Supersonic exhaust nozzle having reduced noise levels for CO.sub.2 cleaning system

• US 5,390,450 A
• Filed: 11/08/1993
• Issued: 02/21/1995
• Est. Priority Date: 11/08/1993
• Status: Expired due to Term

• Current Assignee: Visteon Global Technologies Incorporated (Visteon Corporation)
• Original Assignee: Ford Motor Company
• Inventors: Goenka, Lakhi N.
• Primary Examiner(s): Rose, Robert A.
• Application Number:
  US08/148,233
• Time in Patent Office: 470 Days
• Field of Search: 51/439, 51/410, 51/319, 51/320, 51/321, 51/322
• US Class Current: 451/75
• CPC Class Codes: B24C 1/003 using material which dissolves or changes phase after the treatment, e.g. ice, CO2
• CPC Class Codes: B24C 3/322 for electrical components
• CPC Class Codes: B24C 5/04 Nozzles therefor nozzles in general B05B
• CPC Class Codes: B24C 7/0084 the abrasive material being fed in a mixture of liquid and gas B24C7/0038, B24C7/0076 take precedence; blasting medium with additives B24C11/005
• CPC Class Codes: H05K 3/26 Cleaning or polishing of the conductive pattern

Abstract

A CO₂ nozzle receives and expels liquid CO₂ through orifices sized for converting the CO₂ liquid into CO₂ snow. A body, defining an elongated cavity therein, is coupled to the CO₂ nozzle such that the CO₂ snow is ejected into the cavity. An exhaust nozzle is coupled to the body and the cavity therein for directing the pressurized CO₂ snow toward the workpiece. The exhaust nozzle is operated in an overexpanded mode for containing the shockwave within the nozzle for reducing the shear noise therefrom. Pressurized air is injected into the elongated cavity for exhausting the CO₂ snow under pressure.

Claims

1. An apparatus for cleaning a workpiece with abrasive CO₂ snow, comprising in combination:

a nozzle for receiving and ejecting liquid CO₂ through at least one orifice sized for converting the liquid CO₂ into solid CO₂ snow,

a body defining a cavity therein, with said nozzle being coupled to said body for ejecting the CO₂ snow into said cavity,

first means, coupled to said body, for injecting pressurized air into said cavity for carrying the CO₂ snow from said orifice in said nozzle, and

an exhaust nozzle including a subsonic section coupled to said cavity within said body for receiving the CO₂ snow and air under pressure therefrom, a throat section and a supersonic section for directing the air and CO₂ snow toward the workpiece, with said supersonic section being operated in the overexpanded mode for containing the shockwave therein, thereby reducing the noise produced by the pressurized air and CO₂ snow exiting said exhaust nozzle.

2. The apparatus as described in claim 1 wherein said supersonic section of said exhaust nozzle is shaped to cause the deceleration of the mixture of air and CO₂ snow from supersonic to subsonic speeds fully within said exhaust nozzle, whereby the exhaust nozzle shields the sonic noise therewithin.

3. A method for cleaning a workpiece with abrasive CO₂ snow, comprising:

receiving CO₂ in a liquid form at a first pressure and temperature,

passing the liquid CO₂ through an orifice in a nozzle for changing the CO₂ from the liquid phase along a constant entropy line to a mixture of CO₂ liquid and CO₂ snow,

injecting pressurized air into a cavity adjacent the nozzle for receiving and mixing with the CO₂ snow,

collecting the resulting CO₂ snow and pressurized air within the cavity and then accelerating the mixture to supersonic speeds through a converging/diverging exhaust nozzle, with the diverging section of the exhaust nozzle having a contour for directing the flow of the CO₂ snow toward the workpiece, and then

decelerating the air within the diverging section of the exhaust nozzle to subsonic speed, thereby generating a normal shockwave within said exhaust nozzle and suppressing shear layer noise.

4. The method as described in claim 3 wherein the injecting step includes the additional step of injecting liquid N₂ into the pressurized shop air and then directing the mixture of pressurized shop air and N₂ onto an area of the nozzle operatively adjacent to the aperture therein for removing latent heat resulting from the flashing to the CO₂ from liquid to snow from the nozzle.

5. The method as described in claim 3 wherein the air is decelerated from supersonic speed to subsonic speed within the exhaust nozzle without significantly decelerating the CO₂ snow as it exists the exhaust nozzle.

6. The method as described in claim 3 wherein the step of injecting pressurized air into the cavity includes the substep of generating a swirling turbulence generally along a longitudinal axis within the cavity for improving the coagulation of the CO₂ snow into larger CO₂ particles therein.