Two (K-type) thermocouples were inserted into the flow at the
inlet and outlet of the test section for measuring bulk temperatures
of nanofluid. In order to increase the outlet temperature accuracy
for laminar flow, a static mixer was inserted downstream of the test
section. To record the temperature at the outer surface of the
copper tube and the bulk temperature, four (K-type) thermocouples
were brazed on the inner tube wall and four (K-type) thermocouples
were inserted into the inner tube at equally spaced
10 cm distances (Fig. 6). The thermocouples were calibrated before
tests and had a maximum accuracy of 0.1 C. All the data were
recorded by an Agilent 34970A data acquisition unit.
To determine inner wall temperature, the thermal resistance
due to conduction through the tube was taken into account. To
determine the inner flow bulk temperature Tbi we added a corrective
term by taking into account the fin effect due to the intrusive
thermocouples in writing an energy balance between forced
convective flowperpendicular to the thermocouple and conduction
in the thermocouple between its extremity and the wall