Author
James R. Welty
Bio: James R. Welty is an academic researcher from Oregon State University. The author has contributed to research in topics: Heat transfer & Heat transfer coefficient. The author has an hindex of 13, co-authored 43 publications receiving 1552 citations.
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01 Jan 1972TL;DR: In this paper, the authors present an algorithm for Finned Array Assembly, which is based on linear transformations with simplified constraints and convection coefficients with real constraints, and they show that it achieves the optimum design of Radiating and Convecting-Radiating Fins.
Abstract: Preface. Convection with Simplified Constraints. Convection with Real Constraints. Convective Optimizations. Convection Coefficients. Linear Transformations. Elements of Linear Transformations. Algorithms for Finned Array Assembly. Advanced Array Methods and Array Optimization. Finned Passages. Compact Heat Exchangers. Longitudinal Fin Double-Pipe Exchangers. Transverse High-Fin Exchangers. Fins with Radiation. Optimum Design of Radiating and Convecting-Radiating Fins. Multidimensional Heat Transfer in Fins and Fin Assemblies. Transient Heat Transfer in Extended Surfaces. Periodic Heat Flow in Fins. Boiling From Finned Surfaces. Condensation on Finned Surfaces. Augmentation and Additional Studies. Appendix A: Gamma and Bessel Functions. Appendix B: Matrices and Determinants. References. Author Index. Subject Index.
995 citations
TL;DR: In this article, friction factors and laminar flow friction constants were determined for water flowing in high aspect ratio channels with depths ranging from 128 to 521 μm and Reynolds numbers were between 60 and 3,450.
Abstract: Recent developments in micro-energy and micro-chemical systems have produced a need for greater understanding of flow in small channels. Several recent studies of friction factors and transition Reynolds numbers in rectangular microchannels have produced results that differ from classical theory. In this work, friction factors and laminar flow friction constants were determined for water flowing in high aspect ratio channels with depths ranging from 128 to 521 μm. Reynolds numbers were between 60 and 3,450. Pressure drops were measured within the channel itself to exclude entrance and exit losses. Transitions to turbulence were observed with flow visualization. Uncertainties in measured variables were quantified and propagated into the estimated friction constants. Friction factors were also determined in a 1,050- μm-deep channel that served as a control. After considering experimental uncertainties and systematic errors, significant differences remained between the results and classical theory
226 citations
TL;DR: In this paper, a steady gas convection model of heat transfer to a horizontal cylinder immersed in a large particle gas fluidized bed has been developed, based upon the hypothesis that the large particles will be isothermal and includes the effect of radiation as well as interstitial turbulence.
Abstract: A steady gas convection model of heat transfer to a horizontal cylinder immersed in a large particle gas fluidized bed has been developed. The model is based upon the hypothesis that the large particles will be isothermal and includes the effect of radiation as well as interstitial turbulence.
Results of calculations based on the model, for a two-dimensional bubbling bed, indicate that a single bubble, having a diameter equal to the cylinder diameter, has a relatively small influence on the total heat transfer.
25 citations
TL;DR: In this article, a signal processing technique for calculation of bubble properties such as bubble frequency, local bubble residence time, bubble velocity, pierced length, bubble size, and visible bubble flow is presented.
Abstract: Optical probes are used to study gas-solid fluidized-bed hydrodynamics. The probes each consisting of a light source and photodetector separated by a gap are suitable for use at combustion-level temperatures. The methodology to process the signal for calculation of bubble properties such as bubble frequency, local bubble residence time, bubble velocity, pierced length, bubble size, and visible bubble flow is presented. The signal processing technique is independent of bed operating conditions. The probe signal processing methodology is validated by comparing calculated bubble properties based on the probe signal with properties observed on videotapes of a 2-D bed.
21 citations
TL;DR: In this paper, experimental data were obtained for laminar forced flow in the thermal entry region of a uniformly heated pipe with fluids exhibiting a range of non-Newtonian behavior.
Abstract: Experimental data were obtained for laminar forced flow in the thermal entry region of a uniformly heated pipe with fluids exhibiting a range of non-Newtonian behavior. The Graetz number range was between 240 and 38,000. Contributions to heat transfer made by non-Newtonian fluid behavior, temperature-dependent fluid properties, viscous heating, and secondary flow due to buoyancy were evaluated.
Results indicate that heat transfer is controlled by local wall shear rates. Local wall shear is affected much more by temperature variation of fluid rheological properties than by the degree of pseudoplasticity. Viscous heating was not detected in any of the tests. Natural convection effects were apparent in all cases; however, the heat transfer rates showed contributions due to buoyancy only at the lowest flow rates with low viscosity fluids.
20 citations
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TL;DR: In this article, an experimental investigation was conducted to explore the validity of classical correlations based on conventionalsized channels for predicting the thermal behavior in single-phase flow through rectangular microchannels.
752 citations
TL;DR: In this article, a bibliographical review on the convective heat transfer through microchannels is presented, highlighting the main results obtained on the friction factor, on the laminar-to-turbulent transition and on the Nusselt number in channels having a hydraulic diameter less than 1 mm.
647 citations
TL;DR: In this paper, pressure driven liquid flow through round and square microchannels fabricated from fused silica and stainless steel was investigated and pressure drop data were used to characterize the friction factor for channel diameters in the range 15-150 μm and over a Reynolds number range 8-2300.
432 citations
TL;DR: In this paper, Wang et al. used the Poincare section to analyze the fluid mixing in three-dimensional wavy microchannels with rectangular cross-sections and found that the quantity and the location of the vortices may change along the flow direction, leading to chaotic advection.
423 citations
TL;DR: The use of the Monte Carlo method in radiative heat transfer is reviewed in this paper, where surface-surface, enclosure, and participating media problems are considered, as well as the effects of using parallel algorithms.
Abstract: The use of the Monte Carlo method in radiative heat transfer is reviewed. The review covers surface-surface, enclosure, and participating media problems. Discussio. is included of research on the fundamentals of the method and on applications to surface-surface interchange in enclosures, exchange between surfaces with roughness characteristics, determination of configuration factors, inverse design, transfer through packed beds and fiber layers, participating media, scattering, hybrid methods, spectrally dependent problems including media with line structure, effects of using parallel algorithms, practical applications, and extensions of the method. Conclusions are presented on needed future work and the place of Monte Carlo techniques in radiative heat transfer computations
331 citations