At present, there are several ways to dissipate this heat; however, each of them has its drawbacks and efforts are underway to find better options. A team of researchers at BUT has contributed with a new and interesting solution.
Distribution boxes containing electronics situated in positions without forced air-flow (e.g. tunnels) may have inner temperatures reaching up to 60 °C thanks purely to the heat produced by electronics, whereas a temperature of 50 °C is considered the limit value. Therefore it is necessary to cool down the distribution boxes. This is possible using holes to supply cold air from the outside and allow the heated air to dissipate. Unfortunately, dust and moisture enter the box through the holes and damage electronics. Another cooling option is to use Peltiér cells, which heat on one side and cool down on the other. The disadvantage of these cells is their relatively low efficiency, which decreases with an increasing temperature gradient. An additional factor is the desire to make these distribution boxes as simple and low-cost as possible. Cooling cannot therefore be resolved using special cooling equipment with the forced circulation of cooling liquid. The question is, how to cool the electronics sufficiently without any external air supply in order to achieve longer service life?
The answer to the question has been found by the research team from the Heat Transfer and Fluid Flow Laboratory at the Brno University of Technology, led by Prof.Ing. Miroslav Raudenský, CSc. They replaced one side wall with vertical ribbing. To the ribbing can then be attached six small fans fitted on each side at the base of the ribbing and which can be switched on as necessary.
The tests demonstrated that at a heat output of 100 W inside the distribution box and an outside temperature of 30 °C, the device could not be operated without efficient cooling, as shown by the graph in Fig. 2, where 50 °C is considered the limit temperature which must not be exceeded. However, once ribbing was added to the distribution box, at an outside temperature of 30 °C, the temperature was only a few degrees above 50 °C. The limit temperature was safely met in the configuration with forced convection (fans switched on) outside the box (metal plate 0-1) and the configuration with forced convection both outside and inside the box (metal plate 1-1), when the temperature was reduced to 44 °C. The plastic and metal plate referred to in the graph indicate the material from which the box was made. The configuration metal plate 0-0 refers to the use of ribbing for cooling without the fans switched on. When compared to previous temperatures measured in distribution boxes without ribbing, a significant decrease in temperature can be seen if distribution boxes with vertical ribbing are used.
The distribution box with vertical ribbing and added fans is protected by the IPO CZ as a utility model with the title: “Distribution Box Adapted for Dissipating Heat to the Outside Environment”. Its main advantage over current designs is the sealed nature of the box, so that it cannot be entered by the surrounding air which might admit moisture and dust to the electronics. Thus electronic components are not fouled or endangered by humidity, and their service-life is therefore extended.
Photo: Archive of the Heat Transfer and Fluid Flow Laboratory, Faculty of Mechanical Engineering, BUT
