Generally, domestic refrigerators and freezers are running in non-continuous operation mode most of the time, which is a necessity to match cooling capacity to thermal loads. In currently available domestic appliances this matching is realized either by on/off or variable frequency control of the hermetic compressor, leading to a repetitive and transient change of the system state. In case of longer compressor runtimes when cooling capacity demand is high (e.g. pull down cycles, initial operation) steady state operating conditions might be reached. The cycling transients cause losses in system efficiency, thus they should be reduced or avoided. To understand the complex transient physical processes and to optimize the cooling system efficiency, the use of numerical methods has turned out to be a promising approach. For this reason, a 1D heat exchanger model, which has been successfully implemented in a domestic cooling cycle simulation tool, is presented in this work. The heat exchanger model is a further development of the model being presented in Berger et al. (2012). The same mathematical framework is used for modeling the evaporator and condenser. In order to compute the void fraction, the pressure drop and the heat transfer in case of evaporation and condensation special empirical models, which are proposed in literature, have been implemented. Finally, the numerical predictions are compared to experimental data gained from a purpose-built test rig.
Although the versatility of photodynamic therapy (PDT) is well established, the technical aspects of light delivery systems vary significantly depending on the targeted organ. This article describes the optical properties of a light and drug delivery system (catheter and light diffuser) suitable for intra-arterial PDT by using a planar imaging goniometer to measure the full radiance longitudinal and angular profiles at the surface of the diffuser at 652 nm. The results show that the system emits almost Lambertian and “top hat” profiles, an interesting feature to determine the light dosimetry in the many vascular applications of PDT.
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