Consider an oil-to-oil double-pipe heat exchanger whose flow arrangement is not known. The temperature measurements indicate that the cold oil enters at 15°C and leaves at 55°C, while the hot oil enters at 80°C and leaves at 40°C. Do you think this is a parallel-flow or counter-flow heat exchanger? Why? Assuming the mass flow rates of both fluids to be identical, determine the effectiveness of this heat exchanger.

The heat exchanger has been the system that has been used for the transfer of heat between the fluids. The efficiency of the heat exchanger has been the ratio of the heat exchanger with respect to the ideal exchanger.

The counter flow heat exchanger has been the transfer of the heat in the opposite directions between the liquids. The parallel-flow heat exchanger has a flow of directions in the same directions.

In the given system the heat has been gained by a system and has been lost by another system. Since there has a flow of directions in opposite directions, the system has a counter-flow heat exchanger.

The efficiency of the heat exchanger has been given as:

[tex]E=\dfrac{mc\Delta T_a}{mc\Delta T_{max}}[/tex]

Where the mass of the gas has been m.

The specific heat of the gas has been c.

The actual change in temperature has been [tex]\Delta T_a[/tex]

[tex]\Delta T_a=55-15\;^\circ \rm C\\\Delat T_a=40\;^\circ \rm C[/tex]

The maximum possible change in temperature has been [tex]\Delta T_{max}[/tex]

[tex]\Delta T_{max}=80-15\;^\circ \text{C}\\\Delta T_{max}=65\;^\circ \rm C[/tex]

Substituting the values for efficiency of the heat exchanger, E:

[tex]E=\dfrac{40\;mc}{65\;mc} \\E=0.615[/tex]

The efficiency of the heat exchanger system has been 0.615.

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