M.R. Islam

Bio: M.R. Islam is an academic researcher from National University of Singapore. The author has contributed to research in topics: Air conditioning & Heat exchanger. The author has an hindex of 20, co-authored 45 publications receiving 957 citations. Previous affiliations of M.R. Islam include Curtin University.

Performance evaluation of an indirect pre-cooling evaporative heat exchanger operating in hot and humid climate

Abstract: A hybrid system, that combines an indirect evaporative heat exchanger (IEHX) and a vapor compression system, is introduced for humid tropical climate application. The chief purpose of the IEHX is to pre-cool the incoming air for vapor compression system. In the IEHX unit, the outdoor humid air in the product channel may potentially condense when heat is exchanged with the room exhaust air. A computational model has been developed to theoretically investigate the performance of an IEHX with condensation from the product air by employing the room exhaust air as the working air. We validated the model by comparing its temperature distribution and predicted heat flux against experimental data acquired from literature sources. The numerical model showed good agreement with the experimental findings with maximum average discrepancy of 9.7%. The validated model was employed to investigate the performance of two types of IEHX in terms of the air treatment process, temperature and humidity distribution, cooling effectiveness, cooling capacity, and energy consumption. Simulation results have indicated that the IEHX unit is able to fulfill 47% of the cooling load for the outdoor humid air while incurring a small amount of fan power. Consequently, the hybrid system is able to realize significant energy savings.

Fundamental formulation of a modified LMTD method to study indirect evaporative heat exchangers

Abstract: An analytical model for indirect evaporative heat exchangers has been developed via a modified log mean temperature difference (LMTD) method designed for sensible heat exchangers. The original LMTD method is judiciously modified to extend its computing method to indirect evaporative cooling systems where latent heat transfer is involved. The analytical model is validated by comparing its prediction of thermal performance with experimental data of a counter-flow dew-point evaporative cooler and a cross-flow indirect evaporative cooler. Predictability of the modified LMTD method has a maximum discrepancy of ±8% when compared to experimental data. The model has been demonstrated to be a practical method to provide an accurate result with a short computational time. Several case studies are structured to illustrate that the modified LMTD method is suitable for designing and analyzing indirect evaporative heat exchangers.

Numerical investigation of transfer coefficients of an evaporatively-cooled condenser

Abstract: Vapour compression cooling systems working in tropical climatic conditions make the compressor pressure-lift relatively high. The lowering of the condensing temperature will help reduce this lift, thereby reducing the power required by the compressor. The inclusion of water sprays or droplets in air-cooled condensers is a possible option for improving the performance of the condenser by reducing the temperature lift. This paper reports a numerical investigation of the heat transfer characteristics of an evaporatively-cooled condenser. A detailed model is developed and numerical simulations are carried out using finite difference techniques. The simulations are performed for a single unfinned tube of the condenser with the air flowing across the tube. Water is sprayed on top of the tube in the form of fine sprays and the flow rate is set to achieve film thicknesses of 0.075, 0.1, and 0.15 mm, respectively. The tube wall temperature is assumed constant due to the fact that for most of the tube length, condensation of the refrigerant occurs at the saturation temperature of the refrigerant. Wall to air overall heat transfer coefficient ( U ) value as high as 2000 W/m 2 K is observed with the incorporation of the evaporative cooling. The numerical results are compared with available experimental and theoretical work and the agreement is found to be satisfactory.

Simulation of Liquid Diffusion-Controlled Drying of Shrinking Thin Slabs Subjected to Multiple Heat Sources

Abstract: Although a detailed mathematical model incorporating all physical mechanisms of moisture and heat transfer in the material would yield valuable design information, it is not feasible to do this on a routine basis for the design of dryers. A simple liquid diffusion model was developed in the present study to quantitatively assess the influence of various operating parameters of engineering interest in drying of heat-sensitive materials. Heat of wetting, temperature, and moisture dependent effective diffusivity and thermal conductivity, changes in product density and drying-induced ideal shrinkage of the product are considered in this model. The effects of combining convection with conduction, radiation, and volumetric heating using a microwave field are simulated in view of the increasing interest in multimode heat input drying processes. Numerical results are reported on drying of potato slices to demonstrate how the moisture and temperature profiles as well as drying performance are affected by ...

An Artificial Neural Network Model for Prediction of Drying Rates

Abstract: Drying rate data were generated for training of an ANN model using a liquid diffusion model for potato slices of different thicknesses using air at different velocities, humidities and temperatures. Moisture content and temperature dependence of the liquid diffusivity as well as the heat of wetting for bound moisture were included in the diffusion model making it a highly nonlinear system. An ANN model was developed for rapid prediction of the drying rates using the Page equation fitted to the drying rate curves. The ANN model is verified to provide accurate interpolation of the drying rates and times within the ranges of parameters investigated.

