Master of Engineering / Spray dryers are the core components of a milk powder production plant, where the basic configuration usually features co-current flow of milk powder and air. Spray dryers have to be cleaned frequently due to powder deposit build-up on the walls. Powder deposit build-up gives rise to lower product yields and poses a potential fire risk. If the powder deposits are scorched (from being overheated) they will contaminate, and thus compromise, the quality and consumer safety of the final product, if the powder deposits fall in and mix with it. With milk powder production rates of most industrial spray dryers ranging from 4-28 tonnes of dry powder an hour, these wall deposition problems are significant. This problem is worth investigating because the outcome of reducing or eliminating wall deposition is that a spray dryer could operate for a longer period of time without having to be cleaned. Reduction in downtime due to cleaning would give rise to increased production time and possibly a reduction in the cost of manufacturing the product. The spray dryer used in this work was a modified short-form co-current Niro unit, fabricated from stainless steel. The spray dryer had an internal diameter of 0.80 m, narrowing down to 0.06 m at the base, and a height of 2 m. A two-fluid nozzle was used to spray the process fluids (water, skim milk and grape skin extract) into the drying chamber. To measure the wall deposition fluxes on the internal walls of the spray dryer, four stainless steel plates (dimensions 110 mm by 120 mm) were inserted in place of the windows that were previously used as sight glasses. A fifth plate (dimensions 110 mm by 120 mm) and a sixth plate (dimensions 110 mm by 110 mm) were also placed on the conical section of the spray dryer at different circumferential locations. Before this work, no quantitative data on the effects of spray dryer operating conditions on the wall deposition fluxes of food material were available. This work investigated the effect on the spray deposition flux of skim milk powder on the walls of the spray dryer of (i) flow patterns in the spray dryer, by changing the degree of swirl imparted to the incoming air by using three swirl vane angles of 0o, 25o and 30o, and (ii) the stickiness of the product, through first changing the temperature of the incoming air by using three inlet air temperatures of 170oC, 200oC and 230oC; and then changing the process fluid flowrate by using three flowrates of 1.4 kg hr-1, 1.6 kg hr-1 and 1.8 kg hr-1. Previous researchers have found that the extent to which water droplets spread out in the drying chamber is affected by the amount of swirl in the inlet air. This is likely to affect wall deposition fluxes because the particles will be closer to the walls if the droplets spread out widely. The results of this work have quantitatively confirmed that the spray deposition flux increases at higher swirl vane angles, where the spray deposition flux increased from 7 g m-2 hr-1 (swirl vane angle 0o) to 12.9 g m-2 hr-1 (swirl vane angle 30o). When a swirl vane angle of 0o was used, it was observed that the cross-sectional area of the spray cloud did not change very significantly with time. However, when a swirl vane angle of 25o was used, the spray cloud was observed to “flutter”, and when the swirl vane angle was increased to 30o, the spray cloud was observed to recirculate rapidly back in the direction of the nozzle. Thus, the chance of the particles being thrown further towards the walls of the chamber is likely to increase at higher swirl vane angles. This result suggests that higher wall deposition arises because more swirl is imparted to the air entering the dryer, which in turn affects the stability of the spray cloud and, therefore, the stability of the flow patterns in the spray dryer. The stickiness of the skim milk powder is related to the temperature and moisture content of the particles. In the past, the sticky-point curve has been suggested as a semi-quantitative concept in selecting operating conditions for spray drying food material containing carbohydrates, where it has been implied that there is no significant wall deposition below the sticky-point curve. This work has quantified the spray deposition in spray dryers with respect to the sticky-point curve, where the highest spray deposition flux of skim milk powder on the walls was 16 g m-2 hr-1, and the operating point corresponding to this spray deposition flux was located at and above the sticky-point curve. Hence, both particle stickiness and flow patterns affect the wall deposition of particles in a spray dryer. This work also investigated the effect of wall properties, namely a non-stick food grade material (nylon), adhesive tape and stainless steel, on the spray deposition flux of skim milk powder on the walls. The effect of electrostatics on wall deposition was