Traveling-wave thermoacoustic electric generator
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Line drawing of the traveling-wave thermoacoustic engine and the analogous lumped-element electrical circuit (inset) (see Ref. 4). The engine is instrumented with thermocouples and piezoresistive pressure transducers at locations labeled “” and “”, respectively. The major acoustic and thermodynamic components include: (a) The ambient heat exchanger which is an aluminum cylinder that has 37 -diameter holes drilled through, (b) the regenerator which is a stack of 322 disks of stainless-steel wire mesh with a porosity of 0.755 and a hydraulic radius of packed into a thin-wall Inconel 625 shell, (c) the hot heat exchanger which is a gap between two flat plates, (d) and (f) flow straighteners made from several layers of woven wire screen, (e) the thermal buffer tube which is an open thin-wall Inconel 625 tube, (g) the alternator centerplate which interfaces the engine to the alternator pistons that are mounted on front and back of the centerplate and oscillate on an axis perpendicular to the page, (h) the inertance which is composed of a -inside-diameter stainless-steel tube and hole of the same diameter drilled from the outer edge of the centerplate to the inner edge, (i) the compliance which is a -cylindrical volume, and (j) the jet pump which is a tapered annular flow path whose asymmetric flow resistance can be adjusted by changing the axial position of the central plug to suppress acoustic streaming driven by the acoustic power circulating around the engine loop (see Ref. 4).
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The net heat input to the engine and acoustic power delivered to the pistons versus the magnitude of the acoustic amplitude, , normalized by the mean pressure, . The heat input to the engine is determined by measuring the current and voltage delivered to four electric heaters bonded to the top of the hot heat exchanger. A static heat leak measurement is made by loading the alternator to the point where the engine will not oscillate. The static heat leak due to losses though the thermal insulation surrounding the engine’s hot parts is subtracted off the heat input to yield the net heat input, . The acoustic power delivered to the piston faces, , is calculated from measurements of the complex pressure amplitude at the piston faces and the complex velocity amplitude of the pistons, which is measured with a linear variable differential transducer (LVDT) attached to the back of each piston.
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Alternator loss for the same five data points as in Fig. 2 versus the peak stroke of the pistons. The peak stroke is proportional to plotted on the axis of Fig. 2. The vertical gap between data points indicates the power dissipated by the various loss mechanisms. A model for each mechanism is developed by using different measurements to isolate individual mechanisms: Pressure drop due to steady flow determines the seal loss; vacuum ringdown determines the mechanical and magnetic hysteresis; operation in a pressurized gas without a piston determines the motor windage losses; and the motor space thermal hysteresis is measured using an LVDT attached to the piston and an additional pressure transducer behind the piston.
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