Solid velocity and pressure drop in pneumatic conveying of agricultural grains | |
| Author | Raheman, Hifjur |
| Call Number | AIT Diss. no.AE-91-02 |
| Subject(s) | Pneumatic-tube transportation Grain-handling machinery |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Engineering, School of Environment, Resources and Development |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. AE-91-02 |
| Abstract | In this study, solid velocity and pressure drop in pneumatic conveying of rough rice, milled rice and soybean were investigated using horizontal and vertical pipe line configurations. Experimental variables included three pipe diameters of 54, 68 and 82 mm material feed rate, air velocity, and solid to-air ratio ranging from 2 to 46 kg/ min, 19 to 35 m/s and 0.7 to 3.5, respectively. Analysis of experimental data on both horizontal and vertical pneumatic conveying of test grains indicated the presence of slip between solid and air phase, which apparently increased with an increase in the air velocity, solid to air ratio and kernel size. Consequently, the estimation of mixture density based on solid to air ratio alone turned out to be grossly inaccurate, resulting in much lower values than the experimental ones. Solid velocity for each grain was influenced by solid flow rate per unit cross sectional area of pipe, air velocity and kernel size. However, the effect of pipe diameter was almost negligible. In horizontal conveying, the solid velocities were substantially lower than in vertical conveying, and thus indicating the presence of relatively higher slip. Slip velocities were minimum and close to the difference of air velocity and particle terminal velocity for low solid feed rates. An increase in either air or solid flow resulted in higher slip velocities. The concept of generalized drag coefficients enabled the successful deve10pment of correlations for estimating solid velocity in both horizontal and vertical pneumatic conveying of agricultural grains by extending the basic slip velocity relationship for a single particle to a multi-particle system. Solid velocity could also be estimated based on the direct multiple regression analysis showing comparable results. The observed total pressure drop gradients for all grains in both horizontal and vertical pneumatic conveying depended upon the solid flow rate, air velocity, particle diameter and pipe diameter. Fanning’s equation involving a solid friction factor, dispersed solids density and solid velocity could estimate the pressure drop due to solids consistently showing the small differences between the experimental and estimated values. The solid friction factor was found to be dependent on the solid velocity, ratio of particle to pipe diameter, Froud’s number based on terminal velocity as well as air velocity, solid-to-air ratio and particle Reynold’s number. An alternate approach for direct estimation of the ratio of pressure drop due to solid to that of air was also shown to be reasonably acceptable. The developed correlations successfully predicted the various parameters for the pneumatic conveying of corn and mungbean carried out independently and thus validating their general applicability. Finally, a comparative evaluation of correlations reported in the literature for predicting solid velocity and pressure drop gradients revealed that no such correlation provided reasonable estimates of the solid velocity in pneumatic conveying. However, two published correlations were found suitable for predicting the total pressure dr0p. In contrast, the correlations developed in the present study appeared to be most satisfactory for general application to the pneumatic conveying of agricultural grains. |
| Year | 1991 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. AE-91-02 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Food, Agriculture and Natural Resources (Former title: Department of Food Agriculture, and BioResources (DFAB)) |
| Academic Program/FoS | Agricultural and Food Engineering (AE) |
| Chairperson(s) | Jindal, V. K.; |
| Examination Committee(s) | Mora, J. C.;Athapol Noomhorm; |
| Scholarship Donor(s) | Government of Australia; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 1991 |