Although much academic research has been devoted to the fields of paper drying and air impingement heat transfer, little of the resulting information is in a form usable to dryer manufacturers. The aim of this research was therefore to develop a model suitable for the designing the flotation dryers often used in the production of market pulps. The heat transfer characteristics of several commercial nozzle designs, namely flotation nozzles, slot nozzles and arrays of round orifices, were determined under conditions relevant to pulp drying. Empirical correlations for the Nusselt number for the nozzles were obtained using the property ratio method to account for the variation of the physical properties of air with temperature. The proposed correlations were shown to be in excellent agreement with the experimental results and were sufficiently accurate for use in industrial dryer design. The effect of the nozzle exit velocity and nozzle-to-surface spacing on the profile of static pressure at the impingement surface was also determined for a typical flotation nozzle design. The influence of nozzle conditions and sheet properties on the drying characteristics of papermaking pulp was determined through batch drying experiments. Over 400 experiments were performed using samples produced from four furnishes at basis weights in the range 120 g/m" to 2125 g/m2 and oven dry densities in the range 175 kg/mt to 900 kg/m'. Drying was achieved using heated air emerging from flotation nozzles at air temperatures in the range 100°C to 250°C with nozzle velocities between 15 mls and 55 mls. Temperature profiles through handsheets of both pressed and unpressed pulp were also measured during drying, which showed the presence of a quasi-constant temperature.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:613430 |
| Date | January 1999 |
| Creators | Marson, Andrew D. |
| Publisher | University of Manchester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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