New devices for flow measurements: Hot film and burial wire sensors, infrared imagery, liquid crystal, and piezo-electric model

An experimental program aimed at identifying areas in low speed aerodynamic research where infrared imaging systems can make significant contributions is discussed. Implementing a new technique, a long electrically heated wire was placed across a laminar flow. By measuring the temperature distribution along the wire with the IR imaging camera, the flow behavior was identified

Shape Memory Polymer Resonators as Highly Sensitive Uncooled Infrared Detectors

Uncooled InfraRed (IR) detectors have enabled the rapid growth of thermal imaging applications. These detectors are predominantly bolometers, where the heating of pixel from incoming IR radiation is read out as a resistance change. Another uncooled sensing method is to transduce the IR radiation into the frequency shift of a mechanical resonator. We present here a highly sensitive, simple to fabricate resonant IR sensor, based on thermo-responsive Shape Memory Polymers (SMPs). By exploiting the phase-change polymer as the transduction mechanism, our approach provides 2 orders of magnitude improvement of the temperature coefficient of frequency (TCF). The SMP has very good absorption in IR wavelengths, obviating the need for an absorber layer. A Noise Equivalent Temperature Difference (NETD) of 22 mK in vacuum and 112 mK in air are obtained using f/2 optics. Such high performance in air eliminates the need for vacuum packaging, paving a path towards flexible IR sensors

Thermography and Sonic Anemometry to Analyze Air Heaters in Mediterranean Greenhouses

The present work has developed a methodology based on thermography and sonic anemometry for studying the microclimate in Mediterranean greenhouses equipped with air heaters and polyethylene distribution ducts to distribute the warm air. Sonic anemometry allows us to identify the airflow pattern generated by the heaters and to analyze the temperature distribution inside the greenhouse, while thermography provides accurate crop temperature data. Air distribution by means of perforated polyethylene ducts at ground level, widely used in Mediterranean-type greenhouses, can generate heterogeneous temperature distributions inside the greenhouse when the system is not correctly designed. The system analyzed in this work used a polyethylene duct with a row of hot air outlet holes (all of equal diameter) that expel warm air toward the ground to avoid plant damage. We have observed that this design (the most widely used in Almería’s greenhouses) produces stagnation of hot air in the highest part of the structure, reducing the heating of the crop zone. Using 88 kW heating power (146.7 W∙m−2) the temperature inside the greenhouse is maintained 7.2 to 11.2 °C above the outside temperature. The crop temperature (17.6 to 19.9 °C) was maintained above the minimum recommended value of 10 °C

Differential infrared thermography for rotor aerodynamics

Understanding the flow around helicopter rotors is one of the greatest challenges in modern aerodynamics. The flow field plays a key role in the rotorcraft performance and operational safety, and it is characterized by highly unsteady and three-dimensional phenomena. State-of-the-art computational fluid dynamics (CFD) is applied during the design of future rotorcraft and offers remarkable capabilities, including the simulation of entire helicopter configurations in maneuvering flight. Nevertheless, experiments are still essential for the understanding of complex flow regimes, and for the validation of numerical results. An ever-increasing level of detail in CFD studies motivates the development and refinement of experimental methods, and combined experimental-numerical efforts have been particularly rewarding in recent studies. Starting with early rotorcraft-specific research topics, for example the systematic characterization of pitch-oscillating airfoils in the 1960s, experimental techniques have undergone continuous improvement. This particularly holds true for optical methods, which have developed from providing qualitative and “simple” snapshots of the flow into quantitative and time-resolving diagnostic tools. Optical methods require few modifications of the rotor or rotorcraft under investigation. They are particularly suitable for an application on multiple scales, ranging from small-scale laboratory studies to full-scale free-flying helicopters. This thesis concentrates on the development, validation, and application of the differential infrared thermography (DIT). The DIT method is able to determine the moving position of the laminar-turbulent boundary layer transition, which is a relevant aerodynamic feature on rotor blades, accounting for the unsteadiness introduced by the different inflow conditions on the advancing and retreating sides of the trimmed rotor plane in forward flight. Additional helicopter-relevant applications include the study of pitch-oscillating airfoils or small-scaled rotors in laboratory or wind-tunnel environments. Furthermore, it will be shown that the DIT principle can be adapted to other rotor-relevant topics beyond transition research, such as dynamic stall investigations. DIT is a valuable addition to the larger family of optical measurement techniques for aerodynamic applications

Contribution to non-destructive testing of materials by means of photothermal techniques.

