Thermal Bubbles

Part 1. Presentation of the model. Int J Heat Mass Transfer 47 3375-3385 Tiselj I, Hetsroni G, Mavko B, Mosyak A, Pogrebnyak E, Segal Z (2004) Effect of axial conduction on the heat transfer in micro-channels Int J Heat Mass Transfer 47 2551-2565 Triplett KA, Ghiaasiaan SM, Abdel-Khalik SI, Sadowski DL (1999) Gas-liquid two-phase flow in microchannels. Part I. Two-phase flow patterns. Int J Multiphase Flow 25 377-394 Tsai J-H, Lin L (2002) Transient thermal bubble formation on polysihcon micro-resisters. J Heat Transfer 124 375-382... 

Figure 2.35 Cross sections of thermal/bubble Jet and piezo DOD print heads.

FIGURE 3.10 Principle of the thermal bubble-actuated pump. Qd flow at the diffuser Qn flow at the nozzle [395]. Reprinted with permission from the Institute of Physics Publishing. 

Tsai, J.H., Lin, L.W., A thermal-bubble-actuated micronozzle-diffuser pump. J. Microelectromech. Syst. 2002, 11, 665-671. 

Tsai, J.-H. Lin, L. Active microfluidic mixer and gas bubble filter driven by thermal bubble micropump. Sens. Actuators A. 2002, 97-98, 665-671. 

Tsai H Jr, Lin L (2002) Active microfluidic mixer and gas bubble Alter driven by thermal bubble micropump 1. Sens Actuators A Phys 97 665-671... 

Ink-jet printing Ink droplet ejection from a reservoir to a surface using either thermal (bubble-jet) or piezoelectric means. 

L. Lin, A. P. Pisano, and V. P. Carey Thermal bubble formation on polysilicon micro resistor. Journal of Heat Transfer, 120, 735-742 (1998). 

The bubble-actuated microfluidic switch is actuated by either thermal bubble or electrolysis bubble. The microfluid is driven by cqtillary force and stop by design of hydrophobic property in the microchannels. The switch function of the microfluidic system is to control the fluid sample into the individual desired outlet reservoir for the applicatimis such as selective on-chip sample dosing, microfluidic/bio-sample on-chip transportation and lab-on-a-chip microsystem integration. 

Thermal Bubble Nucleation The growth and collapse of a microbubble via a microheater actuator, with the applications to ink-jet printers, have been studied extensively in the decades. It has been demonstrated that the pressure inside the bubble could reach several MPa during the initial bubble growth period, with the heating duration of within several microseconds. It should be highlighted that most... 

The thermal bubble growth could be mainly classified into two modes in macroscale bubble nucleation experiments, as described in an early literature report [15]. The first mode occurs at the initial stage of bubble growth that is hydrody-namically controlled and dominated by liquid inertia. For this first mode, the bubble diameter increases proportionally with heating time. The second mode occurs at the later stage of bubble growth that is dominated by the heat diffusion. 

Applying the similar principles, we could cmitrol the fluid into multiple microchannels based on the needs. For such multiple-output modes, there are three different operation methods, as shown in Fig. 9, to control the fluid into the microchannels 2 and 4, for example, in the capillary system with a 1 X 4 microfluidic switch. The time-sequence actuation as shown in Fig. 9a, we would generate the growth and collapse of the thermal bubble six times to cmitrol the fluid to pass through the microchannels 4 and 2. The bubble pressure overcomes the barrier pressure to make the fluid pass through all hydrophobic patches of microchannels 2 and 4. Then, the capillary force pulls the fluid through to turn on microchannels 2 and 4. However, Fig. 9b demonstrates the same switch functimi with only... 

To ensure the controllability and reliability of the microfluidic switches, the same total barrier pressure is set as the requirement in the design when the thermal bubble is activated each time. This means that the fluid has to be steady state and stop at hydrophobic patches of each microchannel before each bubble starts being generated. For example, if we desire to control the fluid into the microchannels 2 and 4... 

The experimental setup which is utilized to observe the switch function is schematically represented in Fig. 11a. The volume of thermal bubble is controlled by the input pulse power of the heater with a preset duration which is programmed by the controller, composed of the... 

Cheng CM, Liu CH (2006) A capillary system with thermal-bubble-actuated IxN micro fluidic switches via time-sequence power control for continuous liquid handling. J MEMS 15(2) 296-307... 

Tsai JH, Lin LW (2002) Transient thermal bubble formation on polysilicon micro-resistors. J Heat Transf 124(2) 375-382... 

An expression for the wavefront velocity can be obtained using the information in Fig. 4, by modeling its propagation as a sequence of growing thermal bubbles, each new bubble growing for the time tufo on the upstream surface of the former ... 

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