New paradigms for the design, manufacturing and operation of food processing and packaging equipment 4th Presentation of Final Workshop PARADIGM 2 DEMONSTRATOR ELEMENTS Aimed at modeling and interpretation of the phenomena involved in the physical treatment of food products, for a more efficient and effective automation of food processing Experimental identification of heat exchange models and optimization Project web site: http://www.npfp.it/en

1. Prof. Ing. Fabio Bozzoli
Centro SITEIA.PARMA - Università di Parma
Corrugated tube heat exchangers:
experimental identification of heat exchange
models and optimization

2. NPFP 2
• Savings in materials and energy use provide strong motivation for adopting
techniques of heat transfer enhancement in the design of commercial heat
exchangers.
• Enhanced heat transfer surface: a special surface that provides a higher
thermal performance, per unit base surface area, than a plain surface.
Heat exchangers: enhanced surface
Artificial roughness Wall curvature

3. NPFP 3
Heat exchangers: enhanced surface
• Artificial roughness: wire coil insert,
corrugated tube, dimpled tube, …
• The use of an enhancement technique is
conditioned by the specific application:
 wire coils are not applicable in the food
industry due to hygiene problems but
corrugated and dimpled tubes are;
 in the petrochemical industry, the use of
mechanically deformed tubes is not allowed
for safety reasons but the use of wire coils
does not present any problem.

4. NPFP 4
Heat exchangers: enhanced surface
axial corrugation
• the helical profile is the most widely adopted in industrial applications, since
these tubes can be quite easily manufactured by a continuous cold rolling
process;
• cross-helix type corrugation is obtained by rolling twice the same tube with two
helical corrugations;
• cross-helix type corrugation showed a performance that exceeded the single
helix-type corrugation behavior.
• Different profiles of wall corrugation:
helix corrugation cross-helix

5. NPFP 5
Heat exchangers: enhanced surface
• The aim : the experimental investigation of the effect of the cross-helix type
corrugation profile on the heat transfer mechanism;
• in particular, the effect of both the corrugation depth and of the corrugation
pitch was analysed.
• Nine tubes obtained by embossing a smooth tube made of stainless steel
(produced by Mbs Srl ).

6. NPFP 6
Heat exchangers: enhanced surface
• Experimental set-up:
 uniform heat flux generated by the Joule effect in the wall;
 water-ethylene glycol mixtures as working fluids;
 local, average, asymptotic Nusselt number;
 pressure drops

7. NPFP 7
Heat exchangers: enhanced surface
• effect of the corrugation pitch and corrugation depth
0 200 400 600 800 1000
0
10
20
30
40
50
Re
Nu
Tube N°1 l=13 mm e=0.6 mm
Tube N°4 l=18 mm e=0.6 mm
Tube N°7 l=29 mm e=0.6 mm
Smooth Wall Tube [14]
• the effect of the corrugation pitch is weak;
• the effect of the corrugation depth is strong;
• under a specific value of the corrugation depth the wall corrugation effects are
negligible;
• above a specific value of the corrugation depth the enhancement doesn’t
depend on the severity of the wall corrugation;

8. NPFP 8
Heat exchangers: enhanced surface
• the heat transfer enhancement of the cross-helix corrugated tube exceeds the
one of the single-helix corrugation;
• there is a good matching between the results obtained for the cross-helix
corrugation and the data achieved for the wire coil inserts.
THERMAL PERFOMANCE
optimal geometry

9. NPFP 9
Heat exchangers: enhanced surface
• the global performance of the cross-helix corrugated tube exceeds the one of
the single-helix corrugation.
GLOBAL PERFOMANCE: thermal performance/ pressure drop

10. NPFP 10
Heat exchangers: enhanced surface
• The results obtained by reference fluid (mixture of water and ethylene glycol)
were verified with the ones obtained by real product (apricot juice) :

11. NPFP 11
Heat exchangers: enhanced surface
• The results obtained on the lab-scale heat exchanger were verified by an
industrial-scale one (shell and tube heat exchanger manufactured by Mbs Spa.).
• To perform this comparison, it was applied an original data processing based on
“inverse problem approach” that overcomes the limit of the classical the
"Wilson plot" technique.
• This approach enables to estimate the performances for both the product side
and the service side.

12. NPFP 12
Heat exchangers: enhanced surface
• Very good agreement between the lab-scale results and the industrial-scale
ones.
• Mathematical models were developed to be used for the design of the apparatus
in question.

13. NPFP 13
Heat exchangers: enhanced surface
• As a consequence of the corrugation, the wall heat flux strongly varies along
the tube; this unevenness could impact on the performance of some fluid
thermal treatments (e.g. heat killing of bacteria in food pasteurization )
• Local convective heat transfer coefficient is found by solving the Inverse Heat
Conduction Problem (IHCP) in the solid domain from the temperature
distribution acquired on the exterior wall surface by infrared camera.

14. NPFP 14
Heat exchangers: enhanced surface
Re= 400 Re= 1100
• The here obtained distributions could be particularly useful in the design of
heat exchangers for thermal processing of foods.

15. NPFP 15
Thanks for your attention!
www.npfp.it
Participants to this activity
• Fabio Bozzoli, Sara Rainieri,
Luca Cattani
• Gianluca Bertoluzzi, Pietro
Bertoluzzi