Coupling Fixture Aligns and Seals Ends of Two Tubes

The figure presents a partial cross section of two poly(methyl methacrylate) (PMMA) tubes with machined ends butted and sealed together in a special coupling fixture. This coupling scheme, in conjunction with the careful selection of PMMA tubes to match inner diameters, ensures the precise alignment of the inner tube surfaces. The scheme was devised to satisfy a requirement in a liquid-flow experiment to ensure a smooth, continuous inner tube surface to prevent both flow disturbances and trapping of bubbles. If the inner diameters were not matched and/or the inner tube surfaces not aligned precisely, the junction between the tubes would feature small, sharp corners that could give rise to waves and could trap bubbles.