Question 6.CSGP.87: An automotive radiator has glycerine at 95°C enter and retur......
An automotive radiator has glycerine at 95°C enter and return at 55°C as shown in Fig. P6.87. Air flows in at 20°C and leaves at 25°C. If the radiator should transfer 25 kW what is the mass flow rate of the glycerine and what is the volume flow rate of air in at 100 kPa?
If we take a control volume around the whole radiator then there is no external heat transfer – it is all between the glycerin and the air. So we take a control volume around each flow separately
Glycerine: \dot{ m}h_{ i }+(-\dot{ Q })=\dot{ m }h_{ e }
Table A.4: \dot{ m }_{ gly }=\frac{-\dot{ Q }}{ h _{ e }- h _{ i }}=\frac{-\dot{ Q }}{ C _{ gly }\left( T _{ e }- T _{ i }\right)}=\frac{-25}{2.42(55-95)}= 0 . 2 5 8 \,k g / s
Air \dot{ m }h_{ i }+\dot{ Q }=\dot{ m }h_{ e }
Table A.5: \dot{ m }_{ air }=\frac{\dot{ Q }}{ h _{ e }- h _{ i }}=\frac{\dot{ Q }}{ C _{ air }\left( T _{ e }- T _{ i }\right)}=\frac{25}{1.004(25-20)}=4.98 \,kg / s
