Krishna Kota

• Senior Researcher at United states army institute of infectious diseases

Aerosols such as dust, pollen, smoke, soot, or viruses in our environment can significantly affect air quality, impacting climate and health. For example, virus transmission through aerosols is an important mode of spread for certain respiratory viruses, including the SARS‐CoV‐2 virus responsible for the COVID‐19 pandemic. Numerous measures were pr...

Effective pretreatment is essential for achieving long-term stable operation and high water recovery during the desalination of alternative waters. This study developed a process modeling approach for technical, economic, energetic, and environmental assessments of pretreatment technologies to identify the impacts of each technology treating bracki...

This study explored the relationship between the Nusselt number and the friction factor in the laminar boundary slip flow of a Newtonian liquid between parallel plates. In addition, simplified equations were developed to estimate two key parameters—slip velocity and temperature jump—both of which are typically difficult to measure in experimental s...

The production of freshwater from desalinating abundant saline water on the planet is increasingly considered a climate change adaptation measure. Yet, there are challenges associated with the high cost, intensive energy demand, and environmental implications of desalination. Effective integration of solar energy generation and freshwater productio...

The feasibility of multiple scalable direct solar configurations for small-scale water preheating/desalination was assessed experimentally and complemented using a theoretical model. The physics of the beam-down optics, direct-down optics, and a combination of the two showed to satisfactorily enhance the water yield by 11, 28, and 25% respectively...

This study reports a new observation of rapid particle migration in very dilute suspensions flowing through a microchannel. In microfluidics, passive particle manipulation methods based on shear gradients or inertial forces are usually preferred from an energy consumption perspective. Shear-induced migration is known to be particularly slow (requir...

With a growing population, lack of balance between water demand and traditional freshwater supply has become a critical issue. A solar still is a simple, impactful device for producing freshwater from alternative water sources such as brackish water, wastewater, and brine by sole or partial consumption of solar energy. Solar stills are highly suite...

Systems for energy conversion, heat rejection, and sensing and control often incorporate heat exchange devices. Recent developments in microfabrication and assembly methods have led to significant miniaturization of these systems. Miniaturized heat exchange devices have commonly utilized microchannel flow passages. This chapter reviews the fundamen...

The Virtual Telescope for X-ray Observations (VTXO) will use lightweight Phase Fresnel Lenses (PFLs) in a virtual X-ray telescope with $\sim$1 km focal length and with $\sim$50 milli-arcsecond angular resolution. VTXO is formed by using precision formation flying of two SmallSats: a smaller OpticsSat that houses the PFLs and navigation beacons whil...

The current technologies to treat hypersaline produced water (PW), such as thermal evaporation, are usually energy-intensive and cost-prohibitive. This study developed a low-cost, robust, solar-driven carbon black and airlaid paper-based evaporator (CAPER) for desalination of PW in the Permian Basin, United States. The study aims to better understa...

Day-to-day observations reveal numerous medical and social situations where maintaining physical distancing is either not feasible or not practiced during the time of a viral pandemic, such as, the coronavirus disease 2019 (COVID-19). During these close-up, face-to-face interactions, a common belief is that a susceptible person wearing a face mask...

The Virtual Telescope for X-ray Observations (VTXO) will use lightweight Phase Frensel Lenses (PFLs) in a virtual X-ray telescope with 1 km focal length and with nearly 50 milli-arcsecond angular resolution. Laboratory characterization of PFLs have demonstrated near diffraction-limited angular resolution in the X-ray band, but they require long foc...

Solar distillation is considered a low-cost, environmental-friendly approach for freshwater production. However, water output and photothermal efficiency of conventional solar evaporators are low. This study developed highly efficient bilayer photothermal functional films (noted as CBMCE) by depositing carbon black nanoparticles (CBNPs) dispersion...

With depleting natural resources and the effects of conventional energy sources like coal and petroleum on the environment, clean energy sources have been gaining prominence in recent times. Renewable sources are abundant and improving the efficiency of renewable technologies will provide a viable solution to meet the ever-increasing energy demands...

This study presents a theoretical model to simulate the temperatures and productivity of a single-slope, single-basin solar still when an external solar enhancement is used. Experiments were performed in the New Mexico region (32.3199° N, 106.7637° W) to validate the numerical model. A point focusing Fresnel lens was used in the experiments to enha...

A refraction-based methodology for concentrating sunlight is proposed to augment the pure water production of a conventional solar still. The Fresnel lens (FRL) was integrated with a single-basin, single-slope solar still to refract the incident sunlight to a focal point that was constantly located on the basin bottom. Due to the introduction of th...

