Boiling is a two-phase heat transfer process which is characterized by formation of vapor bubbles at heated surface. Scarcity of freshwater, population growth, and global climate change have increased the demand for desalination and saline water utilization in various energy and chemical plants. Thermal desalination processes use phase change process to separate volatile solvents such as water from nonvolatile solutes such as salts. Thermal desalination systems can be effectively coupled with waste heat recovery systems available in various industries. Thermophysical properties of saline water solution are significantly different from freshwater due to presence of salts. This research work numerically simulates growth and departure of vapor bubbles in water with different concentrations of salts, wall superheat, and pressures during nucleate pool boiling. Salt concentrations significantly influence the wall heat transfer and bubble dynamics. A three-dimensional model of vapor bubble is developed using the level-set method to capture the interface. The Semi-Implicit Method for Pressure Linked Equations Revised algorithm has been used to solve complete Navier-Stokes equations. The bubble growth process is simulated in a rectangular domain with a bubble placed at the bottom on a heated wall. Thermophysical properties of liquid and vapor are adjusted based on the salt concentrations and pressure. Bubbles grow larger in size and take less time to depart at higher salinities. Higher superheat makes bubbles grow larger and depart faster and improves Nusselt number. Increasing pressure suppresses bubble growth and makes it stay for longer duration at the wall.

This study examines direct current measurements in the central equatorial Indian Ocean during the positive phase of the extreme Indian Ocean Dipole (pIOD) in 2019. Analysis of near-surface zonal current at 77°E and 83°E reveals a notable delay in the onset of fall Wyrtki Jets (WJs), typically occurring in October. The WJs formed in December but persisted for a shorter duration. On the other hand, the subsurface currents display a strong eastward flow persistent from October 2019 to June 2020 which is abnormal to a normal condition. The anomalous subsurface zonal currents exhibited magnitudes three times stronger during pIOD 2019 compared to pIOD composites. Due to the continued sub-surface flow, wavelet analysis revealed a dominant semi-annual cycle near the surface and an annual cycle in the subsurface layers. To explore the underlying processes behind these anomalies, we used the Modular Ocean Model in conjunction with a linear, continuously stratified model. Our experiments revealed that the weakening of fall Wyrtki Jets in 2019 was driven by anomalous easterlies associated with the extreme pIOD phase. However, the persistence of eastward subsurface currents was attributed to anomalous westerlies in the western Indian Ocean. These westerlies generated Kelvin waves propagating eastward, which upon impinging the eastern boundary, reflected and propagated downwards as Rossby waves, ultimately intensifying the subsurface currents. Overall, our study underscores the significance of equatorial wave dynamics in driving currents during the extreme IOD event.

A numerical study has been performed to analyze the wall heat transfer mechanisms during growth of multiple vapor bubbles inside a microchannel. The microchannel is of 200 μm square cross section and multiple vapor bubble begins to grow at once and after delay on the walls, with liquid coming in through the channel inlet. The complete Navier-Stokes equations along with continuity and energy equations are solved using the SIMPLER method. The liquid vapor interface is captured using the level set technique. It can be seen that the second bubble which is far from the inlet always got bigger than the first one. When the second bubble nucleates 0.0549 ms after the first one, both bubbles grow almost to the same size. The numerical results show that bubbles with the lowest contact angle resulted in the highest wall heat transfer. Finally, a comparative study was done between single bubble and two bubbles inside a microchannel. wall heat transfer is better when two bubbles do not merge together compared to the single bubble and when they do merge.

