WO2004070488A1

WO2004070488A1 - Microfluidic device

Info

Publication number: WO2004070488A1
Application number: PCT/EP2004/001116
Authority: WO
Inventors: Herbert Grieb; Astrid Lohf
Original assignee: Siemens Aktiengesellschaft
Priority date: 2003-02-07
Filing date: 2004-02-06
Publication date: 2004-08-19
Also published as: DE10305102A1

Abstract

In order to monitor the wear and tear of a microfluidic device with fluid channels (7), sensors (9) for detecting flow-relevant quantities are assigned to said fluid channels. A device (13) stores the values of the detected quantities and a comparison device (14) compares the values of the detected quantities with already stored former values. An evaluation device (15) generate a message when the difference between the values that are compared to one another exceed a predetermined measure.

Description

description

Microfluidic device

Microfluidic systems and their components (valves, pumps, reactors) are extremely sensitive to both blockages and abrasion due to the small diameter (<1 mm) of the fluid channels they contain. While abrasion of a few micrometers is usually negligible in conventional systems, this can e.g. B. in micro gear pumps with gap width of 2 to 3 microns lead to component failure. The same applies not only to the removal of material but also to deposits. Deposits are known for. B. from heat exchangers (so-called fouling) which inter alia interfere with the effectiveness of the heat transfer. The same effects can be expected in micro heat exchangers, only that these lead to blockage of individual or all fluid channels. If one takes into account that microreactors are also used in particular for extreme exothermic reactions, explosive mixtures or toxic chemicals, it is understandable that it must be recognized at an early stage when safe temperature control can no longer be guaranteed due to the blockage of heat exchangers. Fluid channels are often connected in parallel in microreactors and micro-equipment to increase throughput. A

Uniform distribution of the fluids on these fluid channels is achieved by their relatively high flow resistance. If individual fluid channels are now blocked, the residence time distribution in the reactor is widened, as a result of which the selectivity of the reaction decreases. After all, microfluidic systems should be able to be used as multi-product systems, with which different products can be produced in different phases of use, but also the same products can be produced at different times according to a specified recipe. To do this, it is necessary that these systems do not differ significantly due to deposits or abrasion deviate, so the degree of wear must be diagnosed.

The invention is therefore based on the object of making it possible to diagnose wear in microfluidic systems.

According to the invention, the object is achieved by a microfluidic device with fluid channels, sensors assigned to them for detecting flow-relevant variables, a storage device for storing the values of the detected flow-relevant variables, a comparison device for comparing the values of the recorded variables with those already stored earlier values and with an evaluation device for generating a message in the event of a deviation between the values compared with one another that exceeds a predetermined dimension.

The sensors can be flow sensors for detecting the flow in the fluid channels or differential pressure sensors for detecting pressure differences at different locations in the fluid channels. In a particularly advantageous manner, pressure sensors for detecting the fluid pressure in the fluid channels are provided, the difference values of the pressure sensors differing from the pressure sensors being stored and to be compared with one another

Locations of the fluid channels detected pressures are used. In the simplest case, the pressure differences at the fluid inlets and fluid outlets of the microfluidic device and thus the pressure drop in the microfluidic device are recorded.

Increasing contamination or clogging of the fluid channels of the microfluidic device is diagnosed by the fact that the fluid flow decreases or the pressure drop across the microfluidic device increases with unchanged general conditions. Conversely, abrasion is caused by an increase in fluid flow and a decrease in pressure drop detected. There are several types of microfluidic devices:

a) For facilities without control valves or pumps, such as. B. Mixer and dwell modules, the pressure loss is dependent on operating parameters of the device, such as the channel geometries (length, diameter, cross-sectional shape), the flow velocity of the fluid and the dynamic viscosity of the fluid (type of fluid, fluid temperature, pressure). Increasing pressure drops indicate blockages, while decreasing pressure drops are due to abrasion. If multi-way valves are available, they must be open for this.

b) For microfluidic devices with control valves, e.g. B.

