【摘要】 已经证实,选点配比法存在一个最佳的配比时间;只有选这一时间下的流体出口温度进行配比,测温误差对结果的影响才能减到最小。本文求得了在各种流体进口温度条件和λι下的最佳配比时间间隔。文中还分析了各种待测量的测量误差以及流体进口温度条件偏离实际情况对结果的影响,并提供了它们的数值计算结果。计算表明,流体进口温度条件对选点配比法十分敏感,因此,必须采用与实际情况基本相符的数学模型求得的流体出口温度的理论解作为配比基准。为了节省配比时间,本文还提出了一种通过修正值加以校正的近似配比法,由此而引起的附加误差在±3%之内。更多还原

【Abstract】 Experience shows that one would not get satisfactory results when using transient methods to determine the heat transfer performance unless an appropriate matching technique in selected and used in testing. In this paper, the selectedpoint matching technique is studied in detail It is shown that for a given Ntu, there exists an optimum matching time which will produce the best test results for an error in temperature measurements. The appropriate matching time intervals for various boundary conditions and λ(?)are recommended here Effects of measuring errors of various measured quantities and deviations of the inlet fluid temperature boundary conditions from actual situation on test results are analysed, and their numerical results presented. It is shown that of the uncertainties of various measured quantities, the temperature measurement uncertainty is the largest source of error inthis technique. It is concluded that the selected point matching technique is quite sensitive to the deviation of the inlet fluid temperature condition from. actual situation: therefore it is necessary to use theoretical solutions derived from mathematical models which agree basically with actual situation as bases for the matching technique.This paper introduces an approximate matching technique based on the following empirical formula. which can be conveniently employed in the matching to save a lot of the matching time The results obtained from the approximate matching technique agrees completely with the correct result (within±3%)更多还原