Dimension unification and dominance evaluation of multi-physical parameters for nanochannel-based ionic thermoelectric energy conversion using similarity principle

•Similarity principle analysis on nanochannel-based i-TE system is constructed.•Fifteen dimensionless variables are derived to reflect dimension unification.•Performance optimization and sample expansion are realized for applications.•Parameters dominating the nanochannel-based i-TE performance are presented. Ionic thermoelectric (i-TE) systems convert low-grade heat into electricity based on ion migration driven by the Soret effect under a temperature gradient. Current research conducts tentative experiments for superior i-TE materials and performance, whereas universal physical quantities reflecting the unified essence are still needed to guide experiments. In this study, the unified mechanism of i-TE energy conversion is analyzed using similarity principle by establishing nanochannel-based i-TE models, considering the Soret effect and heat transfer. Fifteen dimensionless variables are derived to represent the i-TE energy conversion process. Dimension unification is achieved by normalizing various dimensional phenomena with the deviation of 48.3% into one dimensionless situation with the deviation of 0.011%. These dimensionless variables can be further utilized to practical applications. Specifically, upon equal dimensionless variables, sample expansion is achieved with relative errors within 0.018% and the total time acceleration ratio of 7.33, alleviating experimental burden. Besides, the i-TE output power can be improved by 100% upon higher characteristic output power and equal dimensionless variables. Orthogonal tests are further implemented to clarify the parameter dominance, showing that the cationic reduced Soret coefficient is dominant on performance with contribution rates more than 25%. This work provides unified insight into coupling relations of multi-physical parameters in i-TE energy conversion to guide experimental designs.