Thermal Modelling in Dubai, UAE

Best Thermal Modelling

Thermal Modelling

Thermal Modelling in Dubai, UAE

With the ever-increasing power densities in electronic systems, it is important that your system is designed not only for core functions but also for thermals. Thermal engineering is a critical part of modern electronic systems. Often, thermal management is seen as an after-thought in design considerations until it is determined that there is a problem somewhere in a system due to excessive heating and malfunction. Poorly designed thermal management systems lead to all kinds of problems, including sub-optimal functions, poor mechanical aspects, high failure rates, and shorter lives. This is completely preventable, especially when handled early in the design cycle using in-house seasoned thermal engineers or expert thermal management consultants. Sometimes, the thermal design solutions can be as simple as addressing thermal interface solutions, selecting better materials, heat sink modification, or redirecting airflow to where it should be in the case of active cooling. At other times, it may require extensive [thermal analysis](https://www.thermalds.com/thermal-analysis-thermal-modeling/) and testing to determine the root problem, and hence the solution. In some cases, it may require a totally brand-new approach involving some serious research and development.

Thermal Modelling is the analysis of junctions in your building. These junctions arise where there is a change in building materials, where two different components meet, or where there is a change thickness or direction of adjoining materials.

Thermal Modelling is used to analyse these junctions to examine for performance and provide recommendations on best practice to make sure you get the best from your building.

With the ever-increasing power densities in electronic systems, it is important that your system is designed not only for core functions but also for thermals. Thermal engineering is a critical part of modern electronic systems. Often, thermal management is seen as an after-thought in design considerations until it is determined that there is a problem somewhere in a system due to excessive heating and malfunction. Poorly designed thermal management systems lead to all kinds of problems, including sub-optimal functions, poor mechanical aspects, high failure rates, and shorter lives. This is completely preventable, especially when handled early in the design cycle using in-house seasoned thermal engineers or expert thermal management consultants. Sometimes, the thermal design solutions can be as simple as addressing thermal interface solutions, selecting better materials, heat sink modification, or redirecting airflow to where it should be in the case of active cooling. At other times, it may require extensive [thermal analysis](https://www.thermalds.com/thermal-analysis-thermal-modeling/) and testing to determine the root problem, and hence the solution. In some cases, it may require a totally brand-new approach involving some serious research and development.

Thermal Modelling is the analysis of junctions in your building. These junctions arise where there is a change in building materials, where two different components meet, or where there is a change thickness or direction of adjoining materials.

Thermal Modelling is used to analyse these junctions to examine for performance and provide recommendations on best practice to make sure you get the best from your building.

Why use Thermal Modelling?

Because of increased performance in insulation materials, for both new builds and improvements to existing dwellings, it is now more important than ever to focus on additional factors such as Thermal Bridging to identify heat loss.
In a well-ventilated building, humans find an ambient temperature of about 20°C comfortable. Choosing the right materials and structures allows engineers to smooth out temperature variations and use the natural day-night heating and cooling cycles of the building to minimise the need for artificial heating, cooling and air conditioning.
Thermal Modelling can be used for any building, but is compulsory for buildings which have any of the following features:
Thermal Modelling in Dubai, UAE
  1. Night ventilation strategy
  2. Ventilation with enhanced thermal coupling to the structure
  3. Demand controlled ventilation
  4. Automatic blind control
  5. Atria
A thermal model provides valuable information on a room-by-room basis, including;
“Energy modeling allows designers to push the envelope with less risk”

Even when whole-building energy modeling may be too costly or time consuming, elements of the approach can be tailored to fit many projects.

Thermal Modeling – Keys Steps

Thermal analysis requires a great deal of organization. The end result is the outcome of several activities combined. To begin, the thermal model has to have a physical model built within the analysis tool itself or imported from a CAD system. The physical model must closely represent the real system being modeled. The thermal model must also have numerous properties and boundary conditions assigned to it. These properties and boundary conditions define the nature of the system and its connection with its environment. Unrealistic boundary conditions give unrealistic results. Then the entire model must be discretized and analyzed to achieve a stable and accurate solution. In many cases, the final solution is obtained after a series of steps or iterations. At first, it is common to aim for a preliminary solution, based on basic inputs and a coarse mesh. After the first solution, we may refine the model by adding more details and mesh and re-run the model for another solution. The process continues until we are satisfied with our solution and the design is complete. All of this requires a step by step approach so the whole process is done correctly.

Basic Parameters

The basic parameters of a thermal analysis | thermal modeling are things like ambient temperature, the variables to be solved (temperature and/or flow variables), gravity effects, radiation parameters, whether the flow is laminar or turbulent, steady or transient, transient settings, etc. These parameters define the nature of the thermal system we would like to model. In a conduction-only model, we turn off flow-related specifications. In a highly convective environment with fans and the like, the effects of natural convection (gravity) and radiation may be neglected (and hence turned off). If modeling transient, we need to specify additional parameters such as time steps, start time and end times.