In this article, role of ocean advection and atmospheric heat fluxes on recent decadal (2000–2019) decrease of sea-ice in the Arctic (60 ^∘ N–90 ^∘ N) has been investigated using an ocean sea-ice coupled model, known as Modular Ocean Model of version 5 with Sea Ice Simulator (MOMSIS). MOMSIS successfully simulates AVHRR observed decadal change of sea-ice concentration (SIC) and sea surface temperature (SST) in the Arctic during all four seasons; winter (December–February), spring (March–May), summer (June–August) and autumn (September–November) except few occasions. Also, best performance of the MOMSIS are restricted at south of 80 ^∘ N with statistical significance of more than 90 % . We have also divided Arctic Ocean into eight sectors for our detailed analysis. Maximum decadal decrease of SIC and increase of SST has been observed in the Barents (sector 2), Kara (sector 3) and Laptev (sector 4) Sea regions of the Arctic using both AVHRR and MOMSIS with statistical significance of 90 % . Also, very small decadal decrease (increase) of SIC (SST) has been observed in the Norwegian (sector 1) and Beaufort (sector 7) Sea regions of the Arctic using both AVHRR and MOMSIS. Mixed layer heat budget has been performed to understand role of thermodynamics processes on decadal change of SIC and SST in the Arctic. Strong decadal change of net atmospheric heat (NAH) fluxes are responsible for high decadal change of SIC and SST in the Barents (sector 2), Kara (sector 3) and Laptev (sector 4) Sea regions of the Arctic. In the Norwegian (sector 1) and Beaufort (sector 7) Sea, strong destructive interference between decadal change of NAH fluxes and ocean advection play an important role for small decadal change of SIC and SST during all four seasons. Also, for ocean advection, horizontal part dominate compared to vertical in all eight sector of the Arctic.

The accuracy of six turbulent flow modeling techniques in an unsteady solution is evaluated against experimental data for a square prism in cross flow. The selected models, shear stress transport (SST), SST-SAS, Reynolds stress model (RSM), partially averaged Navier–Stokes (PANS)-SST, detached eddy simulation (DES), and large eddy simulations (LES), models are the same as those presented in Part 1 of this study, which focused on flow in a staggered tube bank. For this geometry, the SST model proved to be effective at capturing the averaged Nusselt values per side of the square with relatively low computational costs. The SST model, however, showed poorer fidelity to the local Nusselt number profile compared to the experimental data. The LES approach provided a more accurate representation of the local Nusselt number but the computational cost was significantly higher. The PANS modification to the SST model did provide a noticeable improvement in accuracy at a reasonable cost while the SAS modification did not see the same improvement. These conclusions are generally consistent with those found for the staggered tube bank in Part 1 of this study. This study can be used as a guide for the industrial user to select a turbulence model for a similar problem with a low Reynolds number and significant flow separation.

Earlier studies suggest that the mixed-layer (ML) temperature or sea surface temperature (SST) of the Bay of Bengal during the summer monsoon is determined primarily by air–sea fluxes. We use an oceanic general circulation model (OGCM) to show that oceanic processes also play a significant role. Model heat-budget computations show that horizontal and vertical advection, constituting the direct role of dynamics, contribute significantly to the SST tendency in the western bay. The eastern limit of this direct-role regime is determined by downwelling Rossby waves, which are forced largely from the equatorial Indian Ocean, but are modified by alongshore winds at the eastern boundary and Ekman pumping along their westward path across the bay. The current and, as a result, advection weaken behind the Rossby waves. To the east of the Rossby wavefront, the thermocline is deep, permitting a deeper ML, but the actual ML depth (MLD) depends on the wind speed, with salinity also playing a role in the northern bay. Yet, there is negligible change in the SST even when MLD changes significantly because the deep thermocline decouples the changes in MLD and SST. In contrast, the shallower thermocline in the western bay limits the potential MLD, leading to larger changes in SST. The upwelling (downwelling) Rossby wave essentially conditions the upper ocean by decreasing (increasing) the potential depth of the mixed layer. SST variation weakens only when the thermocline deepens during downwelling events, which occur later in the western bay because Rossby waves propagate westward. The significant, but subtle, role of the Rossby waves in decoupling the changes in MLD and SST via downwelling is indirect, unlike the direct role of advection estimated in a standard heat-budget computation, and has been largely ignored in earlier studies.

