No abstract

In this study, low quality oils (waste cooking oils) with high acid value (4.81 mg KOH/g) were utilized as the feedstocks for a transesterification reaction enhanced by additional microwave power and the use of an NaOH catalyst. The kinetics of the transesterification reaction under different reaction times and temperatures was studied. It was found that in the microwave-assisted transesterification reaction, the optimum conditions under a microwave power of 600 W were as follows: an NaOH catalyst of 0.8 wt %, a 12:1 molar ratio of methanol to oil, a reaction time of 2 min, and a reaction temperature of 65 °C. The conversion of waste cooking oil into biodiesel reached 98.2% after this short reaction time. This result conformed to 96.5% of the standard value of Taiwan CNS 15072. In addition, with increases in the reaction temperature from 55 to 65 °C, the reaction rate constant increased from 0.635 to 2.396 min−1, and the activation energy required for the transesterification reaction was 123.14 kJ/mole.

No abstract

The purpose of this paper is to create a rapid temperature balancing container which can firstly absorb heat from the stored thing to change its temperature within minutes into a desired value set by the melting temperature and type of the used phase change materials (PCMs), and then keep that temperature last longer as the absorbed heat is later released. Models in different geometrical shapes using a commercial PCM, called PW-70, with melting temperature of 70 o C have been made and tested carefully in laboratory. The best results of the four tested models, derived from the multi-layer model, have shown that average temperature of the boiled water which was acting as the stored substance reached the desired range of 55 ~ 65 o C within only about 15 minutes and this temperature range lasted within nearly 5 hours. It is also shown that this period is even much longer if the desired temperature value is lower. This is a big advantage compared with the vacuum container without PCM in which the desired range was reached after about 4 hours but lasted for only more than 2 hours. With this good performance, the new design has shown much more effective utilization of heat energy in food or beverage preservation purpose.

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Heat flow from the roof together with radiation through glass windows obviously contributes in the total heat gained of a vehicle cabin. The contribution is more significant especially hot and sunny weather with little wind. This paper presents a new design for vehicle roofing structure in order to improve its total thermal resistance. Its main concept is to utilize phase change material properties to first trap the heat from solar radiation and then release it back to the environment by means of the naturally favored external convection when the vehicle is in use or during the nocturnal cycle. Experimental and numerical analyses have been conducted to compare the thermal performance of the new design and the normal roofing with different colors. A general mathematic equation system has been derived for the thermal process through the roof. The results show that the new design could effectively reduce the downward heat flow from the roof into the cabin. As a consequence, the cooling load of the cabin could be significantly lower.

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In this study, a homogenizer in conjunction with a two-stage process was utilized to facilitate biodiesel production from waste edible oil (WEO). This paper contributes to the improvement of the yield and the shortening of the reaction time for biodiesel synthesis. Sulfuric acid was used in the first stage which was the esterification of the free fatty acids (FFA) of the WEO; then the transesterification reaction of triglycerides took place in the second stage with an alkaline catalysis. The present investigation aimed to explore the parameters affecting the reactions, including homogenizer speed, alcohol/oil molar ratio, catalyst dosage, reaction temperature, and reaction time. Under the operating conditions of the first stage (the reaction temperature was 65 °C, the homogenizer speed was 8000 rpm, the methanol/oil molar ratio was 15:1, and the amount of sulfuric acid was 4 wt%), the acid value fell to below 2 mg KOH/g after 10 min. The best base-catalyzed conditions in the second stage were: homogenizer speed of 8000 rpm, NaOH catalyst concentration of 1 wt%, methanol/oil molar ratio of 9:1 (mol/mol), reaction temperature of 65 °C, and reaction time 10 min. Consequently, the conversion rate from WEO to biodiesel achieved 97% after only 20 min, in line with the EU EN14214 standard, which requires a biodiesel production rate of at least 96.5%.