Relaxation factors control the speed by which the solution is achieved. Relaxation factors are necessary because the governing thermo-fluid equations are highly non-linear and cannot be solved in a few steps. Although the default settings are OK in most cases, we may need to adjust the relaxation factors for more complicated cases, so our solution does not diverge.

All of the forms where the basic parameters are specified must be checked properly to make sure that the model or the problem we are trying to solve is well-defined. Otherwise, we will not get accurate results from our thermal modeling exercise.

Thermal systems can be broadly classifieds into two groups: passively-cooled systems and actively-cooled systems.

In passively-cooled systems, there are no air or fluid moving devices, such as fans or blowers. The system is cooled due to air or fluid movement as a result of temperature differences with the ambient. This is called natural convection cooling. Here, the amount of heat loss to the ambient is proportional to the product of the exposed surface areas of the system and the temperature differences with the ambient fluid. In addition to natural convection cooling, passively-cooled systems also lose heat by radiation. In radiation, heat transfer takes place due to temperature differences between the surfaces of the system and the surroundings (walls, air, etc.). Here, as in natural convection, the extent of heat transfer depends on the exposed surface area of the system and its temperature difference with the ambient. In passively cooled systems, the effect of radiation is typically 25-50 percent, depending on how high the system temperature is relative to the surroundings and its surface conditions.

In actively-cooled systems, there is a fluid moving device inside or around the system. Fans, blowers, and pumps are all examples of fluid movers. In such systems, the effects of radiation and natural convection are generally small and may be neglected. In modeling actively-cooled systems, it is important that the flow is modeled accurately. The thermal analysis engineer must know whether the flow is predominantly laminar or turbulent, as these two flows are modeled somewhat differently. It is also important that the physical components, especially around high flow areas, are modeled in sufficient detail – so flow obstructions and turns are captured accurately, including in the vicinity of the air or fluid mover.

The basic parameter input forms must be checked periodically for accuracy in any thermal simulation tool, whether it is Ansys thermal analysis or FloTherm.

Domain Sizing & Boundary Conditions

A thermal model must have a domain within which the analysis must be conducted. The domain should include the key elements of the system that is being modeled, including the device itself. The domain also determines how the system being modeled interacts with the environment. Therefore, it is critical that we use the right domain size and shape for our model to include the device we are modeling as well as its immediate environment. In general, domain boundaries are chosen so that either a given variable has a fixed value at the boundary, or the spatial change of a variable is close to zero at the boundary (adiabatic or symmetry boundary conditions). Therefore, when we establish a domain, we must ensure that such assumptions are realistic and do not deviate from the real system, at least not by a whole lot.

In domain sizing, we must also strike a balance between unnecessarily large domain size and model accuracy. Often, larger domain size means bigger mesh count and longer run time. This can be a problem when you would like to know whether you are on the right track or not quickly, especially in the early stages of thermal modeling. Unnecessarily large mesh sizes will also be a problem in transient simulations, where the wait time can be a lot longer. The seasoned thermal analysis experienced engineer or thermal simulation consultants would know the appropriate domain size by experience, typically from prior models. Otherwise, one may conduct sensitivity analysis with 2-3 variations of domain sizes to see the effect of domain size on key variables.

Model Details

By model details, we mean the physical details of the system being analyzed. If we are modeling a laptop computer, for example, the model will have the key components such as the enclosure, display, PCB with components, Hard Drive and/or SSD, wireless components, power supply, interface materials, cooling solutions, etc. Today’s thermal analysis tools can import the physical model in its entirety. In many cases, small pins, protrusions, and curves do not matter much in thermal modeling, especially when they are far away from the main heat sources inside the system being modeled and/or when they are away from the main flow paths.
When building a model, a special attention must be given to areas in and around major heat sources, such as PCB and IC packages. The model must have the right details in these areas to capture the expected large gradients of the key variables in these areas. 
The physical system may be modeled suspended in air or sitting on (or next to) some surface with the appropriate gap or boundary conditions. Whatever components we include, our assumptions must be realistic and the boundary conditions consistent with the real situation we are trying to analyze.

Thermal Properties

Thermal properties include variables like thermal conductivity, specific heat, and density. In a steady-state analysis, thermal conductivity is the main variable to consider. In transient analysis, density and specific heat will also be important, in addition to thermal conductivity. All components in the thermal model must be assigned the right thermal properties. These properties govern how heat is transferred from one component to the other, and ultimately to the environment. Poor choice of thermal properties will, therefore, lead to poor results as well.
In some cases, the thermal property of a component or space may vary spatially. It may also depend on another variable, such as temperature. In those cases, we may define the appropriate profile of that property and assign it to the components in question. In some cases, such as in PCB modeling or thermal interface solutions, we may need to break up the component itself into layers or parts, so we can specify more exact properties for each part or layer.

