Multiscale Heat, Air and Moisture Modelling and Simulation

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A Study on Buoyancy Driven Turbulent Flow Associated with Radiation in Cavities Partially Filled with Blockages

Fluid flow and heat transfer in cavities partially filled with disconnected blockages is important in the design of a wide range of industrial and engineering applications such as thermal management of indoor environments, cooling of electronic panels, drying of agricultural products, stacking of items in cold storage etc. The flows in such confined spaces develop as a result of temperature and concentration gradient which is further complicated by the interactive effects of turbulence and radiation. The aims of this research are to explore the detailed heat transfer and flow field inside cavities partially filled with solid blockages and, in particular, to address the uncertainties associated with turbulence models, to quantify the influence of double diffusion and to study the effect of surface properties. To achieve the above aims, a systematic numerical investigation has been carried out by validating the computational results against reliable experimental data available in open literature. A selection of turbulence and radiation models has been employed to scrutinise the effects of the above flow physics. An experimental set up capable of establishing low Rayleigh number buoyancy driven flow in a rectangular cavity containing cylindrical blockages was designed and fabricated to obtain temperature data. A series of experiments was conducted to obtain reliable temperature distribution at various positions in the flow domain and on the surfaces of the blockages. This set up also allowed us to study the proximity effect of blockages which has not been reported elsewhere. It has been found that the choice of turbulence model remains to be an important issue and should be given due consideration for natural convection flow with a high Rayleigh number. The results from the parametric study on the specification of passive thermal boundary conditions reveal that the experimental temperature profile is the most accurate boundary condition for passive walls in relation to the adiabatic and linear temperature profiles. Experimental benchmark temperature data evaluated at various positions in the cavity with and without blockages are presented and some of them are compared with CFD simulations. Finally, as an example of the application of the research methodology, a detailed numerical modelling was conducted on a Double-Skin-Façade which is known to reduce energy consumption in building and has become popular in recent years. The current methodology has been applied to establish a number of parameters in connection with the design and performance of DSF which are believed to be useful to practitioners

Heat Transfer

Over the past few decades there has been a prolific increase in research and development in area of heat transfer, heat exchangers and their associated technologies. This book is a collection of current research in the above mentioned areas and describes modelling, numerical methods, simulation and information technology with modern ideas and methods to analyse and enhance heat transfer for single and multiphase systems. The topics considered include various basic concepts of heat transfer, the fundamental modes of heat transfer (namely conduction, convection and radiation), thermophysical properties, computational methodologies, control, stabilization and optimization problems, condensation, boiling and freezing, with many real-world problems and important modern applications. The book is divided in four sections : "Inverse, Stabilization and Optimization Problems", "Numerical Methods and Calculations", "Heat Transfer in Mini/Micro Systems", "Energy Transfer and Solid Materials", and each section discusses various issues, methods and applications in accordance with the subjects. The combination of fundamental approach with many important practical applications of current interest will make this book of interest to researchers, scientists, engineers and graduate students in many disciplines, who make use of mathematical modelling, inverse problems, implementation of recently developed numerical methods in this multidisciplinary field as well as to experimental and theoretical researchers in the field of heat and mass transfer

