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some of the carrier gas or auxiliary detector gas (usually nitrogen or a mixture of argon 95%, methane 5%) and produces a current between a biased pair of electrodes. The ECD is one of the most sensitive gas chromatography detectors available. The sensitivity of the ECD enables it to provide unmatched performance for extremely tough applications. It is the first choice for certain environmental chromatography applications due to its extreme sensitivity to halogenated compounds like PCBs (Polychlorinated biphenyls), organochlorine pesticides, herbicides, and halogenated hydrocarbons. The ECD is 10-1000 time more sensitive than the FID (Flame Ionization Detector), but has a limited dynamic range and finds its greatest application in analysis of halogenated compounds. 1.5.4 Analysis by mass spectrometer Mass spectrometers are sensitive detectors of isotopes based on their masses. For the study of thermal diffusion in isotopic mixtures, a mass spectrometer is necessary. In the mass spectrometer the mixture is first ionized by passage through an electron beam as shown in Fig. 1-9; the ions are accelerated by an electric field and then passed through a slit system into a magnetic field by which they are deflected through an angle which depends on the mass and velocity. The final element of the mass spectrometer is the detector. The detector records either the charge induced or the current produced when an ion passes by or hits a surface. The combination of a mass spectrometer and a gas chromatograph makes a powerful tool for the detection of trace quantities of contaminants or toxins. Fig. 1-9. Schematics of a simple mass spectrometer 18
1.6 Conclusion From the discussion in section 1.3, it is clear that models of transport in porous media are related to scale description. The prediction and modelling of fluid flow processes in the subsurface is necessary e.g. for groundwater remediation or oil recovery. In most applications the fluid flow is determined by, in general, highly heterogeneous distribution of the soil properties. The conclusion of the detailed knowledge of the heterogeneous parameter distribution into a flow model is computationally not feasible. It is therefore an important task to develop upscaling methods to simplify the small-scale flow model while still including the impact of the heterogeneities as far as possible. In this study we have used the volume averaging technique to obtain the macro-scale properties of the porous media because this method has been proved to be suitable tool for modelling transport phenomena in heterogeneous porous media. Different experimental techniques, which permit to measure the separation and therefore calculate the thermal diffusion coefficients, have been presented. It follows that, two-bulb method, among other methods, is a suitable method for this study since we can measure the both diffusion and thermal diffusion coefficients. It is easily adoptable to apply for a porous medium case. In this method thermal diffusion process does not disturb by the free convection which is negligible in this system. Katharometer, despite its limitation to binary mixtures, is still most commonly used detector in many industries. Katharometer is simple in design and requires minimal electronic support and, as a consequence, is also relatively inexpensive compared with other detectors. Its open cell can form part of the diffusion cell, and so it can indicate continuously the changes in composition without sampling. This is why that in this study, we have used a conductivity detector method with katharometer to analyze the separation process in a two-bulb method. 19
Page 1: ��
Page 4 and 5: while the effective thermal conduct
Page 6 and 7: propriétés thermiques, sont ainsi
Page 8 and 9: Remerciements Ma thèse, comme bien
Page 10: Toute mon amitié à Yohan Davit (l
Page 13 and 14: 2.5 Transient conduction and convec
Page 15 and 16: List of tables Table 1-1. Flux-forc
Page 17 and 18: Fig. 2-11. Comparison of closure va
Page 19 and 20: Fig. 4-15. Composition-time history
Page 21 and 22: Chapter 1 General Introduction
Page 23 and 24: interested in the upscaling of mass
Page 25 and 26: possible to ignore the important ve
Page 27 and 28: • mesoscopic or macroscopic scale
Page 29 and 30: macroscopic scale. In these macrosc
Page 31 and 32: different temperatures. A temperatu
Page 33 and 34: 1.4.3 Thermal Field-Flow Fractionat
Page 35 and 36: 1.5.1 From the variation of thermal
Page 37: separated, the compounds are fed in
Page 41 and 42: 2. Theoretical predictions of the e
Page 43 and 44: g Gravitational acceleration, m 2 /
Page 45 and 46: 2.1 Introduction It is well establi
Page 47 and 48: However, for all these models many
Page 49 and 50: At the fluid-solid interfaces there
Page 51 and 52: 2.4 Darcy’s law If we assume that
Page 53 and 54: where F is the Forchheimer correcti
Page 55 and 56: ε β ∂ β ( ρc ) T + ( ρc ) p
Page 57 and 58: Finally, we postulate the functiona
Page 59 and 60: ⎛ ⎜ k ~ . βσ ⎜ p ⎝ β Aβ
Page 61 and 62: − ε V −1 σ ∫ Aβσ n βσ 2
Page 63 and 64: ( ε + ε k ) ( k − k ) ( ρcp )
Page 65 and 66: We see on these figures a very good
Page 67 and 68: If the local equilibrium assumption
Page 69 and 70: epresentation of these coefficients
Page 71 and 72: 2.6 Transient diffusion and convect
Page 73 and 74: ε ε −1 β −1 β ⎛ ⎜ Dβ
Page 75 and 76: Problem I for Chang’s unit cell 2
Page 77 and 78: 1 ∫ Vβ A βσ n βσ b Sβ dA =
Page 79 and 80: 2.7 Results In order to illustrate
Page 81 and 82: Problem IIa ( k ≈ 0 ): closure pr
Page 83 and 84: We have therefore found that the ef
Page 85 and 86: a b c d β D * β D β xx * β ε
Page 87 and 88: 2.7.2 Conductive solid-phase ( k
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diffusion. Fig. 2-13 shows the effe
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β ϕ ϕ * 1.6 1.4 1.2 1.0 0.8 0.6
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Unfortunately we cannot use this ty
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a) κ = 0. 001 , b Tβ b Sβ b) κ
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Chapter 3 Microscopic simulation an
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3.1 Microscopic geometry and bounda
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in the dimensionless system, for th
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Fig. 3-2b and Fig. 3-2c show the di
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3.3 Conductive solid-phase ( k ≠
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Temperature Concentration 1 0.9 0.8
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a b k * = 1. 72ε k . Fig. 3-7a and
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c a Volume averaged temperature. Vo
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c a Volume averaged concentration.
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If we define a new parameter, A S ,
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3.4 Conclusion In order to validate
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4. A new experimental setup to dete
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N N i n The number of chemical spec
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The main purpose of this part is to
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Table 4-1. Thermal conductivity and
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Two vessels containing gases with d
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4.2.2 Two-bulb apparatus end correc
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then the thermal diffusion factor
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4.3 Experimental setup for porous m
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Table 4-2. The properties of CO2, N
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Table 4-3. Molecular weight and Len
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Glass spheres d= 700-1000 μm ε=42
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Concentration of CO2 in bottom bulb
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increases with increasing concentra
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Concentration of CO 2 in bottom bul
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Concentration of N2 in bottom bulb
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convection between the two bulbs th
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Table 4-11. The solid (spheres) and
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Table 4-12. Porous medium tortuosit
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in Fig. 2-6. In this system, the ef
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4.6 Conclusion In this chapter, we
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5. General conclusions and perspect
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this model. Therefore, the next ste
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Temperature Concentration 1 0.8 0.6
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moyennes sont comparées avec les p
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dispositif expérimental avec une c
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Appendix B. Estimation of the therm
Page 171 and 172:
References [1] A. Ahmadi, A. Aiguep
Page 173 and 174:
porous media. Lecture Notes of the
Page 175 and 176:
[51] B. Lacabanne, S. Blancher, R.
Page 177 and 178:
[80] M. Quintard, L. Bletzaker, D.
Page 179:
[106] H. Watts. Diffusion of krypto
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