💥💥💥 What are the methods of modeling the closed gas cycle in Ansys Fluent?

 There are several methods of modeling the closed gas cycle in Ansys Fluent, depending on the type of problem, the assumptions, and the desired results. Some of the possible methods are:

• Using a pressure-velocity coupling algorithm to solve the coupled momentum and continuity equations for the gas flow. Ansys Fluent provides the option to choose among five pressure-velocity coupling algorithms: SIMPLE, SIMPLEC, PISO, Coupled, and (for unsteady flows using the non-iterative time advancement scheme (NITA)) Fractional Step (FSM)¹.
• Using a natural convection and buoyancy model to account for the density variations and the gravitational forces in the gas flow. Ansys Fluent allows you to enable the Boussinesq approximation or the ideal gas law for the density calculation, and to specify the operating density and the reference temperature for the buoyancy effects².
• Using a rotating machinery model to simulate the effects of rotation on the gas flow, such as the centrifugal and Coriolis forces. Ansys Fluent enables you to define the rotating zones, the stationary zones, and the interfaces between them, and to choose the appropriate frame of reference for the solution³.
• Using a mass source term to model the gas injection or extraction in the closed loop system. Ansys Fluent allows you to specify the mass source term as a constant value, a user-defined function, or a table, and to apply it to a cell zone, a face zone, or a point⁴.

For more information and examples of modeling the closed gas cycle in Ansys Fluent, you can refer to the following sources:

• Modeling Flow through Closed Loop System - CFD Online, which is a forum discussion that shows how to break the loop and use an inlet and outlet boundary condition with a known mass flow rate, or how to use a periodic boundary condition to simulate the closed loop system.
• Modelling the diffusion and dispersion of gas (methane) leaks from top of tank (s) into air - Ansys Learning Forum, which is a forum post that shows how to use the species transport model and the mixture material to simulate the gas mixing with the surrounding air.
• Ansys Fluent Rotating Machinery Modeling | Ansys Training, which is a training course that teaches the major classes of rotating machinery problems, steady state and transient simulation methods and the details of conducting accurate simulations of rotating machinery systems using Ansys Fluent.
• Fixed & Closed Box- CFD Inquiry - Ansys Learning Forum, which is a forum post that shows how to use a momentum source term to model the gas flow in a closed box.

How do I model heat transfer in a closed gas cycle?

To model heat transfer in a closed gas cycle, you need to solve the energy equation for the gas flow, in addition to the continuity and momentum equations. The energy equation is a statement of the first law of thermodynamics, which relates the changes in internal energy, kinetic energy, and potential energy of the gas to the heat and work transfer across the system boundary. 

Ansys Fluent can solve the energy equation for the gas flow using various methods and models, depending on the type of problem, the assumptions, and the desired results. Some of the possible methods and models are:

• Using a pressure-based solver or a density-based solver to solve the coupled or segregated equations for the gas flow. Ansys Fluent provides the option to choose among different solvers, algorithms, and discretization schemes for the solution¹.
• Using a constant specific heat or a variable specific heat to account for the temperature dependence of the gas properties. Ansys Fluent allows you to specify the specific heat as a constant value, a polynomial function, or a piecewise-linear function, and to choose the reference temperature for the energy equation².
• Using a compressible flow model or an incompressible flow model to account for the density variations and the compressibility effects in the gas flow. Ansys Fluent enables you to enable or disable the ideal gas law for the density calculation, and to specify the operating pressure and the reference density for the pressure-based solver³.
• Using a heat transfer model to account for the heat transfer mechanisms and the thermal boundary conditions in the gas flow. Ansys Fluent allows you to enable or disable the conduction, convection, and radiation models, and to specify the heat flux, the temperature, or the heat transfer coefficient at the wall boundaries.

For more information and examples of modeling heat transfer in a closed gas cycle in Ansys Fluent, you can refer to the following sources:

• Energy Equation - Ansys Fluent Theory Guide, which is a document that explains the formulation, discretization, and solution methods of the energy equation in Ansys Fluent.
• Materials - Ansys Fluent User’s Guide, which is a document that describes how to define the material properties and the specific heat models in Ansys Fluent.
• Compressible Flows - Ansys Fluent User’s Guide, which is a document that shows how to set up and solve compressible flow problems in Ansys Fluent.
• [Heat Transfer - Ansys Fluent User’s Guide], which is a document that illustrates how to enable and use the heat transfer models and the thermal boundary conditions in Ansys Fluent.

How to define mass source term in closed loops in Ansys Fluent?

To define a mass source term in a closed loop in Ansys Fluent, you need to use a user-defined function (UDF) that specifies the amount of mass added or removed from the system. You can write the UDF in C language and compile it in Ansys Fluent using the DEFINE_SOURCE macro. The UDF should return the value of the mass source term in units of kg/m^3 s for each cell in the domain. You can also use Fluent expressions and cell registers to define the mass source term based on spatial coordinates or other variables. You can apply the UDF to a cell zone, a face zone, or a point in the Cell Zone Conditions menu. You can also use the Phase Interaction menu to define the mass transfer terms between different phases in a multiphase flow.

For more information and examples of defining mass source terms in closed loops in Ansys Fluent, you can refer to the following sources:

• Please help me how to define mass source at a point? - Ansys Learning Forum, which is a forum discussion that shows how to create a small volumetric region and specify a volumetric mass source, or how to use a periodic boundary condition to simulate the closed loop system.
• Mass Source Terms in Multiphase FLUENT - Ansys Learning Forum, which is a forum post that shows how to use the species transport model and the mixture material to simulate the gas mixing with the surrounding air, and how to use the DEFINE_MASS_TRANSFER or the linearized version of it to define the mass transfer terms between different phases.
• ANSYS FLUENT 12.0 UDF Manual - 2.3.19 DEFINE_SOURCE - ENEA, which is a document that explains the syntax, arguments, and usage of the DEFINE_SOURCE macro, and provides some examples of UDFs for mass source terms.
• Source term in volume fraction equation - Ansys Learning Forum, which is a forum post that shows how to use a UDF to define a mass source term for the volume fraction equation in a VoF model.

Are there other methods to define mass source terms instead of defining UDF in Ansys Fluent?

Yes, there are other methods to define mass source terms instead of defining UDF in Ansys Fluent. Some of the possible methods are:

• Using a volumetric mass source to specify the amount of mass added or removed from a cell zone. Ansys Fluent allows you to specify the volumetric mass source as a constant value, a user-defined function, or a table, and to apply it to a cell zone in the Cell Zone Conditions menu¹.
• Using a perforated wall boundary condition to model the gas injection or extraction through small holes on a wall surface. Ansys Fluent enables you to define the hole diameter, the hole spacing, the hole area ratio, and the mass flow rate or the velocity at the perforated wall boundary in the Boundary Conditions menu².
• Using a discrete phase model (DPM) to model the gas as discrete particles that are injected into the continuous phase. Ansys Fluent allows you to define the particle properties, the injection parameters, the particle tracking, and the particle interactions in the Discrete Phase Model menu³.

For more information and examples of defining mass source terms using these methods in Ansys Fluent, you can refer to the sources that I found in my web search.