Cooling of human Body
Human being looses heat by means of radiation, evaporation and convection from body that are necessary for the thermo-regulation. Evaporation and convection processes are reason of cooling effect generated by electric fan.
Cooling due to evaporation
On hot days our bodies sweat for losing body heat in form of evaporation of moisture content. In the still air, evaporating of sweat body moisture occurs due to the air surrounding the human body. But with evaporation, humidity in surrounding air reaches to approx.100 percent which leads to ineffective the cooling process. As air passes it replace hot humid air with cool dehumidified air. Fan at faster rate replaces this hot-humid air forcefully to allow cooler-dehumidified air which increases rate of evaporation of the sweat of human body. Thus electric fan just increases rate of evaporation of human sweat which tends to feel us cooler.
E.g. in the summer season water gets and maintained cooler if we store it in earthen pot. This happens because of cooling due to evaporation. Water evaporates from fine pores of pot thus cause cooling effect. (Manasmayankkarn, 2017)
Cooling due to convection
Even when our body doesn’t sweat it loses heat. This heat is carried away from human body by means of convection. If surrounding air is cooler than body temperature then surrounding air absorbs body heat thus temperature of air rises. As surrounding air temperature rises, it is replaced by cooler air and thus more heat is absorbed from body. Electric fan increases flow rate of air thus human body feels more comfortable with electric fan. (Energy.Saver, n.d.)
E.g. In case of processor of laptop, it also works on concept of convection. As temperature of laptop unit rises, it’s cooling fan starts which lead to increase the flow rate of air. By this flow, warmed air of laptop replaces with cooled air. In cases of bike engine with same concept heat is transferred. Due to speed of bike atmospheric air comes in contact with bike engine at higher rate. Temperature of engine is higher than atmospheric air hence transfer of heat takes place by mean of convection as heat transfer takes place in human body due to convection.
Energy.Saver, n.d. Principles of Heating and Cooling. [Online] Available at: https://www.energy.gov/energysaver/principles-heating-and-cooling [Accessed 5 March 2018].
Manasmayankkarn, 2017. Give five example and explain evaporation cause cooling. [Online] Available at: https://brainly.in/question/1181405 [Accessed 5 March 2018].