我們主要研究了多孔體系在乾燥過程中的兩個現象: 一是裂縫行為，二是污染相在孔隙間的擴散特點、機理以及收集污染相、解決污染問题的方法。 / 在本文的第一部分中，我們用共聚焦顯微鏡觀察到了膠體懸浮體系在溶劑揮發時產生裂縫。我們尋找到一個可令裂縫完全消除的辦法：加入乳液到膠體體系後，裂縫的數量減少；當乳液達到一定濃度時，裂縫完全被消除。同時我們也發現加入乳液帶給體系的另一效應：空氣進入體系的速度也發生改變，從而實現了乾燥速度可控。通過用流變儀研究樣品的基本力學性質，我們找出了裂縫數量減少的根本原因。我們的方法可同時有效地控制裂縫數量和體系乾燥速度，因而在許多涉及到多孔體系乾燥或裂縫的工業過程中有潛在的應用。 / 在本文的第二部分中，我們受到石油洩漏污染海灘的啟發，研究了污染相在多孔體系里的擴散特點及機理，並在此基礎上設計了有效的處理方案。我們搭建了一個小尺度的系統來模擬石油滲入沙灘的過程，記錄了隨著海水沖洗次數的增加污染相在多孔體系里的分佈變化。我們發現不論是親水還是疏水的多孔體系，在幾次海水沖刷週期后，污染相都有了明顯的擴散；但是對於不同的體系，污染相呈現出不同的分佈和擴散特點。通過分析小孔尺度上體系內部的壓強分佈，我們很好地解釋了造成這種不同的基本原因。最後我們尋找到兩種可令污染相集中的方法，這對解決實際污染問题有一定的幫助。 / We study two interesting phenomena occurred during the evaporation of solvent in porous medium: first, the cracking behavior; and second, the expanding mechanism and the collecting methods of the non-evaporative phase. / In the first part of this thesis, we visualize the cracking behavior of colloidal suspensions during drying by a confocal microscope. We develop an effective method which can completely eliminate cracking during drying: by adding emulsion droplets into colloidal suspensions, we can systematically decrease the amount of cracking, and eliminate it completely above a critical droplet concentration. We also find another effect that the emulsion droplets can bring: it varies the speed of air invasion and provides a powerful method to adjust drying rate. Besides, we investigate the samples’ fundamental mechanical properties with a rheometer and clarify the underlying physical mechanism for the decreasing of crack amounts. With the effective control over cracking and drying rate, our study may find important applications in many drying and cracking related industrial processes. / In the second part of the thesis, we conduct a study on the expanding mechanism and collecting methods of the non-evaporative phase in porous medium, which is inspired by a practical pollution problem that occurs when oil spills to the sandy beach. We build a system in a smaller scale to mimic the practical pollution and investigate the distribution change of the polluting phase as the flushing cycle increases. We find an obvious expansion of the polluting phase after several flushing cycles in both hydrophilic and hydrophobic porous media, but with different distributions and expanding behaviors. We explained this difference by analyzing the pressure distribution in the system at the pore level. Finally, we develop two methods to concentrate the polluting phase in some particular regions, which is beneficial to collect and solve the practical pollution problem. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Jin, Qiu = Duo kong ti xi lie feng he you ru qin de yan jiu / Jin Qiu. / Thesis (Ph.D.) Chinese University of Hong Kong, 2014. / Includes bibliographical references (leaves 62-67). / Abstracts also in Chinese.

Phase Change Materials (PCM) absorb and release heat at preset temperatures. Due to their relatively high values of latent heat, they are capable of storing and releasing large amounts of energy during phase change. When a PCM is in its solid phase, it will absorb heat as the external temperature rises. The temperature of the PCM will mirror the external temperature until the melting point of PCM is reached. At this stage, the PCM will begin to melt with almost no change in its temperature. PCM plays an opposite role when the external temperature drops. It releases the stored energy back while going through phase change from liquid phase to solid phase. The present work is a numerical study towards fundamental understanding of the impact of using PCM on enhancement of heat and mass transfer in several scenarios. A numerical analysis has been carried out to determine the impact of presence of PCM on the insulating characteristics of paper board packaging. Two different cases of a layered PCM and uniformly dispersed PCM within the packaging wall are considered. The numerical results illustrate significant reduction in exchange of heat between the exterior and the interior of the packaging. Specifically, the unique concept of utilizing PCM in drying of paper is proposed and a numerical investigation is performed to determine the corresponding transport characteristics. The results indicate that the PCM acts as a heat source and a heat sink alternatingly throughout the conventional paper drying process, enhancing the drying energy efficiency. This study also included presence of gas-fired infrared emitters in the drying process as well for which the spectral absorption coefficient of PCM was measured and incorporated into the theoretical model. Finally, the impact of the presence of PCM in convective air-drying of moist paper is numerically investigated. The hot air ow is generated by an in-line jet nozzle. The air impinges on the exposed surface of the moist paper while the other side is considered to be perfectly insulated. The results provide the corresponding air flow field as well as air temperature distribution in between the nozzle exit and the surface of the moist paper. The results also reveal the enhancement of drying rates with PCM, fundamentally confirming the role of PCM on enhancing the energy efficiency of convective drying of moist paper.

