A new duplex Stirling engine concept for solar‐powered cooling

Abstract

The global cooling demand is one of the fastest growing energy demands and is putting a strain on the electricity infrastructure. Solar-powered cooling could provide most of the cooling demand due to the coincidence of the cooling demand and the solar irradiance. In particular, the solar-powered Stirling-cycle cooler has low maintenance requirement, high theoretical efficiency, and use of environmentally friendly gases. However, Stirling-cycle coolers are expensive due to high driving temperatures, complex heat exchangers, and expensive solar tracking so that they have so far only been successful at high-temperature difference applications. This study introduces a novel directly coupled solar Stirling cooler for which the hot engine cylinders are deployed inside evacuated tube collectors. The machine uses air as working fluid, and its driving mechanism is based on the free-piston, balanced compound technology that was patented by Finkelstein. A second-order mathematical model is used to investigate the performance of the machine for different cylinder arrangements, gas leakage rates, chilling temperatures, and solar irradiance. In addition, the regenerators are optimised to maximise the cold production. It is shown that mechanical frictions can be reduced to 20% by selecting an appropriate cylinder arrangement. The solar cooler achieves a maximum cold production rate of 367.5 W/m 2 without using external heat exchangers at load temperature of 7 C, which is comparable with photovoltaic powered coolers.In addition, the machine is relatively simple, has safe and quiet operation, uses ambient air as working gas, and is able to produce a wide range of chilling including sub-zero temperatures without changing the working gas. The direct thermal coupling of the Stirling cooler to evacuated tube collectors significantly reduces the complexity of the machine and removes intermediate heat transfer steps which reduce the performance. Thus, the suggested cooling technology has great potential for solar refrigeration, especially for low power and near ambient cooling.

A novel Gamma‐type duplex Stirling system to convert heat energy to cooling power: Theoretical and experimental study

“…Equation (25) shows the temperature variation in the regenerator. According to the law of conservation of mass, its variation is stated in Equations ( 26) to (28):…”

“…Duplex Stirling cycle analysis is investigated by an isothermal method (called the Schmidt method) and the Finkelstein method, which is closer to the reality. Daoud et al 25 27 The system is studied thermodynamically by examining its operational and constructional parameters. The main focus is on the overall coefficient of the duplex system.…”

A non‐tracking semi‐circular trough solar concentrator

“…Since the 1970s there have been hundreds of papers on the design, performance and application of very many concentrators based upon the CPC principle. To quote only a few examples, there are papers reporting the performance and efficiency of CPC troughs with various absorber shapes, [8][9][10][11] applications to hot water heating, [12][13][14][15][16][17] to refrigeration, [18][19][20] to chemical processes 21 and for water de-salination. 22 In a recent paper 23 it is suggested to mount an assembly of standard double-wall CPC on the side of buildings for water heating applications.…”

Modeling of the dynamic characteristics and performance of a four‐cylinder double‐acting Stirling engine

“…From the 1940s onwards, many linking mechanism variations were invented and applied to the four‐cylinder DASE, including the crank drive mechanism, swashplate mechanism, 13 and wobble yoke mechanism 14 . Daoud and Friedrich 15 developed a new duplex Stirling engine concept for solar‐powered cooling with double‐acting pistons. Haikarainen et al 16 studied the pressure imbalance phenomenon in a double‐acting heat pump with two double‐acting pistons.…”