{"id":63,"date":"2015-10-13T19:28:03","date_gmt":"2015-10-13T19:28:03","guid":{"rendered":"http:\/\/localhost:8888\/flatsome-next\/?p=1"},"modified":"2026-08-05T13:50:27","modified_gmt":"2026-08-05T05:50:27","slug":"ngatur-keseimbangan-tekanan-aerodinamika-internal-lan-dinamika-aliran-gas-ing-obor-ovd-vad-multi-saluran","status":"publish","type":"post","link":"https:\/\/ovdparts.com\/jv\/managing-internal-aerodynamics-pressure-balancing-and-gas-flow-dynamics-in-multi-channel-ovd-vad-torches\/","title":{"rendered":"Managing Internal Aerodynamics: Pressure Balancing and Gas Flow Dynamics in Multi-Channel OVD\/VAD Torches
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In optical fiber preform manufacturing, the precision of your mass flow controllers (MFCs) means very little if the physical channels inside your deposition burner fail to distribute that gas uniformly. Process engineers often spend weeks calibrating gas ratios\u2014adjusting standard liters per minute (SLM) of silicon tetrachloride (SiCl\u2084) against shielding lines of oxygen (O\u2082) and hydrogen (H\u2082). Yet, erratic flame patterns, high chemical wastage, and internal deposition often persist.<\/p>\n

The root cause is rarely the electronic gas mixing system. Instead, it lies within the internal fluid dynamics and pressure balancing<\/b> of the burner body itself.<\/p>\n

For an Outside Vapor Deposition (OVD) or Vapor Axial Deposition (VAD) torch to deliver a stable, high-yield soot boule, the internal machining must ensure that gases moving at different velocities equalize completely before they reach the nozzle face. Let\u2019s break down the hidden aerodynamics inside a multi-channel burner and look at how internal machining tolerances dictate gas behavior.<\/p>\n

\"\"<\/p>\n

(Our 4-port OVD burner nozzle assembly<\/a> is engineered with precisely these aerodynamics in mind.)<\/p>\n

1. The Challenge of Multi-Layer Gas Distribution Plenums<\/h2>\n

An OVD or VAD burner is essentially a complex chemical manifold wrapped in a compact metal housing. It typically features concentric layers routing three distinct gas categories:<\/p>\n

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  1. \n

    The Core Chemical Stream:<\/b> Vaporized SiCl4 and GeCl4 carried by an inert gas (like Argon or Nitrogen).<\/p>\n<\/li>\n

  2. \n

    The Shielding Gas Layer:<\/b> An intermediate buffer gas ring designed to prevent the raw chemical stream from touching the burner face prematurely.<\/p>\n<\/li>\n

  3. \n

    The Combustion Mixture:<\/b> Concentric rings of H2 and O2 that ignite to create the high-temperature hydrolysis zone.<\/p>\n<\/li>\n<\/ol>\n

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    [Gas Inlet Ports] \u2500\u2500> [Internal Expansion Plenums] \u2500\u2500> [Distribution Baffles] \u2500\u2500> [Concentric Nozzle Rings]\r\n   (High Pressure)          (Velocity Reduction)         (Pressure Equalization)         (Laminar Exit Velocity)\r\n<\/code><\/strong><\/pre>\n<\/div>\n<\/div>\n<\/div>\n
    When these gases enter the base of the burner through individual threaded fittings, they arrive as high-velocity, turbulent streams. The interior of the burner must act as an expansion and equalization plenum.<\/p>\n
    If the internal baffles or milled expansion slots contain asymmetric variations as small as 10 microns, the gas will take the path of least resistance. This creates a pressure imbalance across the circumference of the nozzle, causing the exit velocity to be higher on one side than the other, resulting in a skewed flame that misses the optimal deposition target.<\/p>\n
    (“To understand how this precision requirement scales down to the nozzle face, read our article on Burner Nozzle Precision & Preform Yield<\/a>)<\/p>\n
    2. Preventing Back-Diffusion: The Costliest Failure Mode<\/h2>\n
    One of the most destructive phenomena on a deposition line is back-diffusion<\/b>. This occurs when the static pressure of the outer combustion or shielding gas rings exceeds the pressure of the core chemical stream, or vice versa, causing gases to cross-contaminate inside<\/i> the burner body.<\/p>\n
    If ambient moisture or oxygen backs up into the SiCl4 distribution plate during a low-flow phase or an abrupt shutdown sequence:<\/p>\n