity Ratio ◽  
Small Scale ◽  
Gaussian Form

<p>A recent development in oscillatory baffled reactor technology is down-scaling the reactor, so that it can be used for the applications such as small-scale continuous production of bioethanol. A mesoscale oscillatory baffled reactor (MOBR) with central baffle system was developed and fabricated at mesoscales (typically 5 mm diameter). This present work aims to analyse the mixing conditions inside the MOBR by evaluating the residence time distribution (RTD) against the dynamic parameters of net flow Reynolds number (<em>Re</em><em><sub>n</sub></em>) at 4.2, 8.4 and 12.6 corresponding to flow rates of 1.0, 2.0 and 3.0 ml/min respectively, oscillatory Reynolds number (<em>Re</em><em><sub>o</sub></em>) between 62 to 622, and Strouhal number (<em>Str</em>) between 0.1 to 1.59. The effect of oscillation frequency and amplitude on RTD performance were studied at frequency, amplitude, and velocity ratio ranging from 4 to 8 Hz, 1 to 4 mm and 1 to 118, respectively. Effect of oscillation frequency has resulted in the variance of the RTD increased as the oscillation frequency increased from 5 Hz to 8 Hz and peak at 6 Hz of 0.264. A further increase in the frequency above 5 Hz caused the RTD to slightly broaden and positively skewed. At frequency of 5 Hz, the RTD profiles were close to Gaussian form for all tested amplitude values from 1 mm to 4 mm. At low amplitudes, i.e. xo = 1 mm, the variance exhibited its minimum around 0.842 at <em>Re</em><em><sub>o</sub></em><em> </em>=156. An increase in <em>Re</em><em><sub>o</sub></em><em> </em>above 300 resulted in increased in the variance rapidly to 1.28, and later eliminated the plug flow behaviour and the reactor behaved similar to a single continuous stirred tank reactor.</p><p>Chemical Engineering Research Bulletin 19(2017) 111-117</p>

scholarly journals A novel technique for residence time distribution (RTD) measurements in solids unit operations

2021 ◽  
Vol 32 (2) ◽  
pp. 611-618
Author(s):  
Atena Dehghani Kiadehi ◽  
Mikel Leturia ◽  
Franco Otaola ◽  
Aissa Ould-Dris ◽  
Khashayar Saleh
Keyword(s):  
Residence Time ◽  
Time Distribution ◽  
Residence Time Distribution ◽  
Novel Technique ◽  
Unit Operations
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