Saving energy is considered about by much more people nowadays. The energy use of industrial drying occupies a large part of total energy usage. Not only the governments, but also the industry owners are trying to find ways to cut down the usage of energy. The aim of this work is to find suitable technologies for industrial drying of berries which can be energy-efficient at the same time. More specifically, to find suitable dryers for drying aronia berry in Sweden. The research is based on secondary data collected by literature review. Good options for other circumstances like fluidized bed drying, freeze drying and solar drying were not discussed in detail. After the study, a continuous hot air dryer with explosion puffing system and heat pumping system seems to be the best solution for drying aronia berry in Sweden. It is easy to be controlled, cost acceptable (both capital and operational costs), environmental friendly and has high drying rate and high product quality. The extra means for improve drying process such as combined with dielectric or conductive dryer, adding pre-treatment such as osmotic drying were also discussed. Combined dryers can reduce the drying time and osmotic drying can cut the operation cost. Careful experiments shall be done before large amount of investment due to the complexity of dehydration.

Conical fluidized bed dryers are widely used in the pharmaceutical industry due to their high heat and mass transfer characteristics. Despite their widespread use, very little is known about the hydrodynamics of conical fluidized bed dryers. Wet pharmaceutical granule has high moisture content and wide particle size distribution (PSD), which can lead to poor mixing and non uniform drying. Uneven moisture content in the final product can adversely affect the quality and shelf life of these high value drugs. Previous studies on the conical fluidized bed dryers focused on the study of the gas phase, however motion of particulate phase has never been studied. Particle tracking is an important tool to study the motion of the particulate phase. Two particle tracking techniques were developed and used to study the motion of the particulate phase in a conical fluidized bed dryer. The first technique was radioactive particle tracking (RPT) which was developed at the University of Saskatchewan laboratory for a vessel having conical geometry. Experiments were conducted using dry pharmaceutical granule and during the actual drying of wet pharmaceutical granule. Two radioactive tracers of different sizes (1.6 to 2.6 mm) were tracked in each set of experiments to determine the effect of particle size on particle motion and particle mixing. Superficial gas velocities of 1, 1.5, 2 and 2.5m/s were used in dry bed studies to quantify the effect of superficial gas velocity. The second particle tracking technique was developed at the labs of Merck Frosst Canada Inc. Movies were captured using a high speed video camera coupled to a borescope and then analyzed off-line using image analysis software.Three powders having mean particle diameters of 774, 468 and 200 microns were used. Experiments were conducted at superficial gas velocities of 1.5, 2 and 3 m/s. <p>RPT revealed that there is a distinct circulation pattern of the particulate phase. Particles move upwards at high velocities near the centre of the bed and fall slowly near the walls. Furthermore, most of the gas flow is concentrated near the centre of the bed and the circulation pattern was observed at all the superficial gas velocities. Particle size of the tracer particle and PSD of the bed material had an appreciable impact on particle mixing with bigger particles exhibiting higher segregation tendencies than the smaller ones in the case of dry granule having a broad PSD. Particle segregation due to size difference was more pronounced at a superficial gas velocity of 1 m/s. However, segregation decreased with an increase in superficial gas velocity. During drying of wet granule, particle mixing and motion of the tracer particle was poor during the first 7 minutes of drying suggesting that most of the gas flow was concentrated near the centre of the bed. Particle mixing and average particle speeds increased considerably when the moisture content in the granule was less than 18 wt% suggesting a change in the hydrodynamics of the bed with the gas being more evenly distributed throughout the bed. Image analysis of high speed movies also suggested that a dilute region existed at the center of the bed. These observations were in agreement with the observations made by RPT.

