1. Experimental Investigation of Flow
Patterns over Horizontal Tubes
In partial fulfillment of Bachelors in Engineering
Group Members
Deshpande Ruturaj,
Irabatti Abhilash ,
Masheshwarri Gaurav.
May 2010
Guide Prof V.S. Shinde
Co-Guide Ast. Prof N.U. Korde

2. Introduction
•
Heat transfer is defined as the transfer of energy across the boundary of a system because of
temperature difference.
•
The equipment that aids in this process is a heat exchanger.
•
Heat exchangers are widely used in application such as radiators, air conditioners,
refrigerators, dryers, coolers, and many more.
•
With such wide applications an increasing attention is being given to study of Heat
exchangers.

3. Introduction (cont..)
•
One such heat exchanger is the
falling film heat exchanger.
•
Horizontal tubes are arranged
one bellow the other. (hot fluid)
•
Liquid falls (cold fluid) on this
tubes
© Wolverine Tube, Inc Engineering Data Book III
•
This temperature difference is
sufficient for heat transfer

4. Introduction (cont..)
Advantages
• High heat transfer coefficient.
• Effective when temperature
difference is less.
• Smaller liquid Inventory
• Reduces non condensable gasses
Application
• Refrigeration, desilation, food
industry and petroleum refining.
© Wolverine Tube, Inc Engineering Data Book III

5. Introduction (cont.)
Increase in flow rate
• When liquid falls from one horizontal tube to another bellow it the flow
may take form of droplets, jets, or continuous sheet
•
These flow patterns play an important role in the performance of Heat
exchanger.

6. Present Study
• As a first step to understand the complex phenomenon of
heat transfer in falling film evaporator this study aims to
1.
Plan and setup a experimental arrangement to capture this
phenomenon.
2.
Benchmark the experimental setup, understand the effect of
thermophysical and geometric properties on flow transition over
horizontal tubes with no heat transfer

7. Experimental Setup
Requirements
Solution
•
Even though this study is limited to flow over horizontal tubes without heat
transfer, future studies demand a setup where heat transfer can be
incorporated.
Hollow pipes.
•
One end of the horizontal pipes must be free from obstruction to capture
the thickness of fluid encircling the tubes.
Unique cantilever arrangement.
•
Easy arrangement to change the diameter and spacing between the pipes
Threaded joints with expander-reducers.
•
Over head distributer should be suggested so as to reduces fluctuation and
pulsations.
As one suggested in literature.
•
Flow measurement devices and specification are to be suggested.
Rothameter with specification limited by maxmin Renolds number
Efficient piping should be done to reduce unwanted losses
Based on practical limitations and principles of
fluid mechanics
•

8. Experimental Setup
Concept
Design
Setup

9. Experimental Procedure
•
Arrange the hollow pipes (dia 19.05 mm) for the required spacing, Ensure that
they are aligned and horizontal
•
Run the fluid loop and set the desired flow rate. Wait until flow stabilizes.
•
Meanwhile set the High-speed camera to record the flow over tubes.
•
Save the recording for Analysis.

10. Analysis of recordings
• Frame by Frame analysis was done and the frames were categorized as
droplet, droplet-column, column, column-sheet, or sheet.
• Flow pattern to a particular Reynolds number was assigned based on this
analysis

12. Experimental benchmarking
•
Experimental benchmarking was carried out by comparing the results with Hu and Jocobi (1996)
•
Results were in good agreement and thus validated the experimental setup and procedure

13. Effect of thermo physical properties
•
•
•
Thermo physical properties are grouped in a non dimensional Galileo number
𝐺𝑎 = 𝑅𝑒 × (
𝐺𝑎 =
𝑔𝑟𝑎𝑣𝑖𝑡𝑎𝑖𝑜𝑛𝑎𝑙 𝑓𝑜𝑟𝑐𝑒
)
𝑣𝑖𝑠𝑐𝑜𝑢𝑠 𝑓𝑜𝑟𝑐𝑒
𝑔𝑙 3 𝜌2
𝜂2
•
For numerical ease 𝐺𝑎0.25 values are used
•
In this study distilled water (𝐺𝑎0.25 = 533.02), Ethylene Glycol(𝐺𝑎0.25 =
36.59), and Isopropyl alcohol + water (1:1 𝐺𝑎0.25 = 64.92)

14. Effect of tube spacing
• One of the important geometric features is the tube spacing
(compactness) for a heat exchanger.
• Experimental Analysis was carried to explore the effect of tube spacing
(10,15,20,25 mm)

15. •
For the flow transition Reynolds number increased with increase in Galileo number
•
For each working fluid the tube spacing hardly had any effect on flow transition Reynolds number

16. Key Observations
•
For each working fluid three modes were observed in each case mix mode dominated the
flow.
•
For low flow rate in droplet mode liquid dripped from regularly spaced site, but all sites were
not simultaneously active.
•
Further increase in flow rate resulted in liquid departuring from at least one site into
continuous jet.
•
Sufficient increase in flow rate the diameter of jets increased , et moved closer to each other
forming a sheet of liquid
•
For some cases further increase in flow rate resulted in unsteadiness o flow.

17. Comments
•
Current study helped to design a robust experimental setup to study falling film
evaporator.
•
With increased number of working fluids relation between Reynolds and Galileo
number can be developed.
•
As with in the range of current study tube spacing hardly had any effect further
investigation is required.

18. References
•
Armbruster, R., & Mitrovic, J. (1998). Evaporative cooling of a falling water film on
horizontal tubes. Experimental Thermal and Fluid Science, 18(3), 183-194.
•
Hu, X., & Jacobi, A. M. (1998). Departure-site spacing for liquid droplets and jets
falling between horizontal circular tubes. Experimental thermal and fluid
science, 16(4), 322-331.
•
Hu, X., & Jacobi, A. M. (1996). The intertube falling film: part 1-flow characteristics,
mode transitions, and hysteresis. Journal of heat transfer,118(3), 616-625.

20. Equipment's
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High Speed camera Sony DCR-DVD610E
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Rotameter Eureka
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800K Pixel CCD
HYBRID recording: DVD & Memory Stick
Carl Zeiss Vario-Tessar Lens
40x Optical / 2000x Digital Zoom
Fow rate 5 to 50 LPh
Measuring tube Borosilicate glass
float Material SS
Scale length 175-200 mm
Pump Laxami
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Domestic 0.5 Hp centrifugal single phase pump