Surface wettability effect of plain and plasma-sprayed copper-coated surfaces on CHF enhancement during saturated pool boiling of FC-72

In the current scenario, CHF study is essential for the safe operation of electronics equipment comprising a two-phase heat transfer process. Therefore, the present experimental investigation involves saturated pool boiling and CHF study of FC 72 over a plain stainless steel surface (SS) and microporous copper-coated SS surfaces under atmospheric conditions. Accordingly, three different plasma-sprayed copper-coated surfaces with coating thicknesses of 65 μm, 105 μm, and 145 μm prepared using micro copper particles of size 25–45 μm. The analysis of the results shows that with an increase in heat flux values, the boiling heat transfer coefficient increases over plain as well as coated surfaces. The plasma-spayed copper-coated surfaces with a coating thickness of 65 μm and 105 μm exhibit a higher boiling heat transfer coefficient as than the plain surface. On the other hand, a 145 μm thick coated surface resulted in a comparable boiling heat transfer coefficient with the plain SS surface. Among the three porous-coated surfaces, the boiling heat transfer coefficient decreases continuously from 65 μm to 145 μm of the coated surface. On the contrary, to the observed nucleate boiling behavior, all the porous-coated surfaces show a higher value of CHF than the plain surface, and the CHF value is found to increase continuously from 65 μm to 145 μm of the coated surfaces. The enhancement of CHF values was found to be 66.29%, 69.17%, and 77.75% for a coating thickness of 65 μm, 105 μm, and 145 μm, respectively, compared with the plain surface. The porous coating thickness of 65 μm shows a greater value of heat transfer coefficient than 105 μm and 145 μm whereas 145 μm exhibits a higher value of CHF as than 65 μm and 105 μm.

Critical heat flux enhancement in microgravity conditions coupling microstructured surfaces and electrostatic field

We run pool boiling experiments with a dielectric fluid (FC-72) on Earth and on board an ESA parabolic flight aircraft able to cancel the effects of gravity, testing both highly wetting microstructured surfaces and plain surfaces and applying an external electric field that creates gravity-mimicking body forces. Our results reveal that microstructured surfaces, known to enhance the critical heat flux on Earth, are also useful in microgravity. An enhancement of the microgravity critical heat flux on a plain surface can also be obtained using the electric field. However, the best boiling performance is achieved when these techniques are used together. The effects created by microstructured surfaces and electric fields are synergistic. They enhance the critical heat flux in microgravity conditions up to 257 kW/m2, which is even higher than the value measured on Earth on a plain surface (i.e., 168 kW/m2). These results demonstrate the potential of this synergistic approach toward very compact and efficient two-phase heat transfer systems for microgravity applications.

Pool boiling heat transfer enhancement by using perforated twisted tape fins

The application of twisted tape fins showed a considerable enhancement in pool boiling heat flux. The present study experimentally investigates the effect of solid and perforated twisted tape fins on pool boiling of water by varying the twist ratio (y) and perforation index (PI) from 3 - 4.3 and 5 - 10, respectively. An arrangement of five twisted tape fins with twist ratio of 3 showed 18.6% enhancement as compared to the plain surface whereas an arrangement of five perforated twisted tape fins having perforation index (PI) of 7 and twist ratio of 3 showed a maximum enhancement of 28.7%.

An Approach to Identify Urban Waterlogging on a Deltaic Plain using ArcGIS on CHD based Flow Accumulation Models

The gradient for any point on the land surface can be calculated using the digital-elevation model. Some empirical correlations are available to determine the gradient of any points. A few studies were conducted for hilly forest areas to determine the aspect and gradient of various points using computational hydrodynamics (CHD) based techniques. On a plain surface, the accuracy of such techniques was rarely verified. The application of such techniques for a plain surface is also extremely challenging for its small slope. Therefore, the prime objective of the present study is to find out an advanced technique to more accurately determine the gradient of various points on a plain surface which may help in determining the key areas affected by run-off, subsequent flow accumulation, and waterlogging. Here, Kolkata city as a deltaic plain surface is chosen for this study. Upto 600 m × 600 grid sizes are used on the DEM map to calculate the run-off pattern using a D8 algorithm method and second-order, third-order, and fourth-order finite difference techniques of CHD. After finding out the gradient, the run-off pattern is determined from relatively higher to lower gradient points. Based on the run-off pattern, waterlogging points of a plain surface are precisely determined. The results obtained from all the different methods are compared with one other as well as with the actual waterlogging map of Kolkata. It is found that the D8 algorithm and fourth-order finite-difference-technique are the most accurate while determining the waterlogging areas of a plain surface. Next, true gradients of waterlogging points are calculated manually to compare the calculated gradient points using each method. This is also done to determine the relationship and error between the true and calculated gradient of waterlogged points using various statistical analysis methods. The relationship between true and calculated gradients is observed from weak to strong if the D8 algorithm is replaced by the newly introduced fourth-order finite difference technique. Better accuracy and stronger relationships can be achieved by using a smaller grid size.

Mechanical response of different types of surface texture for medical application using finite element study

Titanium implants are commonly used in dental and other joint replacements and its several modifications have been taken place to improve the adhesion between bone and implant. Different chemical and physical modifications are generally applied to the titanium surface for improving interlocking between bone and implant materials. The present work has been investigated the shear strength stiffness and stress concentration between Representative Volume Element (RVE) model and coating material while the surface of the RVE model modified with different types of surface textures. The surface topology parameters resulted a significant increase in shear strength by 55% and 45% for straight texture and U-shape texture, respectively compared with plain surface. The stiffness reduced significantly by 18% for U-shape and but to 36% only for X-shape, when compared with plain surface. The stress concentration factor in biaxial case both dome shape and X-shape has 45%and 25% in U-shape lower than that of the plain surface. Therefore, this investigation predicted the interfacial shear strength properties generated for different surface topologies to determine the bonding behavior of the implant materials.

Heat Transfer Augmentation of Concentrated Solar Absorber Using Modified Surface Contour

This work aims to compare the cavity surface contour’s thermal performance to that of the solar absorber’s plain surface contour for Scheffler type parabolic dish collectors. The absorber is tested for the temperature range up to 600°C without working fluid and 180°C with the working fluid. The modified absorber surface's thermal performance is compared with the flat surface absorber with and without heat transfer fluid. The peak temperature reached by the surface modified absorber (534°C) is about 8.6% more than that of the unmodified absorber (492°C) during an outdoor test without fluid. The energy efficiency of cavity surface absorber and plain surface absorber are 67.65% and 61.84%, respectively. The contoured cavity surface produces a more uniform temperature distribution and a higher heat absorption rate than the plain surface. The results are beneficial to the design of high-temperature solar absorbers for concentrated solar collectors.

Heat Transfer Augmentation of Concentrated Solar Absorber Using Modified Surface Contour

This work aims to compare the cavity surface contour’s thermal performance to that of the solar absorber’s plain surface contour for Scheffler type parabolic dish collectors. The absorber is tested for the temperature range up to 600°C without working fluid and 180°C with the working fluid. The modified absorber surface's thermal performance is compared with the flat surface absorber with and without heat transfer fluid. The peak temperature reached by the surface modified absorber (534°C) is about 8.6% more than that of the unmodified absorber (492°C) during an outdoor test without fluid. The energy efficiency of cavity surface absorber and plain surface absorber are 67.65% and 61.84%, respectively. The contoured cavity surface produces a more uniform temperature distribution and a higher heat absorption rate than the plain surface. The results are beneficial to the design of high-temperature solar absorbers for concentrated solar collectors.