Sensitivity analysis for the airfoil fin arrangement of airfoil fin PCHE in S-CO2 Brayton cycle
- Sensitivity analysis for the airfoil fin arrangement of airfoil fin PCHE in S-CO2 Brayton cycle
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- A supercritical CO2 Brayton cycle (S-CO2 Brayton cycle) has advantages of both steam Rankine cycle’s low compression work and gas Brayton cycle’s low viscosity. From these characteristics S-CO2 Brayton cycle can achieve high efficiency and compact size. In Korea, Supercritical CO2 Brayton cycle Integral Experiment Loop (SCIEL) is developing to couple with various energy sources. However, heat exchangers in the S-CO2 cycle occupy large space due to working fluid’s low density. Therefore, previous researchers chose printed circuit heat exchanger (PCHE) which is highly compact and strength as a heat exchanger type for S-CO2 cycle and they found that pressure drop in PCHE is mainly dependent on flow channel shape. In these reasons, most of S-CO2 researches conducted for heat transfer and pressure drop performance about flow channel shapes. Among various flow channel shapes, airfoil fin channel shows best performance from the result that pressure drop is 1/20 in same heat transfer rate per volume comparing with zigzag channel shape and 1/3 comparing with S-shaped fin channel. One of previous research showed that pressure drop in same heat transfer rate per volume was maximum 10% different according to airfoil fin shape. Therefore sensitivity analysis for the airfoil fin arrangement of airfoil fin PCHE is conducted for developing SCIEL high temperature recuperator. Numerical simulation for S-CO2 airfoil fin PCHE is conducted using commercial CFD software ANSYS Fluent and validated simulation model using experimental data from previous researchers and airfoil fin wind tunnel experimental data.
Sensitivity analysis is conducted for four design variables which are mass flow rate, staggered arrangement, horizontal pitch, vertical pitch. From the sensitivity analysis results, as mass flow rate increasing heat transfer performance and pressure loss increase. Therefore as pressure loss and structural strength are acceptable, higher mass flow rate is desirable. In the aspect of staggered arrangement, fully staggered arrangement show 70% lower pressure drop even only 5.8% lower heat transfer performance than parallel arrangement. For horizontal pitch effect, heat transfer on the airfoil fins are important for entire heat transfer performance. And pressure loss decreases as horizontal pitch is longer. For vertical pitch effect, vertical pitch does not influence the heat transfer at the airfoil fins. Pressure loss and heat transfer for vertical pitch shows similar tendency with horizontal pitch. However, vertical pitch has more effect on pressure loss and heat transfer. And both horizontal pitch and vertical pitch can effect on heat exchanger performance when the other pitch is quite short to give an airfoil fin flow interaction. To quantify heat exchanger performance, Nu/Eu is introduced for the objective function which represent a ratio of heat transfer rate to pressure loss. As a result, staggered effect shows maximum 80% performance increase. In horizontal and vertical pitch effects, there are rapid performance decreasing point which are relative maximum value for the PCHE performance.
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