Energy Analysis of Control Volumes at Steady StateOil

Chapter 4, Problem 72P

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QUESTION:

Oil enters a counterflow heat exchanger at \(450 \mathrm{~K}\) with a mass flow rate of \(10 \mathrm{~kg} / \mathrm{s}\) and exits at \(350 \mathrm{~K}\). A separate stream of liquid water enters at \(20^{\circ} \mathrm{C}\), 5 bar. Each stream experiences no significant change in pressure. Stray heat transfer with the surroundings of the heat exchanger and kinetic and potential energy effects can be ignored. The specific heat of the oil is constant, \(c=2 \mathrm{~kJ} / \mathrm{kg} \cdot \mathrm{K}\). If the designer wants to ensure no water vapor is present in the exiting water stream, what is the allowed range of mass flow rates for the water, in \(\mathrm{kg} / \mathrm{s}\) ?

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QUESTION:

Oil enters a counterflow heat exchanger at \(450 \mathrm{~K}\) with a mass flow rate of \(10 \mathrm{~kg} / \mathrm{s}\) and exits at \(350 \mathrm{~K}\). A separate stream of liquid water enters at \(20^{\circ} \mathrm{C}\), 5 bar. Each stream experiences no significant change in pressure. Stray heat transfer with the surroundings of the heat exchanger and kinetic and potential energy effects can be ignored. The specific heat of the oil is constant, \(c=2 \mathrm{~kJ} / \mathrm{kg} \cdot \mathrm{K}\). If the designer wants to ensure no water vapor is present in the exiting water stream, what is the allowed range of mass flow rates for the water, in \(\mathrm{kg} / \mathrm{s}\) ?

ANSWER:

Oil enters a counterflow heat exchanger at 450 K with a mass flow rate of 10 kg/s and exits at 350 K. A separate stream of liquid water enters at 20°C, 5 bar. Each stream experiences no significant change in pressure. Stray heat transfer with the surroundings of the heat exchanger and kinetic and potential energy effects can be ignored. The specific heat of the oil is constant, c = 2 kJ/kg · K. If the designer wants to ensure no water vapor is present in the exiting water stream, what is the allowed range of mass flow rates for the water, in kg/s?

Solution

Step 1 of  3

We need to find out the allowed range of flow rates for water.

Given,

For the oil,


        

For water,

At state  

Then,

state, the liquid water turns into vapor.

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