The present discussion queries some results included in the paper.

Natural-convection cooling with oil or other fluids of high Prandtl number plays an important role in many technical applications such as transformers or other electric equipment. For design and optimization, one-dimensional (1D) flow models are of great value. A standard configuration in such models is flow between vertical parallel plates. Accurate modeling of heat transfer, buoyancy, and pressure drop for this configuration is therefore of high importance but gets challenging as the influence of buoyancy rises. For increasing ratio of Grashof to Reynolds number, the accuracy of one-dimensional models based on the locally forced-flow assumption drops. In the present work, buoyancy corrections for use in one-dimensional models are developed and verified. Based on two-dimensional (2D) simulations of buoyant flow using finite-element solver COMSOL Multiphysics, corrections are derived for the local Nusselt number, the local friction coefficient, and a parameter relating velocity-weighted and volumetric mean temperature. The corrections are expressed in terms of the ratio of local Grashof to Reynolds number and a normalized distance from the channel inlet, both readily available in a one-dimensional model. The corrections universally apply to constant wall temperature, constant wall heat flux, and mixed boundary conditions. The developed correlations are tested against two-dimensional simulations for a case of mixed boundary conditions and are found to yield high accuracy in temperature, wall heat flux, and wall shear stress. An application example of a natural-convection loop with two finned heat exchangers shows the influence on mass-flow rate and top-to-bottom temperature difference.

This study deals with the heat transfer characteristics of magnetohydrodynamic (MHD) flow of a third-grade fluid through parallel plates, subjected to a uniform wall heat flux, but of different magnitudes. The effect of viscous dissipation has been included for both heating and cooling of the fluid. The least square method (LSM) has been adopted for solving the nonlinear equations. The expressions for the velocity and temperature fields have been derived which, in turn, is utilized to evaluate the Nusselt number. The results indicate an increase in Nusselt number for higher values of the third-grade fluid parameter during heating and indicate a reverse trend for cooling. Nusselt number increases with an increase in Hartmann number during heating, whereas it decreases with increasing values of the Hartmann number while cooling the fluid.

Polydimethylsiloxane (PDMS)-based casting method was used to fabricate PDMS cell culture platforms with molds printed by a fused deposition modeling (FDM) printer. Cell viability study indicated that the produced plates have the suitable biocompatibility, surface properties, and transparency for cell culture purposes. The molds printed from acrylonitrile-butadiene-syrene (ABS) were reusable after curing at 65 °C, but were damaged at 75 °C. To understand thermal damage to the mold at elevated temperatures, the temperature distribution in an ABS mold during the curing process was predicted using a model that considers conduction, convection, and radiation in the oven. The simulated temperature distribution was consistent with the observed mold deformation. As the maximum temperature difference in the mold did not change appreciably with the curing temperature, we consider that the thermal damage is due to the porous structure that increases the thermal expansion coefficient of the printed material. Our study demonstrated that FDM, an affordable and accessible three-dimensional (3D) printer, has great potential for rapid prototyping of custom-designed cell culture devices for biomedical research.

Cooling of electric machines is a key to increasing power density and improving reliability. This paper focuses on the design of a machine using a cooling jacket wrapped around the stator. The thermal contact resistance (TCR) between the electric machine stator and cooling jacket is a significant factor in overall performance and is not well characterized. This interface is typically an interference fit subject to compressive pressure exceeding 5 MPa. An experimental investigation of this interface was carried out using a thermal transmittance setup using pressures between 5 and 10 MPa. The results were compared to currently available models for contact resistance, and one model was adapted for prediction of TCR in future motor designs.

In this study, the influence of the applied magnetic field is investigated for magneto-micropolar fluid flow through an inclined channel of parallel porous plates with constant pressure gradient. The lower plate is maintained at constant temperature and the upper plate at a constant heat flux. The governing motion and energy equations are coupled while the effect of the applied magnetic field is taken into account, adding complexity to the already highly correlated set of differential equations. The governing equations are solved numerically by explicit Runge–Kutta. The velocity, microrotation, and temperature results are used to evaluate second law analysis. The effects of characteristic and dominate parameters such as Brinkman number, Hartmann Number, Reynolds number, and micropolar viscosity parameter are discussed on velocity, temperature, microrotation, entropy generation, and Bejan number in different diagrams. The results depicted that the entropy generation number rises with the increase in Brinkman number and decays with the increase in Hartmann Number, Reynolds number, and micropolar viscosity parameter. The application of the magnetic field induces resistive force acting in the opposite direction of the flow, thus causing its deceleration. Moreover, the presence of magnetic field tends to increase the contribution of fluid friction entropy generation to the overall entropy generation; in other words, the irreversibilities caused by heat transfer reduced. Therefore, to minimize entropy, Brinkman number and Hartmann Number need to be controlled.

