In Memoriam: Professor Raj M. Manglik (September 30, 1953–August 22, 2025)

A headshot of Professor Raj M. Manglik. It is with great sadness that we share the news of the passing of our colleague and friend Raj M. Manglik, Professor of Mechanical Engineering at the University of Cincinnati on August 22, 2025, at age 71. Raj leaves a legacy of many path-breaking contributions in heat transfer enhancement, interfacial phenomena with surfactant and polymeric solutions, thermal energy storage (TES), and a record of distinguished service to ASME and the broader heat transfer community.Raj was born in Prayagraj, India, on September 30, 1953. He received his B.Tech. in Mechanical Engineering from the Indian Institute of Technology, Madras in 1976. He then worked for Triveni Turbines for 8 years, gaining valuable industrial experience. In 1984, he came to Iowa State University to pursue his M.S. under the tutelage of Professor Arthur E. Bergles. After completing his M.S., he moved to Rensselaer Polytechnic Institute (RPI) with Dr. Bergles and received his PhD in 1991.His doctoral work focused on enhanced heat transfer and compact heat exchangers, especially the tubular longitudinal swirl flows with twisted-tape inserts. Through judicious experimentation, flow visualization, and computational simulations, Raj established the flow-mixing mechanisms that characterize the influence of the tape inserts. By identifying the recirculation structure and its parametric scaling, along with a fundamental decomposition and balance of the fluid-force field, a new Swirl parameter was devised that universally scales confined helical vortex flows [1,2]. The consequent physical phenomena- or mechanism-based generalized correlations that have been devised provide unique and easy-to-use design equations for the practicing engineer that cover laminar, transition, and turbulent flow regimes. These correlations, apart from being highly cited in the archival literature, have become a standard part of numerous thermal engineering design handbooks, reference books, and textbooks. They are included as the preferred design equations in virtually all commercial software and routinely used for designing heat exchangers with twisted-tape inserts for the process, power, and chemical industry. Likewise, his friction factor and Nusselt number correlations for offset strip fins [3] became the industry standard. Working with his collaborators and students, he recently updated [4] these correlations to expand their range of applicability in both flow and geometric parameters.Raj joined the faculty of the University of Cincinnati in 1991 and developed a strong collaboration with Procter & Gamble. His initial focus was to address the need for high-performance and microscale exchangers that guided his research on compact heat exchangers that are characterized by high-density (surface area-to-volume) cores. Raj tackled the complex enhanced convection in cross-corrugated channels with sinusoidal trough profiles of plate-and-frame heat exchangers (PHEs) through extensive experiments to extract the parametric influence of the cross-corrugated flow geometry [5]. The augmented transport mechanisms include periodic disruption of boundary layers at the corrugated peak and trough regions, with re-circulating fluid cells in the resulting separation zones, which evolve into helical vortices with increasing acuteness of cross-corrugation angles. By appropriately scaling these convective transport features, he devised the first-of-their-kind friction factor and Nusselt number correlations for chevron PHEs [6].Thermal processing of non-Newtonian media in both single- and two-phase flows quickly became the second theme of his research focus at the University of Cincinnati. In thermal processing of rheologically complex media in foods, biochemical, and pharmaceutical manufacture, anomalous convection behaviors manifest and lack of close thermal control leads to product loss and degradation. Raj addressed the underlying transport phenomena in both a fundamental and mechanistic manner [7–9]. For example, he published ground-breaking results for heat transfer in nucleate boiling of aqueous, semi-dilute polymeric solutions, which are at once surface active and shear thinning in nature [10]. Besides effects of rheology and interfacial properties on the heat transfer, adsorption of macromolecules or agglomerates of small monomers onto the heater surface favors formation of new nucleation sites, which together with decreased dynamic surface tension promote ebullience growth. Contrarily, high viscosity effects tend