Karakteristik Bahan Komposit High Density Polyethylene yang Diperkuat Serat Pendek Fiberglass untuk Pipa Air Dingin Ocean Thermal Energy Conversion (OTEC)

Abstract

Ocean thermal energy conversion (OTEC) is a new energy source for the future that is clean and environmentally friendly with zero emissions. It is very potential to be developed in Indonesia which is located on the equator, to meet the electricity needs in the outermost and remote islands that the main power plants in Indonesia do not reach. Indonesia has deep seas around the islands with temperatures of 5oC and surface temperatures above 28oC, so a temperature difference of 20oC can be obtained easily for OTEC power plants. A cold water pipe with a length of 500 m is required which is an insulator, does not float, and is able to withstand pressure loads and fluctuations in seawater currents. Therefore, a high-density polyethylene (HDPE) composite with short fiberglass fibers is proposed which is lightweight, strong, not easily broken, low temperature resistant, corrosion resistant, and low maintenance costs. Composite materials are made with weight fractions (30-70)% and (20-80)%. The composite is made by mixing the fiber into HDPE which is melted at a temperature of 138oC with stirring and after mixing it is put into the mold and hot pressed during the hardening process and aging (curing). Tensile test specimens were made according to ASTM D3039, compression test specimens according to ASTM D3410, fatigue test specimens according to ASTM D3479, density test specimens according to ASTM D792, and conductivity specimens according to ASTM C177, using NC Milling. Tensile and compressive tests were carried out with the Universal Testing Machine, fatigue testing with Servopulser at R=-1 and 10Hz, heat conductivity testing with the Guarded-Hot-Plate Apparatus, density testing with a densitometer and fracture interface observations with SEM. After obtaining the best material, a simulation was carried out with the Inventor software to determine the stress due to current velocity in the pipe and a simulation of seawater temperature rise along the pipe due to flow velocity and the temperature outside of the pipe. The test results show that the short fiber composite with a weight fraction of 30-70% has the highest tensile strength of 32.24 MPa at 28oC, has a compressive strength of 10.35 MPa at 28oC and has a fatigue endurance limit of 46.3% of the maximum tensile strength, has a thermal conductivity 0.337 W/mK and a density of 1.22 gr/cm2. Based on the stress simulation that occurs in the pipe, a minimum pipe thickness of 17 cm and a maximum of 30 cm is obtained from a pipe with a diameter of 4 m and a length of 500 m with a current speed of 0.8 m/s, and from the simulation, the temperature of the water leaving the pipe is known to increase 1.19oC, 1.5oC, 2.01oC at a flow rate of water flow in the pipe 5 m/s, 4 m/s, 3 m/s. So from the results of this study, it is recommended that short fiberglass HDPE composites with a weight fraction of 30% -70% met as ocean-based OTEC cold water pipe materials with a temperature increase along the pipe of 1.19oC at a speed of 5 m/s, and a pipe thickness of 25 cm with an life0f 40,53 years.