Chapter 10

# Calorimetry with flow rate

Take 10 minutes to prepare this exercise.

Then, if you lack ideas to begin, look at the given clue and start searching for the solution.

A detailed solution is then proposed to you.

If you have more questions, feel free to ask them on the forum.

A coil is immersed in a calorimeter.

Is passed through the coil a current of water.

is the specific heat of water.

At the input, the water is at a temperature of , the output is the calorimeter temperature which, through an electric heater, is maintained at .

Calorimetry with flow rate

## Question

Calculate the power required from the heating resistance if the water flow rate through the coil is .

### Hint

Consider using a similar assessment to that used for flowing gas in thermal machines.

### Solution

Is selected as the closed fluid system in the calorimeter and a mass to the input at the instant .

At time , the system consists of the fluid in the calorimeter and a mass at the output, at the calorimeter temperature.

The first law of thermodynamics then gives : (assuming steady state)

## Question

The resistance is ; calculate the current intensity .

Write :

So :

## Question

Passing another liquid in the coil and for the same conditions (temperature and intensity), we must ensure a flow rate of .

Calculate the specific heat of the liquid.

### Solution

We have the equality :

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