Dhiman Chatterjee

Transdermal drug delivery (TDD), which enables targeted delivery with microdosing possibilities, has seen much progress in the past few years. This allows medical professionals to create bespoke treatment regimens and improve drug adherence through real-time monitoring. TDD also increases the effectiveness of the drugs in much smaller quantities. The use of polymers in the drug delivery field is on the rise owing to their low cost, scalability and ease of manufacture along with drug and bio-compatibility. In this work, we present the design, development and characterization of a polymer-based TDD platform fabricated using additive manufacturing technologies. The system consists of a polymer based micropump integrated with a drug reservoir fabricated by 3D printing and a polymer hollow microneedle array fabricated using photolithography. To the best of our knowledge, we present the fabrication and characterization of a 3D-printed piezoelectrically actuated non-planar valveless micropump and reservoir integrated with a polymer hollow microneedle array for the first time. The integrated system is capable of delivering water at a maximum flow rate of 1.03 mL/min and shows a maximum backpressure of 1.37 kPa while consuming only 400 mW. The system has the least number of moving parts. It can be easily fabricated using additive manufacturing technologies, and it is found to be suitable for drug delivery applications.

Numerical studies on rocket pumps are computationally expensive and hence the secondary passages such as sidewall clearance gaps, wear ring gaps, axial balancing mechanism, coolant/lubricant paths, etc. in the pump are usually not considered. In this study, a liquid propellant pump with and without secondary passages are modelled and flow simulation results are compared to analyse the differences in cavitation, vortices and radial force predictions arising due to the presence/absence of the secondary flow passages. Single-phase and multiphase simulations are conducted for the design and two off-design points. It is predicted that the presence of secondary passages has a significant effect on the type of cavitation instability predicted and on the volume of cavity generated in the inducer due to which the radial forces generated also differ significantly. The presence of secondary passages predicted large fluctuations from the average radial forces generated by the inducer. These are not obtained if the leakages are not considered. This type of underprediction during the design phase might cause severe wear and tear in the bearings during actual operation. Thus, this study stresses the need for incorporating the secondary passages even at the design stages. This study also highlights the possibility of cavitation instability type manipulation using some means in the inducer which would be significant for cavitation control research in rocket pumps.

In gasoline direct injection engines, fuel injector nozzle is one of the vital components that determine the efficiency of fuel atomization which controls combustion and emission. There is an increased focus on developing better nozzles by studying the internal flow behavior especially during the needle transient phase and at the end of injection phase. Multiphase flow characteristics involving cavitation and hydraulic flip are observed inside the nozzle during its operation. At the end of injection, fuel inside the nozzle sac and nozzle holes is purged with the gas from the engine cylinder. The efficiency of this purging process is critical to prevent the carbon deposit formation on the wall of nozzle holes and on the surface of the nozzle tip. In this article, a numerical method is presented to predict the internal nozzle flow during the needle movement and during the end of injection to predict the purging capacity of a gasoline direct injection nozzle. Needle motion is accomplished using a moving mesh method via a user-defined function. The numerical model is compared with the X-ray measurements from the literature. Based on the validated model, the study is extended to analyze various parameters like injection pressure, nozzle hole location, number of nozzle holes and the inlet rounding of the nozzle hole which affects the effectiveness of nozzle purging. Fuel wetting at the nozzle tip after the end of injection is also numerically modeled to evaluate the thickness profile of the thin liquid film.

The eminent energy crisis and high emission of fossil fuels provide thrust for developing renewable energy-based technologies. Wind and hydrokinetic energies are the most promising renewable energy resources for electric power generation to meet the growing energy demand. The vertical-axis hybrid turbine, which combines the features of good starting characteristics of the Savonius turbine and the operational efficiency of the Darrieus turbine, can serve as a viable option for power generation. A variety of configurations of the hybrid turbine are possible based on several design parameters such as the relative position of the Darrieus and Savonius rotors, overlap ratio, solidity ratio, blade or buckets shape and radius ratio, attachment angle and others. To some extent, the influence of these parameters on the hybrid turbine performance has been investigated through experimental and numerical studies by considering a number of physical and computational models. In most of the findings, the range of maximum power coefficient values is recorded between 0.08 and 0.51. Though individual vertical axis turbines have been widely studied and reviewed, similar review papers on hybrid turbines are scarce. This paper brings out significant developments that have taken place in the area of hybrid turbines, identifies the operating parameters, highlights the challenges related to rotor/turbine aerodynamics, modelling, simulation, testing methodologies. Based on these discussions, the strategies for future hybrid turbine designs are presented.