studied by grounding the spray dryer and an anti-static agent was added to the skim milk to investigate if altering the properties of the feed material could reduce wall deposition. This work has quantitatively confirmed that cohesion occurs at the same rate as adhesion for skim milk powder in this spray dryer, because firstly, decreasing the adhesion tendency of the v wall by using nylon coating had no significant effect on the spray deposition flux compared with a smooth stainless steel wall and a wall covered with a double-sided adhesive tape; and secondly the powder collected on the walls was a linear function of time with and without adhesive on the plates. Furthermore, using a nylon coated wall did not eliminate wall deposition, and the wall deposition flux was found to be the same as when a stainless steel wall was used. This result further supports the finding here that spray deposition on the walls for skim milk powder is controlled by cohesion rather than adhesion. The spray dryer operating parameters that gave rise to the least spray deposition flux on the walls were a swirl vane angle of 0o, an inlet air temperature of 230oC and a process fluid flowrate of 1.4 kg hr-1. Decreasing the feed flowrate from 1.8 kg hr-1 to 1.4 kg hr-1 (decrease by 24%), with the inlet air temperature and swirl vane angle held constant, decreased the wall deposition flux by 43% from 7 g m-2 hr-1 to 4 g m-2 hr-1. Since the spray deposition flux on the walls decreased by 43% when the feed flowrate was decreased by 24%, it might be considered that the production process is in favour of a decrease in the feed flowrate to 1.4 kg hr-1 in this dryer, and consequently a decrease in the spray deposition flux on the walls per unit production output. Finally, this work investigated if the outlet moisture content from this small spray dryer used here was equilibrium limited or controlled by drying kinetics. The findings in this work confirmed the product moisture locus concept, which implies that the outlet moisture content of the skim milk particles approaches the equilibrium moisture content (in equilibrium with the outlet gas), and that the outlet moisture content of spray-dried food material containing carbohydrates is probably not limited by particle drying kinetics, even though the spray dryer is smaller (diameter 0.8 m, height 2 m) than those used in the dairy industry, typically with a diameter of 30 m and a height of 10 m.

Master of Engineering / Spray dryers are the core components of a milk powder production plant, where the basic configuration usually features co-current flow of milk powder and air. Spray dryers have to be cleaned frequently due to powder deposit build-up on the walls. Powder deposit build-up gives rise to lower product yields and poses a potential fire risk. If the powder deposits are scorched (from being overheated) they will contaminate, and thus compromise, the quality and consumer safety of the final product, if the powder deposits fall in and mix with it. With milk powder production rates of most industrial spray dryers ranging from 4-28 tonnes of dry powder an hour, these wall deposition problems are significant. This problem is worth investigating because the outcome of reducing or eliminating wall deposition is that a spray dryer could operate for a longer period of time without having to be cleaned. Reduction in downtime due to cleaning would give rise to increased production time and possibly a reduction in the cost of manufacturing the product. The spray dryer used in this work was a modified short-form co-current Niro unit, fabricated from stainless steel. The spray dryer had an internal diameter of 0.80 m, narrowing down to 0.06 m at the base, and a height of 2 m. A two-fluid nozzle was used to spray the process fluids (water, skim milk and grape skin extract) into the drying chamber. To measure the wall deposition fluxes on the internal walls of the spray dryer, four stainless steel plates (dimensions 110 mm by 120 mm) were inserted in place of the windows that were previously used as sight glasses. A fifth plate (dimensions 110 mm by 120 mm) and a sixth plate (dimensions 110 mm by 110 mm) were also placed on the conical section of the spray dryer at different circumferential locations. Before this work, no quantitative data on the effects of spray dryer operating conditions on the wall deposition fluxes of food material were available. This work investigated the effect on the spray deposition flux of skim milk powder on the walls of the spray dryer of (i) flow patterns in the spray dryer, by changing the degree of swirl imparted to the incoming air by using three swirl vane angles of 0o, 25o and 30o, and (ii) the stickiness of the product, through first changing the temperature of the incoming air by using three inlet air temperatures of 170oC, 200oC and 230oC; and then changing the process