Airflow patterns in ventilated wall cavities

Though heating, insulation, wall claddings and cavity-wall construction are considered as measures for remediating moisture and condensation in buildings, ventilation of wall cavities has however become a mantra among architects and other building professionals. Holes of any size and shape are made and located on building facades based on the accepted wisdom that a little air movement will keep the wall cavities dry. Whilst ventilation has been found to be successful in the control of moisture and condensation in rooms and larger enclosures, there is however insufficient understanding of how it works in thin spaces with high aspect ratios, such as the wall cavities studied in this thesis.In order to put in place good control and management practices in the remediation of moisture and condensation in vertical wall cavities by natural ventilation, it is vital to understand the dynamics of airflow in these cavities. In this thesis therefore, different size and shape of slots were employed to numerically investigate the effects of size, spacing and number of the slots on the characteristics of the velocity fields (patterns of airflow and distributions of velocity) in different cavity models. The Reynolds-Averaged-Navier-Stokes (RANS) methodology was employed to simulate the cavity flows under different modelling conditions using FLUENT. The BS 5925 model, an empirical relation for predicting ventilation rates in rooms and other larger enclosures, was employed and modified to predict ventilation rates in these cavities. Experimentally, the mapping of the airstreams in these cavities was obtained under similar reference (inlet) wind speeds employed for the numerical investigations.The results of this study show that there exists a potential at higher wind speeds for natural ventilation in the remediation of moisture and condensation in the cavities of vertical walls. The steady state approach employed in the RANS-based computation of cavity flows in this thesis averages out the peak values of air velocities and therefore gives no information about regions of maxima or minima velocity values even at higher wind speeds. This makes the predicted air change rates insensitive to the inlet air velocities from the ventilation slots and therefore makes the results more applicable for long term control and management of moisture in these cavities. In order to therefore put in place short, medium and long term plans for remediation of moisture in these wall cavities, a time-dependent computation is required. This will also allow the efficiency of the cavity ventilation to be properly assessed. Using the modified BS 5925 model, reasonable predictions were obtained for the air change rates of the wall cavities with the different size of ventilation slots employed. Close agreements are also obtained at lower and higher wind speeds between the predicted ventilation rates from the modified BS 5925 model and the experimental results employed as benchmark for validating the results.EThOS - Electronic Theses Online ServiceEnglish Heritage and Irish HeritageGBUnited Kingdo

Modelling of airflow and aerosol particle movement in buildings.

SIGLEAvailable from British Library Document Supply Centre-DSC:DX198075 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Identity of the Qingdao algal bloom

In early July 2008, news agencies worldwide reported on a vast algal bloom that was threatening the upcoming Olympic sailing events in Qingdao, China. The identity of the culpable alga, however, remained undiscussed. We have identified the alga that caused the bloom by means of morphological and molecular data, including sequence data of the plastid encoded large subunit ribulose 1,5-bisphosphate carboxylase gene (rbcL) and the nuclear encoded rDNA internal transcribed spacer (ITS) region. The bloom-forming alga falls within the morphological limits of the green seaweed Ulva prolifera O.F. Muller ('Enteromorpha prolifera (O.F. Muller) J. Agardh') but our phylogenetic analyses show that it forms a clade with representatives of the Ulva linza-procera-prolifera (LPP) complex. The Chinese rbcL sequences are identical to those of specimens collected from Japan, New Zealand, Finland and Portugal, suggesting that the taxon is widely distributed. rDNA ITS sequences showed a close affinity with Japanese isolates of the species complex. The Qingdao bloom is a typical illustration of a green tide, which occurs increasingly along several coasts worldwide

A Model for Complex Heat and Mass Transport Involving Porous Media with Related Applications

Heat and mass transfer involving porous media is prevalent in, for example, air-conditioning, drying, food storage, and chemical processing. Such applications require non-equilibrium heat and mass (or moisture) transfer modeling inside porous media in conjugate fluid/porous/solid framework. Moreover, modeling of turbulence and turbulent heat and mass transfer becomes essential for many applications. A comprehensive literature review shows a scarcity of models having such capabilities. In this respect, the objectives of the present thesis are to: i) develop a formulation that simulates non-equilibrium heat and mass transfer in conjugate fluid/porous/solid framework, ii) demonstrate the capabilities of the developed formulation by simulating complex related problems, and iii) extend the developed model to such class of problems that involve turbulence and turbulent heat and mass transfer. To develop the required formulation, we first specify transport equations for each region. In the fluid region, mass, momentum, energy, and water vapour transport equations are solved to model flow and energy of moist air-vapour mixture. The volume-averaged version of these equations form the model for the fluid-constituent of porous media, while the transport equations of energy and water mass fraction are solved inside the solid-constituent of porous media and solid region. Mathematical conditions are developed at all the interfaces to ensure smooth transport of relevant quantities across the interfaces. The developed formulation is demonstrated and validated by simulating the problems of evaporative cooling and convective drying of wet porous materials. In this respect, each simulated case demonstrates critical aspects of the developed formulation. Moreover, the simulated cases are found to be in excellent agreement with experimental data. The developed formulation is extended to turbulent flow regimes often encountered in heat and mass transfer problems related to food stacks. In this respect, the closure is obtained for the macroscopic turbulence and turbulent non-equilibrium heat and mass transfer model inside porous media composed of randomly packed spheres. The closure is obtained by simulating the problem at the pore-level scale of a bed of randomly-packed spheres. Lastly, the closure results are presented in the form of power law-based correlations to be utilized in the macroscopic model