Draft tube of Francis type hydraulic turbine usually consists of: cone, elbow and diffuser. On the contrary, in some power stations an extra pipe should be added to the draft tube at the bottom of cone because of installation limitation. In this paper, this special case has been numerically studied. To this end CFD analysis was applied to simulate all parts of hydraulic turbine. A homogeneous m...

in this research, a cold model of internally circulating fluidized bed is investigated. the aim is to find the effects of some of the operating parameters on the performance of the reactor. experiments were carried out in a glass column (30 mm i.d. and 25 cm height) with a centrally located draft tube (11 mm i.d. and 5 or 7 cm height). the bed was loaded with white silica particles (dp = 0.15 -...

In this research, a cold model of internally circulating fluidized bed is investigated. The aim is to find the effects of some of the operating parameters on the performance of the reactor. Experiments were carried out in a glass column (30 mm i.d. and 25 cm height) with a centrally located draft tube (11 mm i.d. and 5 or 7 cm height). The bed was loaded with white silica particles (dp = 0.15 -...

The effects of acoustic modes in the penstock on the self-excited oscillation in hydraulic power system were studied by assuming a finite sound velocity in the penstock. The flow in the draft tube is considered to be incompressible assuming that the length of the draft tube is smaller than the wavelength of the oscillation. It was found that various acoustic modes in the penstock can become uns...

Based on the actual experiment signals of draft tube, the correlation dimension analysis has been carried on using the time domain signals. Through correlation dimension analysis of pressure fluctuating under different load, the results indicate that the pressure fluctuation conditions in draft tube are not same under different load, the corresponding fractal correlation dimensions are also dif...

One-dimensional stability analysis of a hydraulic system composed of a penstock, a runner, and a draft tube was carried out to determine the cause of the full load draft tube surge. It is assumed that the cavity volume at the runner exit is a function of the pressure at the vortex core evaluated from the instantaneous local pressure at the runner exit and an additional pressure decrease due to ...

Draft tube designs have to a large extend been based on intuition and on the experience of the design engineer. In a close future, CFD simulations coupled with optimisation algorithms will assist in the search for an optimal technical solution. Such a shape optimisation technique to redesign an existing draft tube is presented in this paper. By this method, a design can be predicted in terms of...

Acoustic resonances in Francis turbines often define undesirable limitations to their operating ranges at high load. The knowledge of the mechanisms governing the onset and the sustenance of these instabilities in the swirling flow leaving the runner is essential for the development of a reliable hydroacoustic model for the prediction of system stability. The present work seeks to study experim...

The aim of this work is to use optimization as a tool for scale up in airlift bioreactors and apply this approach to a real life process. To put this approach into practice, Chlamydomonas reinhardtii, a green microalgae, was used as a model microorganism. The effects of the design parameters on the performance of the bioreactors were monitored through the changes in mixing and circulation times...

The hydrodynamic characteristics of flow regime were studied employing different draft tubes during the spouted bed roasting of groundnuts and the dimensionless parameters were employed for predicting the flow regime. The estimated Reynolds's number (Re) under the turbulent convection regime was ≈ 8399. The size of the draft tubes employed ranged from 0.175 to 0.375 m length and 0.065 m diamete...