An adiabatic heat exchanger has 0.3 kg/s of water passing through one flow path.

Question

An adiabatic heat exchanger has 0.3 kg/s of water passing through one flow path. The inlet temperature and pressure are 20C and 150 kPa respectively. The other side has R134-a entering at 52C with a quality of 0.85. If the flow rate of the R134a is 0.1 kg/s and the exit temperature of the water is 25C, then what is the exit temperature of the R134a. If still a saturated mixture, what is the exit quality?   You may assume negligible pressure drop through either stream, and neglect changes in kinetic or potential energy.

Explanation / Answer

This problem is different from the previous one in that we will use ideal gas properties for argon. In addition, we are not given the mass flow rate; however we can find it from the data given on the inlet velocity and area. We have to find the specific volume, using the ideal gas equation at the inlet, to apply this formula. Using v = RT/P for the specific volume, with R = 0.2081 kJ/kg?K for argon gives the mass flow rate as follows.

For noble gases like argon, the heat capacity is constant over a wide temperature range. (See figure 4-24 on page 177.) Thus we can use the equation that hout

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