Needle valves, these generate pressure losses defined by opening and closing the valve path. In this case, the valve position must also be taken into account in addition to the operating parameters mentioned under a). When the valve is open, the fluid channels can be checked for abrasion and deposits as described above, while the valve can be checked for leaks when closed.

c) In the case of microfluidic devices with pumps, the pressure increase or the fluid flow achieved must be determined, the operating parameters to be taken into account depending on the type of pump. Are z. B. Gear pumps are tested, the pump speed must also be taken into account in addition to the operating parameters listed under a). Particular attention should be paid to the use of gas-free liquids, since the pump performance of gear pumps can drop extremely sharply with gases. Then there is the temperature of the pump head. If a cold gear pump is started up, the pump head can heat up, even if fluids are pumped at ambient temperature. As a result, the gaps between the gears become smaller and the pump output increases with otherwise unchanged parameters on. In this case, it must be ensured that the acquisition of the flow-relevant quantities is actually carried out in a stationary state. With gear pumps, the state of wear can be determined via changes in the power consumption instead of the pressure difference generated. However, it must be ensured that there are no fluctuations on the pressure side, which can be the case, for example, if two pumps are fluidly coupled via a micromixer.

Three states can be distinguished for carrying out the diagnosis of the microfluidic device, namely new state, start state and current state. When new, the flow-relevant variables, in particular the pressure drop before the microfluidic device is used for the first time, are determined. The start state describes the state at the beginning of each new phase of use and in the current state the pressure drop is monitored in order to detect wear, i.e. deposits or abrasion.

When new, the pressure drop of the microfluidic device can be determined under defined conditions (pressure, flow rate, temperature of the fluid, type of fluid such as water) and stored in the storage device of the microfluidic device ("water test").

When a new use begins after the microfluidic device has already been used, the pressure drop in the starting state is first determined using the water test. If this result is compared with the pressure drop when new, the degree of wear can be determined. These pressure drops are also stored in the storage device. The microfluidic device can then be operated with the starting materials actually required and the corresponding operating parameters. At the beginning of production, when the desired steady state is reached, the pressure drop in the start state, but now with the real production parameters, determined again and stored in the storage device.

The pressure drops are continuously monitored and evaluated during operation (current status). In comparison to the pressure drops in the initial state with real production parameters, the degree of wear can be concluded. This degree of wear caused by the current use and the degree of wear determined at the start of use based on the water test result in the total degree of wear of the microfluidic device. When the microfluidic device is automated, the determination of the pressure drops of the individual states in the context of automated operating modes, such as, for. B. Start-up, productive operation, shutdown, etc. take place automatically. A separate operating mode can be introduced to determine the pressure drops when new or for additional water tests to be initiated manually.

By storing the values of the detected quantities, here the pressure drops, in the different states of the microfluidic device, e.g. B. a microfluidic module, it is ensured that this data can also be clearly assigned to the entire life cycle of the module, even if the module is used in different system configurations.

The monitoring and diagnosis of the microfluidic device according to the invention enables not only the mere detection of wear but also the prediction of how long it can still be used. Two cases can be distinguished here. In the first case, due to the water test in new condition and the water test before being used again, e.g. B. Production, the degree of wear is determined and the remaining service life is predicted. This is based on the total operating time of the microfluidic device and the current degree of wear, which make up the remaining remaining service life β can be calculated. So that a user can, for. B. decide before the start of production whether the equipment used is still suitable for a planned productive use over a certain period. In the second case, the remaining service life is also continuously calculated during operation, with the current operating parameters also being used for this purpose, which makes the prediction more accurate.

With the procedure described above, a water test is necessary for every productive use of the microfluidic device. However, if characteristic fields are determined in the first water test, varying the operating parameters, which make it possible to determine the pressure drops under the real production conditions, this additional water test can be omitted.

