Q4. State whether the following are true or false with a brief explanation (1-2 sentences). (i)...

Q4. State whether the following are true or false with a brief explanation (1-2 sentences).

(i) Given a control volume with one inlet and two exits, the two exits must have identical mass flow rates.

(ii) You are given a control volume with one inlet and one exit such that more ‘mechanical energy’ is coming in than going out (‘mechanical energy’ is the sum of enthalpy, kinetic energy and potential energy per unit mass), but are given no information on the work or heat interactions. The total energy (Ecv) within the control volume must increase with time.

(iii) You are given a control volume where the mass is changing with time but the control volume itself has no heat or work interactions with the surroundings. The total energy within this control volume must also change with time.

(iv) For a one-inlet, one-exit control volume at steady state, the volumetric flow rates must be equal at the inlet and the exit.

(v) An open control volume (i.e., with inlets and exits), by definition, always describes the same region and therefore, the specific volume of matter inside cannot change.

Solutions

Expert Solution

1) false : For a control volume undergoing a process, the conservation of mass can be stated as:

total mass entering control volume – total mass leaving control volume = net change in mass within control volume

2) true :

For control volumes, an additional mechanism can change the energy of a system: mass flow in and out of the control volume. Therefore, the conservation of energy for a control volume undergoing a process can be expressed as total energy crossing boundary as heat and work + total energy of mass entering Control volume – total energy of mass leaving Control volume = net change in energy of Control volume

5) true

samet mamat answered 1 year ago

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