Question

In an adiabatic mixing device (two inlets and one exit) operating at steady state, a 10 kg/s flow of fluid-A (with a specific entropy of 5 kJ/kg.K) is mixed with a 5 kg/s flow of fluid-B (with a specific entropy of 10 kJ/kg.K). At the exit (the flow rate is 15 kg/s), the specific entropy is measured as 7 kJ/kg.K. Determine the rate of entropy generation in the device.

Answer 1

Step-by-step explanation:

Formula for entropy balance for the given situation is as follows.

`(Q)/(T) + m_(A)S_(A) + m_(B)S_(B) - m_(AB)S_(AB) + S_(gen)` = 0

As the given system is adiabatic, hence Q = 0.

So,
`S_(gen) = m_(AB)S_(AB) - (m_(A)S_(A) + m_(B)S_(B))`

As the given data is as follows.

`m_(A)` = 10 kg/s,
`S_(A)` = 5 kJ/kg K

`m_(B)` = 5 kg/sec,
`S_(B)` = 10 kJ/kg K

`S_(AB)` = 7 kJ/kg K,

`m_(AB) = m_(A) + m_(B)`

= 10 + 5

= 15 kg/sec

`S_(gen) = 15 * 7 - (10 * 5 + 5 * 10)`

= 5 kW/K

Thus, we can conclude that the rate of entropy generation in the device is 5 kW/K.