CFD Thermal Analysis

Computational Fluid Dynamics (CFD) Thermal Analysis

CFD thermal analysis is at the heart of what we do at our Singapore Office in BroadTech Engineering. It is a powerful engineering simulation and analysis method that CFD companies use to help improve the energy efficiency of client’s engineering design in various industries and applications during their CFD consulting.

Application of CFD Thermal Analysis includes

The CFD modeling of various thermal behavior of various engineering applications includes

1. Optimize airflow and heat transfer in building geometry design to improve and Maintain the thermal comfort of occupants in a building indoor environment.
2. Optimize energy and Heat Transfer efficiency of building HVAC system
3. CFD Fluid Flow Analysis to Optimize cooling of data center design projects

Featured Case Studies

Multi-phase Thermal Analysis of PCR Process

The efficiency of any PCR process is dependent on the effectiveness of the enzymes that are responsible for various constituents processes namely denaturing, annealing and extension. These enzymes are activated at different temperatures that are at 92 degrees, 57 degrees and 72 degrees in that order. A rigorous thermal analysis was necessary for the DNA amplification project from dimensionless Rayleigh number in which simulation is performed to actual temperature and time of exposure that is encountered in practice.
We also attempted to simulate the effect of a gas bubble entrapped on the loop since, in practice, bubbles are usually generated due to heating of PCR reagents. In this, we used the volume of fluid method (VOF) to model multi-phase flow. It is also important to note that we were only interested in the steady-state temperature distribution in glass loop. However, we were also interested in the time between the start of heating and beginning of amplification in which transient thermal analysis was necessary.

Numerical study of Fluid Flow & Heat Transfer characteristics Past a Wall Mounted Ribs in the Presence of Crossflow

A detailed three-dimensional numerical investigation on a single array of square ribs is mounted in a duct considered to examine the role of three-dimensional flow structures in heat transfer distribution. A parametric study is also carried out to assess the performance in three-dimensional cross flow for different Re. The equations governing fluid flow and heat transfer are solved using Finite volume method based commercial software called ANSYS-FLUENT. It is observed that flow is accompanied by an unfavorable reduction in heat transfer owing to the increase in the size of horseshoe vortex for lower velocities.
At higher Re or velocities, it exhibits higher overall surface averaged Nusselt number. The turbulence modeling is done with SST k-w model. The present study promotes better understanding in designing of buildings, flow past row of buildings and flow past chimneys.

Fundamental Modes of Thermal Heat Transfer

Basically there 3 Types of heat transfer methods that we need to consider during any performance of a computational fluid analysis in any typical CFD simulation done during the rendering of our CFD consulting services.

1. Thermal Conduction Considerations

Thermal Conduction of heat occurs when there is a temperature differential across the length of a part.
Factors that influence the amount of thermal heat energy transmitted includes

1. Component material Cross-sectional Dimension

The larger the component cross-sectional area, the more the thermal energy that is being transmitted

2. Thermal conductivity of Component Material

How well a material is able to conduct Thermal energy depends on its Thermal conductivity which is an inherent material property. In general, metallic material (eg. Steel) is much better at transmitting more thermal heat energy than non-metal (eg. Ceramics)

3. Amount of temperature differential

Thermal heat energy will flow from the hotter region to the cooler region.
The bigger the temperature differential the more thermal energy that is being transferred

2. Forms of Convection Heat Transfer

Convective heat transfer from a body surface occurs through the motion of the adjacent fluid, such as air or a Liquid medium, whereby the hotter fluid is typically transported away from the surface and replaced with a cooling fluid.
The actual heat transfer mechanism of the fluid movement modeled using fluid dynamic simulation is quite complex in nature where it involves a local conduction of thermal heat transfer which is made enabled by a fluid boundary layer at the surface

Convective heat transfer depends on fluid motion, whereby the thin fluid layer adjacent to the body surface circulates away from the body surface and is immediately replaced by a fresh layer of cooler fluid.
This Convective heat transfer is a function of a number of factors such as

1. Heat transfer Surface area
2. Value of the material Convective heat transfer coefficient
3. Temperature difference between the surface and the free fluid

Basic Forms of Convection Heat Transfer

There are Two basic forms of Convection Heat Transfer to consider during any typical fluid dynamic analysis

1. Forced Convection

In a Forced convective heat transfer, the adjacent fluid is being driven to move along by some external driving force.
Example of such a setup includes having a fan blowing across a body heat transfer surface.
This assist in helps to provide a more energetically driven medium for the fluid to move away from the heated surface.
*Note that as the Calculation of the actual convective heat transfer under forced conditions is mathematically more complicated, a coupled Computational Fluid Dynamic (CFD) analysis can be used to give an accurate simulation solution.

