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由于竹壁较薄,测定液流时安装常规长度(20 mm)的TDP探针易穿破竹壁。与木材的热传导不同,暴露于竹腔内的部分上探针的热量以辐射形式消散,加之竹壁水分传导分子的分布不均匀,导致液流密度的测定值不准确。因此,不少学者主张选用较短的探针,然而,对于改短探针的应用缺乏必要的户外原位验证。本文分析自制的5、8和10 mm的TDP探针原位测定粉单竹液流的适用性和理论依据。结果表明:新建立的液流密度公式与Granier原始经验公式的参数α值的差异较大,主要原因是竹腔的储热效应导致上探针周围温度偏高,竹秆水分含量较低,热消散系数(h0)较小,上探针周围的热量囤积致使上下探针的温差较大;此外,探针的安装方式也影响液流密度的测定结果,是导致相同长度探针测定粉单竹液流密度值明显差别的重要因子。本文通过分析探针周围介质的h0的变化,较合理地解释了这些差异的原因。
Due to the thinness of the bamboo wall, TDP probes of conventional length (20 mm) were easy to break through the wall when measuring flow. Different from the heat conduction of wood, the heat of the probe exposed in the bamboo cavity dissipates in the form of radiation, and the distribution of moisture-conducting molecules in the bamboo wall is uneven, resulting in the inaccurate measurement of the liquid density. Therefore, many scholars advocate the use of shorter probes; however, the lack of necessary outdoor in situ verification for short probe applications. In this paper, we analyzed the applicability and theoretical basis of in situ determination of 5, 8 and 10 mm TDP probes for in situ determination of single-flow bamboo powder. The results show that the difference between the newly established fluid density formula and Granier ’s original empirical formula is mainly due to the fact that the heat storage effect of the bamboo cavity leads to the high temperature around the probe, the low moisture content of the bamboo stalk, the heat dissipation The coefficient (h0) is smaller, the heat accumulation around the probe causes the temperature difference between the upper and lower probes to be larger; in addition, the installation method of the probe also affects the determination of the liquid density, which is the result of the probe of the same length An important factor for the significant difference in flow density values. This paper reasonably explains the reasons for these differences by analyzing the change of h0 in the medium around the probe.