Heat and fluid-dynamic calculations and simulations

Optimizing cooling and heating

Thermal behavior of a system can sometimes have a major influence of the operating life of a mechanism. The analysis is often very complex, due to flow around the structure, as well the effect of moving parts. 3D calculations on the thermal behavior of such a system can therefore become very complicated and time-consuming, while the accuracy of these type of calculations is sometimes doubtful. In situations like this, it can be time-effective to perform analytical 1D or 2D calculations in Mathcad or Python, converting complex convection, conduction or radiation problems to well-known empirical relations. The figure provides an example of such an approach. Heat exchange and heat build-up in the marine propulsor resulted in insight as to appropriate oil viscosity and appropriate cooling methods.

Heat exchange and heat build-up in the marine propulsor resulted in insight as to appropriate oil viscosity and appropriate cooling methods. Heat exchange and heat build-up in the marine propulsor resulted in insight as to appropriate oil viscosity and appropriate cooling methods.

Besides performing analytical calculations, Huygens Engineers also simulates stationary and transient temperature profiles in solids. As heat is transported through (poor) conduction within solids, applications like plastic molding require active cooling and heating, which needs to be predicted accurately to ensure the product quality.

The conductivity can vary largely within one model and is not necessarily constant for the entire temperature range. For example, in case of plastic molding, a steel mold will conduct heat much faster than the plastic product. For organic materials, like meat, varying thermal properties are also very common, as freezing and boiling effects of the water and fat content will influence the specific heat and conductivity. An example of transient cooling in a low conductivity meat product and a video of transient cooling in a high conductivity mold can be viewed in the figure below.

An example of transient cooling in a low conductivity meat product An example of transient cooling in a low conductivity meat product
A video of transient cooling in a high conductivity mold can be viewed in the figure below A video of transient cooling in a high conductivity mold can be viewed in the figure below

In convection-oriented cases, Huygens Engineers determines convection coefficients through detailed simulation, validation and measurement of elements in a flow.

A specific phenomenon with regard to cooling and heating is that of a thermal shock and related material stress. A sensor utilized in a cyclical temperature environment did not reach the desired service-life targets when subjected to cycles where temperature rapidly increased from -30 °C to 60 °C.

Simulation in ANSYS transient thermal showed that two effects caused mechanical stress to exceed acceptable values during this cycle. The first effect is a difference in thermal expansion due to the slow propagation of temperature, which in turn is caused by the low thermal conductivity of stainless steel. The second effect is a large difference in thermal expansion coefficients (almost by a factor 2) between austenitic stainless steel, used in the casing, and precipitation of hardening stainless steel, used in the element containing the strain gauges. The video shows a visualization of this thermal shock as described.
2D finite-difference Python-simulation 2D finite-difference Python-simulation
ANSYS-simulation ANSYS-simulation
Sometimes programming is the way to go.  Huygens Engineers has experience in transient simulation of cyclical two-dimensional cooling of drum motors in interaction with the belt that it drives.

Drum-motors in belting applications cool through cyclical contact of parts of the drum with the belt during rotation and subsequent transient thermal conduction. This cyclical process results in a long-term cyclical thermal equilibrium of the belt and the drum-motor, as each go through their periodic motion. The polymer of the belt conducts heat poorly, and belts may or may not be subjected to temperatures at which mechanical strength drops below specification.

Huygens Engineers developed a 2D finite-difference Python-simulation for hot product environments for application engineering. The figure below shows a simulation of finite difference implementation, thermal performance prediction and a discretized numerical model in Python.
Besides conduction and convection, radiation may play a role in heat transport. Shown in the figure is an ANSYS simulation of radiative heat transfer from Infrared (IR) heaters to a plastic part. This approach is used by one of our customers to realize controlled local heating in the geometry. By performing IR absorption measurements on the material, Huygens Engineers was able to calculate the heat absorption of the plastic material. The figure shows a transient simulation of radiative heating of plastic.

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