Conical fluidized bed dryers are widely used in the pharmaceutical industry due to their high heat and mass transfer characteristics. Despite their widespread use, very little is known about the hydrodynamics of conical fluidized bed dryers. Wet pharmaceutical granule has high moisture content and wide particle size distribution (PSD), which can lead to poor mixing and non uniform drying. Uneven moisture content in the final product can adversely affect the quality and shelf life of these high value drugs. Previous studies on the conical fluidized bed dryers focused on the study of the gas phase, however motion of particulate phase has never been studied. Particle tracking is an important tool to study the motion of the particulate phase. Two particle tracking techniques were developed and used to study the motion of the particulate phase in a conical fluidized bed dryer. The first technique was radioactive particle tracking (RPT) which was developed at the University of Saskatchewan laboratory for a vessel having conical geometry. Experiments were conducted using dry pharmaceutical granule and during the actual drying of wet pharmaceutical granule. Two radioactive tracers of different sizes (1.6 to 2.6 mm) were tracked in each set of experiments to determine the effect of particle size on particle motion and particle mixing. Superficial gas velocities of 1, 1.5, 2 and 2.5m/s were used in dry bed studies to quantify the effect of superficial gas velocity. The second particle tracking technique was developed at the labs of Merck Frosst Canada Inc. Movies were captured using a high speed video camera coupled to a borescope and then analyzed off-line using image analysis software.Three powders having mean particle diameters of 774, 468 and 200 microns were used. Experiments were conducted at superficial gas velocities of 1.5, 2 and 3 m/s. <p>RPT revealed that there is a distinct circulation pattern of the particulate phase. Particles move upwards at high velocities near the centre of the bed and fall slowly near the walls. Furthermore, most of the gas flow is concentrated near the centre of the bed and the circulation pattern was observed at all the superficial gas velocities. Particle size of the tracer particle and PSD of the bed material had an appreciable impact on particle mixing with bigger particles exhibiting higher segregation tendencies than the smaller ones in the case of dry granule having a broad PSD. Particle segregation due to size difference was more pronounced at a superficial gas velocity of 1 m/s. However, segregation decreased with an increase in superficial gas velocity. During drying of wet granule, particle mixing and motion of the tracer particle was poor during the first 7 minutes of drying suggesting that most of the gas flow was concentrated near the centre of the bed. Particle mixing and average particle speeds increased considerably when the moisture content in the granule was less than 18 wt% suggesting a change in the hydrodynamics of the bed with the gas being more evenly distributed throughout the bed. Image analysis of high speed movies also suggested that a dilute region existed at the center of the bed. These observations were in agreement with the observations made by RPT.

No description available.

No description available.

Ph.D.

Sanitation is fundamental to reducing disease and sustaining a high standard of living. The evolution of sewer systems and the modern engineering of wastewater treatment plants work to decrease health risk and manage environmental concerns associated with the reuse and disposal of treated effluent and solid wastes generated as byproducts. The recycling of treated solid wastes (biosolids) continues to be an environmental challenge due to the shear volume produced, and its potentially hazardous composition. Solar drying of biosolids was studied in semi-arid regions as a sustainable method for reducing pathogens. The initial studies were performed with no intervening treatments. Average fecal coliform inactivation rates for digested biosolids during summer experiments were determined to be 0.17 ± 0.03/day⁻¹ and 0.17 ± 0.04/day⁻¹, respectively. Salmonella inactivation rates in aerobically digested biosolids were 0.11 ± 0.08 day⁻¹ and 2.0 ± 2.0 day⁻¹ for aerobically and anaerobically digested biosolids, respectively for the summer seasons. Solar drying during warm dry seasons was effective in reducing pathogens. Microbial testing to verify the quality of biosolids can be expensive. Utilizing a mathematical model to predict pathogen density levels during the solar drying process can minimize such testing. The first order mathematical model, N(t) = N(o) * 10⁻ᵏᵈᵗ where the inactivation constant, k(d), is further defined as a function of moisture (Θ) and temperature (T), i.e. k(d) = f(Θ,T): k(d) = (k₁/( k₁ + Θ) * (T/(k₂-T)) * k₃, k₁ = 0.112, k₂ = -41.88, and k₃ = -0.5357; for all T greater than or equal to 38ºC, T=38°C provided a good estimate of the inactivation rate of fecal coliforms in biosolids. During subsequent field studies, treatments were employed to manage the drying cycle of biosolids - tilling increased the rate of drying, a covered solar drying bed increased the inactivation rate of fecal coliforms by 300%, and an automated rain shield was engineered to limit enteric bacterial regrowth due to rainfall. Finally, since biosolids are to be considered a source of nitrogen when land-applied, temporal samples of biosolids from various solar drying experiments were analyzed to ascertain the levels of NH⁺₄-N and NO⁻₃-N throughout the drying process. Chemical analyses revealed that as much as 34-92% of nitrogen was lost via volatilization during the drying process.

No description available.