Kim Choon Ng

Bio: Kim Choon Ng is an academic researcher from King Abdullah University of Science and Technology. The author has contributed to research in topics: Desalination & Adsorption. The author has an hindex of 57, co-authored 340 publications receiving 10853 citations. Previous affiliations of Kim Choon Ng include National University of Singapore & Tokyo University of Agriculture and Technology.

Energy-water-environment nexus underpinning future desalination sustainability

Abstract: Energy-water-environment nexus is very important to attain COP21 goal, maintaining environment temperature increase below 2 °C, but unfortunately two third share of CO 2 emission has already been used and the remaining will be exhausted by 2050. A number of technological developments in power and desalination sectors improved their efficiencies to save energy and carbon emission but still they are operating at 35% and 10% of their thermodynamic limits. Research in desalination processes contributing to fuel World population for their improved living standard and to reduce specific energy consumption and to protect environment. Recently developed highly efficient nature-inspired membranes (aquaporin & graphene) and trend in thermally driven cycle's hybridization could potentially lower then energy requirement for water purification. This paper presents a state of art review on energy, water and environment interconnection and future energy efficient desalination possibilities to save energy and protect environment.

A 3D Photothermal Structure toward Improved Energy Efficiency in Solar Steam Generation

Abstract: Summary The energy efficiency in solar steam generation by 2D photothermal materials has approached its limit. In this work, we fabricated 3D cylindrical cup-shaped structures of mixed metal oxide as solar evaporator, and the 3D structure led to a high energy efficiency close to 100% under one-sun illumination due to the capability of the cup wall to recover the diffuse reflectance and thermal radiation heat loss from the 2D cup bottom. Additional heat was gained from the ambient air when the 3D structure was exposed under one-sun illumination, leading to an extremely high steam generation rate of 2.04 kg m −2 h −1 . The 3D structure has a high thermal stability and shows great promise in practical applications including domestic wastewater volume reduction and seawater desalination. The results of this work inspire further research efforts to use 3D photothermal structures to break through the energy efficiency limit of 2D photothermal materials.

Experimental investigation of the silica gel–water adsorption isotherm characteristics

Abstract: In designing adsorption chillers that employs silica gel–water as adsorbent-adsorbate pair, the overriding objective is to exploit low temperature waste-heat sources from industry. This paper describes an experimental approach for the determination of thermodynamic characteristics of silica gel–water working pair that is essential for the sizing of adsorption chillers. The experiments incorporated the moisture balance technique, a control-volume-variable-pressure (CVVP) apparatus and three types of silica gel have been investigated, namely the Fuji Davison Type A, Type 3A and Type RD. As evidenced by the experimental results, the Henry-type equation is found to be suitable for describing the isotherm characteristics of silica gel–water working pair at the conditions of adsorption chiller. The regeneration of adsorbent depends on the correct allocation of temperature as well as the amount of regeneration time. From the experiments, the isotherm characteristics of silica gel–water in the low- to high-pressure regimes and hence, its isosteric heat of adsorption will be determined. Key parameters for optimizing the amount of heat recovery such as the cycle and switching time of chiller can also be implied from the measured results.

Modeling the performance of two-bed, sillica gel-water adsorption chillers

Abstract: This article presents a transient model for a two-bed, silica gel-water adsorption chiller. Compared with our previous cyclic-steady-state model, we found very good agreement between our model prediction and experimental data. We found that, regardless of the initial mass distribution, the chiller was able to achieve the same cyclic-steady-state within four cycles or 1800 s. We also demonstrated that the manufacturer had empirically evolved to select a fixed switching and cycle time such that the best peak evaporator temperature suppression, and near maximum cooling capacity can be achieved by a compact design.

