In this article a technical-economic analysis of rotary magnetic liquid chillers is presented. The technical part comprises studies on different magnetocaloric regenerator geometries and different operating parameters. The results are presented by correlations of the Coefficient of Performance (COP) and the cooling capacity of a magnetic chiller. The analysis is based on applications with two different working fluids. The results reveal that magnetic chillers can be more efficient than conventional compressor-based chillers. However, the investment costs for magnetic chillers are higher. A discussion on the cost break-down and possible cost reductions is outlined. Some ideas for future R&D in the field of magnetic refrigeration are given.
COBISS.SI-ID: 12302363
The renewed Energy Performance of Building Directive and European regulations for buildings energy efficiency are becoming increasingly restrictive and moving towards near zero energy buildings. To achieve this goal, amongst others measures, a building utility system has to be carefully designed and optimized to perform efficiently and to utilize renewable energy source to greater extent. This paper is focused on the multi-objective performance optimization of buildings free cooling systems. The optimization was twofold: firstly, the energy consumption and available free cooling potential were estimated using weather forecasts, and secondly, the free cooling system operation regime was optimized to meet the required energy consumption using variable air distribution and flow control. The results of the optimization show the significant influence of such system operation control on system performance indicators.
COBISS.SI-ID: 12591899
The increasing demands for more accurate flow measurements have made the study of pulsating flow effects crucial for the further development of flowmeters. This paper presents the development of an experimental test facility with an integrated water-flow pulsator for experimental investigations of the water pulsation effects on flowmeters. The mechanical implementation of the measurement system with a built-in diaphragm pulsator and integrated expansion chambers was developed with the help of mathematical modeling of the entire test system using the method of characteristics. The mathematically obtained frequency characteristic of the pulsator shows typical resonances, which depend on the acoustic properties of the measurement system and the mechanical properties of the pulsators diaphragm. The water-flow pulsators characteristics were experimentally confirmed by a spectral analysis of the generated water flow pulsations, which were measured with an orifice plate flowmeter. The developed flow pulsator with integrated expansion chambers is able to generate reproducible water flow pulsations with defined properties, such as the frequency and amplitude of the pulsating flow.
COBISS.SI-ID: 12135451
In this paper an exergy-based correlation between thermal comfort and the thermal environment was investigated. The two-node human thermal model was expanded by applying the 2nd law of thermodynamics in order to calculate the exergy destruction. This value was compared to the standard Predicted Mean Vote (PMV) value and a formal analogy between thermal comfort and exergy destruction was established. This indicated that the exergy-based analysis exhibits some advantages: the heat and mass transfer are analysed on a common base and expressed as exergy destruction; environmental (indoor) parameters are considered to be the reference state which also determines the exergy destruction; exergy destruction as a single-valued thermodynamic pseudo-property encompasses all relevant parameters influencing thermal comfort; exergy destruction formally correlates with the expected level of thermal comfort.
COBISS.SI-ID: 12259611
Growth of an isolated bubble and horizontal coalescence events between bubbles of dissimilar size were examined during pool nucleate boiling of water on a horizontal, electrically-heated titanium foil 25 lm thick. Wall temperature measurements on the back of the foil by high-speed IR camera, synchronized with high-speed video camera recordings of the bubble motion, improved the temporal and spatial resolution of previous observations by high-speed liquid crystal thermography to 1 ms and 40 lm, respectively, leading to better detailed maps of the transient distributions of wall heat flux. The observations revealed complex behaviour that disagreed with some other observations and current modelling assumptions for the mechanisms of heat transfer over the wall contact areas of bubbles and interactions between bubbles. Heat transfer occurred from the entire contact area and was not confined to a narrow peripheral triple-contact zone. There was evidence of an asymmetrical interaction between bubbles before coalescence. It was hypothesised that a fast-growing bubble pushed superheated liquid under a slow-growing bubble. Contact of this liquid with regions of the wall that had been pre-cooled during bubble growth caused local reductions in the wall heat flux. During coalescence, movement of liquid under both bubbles caused further changes in the wall heat flux that also depended on pre-cooling. Contraction of the contact area caused a peripheral reduction in the heat fluxand there was no evidence of a large increase in heat flux during detachment. Boiling on very thin foils imposes special conditions. Sensitivity to the thermal history of the wall must be taken into account when applying the observations and hypotheses to other conditions.
COBISS.SI-ID: 12107291