fluid flow tests

Flow tests

Cooling fluid enters the VTX barrel omega pieces through plastic inserts which are glued into the omega pieces, make a 45° bend and have a hose barb on the outside. The target flow rate is 22 cc/second. The cooling fluid is 3M HFE 7200, which has a viscosity 0.6 times that of water.

The inner diameter of the channel through this connector piece is 2mm, the smallest channel by far in the system, dominating the flow resistance.

The staves are mocked up with a 20-cm piece of 3/16" ID hose. Two connectors are glued back-to back, so they form a circular cross section, and the pair is glued into the hose. One of each pair is plugged with a toothpick. Five of these 'staves' are daisy-chained together.

The resevoir is a 2-liter bottle with marks at 100cc intervals. Measurements were made by setting the pressure, filling the reservoir, and marking the time as the water level passed each 100cc mark. The raw data are at the bottom of this page.

Click for a bigger version-->

The flow through 5 mockup staves is plotted vs pressure. Presumably the non-linearity is caused by flow switching from laminar to turbulent in different parts of the system. The sytem was hissing during operation, evidence for turbulence.

By moving the drain we ran with 1, 3, 5 staves, at a constant pressure of 30 psi. The points should lie on a hyperbolic-like curve (flow for large number of staves goes to zero, and flow for zero staves goes to infinity)

Effect of viscosity and density

Earlier we had done a simpler test by mounting a single connector at the bottom of a 1/2" ID vertical tube, which had a funnel on top, and by timing how long it took to fill a 2-liter measuring cup. We did this both for water and HFE 7200. The column height (top of fluid in the funnel to the entry into the connector) was 138 cm.

Water: ----------------- liters time ----------------- 1.0 3m 41s 221s 1.5 5m 50s 350s 129 2.0 7m 40s 460s 110 avg 120sec/500cc = 4.17 cc/sec HFE 7200: ----------------- liters time ----------------- 0.5 1m 44s 104s 0.5 1m 45s 105s 1.0 3m 33s 213s 108 1.5 5m 29s 329s 116 avg 112sec/500cc = 4.46 cc/sec
Since the HFE has density 1.42, and viscosity 0.6, we had expected the HFE times to be 2.4 times faster. We saw only a 7% decrease in time.
Here is the explanation by Don:
Pressure drop is affected by changes in viscosity and density, but the pressure drop is comprised of frictional pressure drop, which is a function of both viscosity and density, and inertial pressure drop (pressure drop due to changes in flow as in elbows and fittings), which is a function of density only. Viscosity is greatly affected by temperature differences but density is only mildly affected by temperature.

Why is the flow so low?

I sanded a barb down to the midplane, and made this image (400% on the copymachine, scan, invert colors). You can see that the outer radius of the channel curves (A), but the inner radius does not curve. In addition, there appears to be a ridge, or thin wall, in line with the red line AB, which further constricts the channel at the bend. You can feel this wall with the tip of a needle. When I cut another barb just below AB, the opening in this plane could be seen. It is approximately a 1mm × 1.5mm oval.

In this picture of the cross section I tried to indicate the edge of the obstruction in red.

I did 4 runs where I progressively cut off more and more from the barb, as indicated on the photo:



C   no cut                                    3.8 cc/sec     
D   cut halfway the inserted section          3.7 cc/sec
E   cut just downstream of the obstruction    5.0 cc/sec
F   cut just below the flange                13.5 cc/sec

(raw data below)

Also see a ppt of a photo by Mike Lenz from 29 Mar 2010.

bigger →

(I enhanced the contrast)

Mike also sectioned and measured some barbs

bigger →

Flow test with Stripixel stave

Using the CO₂ rig shown on top, I measured flow through a stripixel stave, for pressures between 10-40 psi.


  press.  flow
  -------------------
  10 psi  19.6 cc/sec
  20      27.0
  30      33.7
  40      42.3 
-------------------

