Course Project Atomization

8/10/2019 Course Project Atomization

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DROPLET EVAPORATION

BHANU PRATAP

ME13M010


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Applications

Spray Combustion systemsSpray drying systems

Spray cooling systems

Spray dispersion systems


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Assumptions for Evaporation

1. Quasi-steady process.

2. Quiescent and infinite medium.

3. Single component with zero solubility.

4. Binary diffusion with unity Lewis number ( Zeldovich

energy eqn).

5. Constant thermo-physical properties.


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STAGES DURING EVAPORATION


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Evaporation Rate - Procedure

Step 1

Gas phase mass conservation equation.

Gas phase energy equation.

Droplet gas-phase interface energy balance.

Droplet liquid mass conservation equation.

Step 2 Gas phase energy equation gives Temperature distribution in gas

phase.

Step 3

Temperature distribution with surface energy balance yields theevaporation rate.


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Basic Equations

Species Conservation

Energy Conservation

Liquid Vapor Equilibrium


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AlgorithmEvaporation at atm.

Assume

Drop radius Rs.

Drop surface Temperature Ts (All possible values273


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Tvs Tsfor same m.

As Tincreases the

value of Tsincreases

and reaches a fairly

constant value.


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M vs Ts

As Tsincreases

the value of

Mass flow

increases.

0.00E+00

1.00E-07

2.00E-07

3.00E-07

4.00E-07

5.00E-07

6.00E-07

7.00E-07

8.00E-07

9.00E-07

250 270 290 310 330 350 370

Massflowi

nkg/s

Ts in K

M Vs TS

M Vs TS


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Evaporation Time vs Ts

250

270

290

310

330

350

370

390

0 2000 4000 6000 8000 10000 12000 14000 16000 18000

TsinK

Time in S

Td Vs Ts

Time Vs Ts 1 Bar


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AlgorithmVariation in pressure

Assume

Drop radius Rs

Drop surface Temperature Ts& P (All possible values273


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TinfVs Ts

250

270

290

310

330

350

370

390

0 100 200 300 400 500 600 700 800 900

TsinK

Tinf in K

Tinf Vs Ts

Tinf Vs T 0.5 Bar

Tinf Vs Ts 1 Bar

Tinf Vs Ts 1.5 Bar


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M.Vs Ts

250

270

290

310

330

350

370

390

0 0.00000010.00000020.00000030.00000040.00000050.00000060.00000070.00000080.0000009 0.000001

TsinK

Mass flow in Kg/s

M Vs Ts

M Vs T 0.5 Bar

M Vs Ts 1 Bar

M Vs Ts 1.5 Bar


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Time for evaporation Vs Ts

250

270

290

310

330

350

370

390

0 5000 10000 15000 20000 25000

TsinK

Time in S

Td Vs Ts

Time Vs T 0.5 Bar

Time Vs Ts 1 Bar

Time Vs Ts 1.5 Bar


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Inference

The droplet does not reach its saturation temperature, even it itsambient temperature is too high. It evaporates fully before

reaching saturation.

Evaporation time increases with increase in pressure

For 50 % decrease in pressure it reduces by 50.07% For 50 % increase in pressure it increases by 47.34%

Property Reference (liq. -> water)

1. Perrys Chemical Engg. Handbook

2. Properties of Gases and Liquids by Reid

3. An Introduction to CombustionConcepts and Applications by Stephen

R Turns


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ASSUMPTIONS:

Spherically symmetric droplet.

Spherical cap geometry in case of sessile drop. Single component droplet.

Transient processes are ignored.

- droplet heating.

- variable transport properties.

Recirculation within drops, time dependence of gas temperature andthe convection heat transfer coefficient are not taken into account.

SETTLED SCIENCE:

D2 law.

Ficks law of diffusion.


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Research Proposal

To develop a model of evaporation of a drop in quiescent ambientincorporating the effects of internal flow, transient and variable

transport properties separately.

Two aspects of this theory which have received considerableattention for research are :

validity of the quasi-steady assumption and

accounting for variable transport properties.

Approach

Effects of internal flows due to temperature and pressure will have tobe looked upon and incorporated in the governing equations of

droplet evaporation.

Transient & variable properties can be incorporated by integrating the

mass, species and energy equations governing droplet evaporation.


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References

Hubbard, G.L., Denny, V.E., and Mills, A.F., Droplet Evaporation: Effectsof Transient and Variable properties, International journal of Heat and

Mass Transfer, 18:1003-1008(1975).

S. Kotake and T. Okazaki, Evaporation and combustion of fuel droplet.

Inc. J. Weir! Mass Transfer 12. 595-610 (1969).

The Evaporation of Water Droplets. A Single Droplet Drying Experiment,D.E. Walton, Drying Technology: An international journal, 22:3, pp. 431-

456, 2004.

Turns, Stephen R., An introduction to Combustion: Concepts and

Applications, Tata McGraw Hill Education Private Limited, Third Edition.

Williams, F.A., Combustion Theory, 2

nd

Ed., Addison-Wesley, RedwoodCity, CA, 1985.


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Thank You

Course Project Atomization

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