Planar measurements of spray-induced wall cooling using phosphor thermometry

Abstract

The wall cooling induced by spray impingement is investigated using phosphor thermometry. Thin coatings of zinc oxide (ZnO) phosphor were applied with a transparent chemical binder onto a steel surface. Instantaneous spatially resolved temperatures were determined using the spectral intensity ratio method directly after the injection of UV-grade hexane onto the surface using a commercial gasoline injector. The investigations showed that 2D temperature measurements with high spatial and shot-to-shot precision of, respectively, 0.5 and 0.6 K can be achieved, allowing the accurate resolution of the cooling induced by the spray. The presence of a liquid film over the phosphor coating during measurements showed no noticeable influence on the measured temperatures. However, in some cases a change in the intensity ratio at the spray impingement area, in the form of a permanent "stain", could be observed after multiple injections. The formation of this stain was less likely with increasing annealing time of the coating as well as lower plate operating temperatures during the injection experiments. Finally, the experimental results indicate a noticeable influence of the thickness of the phosphor coating on the measured spray-induced wall cooling history. Hence, for quantitative analysis, a compromise between coating thickness and measurement accuracy needs to be considered for similar applications where the heat transfer rates are very high.

Thermochromic Luminescent Nanomaterials Based on Mn4+/Tb3+ Codoping for Temperature Imaging with Digital Cameras

“…The developed nanophosphors were demonstrated to provide sensitive temperature measurements in the range of 25–150 °C, which includes the boiling point of liquids used for spray cooling and the glass transition temperature of polymers used in 3D printing, and which is also relevant to the thermal management of batteries, fuel cells, and electric motors . Those applications demand the observation of complex thermal phenomena which impacts the process performance but the implementation of IR thermography is not possible because of the opacity of liquids and polymers, and to reflections of thermal radiation by inner surfaces of battery, fuel cell, and motor assemblies .…”

A delayed gating approach for interference-free ratio-based phosphor thermometry

“…In a recent work, Zinc oxide (ZnO) was coated onto thin steel plate to image the temperature resulting from the spray impingement [8]. Owing to the short 1/е lifetime below 1 ns [24], the measurement duration was limited by the laser pulse (10 ns), which was easily sufficient to resolve the rapid change in the surface temperature.…”

Self‐Referenced Temperature Imaging with Dual Light Emitting Diode Excitation and Single‐Band Emission of AVO4:Eu3+ (A=Y, La, Lu, Gd) Nanophosphors

“…To calibrate the response of the system at a prescribed temperature, the plate was placed on heating–cooling stage consisting of an aluminum body with internal channels through which silicon oil flows at a prescribed temperature, which is described in Dragomirov et al [ 43 ] The temperatures of the aluminum body and of the fluid were monitored with thermocouples in the solid body and in the oil flow and the accuracy of temperature determination at the center of the plate was of the order of 1 °C. To heat up the plate nonuniformly, the outlet of a 2 mm diameter premixed flame burner was directed toward the back of the coated plate.…”