Theoretical performance analysis of heat pump water heaters using carbon dioxide as refrigerant

The aim of this paper is to simulate the performance of an air source heat pump water heater using carbon dioxide (CO₂) as a working fluid. The heat pump water heating system consists of a compressor, a gas cooler, an expansion device and an evaporator. The computer simulation model has been developed by using the heat transfer data and the thermodynamic properties of CO₂. The effects on the heat pump performance by the operating parameters such as the compressor rotational speed, the inlet water temperature at the gas cooler, the inlet air temperature at the evaporator and the mass flow rate ratio of water to refrigerant were presented. For rated capacities of a 4 kW compressor with a 10 kW gas cooler and a 6 kW evaporator, the coefficient of performance is found to be between 2.0 and 3.0. The mass flow rate ratio of water and CO₂ between 1.2 and 2.2 is the most suitable value for generating hot water temperature above 60°C at 15–25°C ambient air temperature. Copyright © 2007 John Wiley & Sons, Ltd.     

In vitro study of the SBF and osteoblast-like cells on hydroxyapatite/chitosan–silica nanocomposite

Hydroxyapatite/chitosan–silica (HApCSi) nanocomposites were synthesized by co-precipitated method and their potential application as filler materials for bone regeneration were investigated in simulated body fluid (SBF). To study their biocompatibility, they were cultured with rat osteoblast-like UMR-106 cells for 3, 7, 14, and 21 days. Studies of the silica contents in chitosan matrix showed the presence of silinol (Si–OH) groups in CSi hybrid and their decrease after being composited with calcium phosphate (CaP) which is desirable for the formation of the apatite. XRD and TEM studies showed that the HAp formed in the CSi matrix were nanometer (20–40 nm) in size. Nanocomposites of HApCSi20 processed with 20%v/v silica whisker showed a micro hardness of 84.7 ± 3.3 MPa. Mineralization study in SBF showed the formation of apatite crystals on the HApCSi surface after being incubated for 7 days. In vitro biocompatibility, cell morphology, proliferation, and cell adhesion tests confirmed the osteoblast attachment and growth on the HApCSi20 surface. The density of cells and the production of calcium nodules on the substrate were seen to increase with increasing cultured time. The mechanical evaluation and in vitro experiment suggested that the use of HApCSi composite will lead to the formation of new apatite particles and thus be a potential implant material.     

Sol‐gel process of alkyltriethoxysilane in latex for alkylated silica formation in natural rubber

Sol‐gel process of alkyltriethoxysilanes that was dispersed in natural rubber latex was used to generate alkylated silica particles inside the rubber matrix. Three types of alkyltriethoxysilanes were chosen, i.e., vinyltriethoxysilane (VTOS), ethyltriethoxysilane (ETOS), and i‐butyltriethoxysilane (BTOS), as they differed in the type of one substituent group. Together with tetraethoxysilane (TEOS), a typical precursor for silica formation, all silanes were studied for their conversion to silica and subsequent reinforcement capabilities in sulfur‐vulcanized rubber. The in situ generated silicas were fine and well dispersed in the rubber matrix, as analyzed by SEM and TEM. Solid‐state ²⁹Si‐NMR technique was used to confirm the presence of alkyl substituents on the silica particles buried inside the rubber matrix. Tensile and tear properties of the in situ silica‐filled NR vulcanizates were higher than those of the vulcanizate prepared by conventional mixed method. Among the three alkyltriethoxysilanes used, only VTOS, when used as a mixture with TEOS, did not cause a reduction in silica formation. The resulting vinylated silica tended to enhance the tensile modulus and resistant to tear of the rubber vulcanizates. Cure characteristic and swelling behavior in toluene of the silica‐containing vulcanizates were also investigated. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Optimization of processing conditions to reduce oil uptake and enhance physico-chemical properties of deep fried rice crackers

Physico-chemical properties of fried rice crackers were studied as a function of fish powder content, processing conditions, frying temperature and frying time. The results showed that addition of fish powder content at 5, 10 and 15 g/100 g reduced the oil uptake by approximately 10, 14 and 22 g/100 g (db), respectively in comparison to the control without fish powder. The deep fried rice crackers mixed with fish powder tended to be lower in hardness, lower in expansion ratio and higher in bulk density in comparison to the control sample. The color parameter, L^∗ of fried rice crackers decreased with increase in fish powder content. In contrast, a^∗ and b^∗ values increased with increase in fish powder content. The moisture content of deep fried rice crackers decreased with increase in frying temperature and frying time. The oil uptake in fried rice crackers increased with increase in frying time but decreased with increase in frying temperature. With increase in frying temperature and time, the texture of rice crackers became harder, the bulk density increased, and the expansion ratio decreased. The optimum conditions resulting in desirable physico-chemical properties and minimum oil uptake were rice crackers with fish powder content of 9 g/100 g, fried at a temperature of 220 °C for 60 s.     

