Modelling and Evaluation of the Thermohydraulic Performance of Compact Recuperative Heat Exchangers in Supercritical Carbon Dioxide Waste Heat to Power Conversion Systems

Lei Chai,Savvas A Tassou

doi:10.1080/01457632.2021.1943833

Lei Chai, Savvas A Tassou

Open Access

https://doi.org/10.1080/01457632.2021.1943833

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Abstract

Compact recuperative heat exchangers are critical components in supercritical carbon dioxide (sCO2) waste heat to power conversion systems. To investigate their thermohydraulic performance, a model based on the segmental design and the ε-NTU method has been developed. Four different types of heat exchanger have been considered: printed circuit heat exchanger with straight channels (PCHE-SC); printed circuit heat exchanger with zigzag channels (PCHE-ZC); microtube heat exchanger (MTHE) and microtube heat exchanger with separator sheets (MTHE-SS). The performance of the heat exchangers for different fluid mass flow rates, temperatures and lengths was investigated in terms of Nusselt number, heat transfer coefficient, friction factor, pressure drop, heat transfer rate, entropy generation rate and augmentation entropy generation number. Results show that these parameters significantly impact on the thermohydraulic performance of compact recuperative heat exchangers and their optimal design. For the same operating conditions and equal heat transfer rate, PCHE-ZC and MTHE-SS can have a significantly smaller size than PCHE-SC and MTHE. The augmentation entropy generation number also demonstrates the improved performance and compactness that can arise from zigzag channels and separator sheets, making them suitable for demanding high pressure and temperature applications such as sCO2 heat to power conversion systems.

Highlights

Supercritical carbon dioxide has been attracting increasing attention in waste heat to power conversion applications due to its environmental credentials and many advantages over conventional power cycles
The augmentation entropy generation number demonstrates the improved performance and compactness that can arise from zigzag channels and separator sheets, making them suitable for demanding high pressure and temperature applications such as sCO2 heat to power conversion systems
The corresponding Q are, respectively, 131.9 and 264.8 kW for printed circuit heat exchanger with straight channels (PCHE-SC) and 132.8 and 266.1 kW for printed circuit heat exchanger with zigzag channels (PCHE-ZC). These results demonstrate that the use of printed circuit heat exchanger (PCHE)-ZC in sCO2 power cycles can significantly reduce the footprint of the heat exchanger compared to the baseline PCHE-SC

Summary

Introduction

Supercritical carbon dioxide (sCO2) has been attracting increasing attention in waste heat to power conversion applications due to its environmental credentials and many advantages over conventional power cycles. For compact recuperative heat exchangers used in sCO2 power cycles, very few researches focus on the test facilities and experimental work. The PCHE with zigzag channels showed 24–34% larger Nusselt number but 4–5 times higher pressure drops than that with the S-shaped fins. The compact heat exchangers employing the folded wavy fins performed well, achieving the design heat transfer rate with less than half the allowable pressure drop. Three-dimensional computational fluid dynamics (CFD) modeling has been performed by a number of researchers to investigate the heat transfer and pressure drop characteristics of PCHEs with straight and zigzag channels. Chai and Tassou [15] investigated the thermohydraulic performance of sCO2 flow in a PCHE with straight channels and compared the local heat transfer and friction pressure drop results with predictions from empirical correlations.

Methodology

Results and discussion

Conclusions

Notes on contributors