Unlocking the Potential of Magnetic Refrigeration: Investigating the Compatibility of the Ga-Based Liquid Metal with a La(Fe,Mn,Si)13Hz Magnetocaloric Material for Enhanced Long-Term Stability.

Magnetic refrigeration (MR) is a cutting-edge technology that promises high energy efficiency and eco-friendliness, making it an exciting alternative to traditional refrigeration systems. However, the main challenge to its widespread adoption is cost competitiveness. In this context, the use of liquid metals as heat transfer liquids in the MR has been proposed as a game-changing solution. Unfortunately, the toxicity and flammability of these liquid metals have raised serious concerns, limiting their practical use. In this study, we investigate the compatibility of a nontoxic and nonflammable GaInSn-based liquid metal with a magnetocaloric material, La(Fe,Mn,Si)13Hz, over a 1.5 year period. Our findings reveal nearly a 14% reduction in specific cooling energy and peak-specific isothermal magnetic entropy change for the considered magnetocaloric material. Our study provides valuable insights into the long-term stability of magnetocaloric materials and their compatibility with liquid metals, facilitating the development of more cost-effective and sustainable MR systems.

Implementing a bidirectional impulse turbine into a thermoacoustic refrigerator.

A thermoacoustic model is used to efficiently implement a bidirectional impulse turbine into a thermoacoustic refrigerator. Experiments are done for several gas types and mean pressures to identify its influence on the turbine efficiency. A scaling is investigated in an attempt to provide a unique function of the turbine efficiency for all operating conditions. Furthermore, the ratio of acoustic power absorbed by the turbine over to the total amount of available power is examined for varying conditions. Finally, the results are used to present a case study in which the turbine is used to drive the fluid pumps of the device. The remaining acoustic power is used for cooling, thus providing an off-grid thermoacoustic refrigerator that works purely with low-grade heat as an input.

Optimizing bidirectional impulse turbines for thermoacoustic engines.

The design of a bidirectional impulse turbine to convert thermoacoustic power into electricity is experimentally optimized. The turbine efficiency is measured for rotors with and without a shroud ring and for a varying tip clearance. Furthermore, the axial spacing between the guide vanes and rotor is varied with respect to the displacement amplitude of the acoustic wave. All measurements are carried out for several turbine loads and acoustic frequencies. For a chosen implementation, a design study on the guide vane and rotor blade geometry is presented to further optimize the bidirectional impulse turbine for thermoacoustic engines.

Characterization of bidirectional impulse turbines for thermoacoustic engines.

A bidirectional impulse turbine to convert thermoacoustic power into electricity is investigated. Experimental measurements are done with a loudspeaker for varying acoustic conditions and turbine loads. The results are used to characterize the turbine performance and compare it to steady flow turbomachinery and turbines in oscillating water columns. A dimensional analysis is done to identify the variables that influence the turbine performance, after which a scaling is determined that uniquely determines the efficiency of the turbine. The work is finished by providing the impedance of the bidirectional turbine such that it can be implemented in a thermoacoustic engine.

Review on the conversion of thermoacoustic power into electricity.

Thermoacoustic engines convert heat energy into high amplitude acoustic waves and subsequently into electric power. This article provides a review of the four main methods to convert the (thermo)acoustic power into electricity. First, loudspeakers and linear alternators are discussed in a section on electromagnetic devices. This is followed by sections on piezoelectric transducers, magnetohydrodynamic generators, and bidirectional turbines. Each segment provides a literature review of the given technology for the field of thermoacoustics, focusing on possible configurations, operating characteristics, output performance, and analytical and numerical methods to study the devices. This information is used as an input to discuss the performance and feasibility of each method, and to identify challenges that should be overcome for a more successful implementation in thermoacoustic engines. The work is concluded by a comparison of the four technologies, concentrating on the possible areas of application, the conversion efficiency, maximum electrical power output and more generally the suggested focus for future work in the field.

Flow Separation and Turbulence in Jet Pumps for Thermoacoustic Applications.

The effect of flow separation and turbulence on the performance of a jet pump in oscillatory flows is investigated. A jet pump is a static device whose shape induces asymmetric hydrodynamic end effects when placed in an oscillatory flow. This will result in a time-averaged pressure drop which can be used to suppress acoustic streaming in closed-loop thermoacoustic devices. An experimental setup is used to measure the time-averaged pressure drop as well as the acoustic power dissipation across two different jet pump geometries in a pure oscillatory flow. The results are compared against published numerical results where flow separation was found to have a negative effect on the jet pump performance in a laminar flow. Using hot-wire anemometry the onset of flow separation is determined experimentally and the applicability of a critical Reynolds number for oscillatory pipe flows is confirmed for jet pump applications. It is found that turbulence can lead to a reduction of flow separation and hence, to an improvement in jet pump performance compared to laminar oscillatory flows.

