#Comsol multiphysics tutorials how to
#Comsol multiphysics tutorials software
#Comsol multiphysics tutorials series

The moving mesh method is a completely different approach to the same problem. The level set and phase field methods are both field-based methods in which the interface between phases is represented as an isosurface of the level set or phase field functions.

#Comsol multiphysics tutorials software

There are three different interface tracking methods in the COMSOL Multiphysics® software for separated multiphase flow models: In other words, in the dispersed multiphase flow models, the gas and liquid phases can be defined in the same point in space and time, while in the separated multiphase flow models, there is either gas or liquid at a given point and time. The average volume fraction can smoothly find values between 0 and 1 everywhere in the domain, signifying if there are small or large amounts of bubbles in the otherwise homogenized domain. In the dispersed multiphase flow model, the function Φ describes the local average volume fraction of gas, the dispersed phase, in the liquid, the continuous phase. The phase field function does not have a physical meaning other than keeping track of the location of the phase boundaries.

However, in the separated multiphase flow model, the different phases are exclusive, and there is a sharp phase boundary between them where the phase field function, Φ, changes abruptly. In both exemplified cases, a function, Φ, is used to describe the presence of the gas and liquid phases. The figure above shows the principal difference between the two approaches for separated and dispersed multiphase flow models. Separated multiphase flow models describe the phase boundary in detail, while dispersed multiphase flow models only deal with volume fractions of one phase dispersed in a continuous phase. Instead, the presence of the different phases is described using fields, such as volume fractions, while interphase effects such as surface tension, buoyancy, and transport across phase boundaries are treated as sources and sinks in the model equations of so-called dispersed multiphase flow models. On the larger scales, it is impossible to solve the model equations if the phase boundary has to be described in detail. Methods used to describe such models are usually referred to as surface tracking methods. Such models may be referred to as separated multiphase flow models in the COMSOL® software. On the smaller scales, the shape of the phase boundary may be modeled in detail for example, the shape of the gas-liquid interface between a gas bubble and a liquid. For this reason, the modeling of multiphase flow is usually divided into different scales. This implies that it is numerically impossible to resolve multiphase flows from the smallest to the largest scales using the same mechanistic model throughout the whole range of scales. These scales can span about eight orders of magnitude, where the largest length scale may be a hundred million times larger than the smallest scales.

The smallest scale can be around fractions of micrometers, while the largest scales are up to meters or tens of meters. The study of multiphase flows with mathematical modeling may be done at several scales. Multiphase Flow Modeling on Different Scales

We will also review the models and modeling strategies that are available in the CFD and Microfluidics modules.

#Comsol multiphysics tutorials series

This series of blog posts mainly focuses on gas-liquid and liquid-liquid mixtures, although it also briefly discusses solid-gas and solid-liquid mixtures. To illustrate the accuracy of the reduced model, a comparison with the output from the FEM model is also included.Multiphase flow may involve the flow of a gas-liquid, liquid-liquid, liquid-solid, gas-solid, gas-liquid-liquid, gas-liquid-solid, or gas-liquid-liquid-solid mixture.

#Comsol multiphysics tutorials how to

In this tutorial model, it is illustrated how to create a reduced-order model using the Model Reduction study and how the resulting reduced model can be used to investigate different control strategies for thermal control. The system works in a very simple manner: The thermostat turns the heater on and off when its temperature is too low or too high. Inside, there is a heater and a thermostat switch. The dynamical system consists of a metal block that exchanges heat with the exterior. The objective for model reduction is to provide a sufficiently accurate representation of the input-output dynamics of the unreduced model in a given parameter range with a minimal total computational cost, including the cost of creating the reduced model. ROMs are typically valid only in the vicinity of their design conditions and have lower accuracy, but the simulation time is significantly shorter. Large FEM simulations can be costly and, if repeated simulations are needed, it can be beneficial to use reduced-order models (ROMs).