ABSTRACT

Along with the increase of human mobility, the portable refrigerator becomes very important because it can be used to store goods or drinks to be durable or cooler. Therefore, a refrigerator using thermoelectric is an option. Thermoelectric fridge besides easy to carry anywhere is also easy maintenance, durable, more compact, lightweight, no heavy rotating components, no use of freon and small power. Refrigerator research with thermoelectric has been done with series and parallel electric circuits to know the effect of the circuit difference to the performance of refrigerators. This study uses a mini fridge with an overall dimension of 40.8 cm x 32.6 cm x53.8 cm and with 2 thermoelectric modules TEC1-12706 model. The electrical power used for each circuit is about 12 W. The data retrieval in the test uses DAQ MX 9714 NI data logger which is connected to the PC using LabView program. The results show that the test research with a water load of 1500 ml results in the temperature of the refrigerator room of about 22.54oC for the series and 23.10oC for the parallel. While the value of COP obtained with the series circuit is 0.45 and with the parallel circuit is 0.4. There is no effect of the form of the circuit on the performance of the refrigerator.

Due to rapid demand on the thermoelectric cooler box, an investigation concerning the effect of water volume on a thermoelectric cooler box performance and its COP has been conducted. The aim of this study is to know the performance and the COP of the cooler box with water volume variations. The conduction heat transfer rate flowing from the ambient to the cooler box space is discussed deeply as this type of heat transfer rate is seldom to be elucidated in the published literature and it can be the dominant of the heat load when there is no water volume inside the cooler box. The cooler box size was 390 mm x 320 mm x 530 mm and the water volume variations employed were ranging from 0 to 4500 ml. The power used was of approximately 51.27 W. The results indicate that increasing the water volume raises the cooler box space temperature and the COP but decreases the conduction heat transfer rate. At 0 ml water volume, the conduction heat transfer rate increases and it gets constant, while at higher water volumes the COP decreases with the time. The effect of the water volume on the heat transfer rate of the air is negligible but it is significant on the total heat transfer and conduction heat transfer.

Biogas purification process aims to reduce biogas impurities such as carbon dioxide (CO2) and hydrogen sulfide (H2S) to obtain higher methane (CH4) concentration. Adsorption is one method for purifying biogas using solids. The research used 3 adsorbent materials such as natural zeolite mordenite, synthetic zeolite 3A and Fe2O3. To maximize the performance of natural zeolite as adsorbent, it is necessary to activate with NaOH solution which NaOH concentration used is 0%, 5%, and 15% NaOH and then they were activated by physical activation under heating treatment at 250oC for 4 hours. The best biogas purification result with natural zeolite activation mode was obtained at activation of 5% NaOH and followed by 15% and 0% NaOH. This is because activation using NaOH with 1-2N concentration (molarity) led to a macro pore size of the zeolite, more uniform, and the pores on the micro pore can be cleaned. After obtaining the best quality of natural zeolite, a study on the adsorbent ratio of adsorbent tubes obtained from the best results in Fe2O3, synthetic zeolite and natural zeolite (1: 1: 2) was observed because the ability of natural zeolite adsorption is better than of synthetic zeolite and Fe2O3. Therefore, the more natural zeolite in the adsorbent tube the better the refining result.

The dependence of human being on fossil fuels has decreased significantly the conventional energy resources. To overcome this problem it is required alternative substitute fuels which are cheap and accessible which biogas is one of the fuels. Nevertheless, the use of biogas has not yet been maximized because of the low calorific value which is produced from the process without purification. The circulated water absorption method is one mean of effective biogas purification. Under this method it is expected to increase the level of methane (CH4) and to reduce both the level of carbon dioxide (CO2) and hydrogen sulfide (H2S). In order to obtain the aim, the research was carried out under variations of water and biogas volumetric flow rate. The results show that the highest quality of biogas produced was under the variation of water volumetric flow rate of 15 lt/min with biogas volumetric flow rate of 1 lt/min which increased the level of methane (CH4) from 59.36 % to 62.8 % and decreased the carbon dioxide (CO2) content from 33.53 % to 26.8 %, and hydrogen sulfide (H2S) from 208.33 to 86 ppm. Lower biogas and water volumetric rates allowed longer contact between biogas molecule and absorbent. This resulted in an opportunity for absorbent more active to dissolve carbon dioxide and hydrogen sulfide in biogas. These compounds then flowed outward of the scrubbing unit along with the absorbent. The research proved that the raw biogas purification by circulated water scrubbing method was an effective mean in enhancing the quality of biogas.