The purpose of this research was to measure and simulate the major perpendicular to gain strain components and associated stresses which develop as the result of mass transfer and restraint of shrinkage in red oak. Particular emphasis was placed on the rheological or creep components of strain. Mass transfer was measured during the first four days of drying under increasingly severe conditions. The resulting moisture gradient profiles were parabolic in shape under nearly all drying conditions. The pattern developed quickly and was modeled with reasonable accuracy using Fick's second law. Three major strain components occur in drying. These are termed elastic strain, visco-elastic creep and "set" or mechano-sorptive creep. The magnitude and variation of each of these components was measured during the first four days of drying under increasingly severe conditions. Using a slicing technique to cut very thin wafers of wood parallel to the surface, the elastic strain was shown to be quite small. The experiments led to the conclusion that the maximum stress develops within a few cell thicknesses of the surface. Much of the experimental work centered on the t of the rheological or creep components of strain, The magnitude of the visco-elastic creep was found to be about the same order of magnitude as the elastic strain and was clearly a function of the applied stress. The major strain component during drying was shown to be mechano-sorptive creep. This type of creep occurs in a number of polymeric materials undergoing diluent movement or temperature change. The maximum magnitude of the mechano-sorptive component was about 30 times larger than the maximum elastic strain. Mechno-sorptive creep was shown to be directly related to moisture loss and, to a lesser extent, a function of applied load. Using relationships derived from the experimental data, a computerized simulation was developed to predict the development of stress and the probability of checking early in drying. The simulation makes use of data on elastic strain, mechano-sorptive creep and the elastic modulus. The concept worked well in this study, but its application is limited by the lack of strain data for the surface layers representing the outer few cell thicknesses where stress is greatest early in drying. As an adjunct, acoustic response tests were performed on green samples stressed perpendicular to grain in flexure under third point loading conditions. The evidence indicates that the onset of surface failure can be predicted prior to the appearance of macroscopic checking. The acoustic response pattern is typical of that which occurs in brittle glassy polymers such as polystyrene. / Ph. D.

Although High temperature drying (HTD) of southern yellow pine (SYP) is extensively used, quality problems still exist. Approximately 25 percent of all green lumber (2 x 4, 2 x 6 and 2 x 8's) are degraded during HTD. Warp degrade, specifically "crook", is the main cause for the loss of quality of SYP dried at temperatures above the boiling point of water. One of the major causes of warp degrade is excessive shrinkage that results from overdrying. In industrial practices, average final moisture contents for HTD of SYP lumber are usually well below the 15% MC maximum permitted by the grading rules. Overdrying the lumber causes not only lumber quality problems, but also constitutes a waste of energy. In order to improve the overall results of HTD of SYP, it is necessary to perform a better control of the process, so unnecessary extended drying can be prevented. In this study, a mathematical model based on the temperature drop across the load (TDAL) concept was proposed. The model relates TDAL to drying rates and according to the results, it appears to be an important alternative for controlling purposes during HTD of SYP. / Ph. D.

Call number: LD2668 .T4 1978 M65 / Master of Science

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Global concerns about declining resources and climate change mean that industries must do their best to use energy as efficiently as possible. Energy is also an important component of a modern economy. The pulp and paper industry is one of the most energy-intensive industries round the world. In this study energy efficiency opportunities in pulp drying machines are identified and the saving potential is then quantified. The methodology followed was based on comparison of energy saving technologies and practices such as Turbo Vacuum blowers, Shoe Press, Heat pump, Use of low pressure steam etc. The data used for the calculations was taken from the mill data records. Six energy efficiency improvement projects were identified. The total proposed energy saving potential in the two Drying Machines studied in the thesis is 10511 MWh. Installation of the shoe press shows the highest saving potential followed by the turbo vacuum blowers. Although the accuracy of the results is heavily dependent upon the accuracy of the data records from the case study mill. The proposed savings would act as a reference point and depending upon the estimated savings potential, would help the mill to identify areas, projects that need more detailed measurements for further action.

