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A first-principles model for predicting the evolution of the porosity of a frost layer over time was advanced. The theoretical model was used together with experimental data obtained elsewhere to put forward a semi-empirical correlation for the frost density as a function of the time, and the modified Jakob number, which carries information about the thermodynamic conditions of the air stream and the chilled surface. When compared to experimental data, the proposed correlation showed errors within ±10% bounds. Comparisons with other frost density correlations available in the open literature are also reported. 相似文献
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Experiments are performed concerning frost growth and densification in laminar flow over a flat surface under conditions of constant and variable humidity. The flat plate test specimen is made of aluminum-6031, and has dimensions of 0.3 m × 0.3 m × 6.35 mm. Results for the first variable humidity case are obtained for a plate temperature of 255.4 K, air velocity of 1.77 m/s, air temperature of 295.1 K, and a relative humidity continuously ranging from 81 to 54%. The second variable humidity test case corresponds to plate temperature of 255.4 K, air velocity of 2.44 m/s, air temperature of 291.8 K, and a relative humidity ranging from 66 to 59%. Results for the constant humidity case are obtained for a plate temperature of 263.7 K, air velocity of 1.7 m/s, air temperature of 295 K, and a relative humidity of 71.6%. Comparisons of the data with the author's frost model extended to accommodate variable humidity suggest satisfactory agreement between the theory and the data for both constant and variable humidity. 相似文献
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Li Min LinBao Dalian Municipal Design Research Institute Co. LTD. Shenyang jianzhu University 《中国建设信息》2007,(11)
本文针对住宅用新风换气机在冬季运行时,在其排风侧出现结霜现象,以实验测定为研究手段,选用板翅式全热交换器作为能量回收装置,设计加工了防结霜住宅用全热回收换气机样机。样机安装在标准的住宅内,测定了该换气机在冬季运行时,其结霜点的温度随室内外空气温湿度的变化情况,总结其结霜的变化规律,得出通过新风预热能够有效地防止换气机冬季结霜现象的发生,使其应用得到进一步的推广的结果。 相似文献
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本文针对住宅用新风换气机在冬季运行时,在其排风侧出现结霜现象,以实验测定为研究手段,选用板翅武全热交换器作为能量回收装置,设计加工了防结霜住宅用全热回收换气机样机。样机安装在标准的住宅内,测定了该换气机在冬季运行时,其结霜点的温度随室内外空气温湿度的变化情况,总结其结霜的变化规律,得出通过新风预热能够有效地防止换气机冬季结霜现象的发生,使其应用得到进一步的推广的结果。 相似文献
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Freezing behavior of clay differs from that of silt. This difference stems primarily from the low permeability or hydraulic conductivity of clay, and the higher water content of saturated clay. Freezing effects include simultaneous heave and consolidation. Six small physical model columns of clay were frozen: one at 1g; and five on a centrifuge at various scales and with corresponding accelerations, to bring self-weight stresses into similarity with a full scale column of clay 4?m in height. The experimental results demonstrated the importance of replicating the prototype stress conditions in a model. They demonstrated the importance of local water content on development of heave in clay, and the relative insensitivity of heave to location of the phreatic surface. Low permeability caused the clay to behave essentially as a closed system with regard to water flow. A simple analytical model was developed to explain observed soil response. Further research is recommended to provide more guidance in selecting input parameters. 相似文献
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2008年冰雪灾害造成广西电力设施大面积损坏,分析其原因,指出供输电线路重冰区导线局部应力大于导线瞬时破坏应力,是造成大范围断线倒杆的原因。以实例简介了供电线路大电流融冰技术。通过灾后反思,提出了重新建立和完善分层次电网、分层次电源、国防后备电源的建议。 相似文献
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Hui Bing Ping He Chengsong Yang Yehui Shi Shuping Zhao Xiaolin Bian 《Applied Clay Science》2007,35(3-4):189-193
The existence of solutes and their redistribution during freezing have a deep influence on the process of soil freezing. We performed unidirectional freezing experiments in an open system with red clay collected at the Beiluhe test site along the Qinghai–Tibet Railway. The groundwater supply of the soil was simulated in the laboratory experiment by attaching a liquid replenishment system to the bottom of the sample container. In order to see the influence of the salt on the evolution of the sample during unidirectional freezing, two types of experiments were performed. (i) The soil samples were supplied with a sodium sulfate solute of 5% concentration, and (ii) only distilled water without any salty component was added. Based on the freezing temperature measurements of salty soil, migration of sodium sulfate solution towards a lower temperature zone during freezing 0 °C isotherm in the soil moved gently towards deeper layers, but frost depth of the soil ascended slightly with time when the sample was constantly cooled. Compared to the distilled water replenishment, the amount of frost-heaving was smaller in the soil column with sodium sulfate solution replenishment. Based on the frost depth curve, the solubility curve of the Na2SO4–H2O system and the amount of frost heaving and salt expansion in the soil column we have calculated the amount of frost heaving and salt expansion. In an early stage of the experiment deformation of the soil column was mainly caused by frost heaving, while in a later phase crystallization of the sodium sulfate played a lager role. This conclusion is confirmed by the results of the dry density measurement after the experiments. 相似文献