motor Stirling

Al principio tuve un poco de baja temperatura-diferencia (LTD) motor Stirling que podía funcionar con una taza de agua caliente o incluso de calor corporal. El gran motor se muestra aquí es bastante cerca de una escala 2:1 Versión de ese pequeño motor. El pequeño motor era muy similar a la Kontax KS90, algunas fotos de los que se muestran a continuación como referencia (estos son desde el sitio de Kontax en http://www.stirlingengine.co.uk).

Lo primero que te das cuenta al mirar el motor Kontax es que finamente balancea y en la baja fricción está todo. Yo estaba un poco aprensivo acerca de si sería posible simplemente escalar las partes y todavía llegar a trabajar sin problemas. Al final resultó que, todo funcionaba bien en el final.

Fotos de la gran motor se muestran a continuación. No hay dibujos para esto, por desgracia, porque hice las mediciones a medida que avanzaba!

Cilindros y placas desplazador

El cilindro de desplazador se mecaniza de 6 "de diámetro, de tubo de acrílico de ¼" de espesor. La celebración de esta verdad en el torno presentó algunas dificultades. Finalmente he jodido dos bloques de madera de la placa frontal y los rechacé hasta que fueron un ajuste ordenado dentro de la tubería. Entonces me metí una pieza en bruto de corte de la tubería en ambos extremos y se volvió sin mover la tubería. Esto aseguró que ambos extremos eran exactamente paralelo.

Las placas de extremo se convirtieron de alguna placa de aluminio de 5mm encontré en un salto. Hay una pequeña espiga de encendido de modo que cada localizar bien el interior del cilindro desplazador. El aluminio es el material más suave, crappiest que he usado, pero me las arreglé para conseguir un acabado decente en él con un montón de papel de lija. Las dos placas de extremo se sujetan junto con tornillos de cabeza avellanada M3 que van en un Delrin espaciador para prevenir la conducción de calor aislante.

Displacer and connecting rod The displacer itself is turned from a piece of building foam (the dense, closed-cell stuff). A plastic bush is pressed into the middle of this and the displacer connecting rod is screwed into the bush. To reduce friction, the bearing for the displacer rod is made from a small piece of graphite held in a plastic housing. The connecting rod is laser-cut from 2mm acrylic sheet and pivots on small nylon bushes to reduce friction.

Power cylinder and piston The cylinder is made from a short piece of borosilicate test tube glass. It was rough-cut by hand and then ground to exact length/squareness on the lathe using a diamond burr mounted in a Dremel tool. Since the glass is quite cheap, it's not perfectly round, and there is some leakage round the sides of the piston. For the ultimate cylinder, it would be best to cannibalise a ground-glass gas syringe, since they are bored perfectly cylindrical.

The piston is turned from a chunk of graphite, hacked off my massive block of graphite I keep in the shed. A small plastic clevis fork is screwed into the piston, and this attaches to the connecting rod. Another small nylon bush is used as a pivot.

Crankshaft and flywheel I finally found a use for all the stepper motors I keep hoarding - once pulled apart, they provide a nice shaft and pair of ball bearings. These were used for the crankshaft. The ball bearings were mounted inside a PVC housing which was then mounted on a Thorlabs ½" optical post to support it. The flywheel is actually a bicycle disk brake - the technician at uni thought on that, and it's an absolutely brilliant idea. This was a scrounged one, but they're only £15 or so to buy new. It's screwed to an aluminium hub which is attached to the crankshaft. I was extremely pleased when the flywheel ran true!

I realised that it would be difficult to scale this sort of engine up any further without some trickery, as the weight of the displacer becomes signifcant. As the engine is running, you can see it slow down as the displacer is being lifted. At larger sizes, this would eventually stop the engine. Some sort of counterweight would be needed to offset the weight of the displacer. It's probably doable.Here's a video of the engine running from a dish of boiling water. The engine runs really smoothly, and will work in both directions (after reversing the phasing of the displacer).