Numerical analysis on heat transfer characteristics of a multi-vapor channel vapor chamber with novel ultra-thin composite wick

A three-dimensional numerical model is established to predict heat transfer characteristics of a multi-vapor channel vapor chamber (VC) with novel composite wick. In order to validate the numerical model, the surface temperature of the VC is compared with the experimental results. The mass flow rate distribution of working fluid in the wick is obtained. And the effects of the height of the vapor channel on the velocity, pressure drop of the vapor and total thermal resistance are investigated at different heating powers. The velocity, pressure drop of the vapor and total thermal resistance have the same variation trend, which are all inversely correlated to the height of the vapor channel respectively. However, the reduction of the thermal resistance of the vapor decreases as the height of the vapor channel increase. At last, the conduction-based model for the vapor chamber is put forward and the effective thermal conductivity of the vapor channel is derived. The maximum relative error between the VC surface temperature prediction based on the conduction model and the experimental data is less than 5 %

Plant diversity enhances productivity and soil carbon storage

Despite evidence from experimental grasslands that plant diversity increases biomass production and soil organic carbon (SOC) storage, it remains unclear whether this is true in natural ecosystems, especially under climatic variations and human disturbances. Based on field observations from 6,098 forest, shrubland, and grassland sites across China and predictions from an integrative model combining multiple theories, we systematically examined the direct effects of climate, soils, and human impacts on SOC storage versus the indirect effects mediated by species richness (SR), aboveground net primary productivity (ANPP), and belowground biomass (BB). We found that favorable climates (high temperature and precipitation) had a consistent negative effect on SOC storage in forests and shrublands, but not in grasslands. Climate favorability, particularly high precipitation, was associated with both higher SR and higher BB, which had consistent positive effects on SOC storage, thus offsetting the direct negative effect of favorable climate on SOC. The indirect effects of climate on SOC storage depended on the relationships of SR with ANPP and BB, which were consistently positive in all biome types. In addition, human disturbance and soil pH had both direct and indirect effects on SOC storage, with the indirect effects mediated by changes in SR, ANPP, and BB. High soil pH had a consistently negative effect on SOC storage. Our findings have important implications for improving global carbon cycling models and ecosystem management: Maintaining high levels of diversity can enhance soil carbon sequestration and help sustain the benefits of plant diversity and productivity