A magnetocaloric device, especially a magnetic refrigerator, a heat pump or a power generator

The invention concerns a magnetocaloric device, especially a magnetic refrigerator, a heat pump or a magnetic power conversion machine comprising at least a permanent magnet assembly (4, 11) for generating magnetic flux, a rotating ring (2) coaxially disposed to the permanent magnet assembly, a structure containing magnetocaloric material mounted inside the rotating ring (2) and means for conducting a working fluid through the rotating ring (2). The permanent magnet assembly (4, 11) comprises a set of permanent magnets and at least one insert of highly permeable material (1, 9) attached to the magnet assembly (4, 11) adapted for creating high magnetic flux densities around and inside of the rotating ring (2)

A standardization of the coefficient of performance for magnetic refrigerators, heat pumps and energy conversion machines

Publications on magnetocaloric materials, magnetic refrigerators, magnetic heat pumps and magnetic power conversion machines contain experimental results as well as solutions obtained by physical modelling, analytical and numerical calculations. Whereas material scientists usually aim for physical property data, thermal and electrical engineers are interested in the efficiency of the operation and economists in both, production and operation costs of a machine. However, without exact data of the magnetocaloric and magnetic materials, no precise determination of the energy consumption of a magnetic refrigerator can be achieved. Magnetic and thermodynamic measurement techniques must be reviewed and discussed. In the article, a method for an accurate determination of a global COP of a magnetic refrigerator, heat pump, respectively energy conversion machine is proposed, taking all possible losses of the machines into consideration. Only a full account in a machine characterization gives the possibility to estimate correctly its final energy consumption. For a fair comparison of different magnetic refrigerators, a standardization of the COP and cost determination is very much required. The Working Party for Magnetic Refrigeration of the International Institute of Refrigeration aims to coordinate such an activity. This article is a first proposal and recommendation in this direction and shall serve as a basis for further discussions and improvements

Modelling of a two-stage magnetic refrigerator with wavy-structure gadolinium heat exchangers

In a rotary magnetic refrigerator, a porous ring is turning in and out of a magnetic field region. At the outlet the adiabatic demagnetization of the magnetocaloric material (refrigerant) produces the "cold energy". The induced cold is described by a corresponding discontinuous temperature decrease, known as adiabatic temperature difference. For such a machine a sophisticated physical model has been developed, based on a mapping of the magneto-thermodynamic problem from a cylinder onto two rectangles. In this model, in a basic centre cell, two coupled linear partial differential equations are solved, which have been programmed in the Modelica language. To determine the performance of a two-stage magnetic refrigerator, an ensemble of this new designed centre module and some other recently created auxiliary modules are coupled with standard components from a Dymola thermal library, as e.g. pumps, ordinary heat exchangers, tubes, pipes, etc. The operation of a magnetic refrigerator is simulated with numerous parameters. Steady state solutions are obtained to verify the coefficient of performance under stable operation conditions. Optimal running conditions - defined by maximal values of the coefficient of performance - are not presented in this article, but can now easily be obtained with the existing program. Finally, a regulation strategy is proposed and implemented into the Dymola-Modelica program

Front propagation of ice slurry stratification processes

The combined stratification and melting of ice particles of ice slurries is theoretically described by multi-component fluid dynamics and the continuous-properties model (CPM) for melting and freezing, applied only to melting. Ice particle stratification with isothermal conditions are studied. Particle distributions as a function of height in the storage tank and time are presented

The ice slurry technology after some years of its introduction

In this short review paper, two definitions of ice slurry are presented. Furthermore, ice slurry systems and the most relevant components of ice slurry systems are described. Such equipment are ice slurry generators (different physical principles), storage tanks, mixing elements, pumps, piping systems, consumers, e.g. display cabinets in supermarkets, etc. The direct contact ice slurry generator is an efficient low-cost machine, which at present is experimentally and theoretically investigated. A nearly complete list of the advantages and disadvantages of ice slurry systems in comparison with direct expansion systems is given. Advantages to the environment, where ice slurry technology is applied, are addressed. Furthermore, the article lists existing and possible future applications of ice slurry technology

Exergy analyses of low-temperature district heating systems with different sanitary hot-water boosters

This paper presents an exergy-efficiency analysis of low-temperature district heating systems (DHSs) with different sanitary hot-water (SHW) boosters. The required temperature of the sanitary hot water (SHW) was set to 50 °C. The main objective of this study was to compare the exergy efficiencies of a DHS without a booster to DHSs with three different types of boosters, i.e., electric-, gas-boiler- and heat-pump-based, during the winter and summer seasons. To achieve this, we developed a generalized model for the calculation of the exergy efficiency of a DHS with or without the booster. The results show that during the winter season, for a very low relative share of SHW production, the DHS without the booster exhibits favorable exergy efficiencies compared to the DHSs with boosters. By increasing this share, an intersection point above 45 °C for the supply temperatures, at which the higher exergy efficiency of a DHS with a booster prevails, can be identified. In the summer season the results show that a DHS without a booster at a supply temperature above 70 °C achieves lower exergy efficiencies compared to DHSs with boosters at supply temperatures above 40 °C. The results also show that ultra-low supply and return temperatures should be avoided for the DHSs with boosters, due to higher rates of entropy generation

