Assessment of the naphthalene sublimation technique for determination of convective heat transfer in fundamental and industrial applications

• Published in: Heat and Mass Transfer
• Main Authors: Niebles Atencio, Bercelay, Jamshidi, Hamed, Liljemark, Marcus, Nilsson, Håkan, Chernoray, Valery
• Format: Article in Journal/Newspaper
• Language: English
• Published: Mätteknik 2019
• Subjects: Electric generators; Naphthalene; Nozzles; Reynolds number; Scanning; Stators; Sublimation; Ventilation ducts; Convective heat transfer; Experimental methods; Generator modeling; Hydraulic diameter; Local heat transfer distribution; Naphthalene sublimation; Naphthalene sublimation technique; Turbulent impinging jet; Heat convection; Natural Sciences; Naturvetenskap; Chalmers; Nozzle; The Nozzle; Luleå
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:ri:diva-42505; https://doi.org/10.1007/s00231-019-02803-x

The naphthalene sublimation technique is an experimental method for indirectly determining convective heat transfer. The technique is here assessed for two different configurations: the local heat transfer distribution for a circular air jet impinging normal to a flat surface, and the heat transfer occurring in the stator core of an electric generator model. The turbulent impinging jet is fully developed. Two Reynolds numbers based on the nozzle exit condition, 15000 and 23000, and two nozzle diameter distances from the jet exit to the surface, 6 and 8, are considered. For the generator turbulent internal flow with Reynolds number of 4100 is considered, based on the hydraulic diameter of stator ventilation ducts. Modern surface scanning methods and imprints of the naphthalene specimens were used for measuring the naphthalene sublimation rate. The impinging jet results are compared with experimental data found in the literature. Results from the generator model and numerical simulations are compared. For the impinging jet, the results show agreement with the already published experimental data sets. For the generator model, heat transfer results from experiments differ by around 13% compared to numerical results if a scanning of the surface is used for measuring the naphthalene sublimation and around 5% if weights are used for measuring the sublimation rate. Therefore, the results depend on the way the sublimation rate is quantified. From this study, it is possible to affirm that with advanced scanning procedures, the heat transfer can be resolved with very small naphthalene sublimation in cases of both fundamental and complex industrial applications such as electric generators. Funding details: NSC, C3SE; Funding details: Energimyndigheten; Funding text 1: Open access funding provided by Chalmers University of Technology. The research presented was carried out as a part of the “Swedish Hydropower Centre - SVC”. SVC has been established by the Swedish Energy Agency, Energiforsk and Svenska Kraftnät together with Luleå University of Technology, The Royal Institute of Technology, Chalmers University of Technology and Uppsala University. www.svc.nu . The simulations were performed on resources provided by the Swedish National Infrastructure for Computing (SNIC) at C3SE and NSC.