LIQUID OR LIQUIFIED GAS VAPORIZATION SYSTEM

Abstract

This invention pertains to the vapourization of liquids or liquified gases off a heated surface. The invention forces the liquid to maintain thermal contact with the heated surface by imparting acceleration on the liquid and delivering the liquid into acceleration wells or liquid trap on or in the heated surface.

Description

This invention relates to vaporization of liquids or liquefied gases. There are many applications where vaporization of liquids or liquefied gases is necessary for functional systems to work.

The functional operation of internal combustion engines depends as a primary requirement on the vaporization of liquids or liquefied gases. A major problem with fuel delivery systems in internal combustion engines is fuel impingement of various internal surfaces such as piston crowns or cylinder walls which, is detrimental to the vaporization process in the time frame available. This often leads to incomplete combustion of the fuel which results in lower efficiency, higher emissions and soot formation. The invention of this specification applied to internal combustion engines would solve these problems.

In the broadest aspect I provide a hot surface and force liquid to maintain thermal contact with the surface until the liquid has vaporized.

In another aspect I provide a hot surface and force liquid by means of constraining devices in conjunction with the heated surface to maintain thermal contact with the surface until the liquid has vaporized.

In another aspect I provide a hot surface and force liquid, by means of applying an acceleration to the liquid combined with constraining devices in conjunction with the heated surface, to maintain thermal contact with the surface until the liquid has vaporized.

In one form, this is achieved by placing axially concentric V-grooves in a housing cylinder, maintaining the surface at a sufficiently high temperature, and delivering the liquid into the V-grooves with a given velocity so that a tangential velocity is developed by the liquid. The tangential velocity gives rise to radial inertial acceleration which combined with the V-groove suppresses liquid dispersion as well as droplet formation and forces the liquid to maintain physical contact with the hot surface.

If a liquid impinges on a surface which is at a temperature equal to or below the saturation temperature of the liquid, contact between the liquid and surface is not impeded by vapour production at the interface. If a difference between the surface temperature and the saturation temperature of the liquid is applied, vapour is produced at the surface thereby disrupting the liquid to surface contact interface. As this temperature difference increases incrementally from zero, vapour production increases, the vapour production eventually becoming so vigorous that a catastrophic disruption of the liquid to surface contact interface occurs.

If a liquid impinges on a surface which is at a temperature appropriately greater than the saturation temperature of the liquid, wetting of the surface by the liquid becomes impossible. This results in low heat transfer rates and therefore low vapour production rates. For a heated surface immersed in water at one atmosphere this non-wetting temperature difference is approximately 120 degrees C. and is known as the Leidenfrost point. Various regimes of boiling and corresponding heat transfer rates can be observed up to the Leidenfrost point. Above the Leidenfrost point no contact between the surface and the water occurs, heat is transferred via conduction through a vapour film. At or above the Leidenfrost point the surface is rendered non-wetting to the liquid. Up to the Leidenfrost point in such a system the maximum heat transfer rate and therefore the maximum vapour production rate occurs in the nucleate boiling regime at a temperature difference of about 30 degrees C. Above the Leidenfrost point the temperature difference would need to be greater then 1000 degrees C. to equal the maximum heat transfer rate produced in the nucleate boiling regime. Most other liquids exhibit similar phenomena as water which has been used here as an example.

In a system where the a volume of liquid impinging on a heated surface does not immerse the surface as like a drop or several drops impinging on the surface the same phenomena can be observed. The heat transfer rate maximizes at moderate temperature differences and diminishes at elevated temperature differences until very large temperature differences are encountered. If a drop is placed on a surface where the temperature difference between the surface and the saturation temperature of the liquid forming the drop is approaching the Leidenfrost point the drop will be supported by a vapor film and slowly boil away (as observed by Leidenfrost in 1756) whilst retaining its spherical like shape.

A sphere contacts a surface in the ideal at a point and for a deformable liquid drop under an applied force the contact area will be greater then a point but much smaller than the wetted area of the same volume of liquid if the wetting phenomena were able to proceed.

To increase the rate of heat transfer from the surface and therefore vaporization of the liquid at elevated temperature differences it is necessary to force the liquid onto the surface.

By placing the liquid into tangential motion onto heated surfaces forming geometric shapes, as for example a cylindrical shape, radial inertial acceleration (centrifugal acceleration) of the liquid can be generated. The radial acceleration gives rise to a force being exerted by the fluid onto the surface and vice versa. The instantaneous magnitude of the radial acceleration is a function of the tangential velocity and the radius of curvature at any instant.

If a drop of liquid of just sustainable geometry in the gravitational field is placed into tangential motion on a curved surface at a tangential velocity which gives rise to a radial acceleration greater than the gravitational acceleration and where the surface temperature and the liquid temperature difference is at the Leidenfrost point or greater the drop will disintegrate into a number of smaller drops. The greater the applied radial acceleration the greater the number of smaller drops. The same result occurs if a jet of liquid is placed into tangential motion on a similar surface. The drop size will essentially be a function of the radial acceleration, liquid surface tension and liquid density. The surface finish of the surface will also affect the drop size.

