Question

An engine is tested by means of a water brake at 1000 rpm. The measured torque of the engine is 10000 mN and the water consumption of the brake is 0.5 m3/s, its inlet temperature being 20°C. Calculate the water temperature at exit, assuming that the whole of the engine power is ultimately transformed into heat which is absorbed by the cooling water.

Answer 1

Power = T.ω

= 10000 × \(\left(\frac{2\pi \times 1000}{60}\right)\)

= 1.0472 x 10⁶ W

= 1.0472 MW

Let final temperature t°C

\(\therefore\) Heat absorb by cooling water / unit = ms \(\Delta\)t

= vps \(\Delta\)t

= 0.5 x 1000 x 4.2 x (t - 20)

\(\therefore\) 0.5 x 1000 x 4.2 x (t - 20) = 1.0472 x 10⁶

\(\therefore\) t - 20 = 0.4986 \(\approx\) 0.5

\(\therefore\) t = 20.5°C