CN104511258B - Temperature bias field-applied AC electrothermal microfluidic mixer and AC electrothermal microfluidic mixing method - Google Patents

Abstract

The invention provides an AC electrothermal microfluidic mixing method. The AC electrothermal microfluidic mixing method comprises the following specific step of applying a temperature difference to the outer wall of an AC electrothermal microfluidic mixing chamber to generate a temperature gradient inside the AC electrothermal microfluidic mixing chamber so as to promote mixing of a solution in the mixing chamber. The invention further provides an AC electrothermal microfluidic mixer. The AC electrothermal microfluidic mixer comprises at least two liquid inlet microchannels, a liquid outlet microchannel and an electrode pair, wherein the liquid inlet microchannels and the liquid outlet microchannel converge at the same place to form the AC electrothermal microfluidic mixing chamber; the electrode pair is arranged inside the AC electrothermal microfluidic mixing chamber; two liquid channels or a heater is/are arranged on the outer wall of the AC electrothermal microfluidic mixing chamber. Through additional application of the external temperature difference, the temperature gradient is generated inside the AC electrothermal microfluidic mixing chamber so as to promote mixing of liquid in the mixing chamber, so that the effect of mixing the liquid to be mixed by an electrothermal flow is improved, and the requirements on the conductivity, the voltage and the frequency of the solution are lowered.

Description

AC electrothermal microfluidic mixer and method for applying temperature bias field

technical field

The invention relates to the technical field of micro-mixing, in particular to an AC electrothermal micro-mixer and a method for improving the mixing effect by applying a temperature bias field.

Background technique

In the biochip system, the micromixer has become one of the important components of the microfluidic system chip. Some biological solution processes that require fast reactions, such as DNA hybridization, cell activation, enzyme reaction, protein folding, etc., inevitably involve the mixing of reactants.

In recent years, the phenomenon of electrocaloric effect has gradually developed into a common active micro-mixing technology in microfluidic devices and biochip systems. The phenomenon of electrothermal effect can produce chaotic convection effect, thereby increasing the contact surface of different liquids and effectively improving the mixing efficiency of liquids. Therefore, the AC electrothermal micro-mixer has a good application prospect.

The phenomenon of electrocaloric effect is mainly caused by the temperature gradient. The longitudinal and radial temperature gradients in the microchannel will lead to the change of the fluid properties, such as the dielectric constant and conductivity of the electrolyte. These changes in physical properties in turn affect the motion of the fluid through their interaction with the electric field, thereby generating electrothermal flow. The strength of the electrocaloric effect is related to the conductivity of the solution, the voltage, and the temperature gradient inside the liquid. A general micro-mixer for AC electrothermal phenomenon includes a channel for mixing and a pair of electrodes on the bottom surface connected to the two poles of the AC power supply. It is characterized in that the structure of the electrodes can be designed into different shapes. However, although the current micro-mixers using the principle of alternating current electrothermal phenomenon can produce mixing effects, they have relatively strict requirements on the conductivity and voltage of the solution. Excessively high voltage will cause air bubbles to be generated in the microchannel or lead to inactivation of the biological fluid in the channel, while an excessively low voltage cannot achieve the mixing effect. Excessively high conductivity will lead to a sharp rise in the temperature in the micro-mixer, resulting in deformation of the channel wall or a decrease in the activity of the biological fluid, while the mixing effect of the electrothermal micro-mixer is not good when the conductivity is too low.

Contents of the invention

Aiming at the above defects or improvement needs of the prior art, the present invention provides an AC electrothermal micro-mixer and its method, the purpose of which is to generate a temperature bias field in the micro-channel of the electro-thermal fluid mixer by applying a temperature difference, so as to improve the treatment of the electro-thermal flow. The mixing effect of the mixed liquid, thereby relaxing the requirements on the conductivity of the solution, the magnitude of the voltage and the frequency, and solving the technical problem of the poor mixing effect of the electrothermal micro-mixer at a lower voltage.

The invention provides an alternating current heat flow micro-mixing method. A temperature difference is applied to the outer wall of the alternating current heat flow micro-mixing chamber, so that a temperature gradient is generated in the alternating current heat-flow micro-mixing chamber, thereby promoting solution mixing in the mixing chamber.

