This book provides the latest research on a new alternative form of technology, the magnetocaloric energy conversion. This area of research concerns magnetic refrigeration and cooling, magnetic heat pumping, and magnetic power generation. The bookʼs systematic approach offers the theoretical basis of magnetocaloric energy conversion and its various sub domains, and this is supported with the practical examples. Besides these fundamentals, the book also introduces potential solutions to engineering problems in magnetocalorics and to alternative technologies of solid state energy conversion. The aim of the book is therefore to provide engineers with the most up-to-date information, and also to facilitate the understanding, design and construction of future magnetocaloric energy conversion devices. The magnetocaloric energy conversion represents an alternative to compressor based refrigerators and heat pumps. It is a serious alternative to power generation with low enthalpy heat sources. This green technology offers an opportunity to use environmentally friendly solid refrigerants, and the potentially high energy efficiency follows the trends of future energy conversion devices. This book is intended for postgraduate students and researchers of refrigeration, heat pumping, power generation alternatives, heat regenerators and advanced heat transfer mechanisms.
COBISS.SI-ID: 13844763
In order to reduce energy consumption in buildings, a solution using phase change materials (PCMs) as thermal energy storage (TES) is presented. During summer nights, cold is stored and delivered during the day to reduce cooling load, whereas in winter, heat from solar air collector is stored for heating during morning and evening hours. Proposed is a stand-alone unit suitable for offices, which consists of plates filled with paraffin RT22HC. The objective of the paper is to examine the functioning of the suggested TES system on an annual basis and to explore the feasibility of using it for both, cooling and heating. First numerical model is set up, which assumes 2D geometry and evaluates thermal response, calculations are carried out in Fluent. Then validation of simulations with experimental results is established. Finally the feasibility of storage unit on an annual basis is demonstrated.
COBISS.SI-ID: 14117659
This paper presents the design and modelling of the heat transfer of a solar air heating system, which consists of a vacuum tube air solar collector (SC) and latent heat thermal energy storage (LHTES), and a parametric analysis of the performance of this system. LHTES is a form of short-term daily storage that stores the SC heat during the day and releases it into the building during the night. Especially in low energy buildings with a high share of passive heating, this can significantly improve the utilization of solar energy for heating. The design of concentric-tube LHTES was optimized regarding the air temperature at the exit of LHTES during the day and the peak shift of heat supply. The results showed that optimal mass of PCM in LHTES is 150-200 kg/m2 and the optimal air flow-rate is 40 m3/h per m2 of the SC aperture area. The analysis of the system performance at different levels of daily solar irradiation has shown that 54-67% of the heat produced by solar air heating system in daytime can be delivered during the night time for building heating.
COBISS.SI-ID: 13778971
This study presents the application of hydrophobic polydimethylsiloxane-silica coating used for the development of biphilic surfaces that are designed to enhance the heat transfer during boiling. Surface analyses showed that this coating exhibits a high hydrophobicity due to its hierarchical structure and the use of hydrophobic polymer. An appropriate thermal treatment leads to the oxidation of the methyl groups and a formation of silicon oxide and silicon carbide that result in a wettability transition from hydrophobic to superhydrophilic. On this basis, we manufactured hydrophobic/superhydrophilic patterns on stainless-steel foils using a pulsed Nd:YAG laser. The uniform, superhydrophilic surface exhibited a 350% larger critical heat flux (CHF) than bare stainless-steel foil. High-speed IR thermography revealed that the increased wettability reduced the bubble contact diameter, allowed a higher density of active nucleation sites, and delayed the dry-out. The biphilic surfaces with differently sized hydrophobic spots exhibited the highest heat transfer coefficients, with an up to 200% higher CHF compared to the bare stainless steel. Smaller hydrophobic spots reduced the bubble diameter and increased the nucleation frequency. However, surfaces with larger hydrophobic regions promoted boiling incipience and exhibited higher heat transfer coefficients at low heat fluxes. These results suggest that the optimal biphilic pattern could only be determined for a particular operating point. Our data provide a new insight into the complex phenomena of nucleate pool boiling on chemically and mechanically heterogeneous surfaces.
COBISS.SI-ID: 14131227
An understanding of the effects of flow pulsations on the dynamic behavior of Coriolis flowmeters is very important for their further development. In order to determine the phase difference between the vibrational signals, which represents the basic measurement effect of Coriolis flowmeters, there are many methods that include the proper filtering of all the signal components, except those with frequencies close to the drive frequency. Therefore, an understanding of the phenomenon of exciting the meter at its first natural frequency is very important. The results of a simple, linear, two-degree-of-freedom, lumped-parameter, dynamic model of a flowmeter show that the flow pulsations can degrade the accuracy of such a flowmeter as a result of indirect excitations of the measuring tube at the first natural frequency through the second-order perturbations by means of the Coriolis forces induced in pulsating flow conditions. In order to experimentally investigate these flow pulsation effects, a prototype of a straight-tube Coriolis mass flowmeter was developed to enable the processing of the response signals logged directly from the flow tubeʼs sensors with the dual quadrature demodulation method, and therefore to provide the information available within the phase-difference data. The experimental results show that the flow pulsations upset the meter at its first natural frequency indirectly, as well as directly at the frequency of the pulsations due to the geometric imperfections of the measuring tube.
COBISS.SI-ID: 14007579