Adsorption desalination: An emerging low-cost thermal desalination method

Abstract: Desalination, other than the natural water cycle, is hailed as the panacea to alleviate the problems of fresh water shortage in many water stressed countries. However, the main drawback of conventional desalination methods is that they are energy intensive. In many instances, they consumed electricity, chemicals for pre- and post-treatment of water. For each kWh of energy consumed, there is an unavoidable emission of Carbon Dioxide (CO 2 ) at the power stations as well as the discharge of chemically-laden brine into the environment. Thus, there is a motivation to find new direction or methods of desalination that consumed less chemicals, thermal energy and electricity. This paper describes an emerging and yet low cost method of desalination that employs only low-temperature waste heat, which is available in abundance from either the renewable energy sources or exhaust of industrial processes. With only one heat input, the Adsorption Desalination (AD) cycle produces two useful effects, i.e., high grade potable water and cooling. In this article, a brief literature review, the theoretical framework for adsorption thermodynamics, a lumped-parameter model and the experimental tests for a wide range of operational conditions on the basic and the hybrid AD cycles are discussed. Predictions from the model are validated with measured performances from two pilot plants, i.e., a basic AD and the advanced AD cycles. The energetic efficiency of AD cycles has been compared against the conventional desalination methods. Owing to the unique features of AD cycle, i.e., the simultaneous production of dual useful effects, it is proposed that the life cycle cost (LCC) of AD is evaluated against the LCC of combined machines that are needed to deliver the same quantities of useful effects using a unified unit of $/MWh. In closing, an ideal desalination system with zero emission of CO 2 is presented where geo-thermal heat is employed for powering a temperature-cascaded cogeneration plant.

Entropy generation minimization: The new thermodynamics of finite-size devices and finite-time processes

Abstract: Entropy generation minimization (finite time thermodynamics, or thermodynamic optimization) is the method that combines into simple models the most basic concepts of heat transfer, fluid mechanics, and thermodynamics. These simple models are used in the optimization of real (irreversible) devices and processes, subject to finite‐size and finite‐time constraints. The review traces the development and adoption of the method in several sectors of mainstream thermal engineering and science: cryogenics, heat transfer, education, storage systems, solar power plants, nuclear and fossil power plants, and refrigerators. Emphasis is placed on the fundamental and technological importance of the optimization method and its results, the pedagogical merits of the method, and the chronological development of the field.

Technical review and evaluation of the economics of water desalination: Current and future challenges for better water supply sustainability

Abstract: Desalination capacity has rapidly increased in the last decade because of the increase in water demand and a significant reduction in desalination cost as a result of significant technological advances, especially in the reverse osmosis process. The cost of desalinated seawater has fallen below US$0.50/m 3 for a large scale seawater reverse osmosis plant at a specific location and conditions while in other locations the cost is 50% higher (US$1.00/m 3 ) for a similar facility. In addition to capital and operating costs, other parameters such as local incentives or subsidies may also contribute to the large difference in desalted water cost between regions and facilities. Plant suppliers and consultants have their own cost calculation methodologies, but they are confidential and provide water costs with different accuracies. The few existing costing methodologies and software packages such as WTCost© and DEEP provide an estimated cost with different accuracies and their applications are limited to specific conditions. Most of the available cost estimation tools are of the black box type, which provide few details concerning the parameters and methodologies applied for local conditions. Many desalination plants built recently have greater desalinated water delivery costs caused by special circumstances, such as plant remediation or upgrades, local variation in energy costs, and site-specific issues in raw materials costs (e.g., tariffs and transportation). Therefore, the availability of a more transparent and unique methodology for estimating the cost will help in selecting an appropriate desalination technology suitable for specific locations with consideration of all the parameters influencing the cost. A techno-economic evaluation and review of the costing aspects and the main parameters influencing the total water cost produced by different desalination technologies are herein presented in detail. Some recent developments, such as the increase of unit capacity, improvements in process design and materials, and the use of hybrid systems have contributed to cost reduction as well as reduction in energy consumption. The development of new and emerging low-energy desalination technologies, such as adsorption desalination, will have an impact on cost variation estimation in the future.

Water harvesting from air with metal-organic frameworks powered by natural sunlight

Abstract: Atmospheric water is a resource equivalent to ~10% of all fresh water in lakes on Earth. However, an efficient process for capturing and delivering water from air, especially at low humidity levels (down to 20%), has not been developed. We report the design and demonstration of a device based on a porous metal-organic framework {MOF-801, [Zr6O4(OH)4(fumarate)6]} that captures water from the atmosphere at ambient conditions by using low-grade heat from natural sunlight at a flux of less than 1 sun (1 kilowatt per square meter). This device is capable of harvesting 2.8 liters of water per kilogram of MOF daily at relative humidity levels as low as 20% and requires no additional input of energy.