Study On Stirling Cycle Analysis And Heat Transfer Of Tubular Heater

Worldwide attempts are being made to reduce pollution and alleviate energy scarcity. Recent interest in renewable energy utilization has sparked new activity in Stirling engine development. The inadequate understanding of actual working process and the inaccurate of cycle analysis methods may block the rapid development and commercialization of Stirling engines.A deep study on the major factors which affect engine performance and the accuracy of cycle analysis methods is carried out. The five cycle analysis methods based on Martini’s nomenclature and the Finite-time thermodynamics are summarized and compared. The Schmidt method, Adiabatic model and Simple model are applied to estimate the performance of a1kW γ-type Stirling engine with two cylinders. The Finite-time thermodynamics is used to get a quantitative analysis of the optimization between output power and efficiency.In most of cycle analysis methods, the influence of oscillating flow is ignored. The classical laminar or turbulent steady unidirectional correlations and empirical data are used to get approximations of convective heat transfer coefficient in Stirling engines. The heat transfer characteristics of oscillating flows of a tubular Stirling engine heater, whose operating conditions are close to the flow regions of real engines, are experimentally investigated. The heat transfer coefficients reach the maximum value of78.0W/(m2·K) among the testing conditions when the working gas pressure is0.4MPa and the revolution is420rpm. To raise the working gas pressure is positive to decrease the wall temperature and to improve the heat transfer. When the pressure varies from0.1to0.4MPa, the wall temperature reduces17℃and the heat input increases10W. The estimated uncertainty for the heat transfer coefficient is usually within7.69%. An oscillating heat transfer correlation is derived based on the experimental data, where Re and Rew are in the ranges of740-4110and12-71, respectively. The determination coefficient of a regression fitted correlation is0.97. The proposed correlation is respected to predict the heat transfer coefficients of oscillating flows for practical design of tubular heaters and provide experimental basis for considering the influence of oscillating flow in cycle analysis methods, while the classical unidirectional steady correlations are not suitable, especially at high Re conditions.