Drop-Vaporization-Prediction-Model

This repository contains an analytical model to predict the amount of vapor generated by an impinging drop on superheated superhydrophobic (SH) surfaces. The model accounts for drop impact Weber number, surface temperature, and SH surface geometry. The model is capable of handling microscale SH surfaces with rib or post geometry. A temperature jump length is computed using surface dimensions for both types of surface geometry. This temperature jump length is used to characterize each surface with one parameter. Model results are compared to experimental results of thermal atomization of impinging drops.

Source Code

There is one main function with several utility functions. Most function are written by the other, however, polyfitB.m and InterX.m are used from the MATLAB file exchange. Their respective URL's are given below.

VaporGenFunc.m

This is the primary function which will contain all commands to run utility functions. This is the only function that will need to be called.

Inputs:

• Weber number of impacting drop, "We"
• Temperature of the surface, "Tw", in Celsius
• initial radius of the drop, "r0", in meters
• Matlab Struct, "surface", contains surface type ('post','rib',or 'smooth'), surface pitch in microns, surface solid fraction, and surface height in microns

Outputs:

• time, "t", in seconds
• latent heat, "qvap", in W/m2
• sensible heat, "qsens", in W/m2
• mass flow rate of vapor generation, "mdot", in kg/s
• Nondimensional mass of vapor normalized by initial drop mass, "vapor"
• height into drop, "z", in meters
• Temperature profile at various time steps, "T", in Celsius
• Contact Area, "Area", in m^2

We_to_Re.m

Converts Weber number to other important parameters.

Inputs:

• Drop Impact Weber number, "We"
• liquid density, 'rho', in kg/m^3
• liquid dynamic viscocity, "mu", in Pa-s
• liquid surface tension, "sigma", in N/m
• Drop diameter, "D", in meters

Outputs:

• Drop impact velocity, "V", in m/s
• Drop Reynolds number, "Re"
• Drop Ohnesorge number, "Oh"

radius_v_t.m

This contains the ODE which, when solved by ODE45, results in drop radius vs time on impact.

Inputs:

• See documentation on ODE45 for information on how to use t and r which are time and radius respectively
• Temperature jump length normalized by drop initial diameter, "lamhat"
• Static contact angle, "theta", in radians
• Ohnesorge number, "Oh"

Outputs:

• Time, "t", in seconds
• Drop radius, "r", in meters

surface_props.m

Inputs:

• Initial diameter of the drop, "r0", in meters
• Matlab Struct, "surface", contains surface type ('post','rib',or 'smooth'),surface pitch in microns, surface solid fraction, and surface height in microns

Outputs:

• Nondimensional slip length, "lamhat"
• Nondimensional temperature jump length, "lamThat"
• Temperature of max atomization, "Tmax", in Celsius
• Nondimensional time of max atomization, "tmax", normalized by Roisman contact time.
• Static contact angle, "theta", in radians

InterX.m

Function from MATLAB file exchange InterX. Finds the intersection of two curves

polyfitB.m

Function from MATLAB file exchange polyfitB. Fits a curve, which is forced through the origin, to input data.

Plotting Files

Scripts for plotting are included in order for the user to gain a basic understanding of the usage of VaporGenFunc.m. These scripts were used to create plots presented in graduate thesis.

GenerateVaporPlots.m

Shows basic set up of VaporGenFunc.m for a single impact event. User may alter the impact Weber number, surface temperature, surface properties, or drop size. Plots of all relevant outputs are generated. Figure 1 includes latent and sensible heat flux, contact area, mass flow rate of vapor generated on drop impact all plotted vs time. Figure 2 includes the nondimensionalized mass of vapor produced over time, vapor mass is normalized by initial drop mass. Figure 3 shows the evolution of the temperature profile of the drop as time after impact increases.

GenerateVaporPlotsLoop.m

Has similar set up to previous script. However, this script loops over a range of temperature values. At each temperature the total vapor production magnitude is retrieved and normalized by the maximum vapor generation observed on a smooth surface at We = 85. A plot of this vapor magnitude vs surface temperature is generation.