Large quantities of biosolids are produced from treatment of municipal wastewater and can be processed into a nutrient and organic-rich soil amendment that has great value for agriculture. The drying process involves converting solids at approximately 25-30% solids content to a dry, stable biosolids pellet. The majority of the input material is recycled to the mixing step upstream of the dryer to achieve a more uniform particle size distribution. The objective of this work was to investigate use of polyelectrolyte amendments to promote uniformity in dried biosolids pellet size. Biosolids samples were collected at the New England Fertilizer Company (NEFCO) facility located in Quincy, MA, U.S. The biosolids samples were characterized by scanning electron microscopy (SEM), inductively coupled plasma/mass spectrometry (ICP-MS), dynamic light scattering (DLS) and zeta potential measurements. Five polyelectrolytes, polyethyleneimine (PEI), polydiallyldimethyl-ammonium chloride (PDADMAC), polyallyamine (PAM), polyacrylic acid (PAA) and polyethylene oxide (PEO) were selected as candidate amendments for surface properties modification trials. The results indicated that three cationic polyelectrolytes, PDADMAC, PEI and PAM, reduced the (absolute value) zeta potentials of the biosolids surfaces to near zero. The optimal doses for reducing the zeta potentials were found to be 0.008 mg PEI/mg solids; 0.005 mg PAM/mg solids and 0.03 mg PDADMAC/mg solids, respectively. The anionic polyelectrolyte PAA and nonionic polymer PEO were found to be ineffective for modifying the zeta potential of the biosolids. The changes in particle size distributions of the biosolids using the three cationic polyelectrolytes were determined by dynamic light scattering (DLS) measurements. Of the three cationic polyelectrolytes, only PDADMAC was found to increase the biosolids particle size from average size of 340 nm to 3600 nm with 240 min contact time. This indicates the potential for PDADMAC as an amendment for improving the biosolids drying process as it was able to decrease the number of fines and increase the “green” biosolids pellet size.

During open orthopaedic surgical procedures, the articular cartilage covering the exposed joint surfaces can be exposed to air for prolonged periods. This exposure facilitates cartilage drying, characterised by changes to the extracellular matrix and chondrocyte death. Due to cartilage’s limited capacity for regeneration, it has been proposed that this may lead to post-operative joint degeneration. It has been proposed that chondrocyte death occurs as a result of both drying and nutritional deficiency. It is known that death during drying correlates with the drying interval and is initiated in the superficial chondrocytes, progressing to deeper layers at higher intervals. Additionally, it is well established that periodic rewetting (e.g. using 0.9% saline solution) can reduce chondrocyte death. The work presented in this thesis aimed to characterise chondrocyte death during drying, with particular reference to the chondrotoxic/protective effect of environmental variables (airflow) and surgical interventions (irrigation solutions), mechanism of injury and cell death, and the effect of in vivo drying on joint health. An ex vivo model of cartilage drying was developed and carried out on bovine and human intact cartilage and osteochondral explants, while varying environmental factors (drying interval, airflow velocity, oxygen concentration) and interventions (irrigation solutions and protective coverings. Throughout the study, cartilage drying was assessed in terms of 1) cartilage macroscopic appearance, 2) percent chondrocyte death (PCD), 3) cartilage water content, and 4) chondrocyte morphology. Histologically and fluorescently labelled samples were imaged using light and confocal laser scanning microscopy respectively, which formed the basis of the qualitative and quantitative assessments. Experimental drying at high airflow velocities had a more severe effect on cartilage appearance, PCD, and water content than in static air. This relationship was apparent in dried intact joints and osteochondral explants and in bovine and human samples. This suggests that the effects of surgical drying (where ventilation systems and airflow are routine) may be more pronounced than previously suggested and demonstrates a correlation between PCD and water-loss. Irrigation solutions supplemented with glucose (25-100 mM) had no significant effect on the PCD or water content in dried samples. Additionally, PCD was minimal in osteochondral explants cultured in the absence of glucose, even after 24 hr. This suggests that nutritional deficiency is unlikely to contribute to PCD during drying. However, chondrocyte death (in intact bovine cartilage) was reduced when drying was carried out at an oxygen concentration more reflective of the in vivo environment (5 %), which suggests that cell death during drying may be facilitated by a hyperoxic shock. Finally, in vivo cartilage drying was carried out on murine cartilage. Compared to sham operated controls, dried cartilage demonstrated a loss of surface integrity (4 weeks post-surgery) and fibrillations (8 weeks) and an increased modified Mankin score (at 4 and 8 weeks). Microscopically, an altered cartilage thickness, and chondrocyte density and arrangement were visible. These changes are comparable with changes in osteoarthritis. The results of this study demonstrate the importance of maintained cartilage hydration in order to avoid unnecessary chondrocyte death articular cartilage degeneration.