fluid flowrate by using three flowrates of 1.4 kg hr-1, 1.6 kg hr-1 and 1.8 kg hr-1. Previous researchers have found that the extent to which water droplets spread out in the drying chamber is affected by the amount of swirl in the inlet air. This is likely to affect wall deposition fluxes because the particles will be closer to the walls if the droplets spread out widely. The results of this work have quantitatively confirmed that the spray deposition flux increases at higher swirl vane angles, where the spray deposition flux increased from 7 g m-2 hr-1 (swirl vane angle 0o) to 12.9 g m-2 hr-1 (swirl vane angle 30o). When a swirl vane angle of 0o was used, it was observed that the cross-sectional area of the spray cloud did not change very significantly with time. However, when a swirl vane angle of 25o was used, the spray cloud was observed to “flutter”, and when the swirl vane angle was increased to 30o, the spray cloud was observed to recirculate rapidly back in the direction of the nozzle. Thus, the chance of the particles being thrown further towards the walls of the chamber is likely to increase at higher swirl vane angles. This result suggests that higher wall deposition arises because more swirl is imparted to the air entering the dryer, which in turn affects the stability of the spray cloud and, therefore, the stability of the flow patterns in the spray dryer. The stickiness of the skim milk powder is related to the temperature and moisture content of the particles. In the past, the sticky-point curve has been suggested as a semi-quantitative concept in selecting operating conditions for spray drying food material containing carbohydrates, where it has been implied that there is no significant wall deposition below the sticky-point curve. This work has quantified the spray deposition in spray dryers with respect to the sticky-point curve, where the highest spray deposition flux of skim milk powder on the walls was 16 g m-2 hr-1, and the operating point corresponding to this spray deposition flux was located at and above the sticky-point curve. Hence, both particle stickiness and flow patterns affect the wall deposition of particles in a spray dryer. This work also investigated the effect of wall properties, namely a non-stick food grade material (nylon), adhesive tape and stainless steel, on the spray deposition flux of skim milk powder on the walls. The effect of electrostatics on wall deposition was studied by grounding the spray dryer and an anti-static agent was added to the skim milk to investigate if altering the properties of the feed material could reduce wall deposition. This work has quantitatively confirmed that cohesion occurs at the same rate as adhesion for skim milk powder in this spray dryer, because firstly, decreasing the adhesion tendency of the v wall by using nylon coating had no significant effect on the spray deposition flux compared with a smooth stainless steel wall and a wall covered with a double-sided adhesive tape; and secondly the powder collected on the walls was a linear function of time with and without adhesive on the plates. Furthermore, using a nylon coated wall did not eliminate wall deposition, and the wall deposition flux was found to be the same as when a stainless steel wall was used. This result further supports the finding here that spray deposition on the walls for skim milk powder is controlled by cohesion rather than adhesion. The spray dryer operating parameters that gave rise to the least spray deposition flux on the walls were a swirl vane angle of 0o, an inlet air temperature of 230oC and a process fluid flowrate of 1.4 kg hr-1. Decreasing the feed flowrate from 1.8 kg hr-1 to 1.4 kg hr-1 (decrease by 24%), with the inlet air temperature and swirl vane angle held constant, decreased the wall deposition flux by 43% from 7 g m-2 hr-1 to 4 g m-2 hr-1. Since the spray deposition flux on the walls decreased by 43% when the feed flowrate was decreased by 24%, it might be considered that the production process is in favour of a decrease in the feed flowrate to 1.4 kg hr-1 in this dryer, and consequently a decrease in the spray deposition flux on the walls per unit production output. Finally, this work investigated if the outlet moisture content from this small spray dryer used here was equilibrium limited or controlled by drying kinetics. The findings in this work confirmed the product moisture locus concept, which implies that the outlet moisture content of the skim milk particles approaches the equilibrium moisture content (in equilibrium with the outlet gas), and that the outlet moisture content of spray-dried food material containing carbohydrates is probably not limited by particle drying kinetics, even though the spray dryer is smaller (diameter 0.8 m, height 2 m) than those used in the dairy industry, typically with a diameter of 30 m and a height of 10 m.

