Simulation of coupled heat and moisture transfer in air-conditioned buildings

The simultaneous heat and moisture transfer in the building envelope has an important influence on the indoor environment and the overall performance of buildings. In this paper, a model for predicting whole building heat and moisture transfer was presented. Both heat and moisture transfer in the building envelope and indoor air were simultaneously considered; their interactions were modeled. The coupled model takes into account most of the main hygrothermal effects in buildings. The coupled system model was implemented in MATLAB-Simulink, and validated by using a series of published testing tools. The new program was applied to investigate the moisture transfer effect on indoor air humidity and building energy consumption under different climates. The results show that the use of more detailed simulation routines can result in improvements to the building's design for energy optimisation through the choice of proper hygroscopic materials, which would not be indicated by simpler calculation techniques.     

Changes in phytate and minerals during germination and cooking of fenugreek seeds

The effects of germination, cooking and roasting on the phytic acid content, total phosphorus, water soluble inorganic phosphorus and mineral content of fenugreek seeds have been estimated. After 96 h germination, the dry weight of fenugreek seeds decreased while total ash content increased. Phytase and phosphatase activity of the ungerminated and germinated seeds have been assayed. It is observed that during germination the phytic acid values diminish and the water soluble inorganic phosphorus values increase. Phytase activity which is absent in the ungerminated seeds originates after germination and the phosphatase activity is increased in the germinated seeds. Heat treatment practised in cooking and roasting fenugreek seeds has less effect on phytate elimination than does germination. Changes in calcium, magnesium, iron, manganese, copper and zinc are found to be dependent on the loss of dry weight which occurs during processing of fenugreek seeds.     

Preliminary studies on the mucilages extracted from Okra fruits,Taro tubers,Jew's mellow leaves and Fenugreek seeds

Okra fruits, Taro tubers, Jew's mellow leaves and Fenugreek seeds are commonly used in Egypt to prepare popular diets with desired slimy consistency.The mucilages were extracted and preliminary studies conducted to characterise them physically. The pH values of a 1% solution of the mucilages varied from 6·9-7·5 for Okra and Taro, 7·1–7·8 for Jew's mellow, and 5·9-6 for Fenugreek, depending upon extraction conditions. The highest viscosity was observed in Okra solutions, followed by Fenugreek, Jew's mellow and Taro mucilages. Okra and Jew's mellow mucilages are acidic polysaccharides which contain higher amounts of ash than the Taro and Fenugreek mucilages which are neutral polysaccharides. All mucilages are associated with protein. Gel chromatography indicated strong interaction of protein with the polysaccharide. The acid hydrolysis of the mucilages followed by paper chromatography revealed that all mucilages contain methyl pentose, glucose, galactose, and fructose, in different proportions. Taro and Fenugreek mucilages are free of rhamnose. All mucilages are devoid of arabinose and mannose except Fenugreek which contained these two sugars.     

Hygrothermal behavior modeling of the hygroscopic envelopes of buildings: A dynamic co-simulation approach

High levels of humidity in buildings lead to building pathologies. Moisture also has an impact on the indoor air quality and the hygrothermal comfort of the building’s occupants. To better assess these pathologies, it is necessary to take into account the heat and moisture transfer between the building envelope and its indoor ambience. In this work, a new methodology was developed to predict the overall behavior of buildings, which combines two simulation tools: COMSOL Multiphysics© and TRNSYS. The first software is used for the modeling of heat, air and moisture transfer in multilayer porous walls (HAM model: Heat, Air and Moisture transfer), and the second is used to simulate the hygrothermal behavior of the building (BES model: Building Energy Simulation). The combined software applications dynamically solve the mass and energy conservation equations of the two physical models. The HAM-BES coupling efficiency was verified. In this paper, the use of a coupled (HAM-BES) co-simulation for the prediction of the hygrothermal behavior of building envelopes is discussed. Furthermore, the effect of the 2D HAM modeling on relative humidity variations within the building ambience is shown. The results confirm the importance of the HAM modeling in the envelope on the hygrothermal behavior and energy demand of buildings.     

Assessment of temperature gradient effects on moisture transfer through thermogradient coefficient

The objective of this paper is to describe moisture transfer through porous material due to temperature gradient. For that purpose, an experimental device was set up to assess moisture flux under isothermal and non-isothermal conditions. This involves placing samples between two compartments with controlled air conditions and monitoring relative humidity and temperature profiles inside the samples over the time. To interpret these results, we proposed to express the mass flux in terms of two driving potentials: water vapor content gradient and temperature gradient. Accordingly, thermogradient coefficient was calculated and discussed. It represents the difference between the moisture fluxes under isothermal and non-isothermal conditions. The impact of temperature gradient on the moisture buffer value (MBV) was also considered through a numerical experiment taking into account thermogradient coefficient. Results show that temperature gradient implies a relative variation of the MBV for about 14%. Thus, it would be better to consider non-isothermal conditions for its assessment.     

Modeling of water spray evaporation: Application to passive cooling of buildings

The use of water droplet evaporation in shower towers and passive downdraft evaporative cooling needs the estimation of the time needed to completely evaporate the drops. To solve this problem, a cellular approach is proposed in which the spray is considered as a pile of rigid spheres of equal size; each sphere has multiple layers and contains a drop in its center. The evaporation takes place gradually from the superficial layer towards the internal layers. Parametric studies show the influence of each variable on the evaporation time of the droplets. The model may be used for sizing passive evaporative cooling systems and towers for buildings using the passive evaporative down draught effect. A building equipped with a shower tower has been tested in the framework of the European project PDEC/JOULE in Catania (Italy). The spraying system was successfully sized by using the model proposed in this paper.     

Trypsin inhibitor activity in vicia faba beans

Extracts of mature green, dry and germinated Vicia faba beans depressed the trypsin activity of casein. Germination of Vicia faba beans (for 60 h) lowered the trypsin inhibitor (TI) activity. 0.171M Saline was the most efficient extractant for the TI. Minimal amounts of the TI were extracted in the pH range 4 to 5. The TI of Vicia faba beans was undialysable. The inhibitor activity originated in the seeds at the beginning of pod formation and increased with development of maturity. TI was active only towards trypsin and inactive towards papain, rennin and pepsin. Chromatographing Vicia faba bean proteins, possessing antitryptic activity, on a column of DEAE-cellulose yielded six peaks, all of which possessed antitryptic activity.