Modelling of heat and moisture transfer in buildings: I. Model program

Integrated analysis of whole building heat, air and moisture transfer

• Heat and moisture transfer model was developed for fixed-bed column walnut drying. • Temperature and moisture distributions in the column and single walnuts were simulated. • Mechanisms of heat and moisture transfer during the drying process were discussed. • Good predictability achieved for drying under step-down temperature conditions. This research was conducted to better understand the mechanisms of heat and moisture transfer of walnuts during drying in a fixed-bed column dryer with heated air, and to develop a mathematical model to simulate this process. Drying experiments were performed under constant temperature and step-down temperature conditions (43, 55, 65 and 75 °C) with fixed air velocity of 0.7 m/s. The nonequilibrium transfers of liquid moisture, water vapor and heat within the single walnuts (both shell and kernel), as well as between the walnuts and drying air in the column were simulated and studied using a finite element method. The numerical results showed that the distribution of temperature and moisture content in the single walnuts played an important role in the heat and moisture transfer in the deep-bed column. The drying characteristics of walnuts were significantly affected by the non-uniformity of drying conditions surrounding the walnuts (particularly for air temperature and humidity) along the column heights. The predicted values of walnut moisture contents, temperatures, and air relative humidity at different column heights agreed well with the experimental values (R adj 2 > 0.972) under different drying conditions. This study established the theoretical basis for improving and optimizing the walnut drying process in deep-bed dryers. The developed mathematical model can be used to describe the drying characteristics and understand the mechanisms of walnuts drying in deep bed dryers.

Modelling of heat and moisture transfer in buildings: II. Applications to indoor thermal and moisture control

Moisture diffusivity and transfer modelling in dry biscuit

Heat and moisture transfer in wall-to-floor thermal bridges and its influence on thermal performance

Exact solutions of some nonlinear systems of partial differential equations by using the first integral method

Moisture transfer in porous construction materials car Nomenclature c Specific heat capacity [J.kg−¹.K−¹] g Moisture flow [kg.m−².s−¹] ries many causes for their degradation: mould devel opment and freeze-thaw damage are favoured by the gl,r Wind-driven rain [kg.m−².s−¹] −2 accumulation of water, and chemicals such as chloride ions and carbon dioxide may accelerate the fracturing of cementitious composites. Over time, microscopic and macroscopic cracks progressively develop under the effects of mechanical loading and sorption/desorption cycles: their influence is to be accounted for in long-term hygrothermal performance assessments of the building envelope. Current simulation codes for heat and moisture transfer modelling in building facades do not allow accounting for the presence of cracks and defects in the material layers. The present work aims at integrat I Solar irradiance [W.m ] Kl Liquid permeability [s] kf ,l Fracture liquid permeability [s] Lv Latent heat of vaporization [J.kg−¹] pc Capillary pressure [Pa] pv Vapour pressure [Pa] q Heat flow [W.m−²] RH Relative humidity Rh Horizontal rainfall [mm.m−²] T Temperature [K] U Wind speed [m.s−¹] u Crack aperture [m] −3 ing such effects of damage in simulations at the scale of building facades. Experimental measurements of crack patterns were integrated into a newly developed w Moisture content [kg.m ] Greek symbols α Heat transfer coefficient [W.m −2.K−1] numerical model predicting coupled heat and moisture transfer in multi-layered components. The consequences of fractures on the hygrothermal performance of these components were then investigated by comparing damaged and undamaged materials in a series of simulation cases. Cracks were found to accentuate the amplitude of daily sorption/desorption cycles and moisture accumulation in the walls, particularly in case of impacting rain. Their impact on the overall thermal performance is small, although not negligible in case of water infiltration towards an insulation layer.

The work presents the analysis of the free boundary value problem related to the one-dimensional invasion model of new species in biofilm reactors. In the framework of continuum approach to mathematical modelling of biofilm growth, the problem consists of a system of non-linear hyperbolic partial differential equations governing the microbial species growth and a system of semi-linear elliptic partial differential equations describing the substrate trends. The model is completed with a system of elliptic partial differential equations governing the diffusion and reaction of planktonic cells, which are able to switch their mode of growth from planktonic to sessile when specific environmental conditions are found. Two systems of non-linear differential equations for the substrate and planktonic cells mass balance within the bulk liquid are also considered. The free boundary evolution is governed by a differential equation that accounts for detachment. The qualitative analysis is performed and a uniqueness and existence result is presented. Furthermore, two special models of biological and engineering interest are discussed numerically. The invasion of Anammox bacteria in a constituted biofilm inhabiting the deammonification units of the wastewater treatment plants is simulated. Numerical simulations are run to evaluate the influence of the colonization process on biofilm structure and activity.

