Research into Multi-scale Examination of MultiPHase physIcs in flowS (MEMPHIS)

Posted by Joao Vasques | May - 8 - 2017 | 0 Comment

The interfacial wave structure of the liquid phase in both upwards and downwards gas-liquid flows in an 11.7 mm pipe were investigated using the Brightness Based Laser Induced Fluorescence technique (BBLIF). Due to the versatility of the BBLIF technique, film thickness measurements were carried out over different axial locations covering a measurement area with very high spatial and temporal resolution. More specifically this comprises of measurements obtained between 330-430 mm from the inlet (between 28 to 37 z/D), where the flow is close to a fully developed condition.

As extensively reported in literature, increasing the gas superficial velocity results in a linear increase in disturbance wave velocity and frequency, as seen in Fig. 1. An increase in liquid Reynolds number also leads to an increase of both parameters. Figure 1: a) Average disturbance wave velocity; b) Frequency of disturbance waves measured with tracking algorithm. Hollow and full symbols represent upwards and downwards flow, respectively.

Figure 1: a) Average disturbance wave velocity; b) Frequency of disturbance waves measured with tracking algorithm. Hollow and full symbols represent upwards and downwards flow, respectively.

One of the main findings of this work is that although there is no overall discrepancy in the disturbance wave velocity between upwards and downwards flow, it is interesting to observe that this is not the case for the frequency of the disturbance waves. With exception to the lowest liquid Reynolds number tested, Fig. 1b shows that despite having the same velocity, the frequency of disturbance waves is higher in downwards flow than in upwards flow for the same conditions tested, which is an indication that the gravitational action has an impact on the number of disturbance waves present in the film at 37D from the inlet. In the case of lowest Reynolds number, the amount of liquid present in the system is possibly not considerable enough for the gravitational action to affect the number of waves created. However, in overall terms, this discrepancy in wave frequency with flow orientation has implications in parameters such as distance and time separation between disturbance waves, and possibly on the intermittency and width of these disturbance waves. Addiotionally, the effect that the flow orientation has on the ripples present in between consecutive disturbance waves was studied by applying an Omega-K analysis to the spatiotemporal plots of the film thickness time series obtained for both upwards and downwards flow.

The effect of the flow orientation on these parameters will be presented at the 9th World Conference on Experimental Heat Transfer, Fluid Mechanics and Thermodynamics on 12th – 15th of June in Brazil. Both a conference and journal paper will be published soon!

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