14:50   Novel experimental measurement methods II Development of a Novel Atomic Layer Thermopile Sensor Array for Stagnation Point Heat Flux Investigations Simon Kaneider, Tim Roediger Abstract: Atomic layer thermopile (ALTP) sensors provide a temporal resolution in the microsecond range for direct heat flux measurements, yet spatial resolution has remained limited due to the size of individual sensor modules. To address this, we present a novel linear sensor array composed of ALTPs with millimetre-scale spatial resolution. This work details the design and calibration of the sensor array, including sensor separation, electrical integration, and signal amplification. Static and dynamic calibration procedures are described, and the performance of the array is demonstrated in a subsonic stagnation point jet impingement test case - a flow scenario characterised by steep radial heat flux gradients and transient behaviour. The sensor array enables simultaneous, high-resolution measurements of heat flux and temperature across the stagnation region, facilitating the calculation of local heat transfer coefficients and Nusselt numbers. This enhanced spatial resolution supports improved experimental analysis in complex flow environments such as impingement cooling, laminar-turbulent transition, and shock wave/boundary layer interaction (SBLI), potentially providing new insights for the validation and refinement of numerical heat transfer models. Lights, camera, beetroot-juice: measuring mixing in full 4D Chris Ford, Johan Rensfeldt Abstract: Introduction Aqueous solutions are routinely prepared over a wide range of Reynolds numbers (1 ≲ Re ≲ 105) in real-time for the chromatography process. Two component-fluids are independently pumped at the desired flow rate and mixture-ratio, which are then combined by an in-line static mixer. The efficacy of mixing for chromatography is often evaluated at a system level. The conductivity (a standard instrument within a chromatography system) of an aqueous salt solution is measured and the temporal stability of this signal is used as a proxy for ‘mixedness’. While concentration stability is extremely important to chromatography, it provides little information about the mixing process and there is a need to quantify the true spatio-temporal concentration. Optical methods are the de facto choice when quantifying mixing [1]. Measurement methods commonly average the concentration in the view direction and do not allow a full examination of the mixing structures [10, 9, 11, 2]. Alternatively, 2D planes are imaged and resolved in time using PIV [7, 4, 13, 3], confocal microscopy [12], or novel surface-based techniques [8]. Whilst these methods are extremely useful, they remain incomplete and moreover inaccessible to anyone outside of a specialist laboratory. Ford [6] presented a low cost-method of quantifying the 3D concentration field using a visible-light source, digital camera and an absorbing dye-tracer. However, the method was only applicable to steady or quasi-steady flowfields [5]. This paper presents an experimental setup (MORPHEUS) that allows temporal variations in the full 3D con- centration field to be resolved. This is a significant improvement to the method of Ford [6] that also facilitates detailed study of mixing at a much wider range of Reynolds numbers; up to approximately 5,000. The experi- mental setup and reduction method are briefly described. Data from simple T-junction is used to exemplify the capabilities of MORPHEUS with both steady and unsteady flow cases. Method MORPHEUS, see Figure 1, is an entirely novel experimental facility developed specifically to study fluidic mixing. Twelve low-cost digital cameras, visible-light LEDs and a tracer (beetroot juice) allow the full 4D concentration field to be resolved. MORPHEUS has been deliberately designed with simple, readily available, equipment that is inherently safe. This obviates the need for special safety arrangements (as required by the use of lasers, for example), widens the industrial applicability and enables the facility to be used without specialist training. Two-component liquid mixing is studied. The components are water and 5% aqueous beetroot-juice (compo- nents A and B respectively). Component B absorbs light whereas A is optically transparent. Thus the transmission of light at any view-angle becomes an integral measure of dye concentration. Multiple images of the same flowfield captured simultaneously from unique view angles allow the concentration field to be estimated at a cross-section of the flow path. Each image captures an 11 x 15 mm 2D field allowing the 3D field to be reconstructed from mul- tiple slices of the instantaneous field. Time-evolution is obtained by analyzing a time-sequence of image-frames. Spatial features of 75 μm may be resolved at sampling rates of up to 200 Hz. Results Figure 2 presents the concentration field developed by a digitally-pulsating flow (1:1 mixture-ratio) through a T-junction at Re ≈ 85. The pulsation frequency is 1 Hz (St ≈ 0.3) images have been captured at 40 Hz. Data is presented as the time-variation of concentration at a single 2D cross-section of the pipe approximately 10d downstream of the junction. Three example sections: a, b and c which are separated by 1/3 of the pulsation- phase are shown. The full time-development of the field is exemplified by the rectangular images which show the concentration viewed in-plane with the junction (top) and perpendicular to the junction (bottom) with time as the horizontal axis. The approximate temporal-location of the sections are indicated. The image clearly shows coherent packets of fluid associated with the pulsation, with a parabolic shape owing to the laminar advection profile. The Strouhal number is approximately 1/3 of the critical value predicted by Ford [5] and the flowfield adopts a hybrid form; consisting of a pulsating core superimposed on a steady laminar field

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