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K. Sumathy

Bio: K. Sumathy is an academic researcher from University of Hong Kong. The author has contributed to research in topic(s): Air conditioning & Solar air conditioning. The author has an hindex of 17, co-authored 20 publication(s) receiving 4489 citation(s).
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Journal ArticleDOI
Abstract: Nano-sized TiO 2 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 photo-generated electron/hole pairs as well as backward reaction and the poor activation of TiO 2 by visible light. In response to these deficiencies, many investigators have been conducting research with an emphasis on effective remediation methods. Some investigators studied the effects of addition of sacrificial reagents and carbonate salts to prohibit rapid recombination of electron/hole pairs and backward reactions. Other research focused on the enhancement of photocatalysis by modification of TiO 2 by means of metal loading, metal ion doping, dye sensitization, composite semiconductor, anion doping and metal ion-implantation. This paper aims to review the up-to-date development of the above-mentioned technologies applied to TiO 2 photocatalytic hydrogen production. Based on the studies reported in the literature, metal ion-implantation and dye sensitization are very effective methods to extend the activating spectrum to the visible range. Therefore, they play an important role in the development of efficient photocatalytic hydrogen production.

3,378 citations

Journal ArticleDOI
Abstract: 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 attention. This paper reviews past efforts in the field of solar powered air-conditioning systems with the absorption pair of lithium bromide and water. A number of attempts have been made by researchers to improve the performance of the solar applied air-conditioning (chiller) subsystems. It is seen that the generator inlet temperature of the chiller is the most important parameter in the design and fabrication of a solar powered air-conditioning system. While collector choice, system design and arrangement are other impacting factors for the system operation.

128 citations

Journal ArticleDOI
Abstract: 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 TIM cover systems (often referred to as advanced glazing) from such products as polymer sheets, capillaries and cellular profiles, is discussed. Their design and performance characteristics are investigated; results corresponding to experimental measurements, as well as computational models, are presented. An explicit comparative study of absorber parallel and absorber perpendicular configurations of TIM cover systems is presented. The TIM covers with black end cover plates, and cellular walls of high emissivity, as well as those with selective cover plates and cellular walls fully transparent to IR radiations, have relatively lower heat loss coefficients.

117 citations

Journal ArticleDOI
Abstract: 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 averaged COP was found to vary between 4 and 6, while the collector efficiency ranged from 40 to 60%. The simulated results were used to obtain an optimum design of the system and to determinate a proper strategy for system operating control. The effect of various parameters, including solar insolation, ambient temperature, collector area, storage volume and speed of compressor, had been investigated on the thermal performance of the DX-SAHP system, and the results had indicated that the system performance is governed strongly by the change of solar insolation, collector area and speed of compressor. The experimental results obtained under winter climate conditions were shown to agree reasonably with the computer simulation. Copyright © 2003 John Wiley & Sons, Ltd.

111 citations

Journal ArticleDOI
01 Nov 2001-Solar Energy
Abstract: 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 partitioned into two parts. The upper part has a volume of about one-fourth of the entire tank. The performance of this modified system is presented and compared with the conventional system design (whole-tank mode). The study reveals that the solar cooling effect can be realized nearly 2 h earlier for the system operating in partitioned mode. In this system a total solar cooling COPsystem of about 0.07, which is about 15% higher than with traditional whole-tank mode, is attained. Experimental results also show that during cloudy days, the system could not provide a cooling effect, when operated conventionally, however in the partitioned mode-driven system the chiller could be energized, using solar energy as the only heat source.

105 citations

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Journal ArticleDOI
10 Nov 2010-Chemical Reviews
TL;DR: Approaches to Modifying the Electronic Band Structure for Visible-Light Harvesting and its Applications d0 Metal Oxide Photocatalysts 6518 4.4.1.
Abstract: 2.3. Evaluation of Photocatalytic Water Splitting 6507 2.3.1. Photocatalytic Activity 6507 2.3.2. Photocatalytic Stability 6507 3. UV-Active Photocatalysts for Water Splitting 6507 3.1. d0 Metal Oxide Photocatalyts 6507 3.1.1. Ti-, Zr-Based Oxides 6507 3.1.2. Nb-, Ta-Based Oxides 6514 3.1.3. W-, Mo-Based Oxides 6517 3.1.4. Other d0 Metal Oxides 6518 3.2. d10 Metal Oxide Photocatalyts 6518 3.3. f0 Metal Oxide Photocatalysts 6518 3.4. Nonoxide Photocatalysts 6518 4. Approaches to Modifying the Electronic Band Structure for Visible-Light Harvesting 6519