Orientadores: Luis Augusto Barbosa Cortez, Clement Vigneault / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Agricola / Made available in DSpace on 2018-08-13T00:43:44Z (GMT). No. of bitstreams: 1 Pacco_HonoratoCcalli_D.pdf: 2218807 bytes, checksum: 9f384addc930a54138830ae79ac34adf (MD5) Previous issue date: 2008 / Resumo: O tomate destinado tanto ao consumo de mesa, in natura, quanto à produção industrial, é uma hortaliça consumida o ano inteiro, sendo o Brasil um grande produtor, nas regiões Centro Sul e em algumas regiões do Nordeste e Sul do país. Mas as perdas pós-colheita superam 50 % durante o processo de colheita e de pós-colheita. Estas perdas são principalmente de tipos mecânica, fisiológica ou patológica. Portanto a utilização de uma tecnologia apropriada, como neste caso a concepção de um sistema de bomba de calor água/água em cascata, permitirá reduzir consideravelmente as perdas da pós-colheita dos tomates. Utilizando o sistema em conjunto, circuito de baixa e alta pressão na produção de água gelada (2°C) e quente (90°C), pode ser aproveitado para realizar as operações de resfriamento rápido por água gelada por aspersão, tipo chuveiro para tomates em estado de maturação verde maduro antes da embalagem para seu transporte em sistemas refrigerados para os mercados de comercialização em condições de qualidade exigida pelo consumidor. Ao mesmo tempo com a utilização do lado de alta pressão (alta temperatura) do sistema em estudo será possível a produção de uma fonte quente para atingir temperaturas (60 e 75°C) programadas no secador de bandejas e assim realizar a operação de secagem de tomates, previamente pré-tratados (redução de tamanho e eliminação de sementes) com fins de obter uma melhor transferência de calor no produto, e com a conseqüente eliminação de grande quantidade de água contida, reduzindo seu peso e volume, permitindo melhor conservação por tempo mais prolongado, fácil transporte e econômico. Para a determinação do melhor desempenho do sistema de bomba de calor indicado, foram realizados ensaios com a finalidade de encontrar o fluido refrigerante que atinja o melhor coeficiente de performance no ciclo de baixa e alta pressão, em base na melhor capacidade de trabalho na temperatura (abaixo de 0°C) de evaporação e condensação (perto de 90°C), e também com considerações de custo - beneficio. Assim foram testados os fluidos refrigerantes como o MP39, o R22, o R600 e R600a. O R22 mostrou melhor eficiência no circuito de baixa pressão, enquanto que o R600 teve melhor performance no circuito termodinâmico de alta pressão. Depois da escolha do melhor fluido refrigerante, se realizou a operação de resfriamento dos tomates, utilizando o sistema desenvolvido, onde o produto resfriado teve os mesmos resultados quando resfriado em outro sistema de bomba de calor convencional. Realizada a operação de secagem de tomates pré-tratados no sistema de bomba de calor, mostrou-se que o secador de bandejas operando com uma fonte de calor produzida pelo circuito da alta pressão ou de alta temperatura, atingiram-se as características de um produto seco em secador de bandejas com fonte de calor aquecida por resistência elétrica. Com estes resultados os objetivos planejados foram atingidos, mostrando a redução de consumo de energia no resfriamento e secagem de tomates (30%) e com boa qualidade de sabor, cor e umidade no produto final que o consumidor aceitaria. O sistema seria de muita utilidade para os produtores e distribuidores de tomates no Brasil / Abstract: Tomato fruits are destined for consumption all around the year either in their natural form or as industrial product. Brazil is one the largest producers of tomato and its production is mainly located in the Center South regions and some northeast regions the country. Brazil also faces postharvest losses surpassing 50% of the production. The origin of these losses is mainly from mechanical, physiological or pathological injuries. The use of appropriate technologies, in the present case, the conception of an in-cascade water to water heat pump system could allow considerably reducing these losses. The system presented is and inset low and high pressure cycles to generate simultaneously cold and warm water to meet the requirement of fast cooling and drying system. The low pressure cycle generate the cold water for an aspersion hydrocooling system to cool down tomato fruits before being transported and commercialized to meet the increasing demand of the consumer for produce of high quality. At the same time, the high-pressure and high temperature cycle of the system produce heat stored in a form of hot water to produce air at the required temperature for drying tomato fruits previously cut and eliminating seed to eliminate a large amount of water contained in the produce, thus by reducing the weight and volume. Such dried tomato fruits better allow more time to be commercialized and used generating better economic returns and easier transportation. For obtaining optimum performance of the heat pump system, testes were carried out to determine the best cooling fluid, reaching the maximum coefficient of performance (COP). The R22 showed the best efficiency in the cycle of low pressure, while the R600 had better performance in the high-pressure thermodynamic cycle. Using these two fluid, the developed system was operated for cooling tomatoes and showed the same the results than conventional cooler but with better COP. Drying tomato operation using this incascade heat pump system revealed that the batch drier operating with the high-pressure or high temperature heat source cycle produced the same characteristics of dry product than drying batches of tomato fruits with electric resistance heat source. With these results the present objectives were reached, showing an important reduction of energy required for cooling and drying tomato fruits simultaneously and producing of good quality food, a product that the eventual consumer would accept. This system will be of much utility for the producers and processors of tomato in the entire Brazil / Doutorado / Tecnologia Pós-Colheita / Doutor em Engenharia Agrícola

