Modelling cavity ventilation behind brick veneer cladding : how reliable are the common assumptions?

Throughout the years, different numerical HAM-simulation tools have been developed to assess and predict the heat, air and moisture response of building components. But, though commercially available and commonly applied in building practice, still, several simplifications and shortcomings exist in the common models. Probably the most important one, is the fact that most tools neglect or strongly simplify air transport, focusing only on heat and moisture transport. Especially for the analysis of wood frame constructions, these simplified models may cause a large discrepancy between simulation results and real performance. This study aims at a comparison of the outcomes of numerical HAM -simulations for wood frame constructions with experimental data of real test cases. In particular, the focus of this paper is on cavity ventilation behind brick veneer. Therefore, a simplified version of a wood frame wall with brick veneer cladding is studied in this paper. Different common modelling assumptions are compared. Furthermore, a detailed measuring campaign has been conducted at the VLIET test building of the KU Leuven to validate the different modelling approaches. By verifying the results of the numerical simulations by the data of real test cases, the reliability of the modelling assumptions can be analysed. The results of this study clearly show that simplified assumptions on cavity ventilation in HAM-models might cause large discrepancies between simulation results and in-situ measurements

Rheological Model for Wood

Wood as the most important natural and renewable building material plays an important role in the construction sector. Nevertheless, its hygroscopic character basically affects all related mechanical properties leading to degradation of material stiffness and strength over the service life. Accordingly, to attain reliable design of the timber structures, the influence of moisture evolution and the role of time- and moisture-dependent behaviors have to be taken into account. For this purpose, in the current study a 3D orthotropic elasto-plastic, visco-elastic, mechano-sorptive constitutive model for wood, with all material constants being defined as a function of moisture content, is presented. The corresponding numerical integration approach, with additive decomposition of the total strain is developed and implemented within the framework of the finite element method (FEM). Moreover to preserve a quadratic rate of asymptotic convergence the consistent tangent operator for the whole model is derived. Functionality and capability of the presented material model are evaluated by performing several numerical verification simulations of wood components under different combinations of mechanical loading and moisture variation. Additionally, the flexibility and universality of the introduced model to predict the mechanical behavior of different species are demonstrated by the analysis of a hybrid wood element. Furthermore, the proposed numerical approach is validated by comparisons of computational evaluations with experimental results.Comment: 37 pages, 13 figures, 10 table

A rational approach to the harmonisation of the thermal properties of building materials

The Energy Systems Research Unit at the University of Strathclyde in Glasgow was contracted by the Building Research Establishment to review existing data-sets of thermo-physical properties of building materials and devise vetting and conflation mechanisms. The UK Chartered Institute of Building Services Engineers subsequently commissioned a project to extract a sub-set of these data for inclusion in Guide A, Section 3. This paper reports the project process and outcome. Specifically, it describes the source of existing data, comments on the robustness of the underlying test procedures and presents a new approach to data classification and conflation

