K. Sumathy

North Dakota State University | NDSU · Department of Mechanical Engineering

Energy conservation continues to play a crucial role in social and economic development. With the remarkable increase in oil prices and exploring solutions for the replacement of fossil fuels, an ecofriendly energy resource has become the priority among more and more people. Keeping the intension for reducing the global warming impact and looking f...

Tin oxide (SnO₂) nanofibers were prepared by electrospinning polyvinyl and stannic chloride pentahydrate (PVP/SnCl₄·5H₂O) precursor nanofibers, followed by controlled carbonization. The as-spun SnO₂ nanofibers were investigated as a photoanode material in dye-sensitized solar cells. In order to reduce the inherent high charge recombination of “bare...

A simple, first-principles mathematical model has been developed to analyze the effect of interfacial and bulk charge transfer on the power output characteristics of dye-sensitized solar cells (DSSCs). Under steady state operating conditions, the Butler-Volmer equation and Schottky barrier model were applied to evaluate the voltage loss at counter...

Dye-sensitized solar cell (DSSC) offers an efficient and easily implemented technology for future energy supply. Compared to conventional silicon solar cells, it provides comparable power conversion efficiency (PCE) at low material and manufacturing costs. DSSC materials such as titanium oxide (TiO2) are inexpensive, abundant and innocuous to the e...

Activated graphene nanoplatelets (aGNPs) prepared by a hydrothermal method using KOH as activating agent were used as counter electrode for high efficiency dye-sensitized solar cells(DSSCs). After the KOH activation, the scanning electron microscopy image shows that aGNPs demonstrate a more curled, rough, and porous morphology which could contain b...

SnO2 nanofibers and their composites based photoanodes were fabricated and investigated in the application of dye-sensitized solar cells. The photoanode made of SnO2/TiO2 composites yielded an over 2-fold improvement in overall conversion efficiency. The microstructure of SnO2 nanofibers was characterized by X-ray diffraction (XRD) and transmission...

The optical and thermal performance of a linear Fresnel lens solar collector using different types of cavity receiver is presented in this paper. The optical properties of the proposed Fresnel lens solar collector was predicted by employing Monte Carlo ray trace method and thereby radiation distribution as well as the impact of incidence angle on o...

An optimally inclined box type solar cooker with single booster mirror is presented along with design and development of a novel parallelepiped shaped cooking vessel design for efficient cooking especially in winter conditions. The main feature of new parallelepiped shaped design is its longer inclined south wall (facing the sun) and a trapezoidal...

The silica gel–water adsorption refrigeration has attracted much attention especially in the last two decades, due to its environmentally friendly refrigeration that can be powered by low grade heat source. In this paper, we reviewed the research about silica gel–water adsorption technology, cooling systems as well as heat pumps. The technological...

As one of environmentally friendly refrigeration methods, solid adsorption refrigeration has tracked much interest over the world. Silica gel is popularly used in adsorption refrigeration systems as the adsorbent. Like a compressor in a compression refrigeration system, the adsorbent is vital to the performance of adsorption refrigeration systems....

This paper presents a steady-state electrical model of dye-sensitised solar cells with simplified boundary conditions. The codes are considerably concise and the sub-functions had confirmed good extensibility. This model is utilised to predict the current–voltage characteristics and the energy conversion efficiency based on various design and opera...

feasibility and performance of thermosyphon solar water heating (SWH) system using R744 (CO2) as the working fluid. The uniqueness of the system was the use of carbon dioxide as a working fluid; which is one of the most promising alternative natural refrigerants. For supercritical carbon dioxide, a small change in temperature or pressure can result...

The effect of the maximum swing angle of the sun (0°, 15°, 30°, 45° and 60°) away from the normal is observed on the maximum power output of an amorphous silicon solar PV module using a solar simulator. Studies reveal that as the panel inclination is increased, the maximum power produced (Pmp) by the module decreases. Solar equations are used to co...

Modeling of greenhouse microclimate is very important to maintain optimum inside environment during different stages of plant growth. To formulate an accurate thermal model, computation of precise solar radiation input and overall heat transfer coefficient is important as these affect the greenhouse energy and mass balance. Initially, we briefly re...

Alow cost tubular type indigenous solar cooker was developed using an inflated rubber tube of a motorbike. The

One of the most widely known solar thermal applications is solar water heating. In terms of installation expenditures and energy cost over the total life of the system, solar water heating technology has proven to be cost efficient for several domestic and industrial applications. Technological practicability of these systems has long been recogniz...

