Rate of flow - thermal physics

[Kathhhriine]

Homework Statement

"The temperature difference between the inlet and the outlet of an air-cooled engine is 30.0 K. The engine generates 7.0 kW of waste power that the air extracts from the engine. Calculate the rate of flow of air (in kg s–1) needed to extract this power. Specifc heat capacity of air (at constant pressure)
= 1.01 × 10^3 J kg–1 K–1 "

Relevant Equations

power/specific heat capacityXtemperautre

Frankly, i don't even know how to start this. I deducted from the solution, that they must have used power/(specific heat capacity x temperautre), however i don't understand how that will give the rate of flow of air. Could anybody help, please?

 

[BvU]

Frankly, i don't even know how to start this.

Isn't good enough: we are not allowed to help if you don't post your own attempt

https://www.physicsforums.com/threads/homework-help-guidelines-for-students-and-helpers.686781/

pressure/specific heat capacityXtemperautre

What on Earth is that for an equation ?

Homework Statement:: "The temperature difference between the inlet and the outlet of an air-cooled engine is 30.0 K. The engine generates 7.0 kW of waste power that the air extracts from the engine. Calculate the rate of flow of air (in kg s–1) needed to extract this power. Specifc heat capacity of air (at constant pressure)
= 1.01 × 103 J kg–1 K–1 "

Try to re-formulate this in your own words, clearly separating the givens from the results asked for

Specifc heat capacity of air (at constant pressure)
= 1.01 × 103 J kg–1 K–1 "

You mean 1.01 kJ/(kg.K) ?

There is a subscript button under

in the edit window toolbar

I deducted from the solution, that they must have used pressure/(specific heat capacity x temperautre)

unlikely: pressure isn't mentioned in the problem statement.

how that will give the rate of flow of air

Have you done other exercises before ? Call the flow F (kg/s) and manipulate the relevant equation until you have F = ...

 

[Chestermiller]

This is a problem in the application of the open system (control volume) version of the first law of thermodynamics for steady state flow. Are you familiar with this equation. If so, please write it down and also identify the control volume that should be used in this problem.

 

[Kathhhriine]

Isn't good enough: we are not allowed to help if you don't post your own attempt

https://www.physicsforums.com/threads/homework-help-guidelines-for-students-and-helpers.686781/

What on Earth is that for an equation ?

Try to re-formulate this in your own words, clearly separating the givens from the results asked for

You mean 1.01 kJ/(kg.K) ?

There is a subscript button under View attachment 273489 in the edit window toolbarunlikely: pressure isn't mentioned in the problem statement.

Have you done other exercises before ? Call the flow F (kg/s) and manipulate the relevant equation until you have F = ...

I meant power, where i wrote pressure, sorry.

 

[BvU]

Try to re-formulate this (the problem statement) in your own words, clearly separating the givens from the results asked for

Another tip: look carefully at the units

 

[Chestermiller]

I guess I'll answer my own question. The correct equation to use is $$\dot{m}\Delta h=\dot{Q}$$where $\dot{m}$ is the mass flow rate, h is the specific enthalpy, and $\dot{Q}$ is the rate of heat transfer to the coolant air.