COIL VALVE USING SHAPE MEMORY ALLOY
Publication Date: 2013-Sep-12
The IP.com Prior Art Database
The invention proposes a technique to passively valve a fluid dynamic system that benefits from restricted flow in one temperature range and unrestricted flow in another. The technique includes either of a family of shape memory alloy in a form of wire. The wire retains a compact circular coil shape at one temperature range and an extended helical shape at another temperature range. The coil acts as a passive and thermally actuated valve when inserted into an orifice or conduit. The coil provides fluid dynamic blockage when the coil is placed in the conduit which restricts a cross sectional area of the conduit. In relaxed helical shape, the wire does not produce restriction in the cross sectional area of the conduit and maintains free-flow conduit.
The present invention relates generally to piston valves used in gas turbine engines and more particularly to shape-memory alloy based piston valves used in gas turbine engines.
Generally, a gas turbine engine requires free flow cooling fluid of maximum flow rate during peak performance operation, such as, during take-off for a jet engine or base load for a ground based engine, while requires less flow at off-peak points.
In gas turbine engines, several shape memory alloy based valves are deployed at locations where the alloy is used to actuate a piston valve or some other complex linkage system. The shape memory alloy (SMA) is also known as smart metal, memory metal, memory alloy, muscle wire and smart alloy. The SMA is an alloy that remembers its original, cold-forged shape and returns to a pre-deformed shape when heated. However, repeatability of shape recovery is damaged when an overload is applied to the SMA in a state of memorized shape. Further, the alloy is unable to return to original memorized shape due to deterioration of alloys as a result of repetition of overloads with time/age.
Several conventional techniques are known that use the shape memory alloy to actuate piston style valve.
A conventional technique includes an intravenous flow controller for use in a gravity-fed intravenous liquid dispensing apparatus. The controller is designed for intravenous administration of nutrients and medicaments at a preselected flow rate. The intravenous nutrients and medicaments are administered from a liquid reservoir at an upstream end and downward along a flow path bounded over a portion of its length by a flexible intravenous tube to a point of exit. The controller monitors a drop rate in a drop chamber and compares the drop rate with an operator-selected rate. Such controller controls valve by varying a current in a shape memory actuator element.
Another conventional technique discloses a compact valve utilizing shape memory alloy to control open and close of paths for various fluids such as air, liquid, among others.
Yet, another conventional technique relates to actuation of valves such as subsurface safety valves which are adapted for down hole. The valves are used for controlling fluid flow in tubing or conduit.
An electronically actuated valve assembly for an internal combustion engine is disclosed in one of the other conventional technique. The valve assembly includes shape memory alloy actuator.
However, the conventional techniques do not employ shape memory alloy which changes shape with change in temperature.
Therefore, there is a need in the art for an improved shape-memory alloy for use in piston valve assembly.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 depicts a coil valve using shape memory alloy.
Figure 2 depicts a gas turbine with a cooling circuit and coil valves using shaped-memory alloy.
The invention proposes a technique to passively valve a fluid d...