Changes between Version 260 and Version 261 of WikiStart

Timestamp:

Oct 21, 2016, 6:32:08 PM (7 years ago)

Author:

peakall3je

Comment:

--

WikiStart

@@ -92 +92 @@
 '''Siphon rig''' The siphon rig consists of 12 siphon tubes, each with a nominal internal diameter of 1.6 mm (3.2 mm external diameter), and 15 m in length. The siphons are held in place in the channel section by a plastic holder which is in turn connected to a rod attached to the channel. The siphon rig is positioned 80 mm downstream of the inflection downstream of bend 2, offset laterally 78 mm off-axis from the position of the UVP (on the right hand side as looking downstream). The siphons were initially positioned at heights of 7, 16, 26, 56, 86, 116, 146, 176, 206, 236, 266 and 306 mm from the bed for the initial test experiments. For the main experiments the siphons were positioned at heights of 10, 25, 50, 75, 100, 125, 150, 175, 200, 250, 350 and 450 mm above the bed. The siphon tubes are connected to a 12 head Watson Marlow 2058 peristaltic pump which is run at the highest setting of 90 rpm. Samples are taken when the traverse (with ADVs and conductivity probe) is positioned upstream measuring the straight section. Samples are collected in an array of 12 plastic containers over a 60 second period, starting at 5, 10, 15, 20, 25, 30 and 35 minutes into the experiment (the start of the experiment is defined as that point where the input is steady – see Section 3.2). The transit time of fluid moving through the siphons was measured using dye and was found to be 1 min and 50 seconds, thus we are actually sampling the flow at 3 min 10 s, 8 min 10 s, 13 min 10 s, 18 min 10 s, 23 min 10 s, 28 min 10 s, and 33 min 10 s (for the main experiments). Each plastic container was 3 cm in diameter and were placed inside a plastic template consisting of 12 3.2 cm diameter holes. Average fill depth of the containers in the 1 minute measurement period was 2.6 cm. Samples were subsequently measured for conductivity using an Anton Paar DMA35 Portable Density Meter.
 
-'''PME Microscale Conductivity and Temperature Instrument (MSCTI)''' The Microscale Conductivity and Temperature Instrument (MSCTI) is designed to measure the electrical conductivity and temperature of solutions containing conductive ions. This instrument provides two analog outputs, one linearly proportional to the solution conductivity, and one non-linearly proportional to the solution temperature. One probe is positioned on the traverse, alongside the ADVs, whilst a second probe is positioned at the base of the input box, in the centreline, immediately upstream of the honeycomb. For the main experiments, the conductivity probe in the channel is located 7.3 cm downstream from ADV1, and is offset by 5.5 cm such that its initial position is 20.5 cm from the wall; it is positioned xx cm from the floor. The second conductivity probe, positioned in the header box, is situated in the middle of the box and is approximately 1.5 cm above the floor. The MSCTI outputs two continuous voltage signals, one for conductivity and one for temperature, and these are recorded as part of the LVM file [C0 and T0 are conductivity and temperature for the probe on the traverse (though T0 does not work, since that part of the instrument is broken), and C1 and T1 are conductivity and temperature from the probe mounted in the inlet box]. We briefly had a second probe [just C2] in the inlet but this broke when it was damaged by a large input flow. Later files continue to have C2, but these just consist of noise. The probes are calibrated after each draining of the tank. To calibrate, samples of different densities (as measured with the hand-held Anton Paar density meter) are prepared at a given temperature of 21-22C and these are compared to the voltage output for conductivity of each probe. Because the water is so constant in the experiments, around 21-22C then this calibration approach enables a direct correlation between the voltage representing conductivity, and flow density. As such the temperature output from the two probes (note again that T0 is broken) are not required. The effects of temperature are small, a 1 degree C change in temperature for fresh water changes the conductivity by only 2% (see Barron and Ashton, Reagecon Technical Paper). For the test experiments the Conductivity probe was positioned 0.4 cm upstream, and with a lateral offset of 6.1 cm to the left hand side of the channel as looking downstream; it was 4.2 cm above the bed at the lowermost ADV setting.
+'''PME Microscale Conductivity and Temperature Instrument (MSCTI)''' The Microscale Conductivity and Temperature Instrument (MSCTI) is designed to measure the electrical conductivity and temperature of solutions containing conductive ions. This instrument provides two analog outputs, one linearly proportional to the solution conductivity, and one non-linearly proportional to the solution temperature. One probe is positioned on the traverse, alongside the ADVs, whilst a second probe is positioned at the base of the input box, in the centreline, 7.3 cm upstream of the honeycomb (the upstream edge of the honeycomb itself is positioned 10.7 cm upstream of the join between the curved inlet box and the start of the straight section). For the main experiments, the conductivity probe in the channel is located 7.3 cm downstream from ADV1, and is offset by 5.5 cm such that its initial position is 20.5 cm from the wall; it is positioned xx cm from the floor. The second conductivity probe, positioned in the header box, is situated in the middle of the box and is 2 cm above the floor. The MSCTI outputs two continuous voltage signals, one for conductivity and one for temperature, and these are recorded as part of the LVM file [C0 and T0 are conductivity and temperature for the probe on the traverse (though T0 does not work, since that part of the instrument is broken), and C1 and T1 are conductivity and temperature from the probe mounted in the inlet box]. We briefly had a second probe [just C2] in the inlet but this broke when it was damaged by a large input flow. Later files continue to have C2, but these just consist of noise. The probes are calibrated after each draining of the tank. To calibrate, samples of different densities (as measured with the hand-held Anton Paar density meter) are prepared at a given temperature of 21-22C and these are compared to the voltage output for conductivity of each probe. Because the water is so constant in the experiments, around 21-22C then this calibration approach enables a direct correlation between the voltage representing conductivity, and flow density. As such the temperature output from the two probes (note again that T0 is broken) are not required. The effects of temperature are small, a 1 degree C change in temperature for fresh water changes the conductivity by only 2% (see Barron and Ashton, Reagecon Technical Paper). For the test experiments the Conductivity probe was positioned 0.4 cm upstream, and with a lateral offset of 6.1 cm to the left hand side of the channel as looking downstream; it was 4.2 cm above the bed at the lowermost ADV setting.
 
