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Dive into the research topics where Raj M. Manglik is active.

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Featured researches published by Raj M. Manglik.


Journal of Heat Transfer-transactions of The Asme | 1993

Heat Transfer and Pressure Drop Correlations for Twisted-Tape Inserts in Isothermal Tubes: Part II—Transition and Turbulent Flows

Raj M. Manglik; Arthur E. Bergles

Thermal-hydraulic design correlations are developed to predict isothermal f and Nu for in-tube, turbulent flows with twisted-tape inserts. Experimental data taken for water and ethylene glycol are analyzed, and various mechanisms attributed to twisted tapes are identified. Tube blockage and tape-induced vortex mixing are the dominant phenomena that result in increased heat transfer and pressure drop; for loose- to snug-fitting tapes, the fin effects are insignificant. The limiting case of a straight tape insert correlates with the hydraulic-diameter-based smooth tube equation


Experimental Thermal and Fluid Science | 1995

Heat transfer and pressure drop correlations for the rectangular offset strip fin compact heat exchanger

Raj M. Manglik; Arthur E. Bergles

Abstract The development of thermal-hydraulic design tools for rectangular offset strip fin compact heat exchangers and the associated convection process are delineated. On the basis of current understanding of the physical phenomena and enhancement mechanisms, existing empirical f and j data for actual cores are reanalyzed. The asymptotic behavior of the data in the deep laminar and fully turbulent flow regimes is identified. The respective asymptotes for f and j are shown to be correlated by power law expressions in terms of Re and the dimensionless geometric parameters α, δ, and γ. Finally, rational design equations for f and j are presented in the form of single continuous expressions covering the laminar, transition, and turbulent flow regimes.


Journal of Heat Transfer-transactions of The Asme | 1993

Heat Transfer and Pressure Drop Correlations for Twisted-Tape Inserts in Isothermal Tubes: Part I—Laminar Flows

Raj M. Manglik; Arthur E. Bergles

Laminar flow correlations for f and Nu m are developed based on experimental data for water and ethylene glycol, with tape inserts of three different twist ratios. The uniform wall temperature condition is considered, which typifies practical heat exchangers in the chemical and process industry. These and other available data are analyzed to devise flow regime maps that characterize twisted-tape effects in terms of the dominant enhancement mechanisms. Depending upon flow rates and tape geometry, the enhancement in heat transfer is due to the tube partitioning and flow flockage, longer flow path, and secondary fluid circulation; fin effects are found to be negligible is snug-to loose-fitting tapes


Journal of Heat Transfer-transactions of The Asme | 2000

Pool Boiling Heat Transfer in Aqueous Solutions of an Anionic Surfactant

Vivek M. Wasekar; Raj M. Manglik

Saturated nucleate pool boiling of aqueous surfactant solutions on a horizontal cylindrical heater has been experimentally investigated. Sodium dodecyl or lauryl sulfate (SDS or SLS), an anionic surfactant, is employed. Boiling performance, relative to that for pure water, is found to be enhanced significantly by the presence of SDS, with an early onset of nucleate boiling. An optimum level of enhancement is observed in solutions at or near critical micelle concentration of the surfactant; the enhancement, however, decreases considerably in higher concentration solutions. The dynamic surface tension measurements indicate a substantial influence of temperature on the overall adsorption isotherm. The diffusion kinetics of surfactant molecules and micelles is, therefore, expected to be quite different at boiling temperature than at room temperature. This greatly modifies the boiling mechanism that is generally characterized by the formation of smaller-size bubbles with increased departure frequencies, and a decreased tendency to coalesce which causes considerable foaming.


Advances in heat transfer | 2003

Swirl flow heat transfer and pressure drop with twisted-tape inserts

Raj M. Manglik; Arthur E. Bergles

Abstract An extended review of the application of twisted-tape inserts in tubular heat exchangers and their thermal-hydraulic performance is presented. Twisted tapes promote enhanced heat transfer by generating swirl or secondary flows, increasing the flow velocity due to the tube partitioning and blockage, and providing an effectively longer helical flow length. Depending on the tape-edge to tube-wall contact, some fin effects may also be present. Their usage in both single-phase and two-phase (boiling and condensation) flows is considered, and heat transfer and pressure drop results from different investigations are presented. The characteristic features of swirl-induced heat transfer enhancement, nature of swirl flows and their scaling, and development of predictive correlations for heat transfer coefficients and friction factors (or pressure drop) are discussed. Also, some aspects of the use of geometrically modified twisted-tape inserts, as well as compound application with other enhancement techniques, are briefly discussed.


Experimental Thermal and Fluid Science | 2001

Dynamic and equilibrium surface tension of aqueous surfactant and polymeric solutions

Raj M. Manglik; Vivek M. Wasekar; Juntao Zhang

Abstract Dynamic and equilibrium surface tension data for aqueous solutions of four surfactants and two polymers are experimentally obtained using the maximum bubble pressure method. The additives employed are SDS, SLES, Triton X-100, Triton X-305, HEC QP-300, and Carbopol 934. Measurements are obtained at a surface age of 50 ms, which represents the dynamic conditions for bubble frequencies that are typically observed during nucleate boiling of water. To understand the additive adsorption/desorption kinetics during boiling, dynamic surface tension σ measurements at 80°C are also obtained. The results indicate significant differences between the dynamic and equilibrium σ values, as well as between those measured at room and elevated temperatures. Adsorption isotherms with surface tension and concentration normalized by the respective values at critical micelle concentration are shown to represent the generalized behavior of surfactants. In the case of aqueous polymer solutions, the surface-active nonionic polymer HEC is seen to exhibit surfactant-like behavior. For the high viscosity Carbopol 934 solutions, however, measured dynamic σ values are found to be significantly higher than the actual values due to the viscous resistance offered by the test fluid against the growing bubble. A correction procedure is specified, and corrected values of dynamic σ are obtained for Carbopol 934 solutions; for HEC solutions, because of their less viscous nature, this correction shows no significant change.


