Fluid handling – Processes – Cleaning – repairing – or assembling
Patent
1991-10-07
1994-05-17
Chambers, A. Michael
Fluid handling
Processes
Cleaning, repairing, or assembling
137828, 137315, 205 73, 346140R, F16L 5518, F15C 104
Patent
active
053118960
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method for producing a heatable and refrigerable element for a system handling small quantities of liquid, said element being provided with flow channels and at least one liquid space communicating with said channels, and said element being functionally connected at a number of locations to a refrigerator and a heater.
FI patent publication 57850 proposes a procedure and an apparatus for handling small quantities of liquid, whereby the liquid is manipulated within a system consisting of spaces or chambers for holding or processing the liquid and channels interconnecting them, each of said channels being provided with at least one valve which is shut by refrigeration. Each valve is connected to a continuously operated refrigerator and provided with a separate electric heating element, so that when the heating element is active it keeps the temperature of the valve above the congealing point of the liquid in question, thus keeping the valve open, and when inactive, it lets the liquid in the valve be frozen, thereby shutting the valve. Thus, the manipulation of the liquid in the system, based on moving the liquid from one space to another by virtue of pressure differences, is achieved by electrically controlling the heating elements of the valves The apparatus presented in this publication is designed for use mainly as an automatic analyzer, in which the manipulation of the liquid is exclusively based on the pressure differences between the spaces and on electronic control of the heating elements, using no movable mechanical parts.
According to FI patent publication 57850, the refrigerable valves are formed by placing two blocks of material against each other in such manner that a valve is formed between the opposite surfaces One of these blocks contains the flow channels leading to the valves, while the other block, connected to the refrigerator, is provided with heating elements placed in the region of the valve (s) and used for opening and closing the valves To regulate the heating and cooling of the valves, the valve areas are provided with heat insulation, and valves placed side by side are isolated from each other by freezing a liquid in the gaps between the surfaces of the valve body pieces.
FI patent publication 70331 proposes an improved solution based on the aforementioned principle of forming a valve. The main feature of this solution is that the valves are formed by providing cut-outs on the surface of at least one of the oppositely placed blocks, and that the opposite surfaces of these blocks are coated with a thin layer of a chemically inert material which acts as a covering of the heating elements and heat insulation. In this solution, the valves can also be provided with inert stopping elements placed in said cut-outs to allow instantaneous shut-off of the liquid flow into the valve. According to the publication, this inert material consists in the first place of a fluoropolymer, such as teflon, although precious metals are mentioned as a possible alternative. In practical applications of the principle, a fluoropolymer has been used.
It has been found that the solution proposed in the aforementioned FI patent publication 70331 has the disadvantage that in the course of time water penetrates through the thin polymer layer, resulting in the formation of ice under the layer in the areas subject to refrigeration. In practical use, as the valve is alternately heated and refrigerated, the melting and re-freezing of this external layer of ice increases the thermal load, resulting in a slower and less accurate operation of the valve A similar effect also results from the fact that ice conducts heat considerably better than the polymer constituting the valve surface. Consequently, when the valve is being shut, the process of settlement of the boundary layer of the ice blockage is slow.
Furthermore, the valve construction proposed by said FI patent publication 70331 has other drawbacks not associated with the material used as coating of the bodies between which the val
REFERENCES:
patent: 4012293 (1977-03-01), Meyerhoff
patent: 4255237 (1981-03-01), Obert et al.
patent: 4285779 (1981-08-01), Shiga et al.
patent: 4651174 (1987-03-01), Bava et al.
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