to suppress the near-wall microconvection and bubble growth, thereby weakening boiling. The consequent interplay of pseudoplasticity and interfacial tension relaxation provides an effective control mechanism for thermal processing of a variety of viscous non-Newtonian media. He extensively examined bubbling and boiling of aqueous surfactant solutions to understand the effect of liquid–gas interfacial molecular adsorption leading to dynamic surface tension relaxation and physisorption on the liquid–solid interface, resulting in changing surface wettability. A paper on this work [8] earned him ASME's Melville Medal in 2006.More recently, he worked on developing a novel dry cooling system for thermal power plants that incorporated a daytime peak load shifting TES system, with an enhanced air-cooled condenser (ACC) design, to significantly increase power plant efficiency [11]. Extensive work on different fin cores led to optimizing the ACC with highly enhanced heat transfer surfaces [12–14]. For TES, it was shown that plate-fin and tube-fin type grids can be judiciously used to encase the phase change material (PCM) between heating–cooling surfaces to produce very high surface area density cores [15]. In doing so, especially when the finned-core-side is employed for encasing the PCM, the latter's limitations of low thermal-conductivity-driven thermal resistance are overcome [16,17].Raj received several awards for his research contributions, including the American Society of Mechanical Engineers (ASME) Heat Transfer Division 75th Anniversary Medal in 2013, the Heat Transfer Memorial Award of ASME in 2016, and the ASME James Harry Potter Gold Medal for advancing fundamental thermodynamics in research and education in 2018. He also received the AIChE Donald Q. Kern Award in 2020. He was elected as a Fellow of ASME in 2004 and a Fellow of ASHRAE in 2017. In 2025, ASME Board of Governors selected him as an ASME Honorary Member, which is a distinction recognizing his lifetime of service to the profession.Raj was an outstanding teacher and a dedicated mentor. He received several awards recognizing his teaching excellence at the University of Cincinnati. He was the recipient of the 2009 Engineering Tribunal Professor of the Quarter Award, the 2004 BP Faculty Excellence Award, the 2000 Robert Hundley Award for Excellence in Teaching, the 2001 Neil Wandmacher Teaching Award, and 1993 Professor of the Year Award. Besides his excellent classroom instruction, Raj was active in engaging students in design practice through participation in professional societies. He founded and established the ASHRAE Student Chapter at the University of Cincinnati in 1992–1993 and was the faculty advisor throughout his career. Many senior design teams won international student design competitions under his mentorship and coaching. Raj treated his graduate students as his family, and his warmth and guidance created a home away from home for them in his lab.His pedagogical contributions include the well-known undergraduate textbook “Principles of Heat Transfer” that he co-authored with Frank Kreith. The book not only covers physical principles and technical details very clearly but also connects the fundamentals of heat transfer with applications in new emerging technologies. Similarly, his monograph on plate-and-frame heat exchangers and other handbook chapters on enhanced heat transfer provide students and engineering practitioners with important modeling, analysis, and design tools.Raj had a lasting impact on the heat transfer community through his lifelong dedicated service to ASME, AIChE, ASHRAE, and to the broader thermal-fluids community. He served as Editor-in-Chief for the Journal of Enhanced Heat Transfer for over 10 years; he was Associate Editor for the Journal of Heat and Mass Transfer for two terms and Guest Editor for five different special issues. He was Chair of the Heat Transfer Division (HTD) (2018–2019), Chair of K-10 (2013–2016), and served on various HTD committees over the years. He was instrumental in increasing the involvement of AIChE and JSME members in ASME conferences and activities of HTD. As chair of the awards committee, he streamlined the nomination process and was instrumental in developing the Boelter-McAdams Prize. He made a strong mark and left deep footprints on the functioning and vision for the ASME Heat Transfer Division.On a more personal note, Raj is survived by his wife, Vandana; their children, Aditi and Animaesh; and four grandchildren. Raj cherished his time with friends and family and enjoyed theater and music. He will be sorely missed.