Experimental Investigation of Flow Patterns over Horizontal Tubes

Group Members Deshpande Ruturaj, Irabatti Abhilash , Masheshwarri Gaurav.

Guide Prof V.S. Shinde Co-Guide Ast. Prof N.U. Korde

In partial fulfillment of Bachelors in Engineering

May 2010

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.

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

• This temperature difference is sufficient for heat transfer

© Wolverine Tube, Inc Engineering Data Book III

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

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.

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

Experimental Setup

• 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.

• One end of the horizontal pipes must be free from obstruction to capture the thickness of fluid encircling the tubes.

• Easy arrangement to change the diameter and spacing between the pipes

• Over head distributer should be suggested so as to reduces fluctuation and pulsations.

• Flow measurement devices and specification are to be suggested.

• Efficient piping should be done to reduce unwanted losses

Hollow pipes. Unique cantilever arrangement. Threaded joints with expander-reducers. As one suggested in literature. Rothameter with specification limited by max-min Renolds number Based on practical limitations and principles of fluid mechanics

Requirements Solution

Experimental Setup

Concept Design Setup

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.

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

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

Effect of thermo physical properties

• Thermo physical properties are grouped in a non dimensional Galileo number

• 𝐺𝑎 = 𝑅𝑒 × (𝑔𝑟𝑎𝑣𝑖𝑡𝑎𝑖𝑜𝑛𝑎𝑙 𝑓𝑜𝑟𝑐𝑒

𝑣𝑖𝑠𝑐𝑜𝑢𝑠 𝑓𝑜𝑟𝑐𝑒)

• 𝐺𝑎 =𝑔𝑙3𝜌2

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)

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)

• 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

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.

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.

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.

Equipment's • High Speed camera Sony DCR-DVD610E

– 800K Pixel CCD – HYBRID recording: DVD & Memory Stick – Carl Zeiss Vario-Tessar Lens – 40x Optical / 2000x Digital Zoom

• Rotameter Eureka – Fow rate 5 to 50 LPh – Measuring tube Borosilicate glass – float Material SS – Scale length 175-200 mm

• Pump Laxami

– Domestic 0.5 Hp centrifugal single phase pump