Fluid handling – Processes – Affecting flow by the addition of material or energy
Reexamination Certificate
2001-01-29
2001-11-06
Buiz, Michael Powell (Department: 3753)
Fluid handling
Processes
Affecting flow by the addition of material or energy
C137S827000, C137S828000
Reexamination Certificate
active
06311713
ABSTRACT:
The present invention concerns a freeze valve for controlling the flow of small quantities of liquid in a conduit, the valve being defined by a tubular wall integral with said conduit and comprising a thermal bridge connecting said wall to a heat sink, to close the valve by freezing the liquid inside the wall, as well as heating means comprising a source of laser beam targeted at the wall, to open the valve by melting the frozen liquid.
Further objects of the invention are a network of conduits that comprises a plurality of freeze valves, a method of opening a freeze valve as well as a process for the separation of liquid or colloidal fractions from a liquid flow, particularly in capillary electrophoresis and chromatography.
In the FI patent 57850 and the U.S. Pat. No. 5,311,896 there are described systems for handling small batches of liquid comprising a plurality of chambers as well as conduits interconnecting said chambers, each of said conduits being provided with at least one valve which is shut by refrigeration, i.e. by freezing the liquid inside the valve. To that end, each valve is connected to a continuously operated refrigerator constituting a heat sink capable of maintaining the valve at a temperature below the melting point of the liquid. For selective opening of the valves each of them is provided with a separate heating element which, when activated, increases the temperature to melt the frozen liquid. As the heating is switched off, the refrigerator automatically returns the valve to said low temperature where the liquid, if present at the site of the valve, is in a frozen state.
In the two prior art patents cited above the heating element is taught to be an electric resistor lying adjacent the tubular shell of the valve which is of heat conductive metal. The selective control of the valves is thus achieved by controlling the electric current in the resistors.
Such systems are intended for liquid analyzers comprising a large store of liquid samples and reagents and performing operations such as mixing, incubation, detection etc. Said operations are those routinely performed e.g. in clinical chemistry. The freeze valves are non-wearing, self-sealing, hermetic and can be made extremely small and, consequently, the systems utilizing them have the advantages of avoidance of moving mechanical parts, the possibility for automatic control of the system, compactness as well as small size of the liquid samples that are being handled.
However, the electric resistors used as heating elements in the above mentioned prior art patents have drawbacks that have so far prevented the use of liquid handling systems with freeze valves for practical commercial applications. As described in the U.S. Pat. No. 5,311,896 the valve comprises a shell of metal defining the space where the liquid will freeze, and a strip-formed thermal bridge connecting the shell to a heat sink. The electric resistor is positioned in this bridge close to its tip soldered to the metallic shell, but still necessarily at some distance from it. This is due to the soldering process that would damage the sensitive resistor if present in the soldered area. The handicap then is that a considerable part of the heat generated does not reach the shell but is shortcircuited to the heat sink. Another detriment is the need of an isolating plastic layer to prevent access of the current to the shell of the valve. This isolation has also a poor heat conductivity, and therefore it retards the heat flow to the shell and prolongs the time needed to open the valve.
To give an example, assume that the tubular electroformed nickel shell of the valve according to U.S. Pat. No. 5,311,896 has a length of 3 mm, a diameter of 0.3 mm and a wall thickness of 0.02 mm. The shell is connected to a permanent heat sink through a soldered thermal bridge which is a metal strip having a width of 2.5 mm and a thickness of 0.25 mm and carrying an insulated resistor sheet structure of a length of 4 mm. These are the minimum dimensions of this type of thermal bridge that can be manufactured reliably. The solid mass of the thermal bridge is thus about 50 times the mass of the shell of the valve, and the bridge does not allow for a packaging thickness of the valves less than said 2.5 mm, even though the shell could be made much smaller.
In operation closing of a prior art valve as described above does not cause any major problems. The amount of liquid contained in the valve body is about 0.00002 ml and will freeze to close the valve in 20 milliseconds. However, the freezing does not stop there but continues for about 1-2 seconds at a progressively diminishing rate so that the length of the ice block will be about ten times the shell diameter and its total volume will be within a range up to about 0.0003 ml. To open the valve this ice block must be melted along its entire length, and the process here is reverse to that of freezing the valve, i.e. the melting starts rapidly but proceeds then more and more slowly towards the ends of the elongate block. It has turned out that opening the valve will require an amount of heat that is about 10 to 1000 times the net heat flow needed to block it. This is impractical as such, but even more of a problem is the prolonged time needed to turn the valve open.
In the U.S. Pat. No. 5,311,896 there is also a brief mention of the use of a laser beam for heating the freeze valve. However, the disclosure is silent upon how the heating would be arranged in practice and does not cite any advantage to be gained thereby. The detailed teachings relate to the use of electric resistors which must be concluded to be the preferred way of heating. There is nothing to suggest the problems related thereto and nothing to teach how to obviate them.
It is therefore an object of the invention to provide a freeze valve which will overcome the drawbacks of the prior art valves or alleviate them to a degree letting the valves be used in practical systems handling small quantities of liquid. Accordingly, the invention has the aim of providing a freeze valve where the ice block can be melted and the valve turned open substantially faster than what is the case in the prior art valves. The invention also aims to let the valve be opened with a substantially reduced energy consumption, especially in the stand-by mode where most valves are most of the time. Furthermore, the invention has the aim of reducing the size of the valve as an operative unit to allow a tighter packaging of valves and thereby reducing the size of the systems of conduits and valves used for purposes such as analyzers for small liquid samples.
A further object of the invention is to provide a freeze valve achieving the abovementioned goals with the use of a laser beam in a specific novel manner.
A still further object of the invention is to provide an improved process for the separation of liquid or colloidal fractions in a liquid flow with the aid of freeze valves employing a laser beam as means to open the valves.
The freeze valve according to the invention is thus characterized in that there are means provided for producing a laser beam in the form of a transversally extended shroud and targeting said shroud at the wall at a length extending to both sides of the point of connection to the thermal bridge, to melt the block of frozen liquid simultaneously along its entire length.
In contrast to the prior art technique of heating the wall of the valve from a single central point, the concept of the present invention is to spread the heating energy to the whole length of the ice block inside the valve. This is achieved by use of a shroud-formed laser beam emitted from a suitable laser source or a laser beam turned to the desired shroud-form by optical means. These measures will considerably accelerate melting of the block through its whole length as is necessary for getting the valve open. At the same time there is no loss of heating energy to the heat sink.
Preferably, said shroud-formed laser beam has the form of a divergent fan or cone with a radiation intensity higher in
Buiz Michael Powell
McShane Thomas L.
Rothwell Figg Ernst & Manbeck
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