This study investigates the accuracy of computational fluid dynamics (CFD) models to predict heat transfer in turbulent separated flows at low Reynolds numbers. This article will focus on flow in a staggered tube bank, while its companion articular will focus on a square prism (cylinder) in cross flow. Experimental data for both local heat transfer and velocity profiles are available for these cases and have been used extensively in the literature to evaluate various CFD methods. Six unsteady models were used and the results show that the unsteady shear stress transport (SST) model provided good overall accuracy relative to the mean Nusselt number for both cases. However, the SST model failed to accurately predict local variations. The partially averaged Navier–Stokes (PANS) variant of the SST model did show a marked improvement over the baseline SST model. The dynamic Smagorinsky large eddy simulation (LES) showed a much-improved fidelity to the local Nusselt number but unpredicted the actual values. The computational cost for the LES model was significant and it was found that the computationally expensive models with higher degrees of resolved turbulence did not necessarily return better results. Finally, the pressure drop results for the six models were scaled to predict the mean Nusselt number with the generalized Leveque method and were found to be very accurate. This method should prove useful to predict heat transfer performance with computationally less expensive cold flow results.

A ccurate forecasts of specific oceanographic parameters such as currents, temperature, and salinity in the surface and subsurface ocean, tides, and wind waves are essential for planning most maritime activities and securing the lives and livelihoods of millions of people who venture into and onto the oceans.Recognizing this, particularly for the waters around India, the Ministry of Earth Sciences, Government of India, entrusted the Indian National Centre for Ocean Information Services (INCOIS) to design and develop a High-Resolution Operational Ocean Forecast and Reanalysis System (HOOFS)-the operational ocean forecast system of India.A good understanding of the circulation of the Indian Ocean in general, and coastal waters around India in particular, is a prerequisite for designing and developing a forecast system for the Indian Ocean.

In this study, a numerical model of insulin depot formation in the subcutaneous adipose tissue of humans has been developed using the commercial computational fluid dynamics software. A better understanding of the underlying mechanisms can be helpful in the development of novel insulin administration devices and cannula geometries. Developing a model of insulin depot formation can provide faster results compared to extensive experimental studies which are typically done on porcine tissues. The injection method considered in this simulation involves an insulin pump that uses a rapid acting U100 insulin analogue. The depot formation has been studied by simulating Bolus injections ranging from 5 to 15 units of insulin, which corresponds to volumes of 50-150 mu L. The insulin is injected into modeled subcutaneous tissues typically present in human abdominal regions. The subcutaneous tissue has been modeled as a fluid-saturated porous media. An anisotropic approach has been used to define the tissue permeability. The value of the porosity in parallel and perpendicular directions has been varied to modify the viscous resistance to the flow in these directions. The developed model has been validated by comparing with published experimental results, which show qualitative similarities in disk-shaped insulin depot formation. The validated model is then used to study formation of insulin depot inside the subcutaneous tissue at varying insulin flow rates involving different cannula geometries and arrays. The numerical model has been found to be an effective option to evaluate new cannula designs prior to the manufacturing and testing of prototypes, which can be rather time consuming and expensive.