In this study, heat transfer and fluid flow of de-ionized water in two-dimensional parallel plates microchannel with and without micromixers have been investigated for various Reynolds numbers. The effects of heat transfer and fluid flow on height, diameter of micromixer, and also distance between the two micromixers are carried out in the study. Results showed that the diameter of the micromixer does not have much effect on heat transfer with a maximum enhancement of 9.5%. Whereas heat transfer gets enhanced by 85.57% when the height of the micromixer is increased from 100 μ m to 400 μ m, and also heat transfer gets improved by 11.45% when sb2 is increased from 4L to 5L. The separation and reattachment zone at the entry and exit of the micromixer cause the increase in heat transfer with the penalty of pressure drop. It is also found that increase of Reynolds number increases the intensity of the secondary flows leads to rapid increase in heat transfer and pressure drop. Finally, the optimized structure of micromixer is found out based on maximum heat transfer and minimum pressure drop.

The challenge in design and manufacturing tasks includes precise measurement of static friction, stiffness, deformation, raceway relative approach, and heat distribution of slewing ring bearings. These parameters affect the life and performance of the rolling elements bearing at elevated thermal environments. Toward that, sections of a complete bearing called linear model mock-up bearing (LMMB) have been designed and fabricated for the study of heat distribution. The physical significance of the heat distribution on bearing elements was studied using square-guarded hot-plate (SGHP) apparatus. The thermal contact conductance (TCC) experiments were carried out by varying surface roughnesses and interface temperatures under different loading conditions by using the combinations of steel plates and LMMB under dry and lubricated conditions. From this study, it is observed that the TCC values obtained from LMMB were significantly high across the contact surfaces of AISI 42100–AISI 52100–AISI 4140 steel plate's combination. Further, the finite element method (FEM) simulation has been carried out successfully to evaluate the temperature distribution in combination of bearing steel plates and LMMB by solidworks software, and the results are discussed.

The fin effects on laminar forced convection of air in the interfin passages of plate-fin heat exchangers are investigated. Steady state fully developed flows in rectangular, trapezoidal, and triangular plate-fin channels are considered. With H1 and T conditions at the partition plates, the conjugate conduction–convection fin problem is solved computationally. The fin effects on the convective Nusselt number are shown to scale by a new dimensionless parameter Ω, which accounts for the attendant fin material and size; its limits describe perfectly conducting and nonconducting fins. Ineffective fins and the consequent reduction in the convective heat transfer coefficient are most pronounced in low fin density cores with longer fins in low-conductivity metal (stainless steel). However, with increasing fin density and shorter fins, the convection performance is virtually the same as that with 100% fin efficiency; the same is the case when fins are made of very high conductivity metal (copper). These results provide design insights for optimizing the conjugate fin-conduction and fluid-flow convection performance in plate-fin compact heat exchangers.

Fully developed laminar flow heat transfer in a plate-fin heat exchanger with interfin core channels of trapezoidal cross section and by extension, its limiting rectangular and triangular cross section geometries, is considered. With heating or cooling at the partition plates of the core given by the constant wall temperature, or T , and uniform heat flux, or H 1 , conditions, the fin effectiveness is modeled to be zero. This condition is representative of poor contact between the fin and partition plate, encountered in mass-produced compact cores and/or low conductivity fin materials. Computational solutions, obtained by second-order accurate control-volume schemes, highlight the effects of geometry and thermal condition on the Nusselt number ( Nu T and Nu H 1 ), and the results complement and extend the literature on compact-channel internal forced convection. Also, as a design and optimization tool for the practicing engineer, polynomial functions of the flow cross section aspect ratio are presented to predict both the friction factor and the Nusselt number for the different trapezoidal and triangular fin core geometries considered.