Fluid flow and heat transfer in dual-scale porous media

Porous media are omnipresent in various natural and engineered systems. The study of transport phenomena in porous media has attracted the attention of researchers from a wide variety of disciplines. In many applications such as hydrogeology, petroleum engineering and thermochemistry, porous media are encountered, in which heterogeneity exists at a multitude of length-scales. In solar thermochemical reactors, a promising approach to accomplish the thermochemical cycle is to form the reactive solid into a porous structure to promote efficient solid-gas reactions through a high specific surface area, while simultaneously achieving desired transport characteristics. Recently, in light of the apparent trade-offs between rapid reaction kinetics and efficient radiation absorption, reticulated porous ceramics (RPCs) featuring dual-scale porosity have been engineered. These structures are capable of combining the desired properties, namely uniform radiative absorption and high specific surface area. Therefore, investigations are required to understand and analyse different transport phenomena in such structures. This dissertation is motivated by the need for understanding and analysing transport phenomena dual-scale porous media appear and used in many applications such as hydrogeology, petroleum engineering, chemical reactors, and in particular, energy technologies in high-temperature thermochemistry. The main objective of this thesis is to theoretically formulate and numerically demonstrate the fluid flow and heat transfer phenomena in dual-scale porous media. The theoretical and numerical results are used to propose models in forms of effective flow and heat transfer coefficients. The models are capable of estimating the fluid flow and heat transfer phenomena taking place in dual-scale porous media with appropriate fidelity and lower computational cost. The physical understanding of the models of transport phenomena in dual-scale porous structures allows us to tailor and optimise the morphology to accomplish optimal transport characteristics for the desired applications. To determine the flow coefficients, numerical simulations are performed for the fluid flow in a dual-scale porous medium. Two numerical procedures are considered. Firstly, we perform direct pore-level simulations by solving the traditional mass and momentum conservation equations for a fluid flowing through the dual-scale porous structure. Secondly, numerical simulations are performed at the Darcy level. For this purpose, the permeability and Forchheimer coefficient of the small-scale pores are numerically determined. Then, they are implemented in Darcy-level simulations in which the volume-averaged and traditional conservation equations are solved for the small- and large-scale pores, respectively. The results of the two approaches are separately used to determine and compare the permeability and Forchheimer coefficient of the dual-scale porous media. To analyse the energy transport phenomena in dual-scale porous media, a mathematical model is developed by applying volume-averaging method to the convective-conductive energy conservation equation to derive the large-scale equations with effective coefficients. The closure problems are introduced along with the closure variables to establish the closed form of the two-equation model for heat transfer of dual-scale porous media. The closure problems are numerically solved for specific cases of dual-scale porous medium consisting of packed beds of porous spherical particles. The effective coefficients appearing in the two-equation model of heat transfer in dual-scale porous media are determined using the solution of the closure problems. The velocity field in the dual-scale porous structure is calculated using the solution of the fluid flow simulations in dual-scale porous medium. Finally, "numerical experiment" is performed to qualitatively and quantitatively analyse the accuracy of the up-scaled model.The support by the Australian Research Council through Prof Wojciech Lipiński’s Future Fellowship, award no. FT14010121

A novel application for energy efficiency improvement using nanofluid in shell and tube heat exchanger equipped with helical baffles

Hydrothermal characteristics of the water–Al₂O₃ nanofluid are numerically evaluated in shell-and-tube heat exchanger equipped with helical baffles using the two-phase mixture model. Heat transfer and pressure drop increase by increasing nanoparticle concentration and baffle overlapping, and decreasing helix angle. At smaller helix angles, changing the overlapping is more effective on the convective heat transfer coefficient and the pressure drop. Neural network is used for modeling, and based on the test data, the model predicts the convective heat transfer coefficient and the pressure drop with MRE (Mean Relative Error) values of about 0.089% and 0.65%, respectively. In order to obtain conditions of effective parameters which cause maximum heat transfer along with minimum pressure drop, optimization is performed on the neural network model using both two-objective and single-objective approaches. 15 optimal states obtain from two-objective optimization. The results obtained from single-objective optimization indicate that even when a low pressure drop is significantly important for designer, nanofluids with high concentrations can be employed. Meanwhile, when both high heat transfer and low pressure drop are important, a small helix angle can be used. In addition, using large overlapping is recommended only when the heat transfer enhancement is considerably more important than the reduction of the pressure drop

Congenital Malaria in Newborns Presented at Tororo General Hospital in Uganda: A Cross-Sectional Study.