This study reports the numerical analyses of a CO2 transcritical cycle on solar assisted heat pump water heating system in which evacuated tube U-pipe solar collector is utilized as an evaporator. This simulation model can predict operating characteristics for moderate meteorological conditions of North Dakota. The main purpose of this work is to s...

A numerical model has been developed to investigate the performance of dye-sensitized solar cells (DSSCs) under extreme weather conditions. The main purpose of this work is to simulate the temperature influence on the overall efficiency of DSSCs with a consideration of the voltage loss at titanium dioxide (TiO2 )/ transparent conductive oxide (TCO)...

Details of a heat pump assisted solar water heating system, is briefly described. Refrigerants compromising of Fluorocarbons and Chlorofluorocarbons have been generally used as the working fluid. But due to its ozone depletion effect and high Global warming potential, they have been replaced by synthetic refrigerants such as R22, R134 etc. The heat...

A numerical model has been developed to investigate the performance of dye-sensitized solar cells (DSSCs) under extreme weather conditions. The main purpose of this work is to simulate the temperature influence on the overall efficiency of DSSCs with a consideration of the voltage loss at titanium dioxide (TiO2)/ transparent conductive oxide (TCO)...

A gel polymer electrolyte containing I−/I3− redox couple was prepared using polyethylene glycol (PEG) as polymer matrix and propylene carbonate (PC) as organic solvent by sol–gel method. A dye sensitized solar cell (DSSC) employing the gel polymer electrolyte gives an open-circuit voltage of 0.7 V and a short-circuit current of 8.1 mA cm−2 at an in...

A numerical model has been developed to analyze the steady state performance of a direct-expansion geothermal heat pump using carbon dioxide in a transcritical cycle. The system consists of a compressor, counter-flow gas cooler/water heater, expansion device and the ground-coupled evaporator coils. The simulation results are found to be in good agr...

Carbon dioxide is a safe, economic and environmentally sustainable refrigerant which can be used in heat pump and refrigeration systems. Research into the performance and benefits of a transcritical heat pump cycle using carbon dioxide began in the early 1990s. Theoretical and experimental research, as well as commercial system development, has imp...

Solar energy concentration technology using Fresnel lens is an effective way to make full use of sunlight. This paper makes a review about the recent development of the concentrated solar energy applications using Fresnel lenses. The ongoing research and development involves imaging systems and non-imaging systems. Compared with imaging systems, no...

A brief description of the operation and analysis of a solar water pump is given. The performance of the pump is studied for various solar radiation intensities and ambient temperatures, so that a clear picture on the year-round performance of the pump emerges. The prediction reveals that the number of cycles and the overall efficiency increases wi...

This paper presents a review of the available literature covering the latest module aspects of different photovoltaic/thermal (PV/T) collectors and their performances in terms of electrical as well as thermal output. The review covers detailed description of flat-plate and concentrating PV/T systems, using liquid or air as the working fluid, numeri...

The thermal performance of a solar air heater may be enhanced by means of twisted tapes, inserted inside the fluid flow tubes, which induce swirl flow acting as turbulence promoters. Experiments were carried out to investigate the effect of helical tape inserts of two different twist ratios (23 and 11) on the friction factor and heat transfer coeff...

This paper presents the description and operation of a solar-powered modified two-bed adsorption air-conditioning system with activated carbon and methanol as the working pair. A simple lumped parameter model is established to investigate the performance of this continuous adsorption cycle consisting of a twin adsorber immersed in water tanks, whic...

This paper proposes a novel hybrid desiccant dehumidification and air conditioning system. The aim is to achieve a higher energy efficiency to reduce the use of electricity by utilizing the desiccant dehumidification system to remove latent load, while the vapor-compression and IEC system meeting the sensible heat load. Experimental set-up has been...

The effect of helical tape insert on the turbulent flow heat transfer is studied experimentally. A helical tape insert is placed in a tube to generate swirl flow that aids in enhancing the heat transfer rate of the tube. The tube is heated electrically and is subjected to a constant and uniform heat flux. The effect of twist ratio of the insert on...

Nano-sized TiO2 photocatalytic water-splitting technology has great potential for low-cost, environmentally friendly solar-hydrogen production to support the future hydrogen economy. Presently, the solar-to-hydrogen energy conversion efficiency is too low for the technology to be economically sound. The main barriers are the rapid recombination of...

A theoretical model based on an integration of both Schottky barrier model and electron diffusion differential model was developed to determine the TiO2/TCO interfacial effect on the current–voltage (J–V) characteristics of a dye-sensitized solar cell (DSSC). The thermionic-emission theory was appropriately applied to describe the electron transfer...

