3. Liu Hong Drop Generation
1. INTRODUCTION
This project mainly focus on looking for a method which can generate droplets quickly and
conveniently compared to PDMS or glass capillaries device. Microbore tee and cross fittings
used to mix carrier fluid and water to generate water droplet. Flow rate of carrier flow and
water can be controlled by syringe pump. As the result, water droplets can be generated
with constant frequency and visible rate. Finally, water droplets are collected in 500µm ID
Teflon tube. As shown in figure 1 and figure 2, cross fitting and Teflon tube form the droplet
generation device.
Figure 1: Basic structure of the project
Figure 2: Carrier fluid and water
Page 2 of 10
4. Liu Hong Drop Generation
2. MATERIAL USED IN THE PROJECT
According to Table 1, Part numbers for fittings used in drop generation and detailed informa-
tion about fluid are shown.
Table 1: Material properties
ID 500µm
Tubing Upchurch 1548
Drop generator Sigma Aldrich 57663
Interconnect to syringe Upchurch P-659
Qw water and red food color
Qo carrier fluid (silicone oil 100 cst or Trimethylolpropane ethoxylate triacrylate)
BD syringe 10ml
Page 3 of 10
5. Liu Hong Drop Generation
3. METHODS
1. Connect 4 Teflon tubes to every port of cross fittings as shown in figure 3.
Figure 3: Structure of device
2. Connect other end of each tube to 10 ml BD syringe, except output tube.
3. Use 100 cSt silicone oil to fill 2 carrier fluid BD syringe.
4. Use DI water mixed with red food color to fill input BD syringe.
5. Set pumping rate of carrier fluid as 300µl/min.
6. Set pumping rate of DI water as 200µl/min.
7. Use petri-dish to collect droplet from output tube.
8. Repeat step 1-7 with Qw decreasing from 200µl/min to 80µl/min and keep Qo = 1.5Qw .
9. Measure the viscosity of Trimethylolpropane ethoxylate triacrylate by using falling ball
viscometer.
10. Use Trimethylolpropane ethoxylate triacrylate to fill 2 carrier fluid BD syringe.
11. Repeat step 1-7 with Qw decreasing from 200µl/min to 80µl/min and keep Qo = 1.5Qw .
Page 4 of 10
6. Liu Hong Drop Generation
4. RESULT FOR SILICONE OIL
Figure 4,5,6 show the droplets generated by different flow rate of DI water. When flow rate
Qw and Qo is 200µl/min and 300µl/min, droplet frequency is very high, so the droplets can
not be counted by eyes. However, when flow rate decreases, droplets look like sphere and are
clearly visible.
Figure 4: Droplets generated when Qw = 200µl/min
Figure 5: Droplets generated when Qw = 120µl/min
Page 5 of 10
7. Liu Hong Drop Generation
Figure 6: Droplets generated when Qw = 80µl/min
Page 6 of 10
8. Liu Hong Drop Generation
5. RESULT FOR TRIMETHYLOLPROPANE ETHOXYLATE TRIACRY-
LATE
According to the measurement, t = 0.6s and ρf = 1.17g/ml. For size 3 viscometer, K = 35. For
stainless ball, ρ = 8.02g/ml.
K =
µ
(ρf −ρ)t
µ = 133cp
µ = 114cSt
Due to the viscosity of Trimethylolpropane ethoxylate triacrylate is larger than silicone oil,
the frequency of droplet generation is much higher. As the result, it is difficult to take picture
when fluid rate is large. Until Qw is decreased to 80 µl/min, the droplets can be clearly
observed.
Figure 7: Droplets generated when Qw = 80µl/min
Page 7 of 10
9. Liu Hong Drop Generation
6. DISCUSSION
According to figure 8, higher viscosity of carrier fluid means higher droplet generation fre-
quency, which can be proved by the result of experiment. But due to the frequency of droplet
is so high, photo detector is a good idea to help counting the number of droplet. What’s more,
using tube to store the droplet can only last short time. As long as stored period exceed 16
hours, some droplets begin mixing with each other.
Figure 8: Droplet frequency vs Qw for different viscosity carrier fluid
Page 8 of 10
10. Liu Hong Drop Generation
7. CONCLUSION
Cross fitting droplet generation works for quick generation of droplet. It is convenient and
reusable. However, Teflon tubing can not store droplet over 1 day. All droplets need to be
used as soon as possible.
Page 9 of 10
11. Liu Hong Drop Generation
REFERENCES
F. (2010, April). A modular approach for the generation, storage, mixing, and detection of
droplet libraries for high throughput screening
http : //ece.eng.wayne.edu/ abasu/docs/Tr ivediLOC10M odularDropletSystem.pd f
Page 10 of 10