Power

Thermal Modelling in Dubai, UAE
An electronic device becomes hot because heat is generated within some components of this device. This heat comes from the power each component draws from the power supply. Almost all power consumed by a given component within an electronic system is converted into heat. Therefore, it is very important that we know the exact power load on every component in our system. Our solution is as good as the accuracy of these inputs. In case of uncertainty, it is customary to err on the side of more conservative inputs.

In addition to the overall power loads, it is also important that we know the exact location where each power load is being dissipated. In IC Packages, for example, the power consumed by the die is not distributed throughout the die. Rather, much of the power comes from a few regions within the die. In general, the power is dissipated on one side or surface of the die. So, it is important that we specify the exact power load based on location. In today’s thermal analysis tools, these inputs are relatively easy to specify, provided one has the right data.

Meshing

Thermal-Model-Mesh

Thermal analysis | thermal modeling is conducted by digitizing the entire model domain into small areas and volumes called mesh elements or cells. Essentially, we break up the entire domain into thousands of small volumetric cells. Within each cell, we assume an average value for each variable such as temperature. The variables are supposed to vary between neighboring cells according to an assumed profile and governed by partial differential equations.

When it comes to meshing, one thing is critical: mesh refinement. In general, a model will have areas where the mesh is fine and areas where the mesh is coarse. We need a fine mesh in areas where the changes in variables (gradients) are high, and a coarse mesh in areas where the variations are low. This is because, using large cells, we cannot capture rapidly changing variables in a given space or time. In general, we should have much finer mesh close to solid objects or surfaces, as these areas are likely to have high gradients of the variables being solved.

The mesh lines do not have to conform at boundaries since almost all modern analysis tools have non-conformal meshing capability. In a non-conformal mesh, one cell can interface with two or more cells in the same direction. The values of variables at such cells are determined based on the appropriate interpolation of its neighboring cell values.

When we mesh a model, it is always a good idea to examine the mesh on planes and surfaces, so the mesh looks consistent with our expectations. Any areas where the mesh needs improvement must be addressed promptly, including areas where the mesh is too coarse or too fine, or when the cells are too distorted – elements with bad aspect ratios (very long on one side and short on the other, etc.).

The experienced thermal analysis engineer uses various mesh refinement levels and meshing strategies in his/her analysis. For quick runs or rough estimates, one may use coarse meshes. For the final results, we may use fine meshes. Run times are directly proportional to the number of mesh elements we have in a model.

Solving

Thermal Modelling in Dubai, UAE
Solving or running for a solution is one of the last two steps in thermal modeling. Here, the model will go through iterations to arrive at the final solution. As indicated above, the partial differential equations that govern fluid flow and heat transfer are highly none-linear. A This iterative process can involve tens, hundreds, or even thousands of iterations before the solution converges – meaning the values at all cell points cease to change appreciably.
For example, if the relaxation factors for temperature is 1, the cell temperature at the end of a given iteration is updated by the full
‘correction value’ obtained in that iteration. However, in almost all cases, taking the full correction value at the end of each iteration will lead to divergence – meaning, the solution will blow up and becomes worthless. So it is essential that we use values lower than 1, but higher than 0, for each variable being solved (such as flow, pressure, temperature, etc.).
In thermal simulations, one solution run is rarely sufficient to get the end result we want. Typically, our thermal modeling consultants go through a series of runs using a given model. In subsequent runs, we may add more details, adjust basic parameters, mesh refinement levels, domain sizes and run times, until we are satisfied with the final results.

Post-Processing

Thermal Modelling in Dubai, UAE
Thermal Analysis | Thermal Modeling Results
The last step in thermal modeling exercise is post-processing. When a model finishes solving, it is time to check the solution. With today’s state-of-the-art thermal analysis tools, there are numerous ways to display results. We may also build derivatives or functions of variables and display them on points, planes, and surfaces. There is no limit to how much we can slice and dice the thermal solution. In transient simulations, we can also make animations to show how the thermal profile of a system develops over time, which is especially useful to explain things to the uninitiated, including upper management and general customers.
While examining thermal simulation results, in general, the thermal engineer should view the results critically. It is very easy to get excited and carried away with pretty pictures and take their accuracy for granted. This can be a big mistake, especially in the early stages of thermal modeling. Therefore, we must check our solution for consistency and against our expectations to make sure that our solution is not erroneous.

Benefits: