Ali-Adib, Tarif (2008) Estimation and variation laws of heat transfer coefficient surface/ liquid for a liquid food in falling film evaporator. PhD thesis Génie des Procédés, AgroParisTech. UMR GenIAL, AgroParistech 2008AGPT0007 p.182.
Full text available as:
|
|
Abstract
The heat transfer coefficient value is necessary to calculate the eat exchange surface when designing an evaporator, as currently used to concentrate liquids in food industry. The boiling heat transfer coefficient on the liquid side (h) is the most uncertain and: it depends on the liquid thermo-physical properties (ηL, σL, λL, ρL, CpL, ω, ...) as well as on the process conditions (type of evaporator, φ ou Δθ, Γ (δ), P, surface roughness, fouling, etc). Also, h depends on the boiling regime (non-nucleate or nucleate) and on the flow regime (laminar or turbulent) according to the film Reynolds number in falling film evaporators.
The objective of our work is to define an economical and robust method to estimate h in a falling film evaporator which is common in food industry for concentrating fruit juice, milk and sugar solutions.
The first section of our study was a bibliographic analysis which revealed the important dispersion among the h values calculated from the formulas cited in literature
The second section was to design and construct a laboratory scale falling film evaporator (pilot) used to estimate h at stationary parameters conditions.
The third section was to describe the results and variation laws of h versus the liquid dry matter concentration XMS, the boiling temperature θL, the heat flux φ or temperature gap Δθ and mass flow rate per unit of perimeter length Γ (with describing the critical mass flow for some solutions) noted that the nature of heating surface is kept constant during our work. We described the effect of each variable separately on h where, the other variables being kept constant. Also we studied the transition from non nucleate regime, which varied with the nature of liquid and the liquid concentration.
Finally, we presented the experimental models for h = f (XMS,θL,φ,Γ) for a Newtonian liquid (sugar solution) and non Newtonian solution (CMC) that may be used for industrial evaporator design after validation. We have also proposed a method for the simplification or the experimental design.
| Item Type: | PhD Thesis (PhD) |
|---|---|
| PhD Supervisor: | Vasseur, Jean |
| Date: | 08 February 2008 |
| Board of examiners: | Le Bail, Alain and Nadeau, Jean-Pierre and Bohuon, Philippe and Rémond, Bernard and Vasseur, Jean |
| Ecole Doctorale: | ED 435 AGRICULTURE, ALIMENTATION, BIOLOGIE, ENVIRONNEMENTS ET SANTE |
| Discipline: | Génie des Procédés |
| Collection (Fonds): | AgroParistech |
| Institution: | AgroParistech |
| Department: | AgroParisTech. UMR GenIAL |
| Subjects: | 7. Life Sciences and Engineering |
| Uncontrolled Keywords: | Heat transfer coefficient, Coefficient de transfert de chaleur, Boiling, ébullition, Falling film evaporator, évaporateur à flot tombant, Food liquid, Liquide alimentaire, Newtonian liquid, fluide Newtonien, non-Newtonian liquid, fluide non Newtonien, Nucleate boiling, ébullition nucléée |
| ID Code: | 4544 |
| Deposited By: | Agnès Grimal |
| Deposited On: | 13 January 2009 |
Repository Staff Only: edit this item