International Journal of Heat and Mass Transfer | 1999

Fully developed forced convection through trapezoidal and hexagonal ducts

Rajashankar Sadasivam; Raj M. Manglik; Milind A. Jog

Abstract Laminar, fully developed flow through single- and double-trapezoidal (or hexagonal) ducts is modeled using a finite-difference method. A coordinate transformation is employed to map the irregular flow cross-section onto a rectangular computational domain. Both H1 and T thermal boundary conditions are considered as they represent the fundamental limiting conditions in most practical applications. Solutions for velocity and temperature variations are obtained for a wide range of duct aspect ratios and with four different trapezoidal angles. The friction factor and Nusselt number results show a strong dependence on duct geometry (aspect ratio γ and trapezoidal angle θ). The variations of f Re, NuH1, and NuT with duct aspect ratio for each θ-valued duct are presented in the form of polynomials in γ. These equations describe the computed numerical values within ±2% for single-trapezoidal and within ±1.5% for hexagonal ducts and are of much importance to the design of compact heat exchangers.


International Journal of Heat and Mass Transfer | 2002

The influence of additive molecular weight and ionic nature on the pool boiling performance of aqueous surfactant solutions

Vivek M. Wasekar; Raj M. Manglik

Abstract Saturated nucleate pool boiling on a horizontal cylindrical heater in aqueous solutions of surfactants, which have different molecular weights and ionic character, has been experimentally investigated. Two anionic surfactants, sodium dodecyl sulphate (SDS) and sodium lauryl ether sulfate (SLES), and two nonionic surfactants, Triton X-100 and Triton X-305, were used; their molecular weights are 288.3, 422, 624 and 1526, respectively. The boiling performance, characterized by an early onset of nucleate boiling, is significantly enhanced, and the maximum enhancement increases with decreasing surfactant molecular weight. Also, the heat transfer coefficient, normalized by dynamic σ (at 50 ms, 80°C), scales as h∝Mn with n=−0.5 and 0 for anionics and nonionics, respectively. This scaling follows from the postulation that the solutions dynamic surface tension is determined by the surfactant concentration and its interfacial activity in the sublayer around the growing bubble. Correspondingly, boiling of these solutions is directly influenced by the ionic character and molecular makeup of this sublayer.


Journal of Heat Transfer-transactions of The Asme | 1999

Enhanced Heat Transfer Characteristics of Viscous Liquid Flows in a Chevron Plate Heat Exchanger

A. Muley; Raj M. Manglik; H. M. Metwally

Steady-state heat transfer and pressure drop data for single-phase viscous fluid flows (2 ≤ Re ≤ 400) in a single-pass U-type counterflow plate heat exchanger (PHE) with chevron plates are presented. With vegetable oil as test fluid (130 < Pr < 290), three different plate arrangements are employed: two symmetric (β = 30 deg/30 deg and 60 deg/60 deg) and one mixed (β = 30 deg/60 deg). The effects of chevron angle β, corrugation aspect ratio γ, and flow conditions (Re, Pr, μ/μw on Nu and f characteristics of the PHE are delineated. The results show a rather complex influence of plate surface corrugations on the enhanced thermal-hydraulic behavior. Relative to the performance of equivalent flat-plate packs, chevron plates sustain up to 2.9 times higher heat transfer rates on a fixed geometry and constant pumping power basis, and require up to 48 percent less surface area for the fixed heat load and pressure drop constraint.


International Journal of Heat and Mass Transfer | 1997

Laminar flow heat transfer to viscous powerlaw fluids in double-sine ducts

Raj M. Manglik; J. Ding

Abstract Fully developed, constant property, laminar flows of viscous power-law fluids in double-sine shaped ducts are considered. The double-sine cross section represents a limiting inter-plate channel geometry in plate heat exchangers with sinusoidally corrugated plates. The non-Newtonian fluid theology is described by the power-law or Ostwald-de Waele model, and shear thinning (n 1) flows are considered. Both fluid flow and convective heat transfer problems under (T) and (H1) thermal boundary conditions are analyzed. Analytical solutions based on the Galerkin integral method are presented for a wide range of flow behavior index (0.15 ⩽ n ⩽ 2.5) and duct aspect ratio (0.25 ⩽ γ ⩽ 4.0). The effects of fluid rheology (pseudoplasticity or dilatancy), duct geometry, and thermal boundary conditions on the velocity and temperature field, are delineated. Also, isothermal friction factor and Nusselt number results for various conditions are presented, and strategies for predicting f Re and Nu are evaluated.

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Milind A. Jog

University of Cincinnati

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Juntao Zhang

University of Cincinnati

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A. Subramani

University of Cincinnati

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Jiehai Zhang

University of Cincinnati

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O. A. Huzayyin

University of Cincinnati

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