Enhancing fluid flow through capillary tube by modifying inner wall wettability

¹ Department of Aerospace Engineering, Amrita School of Engineering, Coimbatore, Amrita Vishwa Vidyapeetham, India.
² Department of Aerospace Engineering, Khalifa University of Science and Technology, Abu Dhabi, United Arab Emirates.

^* Corresponding author’s email: This email address is being protected from spambots. You need JavaScript enabled to view it.

Published online: 26 September 2025

Abstract

This paper investigates influence of the inner wall wettability on mass flow rate and discharge coefficient (Cd) for the flow of water through a 1 mm diameter capillary tube with circular cross-section. The wettability of the inner wall of the tube was modified by dip coating of the capillary tubes in the solution made out of Trichloro(1H,1H,2H,2H-tridecafluoro-n- octyl) silane (FOTS) and n-hexane. Further, the coated capillary tube is heated to 250 ⁰C and 350 ⁰C for a time span of 2 hours to enable effectiveness of coating. Upon coating and heating to 250 ⁰C, the contact angle was incremented from 32.72° (for uncoated capillary tube), to 114.92°. At the same time, the inner surface contact angle has reduced to 67.72⁰ while heating the coated tube to 350 ⁰C. In order to analyse the effect of length to diameter ratio of the capillary tube on fluid flow behaviour, three different orifices with the length of 10mm, 15mm, and 30mm were chosen with three different wettability conditions. The increase in contact angle resulted in higher mass flow rates and Cd for all the capillary tubes considered in this study. The uncoated orifice tubes resulted in the lowest flow performance, while the orifice with a contact angle of 114.92° led to the highest efficiency, implying that reduced contact of the wall with water liquid minimizes the energy dissipation and enhances the fluid transport. The consistency in the trends which has been observed across the different Length to Diameter ratios proposes the idea that wettability modification can be used as an effective and scalable method for enhancing fluid transport systems. And by refining of this property gives precise manipulation of fluid transports in applications like microfluidics, fuel injection and bio medical devices