Trends in microwave- related drying of fruits and vegetables

Abstract: Microwave (MW)-related (MW-assisted or MW-enhanced) combination drying is a rapid dehydration technique that can be applied to specific foods, particularly to fruits and vegetables. Increasing concerns over product quality and production costs have motivated the researchers to investigate and the industry to adopt combination drying technologies. The advantages of MW-related combination drying include the following: shorter drying time, improved product quality, and flexibility in producing a wide variety of dried products. But current applications are limited to small categories of fruits and vegetables due to high start-up costs and relatively complicated technology as compared to conventional convection drying. MW-related combination drying takes advantages of conventional drying methods and microwave heating, leading to better processes than MW drying alone. This paper presents a comprehensive review of recent progresses in MW-related combined drying research and recommendations for future research to bridge the gap between laboratory research and industrial applications.

A review of different strategies for HVAC energy saving

Abstract: Decreasing the energy consumption of heating, ventilation and air conditioning (HVAC) systems is becoming increasingly important due to rising cost of fossil fuels and environmental concerns. Therefore, finding novel ways to reduce energy consumption in buildings without compromising comfort and indoor air quality is an ongoing research challenge. One proven way of achieving energy efficiency in HVAC systems is to design systems that use novel configurations of existing system components. Each HVAC discipline has specific design requirements and each presents opportunities for energy savings. Energy efficient HVAC systems can be created by re-configuring traditional systems to make more strategic use of existing system parts. Recent research has demonstrated that a combination of existing air conditioning technologies can offer effective solutions for energy conservation and thermal comfort. This paper investigates and reviews the different technologies and approaches, and demonstrates their ability to improve the performance of HVAC systems in order to reduce energy consumption. For each strategy, a brief description is first presented and then by reviewing the previous studies, the influence of that method on the HVAC energy saving is investigated. Finally, a comparison study between these approaches is carried out.

Effects of drying and grinding in production of fruit and vegetable powders: A review

Abstract: In recent years, fruits and vegetables have received considerable attention, as these materials have been reported to contain a wide array of phytochemicals, which are claimed to exert many health benefits including antioxidant activity. In some cases where bioactive compounds extraction cannot be performed on fresh products, drying appears as a necessary step enabling their later use. Drying is a widely used food preservation process in which water removal minimize many of the moisture-driven deterioration reactions impacting the bioproduct quality. Dried fruits and vegetables and their application in powder form have gained interest in the food industry. Drying and grinding conditions during powder processing greatly influence the quality attributes of biological materials. It implies not only nutritional changes but also physical, textural, sensorial and functional changes. These changes are of great importance and require to be controlled through retroengineering approaches. This paper reviews the effect of the different dry drying and grinding methods on the physicochemical and functional properties of the final products. Overviews of some of the innovative concepts as well as approaches to alleviate the above-mentioned changes are discussed.

Advanced computational modelling for drying processes – A review

Abstract: Drying is one of the most complex and energy-consuming chemical unit operations. R&D efforts in drying technology have skyrocketed in the past decades, as new drivers emerged in this industry next to procuring prime product quality and high throughput, namely reduction of energy consumption and carbon footprint as well as improving food safety and security. Solutions are sought in optimising existing technologies or developing new ones which increase energy and resource efficiency, use renewable energy, recuperate waste heat and reduce product loss, thus also the embodied energy therein. Novel tools are required to push such technological innovations and their subsequent implementation. Particularly computer-aided drying process engineering has a large potential to develop next-generation drying technology, including more energy-smart and environmentally-friendly products and dryers systems. This review paper deals with rapidly emerging advanced computational methods for modelling dehydration of porous materials, particularly for foods. Drying is approached as a combined multiphysics, multiscale and multiphase problem. These advanced methods include computational fluid dynamics, several multiphysics modelling methods (e.g. conjugate modelling), multiscale modelling and modelling of material properties and the associated propagation of material property variability. Apart from the current challenges for each of these, future perspectives should be directed towards material property determination, model validation, more complete multiphysics models and more energy-oriented and integrated “nexus” modelling of the dehydration process. Development of more user-friendly, specialised software is paramount to bridge the current gap between modelling in research and industry by making it more attractive. These advanced computational methods show promising perspectives to aid developing next-generation sustainable and green drying technology, tailored to the new requirements for the future society, and are expected to play an increasingly important role in drying technology R&D.

An Overview of Recent Developments and Some R&D Challenges Related to Drying of Foods

Abstract: Thermal dehydration is the most common and cost-effective technique for preservation of foods and for the production of traditional as well as innovative processed products such as snacks with desired functionalities. The basic intent of this article is to provide a global overview of emerging and innovative thermal drying technologies that are already commercialized or show potential of industrial exploitation upon successful R&D to sort out some limitations. New drying technologies are needed to enhance quality, reduce energy consumption, improve safety, and reduce environmental impact. Mathematical modeling can be used for cost-effective development of untested novel designs to reduce the cost and time required for innovation. As examples of emerging drying technologies we consider selected dehydration techniques with imminent commercialization potential. These include heat pump–assisted drying, microwave-assisted drying, low-pressure superheated steam drying, pulse combustion spray drying, pulsed and ...