2. Free Convection

In free convection setup, the fluid is initially in a stationary condition.
Fluid circulation begins when there is an occurrence of localized thermal heating.
*Notes that the orientation of the thermal heat transfer surface relative to the direction of the gravity force also makes an influence the convective heat transfer.
If a surface is vertically positioned, the effects of gravity can help in assisting the fluid circulation. However, if the body surface is horizontally orientated, the effects of gravity does not assist in the heat circulation.

3. Radiation Calculations

The mechanism of Radiation heat transmission involves the emanating of electromagnetic waves or energy photons from the body surface of the heat source. This mechanism does not need a medium to pass through, therefore allowing radiation to occur in a vacuum.
*Note that in theory, any surface that has a temperature above 0° is emitting thermal heat energy by means of radiation heat transfer.
At any given point in time, a typical surface is both emitting as well as absorbing thermal energy via radiation heat transfer with an adjacent body surface.
Factors affecting whether an individual body surface is having a net cooling or heating effect includes

1. The angle of the photon transmission path in relation to the body surface.
2. Emissivity and Absorptivity of the material surface properties

Non-Linearity

heat transfer is dependent on a fourth order temperature term. This means that any heat transfer analysis including radiation effects becomes a nonlinear solution.

View factor

View factor is a parameter which is determined by the effective view a Panel A surface has on Panel B. This Effective view controls the travel path of the energy photons between two panels.
In most practical scenarios, it can be very difficult to compute for arbitrary surfaces, without some kind of actual ray tracing solution.

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CFD Thermal Analysis

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Other Featured CFD Thermal Analysis Case Studies 

Transient Thermal Analysis of Inverse Method Project

 

The objective of the CFD consultancy was to calculate the Heat Generation for one – dimensional Transient Heat conduction using Inverse Techniques.
Prior to using the Inverse techniques, we needed to solve a Direct problem by using the experimental Data and simulation data.
Our engineers considered a case of one-dimensional transient heat conduction, the temperature at the two boundaries has been fixed and when a constant uniform power (electric current) is supplied, there will be a change in temperature at the center which will evolve with time.
The experimental results were considered from the Analytical solution by adding a small amount of noise (up to 2% of the obtained values) in order to represent real-life scenario. The analytical solution has been obtained using the Fourier’s method (variable separation method) to obtain the temperature at three different time steps (ie. t1, t2, t3) using Fortran 95.
Secondly, we had used the Ansys (Transient Thermal Analysis) Module to obtain the simulation results.
Thirdly, Steepest Gradient Method was used for optimization and the Inverse problem was solved with one unknown parameter.
We have considered the one-dimensional Transient Heat conduction with Heat Generation challenge, by known parameter of Temperature varying with time,  we found the unknown parameter  “Qg” using  two Inverse techniques,  Steepest  Gradient  Method, and  Simplex Method.
For this technique, we need a cost function consists of Known Modal values in the function of unknown parameter and experimental values. So, we considered experimental values as the solution of the Forward problem with noise parameter and Modal values as the solution of Simulation Values.
We estimated the error for Qg from both the Techniques, which gives us the result like; Using Steepest gradient Method, Error varies from 5% to 15% approximately and by using Simplex Method Error is approximately 20 %. So, It is concluded that for this case of consideration and comparing the techniques Steepest Gradient Method is giving better results comparing to Simplex Method.

Heat Transfer Analysis of Bi-directional DC/AC Converter

Bi-directional DC/AC converter is used as a voltage source to supply loads that require variable supply voltage from input feed by UPS or generator. The objective of this project was divided into two parts, 1) to analyze the heat transfer of water-cooled components in the system and 2) to a study the cooling of the bidirectional converter by means of a radiator and cooling setup.  The temperature distribution of water-cooled component, the rate of heat transfer due to air and water, and air flow inside the bi-directional converter were calculated. DesignModeler and ANSYS Meshing were used for Model cleanup, fluid volume extraction, and Meshing, respectively. CFD analysis was carried out by using the ANSYS Fluent.

