Abstract
There are two kinds of working mechanisms for the Stirling cycle, i.e., the positive and the reverse cycles, and a Stirling engine (SE) can be operated as a Stirling refrigerator (SR). This indicates that a probable practical method for evaluating the performance of a Stirling engine is to run it as a refrigerator, which is much easier to operate. For this purpose, an improved Simple model for both the positive and the reverse Stirling cycles, considering the various loss mechanisms and actual operating conditions, is proposed and verified by a self-designed Stirling engine. As to the positive cycle with helium and nitrogen at 2.8 MPa, the model errors range from 5.4–11.3% for the indicated power, and 1–10.2% for the cycle efficiency. As to the reverse cycle with helium and nitrogen, the errors of the predicted input power range from 7.9–15.3% and from 2.5–10.9%, respectively. The experimental cooling temperatures can reach −92.2 and −53.6 °C, respectively, for the reverse cycle with the helium and nitrogen at 2.8 MPa. This Stirling-cycle analysis model shows a good adaptability for both the positive and the reverse cycles. In addition, the p-V maps of the positive and reverse cycles are compared in terms of “pressure ratio” and “curve shape”. The pressure ratio of the reverse cycle is significantly higher than that of the positive one at the same mean pressure. A method is proposed to predict the indicated work of the positive Stirling cycles using the reverse ones. A mathematical model to predict the indicated power of the positive Stirling cycles based on the reverse ones is proposed: Wheat2−Wcool1=A·(Tge2−Tgc2Tgc1−Tge1)B. The most critical issue with this method is to establish an associated model of the temperatures of the expansion and the compression space. This model shows a good adaptability for both the positive and the reverse cycles and can provide detailed information for deep discussion between the positive and the reverse cycles.
Highlights
The “cusp phenomenon” refers to the fact that the minimum volume part of the p-V map is sharper than the maximum volume part
The distinction between the p-V maps is mainly reflected in the “pressure ratio” and “curve shape”
In order to develop a practical method to evaluate the performance of a Stirling engine by it running as a refrigerator, an improved Simple model was proposed at first for positive and reverse Stirling cycles simultaneously
Summary
It is imperative to search for other alternative sources of energy on account of the finite amount of fossil fuels in the world. Solar energy is an attractive option due to its availability in a large portion of the world. The Stirling engine is a reciprocating piston power machine driven by flexible heating sources, which has a broad potential for application in the fields of solar thermal power, waste-heat utilization, and combined cooling, heating, and power systems [1,2,3,4]. The Stirling-cycle analysis methods can be divided into five categories (zeroth-order, first-order, second-order, third-order, and fourth-order analysis methods). Some models have been developed to accurately predict the performance of Stirling engines
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