On the application of the light-attenuation technique as a tool for non-intrusive buoyancy measurements

► We describe the light-attenuation technique applied to buoyancy-driven flows. ► We summarise the key factors for the successful application of the technique. ► A comparison between two dying agents is presented. ► Steps for extracting density-field data are outlined discussed. ► The accuracy of the technique is compared with direct measurements. This article describes the application of the light-attenuation technique as a tool for measuring dilution occurring in buoyancy-driven flows. Whilst this technique offers the experimental fluid dynamicist the ability to make rapid synoptic buoyancy measurements non-intrusively, its successful application requires careful selection of chemical dye, dye concentration, illumination and optics. After establishing the advantages offered by methylene blue as a dyeing agent, we assess the accuracy of buoyancy measurements made using this technique compared with direct measurements made with density meters. Density measurements obtained using light-attenuation differ from those obtained using the density meter by typically less than 3%. It is hoped that this article will provide useful advice with regards to its implementation in the field of buoyancy-driven flows.