Cloud cavitation, both in external and internal flow fields, has been an active field of research because of its different harmful effects, such as noise, vibration, and material damage, in several applications. In the present work, the same is studied experimentally using venturi geometries. Venturi geometry was selected because of its diverse applications. The two venturi geometries chosen are nearly identical in all respect except the throat length. The influence of throat length is examined in this study because previously, these two venturi geometries (with and without throat) produced contradictory results in terms of the underlying mechanisms of cavity shedding, namely, re-entrant jets and condensation shocks observed at different cavitation numbers. Different diagnostic strategies were adopted to characterize cavitation events, viz., sound pressure level, dynamic pressure fluctuations, and high-speed imaging. High-speed images were studied to obtain mean cavity length. Proper orthogonal decomposition along with wavelet analysis was also employed. From these analyses, it was shown that for the venturi with 23 mm throat length, the condensation shock is followed by the re-entrant jet as cavitation number is reduced, while reverse is seen for venturi with zero throat length. Simulations of unsteady, non-cavitating, turbulent flow through these venturis show that this difference in the order of predominance of the two mechanisms can be explained by the product of cavity thickness (approximated by boundary layer height) and average pressure gradient value.

In the case of a long, straight rectangular channel, hydrodynamic development of flows is influenced by the growth of the boundary layer along the walls of the channel. Though such a geometry is well-studied in the literature, in reality, the flow often happens in channels with plenums on each end and is not studied extensively. This work addresses this gap. There is a sudden contraction from the plenum to the channel which causes the flow to separate at the entrance of the channel. Hence, the flow development is influenced not only by the boundary layer growth but also by recirculation and the presence of a continuous wall along one direction in the case of planar geometries. This causes the centerline velocity in the entrance region to overshoot the value at the fully developed region, which makes the conventional usage of 99% of the fully developed value difficult. Hence, an alternate method of defining entrance length, based on the slowest development across the channel cross section, is proposed. Based on this approach, the entrance length value shows a non-monotonic variation with the aspect ratio (AR) - its value reduces between 0.6 and 1.66; beyond 1.66, it increases up to 20 before becoming flat. The entrance length also shows a weak dependence on the Reynolds number for AR between 2 and 20. A new set of correlations of entrance and recirculation lengths are proposed.

Transdermal drug delivery using hollow microneedle enables creating small, wearable and minimally invasive closed-loop system. Polymer hollow microneedles are preferable because they are cost-effective and easy to manufacture. SU-8 is chosen for creating the hollow microneedles as it is a biocompatible photopolymer with robust mechanical properties. Previously reported SU-8 microneedles either use melt casting process for coating SU-8 which is laborious or do not have monolithic structures, thereby making these mechanically weak and difficult to integrate. To the best of our knowledge, for the first time, we report the use of a single-step spin coating process to achieve the desired thickness of SU-8 while using UV lithography to create a monolithic microneedle array. Three types of microneedles were fabricated with outer dimensions varying from 90 to 180 μm, and lumen dimensions ranging from 60 to 80 μm and needle height of 600 μm. These needles are fabricated in a 10×10 array with a platform thickness of 300 μm. Geometrical, mechanical and fluid flow characterisations are carried out for the fabricated arrays. We report the use of a non-destructive evaluation method to characterise the lumen of the fabricated microneedles. The fabricated needles are robust and offer low resistance to fluid flow. The triangular needles can withstand a bending load of 0.2 N and an axial load of 0.7 N. The needles with circular lumen offer least resistance to fluid flow of 0.2 Pa-min μL−1.

This comprehensive textbook highlights features of two phase flows and introduces the readers to flow patterns and flow maps. It covers a wide range of fundamental and complex subjects focusing on phase change processes like boiling, condensation or cavitation, and boiling phenomenon starting from pool boiling curves to heat transfer under nucleate boiling, film, and flow boiling. It also discusses themes such as numerical techniques for solving boiling and condensation as well as equipment used in industry for evaporation, boiling, and condensation. It includes pedagogical aspects such as end-of-chapter problems and worked examples to augment learning and self-testing. This book is a valuable addition for students, researchers, and practicing engineers.

Numerical studies on pumps emphasize mainly on modelling the interactions between the impeller and the volute to obtain an accurate understanding of the physics involved. However, the importance of modelling leakage paths, which is known to have a significant influence on the flow structure in the pump, necessitates an in-depth analysis. This activity is undertaken in this paper by investigating a specific case of a centrifugal pump. Numerical studies have been conducted on the pump modelled with and without leakages for the design condition. The sliding mesh method is used to obtain single phase pressure pulsations data at some important locations in the volute and the leakage path, and transient Multiple Reference Frame (MRF) modelling is utilized to conduct the cavitation analysis. It is observed that for the case under study, the pressure pulsations pattern and the cavitation behaviour varies significantly due to the inclusion of leakage paths in the analysis.

Literature review shows that cavitating flows past cylinder have received less attention in comparison to the noncavitating flow. This forms the motivation of the present work. In this work, three flow situations are considered: 6%, 16%, and 20% blockages. The first blockage factor, based on earlier non-cavitation studies, is taken as a reference case where no significant effect of blockage is seen. Airborne noise shows a 3 dB increase in sound level when the flow is blocked 20%. Measurement of static pressure on the surface of these cylinders under non-cavitating condition shows that 9 mm cylinder offers a higher base pressure value and this value increases with an increase in the extent of cavitation. Drag estimated for 9 mm cylinder shows a significant reduction at the lowest cavitation number because of the formation of an elongated cavity. This cylinder also shows a more pronounced cavity structure near inception.