Development and validation of a coupled heat and mass transfer model for green roofs

This paper describes a dynamic model of transient heat and mass transfer across a green roof component. The thermal behavior of the green roof layers is modeled and coupled to the water balance in the substrate that is determined accounting for evapotranspiration. The water balance variations over time directly impact the physical properties of the substrate and the evapotranspiration intensity. This thermal and hydric model incorporates wind speed effects within the foliage through a new calculation of the resistance to heat and mass transfer within the leaf canopy. The developed model is validated with experimental data from a one-tenth-scale green roof located at the University of La Rochelle. A comparison between the numerical and the experimental results demonstrates the accuracy of the model for predicting the substrate temperature and water content variations. The heat and mass transfer mechanisms through green roofs are analyzed and explained using the modeled energy balances, and parametric studies of green roof behavior are presented. A surface temperature difference of up to 25 °C was found among green roofs with a dry growing medium or a saturated growing medium. Furthermore, the thermal inertia effects, which are usually simplified or neglected, are taken into account and shown to affect the temperature and flux results. This study highlights the importance of a coupled evapotranspiration process model for the accurate assessment of the passive cooling effect of green roofs.     

Radon and moisture impacts from interventions integrated with housing energy retrofits

Energy retrofits can reduce air exchange, raising the concern of whether indoor radon and moisture levels could increase. This pre/post-intervention study explored whether simple radon interventions implemented in conjunction with energy retrofits can prevent increases in radon and moisture levels. Treatment homes (n = 98) were matched with control (no energy retrofits or radon intervention) homes (n = 12). Control homes were matched by geographic location and foundation type. t-tests were used to determine whether post-energy retrofit radon and moisture level changes in treatment homes significantly differed from those in control homes. The radon interventions succeeded in preventing statistically significant increases in first floor radon using arithmetic (p = 0.749) and geometric means (p = 0.120). In basements, arithmetic (p = 0.060) and geometric (p = 0.092) mean radon levels statistically significantly increased, consistent with previous studies which found that basement radon levels may increase even if first floor levels remain unchanged. Changes in infiltration were related to changes in radon (p = 0.057 in basements; p = 0.066 on first floors). Only 58% of the change in infiltration was due to air sealing, with the rest due to weather changes. There was no statistically significant association between air sealing itself and radon levels on the first floor (p = 0.664). Moisture levels also did not significantly increase.     

Electrochemical Impedance Spectroscopy as an Alternative to Determine Dielectric Constant of Potatoes at Various Moisture Contents

The dielectric (DE) properties, specifically the DE constant (ε′) and loss factor (ε′′), were measured for vacuum‐dried and freeze‐dried potato samples at a microwave frequency of 2.45 GHz over a range of different moisture contents (MCs) using a DE probe and also a 2‐probe electrochemical impedance spectroscopy (EIS). Third‐order polynomial models (ε′ = f₁(MC); and ε′′ = f₂(MC)) at room temperature were developed for regression analysis. Additionally, at various temperatures (T), biphasic 3rd‐order polynomial models (ε′ = f₁(MC, T); and ε′′ = f₂(MC, T)) were obtained to determine ε′ and ε′′ as a function of MC and T using measured data. The vacuum‐dried potato sample showed a good fitness of ε′ and ε′′ (R² = 0.95 and 0.96, respectively) to the regression model with the range of MCs from 18% to 80% (w/w), while the freeze‐dried potato sample showed a good fitness of ε′ and ε′′ to the 1st‐phase regression model with MC < 50% w/w (R² = 0.95 and 0.96, respectively) and the 2nd‐phase regression model with MC > 50% w/w (R² = 0.94 to 0.96). EIS measurements were also used to obtain correlation impedances for ε′ and ε′′ determined by the DE probe method. The resulted regression analysis meets the demands for simple, rapid, and accurate assessment for transient values of ε′ and ε′′ of food products during dehydration/drying processes. The EIS method was verified to be a successful alternative to direct measurements of ε′ and ε′′.     

保湿剂对鸭肉干品质改良的研究

针对肉干经常出现干硬、口感差、出品率低等问题,通过添加保湿剂对鸭肉干的品质进行了改良研究,结果表明:改善鸭肉干品质的最佳保湿剂组合为山梨醇0.20%,甘露醇0.20%,蔗糖0.15%.此配比具有良好的保湿性,它使肉干在不改变水分活度的条件下,能使水分含量提高将近7%,使肉干质地、口感、持香性均得到了很好的改善.     