Puidu kuivatuse kontrolli ja optimeerimise meetodite arendamine

A Thesis for applying for the degree of Doctor of Philosophy in Forestry.Väitekiri filosoofiadoktori kraadi taotlemiseks metsanduse erialal.The purpose of wood drying is to obtain material with the desired final moisture content. During the process, it is necessary to find a balance between the quality of the wood and the energy and time spent. In order to find an optimal solution, it is important to know the condition of the material to be dried at a specific time. Often, the standard equipment of an industrial kiln is not enough when implementing a new drying schedule. In addition, there is a need for software that simulates wood drying, providing the initial drying regime, which can then be further optimized using the methodologies and sensors presented in this study. This work checks the occurrence of theoretically simulated moistening impulse response in experiments based on synchronous surface displacement, temperature and surface moisture sensors. For this purpose, it was necessary to develop specific sensors used for wood monitoring in the wood dryer climate. A physically justified measurement result is guaranteed when using sensors based on different working principles. When investigating the reliability of the sensors, typical issues and practically usable measurement ranges below and above the saturation point of the wood fiber were identified. The transition of the surface layer of wood from the first phase of drying to the second phase of drying was investigated. It was found that the transition of the surface layer to the second drying phase slows down the diffusion rate in the inner layers of the wood, which otherwise could still be in the first phase of drying due to their moisture content. In order to characterize the influence of the diffusion constant of the surface layer on the inner layers, the concept of critical diffusion constant was defined. In the process of wood drying, individually calibrated carbon fiber needle-electrodes were used to record the moisture content of wood at different depths from the surface of the board being dried. When creating an optimized drying plan taking into account the critical diffusion constant, it was possible to significantly shorten the drying time of a typical industrial drying plan at the same final moisture content. The optimized drying schedule was characterized by a higher drying strain, which can level down by a timed moistening pulse. In this thesis, the relative humidity value of the critical drying air corresponding to the critical diffusion constant for pine wood was found. It is easy for a timber company to use this information to modify its drying schedules on site. An electrical indicator of maximum wood drying stresses was also developed. Since the electrical resistance method is mostly used for wood drying monitoring in practice, the hardware and software of the patented polarization-type moisture meter prototype were improved. Galvanostatic charging mode and depolarization voltage monitoring capability was added.Puidu kuivatamise eesmärgik on saada soovitud lõppniiskusega materjali. Protsessi käigus on vaja leida tasakaal puidu kvaliteedi, kulutatud energia ning aja vahel. Optimaalse lahenduse leidmiseks on oluline teada millises seisus on konkreetsel ajahetkel kuivatatav materjal. Sageli ei piisa tööstusliku puidukuivati standardvarustusest uue kuivatusplaani juurutamisel. Lisaks on vaja puidu kuivatamist simuleerivat tarkvara, mis annab esialgse kuivatusrežiimi, mida saab edasi optimeerida, kasutades käesolevas töös toodud metoodikaid ja andureid. Käesolevas töös on kontrollitud kas teoreetiliselt simuleeritud niisutusimpulsi reaktsioon ilmneb ka katses, tuginedes sünkroonselt pinna nihke-, temperatuuri-, ja pinnaniiskuse andurile. Selleks oli tarvis välja töötatada spetsiifilised puidukuivati kliimas puidu monitooringuks kasutatavad andureid. Erinevatel tööprintsiipidel põhinevate andurite kasutamisel on tagatud füüsikaliselt põhjendatav mõõtetulemus. Andurite töökindluse uurimisel selgitati välja tüüpilised probleemid ja praktikas kasutatav mõõtepiirkond alla ning üle puidu kiu küllastuspunkti. Uuriti puidu pinnakihi üleminekut kuivatuse esimesest faasist teise kuivatuse faasi. Leiti, et pinnakihi üleminek teise kuivatuse faasi aeglustab difusiooni kiirust ka puidu sisekihtides, mis muidu oma niiskusesisalduse poolest võiksid veel olla kuivatuse esimeses faasis. Pinnakihi difusiooni konstandi mõju iseloomustamiseks sisekihtidele defineeriti kriitilise difusiooni konstandi mõiste. Puidukuivatuse protsessis puidu niiskusesisalduse registreerimiseks kuivatatava laua pinnast erinevatel sügavustel kasutati individuaalselt kalibreeritud süsinikkiud nõel–elektroode. Kriitilise difusioonikonstandi arvesse võtmisega optimeeritud kuivatusplaani koostamisel õnnestus tüüpilise tööstusliku kuivatamise plaani kuivatuse aega oluliselt lühendada sama lõppniiskuse juures. Optimeeritud režiimi iseloomustasid mõnevõrra suuremad suhtelised pinged mis on tasandatavad ajastatud niisutusimpulsiga. Käesolevas väitekirjas leiti männipuidu jaoks kriitilisele difusiooni konstandile vastav kriitilise kuivatusõhu suhtelise niiskuse väärtus. Seda infot on puiduettevõtetel lihtne kuivatusplaanide modifitseerimiseks kasutada. Samuti töötati välja puidukuivatuse pingete maksimumi elektriline indikaator. Kuna puidukuivatuse monitooringuks kasutatakse praktikas valdavalt elektrilist takistusmeetodit siis täiustati patendeeritud polarisatsioon-tüüpi niiskusmõõturi prototüübi riistvara ja tarkvara

Analytical Modeling of Rheological Postbuckling Behavior of Wood-Based Composite Panels Under Cyclic Hygro-Loading

This study was conducted to develop analytical models to predict postbuckling behavior of woodbased composite panels under cyclic humidity conditions. Both the Rayleigh method and von Karman theory of nonlinear plate with imperfection were used to obtain a closed form solution to the hygrobuckling and postbuckling. In addition, mechano-sorptive creep effects were also taken into account for the derivation of analytical models. The closed-form solutions derived for both isotropic and orthotropic materials showed a good agreement with the experimental results in terms of the center deformation of hardboard, especially in the case of the edge movements. The unrecovery deformation was much greater at the first cycle and then decreased as the number of cyclic hygro-loading increased