In vitro study of vancomycin release and osteoblast-like cell growth on structured calcium phosphate-collagen

A drug delivery vehicle consisting of spherical calcium phosphate-collagen particles covered by flower-like (SFCaPCol) blossoms composed of nanorod building blocks and their cellular response is studied. The spherical structure was achieved by a combination of sonication and freeze-drying. The SFCaPCol blossoms have a high surface area of approximately 280 m²g^? 1. The blossom-like formation having a high surface area allows a drug loading efficiency of 77.82%. The release profile for one drug, vancomycin (VCM), shows long term sustained release in simulated body fluid (SBF), in a phosphate buffer saline (PBS, pH 7.4) solution and in culture media over 2 weeks with a cumulative release ~ 53%, 75% and 50%, respectively, over the first 7 days. The biocompatibility of the VCM-loaded SFCaPCol scaffold was determined by in vitro cell adhesion and proliferation tests of rat osteoblast-like UMR-106 cells. MTT tests indicated that UMR-106 cells were viable after exposure to the VCM loaded SFCaPCol, meaning that the scaffold (the flower-like blossoms) did not impair the cell's viability. The density of cells on the substrate was seen to increase with increasing cultured time.     

Alginate-loofa as carrier matrix for ethanol production

An alginate-loofa matrix was developed as a cell carrier for ethanol fermentation owing to its porous structure and strong fibrous nature. The matrix was effective for cell immobilization and had good mechanical strength and stability for long-term use. After a storage period of 4 months, yeast cells remained firmly immobilized and active.     

Biocomposite of hydroxyapatite-titania rods (HApTiR): Physical properties and in vitro study

The aim in this research is to study the physical and biocompatible properties of hydroxyapatite (HAp) composites (HApTiR) having different amounts of titania rod (TiR) in them (10–90 wt.%). The HAp and TiR were produced using hydrothermal and co-precipitation under reflux methods, respectively. The physical properties and the in vitro biocompatibility of the composites to simulated body fluid (SBF) were investigated. They were also cultured with rat osteoblast-like UMR-106 cells. The synthesized powder showed a core-shell structure with the titania rod as the core and the apatite as the shell. The hardness of the composites of HApTiR's whisker increased from 74.8 to 92.9 MPa as the TiR content was increased from 10 to 90 wt.%. Mineralization study in SBF showed the formation of apatite crystals on the HApTiR's surface after 7 days of incubation. In vitro cell adhesion tests confirmed the osteoblast attachment and growth on the HApTiR's surface. The density of cells, spread and the production of calcium nodules on the substrate were seen to increase with increasing TiR contents except for HApTiR90 (TiR = 90 wt.%) which exhibited lesser growth. MTT tests on HApTiR70 indicated that UMR-106 cells were viable and the density of cells on the substrate was seen to increase with increasing culturing time.     

STUDY OF LONGAN FLESH DRYING

The objectives of this research were to study the characteristics and quality of longan flesh drying and to develop the models for drying simulations. Finite difference method was applied to solve the drying kinetic equations. Three alternative diffusion models were developed by modifying the Arrhenius factor and/or the energy of activation as a function of moisture content. The results using effective diffusion coefficients obtained from each model were compared. Desorption isotherms were also developed by fitting experimental results to various well-known models. The development and simulation of mathematical drying model of a cabinet dryer were also studied. The effects of drying air temperature and specific air flow rate on specific energy consumption were described. Additionally, the effect of drying air temperature on product quality was investigated by experiment.     

Antimicrobial properties and action of galangal (Alpinia galanga Linn.) on Staphylococcus aureus

The ethanol extracts of the Zingiberaceae family (galangal, ginger, turmeric and krachai) were evaluated for antimicrobial action on Staphylococcus aureus 209P and Escherichia coli NIHJ JC-2 by using an agar disc diffusion assay. The galangal extract had the strongest inhibitory effect against S. aureus. The minimum inhibitory concentration (MIC) of the galangal extract was 0.325 mg/ml and the minimum bactericidal concentration (MBC) at 1.3 mg/ml using the broth dilution method. Transmission electron microscopy clearly demonstrated that the galangal extract caused both outer and inner membrane damage, and cytoplasm coagulation. The disruption of the cytoplasmic membrane properties was determined by the releasing of cell materials including nucleic acid which absorbed UV/VIS spectrophotometer at 260 nm. The major compound of the extract was d,l-1′-acetoxychavicol acetate which was identified by GC-MS and NMR.