Heat Transfer Analysis of LED Position Lights

LED position lights are installed in aircraft wings for the use by pilots of other aircraft who needed to be able to see and determine the flight path of aircraft. Design and functioning of position light are given by FAA. The goal of this study was to find the temperature of electronic components as well as the temperature distribution of air inside the casing. Conduction, convection, and radiation are the mode of heat transfer considered this simulation. DesignModeler was used for model cleanup and fluid volume extraction. ANSYS Meshing was used for meshing and FLUENT was used for CFD.

Call Us for a Free Consultation

After the completion of the CFD service, Clients will be provided with fully customized CFD thermal analysis reports which detail the Methodology, in-depth analysis, and recommendations. This insight allows our customers to optimize performance and make informed engineering decisions in a scientific, proven manner.

If you are still interested in learning more about CFD Thermal Analysis services and to see what it can do for your engineering project, simply call to contact us today at +6581822236 for a no obligation discussion of your needs.
Our knowledgeable and friendly consultants will be happy to assist and understand more about your needs and requirements
Alternatively, for quote request, simply email us your technical specifications & requirements to info@broadtechengineering.com

Four Types of Analysis Solutions

1. Transient Thermal Analysis

In the Transient Thermal analysis the initial conditions are defined and then an incremental time stepping solving method is carried out base on the thermal loading and thermal boundary conditions.
The simulation computation can be performed through to a steady-state thermal condition, or to evaluate initial thermal shock loadings, for example where the steady state analysis condition is not of main concern.
One of the considerations in the transient thermal analysis, which is in a lot of ways similar to a transient dynamic analysis, is an accurate calculation of the time step required.

Stability Criteria

This time step requirement can be determined by the Stability criteria, either automatically by the CFD simulation software solver or manually controlled by the end-user.

Adaptive Time Stepping

The Adaptive time stepping functionality included in many simulation solvers can optimize the time step by dealing with

1. Variability in Rate of change of Thermal effects for example which is dominant at the start of the analysis
2. The occurrence of Nonlinearity in Thermal effects which need granular time steps.

Note that it is not recommended to have a Time steps with a granularity coarser than the stability limit.

2. Steady-State Thermal Analysis

The steady-state condition in a thermal situation occurs when the thermal temperature distribution and all flow of thermal heat energy are stable and remain relatively constant through time.
The steady-state analysis can be easily derived by performing an energy balance computation which assumes a stabilized condition.
Often times such Steady-state conditions are important for simulating the temperature distribution over component, which is then used as an input parameter to perform structural stress analysis.

3. Nonlinear Solutions

In a nonlinear analysis solution, whereby radiation is present, most simulation parameters involved can change with temperature variations.
Such physics parameters with nonlinearity properties can encompass

1. Material Thermal properties

This includes Thermal conductivity, Convective Heat transfer coefficient

2. Thermal Loading conditions

This includes externally applied thermal flux from the heat source which is dependent on temperature. It is important to note that a Nonlinear simulation modeling requires an incremental loading strategy whereby the Total thermal loading is broken down into successive steps.

3. Thermal Boundary conditions

4. Linear Solutions

In a Linear simulation solution, the material thermal properties are not dependent on time or temperature. In addition to Linear solution scenarios, it is required that there is an absence of heat transfer due to radiation and no presence of other nonlinear physical effects.
* Because the default strategy defined in most simulation software solvers is usually nonlinear, it can sometimes be administratively confusing to define a linear solution during the initial simulation setup.

5. Thermal Strain Loading in a Stress Analysis

In often cases, the primary objective of FEM thermal analysis is to reveal insights into the thermal temperature distribution for use as an input parameter into a component stress analysis.
In a standard uncoupled thermal and structural simulation solution, a steady-state temperature distribution is mapped from the thermal model to the structural model.
Mapping can either be direct mapping within the same physical mesh or interpolated between dissimilar mesh models. In either case, both mapping methods will cause thermal strains throughout the structure.

Thermal strain values vary proportionally to the change in temperature from initial conditions and are influenced by the value of the thermal expansion Coefficient.

Free Expansion – Zero Stress

If a physical component subjected to a uniform change in temperature is allowed to expand freely, it will result in a uniformly constant thermal strain throughout the component and result in Zero/no stress.

Restrained Expansion – Thermal Stress

when a component subjected to thermal expansion is anchored at 2 points, the component is mechanically restrained from expanding freely.
This mechanical strain induces Thermal Stress and Thermal strain which has a relatively more complex temperature distribution & Mechanical boundary conditions.

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