The method of the present invention generates a temperature gradient inside the AC electric heat flow micro-mixing chamber through an additional external temperature difference or a set heater, promotes the mixing of liquids in the mixing chamber, improves the mixing effect of the electric heat flow to be mixed liquid, and relaxes the conductivity of the solution. , voltage size and frequency requirements.

In order to realize the above method, the present invention provides an AC heat flow micro-mixer, comprising at least two liquid inlet microchannels, a liquid outlet microchannel and electrode pairs, and the liquid inlet microchannel and the liquid outlet microchannel converge at the same place to form an alternating current The heat flow micro-mixing chamber, the electrode pair is arranged in the AC heat flow micro-mixing chamber, and it is characterized in that it also includes two liquid channels, which are symmetrically arranged on both sides of the outer wall of the AC heat flow micro-mixing chamber, and are used to feed liquids with temperature differences. A temperature difference is generated on both sides of the mixing chamber, and the external temperature difference drives a temperature gradient inside the alternating current heat flow micro-mixing chamber, thereby promoting the mixing of solutions in the mixing chamber.

The microchannel material adopts PDMS, PMMA, silicon or glass. Metals such as gold, platinum and copper are used as the conductive material. Said liquid adopts water, oil or organic solution.

The implementation of the AC electric heat flow micro-mixer has the beneficial technical effects of low processing difficulty, simple temperature control and obvious mixing effect.

In order to realize the above method, the present invention also provides an AC heat flow micro-mixer, comprising at least two liquid inlet microchannels, a liquid outlet microchannel and electrode pairs, and the liquid inlet microchannel and the liquid outlet microchannel converge at the same place to form In the AC heat flow micro-mixing chamber, the electrode pair is arranged at the bottom of the AC heat flow micro-mixing chamber, and it is characterized in that it also includes a heater, which is symmetrically arranged on the outer wall of the AC heat flow micro-mixing chamber. Uniform temperature field, thereby promoting liquid mixing in the mixing chamber.

The position of the heater is not limited, and may be the bottom or top of the flow chamber, or the side wall of the flow chamber. The heater is made of conductive oxide films such as indium tin oxide (ITO) or other conductive materials with high resistance, and both ends are externally connected with DC or AC power.

The implementation of the AC heat flow micro-mixer has the beneficial technical effects of easy temperature control and obvious mixing effect.

Description of drawings

Fig. 1 is the top view of the electrothermal flow micro-mixer that is respectively provided with the liquid channels of different temperatures on both sides;

Fig. 2 is the structural schematic diagram of section A-A;

Fig. 3 is a schematic diagram of electrode shape;

Fig. 4 is the plan view that is provided with resistance heater to improve the AC heat flow micro-mixer of mixing efficiency;

Fig. 5 is a structural schematic diagram of section B-B;

Fig. 6 is a schematic diagram of the structure of section C-C;

Fig. 7 is the geometric model figure of simulation experiment;

Figure 8 is a schematic diagram of the concentration distribution results on each section of the micro-mixer in the simulation experiment, Figure 8(a) is a schematic diagram of the concentration without a temperature gradient, and Figure 8(b) is a schematic diagram of the concentration with a temperature gradient applied.

detailed description

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not constitute a conflict with each other.

Embodiment 1: AC electrothermal micro-mixer that improves mixing effect through external temperature difference

As shown in Figure 1, the micro-mixer with constant temperature liquid channels on both sides includes a Y-shaped flow chamber for mixing solutions and two U-shaped liquid channels with constant temperature fluid. The four walls of the flow chamber are made of common For the microchannel material, the choice of material is not limited. The connection of the three microchannels of the Y-shaped flow chamber forms an alternating current heat flow micro-mixing chamber. An electrode is placed at the bottom of the mixing chamber. The electrode position is shown in Figure 1. It is located after the intersection of the two solutions. The electrode material is a conductive material. The shape is not limited, and the two electrodes have a first AC voltage indirectly. On both sides of the Y-shaped flow chamber, a U-shaped channel A and a channel B through which a constant temperature liquid flows continuously are arranged respectively.