The microfluidic device can be a complete microfluidic system, individual microfluidic modules or module combinations of several microfluidic modules connected in series and / or in series. In the case of microfluidic modules, each individual module preferably has its own sensors and its own storage device, comparison device and evaluation device. The sensors preferably record input and output variables of the modules, with either only the input variables or only the output variables being recorded on each module in order to reduce the sensor effort, and as a replacement for the output variables or the input variables the input variables or those recorded on a subordinate module output variables recorded in a preceding module can be used.

To further explain the invention, reference is made below to the figure of the drawing, which shows a simplified block diagram of the microfluidic device according to the invention. In the exemplary embodiment shown here, the microfluidic device consists of a plurality of microfluidic modules 1, 2, 3, 4 connected in series, which are connected to one another at their fluid inputs 5 and fluid outputs 6. Between the fluid inputs 5 and the fluid outputs 6 extend 1 to 4 fluid channels 7 within each module, in the course of which functional units, such as. B. a mixer 8 can be arranged. In the area of the fluid inlets 5, the individual fluid channels 7 are assigned pressure sensors 9 which detect the fluid pressure in the fluid channels 7. The pressure sensors 9 are connected to a module-specific computing device 10, which also receives the values of the fluid pressures detected by the pressure sensors 9 in the subsequent module via a bus connection 11, and the difference values of the pressure sensors 9 of the modules 2 and 12, for example, in a subtraction device 12 3 recorded pressures. The pressure difference values are stored in a memory device 13 and at the same time fed to a comparison device 14 where they are compared with the differential pressure values stored in the memory device 13 at an earlier point in time. A subordinate evaluation device 15 evaluates the comparison result coming from the comparison device 14 with additional consideration of the operating parameters of the module 2 and generates a message when the deviation between the values compared with one another exceeds a predetermined level and thus indicates increased wear. The message can be transmitted to a central monitoring device 16 via the data bus 11. The operating parameters, such as. B. geometries of the fluid channels 7, type of fluids, fluid temperature, can, as far as possible, be measured by means of further sensors or entered at the monitoring device 16 and transmitted via the bus connection 11 to the individual modules 1 to 4 and stored there in the storage device 13 become. The results of the evaluation by the evaluation device 15, in particular the calculated degree of wear or the remaining service life, are likewise stored in the storage device 13.

Claims

claims

1. Microfluidic device with fluid channels (7), sensors (9) assigned to them for detecting flow-relevant variables, a memory device (13) for storing the values of the recorded variables, a comparison device (14) for comparing the values of the recorded variables with those already stored earlier values and with an evaluation device (15) for generating a message in the event of a deviation between the values compared with one another that exceeds a predetermined dimension.

2. Microfluidic device according to claim 1, so that the sensors (9) are flow sensors for detecting the flow in the fluid channels (7).

3. Microfluidic device according to claim 1, that means that the sensors (9) differential pressure sensors for detecting differential pressures of the

Are fluids at different locations of the fluid channels (7).

4. Microfluidic device according to claim 1, characterized in that the sensors (9) are pressure sensors for detecting the fluid pressure in the fluid channels (7) and that, as values to be stored and compared with one another, the difference values from the pressure sensors at different locations of the fluid channels (7) recorded pressures can be used.

5. Microfluidic device according to one of the preceding claims, characterized in that the values are stored together with operating parameters of the microfluidic device and that the further processing of the values in the comparison device (14) and / or evaluation device (15) takes place as a function of the operating parameters ,

6. Microfluidic device according to one of the preceding claims, that the evaluation device (15) calculates the wear of the microfluidic device and / or its remaining useful life from the deviation between the values compared with one another.

7. Microfluidic device according to one of the preceding claims, since you rchgek characterized in that it comprises different microfluidic modules (1, 2, 3, 4), each module (1 to 4) each having its own sensors (9) and its own storage device (13), comparison device (14) and evaluation device (15).

8. microfluidic device according to claim 7, since you rchgek characterized that the sensors (9) detect flow-relevant input and output variables of the modules (1 to 4), with each module (z. B. 2) either only the input variables or only the output variables are recorded and the input variables recorded on a subordinate module (e.g. 3) or the output variables recorded on a preceding module are used as a replacement for the output variables or the input variables.