A computer controlled dry kiln system, designed and assembled at Virginia Tech, was used in a comparison study of end check damage and acoustic emission count rate for red oak wood samples using two variations of a drying schedule based upon a standard 4/4 red oak drying schedule (T4D2). Time was the controlling variable for the system. In run A, the lumber samples were dried using eight large step changes in temperature and relative humidity. In run B, a similar charge was dried over the same time period using 48 smaller step changes in temperature and relative humidity. The lumber samples that were dried with the schedule featuring large changes in temperature and relative humidity suffered much more extensive end check damage than the wood samples dried with a schedule employing smaller changes in temperature and humidity. The acoustic emission count rate data were not recorded in the final tests due to equipment malfunction. Acoustic emission count rate data recorded from preliminary drying runs indicated that the acoustic emission count rate from a sample board increases with large changes in the ambient air temperature and relative humidity. It then decreases to zero as the wood surfaces achieve an equilibrium state. The automated kiln control system performed successfully. / M.S.

The objectives of this research were to modify and test a prototype sawdust dryer designed by Arrowhead Forest Products and a sawdust-fueled suspension burner developed at Virginia Tech. The dryer was designed to process green sawdust at small to medium-sized sawmills and pallet mills. The sawdust burner was designed to be the heat source for the dryer and serve more general needs. A series of trials were conducted to develop the operating parameters of the dryer and measure the dryer's effectiveness at reducing moisture content to 0%. Separate tests were conducted on the burner to determine maximum heat outputs and combustor efficiencies using sawdust fuel of various moisture contents and particle sizes. The sawdust dryer proved capable of reducing the moisture content to 0% after several passes through the system. The sawdust burner produced close to 400,000 BTU's/HR at calculated efficiencies over 90% and proved relatively insensitive to ranges of fuel moisture contents and particle sizes. / Master of Science

Under certain circumstances pulse combustors have been shown to improve both heat transfer and drying rate when compared to steady flow impingement. Despite this potential, there have been few investigations into the use of pulse combustor driven impingement jets for industrial drying applications. The research presented here utilized experimental and numerical techniques to study the heat transfer characteristics of these types of oscillating jets when impinging on solid surfaces and the heat and mass transfer when drying porous media. The numerical methods were extensively validated using laboratory heat flux and drying data, as well as correlations from literature. As a result, the numerical techniques and methods that were developed and employed in this work were found to be well suited for the current application. It was found that the pulsating flows yielded elevated heat and mass transfer compared to similar steady flow jets. However, the numerical simulations were used to analyze not just the heat flux or drying, but also the details of the fluid flow in the impingement zone that resulted in said heat and mass transport. It was found that the key mechanisms of the enhanced transfer were the vortices produced by the oscillating flow. The characteristics of these vortices such as the size, strength, location, duration, and temperature, determined the extent of the improvement. The effects of five parameters were studied: the velocity amplitude ratio, oscillation frequency, the time-averaged bulk fluid velocity at the tailpipe exit, the hydraulic diameter of the tailpipe, and the impingement surface velocity. Analysis of the resulting fluid flow revealed three distinct flow types as characterized by the vortices in the impingement zone, each with unique heat transfer characteristics. These flow types were: a single strong vortex that dissipated before the start of the next oscillation cycle, a single persistent vortex that remained relatively strong at the end of the cycle, and a strong primary vortex coupled with a short-lived, weaker secondary vortex. It was found that the range over which each flow type was observed could be classified into distinct flow regimes. The secondary vortex and persistent vortex regimes were found to enhance heat transfer. Subsequently, transition criteria dividing these regimes were formed based on dimensionless parameters. The critical dimensionless parameters appeared to be the Strouhal number, a modified Strouhal number, the Reynolds number, the velocity amplitude ratio, and the H/Dh ratio. Further study would be required to determine if these parameters offer similar significance for other configurations.