Capillary microviscometer

Abstract

Low-cost and easily-operated microviscometer suitable for medical diagnosis clinical studies and other fluid tests. The equipment consists of a microchannel (2) formed by concatenated microchannels made by micro-manufacturing techniques, and a fluid column position detector inside the microchannel. The microchannels are open at one end and closed at the other end and are made of a single biocompatible material. When a liquid drop is put into the inlet of the microchannel (2), the fluid enters by capillary until the compressed air pressure equals the capillary pressure plus atmospheric pressure. The fluid transient movement from entering the channel until stopping at its balance position is analyzed thus obtaining as a result the viscosity and the capillary pressure of the liquid tested.

Claims

1. A capillary microviscometer comprising: a wafer within which only one microchannel is formed, the only one microchannel being open at one end and closed at the remaining end and formed by micromachined concatenated microchannels; a base; and a sensor device configured to measure a position of a fluid column within the microchannel, the sensor device being located in the base and capable of recording the dynamics of a fluid entering said only one microchannel; the sensor device being connected to a data processor, the data processor comprising a display, wherein the processor calculates a viscosity from a transient dynamics analysis of the fluid entering the microchannel by capillary action, by detecting position x of the fluid inside the microchannel (2) in relation to time t, from the equation: $t=\frac{\mathrm{\alpha \mu }}{r^2}\frac{\left(L_T-L\right)}{L_T{P}_0}\left(\frac{1}{2}{x}^2-\left(L_T-L\right)x+L\left(L_T-L\right)\ln \left(1-\frac{x}{L}\right)\right)$ where L is a maximum length up to which the fluid enters within the microchannel, r is the average channel radius, α is a geometrical factor determined by the section of the microchannel, μ is the viscosity, L.sub.T is the total channel length of the microchannel, and P.sub.0 is the atmospheric pressure.

2. The capillary microviscometer of claim 1, wherein the concatenated microchannels are concatenated in a zigzag shape.

3. The capillary microviscometer of claim 1, wherein the wafer is made of a single micromachined biocompatible material.

4. The capillary microviscometer of claim 1, wherein a diameter of the microchannel is such that the fluid moves within the microchannel by capillary action.

5. The capillary microviscometer of claim 2, wherein the microchannel is placed horizontally.

6. The capillary microviscometer of claim 1, wherein the base is integrated with or attached to a thermal actuator of a temperature controller.

7. The capillary microviscometer of claim 1, wherein the sensor device is an optical sensor.

8. The capillary microviscometer of claim 1, wherein the sensor device comprises an atmospheric pressure sensor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For a better understanding of the subject matter of the present invention, the same has been illustrated with schematic figures, in a preferred embodiment thereof, which are to be taken as demonstrative examples, wherein:

(2) FIG. 1 illustrates a scheme of a microchanneled wafer;

(3) FIG. 2 shows a block diagram of the microviscometer of the present invention;

(4) FIG. 3 presents schemes of the dynamics of a liquid drop entering a closed channel;

(5) FIG. 4 illustrates the graphical result of a numerical simulation for the dynamics of the present invention;

(6) In FIG. 5 the measurement of a referenced fluid shows the same behavior as the numerical simulation.

(7) In all the figures, equal reference numerals correspond to equal elements of the invention.

DETAILED DESCRIPTION OF THE INVENTION

(8) FIG. 1 shows a micromachined wafer 1, preferably made of glass or other biocompatible material, with a single microchannel 2, open at end 2a and closed at the other end 2b, formed by microchannels concatenated preferably zigzag-shaped, located horizontally-wise, this geometry permitting to reduce the size of sensor base 3.

(9) In FIG. 2 the block diagram of the sensor system shows the interconnection between the microviscometer various stages or parts. Base 3 is integral with or attached to the thermal actuator of temperature controller 4, the data processing unit 5 controls the detector system 6, the measurement of atmospheric pressure 8 and the screen or display 7.

(10) In FIG. 3, a liquid drop is introduced at inlet 2a of the closed microchannel, and it is shown schematically the entry of the drop at different times to reach a final position. Position “x” of the meniscus of the liquid column in relation to time “t” is expressed by the differential equation:

(11) $\frac{\mathrm{dx}}{\mathrm{dt}}=\frac{r^2}{\mathrm{\alpha \mu }}\left(\frac{L_T\left(P_C-P_0\right)-L\left(P_C-P_0\right)}{\left(L_T-L\right)}\right)$

(12) Where

(13) $L=\frac{P_C{L}_T}{\left(P_0+P_C\right)}$
is the maximum length up to which the liquid enters within microchannel 2, r is the average channel radius, α is a parameter unequivocally determined by the section of microchannel 2 (microcapillary), μ is the liquid viscosity, L.sub.T is the total channel length, P.sub.C is the capillary pressure and P.sub.0 is the atmospheric pressure.

(14) The differential equation result is:

(15) $t=\frac{\mathrm{\alpha \mu }}{r^2}\frac{\left(L_T-L\right)}{L_T{P}_0}\left(\frac{1}{2}{x}^2-\left(L_T-L\right)x+L\left(L_T-L\right)\ln \left(1-\frac{x}{L}\right)\right)$

(16) where it is observed that the final position the fluid reaches is achieved when the logarithm argument is null (zero).

(17) From this equation, it can be seen that there are only two parameters determined by the liquid and their interaction with the capillary: μ and L, and both can be determined from the measurements of x in relation to time. These data are subjected to a non-linear least squares adjustment, being μ and L the only free parameters.

(18) FIG. 4 shows a graphical result of a numerical simulation of a fluid drop entering a cannel with the design dimensions and FIG. 5 shows such reference fluid measurements using an optic detection system.

(19) It is worth pointing out that the channel concatenated zigzag-shape makes it possible to perform an optical detection with a fixed optical system that makes the most of the vision field provided by the lens.