On cold winter mornings, a driver’s vision is often blurred by moisture precipitating on the inside of the windshield. This happens when warm, humid air comes into contact with a cold surface. At a particular temperature, known as the dew point, the moisture in the air condenses and forms a layer on the colder surface; irrespective of whether this is a glass containing a cold drink, the bathroom mirror after a shower, or the windshield of a cold car. Cold air is not able to contain as much moisture as warm air and this fact is much more noticeable in small spaces, in a car for example. Condensation can be prevented by increasing the volume of air (opening the windows), by heating the whole of the vehicle’s interior, or by heating at least the windshield to a temperature above the dew point.
Ivica Kolaric of the Fraunhofer Technology Development Group TEG in Stuttgart favors the third option. His new process warms up the windscreen – though not with costly copper heating elements, but instead with a transparent coat of carbon lacquer, or more exactly carbon nano tubes (CNT). Kolaric and his team are currently working on a bonding system which, in a year or two from now, could keep not only windshields but also bathroom mirrors free from condensation. When attached to an electricity supply, the lacquer coating is transformed into a wide, flat heater which exactly covers the surface to be heated and continues to function even when it is damaged in places. If a heated windshield containing wire heating elements is chipped by a stone, for example, and one of the wires is severed, the entire heater could very well cease to function because of the interruption to the current. For the CNT heater, however, a few small defects in the coating are not a problem because the current flows over the whole surface. A further advantage of the “flat” conductor is its uniform heat distribution. Every single point on the surface of the windshield is heated evenly, rather than the warmth radiating outwards from the heating elements. The CNT coating itself does not store any heat. “The lacquer converts the electricity almost entirely into warmth and transfers this to the windshield,” explains Kolaric. The windshield is clear in a very short time with minimal power consumption. “What’s more,” he stresses, “the CNT resistance heater can be integrated in the vehicle’s standard 12-volt power supply.”