On the performance and flow characteristics of jet pumps with multiple orifices.

The design of compact thermoacoustic devices requires compact jet pump geometries, which can be realized by employing jet pumps with multiple orifices. The oscillatory flow through the orifice(s) of a jet pump generates asymmetric hydrodynamic end effects, which result in a time-averaged pressure drop that can counteract Gedeon streaming in traveling wave thermoacoustic devices. In this study, the performance of jet pumps having 1-16 orifices is characterized experimentally in terms of the time-averaged pressure drop and acoustic power dissipation. Upon increasing the number of orifices, a significant decay in the jet pump performance is observed. Further analysis shows a relation between this performance decay and the diameter of the individual holes. Possible causes of this phenomenon are discussed. Flow visualization is used to study the differences in vortex ring interaction from adjacent jet pump orifices. The mutual orifice spacing is varied and the corresponding jet pump performance is measured. The orifice spacing is shown to have less effect on the jet pump performance compared to increasing the number of orifices.

Characterization and reduction of flow separation in jet pumps for laminar oscillatory flows.

A computational fluid dynamics model is used to predict the oscillatory flow through tapered cylindrical tube sections (jet pumps). The asymmetric shape of jet pumps results in a time-averaged pressure drop that can be used to suppress Gedeon streaming in closed-loop thermoacoustic devices. However, previous work has shown that flow separation in the diverging flow direction counteracts the time-averaged pressure drop. In this work, the characteristics of flow separation in jet pumps are identified and coupled with the observed jet pump performance. Furthermore, it is shown that the onset of flow separation can be shifted to larger displacement amplitudes by designs that have a smoother transition between the small opening and the tapered surface of the jet pump. These design alterations also reduce the duration of separated flow, resulting in more effective and robust jet pumps. To make the proposed jet pump designs more compact without reducing their performance, the minimum big opening radius that can be implemented before the local minor losses have an influence on the jet pump performance is investigated. To validate the numerical results, they are compared with experimental results for one of the proposed jet pump designs.

Jet pumps for thermoacoustic applications: Design guidelines based on a numerical parameter study.

The oscillatory flow through tapered cylindrical tube sections (jet pumps) is characterized by a numerical parameter study. The shape of a jet pump results in asymmetric hydrodynamic end effects which cause a time-averaged pressure drop to occur under oscillatory flow conditions. Hence, jet pumps are used as streaming suppressors in closed-loop thermoacoustic devices. A two-dimensional axisymmetric computational fluid dynamics model is used to calculate the performance of a large number of conical jet pump geometries in terms of time-averaged pressure drop and acoustic power dissipation. The investigated geometrical parameters include the jet pump length, taper angle, waist diameter, and waist curvature. In correspondence with previous work, four flow regimes are observed which characterize the jet pump performance and dimensionless parameters are introduced to scale the performance of the various jet pump geometries. The simulation results are compared to an existing quasi-steady theory and it is shown that this theory is only applicable in a small operation region. Based on the scaling parameters, an optimum operation region is defined and design guidelines are proposed which can be directly used for future jet pump design.

A numerical investigation on the vortex formation and flow separation of the oscillatory flow in jet pumps.

A two-dimensional computational fluid dynamics model is used to predict the oscillatory flow through a tapered cylindrical tube section (jet pump) placed in a larger outer tube. Due to the shape of the jet pump, an asymmetry in the hydrodynamic end effects will exist which will cause a time-averaged pressure drop to occur that can be used to cancel Gedeon streaming in a closed-loop thermoacoustic device. The performance of two jet pump geometries with different taper angles is investigated. A specific time-domain impedance boundary condition is implemented in order to simulate traveling acoustic wave conditions. It is shown that by scaling the acoustic displacement amplitude to the jet pump dimensions, similar minor losses are observed independent of the jet pump geometry. Four different flow regimes are distinguished and the observed flow phenomena are related to the jet pump performance. The simulated jet pump performance is compared to an existing quasi-steady approximation which is shown to only be valid for small displacement amplitudes compared to the jet pump length.

Voluntary and therapeutic castration of sex offenders in The Netherlands (1938­1968).