Pyrolysis kinetics of hydrochars produced from brewer’s spent grains

The current market situation shows that large quantities of the brewer's spent grains (BSG)-the leftovers from the beer productions-are not fully utilized as cattle feed. The untapped BSG is a promising feedstock for cheap and environmentally friendly production of carbonaceous materials in thermochemical processes like hydrothermal carbonization (HTC) or pyrolysis. The use of a singular process results in the production of inappropriate material (HTC) or insufficient economic feasibility (pyrolysis), which hinders their application on a larger scale. The coupling of both processes can create synergies and allow the mentioned obstacles to be overcome. To investigate the possibility of coupling both processes, we analyzed the thermal degradation of raw BSG and BSG-derived hydrochars and assessed the solid material yield from the singular as well as the coupled processes. This publication reports the non-isothermal kinetic parameters of pyrolytic degradation of BSG and derived hydrochars produced in three different conditions (temperature-retention time). It also contains a summary of their pyrolytic char yield at four different temperatures. The obtained KAS (Kissinger-Akahira-Sunose) average activation energy was 285, 147, 170, and 188 kJ mol(-1) for BSG, HTC-180-4, HTC-220-2, and HTC-220-4, respectively. The pyrochar yield for all hydrochar cases was significantly higher than for BSG, and it increased with the severity of the HTC's conditions. The results reveal synergies resulting from coupling both processes, both in the yield and the reduction of the thermal load of the conversion process. According to these promising results, the coupling of both conversion processes can be beneficial. Nevertheless, drying and overall energy efficiency, as well as larger scale assessment, still need to be conducted to fully confirm the concept

Effect of curing conditions and harvesting stage of maturity on Ethiopian onion bulb drying properties

The study was conducted to investigate the impact of curing conditions and harvesting stageson the drying quality of onion bulbs. The onion bulbs (Bombay Red cultivar) were harvested at three harvesting stages (early, optimum, and late maturity) and cured at three different temperatures (30, 40 and 50 oC) and relative humidity (30, 50 and 70%). The results revealed that curing temperature, RH, and maturity stage had significant effects on all measuredattributesexcept total soluble solids

Smart Sensing Applications in the Agriculture and Food Industry

This chapter is structured in three main sections: an introduction to the smart concept and smart quality control, a review of the state of the art in integrated sensors, embedded systems, and the third one which is dedicated to a review of three case studies. The case studies refer to three results lines that are under taken by the LPF-TAGRALIA in the field of smart sensing. It provides examples of how to develop smart capabilities within standard low cost sensors. A variety of smart capabilities have been selected such as dynamic analysis of physical magnitudes, transmission diagnosis and such reliability and a full range of examples of analytical models of wood drying that can be incorporated to sensor chips to enhance sensor performs and to enable the term smart sensor. Each of the three sections of the chapter is independent and so the reader can decide where to start from according to their particular expertise. For unfamiliar readers with smart technologies, all of them might be of interest, while for experienced readers in the subject the case studies directly are probably the most relevant issue

Measuring and monitoring the moisture content of timber and investigation of sorption processes

A thesis submitted to the University Research Degree Committee in fulfilment of the requirements for the degree of Doctor of Philosophy in Science and Technology.There is little doubt that moisture is a very important factor in relation to material durability. The need for tools to assist in the better understanding and systematic evaluation of moisture movement with the view of incorporating the results within the overall framework of the defect investigation, quality control, and long-term monitoring of moisture, have led to the development of various moisture monitoring and predicting techniques. With the purpose of helping to harmonise the interests in this field, this thesis addresses three major issues in the area of wood moisture. Various studies carried out have been shown that there are substantial discrepancies between specific timber species and published charts for equilibrium moisture content. One of the main objectives of this research was to focus on establishing the equilibrium moisture content for a range of relative humidity and temperature on an individual basis, for twenty commercially important species used in the United Kingdom. The rationale for carrying out the project, the results from the initial trial and the mainstream experiment, the hardware and methodology developed are provided. To meet the requirements of long term accurate and reliable moisture monitoring and to provide comprehensive moisture information, a new type of moisture sensor and related measurement system were developed. The methodology of system design and test procedures are described, emphasising the anti-polarisation method, noise rejection and contact resistance reduction techniques employed. Other aspects of the electrical performance of timber were also investigated. Results from a case study showed that the sensor developed can operate in the critical range of relative humidity with sensitive and accuracy. In the final part of the project, two moisture transport models were developed. Mathematical prediction models in both one dimension and three dimensions are presented for simulating the adsorption and desorption processes in wood. Comparisons are made against long-term experimental data for the one dimensional model. The finite differential method was employed to solve the mathematical expressions developed, resulting in accurate prediction of concentration-driven moisture flows. Investigations were also carried out into the moisture diffusion coefficient and moisture behaviour in the three principal wood directions by using the sensor developed which provided isothermal real-time continuous data