152 p.Esta tesis engloba el uso y aplicaciones de algunas técnicas no-destructivas que involucran la generación y propagación de calor y la medición del campo de temperatura resultante en un medio. Las técnicas que fueron utilizadas son la fotoacústica, la fotopiroeléctrica, la termografía infrarroja y el método del alambre caliente transitorio. Los parámetros térmicos de difusividad, conductividad y efusividad térmica fueron medidos en diferentes medios usando estas técnicas, cuyo potencial de aplicación está direccionado a los procesos de certificación y control de calidad en distintos campos de la industria. Sus aplicaciones fueron demostradas en cuatro trabajos de investigación principalmente. En el primero de ellos se midieron las propiedades térmicas de mezclas líquidas de heptano/isooctano en función de su número de octano, así como también las fases gaseosas de algunas componentes puras con el fin de contribuir en posibles normas de certificación para la escala del índice de octano. En el segundo se hicieron mediciones de la efusividad térmicas y espectros de absorción óptica en el infrarrojo de muestras de aceite de café provenientes de cultivos orgánicos y convencionales con el fin de encontrar un posible criterio de discriminación entre estos tipos de aceites usando técnicas fototérmicas. En el tercero se determinó el ancho de una interfaz vertical o grieta entre dos medios de diferente material a través de sus resistencia térmica de contacto usando termografía infrarroja, así como también se midió la conductividad térmica de fluidos que llenan la interfaz. En el cuarto trabajo se midió la difusividad térmica de sólidos (an) isotrópicos en movimiento a velocidad constante, lo cual mimetiza los procesos de producción de línea. Estudios que están direccionados a su aplicación como posibles métodos de inspección y control de calidad de los materiales

Review of measurement techniques for unsteady helicopter rotor flows

The helicopter group at the DLR in Göttingen has been actively involved in the development of measurement techniques for unsteady flows, particularly as they apply to the problems found in unsteady rotor blade aerodynamics. This includes the development and validation of new techniques for the detection of dynamically moving boundary layer transition, and for the detection of dynamic stall and other transient flow separation events. These new techniques include pressure sensor analysis, differential infrared thermography, local infrared thermography and the automated analysis of hot-film data. Particle image velocimetry (PIV) and background oriented schlieren (BOS) have been used for the analysis of the unsteady off-body flow, and synchronised PIVBOS-pressure measurements have allowed direct comparisons between different methods. The Lagrangian volumetric PIV variant, shake-the-box, has been used to analyse secondary vortex structures in the vortex wake. This review article will give an overview of the advances in that group, as well as placing their activities in the context of international advances in these areas

Neonatal Infrared Thermography Image Processing

Tesina feta en col.laboració amb RWTH AachenThe temperature changes inside incubator a ect the newborns, who are the most delicate patients. The project proposes an innovative method to monitor the skin temperature of the neonates. The temperature monitoring is carried out by a virtual sensor. This virtual sensor is based in an infrared thermal camera that is placed outside the incubator. In order to obtain the infrared radiation through the incubator Plexiglas, an infrared transparent window is required. The experiment carried out was focused on obtaining the transparent properties in the infrared spectral range measurement of this window. On the other hand, the thermal imaging processing is necessary to obtain the thermal information from the infrared imager and to be able to track the region of interest throughout the eld of view

Infrared Thermography in Marine Applications

Infrared (IR) thermography has become a powerful tool for basic and applied scientifi c research and for the application in various fi elds such as industry, environment, military and maritime affairs, etc. As a „predictive“ maintenance tool, IR thermography has the ability to identify problems before they occur. It is especially helpful for trouble shooting potential electrical overloads, worn or bad circuit breakers and buses. IR thermography can also be used to detect bad bearings, shafts, worn pulleys or any application where heat detection would be benefi cial. This paper has the intention to familiarize researchers, engineers and sea business staff with possibilities of applying IR thermography in the fi eld of maritime affairs. Therefore, basic principles of IR thermography are presented and examples of the tool application are given