Hong Kong is highly vulnerable to energy and economic security due to the heavy dependence on imported fossil fuels. The combustion of fossil fuels also causes serious environmental pollution. Therefore, it is important to explore the opportunities for clean renewable energy for long-term energy supply. Hong Kong has the potential to develop clean...

In this study, silica gel (SG), calcium chloride (CaCl2) and composite desiccant (SG–CaCl2) applied to a corrugated paper (CP) based desiccant rotary wheel are compared for their abilities to remove moisture from wet air. The experimental data shows that the CP–SG–CaCl2 material could attain equilibrium within a very short period, and its hygroscop...

Hydrogen production plays a very important role in the development of hydrogen economy. One of the promising hydrogen production approaches is conversion from biomass, which is abundant, clean and renewable. Alternative thermochemical (pyrolysis and gasification) and biological (biophotolysis, water–gas shift reaction and fermentation) processes ca...

The porosity in a dye-sensitized solar cell (DSSC) can affect light absorption and electron diffusion that govern the overall electrical current–voltage (I–V) characteristics. In this research, two methods, namely, constant overlap and variable overlap, were developed to determine the connectivity of dye-sensitized TiO2 particles in high and low po...

This paper presents the experimental tests on hybrid desiccant dehumidification and air conditioning systems. Experimental tests are Carried out with LiCl desiccant at typical operative ranges for air conditioning applications, particularly for high humid regions like Hong Kong. Results are reported in terms of coefficient of performance (COP) base...

The basic mechanism of titanium dioxide photocatalytic water-splitting for hydrogen production is introduced. The methods to enhance hydrogen production are reviewed, including addition of sacrificial reagent, addition of sodium carbonate, noble metal loading, metal ion doping, anion doping, dye sensitization, semiconductor composition and ion impl...

A multi-bed adsorption rotary cooling system can make use of the concept of heat regeneration cycle and recently developed technology of heat enhancement in adsorbent bed. In the present study, the performance parameters such as COP and specific cooling power (SCP) of the rotary system are initially analyzed based on heat recovery temperature diffe...

In this paper a family of new silica gel–calcium chloride composite adsorbents is presented for desiccant rotary wheel in dehumidification system. For these desiccants the water sorption equilibrium has been measured in a wide relative vapour pressure range. This experimental study shows that the vapour adsorption properties of the composites using...

A simple lumped parameter model is established to investigate the performance of a solar powered adsorption air conditioning system driven by flat-type solar collectors with three different configurations of glazes: (i) single glazed cover; (ii) double glazed cover and (iii) transparent insulation material (TIM) cover. The dynamic performance of a...

The heat and mass transfer (HMT) model for transportation process in adsorbent bed is studied in relation to heat transfer (HT) model, which is dependent on assumptions such as the conduction dominance and negligible mass transfer resistance. Two general criteria are generated by performing an order of magnitude analysis to determine when the HT mo...

A simple lumped parameter model is established to investigate the performance of a solar-powered adsorption air-conditioning system driven by flat-type solar collectors. The dynamic performance of a continuous adsorption cycle using a double adsorber along with heat recovery is measured in terms of the temperature histories, gross solar coefficient...

Solar adsorption refrigeration devices are of significance to meet the needs for cooling requirements such as air-conditioning, ice-making and medical or food preservation in remote areas. They are also noiseless, non-corrosive and environmentally friendly. Various solar powered cooling systems have been tested extensively; however, these systems a...

This paper reports the performance of a modified solar powered air-conditioning system, which is integrated with a partitioned storage tank. In addition, the effect of two main parameters that influence the system performance is presented and discussed. The study shows that by partitioning the storage tank, the solar cooling effect can be realized...

This paper presents the description and operation of a solar-powered hybrid adsorption ice-maker with activated carbon fibre and methanol as the working pair. The analysis indicates that for the given amount of adsorbent/adsorbate, by adapting more adsorbers instead of conventionally used single adsorber bed, the performance of the adsorption syste...

A solar adsorber with glass tube insulation used in a solar adsorption cooling system is proposed and investigated. The adsorber is a metal tube packed with activated carbon methanol pair surrounded by a vacuum tube glazing. A mathematical model, which accounts for the heat and mass transfer of sorption (adsorption and desorption) processes as well...

