Re‐circulating heat pump assisted continuous bed drying and energy analysis

Specialty crops such as ginseng, herbs and echinacea need to be dried at low temperatures (30–35°C) for product quality optimization. A drying system that is both energy efficient and preserves product quality is desired. A re‐circulating heat pump continuous bed dryer system was designed, constructed and field‐tested for this purpose. The heat pump dryer system was experimentally evaluated using several potential herbal and medicinal crops such as alfalfa, catnip, wormwood, red clover, portulaca, dandelion and ginseng. These crops were dried either in chopped, sliced or whole form, depending on the part of the plant (aerial or root). The specific moisture extraction rates (SMER) obtained for various crops were in the range of 0.06–0.61 kg kWh^?1. It took 5 days and 190 kWh of energy to reduce the average moisture content of ginseng roots below 10% (wb), while commercial dryers currently in use would take on an average 14 days and 244 kWh of energy at comparable loading rates. The re‐circulating nature of the heat pump dryer made it 22% more energy efficient and resulted in 65% reduced drying time compared to conventional dryers incorporating electric coil heaters. Copyright © 2005 John Wiley & Sons, Ltd.     

Energy analysis of hazelnut drying system‐assisted heat pump

In this experimental study, a proportional integral derivative (PID) controlled heat pump dryer was designed and manufactured. Heat pump dryer was tested drying of hazelnut and energy analyses were made. Drying air temperatures were changed as 50,45 and 40°C in the drying system. Drying air velocities were changed as 0.25 m s^?1 for 50°C, 0.32 m s^?1 for 45°C and 0.38 m s^?1 for 40°C. Heating coefficient of performance of whole system (COP_ws) of the heat pump dryer was calculated as 1.70 for 50°C, 1.58 for 45°C and 1.40 for 40°C drying air temperatures. Energy utilization ratio changed between 24 and 65% for 50°C, 17 and 63% for 45°C and 14 and 43% for 40°C drying air temperatures in the heat pump dryer. Copyright © 2008 John Wiley & Sons, Ltd.     

Expansion of multi-jet bed with large particles

An experimental investigation under cold conditions was made to study the effect of some operating parameters on average porosity in a 1·1 m long, 0·35 m wide and 1·2 m high multi-jet bed (Ingnifluid type) with air flow rate varying from 1200 m³ h⁻¹ to 3500 m³ h⁻¹ and total bed inventory from 26 kg to 45 kg. Rice, peas and one rice-pea mixture (mass ratio 70–30) of sizes 1·95 mm, 5.0 mm and 2·44 mm, respectively, were used as bed material to simulate coal particles. Average bed porosity was estimated based on pressure drop along the bed height. It was found to be in the range 0·58 to 0·72, 0·51 to 0·62 and 0·55 to 0·65 for rice, peas and rice-pea mixture, respectively. One mathematical correlation has been developed from the experimental results to predict average porosity as a function of air flow rate, total bed inventory and particle size used. This correlation is developed for hydrodynamic modelling of an industrial multi-jet combustor.     

An Experimental Investigation on the Drying of Sliced Food Products in Centrifugal Fluidized Bed

INTRoDUCTIONCelltrifugalfluldizedbed(CFB)dryingisanewtechnologyinwhichthewetmaterialisundergoneahighlyeIiliancedheatandmasstransferprocessinacenirifugalforcefieldbyr0tatingthebed.Thebedisesseatiallyacyllndricalbasketrotatingarounditssymmetricedswithp0rouscylindricalwa-ll.Thedry-ingmaterialisintroducedintothebasketandf0rcedtoformanannularlay6ratthecircumferenceofthebasketduetothelargecentrifUgalforcesproducedbytherotation.Thegasisinjectedinwardthroughtheporouscylindricalwallandthebedbegin…     

Direct‐contact heat exchange between fluidizing particles and a heat transfer surface in a fluidized bed: Temperature visualization of fluidizing particles

Heat conduction during contact between a heat transfer surface and fluidizing particles, a phenomenon which is one of the effective heat transfer mechanisms in a gas–solid fluidized bed, has been empirically investigated. The temperature profile of the fluidizing particles during the contact period is visualized with the aid of an infrared imager. The visualization reveals that the particles have been considerably heated in the thermal boundary layer on the heat transfer surface before contact. Based on the visualized temperature profile of the particles, the contact conductance between a fluidizing particle and the heat transfer surface is estimated by an in inverse analysis. Using the evaluated contact conductance, the contributions of the conductive heat transfer to the total heat transfer are also evaluated. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(3): 165–181, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10027     