Abstract. The Indian Ocean presents two distinct climate regimes. The North Indian Ocean is dominated by the monsoons, whereas the seasonal variation is less pronounced in the south. The prevailing wind pattern produces upwelling along different parts of the coast in both hemispheres during different times of the year. Additionally, dynamical processes and eddies either cause or enhance upwelling. This paper reviews the phenomena of upwelling along the coast of the Indian Ocean extending from the tip of South Africa to the southern tip of the west coast of Australia. Observed features, underlying mechanisms, and the impact of upwelling on the ecosystem are presented. In the Agulhas Current region, cyclonic eddies associated with the Natal pulses drive slope upwelling and enhances chlorophyll concentration along the continental margin. The Durban break-away eddy spun-up by the Agulhas upwells cold nutrient-rich water. Besides, topographically induced upwelling occurs along the inshore edges of Agulhas Current. Wind-driven coastal upwelling occurs along the South coast of Africa and augments the dynamical upwelling in the Agulhas Current. Upwelling hotspots along Mozambique are present in the northern and southern sectors of the channel, and they are ascribed to dynamical effects of ocean circulation in addition to wind forcing. Interaction of mesoscale eddies with the western boundary, anticyclonic eddy pair interactions, and passage of cyclonic eddies cause upwelling. Upwelling along the southern coast of Madagascar is caused by Ekman wind-driven mechanism and by eddy generation and inhibited by Southwest Madagascar Coastal Current. The seasonal upwelling that occurs along the East African coast is primarily driven by the Northeast monsoon winds and enhanced by topographically induced shelf-breaking and shear instability between the East African Coastal Current and the island chains. Somali coast presents a strong case for the classical Ekman type of upwelling. This upwelling can be inhibited by the arrival of deeper thermocline signals generated in the offshore region by wind stress curl. The upwelling is nearly uniform along the coast of Arabia, it is caused by the alongshore component of the summer monsoon winds and modulated by the arrival of Rossby waves generated in the offshore region by cyclonic wind stress curl. Along the west coast of India, upwelling is driven by coastally trapped waves together with the alongshore component of the southwesterlies. Along the southern tip of India and Sri Lanka, the strong Ekman transport dives upwelling. Upwelling is feeble along the east coast of India and occurs during the summer, caused by alongshore winds. In addition, mesoscale eddies lead to upwelling but the arrival of river water plumes inhibits upwelling along this coast. Southeasterly winds drive upwelling along the coast of Sumatra and Java during summer. Kelvin wave propagation originating from the Equatorial Indian Ocean affects the magnitude and extent of Sumatra and Java upwelling. Both ENSO and IOD events cause large variability of upwelling here. Along the west coast of Australia, southerly winds can dominate over the Leeuwin Current, causing sporadic upwelling, which is prominent along the southwest, central, and Gascoyne coasts during summer. The open ocean upwelling in the southern tropical Indian Ocean and within the Sri Lanka Dome is driven primarily by the wind stress curl but also impacted by Rossby wave propagations. Upwelling is a key driver in enhancing biological productivity in all sectors of the coast, as indicated by enhanced sea surface chlorophyll concentrations. Additional knowledge at varying levels has been gained through in situ observations and model simulations. In the Mozambique channel, upwelling simulates new production, and circulation redistributes the production generated by upwelling and mesoscale eddies leading to observations of higher ecosystem impact along the edges of eddies. Similarly, along the southern Madagascar coast, biological connectivity is influenced by the transport of phytoplankton from upwelling zones. Along the coast of Kenya, both productivity rates and zooplankton biomass are higher during the upwelling season. Along the Somali coast, accumulation of upwelled nutrients in the northern part of the coast leads to spatial inhomogeneity in productivity. On the other hand, productivity is more uniform along the coasts of Yemen and Oman. Upwelling along the west coast of India has several biogeochemical implications, including oxygen depletion, denitrification, and high production of CH4 and dimethyl sulfide. Though feeble, wind-driven upwelling leads to significant enhancement of phytoplankton in the northwest Bay of Bengal during the summer monsoon. Along the Sumatra and Java coasts, upwelling affects the phytoplankton composition and assemblages. Dissimilarities in copepod assemblages occur during the upwelling periods along the west coast of Australia. Phytoplankton abundance characterizes inshore edges of the slope during upwelling season, and upwelling eddies are associated with abundance in Krill. The review identifies the northern coast of the Arabian Sea and eastern coasts of the Bay of Bengal as the least observed sectors. Further, sustained long-term observations with high temporal and spatial resolutions along with high-resolution modeling efforts are suggested for a proper description of upwelling, its variability, and its relationship to the ecosystem.

A good understanding of the general circulation features of the oceans, particularly of the coastal waters, and ability to predict the key oceanographic parameters with good accuracy and sufficient lead time are necessary for the safe conduct of maritime activities such as fishing, shipping, and offshore industries. Considering these requirements and buoyed by the advancements in the field of ocean modeling, data assimilation, and ocean observation networks along with the availability of the high-performance computational facility in India, Indian National Centre for Ocean Information Services has set up a "High-Resolution Operational Ocean Forecast and Reanalysis System" (HOOFS) with an aim to provide accurate ocean analysis and forecasts for the public, researchers, and other types of users like navigators and the Indian Coast Guard. Major components of HOOFS are (i) a suite of numerical ocean models configured for the Indian Ocean and the coastal waters using the Regional Ocean Modeling System (ROMS) for forecasting physical and biogeochemical state of the ocean and (ii) the data assimilation based on local ensemble transform Kalman filter that assimilates in situ and satellite observations in ROMS. Apart from the routine forecasts of key oceanographic parameters, a few important applications such as (i) Potential Fishing Zone forecasting system and (ii) Search and Rescue Aid Tool are also developed as part of the HOOFS project. The architecture of HOOFS, an account of the quality of ocean analysis and forecasts produced by it and important applications developed based on HOOFS are briefly discussed in this article.