Drops of any size will be supported by a vapor film and hence heat transfer will be at a minimum unless large temperature differences are employed. Therefore it is necessary to suppress the evolution of drops and to allow vapor as it is produced to be pumped away without carrying liquid with it. The curved surface that imparts the radial acceleration to the liquid can be any geometric shape that inhibits axial spread of the liquid i.e. imparts an axial acceleration on the liquid as well. A concentric V-groove is one example. Such a configuration forces the fluid back onto itself in three orthogonal directions thereby suppressing drop formation and ensuring physical contact with the hot surface. The applied radial inertial acceleration produces in the liquid a radial pressure, a hoop pressure and the sides of the V-groove producing an opposing axial pressure. Liquid cannot escape from the groove it is caught in an acceleration well, a liquid trap. Vapor can be buoyed through the liquid in the direction of diminishing pressure i.e. towards the origin of the radius of curvature of the surface, and as well pumped along the groove walls. Once the vapor is clear of the liquid it is free to expand or be entrained in ambient gas.

Experiments have shown that quantities of hydrocarbons commensurate with that of stoichiometric quantities for typical automotive engines can be vaporized in very short periods of time. The time periods are of a functional duration for automobile engines making the invention suitable for automobile use as one application.

These experiments showed that heat flux of tens of megawatts per meter squared is possible from the heated surface into the liquid.

Non-wetting surfaces can be used in the same way as wetting surfaces. The surface finish can be from extremely smooth to any suitable finish and be of the base material or coated with a suitable material such as Teflon.

Liquid can be delivered to the invention by any suitable means and can be continuous or intermittent and can include one or several intermittent liquid jets.

In this specification a V-groove has been used to describe the acceleration well or liquid trap geometry however it is understood that the curved surface that imparts the radial and axial acceleration to the liquid can be any geometric shape capable of causing an acceleration well or liquid trap. One or many acceleration wells can be deployed depending on the vaporization load. The grooves or surfaces can be concentric or otherwise.

The V-groove or the curved surface that imparts the radial and axial acceleration to the liquid and produces the acceleration well or liquid trap can have a helical path or trajectory or any other suitable path or trajectory, can be open ended or closed, have a lead in or out or can begin or terminate smoothly or abruptly. The depth of the V-groove or the curved surface can be any suitable depth.

The acceleration well or liquid trap may be provided for by forming raised profiles on the heated surface.

The radius of curvature of the acceleration well or liquid trap can be constant or varying, continuous or piecewise, small or large along the path or trajectory of the acceleration well or liquid trap.

The geometry of the surfaces may well be variable over time as in an enforced shape change, may well have shape discontinuities imposed on the surfaces as required and may change shape with changes in temperature.

The heated surface can be heated by any suitable means.

The temperature difference between the surface and the liquid need not approach or be greater than Leidenfrost point temperature differences.

The acceleration wells may well be used to constrain the liquid at some predefined position in a system where diffusing molecules of the liquid enter a stationary or moving gas.

Applied radial acceleration combined with a non-wetting surface will produce a very high degree of atomization of liquids. If a wetting surface is used then it is necessary to take advantage of the Leidenfrost phenomena i.e. cause a catastrophic breakdown of the surface wetting phenomena. A small diameter cylindrical surface combined with moderate tangential velocity caused by injecting fuel onto the cylindrical surface will produce droplets of several micrometer diameters. Appropriately shaped grooves or guides will convert the tangential velocity into axial velocity or a vector sum of both tangential and axial velocities. Such a device would be useful in many applications such as applied to the intake of an automobile engine or in the cylinder of direct injection engines as one example of an application.

Use of the non-wetting properties of surfaces can be taken advantage of in the delivering of liquid into the flow stream of gas such as air. If the liquid is delivered either by injection or whatever at or into particular geometric shapes positioned in the wall of the conduit containing the gas, with the shapes being non-wetting or wetting but raised to a temperature above the Leidenfrost point, liquid will not wet the surface and be reflected in directions governed by the orientation of the surfaces of the particular geometric shapes. For example, liquid injected at a sufficient velocity into an inverted Mexican hat like shape along the axis of revolution of the shape will have atomized fuel reflecting back into the air stream as it discharges from the outer rim of the shape. The geometric configuration of the shapes can be any configuration that reflects the liquid into the gas flow stream allowing the liquid to become entrained in the gas flow stream. The shapes could be one or many, co-reflective or directed in any suitable direction. This could be used in the fueling system of internal combustion engines as one example of an application.

Use of the non-wetting properties of surfaces can be taken advantage of in the delivering of liquid into the flow stream of gas such as air. If the liquid is delivered either by injection or whatever to travel at a given tangential velocity on the non wetting walls of a conduit having a polygon cross section, symmetrical or otherwise, or a circular section with rises or ribs, all or some of the liquid can be reflected off the corners or rises or ribs into the gas stream as the liquid encounters these reflective surfaces. If only a portion of the liquid is reflected at any one reflection event then another portion will be reflected at the next reflection event. This could be used in the fueling system of internal combustion engines as one example of an application.

Use of the non-wetting properties of surfaces can be taken advantage of in the delivering of liquid into the flow stream of gas such as air. If the liquid is delivered either by injection or whatever into a sufficiently hot cavity such as a hole the liquid will be pushed out of the hole into the gas stream as vapour is produced. This could be used in the fueling system of internal combustion engines as one example of an application.

Whilst in this specification I have described a specific form of the invention, it will be understood that a person skilled in the art of heat transfer or engineering can well present variations in some of these aspects without departing from the spirit and scope of the invention.

Claims

1. A vaporization device having a heated surface and a means to constrain the vaporizing fluid to maintain thermal contact with the surface.

2. A vaporization device having a heated surface where the means to constrain the liquid is through imparting an acceleration on the liquid.

3. A vaporization device having a heated surface where the means to constrain the liquid is through imparting a radial acceleration on the liquid.

4-29. (canceled)