Conditional Thermomechanical Feasibility of a Bimetal Actuated Thermal Capsule
Abstract
A miniature thermal capsule must cool rapidly into a narrow temperature band while suppressing heat loss after contact release. This study couples geometry-dependent actuator stiffness, unilateral contact and pressure-dependent gap transfer to a two-node enthalpy model. A massless intermediate node enforces heat-flux continuity between the joint and its downstream resistance. A grid of 10,800 configurations tests entry into −21 to −19 °C within 3 s and uninterrupted residence for at least 30 s, together with provisional displacement and force requirements. At 1, 10 and 100 Pa, respectively, 148, 68 and 0 of 3600 configurations pass at nominal inputs. No nominally feasible candidate passed all 16 tested tolerance corners. Nominal residence at 1 and 10 Pa is right-censored, with lower bounds of 30.253 and 30.254 s, respectively; at 100 Pa the observed residence is 7.333 s. These results assume an external resistance of 22.80 K W⁻¹ and a gap regularization length of 1 μm. Illustrative metal sections explain only 1.03% of that resistance, making the counts conditional on an unidentified assembly and boundary network. Removing phase excess leaves the nominal zero-gas response unchanged, indicating isolation-dominated residence in that scenario. The contribution is a quantified loss of feasibility at tested tolerance corners, not experimental performance or an exclusion of all continuous designs.
Downloads
References
Aperam Alloys Imphy. (2025, May). Thermostatic bimetal high flexivity SP series [Data sheet]. https://www.aperam.com/sites/default/files/documents/BIMETAL%20High%20Flexivity%20EN%20MAY%202025%20EN.pdf
Bianco, V., De Rosa, M., and Vafai, K. (2022). Phase-change materials for thermal management of electronic devices. Applied Thermal Engineering, 214, Article 118839. https://doi.org/10.1016/j.applthermaleng.2022.118839
Castelli, L., Garg, A., Zhu, Q., Sashital, P., Shimokusu, T. J., and Wehmeyer, G. (2023). A thermal regulator using passive all-magnetic actuation. Cell Reports Physical Science, 4, Article 101556. https://doi.org/10.1016/j.xcrp.2023.101556
COMSOL AB. (n.d.). Theory for thermal contact (COMSOL Multiphysics 6.4 Heat Transfer Module documentation). Retrieved October 26, 2026, from https://doc.comsol.com/6.4/doc/com.comsol.help.heat/heat_ug_theory.07.094.html
Cooper, M. G., Mikic, B. B., and Yovanovich, M. M. (1969). Thermal contact conductance. International Journal of Heat and Mass Transfer, 12, 279–300. https://doi.org/10.1016/0017-9310(69)90011-8
Farid, M. M., Khudhair, A. M., Razack, S. A. K., and Al-Hallaj, S. (2004). A review on phase change energy storage: materials and applications. Energy Conversion and Management, 45, 1597–1615. https://doi.org/10.1016/j.enconman.2003.09.015
Guo, L., Zhang, X., Huang, Y., Hu, R., and Liu, C. (2017). Thermal characterization of a new differential thermal expansion heat switch for space optical remote sensor. Applied Thermal Engineering, 113, 1242–1249. https://doi.org/10.1016/j.applthermaleng.2016.11.102
Heinz, A., and Moser, C. (2023). Numerical modelling and experimental testing of a thermal storage system with non-spherical macro-encapsulated phase change material modules. Journal of Energy Storage, 58, Article 106427. https://doi.org/10.1016/j.est.2022.106427
Joint Committee for Guides in Metrology. (2008). Evaluation of measurement data—Guide to the expression of uncertainty in measurement (JCGM 100:2008). https://doi.org/10.59161/JCGM100-2008E
Kommandur, S., and Kishore, R. A. (2023). Contact-based passive thermal switch with a high rectification ratio. ACS Engineering Au, 3, 76–83. https://doi.org/10.1021/acsengineeringau.2c00046
Park, S. W., Li, J., and Weisensee, P. B. (2024). Development of a fully packaged passive thermal regulator. Scientific Reports, 14, Article 16979. https://doi.org/10.1038/s41598-024-67758-4
Righetti, G., Zilio, C., Doretti, L., Longo, G. A., and Mancin, S. (2021). On the design of phase change materials based thermal management systems for electronics cooling. Applied Thermal Engineering, 196, Article 117276. https://doi.org/10.1016/j.applthermaleng.2021.117276
Rubitherm Technologies GmbH. (2022, July 12). SP-21 technical data sheet [Data sheet]. https://www.rubitherm.com/media/products/datasheets/Techdata_-SP-21_EN_12072022.PDF
Shivalik Bimetal Controls. (n.d.). Thermostatic bimetal handbook. https://www.shivalikbimetals.com/Catalogue.pdf
Specialty Coating Systems. (2022, March 2). A guide to Parylene service temperatures. https://scscoatings.com/newsroom/blog/a-guide-to-parylene-service-temperatures/
Tan, B., Lyu, J., Yang, F., Xu, K., Qiao, S., Song, B., Yang, L., and Liu, K. (2026). Bistable origami thermal switch with high switching ratios. Nature Communications, 17, Article 3177. https://doi.org/10.1038/s41467-026-69956-2
Timoshenko, S. (1925). Analysis of bi-metal thermostats. Journal of the Optical Society of America, 11(3), 233–255. https://doi.org/10.1364/JOSA.11.000233
Voller, V. R., Cross, M., and Markatos, N. C. (1987). An enthalpy method for convection/diffusion phase change. International Journal for Numerical Methods in Engineering, 24, 271–284. https://doi.org/10.1002/nme.1620240119
Voller, V. R., and Prakash, C. (1987). A fixed grid numerical modelling methodology for convection-diffusion mushy region phase-change problems. International Journal of Heat and Mass Transfer, 30(8), 1709–1719. https://doi.org/10.1016/0017-9310(87)90317-6
Xiao, Z., Kishore, R., and Booten, C. (2025). Demonstration and characterization of insertable passive thermal switches for dynamic building envelopes. Cell Reports Physical Science, 6, Article 102668. https://doi.org/10.1016/j.xcrp.2025.102668
Zalba, B., Marín, J. M., Cabeza, L. F., and Mehling, H. (2003). Review on thermal energy storage with phase change: materials, heat transfer analysis and applications. Applied Thermal Engineering, 23, 251–283. https://doi.org/10.1016/S1359-4311(02)00192-8
Copyright (c) 2026 Thanh Duong Nguyen
This work is licensed under a Creative Commons Attribution 4.0 International License.
