Experimental investigation on rheological, momentum and heat transfer characteristics of flowing fiber crop suspensions Samira Gharehkhani a,b , Hooman Yarmand c , Mohammad Shahab Goodarzi d , Seyed Farid Seyed Shirazi e , Ahmad Amiri c , Mohd Nashrul Mohd Zubir c , Khalid Solangi f , Rushdan Ibrahim g , Salim Newaz Kazi c, ⁎, Somchai Wongwises h, ⁎ a Department of Mechanical Engineering, University of Tehran, Tehran, Iran b Chemical Engineering Department, Lakehead University, Oliver Road, Thunder Bay, Ontario, Canada c Department of Mechanical Engineering, Faculty of Engineering, University of Malaya, Kuala Lumpur, Malaysia d Department of Mechanical Engineering, Mashhad Branch, Islamic Azad University, Mashhad, Iran e Department of Mechanical and Aerospace Engineering, Science and Research Branch Islamic Azad University, Tehran, Iran f Department of Mechanical and Aerospace Engineering, Missouri University of Science and Technology, Rolla, United States g Forest Research Institute Malaysia, 52109 Kepong, Selangor, Malaysia h Fluid Mechanics, Thermal Engineering and Multiphase Flow Research Lab (FUTURE), Department of Mechanical Engineering, Faculty of Engineering, King Mongkut’s University of Technology Thonburi, Bangmod, Bangkok, Thailand abstract article info Available online 13 December 2016 The study of pulp suspension flow is one of the most significant scientific interests since the considerable changes in the flow behavior of water were noticed after adding a small amount of fiber to water. The rheological studies on Kenaf pulp (a fiber crop) suspensions revealed that concentration has a great influence on variations of viscos- ity and yielded stress values. Heat transfer and pressure loss data were obtained from Kenaf suspension flow at different concentrations over a wide velocity range in a straight pipe. Kenaf suspension at the concentration of 0.6 wt.% showed maximum drag reduction. A considerable increase in the heat transfer coefficient of Kenaf sus- pension (0.2 wt.%) was also observed. Such an increment in the heat transfer coefficient ratio of Kenaf suspension flow is interesting since the enhancement of heat transfer has mostly been reported for suspensions containing nanoparticles and not for natural fibers in microscale. Moreover, the effects of fiber length and flexibility on mo- mentum and heat transfer data were studied. © 2016 Elsevier Ltd. All rights reserved. Keywords: Pulp suspension Viscosity Heat transfer Pressure drop Drag reduction 1. Introduction The flow of fiber suspensions has been applied in many industries, such as reinforcing composites, food processing, textiles, pulp, and the paper industry. Pulp and paper industries are the biggest users of fiber suspension. The major raw material in paper-making is pulp, which consists of cellulose fibers that come from wood and non-wood plants. The main sources for wood pulps are softwood trees (e.g., spruce and pine) and hardwood trees (e.g., eucalyptus and aspen). Concerning non-wood, crops and agriculture residues are used (e.g., empty fruit bunch and Kenaf) [1–3]. Presently, due to the rising global demand for fibrous material, the shortage of trees in many areas, and increasing en- vironmental awareness, fiber crops have become one of the most im- portant alternative sources of fibrous material in the 21st century [4]. One of the fiber crops used as a source for paper-making is Kenaf (Hibiscus cannabinus L.) Southern Asian countries such as India, China, and Thailand account for 90% of the world's plantations and more than 95% of the world's production of Kenaf [5]. An understanding of pulp suspension's flow behavior can be used to design pipelines in the paper industry, which may curb the rejected paper production. From the standpoint of flow behavior studies, knowledge of the rheological properties of suspensions is es- sential. There are many studies on the viscosity variations of suspen- sions containing solid particles in both nanoscales and microscales [6,7]. Fibers in water change the water's rheological behavior. The in- teractions between the fibers and the hydrodynamic disturbance to the flow field result in increased viscosity. There have been a few studies on the rheological properties of very dilute pulp suspensions International Communications in Heat and Mass Transfer 80 (2017) 60–69 ⁎ Corresponding authors. E-mail addresses: salimnewaz@um.edu.my (S.N. Kazi), somchai.won@kmutt.ac.th (S. Wongwises). http://dx.doi.org/10.1016/j.icheatmasstransfer.2016.11.013 0735-1933/© 2016 Elsevier Ltd. All rights reserved. Contents lists available at ScienceDirect International Communications in Heat and Mass Transfer journal homepage: www.elsevier.com/locate/ichmt