This paper presents a status report on solar transparent insulation materials (TIM). It covers a survey of the literature, various physical and other properties of TIM devices, their classifications, applications, fabrication procedures, availability and cost trends. The global resurgence of research is clarified. Subsequently, the development of T...

Analytical and experimental studies were performed on a direct-expansion solar-assisted heat pump (DX-SAHP) water heating system, in which a 2 m2 bare flat collector acts as a source as well as an evaporator for the refrigerant. A simulation model was developed to predict the long-term thermal performance of the system approximately. The monthly av...

This paper presents a parametric analytical study on the enhancement of natural ventilation in a solar house induced by a solar chimney and a solid adsorption cooling cavity. Some details on sizing such a system are also provided. Theoretical analyses are carried out to investigate the ventilation in the solar house with solar chimney alone, coolin...

The role of renewable energy resources in developing countries has increased considerably over the last decade. Technological developments are so advanced that the renewables can be conveniently substituted for commercial energy sources. The extent to which renewable energy could be substituted in the commercial energy scene in respect of environme...

Quasi-local absorption heat transfer coefficients and pressure drop inside a horizontal tube absorber have been investigated experimentally, with R-22/DMA as the working pair. The absorber is a counterflow coaxial tube-in-tube heat-exchanger with the working fluid flowing in the inner tube while the water moves through the annulus. A large temperat...

A cross-flow direct evaporative cooler, in which the wet durable honeycomb paper constitutes as the packing material, is investigated. The system is expected to act as both humidifier and evaporative cooler to create a comfortable indoor environment in arid regions. A mathematical model, including the governing equations of liquid film and gas phas...

Accurate modeling of solar heating or cooling with storage generally requires an accounting of the stratification within such storage tank, since overall system performance is significantly affected by the storage temperature distribution. In this study, a simple one-dimensional multi-node approach, taking into account of the axial heat conduction...

A mathematical model of the closed adsorption heat pump and cooling systems is particularly used to assist in interpreting the observed phenomena, to design the system, to predict the trends, and to assist in optimization. In this paper, various mathematical models mainly analyzing the heat and mass transfer process of an adsorption bed in closed a...

Based on experiences with an operating solar cooling system in south China, a low temperature driven solar cooling system has been proposed, and a new model of two-stage lithium bromide absorption chiller has been developed. Test results have proved that the two-stage chiller could be driven by low temperature hot water ranging from 60 to 75°C, whi...

This paper reports on the performance of a solar powered absorption air conditioning system with a partitioned hot water storage tank. The system employs a flat-plate collector array with a surface area of 38 m2 to drive a LiBr–H2O absorption chiller of 4.7 kW cooling capacity. The system is provided with a storage tank (2.75 m3) which is partition...

Thermodynamic analysis has been carried out in detail, to predict the performance of a solar thermal water pump working at different discharge heads. It is shown that the heating time of the working fluid and the condensation time of the spent vapour play an important role in determining the number of cycles that a pump can perform in a day. The he...

This paper presents the description and operation of a solar-powered thermal water pump with ethyl ether as the working fluid. A simple flat-plate collector with an exposed area of 1 m2 is employed to pump water ranging from 700–1400 l/day depending upon the lift (6–10 m). Such a pumping system could achieve efficiency of about 0.42–0.34%.

This paper presents the simulation of a solar-powered absorption air conditioning system with the absorption pair of lithium bromide and water. An attempt is made to increase the COP of the system by partitioning a single storage tank into two parts. In the morning when sunshine is low, the upper part is activated, and in the afternoon, the whole (...

This paper reports the performance of a lithium bromide absorption chiller in a solar powered air conditioning system, when being operated conventionally. The chiller performance based on a modified solar powered absorption air conditioning system which is integrated with a partitioned storage tank has been presented and discussed. It is shown that...

Solar, wind and biomass are accepted as dependable and widely available renewable sources of energy. Generation and utilization of energy from these renewables is non polluting in nature and are acceptable as environmentally clean sources. These renewable energy sources can contribute significantly in meeting the energy demands of the Indian energy...

The role of renewable energy resources in the developing countries has been increasing considerably in the last decade. Technological developments are so advanced that the renewable can be conveniently substituted for commercial energy sources. The extent to which renewable energy could be substituted in the commercial energy scene in respect of en...

An environmental control system utilizing solar energy would generally be more cost-effective if it were used to provide both heating and cooling requirements in the building it serves. Various solar powered heating systems have been tested extensively, but solar powered air-conditioners have received little more than short-term demonstration atten...