The contact angle (CA) of a water droplet on the polished aluminum surfaces is usually between 60° and 90°. This paper discusses a tuned bulk micro-manufacturing approach for transforming the surface topology of aluminum simultaneously at the micro- and nano-length scales, thereby significantly influencing its wetting characteristics. The approach...

With increasing heat densities of electronics such as in servers in electronic and photonic data centers, liquid cooling has gained momentum in recent years. In this effort, forced convective performance of a dielectric liquid (mineral oil) was numerically and experimentally analyzed in a channel with two Conducting-Lubricating (CO-LUB) surface wal...

A novel idea for the improvement of boiling heat transfer is that of a binary surface – where a non-boiling liquid coats sub-surface irregularities and aids in heat transfer to the primary working fluid. The threefold goal of this effort was to: (i) prepare durable, low-cost, scalable binary surfaces for boiling heat transfer enhancement, (ii) cond...

In this study, exergy analysis of a two-parallel-step organic Rankine cycle (ORC) for waste heat recovery from an internal combustion engine (ICE) is performed. A novel two-step configuration to recover waste heat from the engine coolant fluid and the exhaust gas simultaneously is first introduced. The working fluids considered for this heat recove...

Altering the wetting characteristics of copper will positively impact numerous practical applications. The contact angle (CA) of a water droplet on the polished copper surface is usually between 70° and 80°. This paper discusses a facile, scalable, tuned bulk micro-manufacturing approach for altering the surface topology of copper concomitantly at...

Acne vulgaris (acne) is a chronic inflammatory disease prevalent among adolescents and adults, with significant psychological effects. The aetiology of acne is multifactorial. Several pathophysiological associations have been identified in which Propionibacterium acnes plays a major role. This bacteria primarily affects areas containing oil glands...

Long duration thermal control of cryogenic propellants is a high priority mission activity for NASA. A 20 K cryocooler capable of 20 W of refrigeration would offer a significant mass savings in cryogen storage by facilitating propellant zero boil-off and hence long term cryogen storage, which would provide scope for long duration missions beyond lo...

Addressing the traditionally contradictory problem of obtaining considerable drag reduction without negatively impacting heat transfer as much is an arduous scientific challenge. In this paper, prior efforts on frictional drag reduction and the associated issues are discussed in relevant detail, and the effectiveness of Conducting-Lubricating (CO-L...

Thermodynamics indicates that the lower the temperature of a resource, the less energy that could be extracted from it due to lower maximum thermal efficiency. Geothermal resources exist in varying temperatures. The lowest ones (around 120°C), are too small for economic power production. On the other hand, concentrating solar power (CSP) can achiev...

Plastics are typically polymers of high molecular weight and one of the chemical materials which cause severe environmental problems. Improper disposal of plastic bags blocks the porosity of the soil and causes problems for groundwater recharge. Due to its non-biodegradable nature, littering of plastics causes irreversible damage to the environment...

An experimental investigation of a scheme for cooling electronics packaged in a 3D stack arrangement will be presented in this paper. The scheme utilizes immersion cooling of the stacked electronics in an enclosure filled with a dielectric fluid. Convection and conduction within the dielectric fluid drive heat from the 3D stack to the walls of the...

This paper focuses on the design and parametric numerical study of a hybrid heat sink combining a liquid thermal interface with an array of synthetic jet actuators for 3-D chip stack cooling. The air-side heat sink exploits enhanced localized heat transfer achieved via a central array of synthetic jet actuators. The key focus of this paper is the n...

The objective of this effort is to pursue artificial microscale surface roughness features in the form of dimples, on the fins of an air cooled heat sink, as a passive option to energy-efficiently augment heat transfer in forced convection flows. High fidelity numerical simulations were employed for realizing an optimized dimple configuration and t...

The continued increase in electronic device packaging densities is placing ever more challenging performance requirements on air-cooled heat sinks. In cases where the state-of-the-art heat sink technology is unable of to meet these requirements, this often results in either a relaxation of design specifications, or the exploration of other thermal...

This paper focuses on numerically analyzing the thermal transport phenomena in the transient conjugate problem of melting and laminar film condensation. The key focus is to identify an optimum container aspect ratio/shape and conditions for which the heat storage time and the storage capacity are minimum and maximum respectively. Since most solid–l...

Wavy walls are investigated in this paper as a passive scheme to improve the heat transfer performance of low-Reynolds-number laminar flows in microchannel heat sinks for electronics cooling applications. 3-D laminar fluid flow and heat transfer characteristics in microchannels with wavy walls are numerically studied for a 500-μm hydraulic diameter...