Solution A enters channel 4 from inlet 1 through a syringe pump, solution B enters flow chamber 5 from inlet 2, flow chamber 4 and flow chamber 5 merge and form flow chamber 6, solution A and solution B are mixed in flow chamber 6 and flow from Outlet 3 flows out. The liquid C enters the flow chamber 9 from the inlet 7 through the peristaltic pump, and flows out from the outlet 8 . The liquid D enters the flow chamber 12 from the inlet 10 through the peristaltic pump, and flows out from the outlet 11 . Liquid C and liquid D both have different temperatures. Electrodes 13 and 14 provide the AC voltage required for the electrocaloric effect.

Fig. 2 is a schematic diagram of the channel A-A cross-section in Fig. 1 . The material of the cover plate 15 is PDMS, and the material of the substrate 16 is glass. The channel cross-section 6 is filled with the microchannel of the solution to be mixed, and the constant temperature fluid A (20°C) and the constant temperature fluid B (30°C) of continuous flow are respectively passed through 9 and 12, and the temperature of the two can be controlled separately and the temperature in the two The temperatures are not equal. Fig. 3 is a diagram of microelectrodes processed on the bottom surface of the channel.

By changing the temperature difference between the channel cross-sections 9 and 12, a temperature gradient is generated in the cross-section 6 in the width direction, thereby enhancing the electrothermal flow and achieving the purpose of enhancing the solution mixing effect in the microchannel.

Embodiment 2: An AC heat flow micro-mixer equipped with a resistance heater to improve mixing efficiency

As shown in Figure 4, solution A enters channel 4 from inlet 1 through a syringe pump, solution B enters flow chamber 5 from inlet 2, flow chamber 4 and flow chamber 5 meet and merge into flow chamber 6, solution A and solution B are in the flow chamber 6 to mix and flow out from outlet 3. Fig. 5 is a B-B cross-sectional view in Fig. 4, electrodes 13 and 14 provide the AC voltage required by the electrocaloric effect. Fig. 5 is C-C longitudinal sectional view among Fig. 4, and resistance heater 17 provides additional temperature gradient, has a layer of 1 micron thick silicon dioxide insulation layer as electric field isolation layer between electrode 13 and electrode 14 and resistance heater 17, prevents The electric field generated by the resistive heater interferes with the electric fields generated by electrode 13 and electrode 14 . The two ends of the resistance heater 17 are loaded with a DC voltage, and by controlling the voltage at both ends of the resistance heater 17, the resistance heater generates heat, so that an additional temperature gradient is generated in the channel, so as to achieve the purpose of improving the electrothermal effect and improve the mixing effect.

The heat source is not limited to the above-mentioned method, and it is sufficient to apply various forms of heat sources outside the mixing chamber to generate a non-uniform temperature gradient and temperature field inside the mixing chamber.

Example:

Using COMSOL Multiphysics 4.3a to numerically simulate the AC electrothermal micro-mixer that improves the mixing effect through the external temperature difference, encode the control equations of flow field, electric field and temperature gradient and their boundary conditions into the software for calculation, and establish a The discrete 3D model of the triangular unit of the Grangian quadratic function, the channel in the calculation domain is 600 μm long, 50 μm high, and 100 μm wide, as shown in Figure 7. Figure 4 is a design diagram of the AC electrode on the bottom surface. As shown in Figure 5, a total of 355,460 tetrahedral unstructured grids were generated on the 3D model, which were coupled and numerically solved by the finite element method. Convergence studies show that the solution does not change with mesh refinement at this time. Use software to solve algebraic equations and repeat the iterative process until the absolute tolerance between two consecutive iterative steps is less than a specified value (0.001 in this simulation). The frequency of AC voltage is 10 ⁷ Hz, the root mean square voltage is 7V, and the conductivity is 0.1S/m. Discuss the situation that there is a temperature difference in the width direction of the channel in the microchannel, and the fixed temperatures are set at 293K and 303K on the channel side walls, respectively. Since the AC electrode itself can generate a small amount of Joule heat when electrified, it is assumed that the surface boundary of the bottom AC electrode is at a fixed temperature of 298K. The concentration boundary condition is set at the entrance of the channel, the concentration C _1in =1 is set locally on the left half of the entrance boundary, and the concentration boundary condition C _2in =0 is set locally on the right half of the entrance boundary. The channel entrance is a velocity boundary condition, and the entrance velocity is 200 μm/s.

