Showing papers by "Mohammed Farid published in 2012"

Improving thermal performance of freezers using phase change materials.

Abstract: Food transport and storage at low temperatures is a matter worldwide due to changes of the dietary habits and the increasing of the population. The issue of improving food storage applies at different applications such as commercial freezers or refrigerated trucks. The aim of this work is to improve the thermal performance of commercial freezers using phase change materials (PCMs) under door openings and electrical power failure. A commercial PCM was selected (Climsel-18) with a melting temperature of −18 °C, which is contained in 10 mm thick stainless steel panels placed at different locations in the freezer. During 3 h of electrical power failure, the use of PCM maintained the freezer temperature 4–6 °C lower and that of the frozen products remains at acceptable levels for much longer time. With frequent door openings the benefit of the PCM is evident when the temperature of the cabinet is near the melting temperature of the PCM.

Thermal analysis of a low temperature storage unit using phase change materials without refrigeration system

Abstract: Frozen food transportation and storage at low temperature is becoming an important issue worldwide as it is related to lifestyle and growing population. The issue of improving the cold chain applies to different applications such as low temperature storage and food transportation. The aim of this paper is to evaluate the thermal response of low temperature chambers incorporating phase change materials (PCM) having low freezing temperature when subjected to refrigeration system failure. This is to simulate food transportation in non-refrigerated trucks or vans. Two commercial PCMs with different melting temperature were tested (Climsel C-18 from CLIMATOR and E-21 from CRISTOPIA). The results show that when there is no refrigeration, both the air and the frozen product temperatures remained at lower values for much longer time when PCM was employed.

Feasibility Study for Production of Biofuel and Chemicals from Marine Microalgae Nannochloropsis sp. Based on Basic Mass and Energy Analysis

Abstract: Algae are believed to be a good source of renewable energy because of their rapid growth rate and their ability to be cultivated in waste waters or waste land. The algae Nannochloropsis sp. was chosen for this study, where lipids were extracted and transesterified for biodiesel production. The FFA (free fatty acid) content in the lipid was estimated to be 27 wt% of the total fatty acids. The remaining biomass after lipid extraction was pyrolyzed at 200∘C, 300∘C, and 400∘C to produce solid, liquid, and gas products. The GC/MS showed that the lipids of Nannochloropsis sp. consist of high concentration of polyunsaturated fatty acids (29 wt%), eicosapentaenoic acid. The bio-oil produced from pyrolysis of algae biomass (after lipid extraction) at 300∘C was composed of 50 wt% acetone, 30 wt% methyl ethyl ketone and 19 wt% aromatics such as pyrazine and pyrrole. The heating value of bio-oil is 32 MJ/kg of oil.

Microencapsulation of a PCM through membrane emulsification and nanocompression-based determination of microcapsule strength

Abstract: Microencapsulating a phase-change material (PCM) has become a prominent method of creating a stable environment in which the PCM can undergo its phase change without affecting the environment in which it is used. The method of encapsulation used in this study takes advantage of a new technology known as membrane emulsification and suspension polymerization. This study investigates the encapsulation of the paraffin wax RT21® in a poly(methyl methacrylate) shell, which could be used to increase the thermal mass of a building. The objectives of the study are: (1) to encapsulate RT21® through the use of membrane emulsification and (2) to test the mechanical properties of the microcapsules under nanocompression. Membrane emulsification was carried out using Shirasu porous glass hydrophilic membranes of pore sizes 10, 10.2, and 20 μm. Polymerization was conducted in a batch reactor with methyl methacrylate as the monomer in the temperature range 70–90 °C. The thermal properties (the latent heat of melting and melting temperature) of the microcapsules were tested using a differential scanning calorimeter. Particle size analysis was conducted to determine the average size distribution of the microcapsules produced. Membranes with pore sizes of 10, 10.2, and 20 μm produced microcapsules with average diameters of 22.40 ± 1.47, 25.38 ± 0.80, and 37.50 ± 1.69 μm, and average latent heats of 113.91 ± 12, 116.69 ± 1.40, and 109.89 ± 8.69 J/g, respectively. In order to determine the mechanical properties of these microcapsules, a modified nanoindentation compression technique was used to test the bursting force for individual microcapsules.

