Modeling Water Adsorption and Retention of Building Materials From Pore Size Distribution

Water adsorption and capillarity are key phenomena involved during heat and moisture transfer in porous building materials.They account for interaction between solid matrix,liquid water and moist air.They are considered through Water Vapor Adsorption Isotherm(WVAI)and Retention Curve(RC)functions which are constitutive laws characterizing water activity within a porous medium.The objective of this paper is to present a water vapor adsorption and retention models built from multimodal Pore Size Distribution Function(PSDF)and to see how its parameters modify moisture storage for hygroscopic and near saturation ranges.The microstructure of the porous medium is represented statistically by a bundle of tortuous parallel pores through its PSDF.Firstly,the influence of contact angle and temperature on storage properties were investigated.Secondly,a parametric study was performed to see the influence of the PSDF shape on storage properties.Three cases were studied considering the number of modalities,the weight of each modality and the dispersion around mean radius.Finally,as a validation,the proposed model for WVAI were compared to existing model from literature showing a good agreement.This study showed that the proposed models are capable to reproduce various shapes of storage functions.It also highlighted the link between microstructure and adsorption-retention phenomena.

Modeling the Synergetic Effect of Various Factors on Chloride Transport in Nonsaturated Concrete

Diffusion has been systematically described as the main mechanism of chloride transport in reinforced concrete（RC） structure, especially when the concrete is in a saturated state. However, the single mechanism of diffusion is not able to describe the actual chloride ingress in the nonsaturated concrete. Instead, it is dominated by the interaction of diffusion and convection. With the synergetic effects of various factors taken into account, this study aimed to modify and develop an analytical convection- diffusion coupling model for chloride transport in nonsaturated concrete. The model was verified by simulation of laboratory tests and field measurement. The results of comparison study demonstrate that the analytical model developed in this study is efficient and accurate in predicting the chloride profiles in the nonsaturated concrete.

Model-based investigation on building thermal mass utilization and flexibility enhancement of air conditioning loads

Building air conditioning systems(ACs)can contribute to the stable operation of power grids by participating in peak load shaving programs,but the participants need a fast and accurate zone temperature prediction model,e.g.,the detailed room thermal-resistance(RC)model,to improve peak shaving effect and avoid obvious thermal discomfort.However,when applying the detailed room RC model to multi-zone buildings,conventional studies mostly consider the heat transfer among neighboring rooms,which contributes little to the prediction accuracy improvement,but leads to complicated model structure and heavy computation.Thus,a distributed RC model is developed for multi-zone buildings in this study.Compared to conventional models,the proposed model considers the total heat transfer between the building and the air,and ignores the heat transfer among indoor air in neighboring rooms through internal walls with heavy thermal mass,thereby having comparable temperature prediction accuracy,simpler structure,and stronger robustness.Based on the model,the effectiveness of passive pre-cooling strategies in reducing the air conditioning loads during peak periods is investigated.Results indicate that the thermal insulation performance of opaque building envelope is quite important to the flexibility enhancement of air conditioning loads.With an uninsulated building envelope,passive pre-cooling is useless for the peak load shaving.In comparison,well insulated opaque building envelope enables the building thermal mass to be utilized through passive pre-cooling,which leads to the air conditioning loads during peak periods being further reduced by about 12%.

Influence of stealth aircraft dynamic RCS peak on radar detection probability

For modern stealth aircraft,it is important to analyze the influence of Radar Cross Section(RCS)peak exposure on penetration for guiding stealth design and penetration trajectory planning,which needs to reflect the RCS statistical uncertainty and the RCS difference with the change of incident angle.Based on the RCS characteristics of typical stealth aircraft,this paper established a simplified RCS dynamic fluctuation statistical model with the parameters log mean and log standard deviation.According to the detection probability algorithm in radar signal processing field,this paper built the algorithm of radar detection probability based on the RCS dynamic fluctuation statistical model.The analysis of examples concluded that the key to successful penetration is to shorten the RCS peak exposure time,which can be reduced by decreasing the RCS peak width or increasing velocity.Based on the conclusion,this paper proposed the method of turning maneuvering to reduce RCS peak exposure time dramatically.

Frequency equation for the submicron CMOS ring oscillator using the first order characterization

By utilizing the first order behavior of the device,an equation for the frequency of operation of the submicron CMOS ring oscillator is presented.A 5-stage ring oscillator is utilized as the initial design,with different Beta ratios,for the computation of the operating frequency.Later on,the circuit simulation is performed from 5-stage till 23-stage,with the range of oscillating frequency being 3.0817 and 0.6705 GHz respectively.It is noted that the output frequency is inversely proportional to the square of the device length,and when the value of Beta ratio is used as 2.3,a difference of 3.64%is observed on an average,in between the computed and the simulated values of frequency.As an outcome,the derived equation can be utilized,with the inclusion of an empirical constant in general,for arriving at the ring oscillator circuit’s output frequency.