FEATURE RACKS, CABINETS & ENCLOSURES
(RE)DESIGNING RESISTORS WITH COMPUTATIONAL FLUID DYNAMICS
Computational Fluid Dynamics (CFD) combines the principles of fluid mechanics with numerical algorithms to analyse the behaviour of a fluid (like air or water) and the forces they exert on bodies. Here Damiano Natali, research and development engineer at Cressall Resistors, explains how this technique can be utilised for improving electronics systems enclosures product design
C
omputational Fluid Dynamics (CFD) is one of the Computer Aided
Engineering (CAE) technologies that has flourished in the last decade, given its flexibility in allowing manufacturers to understand their products better and improve product performance quicker and with fewer resources. CAE is used in factory settings in a wide range of stages: from first design and proof of concept through to the development and verification of a product. By providing a reliable and accurate
digital simulation of how a resistor will perform in a given situation, the manufacturer can identify potential drawbacks and improvements early in the design process. Moreover, CAE tools allow engineers to perform simulations on existing products without having to design, set up and maintain a highly complex testing rig. Finally, CAE allows design engineers to experiment with changing different parameters (the so- called “what-if” analysis) and –hopefully - to find the optimum design. In turn, this translates into time and cost savings.
WIND/WAVE FORCE ON ENCLOSURES OUT IN THE FIELD One challenge power resistor manufacturer, Cressall continuously faces is the brittle nature of ceramic post insulators. Apart from the primary function of providing electrical insulation, post insulators play a fundamental part in the structure of the enclosure. This problem is sharpened by the brittle nature of the porcelain ceramic from which they are made. Post insulators need to withstand the impact of the journey from factory to site, the installation and the strong winds they will be facing throughout their lifetime, especially for offshore or near coast projects such as wind farms. By using CFD, Cressall’s design engineers can assess the wind force that an enclosure can be subjected to - ensuring that the product is fit for purpose and for the environment it will operate in.
34 JUNE 2018 | ELECTRONICS Figure 1:
Power resistors reach high temperatures in service which makes the design of the cooling mechanism a critical part of the design process
Figure 2:
By providing a reliable and accurate digital simulation of how a resistor will perform in a given situation, the manufacturer can identify potential drawbacks and
improvements early in the design process
NATURAL AIR CONVECTION Power resistors reach high temperatures in service which makes the design of the cooling mechanism a critical part of the design process. The principle cooling method is defined by the exact application of the resistor and location in which it is going be installed. The three methods used are natural or forced air convection or forced water-cooling. For all types, CFD allows engineers to understand the performance of the cooling system and make adjustments to refine a design. Furthermore, by experimenting with
different set-ups, design engineers can identify the best solution and maximise the power rating that can be assigned to the resistor – all using digital tools.
EV2 WATER-COOLED RESISTORS The EV2 water-cooled resistor has a very high power density which enables Cressall to offer a compact solution where water cooling is a preferred option. An accurate design aimed at streamlining and reducing all possible pressure drops is therefore crucial to enable customers to use smaller pumps and save energy in the long run. Thus CFD plays an important role in the design of water cooled resistors such as Cressall’s EV2. Recently, Cressall was asked to reduce the pressure drop in one of the systems where an EV2 water-cooled resistor was installed. In particular, the customer was limited on the amount of pressure available from the pumping system in such a way that the minimum flow rate needed to cool down the EV2 modules could not be reached. In this case, Cressall was able to replicate accurately the bottleneck in the system and quickly identify the necessary improvements. Cressall designed a new assembly to fit these customer requirements. The design went directly into production following a simple proving test without time- consuming iterative physical testing. The revised product was delivered in-line with the customer’s maintenance schedule. The applications of CFD are almost
endless, but the bottom line is that the software enables designers to pin-point specific performance of new products and improvements to established designs with confidence. It allows Cressall Resistors to meet the bespoke requirements of customers, making its products more precise and reliable, while also minimising design and test costs for clients. By using computer-aided engineering, Cressall Resistors is creating bespoke, reliable products, refining the classic design of the electrical resistor and bringing it into the era of smart manufacturing.
Cressall Resistors
www.cressall.com T: 0116273 3633
/ ELECTRONICS
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