Introduction
Here at Ritherdon we are always aiming to improve the performance of our products based on customer requirements, and one of the ways we do this is through in-house testing, which is part of Ritherdon’s commitment to the continuous improvement of our products and our business.
Earlier in the year, we carried out an investigation to determine how best to optimise the heat transfer out of Ritherdon cabinets with the aim of making our cabinets as versatile as possible.
Our cabinets house hardware ranging from networking equipment to power supplies, all of which generate heat during their use. During the hot season, the higher temperatures causes the equipment in the cabinets to overheat, tripping the temperature sensor and turning the equipment off.
Our cabinets are sold as standard with venting (placed on the sides), however if the customer desires a higher IP rating, the venting can be removed from the design, however this may impact on the cabinet thermodynamics. This investigation took into account both scenarios.
Experiment Overview
Experiments were carried out using ventilated cabinets and sealed cabinets containing a 400W heating element. Up to four 19W fans were used to circulate air around and extract air from the system to determine the most effective arrangement. A diagram of the rig can be found below.
 Each arrangement was tested over the course of a day and repeated once to obtain reliable results. The average inside cabinet temperature was measured continuously using eight thermocouples, the surface temperature was measured at 90 points, 6 times per test to calculate an average, and the ambient temperature was measured continuously using an ambient temperature sensor, all of which were used to calculate convective heat transfer coefficients.
Air flow and temperature in and out of the cabinet was measured and used to produce a heat and mass balance around the cabinet.
Conclusions
The following conclusions were made from the experiment:
- It was found that there was a limit to the overall heat transfer coefficient of approximately 4.1 W/m2K for sealed cabinets.
- Stirring fans were found to have a similar effect to extraction fans when running in a sealed cabinet, despite the extraction fans running directly against a sealed surface.
- Pure natural convection was found to be as effective as the use of a single stirring fan for a ventilated cabinet.
- Stirring fans were found to have a negative effect when used in conjunction with extraction fans for a ventilated cabinet.
- The lowest temperature difference was found to be 20°C, using two extraction fans at the top sides of the cabinet.
