Evaluation of Existing Heat Transfer Correlations in Designing Helical Coil Evaporators for Low-Temperature Organic Rankine Cycles via Inverse Design Approach

Abstract

ABSTRACTFor evaluating the heat transfer correlations from literature in designing helical coil evaporators for low-temperature organic Rankine cycles (ORC), an inverse evaporator design methodology is used. This is done by taking four already performed measurements with different working fluid mass flow rates (0.21–0.23 kg/s) and saturation pressures (1.93–3.05 MPa, reduced pressures of 0.51–0.82) at the helical coil evaporator (66 m long) in an already operational experimental solar/thermal ORC system as real-case references for the evaporator inverse design's boundary conditions. R-404A is considered as the working fluid. The heating water inlet temperature is changed between 353 K and 373 K. The total length is inversely calculated via 15 helical coil two-phase heat transfer correlations for each case. Their end designs are compared with the actual length. Results show that the correlations can be used interchangeably for designing helical coil evaporators for low-temperature ORCs since the heat transfer resistance is dominant on the shell-side. For evaluating the sensitivity of these results, a secondary analysis was made by means of changing the shell-side correlation's accuracy from its initial value of 10% to more accurate 7%. Predictions with several correlations design shorter heat exchangers at reduced pressures less than 0.7.