5,825 citations

Journal ArticleDOI
01 May 2010-Water Research
TL;DR: For the first time, a multi-variables optimization approach is described to determine the optimum operation parameters so as to enhance process performance and photooxidation efficiency in the photocatalytic water treatment process.
Abstract: In recent years, semiconductor photocatalytic process has shown a great potential as a low-cost, environmental friendly and sustainable treatment technology to align with the “ zero ” waste scheme in the water/wastewater industry. The ability of this advanced oxidation technology has been widely demonstrated to remove persistent organic compounds and microorganisms in water. At present, the main technical barriers that impede its commercialisation remained on the post-recovery of the catalyst particles after water treatment. This paper reviews the recent R&D progresses of engineered-photocatalysts, photoreactor systems, and the process optimizations and modellings of the photooxidation processes for water treatment. A number of potential and commercial photocatalytic reactor configurations are discussed, in particular the photocatalytic membrane reactors. The effects of key photoreactor operation parameters and water quality on the photo-process performances in terms of the mineralization and disinfection are assessed. For the first time, we describe how to utilize a multi-variables optimization approach to determine the optimum operation parameters so as to enhance process performance and photooxidation efficiency. Both photomineralization and photo-disinfection kinetics and their modellings associated with the photocatalytic water treatment process are detailed. A brief discussion on the life cycle assessment for retrofitting the photocatalytic technology as an alternative waste treatment process is presented. This paper will deliver a scientific and technical overview and useful information to scientists and engineers who work in this field.

3,662 citations

Journal ArticleDOI
15 Sep 2009-Catalysis Today
Abstract: In recent years, there has been a tremendous amount of research and development in the area of photocatalysis (heterogeneous and homogeneous), a process included in a special class of oxidation techniques defined as Advanced Oxidation Processes (AOPs), all characterized by the same chemical feature, production of OH radicals. This paper reviews the use of sunlight to produce the OH radicals by TiO2 photocatalysis and photo-Fenton process. The reacting systems necessary for performing solar photocatalysis are described. The paper also summarizes most of the research carried out related to solar photocatalytic degradation of water contaminants, and how it could significantly contribute to the treatment of persistent toxic compounds. It outlines how to enhance the process efficiency by integration with biotreatment. Various solar reactors for photocatalytic water treatment mainly based on non-concentrating collectors built during the last few years are also described in detail in this review, as well as the use of the solar photocatalytic processes to inactivate microorganisms present in water, placing special emphasis on experimental systems made to optimize this disinfection technique.

2,258 citations

Journal ArticleDOI
04 Mar 2015-Nanoscale
TL;DR: An overview of the key aspects of graphene and related materials, ranging from fundamental research challenges to a variety of applications in a large number of sectors, highlighting the steps necessary to take GRMs from a state of raw potential to a point where they might revolutionize multiple industries are provided.
Abstract: We present the science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems, targeting an evolution in technology, that might lead to impacts and benefits reaching into most areas of society. This roadmap was developed within the framework of the European Graphene Flagship and outlines the main targets and research areas as best understood at the start of this ambitious project. We provide an overview of the key aspects of graphene and related materials (GRMs), ranging from fundamental research challenges to a variety of applications in a large number of sectors, highlighting the steps necessary to take GRMs from a state of raw potential to a point where they might revolutionize multiple industries. We also define an extensive list of acronyms in an effort to standardize the nomenclature in this emerging field.

2,215 citations

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Author's H-index: 17

No. of papers from the Author in previous years

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Author's top 5 most impactful journals

Applied Thermal Engineering

5 papers, 206 citations

Renewable & Sustainable Energy Reviews

5 papers, 3.7K citations

Solar Energy

4 papers, 286 citations