Between 1938 and 1968 some 400 sex offenders in the Netherlands who by court orders had been put at 'the discretion of the government' and were incarcerated in asylums for the criminally insane, 'voluntarily' submitted themselves to 'therapeutic' castration, the surgical removal of their testes. Prior to 1938, inspired by a Danish castration act from 1929, and urged by asylums that were overcrowded by sex offenders, the ethics of the surgery had been discussed for nearly a decade amongst theologians, (forensic) psychiatrists, jurists and politicians, mostly in the context of eugenic sterilization. Discussions of conflicting Catholic, Protestant and non-denominational points of view vis-à-vis eugenics resulted in consensus about 'therapeutic' and 'voluntary' castration. Sexual deviancy, according to some, was like a tumor located in the testes, which could therefore be removed without moral objections and the person was thus cured of his disease. Although obviously related to forensic psychiatry and concerned with issues like protection of society and treatment of offenders, discussions were never held in a strictly forensic context. Unlike in other countries in which castration policies were enforced, in The Netherlands the surgery was never embodied in law but subject to an informal protocol that covered political accountability. To satisfy Catholic objections references to eugenic aims were omitted from the documents, as were references to castration as a penalty.Based on international and Dutch literature (from both before and after 1938) as well as case histories, this article will show that the compromise about the therapeutic value of castration had no basis in medical knowledge, while 'voluntariness' (as elsewhere) was an acknowledged fallacy once surgeries had started. It was also acknowledged that castration did not really cure deviancy, but curbed libido and helped the castrate to suppress his urges. Nonetheless, because of the eugenic origins of discussions, associated with persistent confusion about the difference between castration and sterilization, it never became fully clear whether the surgery was meant to curb libido or to prevent the offenders from begetting inferior progeny.

The water footprint of bioenergy.

All energy scenarios show a shift toward an increased percentage of renewable energy sources, including biomass. This study gives an overview of water footprints (WFs) of bioenergy from 12 crops that currently contribute the most to global agricultural production: barley, cassava, maize, potato, rapeseed, rice, rye, sorghum, soybean, sugar beet, sugar cane, and wheat. In addition, this study includes jatropha, a suitable energy crop. Since climate and production circumstances differ among regions, calculations have been performed by country. The WF of bioelectricity is smaller than that of biofuels because it is more efficient to use total biomass (e.g., for electricity or heat) than a fraction of the crop (its sugar, starch, or oil content) for biofuel. The WF of bioethanol appears to be smaller than that of biodiesel. For electricity, sugar beet, maize, and sugar cane are the most favorable crops [50 m(3)/gigajoule (GJ)]. Rapeseed and jatropha, typical energy crops, are disadvantageous (400 m(3)/GJ). For ethanol, sugar beet, and potato (60 and 100 m(3)/GJ) are the most advantageous, followed by sugar cane (110 m(3)/GJ); sorghum (400 m(3)/GJ) is the most unfavorable. For biodiesel, soybean and rapeseed show to be the most favorable WF (400 m(3)/GJ); jatropha has an adverse WF (600 m(3)/GJ). When expressed per L, the WF ranges from 1,400 to 20,000 L of water per L of biofuel. If a shift toward a greater contribution of bioenergy to energy supply takes place, the results of this study can be used to select the crops and countries that produce bioenergy in the most water-efficient way.

Eugenic and sexual folklores and the castration of sex offenders in the Netherlands (1938-1968).

This contribution questions the positive/negative eugenics dichotomy that typifies the historiography on the eugenic movement in the Netherlands and the claim that this movement was mostly marginal because only positive eugenics was pursued. From 1938 to 1968 in the Netherlands, after a decade of debates, 400 sex offenders who had been committed to asylums for the criminally insane were 'voluntarily' and 'therapeutically' castrated. For political reasons debates on castration, meant to create consensus, eliminated any reference to or connotation with eugenics, yet these policies were unthinkable without them. This article shows that thinking about social and sexual problems and their solutions in the 1930s were permeated by eugenic folklore which in turn was informed by sexual folklore. Both eugenic and sexual lore, as common sense, or as ways of knowing, were about individual and collective loss of self control which was referred to with a catch-all phrase: 'hypersexuality'. Although sexual classifications used in diagnosing sex offenders suggested the existence of discrete sexual categories, homosexuality for instance was not seen as a sexual alternative or as an identity but as the extent to which an offender suffered from a form of hypersexuality that threatened the fabric of society.