| Titre : | BY-PASS FLOW ACROSS BENDS AND ELBOWS FOR CHEMICAL INJECTION INTO MICROIRRIGATION SYSTEMS |
| Auteurs : | LARHRAFI MHAMMED, Auteur |
| Type de document : | texte imprimé |
| Editeur : | United Graduate School of Agricultural Sciences Ehime University, 1996 |
| Format : | 98 |
| Langues: | Anglais |
| Mots-clés: | By-pass flow ; hydraulic characteristics ; Plexiglas bends ; PVC elbows ; pressure head differential ; by-pass discharge ; head losses ; coefficient Kb |
| Résumé : |
In the present study, by-pass flow hydraulic characteristics were clarified for 90° Plexiglas bends and 90° PVC elbows. A comparative study of the results for both types showed that PVC elbows gave higher pressure head differences and consequently higher by-pass discharges in comparison with Plexiglas bends. The ratio of by-pass discharge to the main discharge for a given bend or elbow was found to be constant. This means that a constant dilution rate could be achieved when using by-pass injectors which operate on the basis of the head differential across bends and elbows.
The flow pattern at the bend or elbow midpoint becomes complex when by-pass flow occurs due to the change in centrifugal force. Therefore, the head losses caused by the entrance and exit of fluid through the by-pass inlet and outlet differ considerably from those corresponding to common pipe transitions. Knowledge of this head loss is of major importance in the hydraulic analysis of by-pass flow across bends and elbows. By introducing the coefficient K b , estimation of this head loss caused by the entrance and exit of fluid through the 5 mm and 10 mm by-pass inlet–outlet orifice sizes was achieved. By using crested bends, by-pass flow rates could be considerably increased. This study showed that by-pass flow rates were 2.5 times higher than those obtained with the non-crested ones, and general bends may give discharges in the same range as those given by PVC pipe elbows. By inserting a high resistance within the by-pass circuit, a bend can serve as a low-cost device for flow metering based on by-pass flow measurements. By-pass injectors operating on the basis of the pressure differential generated between the inner and outer walls of an elbow have received less attention because it was claimed that they require high energy for their operation. However, by-pass injection was found to be achieved at pressure head differentials of less than 0.08 m (Bennett et al., 1987). The results of this study showed that by-pass flow rate depends not only on the available pressure head differential but also on the by-pass inlet–outlet size and the by-pass tubing length. Hydraulic analysis of by-pass flow across bends and elbows has been achieved. Knowledge of the coefficient K is fundamental and will allow prediction of by-pass flow rates for any given setting. The results of this study will ease the design of bend injection systems, which can serve as low-cost and low-energy-requirement chemical injectors to reduce agricultural production costs. |
| En ligne : | http://10.2.0.27/PDF_CDA/uploads/PDF/LARHRAFI_Mhammed_1996.pdf |
Exemplaires (1)
| Code-barres | Cote | Support | Localisation | Section | Disponibilité |
|---|---|---|---|---|---|
| 200042067 | LAR | Support papier | Salle des thèses/PFE (RDC) | Doctorat d'Etat | Consultation sur place Exclu du prêt |