Determination of an Effective Treatment Temperature of Chemical and Biological Reactions

Abstract: Thermal microbial inactivation kinetics can be influenced significantly by the non-isothermal condition of the sample tested. In many instances, it is practically difficult to maintain the temperature constant during chemical and biological reactions. To minimise error caused by such non-isothermal condition, an effective treatment temperature was derived based on fundamental principles of reaction kinetics. This effective temperature was significantly different from the arithmetic mean temperature due to the exponential effect of temperature on reaction rate. In order to validate the developed concept, Escherichia coli ATCC 25922 suspended in simulated milk ultra filtrate was thermally inactivated using test tubes of different diameters. As expected, the D value was accurately related to the water bath temperature only when small capillary tube was used for the measurements. As the tube diameter increased, the D value increased and was found not to be related to the water bath temperature. On the other hand, the measured D values using different tube diameters correlated very well with the calculated effective treatment temperature. Our calculations show that the effective temperature can be calculated with reasonable degree of accuracy even if there is some uncertainty in the value of the activation energy of the reaction. A number of important applications are addressed in this paper to show the importance of using such a concept. The use of effective temperature will allow accurate comparison of reaction kinetics reported in the literatures on chemical and biological reactions.

High Pressure Processing of Honey: Preliminary Study of Total Microorganism Inactivation and Identification of Bacteria

Abstract: Due to the demand for better quality and safety food as it provides health benefits, the study of innovative high pressure processing (HPP) is currently one of the most interesting researches in food processing and preservation. As an alternative to classical thermal processing, HPP has potential to produce high quality foods that are microbiologically safe with ‘fresh-like’ characteristics and improved functionalities. In present work, the use of HPP will be investigated for its ability to inactivate bacteria spores, the heat resistance microbes. Preliminary results show that it is possible to use HPP to inactivate microorganisms present in high sugar content foods, particularly in Manuka honey. Further investigation will be carried out to find an optimal combination of treatment pressure, temperature and time. This project will generate a new approach in honey processing which can guarantee the safety of honey without a compromise on its quality and natural freshness.

High pressure processing of honey: Preliminary study of saccharomyces cerevisiae inactivation and total phenolic content

Abstract: Due to the demand for better quality and safety food as it provides health benefits, the study of innovative high pressure processing (HPP) is currently one of the most interesting researches in food processing and preservation. As an alternative to classical thermal processing, HPP has potential to produce high quality foods that are microbiologically safe with 'fresh-like' characteristics and improved functionalities. In present work, the use of HPP will be investigated for its ability to inactivate Saccharomyces cerevisiae, the dominant yeast fermenting honey. The study also highlights the need to preserve bioactive compounds of natural origin of honey. Our preliminary results confirmed that HPP alone was insufficient to inactivate osmophilic yeasts in highly sugar content food. Treating Manuka honey at 600 MPa, 20 degreesC for 10 min shows a reduction of log 1.0 CFU/g of Saccharomyces cerevisiae. With respect to quality, the result shows an increment of total phenolic content in Manuka honey by about 47 % after being treated with HPP. Further investigation will be carried out to find an optimal combination of treatment pressure, temperature and time. This project will generate a new approach in honey processing which can guarantee the safety of honey without a compromise on its quality and natural freshness.

Microencapsulation of phase change materials for thermal energy storage in building application

Abstract: This paper presents an investigation on microencapsulation of paraffin as a phase change materials (PCMs) for application in buildings. Encapsulated PCM particles were prepared by suspension-like polymerization technique. The effect of surfactant concentration and mass ratio of PCM to monomer on the final characteristics and performance of the microcapsules were investigated. The distribution of particle size, morphology surface, thermal energy storage and thermal stability of the synthesis microcapsules were analyzed using particle size analyser (PSA), optical microscope, differential scanning calorimeter (DSC) and thermal gravimetric analyzer (TGA) respectively. Results show that 1 wt% of PVA and 1.5 mass ratio of PCM (RT21) to monomer had a good compromise between particle surface morphology and PCM mass content of 65 %. In addition, results obtained from a differential scanning calorimeter (DSC) show that microcapsules prepared using the above method have a thermal energy storage capacity of 85.8 J/g, peak melting temperature of 22 degreesC and mean volume particle diameter of 15 mum. TGA analysis indicated that the PCM microcapsules degrade in two steps and had good chemical stability.

Kinetic modelling for tranesterification of alcohols

Abstract: Biodiesel is an alternative diesel fuel that is produced from vegetable oils and animal fats. It consists of the monoalkyl esters formed by a catalysed reaction of the triglycerides in the oil or fat with a simple monohydric alcohol (i.e. methanol and ethanol). In this study the reaction kinetics, which controls the overall conversion of triglycerides (TG) to alcohol esters was examined. The kinetics of the transesterification of vegetable oils with methanol, ethanol and butanol were analysed using different kinetic models to establish the overall reaction rate constant. These models have been proposed so that an effective method of analysis can be developed to analyse the overall reaction kinetics of any transesterification reaction. It was found that the reactions can be modelled using irreversible pseudo first order if excess alcohol is used, while at lower alcohol concentration; the reaction can be modelled using second order models. The overall reaction is controlled by the initial transesterification step, which is the conversion of TG to DG. The focus of this research was directed towards developing a generic model that can describe the reaction kinetics of all types of alcohols (i.e. methanol, ethanol, propanol and butanol) being used for transesterification process.