G. W. Swift

An intrinsically irreversible thermoacoustic heat engine

Certain thermoacoustic effects are described which form the basis for a heat engine that is intrinsically irreversible in the sense that it requires thermal lags for its operation. After discussing several acoustical heating and cooling effects, including the behavior of a new structure called a ‘‘thermoacoustic couple,’’ we discuss structures that can be placed in acoustically resonant tubes to produce both substantial heat pumping effects and, for restricted heat inputs, large temperature differences. The results are analyzed quantitatively using a second‐order thermoacoustic theory based on the work of Rott. The qualities of the acoustic engine are generalized to describe a class of intrinsically irreversible heat engines of which the present acoustic engine is a special case. Finally the results of analysis of several idealized intrinsically irreversible engines are presented. These suggest that the efficiency of such engines may be determined primarily by geometry or configuration rather than by temp...

Understanding some simple phenomena in thermoacoustics with applications to acoustical heat engines

Thermoacoustical phenomena have a long history and are frequently characterized by great complexity. In the present paper, we describe how, by the use of suitable acoustical structures, the phenomena can both be simplified and readily demonstrated. A heuristic discussion is emphasized, which we hope will be useful in teaching the principles. The qualities of certain model apparatus that demonstrate acoustically stimulated entropy flow, a thermally driven acoustic oscillator, and an acoustically driven refrigerator are also presented in semiquantitative detail.

Theory and calculations for an intrinsically irreversible acoustic prime mover using liquid sodium as primary working fluid

A theory describing a thermoacoustic heat engine using a liquid as primary working substance is developed and applied to the design of a high‐power prime mover using liquid sodium. After an introduction that explains the physical principles of this type of engine in a heuristic way, we derive expressions for the acoustic variables and consequent energy flows in the engine. These expressions are easily understandable only in special limiting cases; to discuss practical applications we resort to numerical computations. We find that a reasonably designed thermoacoustic prime mover using liquid sodium and operating between thermal reservoirs at 1000 and 400 K can generate about 60 W/cm2 of acoustic power at about (1)/(3) of Carnot’s efficiency. We also discuss the relative importance of various sources of inefficiency, such as viscosity, that are not essential to the production of power in this type of engine but are unavoidable in practice because of the thermophysical properties of real substances.

A Stirling engine with a liquid working substance

A theoretical and experimental study of a Stirling engine using a liquid (propylene) as its working substance is presented. This is the first experimental work on liquid Stirling engines (or Malone engines) since the 1920s. Liquid‐Stirling technology appears advantageous to conventional freon‐based Rankine‐cycle technology in many applications. The theory developed here is simple, intuitive, and modular because of the nature of liquid working fluids and because the temperature spanned by liquid Stirling engines is not large. The experimental engine is extremely versatile, and can operate as either a heat pump or prime mover. Extensive measurements with it are in substantial agreement with the simple theory.

Fabrication and leak‐tight furnace brazing of intricate objects

An extremely compact crossflow heat exchanger has been constructed by hydrogen furnace brazing together a stack of hundreds of chemically milled stainless‐steel sheets. The resulting structure is leak tight and very strong, but fluid channels as small as 51 μm are not plugged by excess brazing material. The construction technique is easily adapted to mass production and should be useful for structures of an intricate but repetitive three‐dimensional nature.

Measurements with an optimized regenerator for a liquid-working-substance heat engine

A regenerator for use with a liquid in a Stirling cycle heat engine is described. Because of the thermophysical characteristics of liquids, such a regenerator can be nearly ideally effective and has thermal properties that can be calculated directly without resort to empirical information. The regenerator described here is designed to minimize loss arising from three sources: thermal conductivity along the regenerator, viscous heating in the working fluid, and imperfect thermal contact between the working fluid and the second thermodynamic medium in the regenerator. Measurements using liquid propylene as a test fluid in the regenerator confirm the design calculations.

Liquid metal thermoacoustic engine

A liquid metal thermoacoustic engine is studied both theoretically and experimentally. This type of engine promises to produce large quantities of electrical energy from heat at modest efficiency with no moving parts except the acoustic oscillations in the liquid metal. In the engine, heat flow from a high‐temperature source to a low‐temperature sink amplifies a standing acoustic wave in liquid sodium. This acoustic power is simply converted to electric power by means of a magnetohydrodynamic effect at the acoustic oscillation frequency. A detailed thermoacoustic theory applicable to this engine is developed, and it is found that a reasonably designed liquid sodium engine operating between 700 °C and 100 °C should generate about 60 W/cm2 of acoustic power at about 1/3 of Carnots efficiency. Construction of a 3000‐W thermal laboratory model engine is almost complete. A 1‐kW, 1‐kHz liquid sodium magnetohydrodynamic transducer has also been designed and built. It is now very well characterized both experime...