For a class of nonlinear systems of partial differential equations of high order in a cylindrical domain the following boundary value problem is considered: Cauchy-type conditions are prescribed on the upper and lower bases of the cylinder, and a Robin-type condition is prescribed on the lateral part of the boundary. This boundary value problem is reduced in an equivalent way to a nonlinear functional equation in a certain subspace of the Sobolev space. Under certain assumptions about the nonlinear terms an a priori estimate is obtained for the solution of the problem in question and the existence of the solution is established, while in the case when these conditions fail, the absence of a solution is established. The question of uniqueness is also discussed for the solution. Bibliography: 18 titles.

Existence of series solutions for certain nonlinear systems of time fractional partial differential equations

This paper deals with the numerical and analytical modelling of two-dimensional heat and moisture transfer during drying of a spherical object. Drying is considered to be a process of simultaneous heat and moisture transfer whereby moisture is vapourized by means of a drying fluid (e.g. air), as it passes over a moist object. Numerical modelling of two-dimensional heat and moisture transfer during drying of a spherical object is carried out using an explicit finite-difference approach. Temperature and moisture distributions inside the object are determined by using the developed computer code. Moreover, the results predicted from the present model are compared with the experimental data available in the literature and a considerably high agreement is found. Copyright © 2003 John Wiley & Sons, Ltd.

Purpose Building envelopes are crucial elements that control the quality of indoor building environments. There has been a lack of focus on developing a sustainable building envelope for tropical climates. This study aims to evaluate the indoor thermal comfort performance of passive building envelope typologies modelled for tropical climates. Design/methodology/approach This study adopted an experimental research strategy by modelling cavity and non-cavity building envelope prototypes. Structural equation modelling and regression analysis techniques were employed to investigate the relationship between indoor environmental quality and outdoor environmental factors for various building envelope typologies. Findings This study revealed that cavity and non-cavity building envelope prototypes have different influences on indoor environmental parameters. External environmental elements, such as air pressure, wind speed, cloudiness, air quality, temperature, precipitation and humidity, influence the building envelope system to maintain or destabilise a sustainable indoor environment. Practical implications Building codes and standards for the construction industry should consider the influence of external environmental conditions on indoor environmental quality. Furthermore, building design teams will find the research findings useful in their efforts to achieve sustainable designs by relying on the building envelope to achieve thermal comfort, rather than relying on artificial means. Social implications Improvements in indoor environmental quality lead to enhanced health and well-being among occupants. Originality/value This study is one of the pioneering research works in the tropical region that proposes using the building envelope as a passive design means to attain a sustainable indoor environment by experimenting with two different modelled wooden building envelope typologies.

This paper reports the development of a mathematical model of moisture and heat transfer coupled with phase change materials (PCM) in porous textiles. On the basis of a finite volume difference scheme, the thermal buffering effect of PCM is simulated. The distributions of temperature and moisture concentration in porous textiles with PCM are numerically computed by this technique. For comparison, the distributions of temperature and moisture concentration in porous textiles without PCM are also numerically computed. A series of experiments measuring a fabric's surface temperature with PCM is conducted to validate the model, and there is reasonable agreement between the predictions and the measurements. The results indicate that this model is satisfactory.

A design method of finite dimensional nonlinear disturbance observer based control (NLDOBC) is proposed for a class of nonlinear dissipative partial differential equation (PDE) systems, where the disturbance is modeled by an exosystem of nonlinear ordinary differential equations (ODEs). Motivated by the fact that the dominant structure of the dissipative PDE is usually characterized by a finite number of degrees of freedom, the modal decomposition technique is initially applied to the PDE system to give a slow subsystem of low dimensional nonlinear ODEs. By using the nonlinear slow subsystem and exosystem, a nonlinear disturbance observer (NLDO) is constructed to estimate the disturbance. Then, on the basis of NLDO, an NLDOBC method is proposed in terms of linear matrix inequality (LMI) to ensure the exponential stability of the closed-loop PDE system in the presence of the modeled disturbance. Finally, the simulation results on control of one dimensional Fisher diffusion-reaction system show the effectiveness of the proposed method.

The purpose of this paper is to present a numerical model of coupled heat, moisture transfer and their effects on the porosity changes of soil during the freezing process. Coupling among heat, moisture, and mechanical deformations is solved based on finite element method. The equilibrium equations of freezing process are investigated based on segregation theory. The numerical model is applied to a 2D problem of a laboratory frost heave test. Numerical simulation reveals the porosity characters during the freezing process. The frost depths and deformations also the porosity in consideration of the orthotropic properties of frozen soil is discussed.