Exergy‐based performance analysis of packed‐bed solar air heaters

This paper presents an experimental investigation of the thermal performance of a solar air heater having its flow channel packed with Raschig rings. The packing improves the heat transfer from the plate to the air flow underneath. The dimensions of the heater are 0.9 m wide and 1.9 m long. The aluminium‐based absorber plate was coated with ordinary black paint. The characteristic diameter of the Raschig rings, made of black polyvinyl chloride (PVC) tube, is 50 mm and the depth of the packed‐bed in flow channel is 60 mm. Energy and exergy analyses were applied for evaluating the efficiency of the packed‐bed solar air heater. The rate of heat recovered from the packed‐bed solar air heater varied between 9.3 and 151.5 W m^?2, while the rate of thermal exergy recovered from the packed‐bed solar air heater varied between 0.04 and 8.77 W m^?2 during the charging period. The net energy efficiency varied from 2.05 to 33.78%, whereas the net exergy efficiency ranged from 0.01 to 2.16%. It was found that the average daily net energy and exergy efficiencies were 17.51 and 0.91%, respectively. The energy and exergy efficiencies of the packed‐bed solar air heater increased as the outlet temperature of heat transfer fluid increased. Copyright © 2004 John Wiley & Sons, Ltd.     

Thermodynamic analysis of fluidized bed drying of carrot cubes

In this study, the energy and exergy analyses of fluidized bed drying of carrot cubes were investigated. Drying experiments were conducted at inlet air temperatures of 50, 60, and 70 °C, BD (bed depths) of 30, 60, and 90 mm and square-cubed carrot dimensions of 4, 7, and 10 mm. The effects of drying variables on energy utilization, energy utilization ratio, exergy loss and exergy efficiency were studied. The energy utilization and energy utilization ratio varied between 0.105–1.949 kJ/s and 0.074–0.486, respectively. The exergy loss and exergy efficiency were found to be in the range of 0.206–1.612 kJ/s and 0.103–0.707, respectively. The results showed that small particles, deep beds and high inlet air temperatures increased energy utilization, energy utilization ratio, and exergy loss due to high value of heat and mass transfer. Also, the exergy efficiency had maximum value when higher drying air temperature, larger CS (cube size) and shorter BD were used for drying experiment.     

Thermal analysis of a fluidized bed drying process for crops. Part I: Mathematical modeling

Development of a comprehensive mathematical model to simulate the simultaneous heat and mass transfer processes in a bubbling fluidized bed is described. Although the model is applicable to a wide range of particles, wheat is chosen as an example. In the development of the model, the commonly used two‐phase theory is not used because of its insensitivity to the particle group used in the bed. Instead, a new hydrodynamic model is developed for each specific particle group. The behaviour of bubbles in a bed of group D particles (wheat) is modelled with the consideration that they grow in size as they rise in the bed, but are of the same size at any height in the bed. The voidage of bubbles, particles and interstitial gas is modelled separately. A newly developed expression to determine the minimum fluidization velocity of wet particles is used. The model considers the presence of different phases inside the bed, and their physical variation along the bed. The interstitial gas phase, the bubble phase, and the solid phase are modelled separately. The drying mechanism for the solid phase is considered in two stages: the falling rate, and the constant rate, with appropriate temperature and moisture diffusion coefficients and wall effects. The simultaneous heat and mass transfer processes during the drying process including the internal and external effects are modelled for each phase. A set of coupled nonlinear partial differential equations is employed to accurately model the drying process without using any adjustable parameters. A numerical code is developed to solve the governing partial differential equations using a control volume‐based discretization approach. Piecewise profiles expressing the variation of dependent variables between the grid points are used to evaluate the required integrals. Copyright © 2000 John Wiley & Sons, Ltd.     

Energy and exergy analyses in convective drying process of multi-layered porous packed bed

This paper is concerned with the investigation of the energy and exergy analyses in convective drying process of multi-layered porous media. The drying experiments were conducted to find the effects of multi-layered porous particle size and thermodynamics conditions on energy and exergy profiles. An energy analysis was performed to estimate the energy utilization by applying the first law of thermodynamics. An exergy analysis was performed to determine the exergy inlet, exergy outlet, exergy losses during the drying process by applying the second law of thermodynamics. The results show that the energy utilization ratio (EUR) and the exergy efficiency depend on the particle size as well as the hydrodynamic properties and the layered structure, by considering the interference between capillary flow and vapor diffusion in the multi-layered packed bed.     

