Experimental data of free convection heat transfer for 12.7 and 25 um horizontal wires in rarefied atmospheres

When free convection is to be calculated for very thin wires in rarefied atmospheres, the Rayleigh number becomes very small. At these small Rayleigh numbers, available correlations are no longer applicable and there is also a lack of published experimental data. Therefore, new tests were performed using 12.7 and 25 um horizontal wires at low pressures. The wires were heated using electrical current and the temperature of the wires was calculated using the electrical resistance temperature coefficient. The heat transfer parameters and non-dimensional numbers were obtained using usual theoretical analysis. The gathered experimental data show that the Knudsen number must be incorporated in order to reliably describe the heat transfer in above-mentioned conditions. Data are in CSV format with utf-8 encoding. The header of each columns is the variable's name as follows: Gr: Grashof number Pr: Parndtl number Nu: Nusselt number Kn: Knudsen number h: heat transfer coefficient ( W/(m**2 K) ) Tw: wire's temperature (K) Ti: air's temperature (K) p: pressure (Pa) d: wire's diameter (m) L: wire's length (m)当需计算稀薄大气中极细导线的自由对流换热时，瑞利数（Rayleigh number）会变得极小。在这类瑞利数极小的工况下，现有换热关联式已不再适用，且公开的实验数据也较为匮乏。为此，本研究采用直径为12.7 μm与25 μm的水平导线，在低压环境中开展了全新的实验测试。实验通过电流对导线加热，并借助电阻温度系数计算导线温度。通过常规理论分析得到了换热参数与无量纲数。所收集的实验数据表明，为可靠描述上述工况下的换热过程，必须纳入克努森数（Knudsen number）。数据集采用CSV格式存储，编码为UTF-8。各列的列标题为对应变量的名称，具体如下： Gr：格拉晓夫数（Grashof number） Pr：普朗特数（Prandtl number） Nu：努塞尔数（Nusselt number） Kn：克努森数（Knudsen number） h：换热系数，单位为W/(m²·K) Tw：导线温度，单位为K Ti：空气温度，单位为K p：压强，单位为Pa d：导线直径，单位为m L：导线长度，单位为m