Efficiently cooling down systems that generate heat

In recent research, scientists from the Indian Institute of Technology Bombay (IIT Bombay) have used the Laws of Thermodynamics to establish optimal designs for cooling down gas turbine blades and other devices.  The researchers worked with the mathematical equations that govern the fluid flow through the microchannels and clubbed them with the known laws of Thermodynamics to study how the entropy depends upon the dimension of the tubes. The research was carried out by Dr Pallavi Rastogi during her doctoral studies, under the guidance of her advisor Prof Shripad P. Mahulikar from the Department of Aerospace Engineering. 

First, the researchers modelled a cooling system having a single microchannel of length 10 centimetres carrying the cooling fluid. They found that the entropy of the system increases negligibly on decreasing the diameter from 1 millimetre. Even then, they showed that it is possible to carry out cooling efficiently until the diameter is about 0.2 millimetres. Below this diameter, however, the flow of the fluid becomes unpredictable and deteriorates in quality. Moreover, the amount of power needed to pump the coolant shoots up. When the diameter of the tube falls below a millimetre, studying the flow of fluid becomes more complicated. “Properties of the fluid, like velocity and temperature, vary along the flow, which we need to take into account in our calculations. Also, the different layers of the fluid have considerable mutual friction, which generates heat,” explains Dr Rastogi.

The researchers looked into making the system more efficient in transporting the heat by using multiple microchannels of the same dimension. “The question was whether we could use multiple microchannels to minimise the entropy. Although convection through microchannels has been studied before, convection through multiple microchannels has not been,” says Dr Rastogi. As the researchers decreased the diameters of each tube, their theoretical study predicted that two competing mechanisms of generating entropy in the fluid come into play.  The researchers found that there exists an optimum number of tubes, and an optimal diameter of each tube, that can successfully carry away the required amount of heat. According to the researchers, the mechanism can be used to cool down other devices such as microchips in integrated circuits and photovoltaic cells, the fundamental components required for converting solar energy into electricity.

(Source: Indian institute of Technology Bombay news release)