This stave is 39.5×3.6×0.5 mm

Raw data:

      5 staves   30 psi
-------------------------------------
liters    min:sec, seconds from 0
        run 1      run 2      run 3
      ---------  ---------  ---------
 0.0  0:05  000  0:29  000  0:05  000
 0.1  0:29  024  0:51  022  0:26  021
 0.2  0:50  045  1:12  043  0:50  045
 0.3  1:11  066  1:34  065  1:11  056
 0.4  1:35  090  1:57  088  1:33  088
 0.5  1:57  105  2:19  110  1:55  110
 0.6  2:19  134  2:41  132  2:17  132
 0.7  2:42  157  3:01  152  2:29  144
 0.8  3:04  179  3:26  177  3:02  177
 0.9  3:29  204  3:51  202  3:27  197
 1.0  3:49  224  4:11  226  3:47  222  4.5 cc/sec = 0.27 l/min

     5 staves   20 psi
--------------------------
  l          min:sec
        run 1      run 2  
      ---------  ---------
 0.0  0:26  000  0:01  000 
 0.1  0:53  027  0:28  027  
 0.2  1:20  054  0:55  054  
 0.3  1:47  081  1:23  082  
 0.4  2:16  110  1:51  110  
 0.5  2:42  136  2:17  136  
 0.6  3:09  163  2:45  164  
 0.7  3:37  191  3:12  191  
 0.8  4:05  219  3:40  219  
 0.9  4:35  249  4:10  249  
 1.0  5:00  274  4:36  275  3.6 cc/sec = 0.22 l/min
 
     5 staves   10 psi
--------------------------
  l          min:sec
        run 1      run 2  
      ---------  ---------
 0.0  0:12  000  0:40  000
 0.1  0:51  039  0:--  ---
 0.2  1:29  077  1:55  075
 0.3  2:09  117  2:34  114
 0.4  2:48  156  3:14  154
 0.5  3:26  194  3:52  192
 0.6  0:--  ---  4:30  230
 0.7  4:45  273  5:09  269
 0.8  5:22  310  5:47  307
 0.9  6:07  355  6:31  351
 1.0  6:42  390  7:07  387  2.6 cc/sec = 0.15 l/min
 
      5 staves   40 psi
--------------------------
  l          min:sec
        run 1      run 2  
      ---------  ---------
 0.0  ----  ---  0:05  000
 0.1  0:07  000  0:26  021
 0.2  0:26  019  0:50  045
 0.3  0:45  038  1:11  056
 0.4  1:05  058  1:33  088
 0.5  1:24  077  1:55  110
 0.6  1:43  096  2:17  132
 0.7  2:02  115  2:29  144
 0.8  2:22  135  3:02  177
 0.9  2:44  157  3:27  202
 1.0  3:01  174  3:47  222  4.8 cc/sec = 0.29 l/min

      3 staves   30 psi
--------------------------
  l          min:sec
        run 1      run 2  
      ---------  ---------
 0.0  0:52  000  0:27  000
 0.1  1.08  016  0:44  017
 0.2  1.25  033  1:01  034
 0.3  1.43  051  1:19  052
 0.4  2.00  068  1:36  069
 0.5  2.17  085  1:53  086
 0.6  2.34  102  2:11  101
 0.7  2.51  119  2:28  121
 0.8  3.01  129  2:45  138
 0.9  3.28  156  3:05  158
 1.0  3.44  172  3:21  174  5.7 cc/sec = 0.35 l/min

