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The results are presented of an experimental investigation of heat transfer in an air-liquid cooling system for a Switch-Mode Power Supply (SMPS) for TV digital power amplifiers. Since these SMPSs are characterized by high power and high compactness, thereby making the standard cooling techniques difficult to be used, a new cooling system is developed, using water and air as the cooling media. The active components (MOSFETs) are cooled with a liquid cold-plate, the passive ones (condensers, transformers, coils) with an air flow, in turn cooled by the cold-plate. By inserting the cooling system in an experimental tool where it is possible to control the cooling water, measurements are made of temperature in the significant points of the SMPS. The electric efficiency is also measured. The evaluation of the thermal performance of this cooling system is useful in order to limit its maximum operational temperature. The efficacy of the cooling system is demonstrated; the trends of efficiency and power dissipation are evidenced.

Heat storage systems using phase change materials (PCMs in the following) are an effective way of storing thermal energy due to the high energy storage density and the isothermal nature of the storage process. In recent years the utilization of PCMs has been also considered in the thermal control of compact electronic devices. In the present work a parametric analysis is presented for an energy storage system with a phase change material, undergoing a heat flow boundary condition, as happens in the electronic equipment cooling. In particular we analyze a hybrid systems composed of a finned surfaces partially filled with PCM. This solution which combine both passive (PCM) and active (fins and fans) cooling solutions, seems to be of interest in high power amplifiers characterized by different levels of power dissipation. This is the case of the telecom base station power amplifiers, where the power is proportional to the traffic load. The results are obtained with a specific finite volumes code. The mathematical model is made dimensionless to allow the characteristic parameters to be evidenced. The proposed parameterization lends generality to the results obtained. In particular the relationships have been investigated between the melting point of the PCM and the operating temperature reached during the peak of the input power. The study provides useful information for the design of these passive cooling systems.

Medium temperature solar thermal applications have received remarkable interest in the recent years in both residential and industrial sectors. These applications, typically in a temperature range of 80 -250°C, require thermal collectors coupled to solar concentrators. Concerning these applications, a prototype of Compound Parabolic Concentrator coupled to an Evacuated Tube solar collector, was developed and built. The instantaneous efficiency of the prototype was measured according to the suggestions of the European Standard EN 12975-2. The "Outdoor steady-state" test method, well accepted for testing flat plate and evacuated tubular collectors, was used. The specific useful power extracted from the prototype was also derived. The measured performance is in line with theoretical derivations. However, when using the instantaneous efficiency of the Outdoor steady state test method some discrepancies arise in simulating the daily behavior of the collector, suggesting a different testing approach.