Wavy channels are investigated in this paper as a passive scheme to improve the heat transfer performance of laminar fluid flow as applied to microchannel heat sinks. Parametric study of three-dimensional laminar fluid flow and heat transfer characteristics in micro-sized wavy channels was performed by varying the wavy feature amplitude and wavelen...

Wavy walls are investigated in this paper as a passive scheme to improve the heat transfer performance of low Reynolds number laminar flows in microchannel heat sinks for electronics cooling applications. Three-dimensional laminar fluid flow and heat transfer characteristics in micro-wavy channels are numerically studied for a 500 μm hydraulic diam...

The present investigation focuses on the design and thermal parametric study of a unique liquid interface thermal management solution for a 3D chip stack that is embedded within a cavity, in a radial heat sink cooled by an array of synthetic jet actuators. The heat sink module was previously reported by the authors, who achieved an overall heat tra...

Wavy channels are investigated in this paper as a passive scheme to improve the heat transfer performance of laminar fluid flow as applied to microchannel heat sinks. Parametric study of three-dimensional laminar fluid flow and heat transfer characteristics in micro-sized wavy channels was performed by varying the wavy feature amplitude and wavelen...

Systems for energy conversion, heat rejection, and sensing and control often incorporate heat exchange devices. Recent developments in microfabrication and assembly methods have led to significant miniaturization of these systems. Miniaturized heat exchange devices have commonly utilized microchannel flow passages. This chapter reviews the fundamen...

The present investigation focuses on the design of a unique liquid interface thermal management solution for a 3D chip stack that is embedded within a cavity, in a heat spreader cooled by an array of synthetic jet actuators. The heat sink module was previously reported by the authors, who achieved an overall heat transfer coefficient of ~70 W/m<sup...

A generic model was developed that can provide an estimate of the mass and volume and characterize the usefulness of thermal energy storage (TES) for various thermal management (TM) applications in advanced military aircraft. Conceptual design for low thermal duty cycle electronic heat sink applications was described. The criteria are presented for...

Microchannels are used in applications where large amount of heat is produced. Phase change material (PCM) slurries can be used as a heat transfer fluid in microchannels as they provide increased heat capacity during the melting of phase change material. For the present numerical investigation, performance of a nano-encapsulated phase change materi...

High heat flux removal from devices such as Insulated-Gate Bipolar Transistor (IGBT) and Monolithic Microwave Integrated Circuit (MMIC) will be important for future Navy ships. Micro encapsulated phase change material (MEPCM) slurry was used as a heat transfer fluid inside a microchannel instead single phase fluid. Presence of phase change material...

This paper focuses on the numerical analysis of the heat storage phenomenon in a dual latent heat sink intended for low thermal duty cycle electronic heat sink applications. The effectiveness of this heat sink depends on the rapidness of the charging facility in the design during the pulse heat generation period of the duty cycle. Heat storage in t...

This paper focuses on the thermal transport phenomena in renewable thermal energy systems as in solar and geothermal based systems. The key focus is on numerically analyzing the coupled problem of vapor condensing on phase change material (PCM) storage containers in thermal based renewable energy systems. Since most solid-liquid phase materials suf...

A conceptual design of a dual latent heat sink basically intended for low thermal duty cycle electronic heat sink applications is presented. In addition to the concept, end-application-dependent criteria to select an optimized design for this dual latent heat sink are presented. A thermal resistance model has been developed to analyze and optimize...

This paper presents the concept of a dual latent heat sink for thermal management of pulse heat generating electronic systems. The focus of this work is to verify the effectiveness of the concept during charging through experimentation. Accordingly, custom components were built and a prototype version of the heat sink was fabricated. Experiments we...

Future defense, aerospace and automotive technologies involve electronic systems that release high pulsed waste heat like during high power microwave and laser diode applications in tactical and combat aircraft, and electrical and electronic systems in hybrid electric vehicles, which will require the development of an efficient thermal management s...

Conceptual design of a dual latent heat sink basically intended for low thermal duty cycle electronic heat sink applications is presented. In addition to the concept, end-application dependent criteria to select an optimized design for this dual latent heat sink are presented. A thermal resistance model has been developed to analyze and optimize th...

A numerical model to investigate heat transfer characteristics of the MEPCM slurry flow inside a typical microchannel is presented in the paper. The temperature field inside the channel wall is solved three dimensionally and is coupled with the three dimensional velocity and temperature fields of the fluid. The effective specific heat method is use...