This paper presents a technique to estimate moisture content in XLPE cable insulation through frequency domain spectroscopy. Tan δ over the frequency range 0.2 mHz to 110 Hz is correlated with moisture in the samples. The Havriliak-Negami (H-N) model is applied to investigate the changes in relaxation characteristics due to moisture and the moisture content is estimated through the correlation, which is used to cross validate the results. The comparative study shows that the estimated moisture content through the H-N model provides better accuracy than using tan δ.

Cross-linking Polyethylene (XLPE) insulation cable is most preferable power cable in underground transmission and distribution system. Power cables are operated for several years undergrounded and many factors like moisture, temperature can affect cable insulation over the years which may leads to insulation failure. The maintenance & detection of cable insulation status is thus very important as any kind of failure leads to economic losses and lot of problems. Dielectric response analysis is one of the advanced tool for condition monitoring of cable insulation. This paper is aimed to address the effect of temperature on thermally aged cable within its maximum operating temperature. To study the effect of temperature, PDC is performed on thermally aged cable at a temperature ranging between 25°C to 70°C. Based on the PDC results R-C parallel branch parameters of Debye model and Aging factor for different temperatures are calculated.

We have investigated interannual variations of the spring (February–April average) East India Coastal Current (EICC) magnitude between 2000 and 2018 using OSCAR (Ocean Surface Current Analysis Real-time) current and a linear, continuously stratified (LCS) model. Interannual variability of the EICC shows significant decrease in magnitude during spring of 2000, 2008 and 2011, the years when high negative ONI (Oceanic Niño Index for sea surface temperature) value has been observed due to dominance of strong La Niña events. Our LCS model also successfully simulates these interannual variability of the spring average EICC between 2000 and 2018. We carried out numerical experiments using LCS model related to local and remote forcing response on EICC. Dynamics of the EICC during spring are dominated by four different forcing processes; local wind along east coast of India, remote forcing response from the eastern and northern boundary of the BoB including islands, interior BoB and the Equatorial Indian Ocean (EIO). During El Niño and normal spring years, strong poleward interannual EICC are due to very weak negligible (order of 0–5 cm s $$^{-1}$$ ) EICC from EIO remote response and in-phase poleward EICC formation using other three forcings. However, during La Niña spring years, weak (order of 0–10 cm s $$^{-1}$$ ) poleward interannual EICC are formed due to destructive interference between equatorward current (order of 10–25 cm s $$^{-1}$$ ) from EIO forcing and in-phase poleward current from other three forcings. We have also found propagation of interannual upwelling (downwelling) favorable Kelvin wave from EIO via eastern and western boundary of the BoB during spring in the El Niño (La Niña) years. The interannual variations in the propagation of EIO Kelvin wave are associated with the changes in the EIO zonal wind direction by climate mode like ENSO (El Niño–Southern Oscillation).

In recent years, advancements in computational hardware have enabled massive parallelism that can significantly reduce the duration of many numerical simulations. However, many high-fidelity simulations use serial algorithms to solve large systems of linear equations and are not well suited to exploit the parallelism of modern hardware. The Tri-Diagonal Matrix Algorithm (TDMA) is one such example of a serial algorithm that is ubiquitous in numerical simulations of heat transfer and fluid flow. Krylov subspace methods for solving linear systems, such as the Bi-Conjugate Gradients (BiCG) algorithm, can offer an ideal solution to improve the performance of numerical simulations as these methods can exploit the massive parallelism of modern hardware. In the present work, Krylov-based linear solvers of Bi-Conjugate Gradients (BCG), Generalized Minimum Residual (GMRES), and Bi-Conjugate Gradients Stabilized (BCGSTAB) have been incorporated into the SIMPLER algorithm to solve a three-dimensional Rayleigh-Bénard Convection model. The incompressible Navier-Stoke’s equations, along with the continuity and energy equations, are solved using the SIMPLER method. The computational duration and numerical accuracy for the Krylov-solvers are compared with that of the TDMA. The results show that Krylov methods can improve the speed of convergence for the SIMPLER method by factors up to 7.7 while maintaining equivalent numerical accuracy to the TDMA.

