Use of optical distributed temperature sensors for condensation heat transfer measurements of R-134a in circular channels

In this paper, we experimentally demonstrate the viability of using distributed temperature sensors to obtain coolant temperature profiles during condensation of R-134a in a tube-in-tube heat exchanger configuration. The measurements from the distributed temperature sensors are compared with conventional RTD measurements co-located within the test section. The deviations between the temperatures measured by the RTDs and fiber optic sensors were less than 1 ?, and on average 0.4 ?. Successful demonstration of this new temperature measurement technique allows use of fiber optic distributed sensors to collect temperature data with very high spatial resolution for a wide range of experiments. The spatial resolution of fiber optic sensors is 0.65 mm which is impossible to achieve using traditional discreet point measurements such as Resistance Temperature Detectors (RTDs) and thermocouples due limitations in data acquisition systems and invasiveness of the sensor. These temperature readings are then be used to compute local condensation heat transfer coefficients over a range of operating conditions and compared to established literature correlation. The experimental data agreed best with the condensation correlation proposed by Cavallini et al. [1], with absolute average deviation equal to 7.8 %.