DIFFUSION COEFFICIENTS FOR PREDICTING ROUGH RICE RE-WETTING BEHAVIOR

ABSTRACT

Thin-layer re-wetting experiments were conducted with medium grain rough rice in the temperature range of 17.8 to 45^°C and for relative humidities between 56 and 89.3%, with initial moisture contents in the range of 10.26 to 12.71% dry-basis to determine the diffusion coefficient of rough rice. Recent efforts to characterize the re-wetting characteristics of rough rice are summarized. New equation for temperature dependent liquid diffusion coefficients for medium grain rough rice are presented. The diffusion coefficient in re-wetting was lower than the drying. The results presented here, over typically five day re-wetting, will be useful in studying the longer term moisture transfer process occurring during ventilated storage.     

DRYING RATE AND TEMPERATURE PROFILE FOR SUPERHEATED STEAM VACUUM DRYING AND MOIST AIR DRYING OF SOFTWOOD LUMBER

Abstract

Two charges of green radiata pine sapwood lumber were dried, either using superheated steam under vacuum (90°C, 0.2 bar abs.) or conventionally using hot moist air (90/60°C). Due to low density of the drying medium under vacuum, the circulation velocity used was 10 m/s for superheated steam drying and 5.0 m/s for moist air drying, and in both cases, the flow was unidirectional. In drying, stack drying rate and wood temperatures were measured to examine the differences between the superheated steam drying and drying using hot moist air.

The experimental results have shown that the stack edge board in superheated steam drying dried faster than in the hot moist air drying. Once again due to the low density of the steam under vacuum, a prolonged maximum temperature drop across load (TDAL) was observed in the superheated steam drying, however, the whole stack dried slower and the final moisture content distribution was more variable than for conventional hot moist air drying. Wood temperatures in superheated steam drying were lower.     

用于木材粘接的反应型聚氨酯胶粘剂

本文讨论了反应型聚氨酯胶粘剂的配方及其在木材粘接中应用。重点讨论单组分液体型、热熔型和木材复合板粘接用反应型、湿气固化聚氨酯胶粘剂。     

成型工艺条件对铈锆铝复合载体性能的影响

采用压缩成型法对铈锆铝复合载体进行了放大制备,考察放大制备过程中造粒粉含水量、成型压力、焙烧温度等成型工艺条件对载体机械强度、吸水量、密度、织构性质及晶相的影响。结果表明,造粒粉含水量是影响颗粒成型的主要因素,含水量过高,颗粒不能成型或容易层裂;成型压力是影响载体强度、吸水量、密度等机械性能的主要影响因素,适宜的成型压力有助于获得各项机械性能均衡的载体;焙烧温度是影响载体比表面积及晶相结构的关键因素。结合生产要求确定最佳工艺条件为造粒粉含水量为15%,半成品强度(7~9)N·mm-1,焙烧温度(800~900)℃。     

伊蒙粘土/炭黑/天然橡胶复合材料的性能研究

采用伊蒙粘土替代部分炭黑,研究伊蒙粘土用量对伊蒙粘土/炭黑/天然橡胶复合材料硫化特性、物理性能、动态力学性能和导热性能的影响。结果表明:随着伊蒙粘土用量增大,混炼胶的Payne效应减弱,最大转矩减小,正硫化时间缩短;硫化胶的耐热老化性能、气密性、抗冲击性能提高;添加5和7份伊蒙粘土的硫化胶物理性能和耐磨性能与未添加伊蒙粘土的硫化胶相当,且明显好于添加10和15份伊蒙粘土的硫化胶;伊蒙粘土可明显提高硫化胶的抗湿滑性能、减小滚动阻力。     

影响煤质快速灰分仪测定准确性的因素分析

针对洗煤灰分常规测定方法时间长,不能及时反映洗煤质量的问题,采用了XL-6338A快速煤质分析仪测定洗煤灰分。分析了该仪器测定灰分时影响其准确性的因素。通过各因素下该仪器测定数据与重量法测定数据的多次对比,得出把洗煤试样粒度控制在≤3mm、水分控制在≤10%、堆密度控制在每桶(2.53±0.05)kg,可得到较准确的灰分测定数据。