Direct current measurements observed from the acoustic Doppler current profilers in the equatorial Indian Ocean (EIO) and solutions from an ocean general circulation model are investigated to understand the dynamics of the Wyrtki jet. These jets are usually described as semiannual direct wind forced zonal currents along the central and eastern EIO. We show that both, spring and fall, Wyrtki jets show predominant semiannual spectral peaks, but significant intraseasonal energy is evident during spring in the central and eastern EIO. We find that for the semiannual band, there is a strong spectral coherence between the overlying winds and the currents in the central EIO, but no coherency is observed in the eastern part of the EIO. Moreover, for the intraseasonal band, strong coherency between the winds and currents is evident. During spring, intraseasonal currents induced by the Madden–Julian oscillation (MJO) superimpose constructively with semiannual currents and thus intensify the strength of the spring Wyrtki jet. Also, the atmospheric intraseasonal variability accounts for the interannual variabilities observed in spring Wyrtki jets.

Eddies along western boundary of the Bay of Bengal (WBoB) play an important role in regulating regional climate and marine productivity of the north Indian Ocean. In this paper, role of Andaman and Nicobar islands (ANIs) in the formation of eddies along the WBoB is studied using an ocean general circulation model. Our analysis shows that, in the absence of ANIs, there is a significant reduction in the total number of mesoscale eddies in this region. The impact is particularly evident for the cyclonic eddies as a reduction of ~50% can be noticed in the absence of the islands. In contrast, influence of ANIs on anticyclonic eddies is not homogeneous in the WBoB; while absence of ANIs significantly increases anticyclonic eddies in the central part of the WBoB, a decrease can be noticed in the southern part. We further show that the reduction in number of cyclonic eddies along the WBoB is primarily driven by reduced baroclinic and barotropic instabilities. This process is more conspicuous during winter (October–January) season compared to summer (June–September) and spring (February–May) seasons.

We simulate the East India Coastal Current (EICC) using two numerical models (resolution \(0.1^{\circ } \times 0.1^{\circ }),\) an oceanic general circulation model (OGCM) called Modular Ocean Model and a simpler, linear, continuously stratified (LCS) model, and compare the simulated current with observations from moorings equipped with acoustic Doppler current profilers deployed on the continental slope in the western Bay of Bengal (BoB). We also carry out numerical experiments to analyse the processes. Both models simulate well the annual cycle of the EICC, but the performance degrades for the intra-annual and intraseasonal components. In a model-resolution experiment, both models (run at a coarser resolution of \(0.25^{\circ } \times 0.25^{\circ }\)) simulate well the currents in the equatorial Indian Ocean (EIO), but the performance of the high-resolution LCS model as well as the coarse-resolution OGCM, which is good in the EICC regime, degrades in the eastern and northern BoB. An experiment on forcing mechanisms shows that the annual EICC is largely forced by the local alongshore winds in the western BoB and remote forcing due to Ekman pumping over the BoB, but forcing from the EIO has a strong impact on the intra-annual EICC. At intraseasonal periods, local (equatorial) forcing dominates in the south (north) because the Kelvin wave propagates equatorward in the western BoB. A stratification experiment with the LCS model shows that changing the background stratification from EIO to BoB leads to a stronger surface EICC owing to strong coupling of higher order vertical modes with wind forcing for the BoB profiles. These high-order modes, which lead to energy propagating down into the ocean in the form of beams, are important only for the current and do not contribute significantly to the sea level.