锂电池极片干燥系统耗能分析

介绍了锂电池极片干燥系统的组成及工作原理。根据热力学第一定律,建立了干燥系统的能量平衡分析模型。该模型描述了极片基材和涂层的升温耗能、溶剂蒸发相变耗能、干燥介质加热耗能、系统通风耗能的计算方法及其与系统总投入能之间的平衡关系。以水溶剂负极涂层的典型工况干燥过程为例进行了实际分析计算。结果表明：系统的主要耗能用于干燥介质升温,占系统总耗能的93.30%;干燥介质的能量中,用于基材、干涂层升温部分甚微,分别占0.14%和0.21%,另有6.74%用于溶剂耗能;而系统通风耗能主要用于克服干燥系统的阻力和输送干燥介质,且其在总能耗中所占比例不高,为6.70%。分析了供风量变化、极片走带速度变化等变工况与系统各项耗能的关系。为实际干燥过程中合理选择加热器功率和风机选型提供了参考依据。     

Energy and exergy analyses in drying process of non-hygroscopic porous packed bed using a combined multi-feed microwave-convective air and continuous belt system (CMCB)

This paper is concerned with the energy and exergy analyses in the drying process of non-hygroscopic porous packed bed by combined multi-feed microwave-convective air and continuous belt system (CMCB). Most importantly, this work focused on the investigation of drying phenomena under industrialized microwave processing. In this analysis, the effects of the drying time, hot-air temperature, porous structure (F-Bed and C-Bed) and location of magnetron on overall drying kinetics and energy utilization ratio (EUR) were evaluated in detail. The results showed that using the continuous microwave application technique had several advantages over the conventional method such as shorter processing times, volumetric dissipation of energy throughout a product with higher energy utilization and less exergy efficiency in drying process. The results presented here provided fundamental understanding for drying process using CMCB in industrial size.     

Exergy analysis of industrial pasta drying process

In this study we present an energy and exergy modelling of industrial final macaroni (pasta) drying process for its system analysis, performance evaluation and optimization. Using actual system data, a performance assessment of the industrial macaroni drying process through energy and exergy efficiencies and system exergy destructions is conducted. The heat losses to the surroundings and exergy destructions in the overall system are quantified and illustrated using energy and exergy flow diagrams. The total energy rate input to system is 316.25 kW. The evaporation rate is 72 kg h^?1 (0.02 kg s^?1) and energy consumption rate is found as 4.38 kW for 1 kg water evaporation from product. Humidity product rate is 792 kg h^?1 (0.22 kg s^?1) and energy consumption rate is found about 0.4 kW for 1 kg short cut pasta product. The energy efficiencies of the pasta drying process and the overall system are found to be as 7.55–77.09% and 68.63%. The exergy efficiency of pasta drying process is obtained to be as 72.98–82.15%. For the actual system that is presented the system exergy efficiency vary between 41.90 and 70.94%. Copyright © 2006 John Wiley & Sons, Ltd.     

Heat and mass transfer of seed drying in a two‐pass infrared radiation vibrated bed

Based on the investigation of drying of seeds by one‐pass infrared radiation vibration, the present study developed a two‐pass infrared radiation vibrated dryer. One of its characteristics was that during the drying process both seeds and the inlet hot air went through outer and inner cylinders (two‐pass) so that the drying travel distance of seeds was extended by 20%. Unsteady drying dynamic experiments showed that by increasing the inner travel distance, the seed dehydration rate increased by 87%, the total drying period was 1/1.8 times that of the one‐pass dryer, and the seed temperature was 0.82 times that of the one‐pass dryer. With the constant‐drying‐rate period prolonged and the drying rate increased due to the addition of the inner cylinder, the whole drying process was better adaptable to the physiology and biology of seeds and thus kept the seeds viable and enhanced heat and mass transfer. Against the drying rate equation, the paper experimentally studied the effects of radiation, convection, and conduction on the seed drying process. The study provided theoretical and technical bases for the drying of various vegetable seeds. © 2002 Scripta Technica, Heat Trans Asian Res, 31(2): 141–147, 2002; DOI 10.1002/htj.10024     

35t/h沸腾炉改造问题探讨

分析开滦赵各庄电厂3#沸腾炉运行中出现的燃烧效率低、受热面磨损严重等问题,探讨沸腾炉强化燃烧与减轻受热面磨损的关键技术,制定了相应的改造方案,并在锅炉大修中实施。运行结果表明,改造后的锅炉达到了预期效果。     

A review of oxy‐fuel combustion in fluidized bed reactors

Presently, there is no detailed review that summarizes the current knowledge status on oxy‐fuel combustion in fluidized bed combustors. This paper reviewed the existing literature in heat transfer, char combustion and pollutant emissions oxy‐fuel combustion in fluidized beds, as well as modelling of oxy‐fuel in FB boiler and gaps were identified for further research direction. Copyright © 2016 John Wiley & Sons, Ltd.     

