Informe sobre materiales porosos.

REPORT




REQUIREMENTS AND DESIGN INTRODUCTION ON POROUS MEDIA.




Table of Contents


1 INTRODUCTION 4
2 DESIGN REQUIRMENTS 4
3 PARAMETER STUDY: 5
3.1 Pressure drop. 5
3.2 Forced air or natural convection? 9
4 LAB TEST CORRELATION. 11
5 DESIGN AND RESULTS. 11
6 CONCLUSIONS. 11



Table of Figures



Figure 1 Reynolds vs. fluid velocity for different pelletsdiameter v=1m/s ε=0.8. 6
Figure 2 Pressure vs. porosity for v=1 m/s 7
Figure 3 Zoom of the Pressure vs. porosity. 7
Figure 4 Pressure per meter vs. diameter of pellets 8
Figure 5 Pressure vs. velocity 8
Figure 6 Chimney pressure related to the temperature jump 9
Figure 7 Chimney pressure related with the height. 10




 
1 INTRODUCTION
The aim of this report is to establish the requirementsand assign a start point for the design of the bio filter.

2 DESIGN REQUIRMENTS
There are some important concepts that control de design process. This points are very important to be clear an fixed to achieve successful design:


1. Contact time. Contact time depends on the filtering media used. It can go from 1-10 second for active carbon and also need up to 60 seconds depending on thefiltration requirements. This value and the flow rate will the most important to dimension the size of the filter.

2. Flow rate. No flow rate was fixed as restriction for the design

3. Filtering Media. Many factors affect the resistance of the bulk filter material to the airflow. Viscosity and density of the air (depending on ambient conditions). Also porosity, particle size, shape, surfacecondition and orientation influence the resistivity.


4. Cartridge material. Plastics like PVC and polypropylene can be suitable for the allocation of the filter. Also steel or aluminum could be a good alternative to improve the life span in rigorous ambient.


5. Location and usage. The location is important to include temperature and humidity conditions in the design of the filter.This could be important to keep in range the active chemical filtering (15-35ºC) and decide other factors as enable natural ventilation due thermal buoyancy across the filter avoiding forcing the air with fans or other electric devices.

3 PARAMETER STUDY:
Different aspects were modelled and parameterized to create a design guide of the system. At this early stage of the project we don’t haveenough data neither requirements to guide the design in a robust way. To solve this lack of data and start the design a parametric study was done to delimit the wide range of design options.
The possibility to model the filter with equations allows the prediction of some quantities very important to the design.
3.1 Pressure drop.

Packed beds are used extended in all industries covering awide range of applications, as reactor, filter beds, filtration, separation, etc. One important issue is the resistivity of the packed medium to the fluid; this resistance will characterize the amount of energy needed to feed the system. The pressure drop is also directly related with the energy waste, this value accounts for the driving force behind the flow that is needed to make it pass throughthe filter media for a given rate.
The porpoise of this section is to study and predict the dynamic fluid behaviour of the pellets packed bed used to filter media. For this task we will use an analytical model. The Ergun equation relates the pressure drop, material parameters, diameter and porosity with the kinetic fluid state described in the Reynolds number. In the next expression the equationis presented.

Where µ is the viscosity of the fluid, ε is the porosity (The porosity is defined as the ratio between the void volume of the filter media and the total volume), ρ is the density, ΔL is the length, ΔP is the pressure drop, v´ is the velocity divided by the porosity. The first terms accounts for the viscous friction mainly since the second term (squared velocity) cover the...