Performance comparison of the liquid–vapor separation, parallel flow, and serpentine condensers in the organic Rankine cycle

Abstract

Organic Rankine cycle (ORC)-based power generation is a promising technology for recovering waste energy and effectively utilizing renewable energy with low enthalpy. A condenser is an important unit in ORC. The screening and design optimization of the condenser is significant in achieving high efficiency and low cost. Liquid–vapor separation (LSC) is a newly developed air-cooled fin-tube condenser with low pressure drop, low investment cost, and high compactness. The advantages of LSC have been proven in the refrigeration system. This study theoretically investigates the comprehensive performance of LSC in ORC. A mathematical model of LSC and an ORC that contains LSC is formulated. The effects of some key geometric parameters on the total heat transfer surface area and pressure drop of the condenser are examined. The total cost of investment and operation is selected as the objective function to identify the comprehensive performance of the heat transfer coefficient and presser drop at a constant heat transfer rate. The LSC is also compared with the serpentine condenser (SC) and parallel flow condenser (PFC) in terms of heat transfer coefficients, pressure drop, heat transfer area, and economic cost. The systematic performance of ORC containing different types of condensers is examined and compared in the context of ORC at fixed heat resource parameters and environment parameter. The structural parameter analysis shows that the tube length, tube inner diameter and tube pass arrangement with minimum cost of LSC are 1.5 m, 11 mm and 17-15-10-5-1, respectively. The optimal total cost of LSC is 3.74% and 34.50% lower than that of PFC and SC under a given design condition. The comparison of ORC with different condensers shows that the thermal efficiency (exergy efficiency) of ORC-LSC and ORC-PFC are 0~13.75% (0~11.82%) and 25.25~65.53% (21.83~52.3%) higher than those of ORC-SC, respectively. The sensitivity analysis of heat resource parameters and environment parameter is also performed, and quantitative comparisons of three ORCs are provided.