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.Comment: The following article appeared in J. Acoust. Soc. Am 143(2) and the final version in a proper two-column format may be found at: http://scitation.aip.org/content/asa/journal/jasa/143/2/10.1121/1.502339

Computational fluid dynamics analysis of the oscillatory flow in a jet pump: the influence of taper angle

A two-dimensional CFD model for predicting the oscillating flow through a jet pump is developed. Various taper angles are investigated and total minor loss coefficients are derived. A good correspondence is achieved with experimental results from the literature. However, at higher taper angles a dramatic decay in the jet pump pressure drop is observed, which serves as a starting point for the improvement of jet pump design criteria for compact thermoacoustic application

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.Comment: The following article has been accepted by the Journal of the Acoustical Society of America. After it is published, it will be found at http://scitation.aip.org/JAS

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, there will exist an asymmetry in the hydrodynamic end effects 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.Comment: The following article has been accepted by the Journal of the Acoustical Society of America. After it is published, it will be found at: http://scitation.aip.org/JAS

Different effects of continuous infusion of interleukin-1 and interleukin-6 on the hypothalamic-hypophysial-thyroid axis

The cytokines interleukin-1 (IL-1) and IL-6 are thought to be important mediators in the suppression of thyroid function during nonthyroidal illness. In this study we compared the effects of IL-1 and IL-6 infusion on the hypothalamus-pituitary-thyroid axis in rats. Cytokines were administered by continuous ip infusion of 4 micrograms IL-1 alpha/day for 1, 2, or 7 days or of 15 micrograms IL-6/day for 7 days. Body weight and temperature, food and water intake, and plasma TSH, T4, free T4 (FT4), T3, and corticosterone levels were measured daily, and hypothalamic pro-TRH messenger RNA (mRNA) and hypophysial TSH beta mRNA were determined after termination of the experiments. Compared with saline-treated controls, infusion of IL-1, but not of IL-6, produced a transient decrease in food and water intake, a transient increase in body temperature, and a prolonged decrease in body weight. Both cytokines caused transient decreases in plasma TSH and T4, which were greater and more prolonged with IL-1 than with IL-6, whereas they effected similar transient increases in the plasma FT4 fraction. Infusion with IL-1, but not IL-6, also induced transient decreases in plasma FT4 and T3 and a transient increase in plasma corticosterone. Hypothalamic pro-TRH mRNA was significantly decreased (-73%) after 7 days, but not after 1 or 2 days, of IL-1 infusion and was unaffected by IL-6 infusion. Hypophysial TSH beta mRNA was significantly decreased after 2 (-62%) and 7 (-62%) days, but not after 1 day, of IL-1 infusion and was unaffected by IL-6 infusion. These results are in agreement with previous findings that IL-1, more so than IL-6, directly inhibits thyroid hormone production. They also indicate that IL-1 and IL-6 both decrease plasma T4 binding. Furthermore, both cytokines induce an acute and dramatic decrease in plasma TSH before (IL-1) or even without (IL-6) a decrease in hypothalamic pro-TRH mRNA or hypophysial TSH beta mRNA, suggesting that the acute decrease in TSH secretion is not caused by decreased pro-TRH and TSH beta gene expression. The TSH-suppressive effect of IL-6, either administered as such or induced by IL-1 infusion, may be due to a direct effect on the thyrotroph, whereas additional effects of IL-1 may involve changes in the hypothalamic release of somatostatin or TRH.(ABSTRACT TRUNCATED AT 400 WORDS