Thermal drying technologies : new developments and future R&D potential

Paper presented at the 5th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 1-4 July, 2007.Thermal dehydration processes are highly energy-intensive and are found in almost all industrial sectors, accounting for 10 to 20 percent on national industrial energy consumption in developed countries. With escalating energy costs and need to mitigate environmental pollution due to emissions from combustion of fossil fuels, it is increasingly important to develop innovative drying technologies. Furthermore, drying also affects quality of the dried product due to physical and/or chemical transformations that may occur during the heat and mass transfer operation. With tens of thousands of products that are dried in hundreds of dryer types, it is a formidable task indeed to develop design and scale-up procedures of wide applicability. Attempts have been made over the past three decades to make fundamental and applied contributions to transport phenomena and material science aspects in drying of various forms of wet solids, pastes and liquids. This presentation will attempt to summarize the state-of-the-art as far as theoretical understanding of drying processes and provide examples of some new technologies being developed. Opportunities for challenging fundamental and modeling studies to enhance drying technologies will be identified. Illustrative results will be presented to show how mathematical modeling of spray, spouted bed and heat pump dryers can be utilized to develop new conceptual designs and to optimize operating conditions as a cost-effective route to intensify innovation in thermal dryer design.cs201

Influence of Temperature, Air Velocity, and Ultrasound Application on Drying Kinetics of Grape Seeds

The objective of this work was to determine the influence of temperature, air velocity, and ultrasound application on the drying kinetics of grape seeds. The drying kinetics were determined at 1.0, 1.5, 2.0, and 3.0 m/s and at 40, 50, 60, and 70 C. At 1.0 and 1.5 m/s, the experiments were carried out with and without ultrasound application. To establish the influence of the variables on the drying kinetics, the results were modeled by means of both the Peleg and a diffusion model. The activation energy was determined (Arrhenius equation). For an air velocity of over 1.5 m/s, it was determined that the external resistance to mass transfer was negligible. No influence of ultrasound application was observed, probably due to the fact that grape seeds are very hard and have a low level of porosity.The authors of this article acknowledge financial support from the Valencian Government ("Generalitat Valenciana,'' Valencia, Spain, PROMETEO/2010/062).Clemente Polo, G.; Sanjuán Pellicer, MN.; Cárcel Carrión, JA.; Mulet Pons, A. (2014). Influence of Temperature, Air Velocity, and Ultrasound Application on Drying Kinetics of Grape Seeds. Drying Technology. 32(1):68-76. https://doi.org/10.1080/07373937.2013.811592S687632

A numerical study and design of multiple jet impingement in a PEMFC

Paper presented at the 6th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 30 June - 2 July, 2008.Impinging jets are widely used in applications where high rates of heat and mass transfer are required. Similarly, an efficient operation of the Proton Exchange Membrane Fuel Cell (PEMFC) relies on high heat and mass transfer rates to and from the catalyst layers on the anode and cathode side, which raises the question of whether jet impingement could be employed for a PEMFC as well. To answer this question, a laminar non-isothermal gas-phase model for a PEMFC equipped with a porous flow field is solved numerically for five different cases: (i) single jet (cathode); (ii) double jet (cathode); (iii) triple jet (cathode); (iv) single jets (anode, cathode); (v) ordinary flow without jets. It is found that the jets reduce the size of the concentration boundary layers in the net at the flow field/gas diffusion layer interface (GDL), but do not penetrate significantly into the GDL for low permeabilies of around 10-12 m2. For macroporous layers with permeabilities of around 10-9 m2, the jets are able to penetrate deeply. For multiple jets, the risk of entrainment with oxygen depletion between jets is demonstrated, with a resulting loss in cell performance. Overall, this initial study indicates that jets can enhance cell performance, but care must be taken so as to avoid entrainment effects when employing multiple jets in a PEMFC.vk201

Editorial

Drying Technology2210vii-viiiDRTE

Editorial

10.1080/07373937.2012.711215Drying Technology30141505-DRTE

Editorial: Role of R&D in Innovation

10.1080/07373937.2013.813217Drying Technology3211-DRTE

Editorial: R&D: A Historical Perspective

Drying Technology31111191-DRTE

Editorial: Role of R&D in Innovation

Drying Technology3211-DRTE

Editorial

10.1081/200054945Drying Technology234999-1000DRTE