The ideal magnetic Ericsson refrigeration cycle should have a constant induced magnetic entropy change as a function of temperature over the whole refrigeration range. To realize this condition using composite materials, a numerical method has been developed to determine the optimum proportions of the component materials in such refrigerants. This paper investigates the effects of increasing the number (n) of the components on the constancy of the magnetic entropy change of the composite (ΔScom), and suggests some new composite refrigerants. For this purpose, the Gd1−x–Dyx (with x=0, 0.12, 0.28, 0.49, and 0.70) alloys, have been used. The values of ΔS have been calculated both from mean-field theory as well as from experimental magnetization curves of these alloys, in the 0.1–7 T magnetic field range and the 200–300 K temperature range. Two sets of composite materials have then been proposed as refrigerants, operating, respectively, over the temperature range 240–290 K and 210–290 K. The ΔS data of the individual Gd–Dy alloys were then used to calculate the optimum mass ratio of the composites. The resultant ΔScom is practically constant in the required temperature range and amounts to 8.0 and 7.3 J/kg K for the two respective sets. The results show that a subsequent increase of n can improve the constancy of the value of ΔScom, and, hence, the corresponding refrigerant should operate more efficiently. Thus, it is found that the appropriate values of n are 3 and 4, respectively, for the first and the second set.

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This article presents a numerical method for predicting unsteady aerodynamics of horizontal axis wind turbines (HAWTs). In this method the flow field is described by the unsteady incompressible Navier–Stokes equations. The rotor and tower are idealized respectively as actuator disc and flat plate permeable surfaces on which external normal surficial forces are balanced by fluid pressure discontinuities. The external forces exerted by the rotor and tower on the flow are prescribed according to blade element theory. Dynamic behaviour of the rotor aerodynamic characteristics is simulated using either the Gormont or the Beddoes–Leishman model. The resulting mathematical formulation is solved using a control volume finite element method. The fully implicit scheme is used for time discretization. In general, the proposed method has demonstrated its capability to adequately represent the field data. It has been demonstrated that the accuracy of the predicted results depends primarily on the dynamic stall model as well as on the turbulence model employed. Copyright © 2001 John Wiley & Sons, Ltd.

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The objective of this paper is to study the typical atmospheric turbulent flow around the rotor and nacelle of a HAWT, in order to (i) investigate the impact of the turbine's rotating blades on the flow field over the nacelle, i.e. the rotor-nacelle interaction; (ii) assess the appropriate anemometer location on the nacelle, and therefore (iii) establish the relationship between wind speed measured near the nacelle and free stream wind speed. The paper presents a numerical method for investigating the effects of rotating rotor blades on the nacelle anemometry of a horizontal axis wind turbine (HAWT). The flow field around the turbine and nacelle is described by the Reynolds averaged Navier-Stokes equations. The k – ε model has been chosen for the closure of time-averaged turbulent flow equations. The rotor is modelled using the actuator-disk concept. The simulation results were performed using a commercial wind turbine rated at 750kW. In general, good qualitative agreements have been found, supporting the validity of the proposed method. However, quantitatively, the accuracy of the simulation results should be confirmed before any use is made in power performance testing.