DEVELOPMENT OF A TWO-ZONE MODEL FOR THE HEATING AND EVAPORATION OF A DROPLET
DEPARTMENT OF FLOW, HEAT AND COMBUSTION MECHANICS Martin THIELENS, Supervisors : Bart MERCI and Tarek BEJI
Mass Transfer 𝑑 𝑚
𝑑𝑡 = − 𝜋
𝑑 ℎ 𝜌ln(1 + 𝐵 ) Heat Transfer
Outer layer Inner layer
𝑚 𝑐
,𝑑 𝑇
𝑑𝑡 = 𝐴 ℎ 𝑇 − 𝑇 + 𝑑 𝑚
𝑑𝑡 𝐿 + 𝑑 𝑚 𝑑𝑡
𝐴
𝐴 𝑐
,𝑇 − 𝑇 𝑚 𝑐
,𝑑 𝑇 𝑑𝑡 = − 𝑑 𝑚
𝑑𝑡 𝐴
𝐴 𝑐
,𝑇 − 𝑇
Conclusion
Better representation of the instantaneous temperature fields
Almost no impact on saturation temperature
still overpredicted
Almost no impact on droplet life time
still overpredicted
Very small impact on convective heat exchange BUT in sprinklers millions of droplets may have an impact
Results for the case: “ Initial conditions : 𝑈 = 3 𝑚/𝑠, 𝑇 = 800 °𝐶 ”
𝛿 𝑟
𝑟 𝑇
𝑇 𝑇
[1] Volkov, R. and Strizhak, P. (2017) Planer laser-induced fluorescence diagnostics of water droplets heating and evaporation at high-temperature, Applied Thermal Engineering, 127:141-156, https://doi.org/10.1016/j.applthermaleng.2017.08.040
Saturation temperature Comparison temperature fields
Droplet lifetime Heat exchange with surrounding
Main equations and concept two-zone model
Contact
martin.thielens@ugent.be http://www.floheacom.ugent.be/
Universiteit Gent
@ugent Ghent University 0
20 40 60 80 100
0 5 10 15 20 25
Temperature [°C]
time [s]
Evolution of the temperature with time
T outer layer (Two zone) T inner layer (Two zone) T Isotherm
0 0.5 1 1.5 2 2.5 3
0 5 10 15 20 25
Droplet diameter [mm]
time [s]
Evolution of the droplet diameter with time
Two zone model Isotherm model Experiments
𝑡 ≈ 1,5 𝑠
Experiments[1] NEW MODEL:
Two zone model Standard model:
Isotherm model
Context and motivation
Fire Safety Engineering (FSE)
Improved modelling of the effect of sprinklers on fire
Fast and reliable calculation methods
Avoid lengthy CFD calculations
https://www.expressplumbingidaho.com/blog/fire-sprinklers/ http://www.deltafire-egy.com/productsdetails.php?id=11
0.51.5021 2.53
0 5 10 15 20 25
-q_conv [W]
time [s]
Evolution of the convective heat transfer with time
2.2 2.3 2.4 2.5 2.6 2.7 2.8
0 0.5 1 1.5 2 2.5
-q_conv [W]
time [s]
Zoom : Convective heat transfer
Two zone model Isotherm model
Martin Thielens holds a grant for fundamental research from the Fonds Wetenschappelijke Onderzoek - Vlaanderen (file number 1182919N)