Despite recent large-scale investments, malaria remains a major public health concern. Few studies have examined congenital malaria, defined as the presence of malaria parasitemia within the first 7 days of life, in endemic areas. This study aimed to determine the prevalence, to describe the clinical presentation, and to examine factors associated with congenital malaria in newborns aged up to 7 days attending Tororo General Hospital in Uganda. A total of 261 mother/baby pairs were recruited in this cross-sectional study. Giemsa-stained thick blood smears for malaria parasites and rapid malaria diagnostic tests were performed on capillary blood samples from all newborns and mothers, as well as on placental and cord samples from newborns delivered in the hospital. The prevalence of congenital malaria in the newborns was 16/261 (6.1%). No single clinical feature was associated with congenital malaria. However, there were associations between congenital malaria and maternal parasitemia (P < 0.001), gravidity of one (P = 0.03), maternal age < 19 years (P = 0.01), cord blood parasitemia (P = 0.01), and placental malaria (P = 0.02). In conclusion, congenital malaria is not rare in Uganda and there are no obvious clinical features associated with it in the newborn. Based on these findings, we recommend strengthening malaria prevention during pregnancy to reduce the occurrence of congenital malaria in newborns

Malaria amongst febrile children: call for a pediatric malaria assessment tool

In 2017, malaria accounted for 435 000 deaths worldwide. Eleven percent (11%) of these deaths occurred in the Democratic Republic of Congo (DRC), where malaria continues to be a leading cause of morbidity and mortality. Children are amongst the most vulnerable to malaria, which causes 40% of childhood deaths in the country. Although many risk factors for developing malaria have been identified, there is a paucity of data available on the sociodemographic risk factors for pediatric malaria. A cross-sectional study including 131 febrile children aged 2 months to 14 years presenting to Heal Africa Hospital due to febrile illness. Guardians of participants answered a questionnaire about household and maternal characteristics, as well as child symptomatology. Malaria status was confirmed via blood smear. Results were analyzed using the chi-square test, likelihood ratios and a logistic regression. The absence of father as head of household (p=0.011) and gestational malaria (p=0.044) were significantly associated with pediatric malaria. This study provides insight into sociodemographic risk factors associated with pediatric malaria in the DRC. While further investigation is required, this study highlights the benefit of considering these factors when approaching the febrile child. A pediatric malaria assessment tool incorporating socio-demographics, symptoms and physical exam findings may guide investigations to reduce unnecessary testing and provide better patient-centred care

Barriers to access to holistic care for women victims of sexual violence in the eastern region of the Democratic Republic of Congo: A brief report

Synopsis: Sexual violence against women is a human rights violation and a major and serious problem for women's health

Modelling of Solar Thermochemical Reaction Systems

This article reviews the progress, challenges and opportunities in numerical modelling of thermal transport, thermochemical reactions and thermomechanics in high-temperature solar thermochemical systems. Continuum-scale models are presented in mathematical detail while highlighting the literature that uses them. The discussion is enhanced by selected examples of numerical studies of solar thermochemical systems for solar fuels and commodity material production. Property predictions necessary for the modelling of solar thermochemical reaction systems are covered

A New Method for Designing Lightweight S-boxes with High Differential and Linear Branch Numbers, and Its Application

Bit permutations are efficient linear functions often used for lightweight cipher designs. However, they have low diffusion effects, compared to word-oriented binary and MDS matrices. Thus, the security of bit permutation-based ciphers is significantly affected by differential and linear branch numbers (DBN and LBN) of nonlinear functions. In this paper, we introduce a widely applicable method for constructing S-boxes with high DBN and LBN. Our method exploits constructions of S-boxes from smaller S-boxes and it derives/proves the required conditions for smaller S-boxes so that the DBN and LBN of the constructed S-boxes are at least 3. These conditions enable us to significantly reduce the search space required to create such S-boxes. In order to make cryptographically good and efficient S-boxes, we propose a unbalanced-Bridge structure that accepts one 3-bit and two 5-bit S-boxes, and produces 8-bit S-boxes. Using the proposed structure, we develop a variety of new lightweight S-boxes that provide not only both DBN and LBN of at least 3 but also efficient bitsliced implementations including at most 11 nonlinear bitwise operations. The new S-boxes are the first that exhibit these characteristics. Moreover, we propose a block cipher PIPO based on one of the new S-boxes, which supports a 64-bit plaintext and a 128 or 256-bit key. Our implementations demonstrate that PIPO outperforms existing block ciphers (for the same block and key lengths) in both side-channel protected and unprotected environments, on an 8-bit AVR. The security of PIPO has been scrutinized with regards to state-of-the-art cryptanalysis