Renewable energy sources are likely to play a significant role in meeting the future energy requirement of a developing country like India. The effect of introducing renewable energy sources on the commercial energy scene may have to be analyzed carefully. In this paper, we present an Optimal Renewable Energy Model that minimizes the cost/efficienc...

In this study, the performance of a solar thermal water pump with two different working fluids such as n-pentane and ethyl ether, is reported. The theoretical comparison is made in terms of the number of cycles the pump can work per day, the amount of water that can be pumped per day and the overall efficiency of the system. It is found that the ef...

Energy demand is increasing rapidly because of developments in the industrial, agricultural, commercial and transportation sectors. The population rise and improved life style are other reasons for the increase in energy demand. Since commercial energy sources are non-renewable and depleting in nature, it is essential to seek renewable energy sourc...

A greenhouse of semi-circular shape was employed to study the effect of spectral light response on the stem-cutting propagation of horticultural plants. The number of days taken for the root formation were noted and it was observed that the stem cuttings showed earlier root formation under a red-tinged greenhouse followed by a blue-tinged greenhous...

A number of attempts have been made by scientists to utilize solar energy for irrigation water pumping. It is mainly a problem of conversion of heat energy available from the sun, to mechanical energy. Some ingenious methods have been devised to utilize the available energy at low temperatures. This paper reviews past efforts to develop solar therm...

This paper presents the description and operation of a solar-powered ice-maker with the solid adsorption pair of activated carbon and methanol. A domestic type of charcoal was chosen as the adsorbent, and a simple flat-plate collector with an exposed area of 0.92 m2 was employed to produce ice of about 4–5 kg d−1 at an evaporator temperature of abo...

The performance of a solar water pump which works on the basis of vapour generated by a flat-plate solar collector of exposed area 1m2 has been studied for three different discharge heads, namely 6, 8 and 10m. The design and experimental results of the pump which entailed detailed calculations to obtain the optimal volumes of the vessels, are prese...

This paper presents the description and operation of a solar-powered ice-maker with the solid adsorption pair of activated carbon and methanol. A domestic type of charcoal is chosen as the adsorbent, and a simple flat-plate collector with an exposed area of 0.92 m2 is employed to produce ice of about 4–5kg/day. The above system could achieve solar...

The time constant for the given typical collector is determined which shows the transient behaviour of the collector and the proper time interval to be selected for steady and quasi-steady state efficiency tests. The thermal performance of a flat-plate solar collector for the Hong Kong climate is presented. The fluid inlet-temperature strongly infl...

This paper details the experimental investigation and the methodology of fluid bed incineration of three different oil sludge wastes from one of the major refineries of South India using the pilot plant facility at School of Energy, Bharathidasan University, Trichy. The trial runs conducted in the fluid bed incinerator system show that more than 98...

The pump employs pentane as the working substance -- an organic fluid with a low boiling point. A flat-plate solar collector generates vapour and its pressure is adequate to pump water from a well. Provision of a separate tank for storing the vapour under pressure improves the performance of the pump. Experiments prove its feasibility and yield use...

Measured values of temperature and pressure of pentane in the collection system of a laboratory model solar thermal water pump are reported. In one set of experiments the pentane was merely heated without tapping the vapour for pump operation and in the other actual pump operation was performed. Theoretical values evaluated using the model already...

The principle of the workings of a solar thermal water pump with n-pentane as the working fluid is described briefly. The performance of the pump is predicted from the thermodynamic analysis of the cycle of events. Experiments were carried out with a small solar thermal pump having a collector area of 1 m2. The experimental and theoretical results...

A brief description of the operation and analysis of a solar water pump is given. It is shown that one of the parameters affecting the performance of the pump is the time taken for condensation of the working fluid in each cycle. The condensation time in each cycle is determined through heat transfer analysis of the condenser. The effects of inlet...

A solar thermal water pump using a flat-plate collector with n-pentane as the working fluid is described. A heat-transfer analysis has been carried out for this system with account for all heat losses. Variations in temperature and pressure of pentane in the collection system with time are predicted. Two different situations are considered: one wit...

Presented in the paper is a brief description of the solar thermal water pump and its operation. The performance of such a solar water pump working on a flat-plate collector of exposed area of 1 m2 is studied for three different discharge heads, namely 6, 8 and 10 metres. The thermodynamic analysis reveals that, while the number of cycles and the q...

International environment protection initiatives have led to the intensification of research efforts on development of ozone and global warming safe heat pump technology. Adsorption refrigeration has been intensively investigated in Japan, Europe and USA, because of its promising potential for competing with conventional vapor compression refrigera...