Theoretical performance analysis of the multi‐stage gas–solid fluidized bed air preheater

The multi‐stage fluidized bed can be used to preheat the combustion air by recovering the waste heat from the exhaust gas from industrial furnaces. The dilute‐phase fluidized bed may be formed to exclude the excessive pressure drop across the multi‐stage fluidized bed. But, in this case, the solid particles do not reach to the thermal equilibrium due to relatively short residence time in each layer of fluidized bed. In this study, a theoretical analysis on the dilute phase multistage fluidized bed heat exchanger was performed. A parameter related to the degree of thermal equilibrium between gas and solid particles at the dilute‐phase fluidized beds was derived. Using this parameter, a relatively simple expression was obtained for the thermal efficiencies of the multi‐stage fluidized bed heat exchanger and air preheater. Copyright © 2001 John Wiley & Sons, Ltd.     

Analysis of steam flow behavior in packed bed of coal particles

The steam outflow rate and temperature distribution in a packed bed of coal particles were measured and compared with the results of a numerical analysis in order to determine the steam flow behavior in a coke oven chamber. The moisture-controlled and size-graded pulverized coal particles were packed in a cylindrical stainless steel vessel with steam flow pipes at both ends of the vessel. The upper end of the vessel was heated from 293 K to 653 K with constant heating rate of 3 K/min and maintained at 653 K. The numerical analysis, which was based on a new concept of the evaporation/condensation behavior, was conducted in an axisymmetrical coordinate system. The unsteady heat conduction equation in the solid phase and the mass, momentum, and energy conservation equations in the gas phase were solved simultaneously. The condensed water in the bed is assumed to be static and a part of the solid phase under the assumption of local thermal equilibrium. Estimated results on the temperature distribution and the steam outflow rate are quantitatively in good agreement with experimental results and the model performance is verified. The steam flow toward the heated side decreases the heat transfer rate to the inside, while the flow toward the insulated side increases it. © 1997 Scripta Technica, Inc Heat Trans Jpn Res 25(4): 238–253, 1996     

Energy conservation with tumbler drying in laundries

While the energy consuming process of drying paper, textiles and construction materials during manufacturing has warranted a large number of studies, the more dispersed everyday activity of laundry drying seems not to have awakened as much interest. This is perhaps because laundry drying installations are usually either domestic or comparatively small. Nevertheless, the energy used for laundry drying represents 0.5% of the total electrical energy use in Switzerland for example, and that figure is bound to be still higher in other countries. In this article it is demonstrated that conventional tumbler dryer technology is susceptible to improvement by the use of heat recovery heat exchangers. The energy recovery potential may be as high as 20% of that required for heating the drying air. The additional investment required for the heat recovery heat exchanger is paid back in less than two years of normal use.     

Performance analysis of double-pass oscillating bed solar dryer for drying of non-parboiled paddy grains

Drying of agricultural produce like paddy grains is necessary for reducing moisture content in them to the required level towards diminishing the deterioration and enhancing the storage time. Conventionally, open-space sun drying is widely used to reduce the moisture content of the most of the agricultural produce.. Now-a-day, so many solar dryers are used for drying agricultural produce. In the present work, a double-pass oscillating bed with a double-pass flat plate collector has been used for drying of non-parboiled paddy grains. The bed oscillated at a frequency of 2.75 Hz. The oscillating bed solar dryer can dry 45 kg of non-parboiled paddy grains in just a single day to the required level of moisture content, and the average moisture present in the dried grains was 13.55%. The average dryer thermal efficiency and pick-up efficiency in non-parboiled paddy were 28.79% and 52.17%, respectively.     

褐煤在鼓泡流化床和循环流化床燃烧的汞迁移试验研究

对褐煤在小型电加热鼓泡流化床和小型电加热循环流化床中燃烧时的汞迁移特性进行了对比试验研究,重点考察了不同燃烧工况对汞迁移特性的影响。试验结果表明,炉膛温度和给煤量增加,鼓泡流化床和循环流化床的烟气总汞HgT均增加,飞灰颗粒汞含量Hg(p)均减少,并且循环流化床的烟气总汞HgT值均低于相同燃烧工况的鼓泡流化床值,循环流化床的飞灰颗粒汞含量Hg(p)值均高于相同燃烧工况的鼓泡流化床的值;流化风速增加,循环流化床的烟气总汞HgT减少,飞灰颗粒汞含量Hg(p)增加,鼓泡流化床烟气总汞HgT增加,飞灰颗粒汞含量Hg(p)减少。