Figure 8 shows the concentration distribution on each section of the micro-mixer, a is considering the electrothermal effect, without external temperature gradient; b is considering the electrothermal effect, with external temperature gradient. It can be seen from the concentration distribution results that the concentration distribution is closely related to the shape of the corresponding streamline. After the temperature gradient is applied, the contact surface of the two solutions increases, and the effect of solution mixing is improved. After the external temperature gradient is applied, the two liquids on the cross-section of the channel are asymmetrically mixed due to the asymmetry of the flow, and the contact area increases. It can be seen from the figure that the mixing is more complete after the external temperature gradient is applied.

The calculation formula for evaluating the mixing efficiency on the section at the exit of the channel is:

Among them, C is the concentration distribution on the outlet section, C _∞ is the concentration when it is completely mixed and uniform, and the value is 0.5, and C ₀ is the concentration that is not mixed and the value is 0. The mixing efficiency is 61.0% when there is no external temperature gradient, and 99.4% when there is an external temperature gradient on both sides. The results show that the temperature difference is beneficial to the improvement of the mixing efficiency.

It is easy for those skilled in the art to understand that the above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention. For example, the Y-type micro-mixer selected by the example of the present invention is not limited thereto and contains multiple inlets. All channel mixers are suitable for the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (5)

1. A micro-mixing method for alternating current and heat flow, characterized in that, the method is specifically: The two electrodes in an electrode pair are arranged on both sides of the flow path inside the alternating current heat flow micro-mixing chamber, and the electrodes provide an alternating voltage to cause the electrothermal effect of the solution to be mixed, so that the solution to be mixed generates electrothermal flow; A temperature difference is applied to the outer wall of the AC heat flow micro-mixing chamber, so that a temperature gradient is generated in the AC heat flow micro-mixing chamber, thereby promoting the mixing of the solutions to be mixed in the mixing chamber. 2. An AC heat flow micro-mixer, comprising at least two liquid inlet microchannels, a liquid outlet microchannel and an electrode pair, the liquid inlet microchannel and the liquid outlet microchannel converge at the same place to form an AC heat flow micro-mixing cavity, and the electrode pair It is arranged on both sides of the flow path inside the AC electric heat flow micro-mixing chamber, and is used to provide an AC voltage to cause the solution to be mixed to generate an electrothermal effect, thereby causing the solution to be mixed to generate an electrothermal flow. It is characterized in that it also includes two liquid channels, symmetrically arranged in The two sides of the outer wall of the AC heat flow micro-mixing chamber are used to feed liquid with a temperature difference to generate a temperature difference on both sides of the outer wall of the mixing chamber. of the solution to be mixed. 3. An AC heat flow micro-mixer, comprising at least two liquid inlet microchannels, a liquid outlet microchannel and an electrode pair, the liquid inlet microchannel and the liquid outlet microchannel converge at the same place to form an AC heat flow micro-mixing chamber, and the electrode pair It is arranged on both sides of the flow path at the bottom of the AC heat flow micro-mixing chamber, and is used to provide an AC voltage to cause the solution to be mixed to generate an electrothermal effect, thereby causing the solution to be mixed to generate an electrothermal flow. It is characterized in that it also includes a heater. The bottom or side of the outer wall of the mixing chamber generates heat through the heater to generate a temperature bias field inside the alternating current heat flow micro-mixing chamber, thereby promoting the mixing of the liquid to be mixed in the mixing chamber. 4. The AC heat flow micro-mixer according to claim 3, further comprising an electric field isolation layer arranged between the electrode pair and the heater, for preventing the electric field generated by the heater from interfering with the electric field generated by the electrode pair. electric field. 5. The AC heat flow micro-mixer according to claim 3 or 4, characterized in that the heater is a conductive device.