Abstract:
The organic Rankine cycle (ORC) is a suitable technology
for utilizing low-grade temperature heat sources of ~100 °C
from various industry processes. In the ORC cycle an organic
fluid with a lower boiling point is used as a working medium.
The performance of the ORCs has advanced significantly in the
last decades. However, there is still a possibility of improving
the efficiency of this cycle. The supercritical heat transfer in the
heat exchanger ensures better thermal match between the
heating and working fluids temperatures glides in the heat
exchanger. Hence, better understanding of the heat transfer
phenomena to a fluid at supercritical state in a horizontal flow
and in a large diameter tube is of great importance. Therefore,
the tests are performed in a counter-current tube-in-tube test
section positioned horizontally with a total length of 4 m and a
tube diameter of 0.0286 m. R-125 is used as a working fluid in
the experiments. During the measurements the temperature of
the heating fluid was 90 °C, the mass flow rate and the pressure
of the working fluid R-125 was in the range of 0.2–0.3 kg/s and
38–55 bar respectively. Furthermore, results from the pressure
and temperature measurements obtained at the inlet and at the
outlet of the test section are reported. The results show that the
overall heat transfer coefficient is influenced by the mass flow
rate of the organic fluid. At pressures close to the critical
pressure of R-125 higher values of the overall heat transfer
coefficients are determined. Deteriorated heat transfer is not
likely to occur at these operating conditions because the critical
heat flux is higher than the one obtained from the
measurements. A comparison between the experimental Nusselt
number with heat transfer (Nusselt) correlations from the
literature is done and the measurement points fall within the
uncertainty ranges of both heat transfer correlations.
Description:
Papers presented at the 13th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Portoroz, Slovenia on 17-19 July 2017 .
