Thermoelectric cooling (TC), based on the Peltier Principle current when passed through a junction of two specific metals, generates heating or cooling depending on the direction of the current had been observed in the early 20th century but the effect was too weak to have practical application, Guha said.

Practical use of TC began about two decades ago when metals were replaced by semiconductors, he said.

The IIT-D Had designed a vaccine carrier based on TC in the eighties in which the temperature difference between the carrier chamber and the outside was 25 degree Celsius.

This did not work in summer as vaccines required a minimum temperature of nine degrees during transport under normal condition and much less in summer. Hence the project was abandoned, Guha said. Last year, Guha decided to combine TC with the principle of evaporation of water to design a carrier. The reason cited was that a thermoelectric module was good for high temperature differences but could cool small volumes, whereas evaporation, though allowed for low temperature difference, could cool relatively larger volumes.

Guha was successful in achieving sub-zero temperatures upto minus 20 degree Celsius by applying some active processes which could make heat flow from the `cold zone' to the `heat zone' against the normal rule.

Available foreign models of vaccine carriers are basically of two types. The popular model uses a special mixture which when refrigerated acquires great thermal capacity and is used as a substitute for ice for cooling. The other type is based on `electrolux cooling', a principle used in refrigerators half-a-decade ago, before the advent of compressors, but is not so popular, Guha said. The new self-independent system, having a size of 45 CM X 20 CM X 30 CM, could run as long as it was powered by a 12 volts battery or direct current or from a solar panel, Guha said.

A patent has been filed by IIT-D's Foundation for Innovation in Transfer of Technology (FITT) and an agreement signed with a Delhi-based company to commercialise the product, he said.