Faktor primarne energije sistema daljinskega hlajenja

The primary energy efficiency for various energy-related processes can be calculated using the primary energy factor (PEF). In this paper, the PEFs of district cooling systems (PEF DC) for different types of cold production are derived. These concern cold production with an absorption chiller driven by different available sources and cold production with a compressor chiller driven by different types of engines and related energy sources. Based on the fundamental definition of the PEF, a mathematical model for calculating the PEF DC for different types of cold production was developed. The results in this study reveal that the PEF DC can be significantly improved in the case of combined cooling and power generation. The PEF DC in the case of combined cooling and power generation is lower than when cooling with electrically driven compressor chillers when the energy efficiency of the electricity generation in thermal power plant is low or the PEF of the electricity (PEF el) is high. In cold production technologies where coal is used as the primary energy source more primary energy is consumed compared to other primary energy sources (i.e. naturaThe primary energy efficiency for various energy-related processes can be calculated using the primary energy factor (PEF). In this paper, the PEFs of district cooling systems (PEF DC) for different types of cold production are derived. These concern cold production with an absorption chiller driven by different available sources and cold production with a compressor chiller driven by different types of engines and related energy sources. Based on the fundamental definition of the PEF, a mathematical model for calculating the PEF DC for different types of cold production was developed. The results in this study reveal that the PEF DC can be significantly improved in the case of combined cooling and power generation. The PEF DC in the case of combined cooling and power generation is lower than when cooling with electrically driven compressor chillers when the energy efficiency of the electricity generation in thermal power plant is low or the PEF of the electricity (PEF el) is high. In cold production technologies where coal is used as the primary energy source more primary energy is consumed compared to other primary energy sources (i.e. natural gas, waste heat, etc.).V zadnjem desetletju EU zavzema aktivnejšo vlogo na področju energijske učinkovitosti oziroma zmanjšanja rabe energije ter na področju izkoriščanja obnovljivih virov energije. Kot orodje za določitev energijsko učinkovitejših procesov v smislu minimalne rabe primarne energije nam lahko služi faktor primarne energije (PEF). Definiran je kot razmerje med celotno primarno energijo, ki je potrebna za proizvodnjo nekega končnega energetskega produkta, in končnim energetskim produktom. V primeru sistema daljinskega hlajenja je energetski produkt hlad, ki ga dobavljamo končnim odjemalcem. Faktor primarne energije upošteva energijo, ki je potrebna za pretvorbo primarnih virov energije, shranjevanje, transport, distribucijo končnega produkta do odjemalcev ter celotne izgube, povezane s temi procesi

Exergoeconomic optimization of a district cooling network

A district cooling system (DCS) is superior to conventional air conditioning as it helps to reduce energy consumption and protect the environment by reducing carbon dioxide emissions. The main disadvantages of a DCS are the high initial investment costs and the long payback period. The distribution network (DN) represents a large share of initial investment coststherefore, it has a great impact on the decision to construct a DCS. In order to ensure the competitiveness of DCS, the DN has to be optimized. In this paper the exergoeconomic concept is applied to evaluate a DN in a DCS. The objective function in the analysis is defined as the exergy based cost of the final product-cold. The exergy-based cost of cold depends on the total annual cost of a DN, the input exergy to the DN, the exergy losses and the exergy destruction. The aim of this study is to find the exergetic optimal pipe diameter and the insulation thickness, as well as the exergoeconomic optimal pipe diameter and the insulation thickness. The analysis was made for different cooling capacities and for two types of pipes: pre-insulated steel pipes, where the insulation material is polyurethane, and polyethylene pipes, without any insulation

Thermal control elements for caloric energy conversion

Caloric energy conversion is an emerging field of cooling, heat-pumping and power-generation technologies. The potentially high energy efficiency and use of environmentally friendly and safe solid-state working substances in the form of refrigerants has stimulated increased research activity in the past two decades. Most of today\u27s caloric devices apply so-called active regeneration, which involves the oscillation of the working fluid through the matrix of the caloric material % the caloric regenerator. However, the unavoidable, irreversible viscous and heat-transfer losses apply limits to the caloric device\u27s performance as well as its size. The quest for better caloric-device performance has led to the development of thermal control elements, which control the heat flux on different size and time scales. In this paper we describe the working principles of these elements: thermal switches, thermal diodes and thermal regulators. This is followed by the first up-to-date critical review of the research activities and applications of thermal control elements in all types of caloric devices. We show that thermal control elements have the potential to improve the power density of caloric devices. Finally, we propose target features for these elements with respect to future research activities in the field of caloric technologies