Water is stirred by an electric mixing machine The mixing ma

Water is stirred by an electric mixing machine. The mixing machine operates at steady state and draws 15 amps of current from a 110V power supply. The mixing machine also discharges heat at a rate of 2 kW. If there is 100 kg of water that is initially at 20 degree C being mixed in a well-insulated (adiabatic tank), what is the temperature of the water after 3 hours of mixing?

Solution

Power Input to machines is

P=VI =15*110 =1.65 KW

Total Power

P_T=1.65+2 =3.65 KW

Energy

E=P_Tt =3650*3*60*60 =3.942*10⁷ J

Since

Q=m*c_w*(T₂-T₁)

3.942*10⁷ =100*4186*(T-20)

T=114.2^oC