      1 staves   30 psi
--------------------------
  l          min:sec
        run 1      run 2  
      ---------  ---------
 0.0  0:31  000  0:09  000 
 0.1  0:42  011  0:19  010
 0.2  0:50  019  0:29  020
 0.3  1:01  030  0:39  030
 0.4  1:12  041  0:50  041
 0.5  1:22  051  1:00  051
 0.6  1:33  062  1:11  062
 0.7  1:43  072  1:21  072
 0.8  1:53  082  1:31  082
 0.9  2:05  094  1:42  093
 1.0  2:14  103  1:52  103   9.7 cc/sec = 0.58 l/min





barb connector  full length
----------------------------------
ltr  run 1  delta t  run 2 delta t
     --------------  -------------
0.5  15:44:57  -     15:56:50
1.0     47:10  133      59:10  140
1.5     49:30  144      01:25  135
2.0     51:33  122      03:35  130    266 sec/liter = 3.76 cc/sec

barb connector 5.5mm cut off
----------------------------------
ltr  run 1  delta t
     --------------
0.5  16:09:09  -     
1.0     11:28  139   
1.5     13:38  135   
2.0     15:53  130  268 sec/liter = 3.73 cc/sec 

barb connector cut after bend
----------------------------------
ltr  run 2  delta t  run 1 delta t
     --------------  -------------
0.5  16:40:50  -     16:33:00
1.0     42:27  97       34:50  110
1.5     44:06  99       36:16   86
2.0     45:45  99       38:06  110   200 sec/liter = 5.0 cc/sec

barb connector cut in front of bend
----------------------------------
ltr  run 1  delta t  run 2 delta t
     --------------  -------------
0.5  16:57:55  -     16:57:00  
1.0     58:30  35    16:58:38  38
1.5     59:10  40    16:59:12  34
2.0     59:47  37    16:59:50  38 74sec/liter = 13.5 cc/sec

Stripixel stave:



stripixel stave 10 psi
--------------------------
  l          sec
      run 1   run 2  
      -----   -----
 0.0  43      53    
 0.1  48  5   58  5
 0.2  53  5   02  4
 0.3  58  5   08  6
 0.4  03  5   13  5
 0.5  08  5   18  5
 0.6  13  5   23  5
 0.7  18  5   28  5
 0.8  23  5   33  5
 0.9  29  6   40  7
 1.0  34  5   44  4    avg 5.1 sec/100cc = 51 sec/l = 19.6 cc/sec


stripixel stave 20 psi
--------------------------
  l          sec
      run 1   run 2   run 3 
      -----   -----   -----
 0.0  07      23      30   
 0.2  14  7   31  8   38  8
 0.4  22  8   38  7   45  7
 0.6  30  8   46  8   52  8
 0.8  38  8   52  6   59  7
 1.0  45  7   59  7   06  7    avg 7.4 sec/200cc = 27.0 cc/sec


stripixel stave 30 psi
--------------------------
  l          sec
      run 1   run 2   run 3 
      -----   -----   -----
 0.0  05      05      09  
 0.2  11  6   11  6   --  6
 0.4  16  5   16  5   21  6
 0.6  23  7   23  7   27  6
 0.8  28  5   29  6   33  6
 1.0  34  6   36  7   38  5   avg 5.93 sec/200cc = 33.7 cc/sec


stripixel stave 40 psi
--------------------------
  l          sec
      run 1   run 2   run 3 
      -----   -----   -----
 0.0  41      44      51
 0.2  47  6   49  5   55  4
 0.4  51  4   55  4   01  4
 0.6  56  5   59  4   05  4
 0.8  01  5   04  5   10  6
 1.0  06  5   10  6   16  4   avg 4.73 sec/200cc = 42.3 cc/sec

Mar 2010 HvH

The resevoir is a 2-liter bottle with marks at 100cc intervals. Measurements were made by setting the pressure, filling the reservoir, and marking the time as the water level passed each 100cc mark. The raw data are at the bottom of this page. Click for a bigger version-->
The flow through 5 mockup staves is plotted vs pressure. Presumably the non-linearity is caused by flow switching from laminar to turbulent in different parts of the system. The sytem was hissing during operation, evidence for turbulence.
By moving the drain we ran with 1, 3, 5 staves, at a constant pressure of 30 psi. The points should lie on a hyperbolic-like curve (flow for large number of staves goes to zero, and flow for zero staves goes to infinity)