**4. Conclusions**

The current research provides a comprehensive numerical and experimental analysis for fibres produced using solution blow spinning (SBS). The flow characteristics of high-speed air through a bespoke nozzle were investigated numerically using computational fluid dynamics (CFD) and experimentally in a custom-built SBS setup to produce polyvinylidene fluoride (PVDF) submicron fibres. It has been concluded that under both laminar and k-ε turbulent flow conditions, a reverse flow was observed in the vicinity of polymer solution syringe outlet. As a result of this, if polymer solution droplets go<sup>t</sup> trapped by this reverse flow, there is high possibility that the droplets will not move forward causing the syringe/nozzle to choke. However, chocking of nozzle does not take place at air pressures up to 10 bar. Submicron fibres were produced at air pressures ≥ 2 bar. However, higher pressure of 4 bar was found to be more e ffective in producing fibres in the range of 150–200 nm. Upon increasing the air pressure to 5 bar, the fibre diameter increased and interlaced fibre ropes were produced as significant temperature drop (~251 K (−22 ◦C)) was observed due to Joule–Thomson effect. The results presented in the paper will pave the way for future research in fibre manufacturing using SBS.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2073-4360/12/5/1140/s1, Figure S1. Solid enclosure with zero slip around SBS nozzle. Figure S2. Meshed system for CFD of SBS nozzle. The mesh comprises of 793,731 nodes with 33,55,960 elements. Figures S3–S12. Laminar flow results. Figures S13–S22. CFD contours for k-ε turbulent model at di fferent values of ε*c*1 and ε*c*2. Figures S23–S71. k-ε turbulent model-based contours with default parameters.

**Author Contributions:** I.S. and A.H.H. conceived the project; E.E., N.S. and A.H.H. carried out the experimental work; M.C. and R.A. carried out the CFD; I.S. supervised all project activities; R.A. analysed SEM images and wrote the manuscript; J.K. supported manuscript writing and editing. All authors read and refined the data to make a compelling and coherent writing. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by British Council gran<sup>t</sup> number 352360451 and Newton-Mosharafa Call between UK and Egypt, ID: 30886.

**Acknowledgments:** The authors would like to thank British Council for providing funding for the Institutional Links Project (Project ID: 352360451) between Alexandria University, Egypt, and Northumbria University, Newcastle upon Tyne, UK. This work is part of the project of (Newton-Mosharafa Call between UK and Egypt, ID: 30886) which has been funded by Science, Technology & Innovation Funding Authority (STIFA), Egypt.

**Conflicts of Interest:** The authors declare no conflict of interest.
