Investigation of fabric movement in a tumble dryer for the development of drying methods for wool fabrics to save energy

Tumble dryers are widely used for drying garments, but felting shrinkage can be caused to wool garments during the tumble drying process. To dry wool fabrics or garments in tumble dryers, the flat dry function has been introduced in the dryers; however, the energy efficiency is very low. The current study investigated fabric movement at different rotation speeds in the tumble dryer and their resultant performances in terms of specific moisture extraction rate, evenness of drying, fabric shrinkage, and fabric smoothness. For shrink-resist-treated wool fabrics, tumble drying at the rotation speed to keep fabric movement in projectile motion accompanied with occasional tumbling could achieve better energy efficiency, drying uniformity, and fabric smoothness. For untreated wool fabrics, introducing vertical movement to the flat dry in the tumble dryer can improve the heat exchange between the fabric and hot air, resulting in an increase in energy efficiency of approximately 30% compared with motionless flat drying. Wool fabric shrinkage can be controlled at less than 2% with the smooth appearance of fabric at grade 3.5 after drying under the recommended drying condition. This study could help tumble dryer manufacturers design optimal drying methods for wool fabrics with the potential for the reduction of energy consumption.

OPTIMIZATION OF THE DRYING PROCESS GRAIN CROP IN A TUMBLE DRYER WITH HEAT PUMP

Рассмотрена возможность автоматической оптимизации процесса сушки зернобобовых культур в барабанной сушилке с парокомпрессионным тепловым насосом по технико-экономическому показателю при выполнении ограничений на качество готового продукта. В качестве критерия оптимизации использованы суммарные энергетические затраты, приходящиеся на единицу массы испаряемой влаги. Определены три составляющие числителя критерия оптимизации: затраты на преодоление аэродинамического сопротивления слоя продукта в барабанной сушилке, затраты электроэнергии на привод компрессора парокомпрессионного теплового насоса (ТНУ), привод вращения барабана. Затраты электроэнергии на привод компрессора рассчитывали через холодопроизводительность ТНУ. Установлена зависимость разности влагосодержаний сушильного агента до сушки и после нее от степени заполнения сушильного барабана зернистым продуктом при различных значениях его начальной влажности. Получена однозначная функциональная связь суммарных энергетических затрат, приходящихся на единицу массы испаряемой влаги от степени заполнения барабана. На примере сушки зерна пшеницы в барабанной сушилке с профильной канальной насадкой, укомплектованной парокомпрессионным тепловым насосом, показана возможность управления степенью заполнения барабана по минимальной величине удельных энергетических затрат. Сочетанием экспериментальных и аналитических методов исследования разработана система экстремального управления процессом сушки зерна в барабанной сушилке с тепловым насосом, позволяющая с помощью микропроцессора осуществлять оперативный поиск оптимального значения степени заполнения барабана, что существенно снизит удельные энергозатраты на процесс сушки. При этом по текущей информации, получаемой с датчиков, микропроцессор непрерывно вырабатывает сигнал отклонения текущего значения степени заполнения от оптимального и посредством исполнительного механизма воздействует на расход влажного зерна, а следовательно, и на степень заполнения барабана продуктом, так чтобы суммарная удельная мощность энергооборудования для выбранного режима сушки была бы минимальной. Для многозонной барабанной сушилки предложенный алгоритм управления необходимо повторять для каждой из зон, в которых степень заполнения регулируется с помощью секторных заслонок. The possibility of automatic optimization of the drying process of legumes in a tumble dryer with a steam compression heat pump according to the technical and economic indicator when the quality of the finished product is limited. As an optimization criterion, the total energy costs per unit mass of evaporated moisture. Three components of the numerator of the optimization criterion are determined: the costs of overcoming the aerodynamic resistance of the product layer in the drum dryer, power consumption for the compressor drive of a steam compression heat pump (HPI), drum rotation drive. The energy costs for the compressor drive were calculated through the cooling capacity of the HPI. The dependence the difference in the moisture content of the drying agent before and after drying on the degree of filling the drying drum with a granular product is established for different values its initial humidity. An unambiguous functional relationship between the total energy costs per unit mass of evaporated moisture, the degree filling the drum. On the example wheat grain drying in a drum drier with a profile channel nozzle equipped with a steam compression heat pump, it is shown that it is possible to control the degree of filling of the drum by the minimum value of the specific energy costs. A combination experimental and analytical research methods developed a system for extreme control of the drying process grain in a drum dryer with a heat pump, allowing using the microprocessor to perform an operative search for the optimal degree of filling of the drum, which will significantly reduce the specific energy consumption for the drying process. At the same time, according to the current information received from the sensors, the microprocessor continuously generates a signal of deviation of the current value the filling degree from the optimal one and by means of the actuator it affects the consumption wet grain, and consequently, the degree of filling of the drum with the product, so that the total specific power of the power equipment for the selected drying regime would be minimal. For a multi-zone drum dryer, the proposed control algorithm must be repeated for each zone in which the degree of filling is controlled by sectoral dampers.

Performance of the Condensation Process for Water Vapour in the Presence of a Non-Condensable Gas on Vertical Plates and Horizontal Tubes

The condensation of humid air is a crucial step in air conditioning and process engineering. However, the models that describe the condensation of vapour in the presence of a non-condensable gas require time-consuming numerical calculations that go beyond the Nusselt film theory. Only a small number of publications exist, where simple and computationally effective correlations for the condensation of water vapour in the presence of air are presented for specially designed condenser heat exchangers. Therefore, the objective of this paper is to extend the existing semi-empirical correlations for different geometries and process parameters. For the purpose of the study, an experimental setup with two different condenser heat exchangers based on vertical plates (height 74 mm) and horizontal tubes (3 tubes, diameter 40 mm and 7 tubes, diameter 15 mm) was built. Additionally, based on existing correlations, we developed two semi-empirical models that predict the condensation mass flux for the proposed geometries. Here, we report that the agreement between the experimental and theoretical values predicted by the new, semi-empirical correlations is excellent, with an average uncertainty of less than ±6%. Their usability was demonstrated by a possibly significant performance improvement of the condenser inside a condensation-type tumble dryer.