Chemical Engineering book on transport phenomena by Bird Stewart Lightfoot
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Transport phenomena
Transport phenomenaFull description
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A brief note on urban public transport
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Descripción: This is an exceptional source for introducing sediment transport.
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Chemical Engineering book on transport phenomena by Bird Stewart Lightfoot
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Transport Process
Laboratory Module
EXPERIMENT 6 Flow Through Particle Layers: Fluidized Beds 1. BACKGROUND: A fluidized bed is a fine-grained layer of solid particles (Deposition) which has been loosened by a passage of fluid such that the particles are moveable to a certain extent. This lends the solid particle layer properties similar to those of a liquid. A fluidize bed can be characterized by the pressure loss (∆p) of the fluid passing through the bed. During passage through the deposited layer, the pressure below this layer initially rises with the flow rate (w) until the thrust exerted on the deposit is equal to its weight, causing the layer to “float”. If the flow rate continues to rise, the layer is set in motion and attains a fluid state. From this stage, the pressure loss remains nearly constant as the flow rate rises. From a certain flow rate onward, the particles at the top no longer fall back onto the fluidized bed; instead, they are swept away by the fluid stream. Fluidized beds are employed on a widespread basis in process engineering. With their help, gaseous, solid and liquid reaction components are mixed thoroughly and brought into close contact with each other. This applies especially to fluidized bed firing employed for low-pollutant combustion of problematic substance. 1.1 Pressure loss in fluidized beds A state of equilibrium between resistance, weight and lifting force results in the following equation for the pressure loss p occurring during passage through a swirling particle mass:
1.2 Pressure characteristic across a fluidized bed Equilibrium between resistance, weight and lifting force applies not only at the floor, but also at any other deposit height. The pressure loss is linearly dependent on the height H of the deposit. As a result, the pressure drops linearly from the floor to a value of zero at the surface. If y is the immersion in the deposit: p(y)=
1.3 Loosening rate of the fluidized bed The loosening rate is the speed at which the solid deposit merges with the fluidized bed. The speed w10 of the fluid in the space between the particles can be calculated from the Reynolds number ReI0, particle diameter
WI0=
and kinetic viscosity
the fluid.
As this calculation of the fluid speed applies to spherical particles, the speed in the case of unevenly shaped particles needs to be corrected by a form factor W= WI0 .
ᵠ
The void factor indicates the proportion of cavities forming past of the deposit. This value is calculated from the particle density ρp and the average deposit density ρps.
ɛ=1-
A state of equilibrium between the pressure loss and particle resistance indicates the relationship between the non-dimensional characteristic values Re (Reynolds number) and Ar (Archimedes number). Re I0 = 42.86 (1- ɛ).
Archimedes number the fluid.
Ar =
ρp = Particle density
Ar is
calculated from the density, particle diameter and viscosity of
Transport Process
Laboratory Module
ρf = Fluid density
dp = Particle diameter
= Kinematic viscosity
2. OBJECTIVE: i)
To study the flow properties of deposited layers comprising different granular materials and sizes.
ii)
To study the flow properties of deposited layers off different heights.
iii)
To study the flow properties of different particle materials, sizes and layer heights forming part of fluidized beds.
iv)
To determine the porosity of deposited layers
3. EQUIPMENTS 3.1 Filtration Devices 3.2 Particles Layers a) Ballotini 180 – 300um b) Ballotini 420 – 590 um c) Gravel (1-2mm)
4. PROCEDURE: 1) Device Setup 4.1
During investigations of fluidized beds, flow takes place from the bottom to the top of the filtration unit.
4.2
The water is conveyed out of the filtration unit into the overhead, open compensation tank.
4.3
The upper end of the hose on the in-flow distributor is disconnected and coupled with the compensation tank (see Fig 1).
4.4
The upper valve on the flow distributor is closed and the lower valve opened. The water will goes to bottom filter’s layer then into the compensation tank then to the drain.
4.5
All segments need to be filled with water to ensure out of leakage.
2) De-aeration Process 2.1
Connect the water supply and fill the system with water by opening the valve for adjusting volumetric flow.
Transport Process
2.2
Laboratory Module
The filtration unit is de-aerated via the corresponding valve on the filter crown (see Figure 1).This valve then close again when air bubbles no longer be seen in the filtration unit and hoses.
2.3
The 2-tube manometer is de-aerated by opening the corresponding valve. The valve is closed again when the water level has risen at the middle of the tube.
2.4
After the system has been filled with water and de-aerated, the volumetric flow adjustment valve is closed. The system is now ready for the experiment.
500 600 700 800 0 100 200 300 400 500 600 700 800 Questions: 1) Plot graph for pressure loss P vs Q(ml/min) 2) Plot graph for particles height S vs Q(ml/min) 3) Calculate the porosity of the particles.
= Thickness of
deposited layer
Transport Process
Laboratory Module
Appendix: 1- Compensation Tank 2- Drainage Hose 3- Inflow distributor 4- 2-tube Manometer 5- Pressure gauge 6- Drainage Hose 7- Inflow Line 8- Pressure Distributor 9- Flow Meter 10- Filtration Unit
