Thermographic imaging is a known technology to detect temperature differences. For medical applications, the patterns of heat distribution are used for diagnosis. It is already tested to visualize blood supply, inflammatory processes, and superficial or more extensive tumors, e.g. in the breast tissue. This method was promoted for breast screening purposes and as a substitute for mammography for mid aged women, but the results were not convincing for younger women, where tissue density is higher, tumor growth is often connected to local temperature increase and radiation-based mammography is not an option. Infrared (IR) thermography can support tumor screening. The screening should allow the early detection of small lesions even in the depth. Therefor we evaluated the feasibility of dynamic cooling in combination with IR imaging in a phantom study. A temperature-controllable gel phantom including a heating plate, a depth-adjustable heat source mimicking a tumor, and three sensors for temperature monitoring was built up. A raspberry pi device serves as a control unit to create a stable temperature balance comparable to a human breast. For the experiments, the tumor was placed in various depth. After cooling, the thermal recovery phase of the phantom was imaged using an IR camera and a webcam. A pixel-wise analysis of the IR data detects a higher gradient of temperature change in the tumor region. The experiments demonstrated the feasibility of tumor detection based on dynamic cooling and IR imaging.
This article presents experimental results of the thermal conductivity of sintered metal foams, which were manufactured by the Slip Reaction Foam Sintering (SRFS) process. For the determination of the thermal conductivity, the Transient Plane Source Technique, also known as Hot Disk, was employed. The thermal conductivity of cellular solids differs from that of their corresponding dense material. Therefore, the various pore size level effects contributing to the thermal conductivity are accounted for by introducing an effective thermal conductivity λeff. The thermal conductivity of the strut material, a sintered packed bed, was determined up to 700°C and compared to similar materials. The thermal diffusivity could also be determined by the Laser-Flash method and compared to the Hot Disk values. For the foams, λeff was determined for a total porosity of 0.85 up to 700°C. In this article, a dependency between the porosity and λeff can be shown. The linear rise of λeff up to 400°C can be due to the increase of the thermal conductivity of the solid phase. The measurements are validated by comparison of the received specific heat with values received by thermogravimetry measurements. The general applicability of the measurement method to heterogeneous materials such as metal foams is discussed and an outlook about further investigations is given.
Due to their electro-mechanical behaviour, electrical motors are able to generate high power densities. For a 20 kg motor based on a modified air gap winding, a mechanical load of 80kW is theoretically possible. However, the achievable power density is generally limited by the thermal loads induced by Joule heating due to the Ohmic resistances in the motor's wiring. This paper discusses the potentials of cooling channel modifications, such as the overall geometry as well as surface variations, to enhance the convective heat transfer from the solid material in the coolant with focus on motors using an air gap winding. The convective heat transfer acts as a relevant thermal resistance, which becomes critical at elevated loads, because it is lies between the wiring, acting as a heat source, and the liquid coolant, acting as heat sink. The thermal resistance of the interface material between the wiring and the stator is in the same order of magnitude as the convective heat transfer. These non-metallic materials such as foils, coatings and glues for electrical insulation and mechanical bonding are highly limited in their temperature resistance. To evaluate the behaviour of modified cooling channels and investigate novel interface materials under motor-like conditions, experimental and numerical methods are employed to determine thermo-physical properties, heat and mass transfer and finally the temperature distributions. The experimental results are discussed in comparison with numerical and analytical models and validated thereby. Because of the limited possibilities for experimental investigations within a real electrical motor, a flat test bed, based on the boundary conditions of an existing 16" wheel hub motor was developed. The Ohmic heating was realised, applying a thin sheet foil of Inconel, so that specific heat loads up to 100 kW/mK could be realised. Here, the surface temperature could be measured contact-free at a high optical resolution, using infrared thermography. The most advantageous test bed feature is the optical accessibility of cooling channels which allows the visualisation of fluid flow regimes. As results, the influence of large-scale coolant duct geometry modifications on the motor temperatures and hydraulic characteristics as well as of small-scale modifications will be presented in comparison to non-modified geometries. Also, the outcomes and capabilities of novel thermal interface materials consisting of laminated foils will be discussed and an outlook on a modified motor design to increase the thermal limits will be given.
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