05.04.2016 Views

Modern Engineering Thermodynamics

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

524 CHAPTER 13: Vapor and Gas Power Cycles<br />

CASE STUDIES IN APPLIED THERMODYNAMICS Continued<br />

published by Ross Experimental, 1660 W. Henderson Rd.,<br />

Columbus, Ohio); however, most require machinist skills. The<br />

Stirling engine described here can be made from commonly available<br />

components and requires minimum manual skill to assemble.<br />

Stirling engine 1. A test tube engine<br />

This project has been designed for any engineering student with<br />

access to simple hand-tools. It was originally developed in 1992 by<br />

Wilfried Schlagenhauf in Germany. If you follow the instructions<br />

carefully, you can make a simple Stirling cycle engine that runs<br />

under its own power. Figure 13.65 shows the eight basic parts. You<br />

need a standard test tube (about ¾ inch in diameter and 6 inches<br />

long) (1), and five glass marbles (2) that roll freely inside the test<br />

tube and function as a free piston displacer. The power cylinder (5)<br />

is a 1-inch diameter plastic snap-cap pill bottle with the bottom<br />

cut off. Cut the neck off a small balloon (6) and stretch the opening<br />

over the uncut end of the pill bottle and snap the cap in place<br />

to hold and seal the balloon. Then, cut a small hole in the pill bottle<br />

top to insert the air tube and mount it upside down on the base<br />

(8). The power piston assembly (4) consists of another plastic bottle<br />

cap, small enough to fit inside the power cylinder without jamming<br />

when at an angle. A 3 inch long nail is pushed through the<br />

center of the bottle cap to provide the piston connecting rod. The<br />

test tube support assembly (3) consists of an angle bracket<br />

mounted to the base (8), and an adjustable (erector set) member<br />

attached to the test tube pivot joint. The air tube (9) is 2 or 3 mm<br />

ID pliable plastic or rubber tubing. Finally, counterweights (10)<br />

need to be added to the cold end of the test tube to control its<br />

motion. The engine is driven by the heat of a single candle (7).<br />

A complete engine kit is available from Ginsberg Scientific<br />

(ginsbergscientific.com).<br />

towards the free end of the test tube, displacing the hot air to the<br />

higher, cold end, where it cools, causing the balloon to retract, lowering<br />

the piston assembly, and the cycle begins again. When properly<br />

adjusted, the engine operates at about one to three cycles per<br />

second, and the engine generates enough power to drive a small<br />

external device.<br />

Heating<br />

(a) Heating the air<br />

Cooling<br />

1<br />

2<br />

8<br />

7<br />

FIGURE 13.65<br />

A test tube Stirling engine.<br />

6<br />

5<br />

4<br />

Here is how the cycle works (Figure 13.66): (a) When the free end<br />

of the test tube is pointing up, the air it contains is heated. The<br />

heated air expands and inflates the balloon. (b) The expanding balloon<br />

pushes the power piston assembly up, which in turn causes<br />

the test tube to pivot its free end downward. Then the marbles roll<br />

3<br />

10<br />

9<br />

FIGURE 13.66<br />

How this engine works.<br />

(b) Cooling the air<br />

Stirling engine 2. A liquid piston fruit-jar engine<br />

A number of easily made liquid piston Stirling cycle engines can be<br />

found in the text Liquid Piston Stirling Engines, byC.D.West(New<br />

York: Van Nostrand Reinhold, 1983). One of the most intriguing is<br />

the fruit-jar engine, shown in Figure 13.67, connected to a water<br />

pump. This unit should pump about 5 gallons per hour when<br />

properly adjusted. In some cases, the water level in the cylinders<br />

and the length of the tuning line inserted into the hot cylinder may<br />

require careful adjustment. Some very interesting thermodynamic<br />

experiments can be done with this design. For best results, see the<br />

details provided in the text by C. D. West.

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!