 '''Particle Imaging Velocimetry (PIV)''' A Spectra-Physics Millennia ProS 6W YAG continuous laser (532 nm) in conjunction with 3 cameras was used to provide PIV images. The laser light sheet was brought in parallel to the floor of the channel. The light sheet can then be racked in the vertical through a series of steps through the use of a motorized traverse (tilted at 3.5 degrees to match the slope of the channel) and a mirror set at 45 degrees. The laser has another set of optics to point the light sheet down at the mirror, producing the light sheet. There is a glass window that enables the laser beam to go through the surface of the water tank. A 3D animation of the laser is in the ‘videos’ subfolder of the Photos folder. The laser light sheet positions are then synchronized with the PIV cameras. The field of view extends from close to the upstream end of the first bend, towards the mid-point of the second bend.
 
-Later experiments used larger seeding particles, 200 micron polystyrene particles for the flow seeding. These work very well for these situations where the measurement area is larger than 2 square metres. The three PIV cameras consist of one Falcon1 camera (Falcon 4M, CMOS 2432*1728 pixels, 10 bits) over the upstream part – with a 35 mm objective lens, PCO2 over the first bend with a 35 mm objective lens, and PCO3 over the most downstream part of the PIV measurement area, which has a 20 mm objective lens. 15 slices in the vertical are taken, and these are repeated multiple times. The two PCO cameras are PCO.edge5.5 CMOS cameras (2560*2160 pixels). The general approach is to have the lowest slice at approximately 2 cm above the floor, and then there are 2.5 cm heights between each successive level. These varied over time however, so there are a number of slightly different setups – see below. The sequence starts at the highest point, and then steps down through the flow, to the bottom, before switching back to the top again. Heights of laser slices (22/09/16 – 2.5 cm but after that 12/10/2016 and 14/10/2016 and 19/10/2016 all at basal 2 cm).
+Later experiments used larger seeding particles, 200 micron polystyrene particles for the flow seeding. These work very well for these situations where the measurement area is larger than 2 square metres. The three PIV cameras consist of one Falcon1 camera (Falcon 4M, CMOS 2432*1728 pixels, 10 bits) over the upstream part – with a 35 mm objective lens, PCO2 over the first bend with a 35 mm objective lens, and PCO3 over the most downstream part of the PIV measurement area, which has a 20 mm objective lens. 15 slices in the vertical are taken, each containing 20 images and these are repeated 10 times. Four different times between frames are used, since the velocities were not known a priori and vary as a function of height in the gravity current. So as such, no specific frame rate is used. All this is in the .xml files which can be read by a text editor. The two PCO cameras are PCO.edge5.5 CMOS cameras (2560*2160 pixels). The general approach is to have the lowest slice at approximately 2 cm above the floor, and then there are 2.5 cm heights between each successive level. These varied over time however, so there are a number of slightly different setups – see below. The sequence starts at the highest point, and then steps down through the flow, to the bottom, before switching back to the top again. Heights of laser slices (22/09/16 – 2.5 cm but after that 12/10/2016 and 14/10/2016 and 19/10/2016 all at basal 2 cm).
 
 == 3.2 Definition of time origin and instrument synchronisation ==