Pumps – Expansion and contraction of pump fluid
Reexamination Certificate
1999-07-07
2001-09-04
Tyler, Cheryl J. (Department: 3746)
Pumps
Expansion and contraction of pump fluid
C417S208000, C417S207000, C347S056000
Reexamination Certificate
active
06283718
ABSTRACT:
DESCRIPTION
Background of the Invention
1. Field of the Invention
The present invention generally relates to a liquid pump and, more particularly, to a liquid pump which forms vapor bubbles in order to transport either electrically conductive or non-conductive liquid through channels and/or micro-devices.
2. Background of the Invention
Micro-pumps have considerable applications, for example in existing and prospective micro-fluid-handling systems such as “laboratory-on-a-chip” devices increasingly used in biomedicine, pharmaceuticals, environmental monitoring, and other applications. Other applications, actual or under consideration, include, for example, miniature polymerase chain reactors, electronic cooling systems, micro-mixing apparatuses, etc. In all of these applications, micro-pumps increase the pressure of the fluid and/or cause the motion of liquid for the transport of chemicals, heat transfer, or other known purposes.
Many micro-pumps use mechanical moving parts in order to provide pumping action. By way of example known actuation mechanisms include (i) piezoelectric micro-pumps and (ii) thermo-pneumatic micro-pumps.
As a general background, a piezoelectric micro-pump uses piezoelectric disks to drive valves (e.g. check valves) that, opening and closing at opportune times during the cycle, promote the motion of the fluid in one direction only. In a thermo-pneumatic micro-pump the same action is achieved by means of a small amount of gas (or a gas/liquid mixture) contained in a cavity separated by a suitable membrane from the liquid. By alternatively heating and cooling the gas (or the mixture), the gas (or the mixture) pressure rises and falls and actuates the membrane. This motion of the membrane then displaces the liquid within the cavity of the thermo-pneumatically driven micro-pump, much as in the piezoelectric system previously described.
Many of these micro-pumps have known drawbacks which contribute to their inefficiency. For example, a drawback of the piezoelectric micro-pump is the size of the piezoelectric disks (about 10 mm) that prevents a true miniaturization of the device. In addition, these systems require high voltages (with attendant high costs), and only provide small displacements, of the order of a few microns. Due to the relative slowness of heat transport in the existing devices, thermo-pneumatically driven micro-pumps suffer from a low frequency of operation which severely limits the liquid flow rate achievable with these systems. Moreover, since all the above devices (and pumps in general) contain moving mechanical parts, they are subject to mechanical failure due to imperfection of construction or materials, stress, fatigue, and other mechanical factors.
Of course other micro-pumps also exist that are based on non-mechanical moving parts, for example (i) ultrasonically driven micro-pumps, (ii) evaporation/condensation systems, and (iii) valveless micro-pumps. By way of example, ultrasonically driven micro-pumps induce fluid motion by the peristaltic action of traveling flexural waves. Similar to the piezoelectric pumps described above, these systems cannot be made very small due to the intrinsic size of the ultrasonic source and vibrating membranes. Evaporation/condensation systems do provide transport of liquid by causing evaporation in one place and condensation in another one (e.g., micro-heat pipes) but, again, their smallest size is limited to the centimeter scale and requires that the entire amount of liquid achieve a high temperature, which may cause undesirable degradation and would not be applicable to the transport, e.g., of liquid with dissolved proteins or other biological material. Some arrangements have been proposed in which ordinary valves are not required (hence the denomination “valveless”), but again one needs an actuation mechanism—piezoelectric or thermo-pneumatic—with all the above described drawbacks. What is thus needed is a micro-pump that does not rely on any mechanical moving parts in order to provide proper transport of fluid. What is further needed is a micro-pump that offers greater simplicity of construction and operation and the ability to work “on demand” with great flexibility of operation in terms of pumping rates and faster flow rates than those presently known.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a micro-pump which forms vapor bubbles in order to transport either electrically conductive or non-conductive liquid through channels of the micro-pump and/or micro-devices.
It is a further object of the present invention to provide a micro-pump capable of pumping liquid in very small channels by exploiting bubbles properties.
It is still a further object of the present invention to provide a micro-pump that does not utilize any mechanical moving parts.
It is also another object of the present invention to provide a micro-pump that offers simplicity of construction and operation.
The present invention is directed to a micro-pump for pumping either electrically conductive or non-conductive liquids through channels of the micro-pump and/or micro-devices. In order to accomplish the above objectives, a conductive or non-conductive liquid, depending on the specific application of the present invention, is disposed within a liquid chamber and/or channel of the micro-pump. An energy source is then applied to the micro-pump of the present invention in order to form one or more vapor bubbles within the chamber and/or channel. Thereafter the vapor bubble(s) is collapsed, and the process of forming and collapsing the vapor bubble may thereafter be repeated. By the formation and collapsing cycle of the vapor bubble, a pumping action of the liquid is effectuated thereby transporting the liquid within the micro-pump of the present invention and/or micro-devices.
In use, the underlying concepts of the present invention may be utilized in several known embodiments, all of which form and collapse vapor bubbles in order to transport liquids. For example, in one embodiment, an electrically conductive liquid is disposed within opposing electrically conductive channels of different diameters. Electrical current in then provided to the conductive channels (thereby completing a conductive path between the conductive channels and the conductive liquid) in order to form the vapor bubble in a conical section disposed between the opposing conductive channels. In other embodiments, a heat source is applied to the liquid disposed within a channel in order to create the vapor bubbles therein. In some of these other embodiments, liquid disposed within a conical section of the channel is contemplated for use by the present invention, such that the heater is placed in the conical section (partially or fully surrounding it) and the vapor bubble is formed therein. It is important to note that the pumping action is due to the asymmetrical properties of the micro-pump of the present invention, whether it be the asymmetrical properties presented by the conical section or the asymmetrical properties created by the placement of the energy source along the chamber and/or channel.
A method of using the micro-pump of the present invention is also contemplated for use herein.
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Oguz Hasan N.
Prosperetti Andrea
Yuan He
John Hopkins University
McGuireWoods LLP
Tyler Cheryl J.
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