Pengujian Rancangan Simulator Resistansi Termal dan Rugi-rugi Kalor pada Sistem Aliran Fluida dalam Pipa Tersekat dengan Metode Adaptive Neuro Fuzzy Inference System (ANFIS) dan Least-squares Estimation (LSE)

Thermal resistance is essential for designing insulation systems to prevent heat losses in fluid flow through pipes. The testing method for obtaining data on the thermal resistance of nanoscale insulators is still not agreed upon, as is the explanation of the physical phenomena in the mechanism of inhibiting heat flow. This research aimed to design a simulator for testing the thermal resistance of insulators and heat losses through pipes as an alternative testing method for various insulation materials. Hot air flows through a pipe equipped with a measurement and data processing system to obtain the temperature distribution of the fluid flow in the pipe and the pipe surface temperature along the pipe. Thermal resistance and heat loss are the parameters of the insulation material. The mathematical model was solved numerically and validated with COMSOL Multiphysics software. In designing the simulator, both properties are estimated using the ANFIS and LSE methods. The ANFIS method yields the best estimation for thermal resistance and heat losses. The ANFIS estimation for thermal resistance yields an error of 0.163 m2K/W, and for heat losses yields an error value of 12.64 W/m. The developed ANFIS estimation method is highly resilient to errors in the measurement data.Data resistansi termal sangat diperlukan untuk merancang sistem sekatan (insulasi) untuk pencegahan rugi-rugi kalor pada sistem aliran fluida melalui pipa. Metode penguiian untuk mendapatkan data sifat resistansi termal dari sekatan (insulator) jenis bahan sekatan berskala nano masih belum disepakati, begitu juga dengan penjelasan fenomena fisis dalam mekanisme menghambat aliran kalor. Penelitian ini dilakukan untuk mendapatkan rancangan simulator pengujian sifat resistansi termal sekatan dan rugi-rugi kalor melalui pipa sebagai metode pengujian alternatif untuk berbagai jenis bahan sekatan. Udara panas dialirkan melalui pipa yang dilengkapi dengan sistem pengukuran dan pengolahan data untuk mendapatkan data distribusi suhu aliran fluida dalam pipa dan suhu permukaan di sepanjang pipa. Sifat resistansi termal dan rugi-rugi kalor merupakan parameter bahan sekatan yang diuji. Model matematik diselesaikan secara numerik dan divalidasi dengan perangkat lunak COMSOL Multiphysics. Pada rancangan simulator, kedua sifat diestimasi menggunakan metode ANFIS dan LSE. Metode estimasi ANFIS menunjukkan kinerja estimasi terbaik, baik untuk resistansi termal maupun rugi-rugi kalor. Metode estimasi ANFIS untuk resistansi termal memberikan nilai galat sebesar 0,163 m2K/W, sedangkan untuk rugi-rugi kalor memberikan nilai galat sebesar 12,64 W/m. Metode estimasi ANFIS yang telah dikembangkan memiliki ketahanan yang cukup baik terhadap kesalahan dalam simulasi data pengukuran

Noise Attenuation of a Duct-resonator System Using Coupled Helmholtz Resonator - Thin Flexible Structures

Several studies have been devoted to increasing the attenuation performance of the Helmholtz resonator (HR). One way is by periodic coupling of HRs in a ducting system. In this study, we propose a different approach, where a membrane (or a thin flexible structure in general) is added to the air cavity of a periodic HR array in order to further enhance the attenuation by utilizing the resonance effect of the membrane. It is expected that three attenuation mechanisms will exist in the system that can enhance the overall attenuation, i.e. the resonance mechanism of the HR, the Bragg reflection of the periodic system, and the resonance mechanism of the membrane or thin flexible structure. This study found that the proposed system yields two adjacent attenuation peaks, related to the HR and the membrane respectively. Moreover, extension of the attenuation bandwidth was also observed as a result of the periodic arrangement of HRs. With the same HR parameters, the peak attenuation by the membrane is tunable by changing its material properties. However, such a system does not always produce a wider attenuation bandwidth; the resonance bandwidths of both mechanisms must overlap

Noise Attenuation of a Duct-resonator System Using Coupled Helmholtz Resonator - Thin Flexible Structures

Several studies have been devoted to increasing the attenuation performance of the Helmholtz resonator (HR). One way is by periodic coupling of HRs in a ducting system. In this study, we propose a different approach, where a membrane (or a thin flexible structure in general) is added to the air cavity of a periodic HR array in order to further enhance the attenuation by utilizing the resonance effect of the membrane. It is expected that three attenuation mechanisms will exist in the system that can enhance the overall attenuation, i.e. the resonance mechanism of the HR, the Bragg reflection of the periodic system, and the resonance mechanism of the membrane or thin flexible structure. This study found that the proposed system yields two adjacent attenuation peaks, related to the HR and the membrane respectively. Moreover, extension of the attenuation bandwidth was also observed as a result of the periodic arrangement of HRs. With the same HR parameters, the peak attenuation by the membrane is tunable by changing its material properties. However, such a system does not always produce a wider attenuation bandwidth; the resonance bandwidths of both mechanisms must overlap

Oxygen Reduction Reaction Mechanism on the Square Paddle-Wheel Cage Site of TM-BTC (TM=Mn, Fe, Cu) Metal Organic Framework

We study the oxygen reduction reaction (ORR) mechanism on the square paddle-wheel cage active site of TM-BTC (TM= Mn, Fe, Cu) metal organic framework by using a combination of DFT and microkinetic calculations. By using a small cluster for modeling the TM-BTC active site structure, we have successfully reproduced the experimental trend of ORR activity on the TM-BTC systems: Mn-BTC > Fe-BTC > Cu-BTC. We also show that the unusual ORR activity trend from experiments for Mn and Fe systems is originated from the strength of OH adsorption on these systems. Mn-BTC system has better ORR activity than the Fe-BTC system because it has weaker OH adsorption. A very strong OH adsorption makes the final OH reduction step become more sluggish, and hence hindering the ORR process

Oxygen Reduction Reaction Mechanism on the Square Paddle-Wheel Cage Site of TM-BTC (TM=Mn, Fe, Cu) Metal Organic Framework

We study the oxygen reduction reaction (ORR) mechanism on the square paddle-wheel cage active site of TM-BTC (TM= Mn, Fe, Cu) metal organic framework by using a combination of DFT and microkinetic calculations. By using a small cluster for modeling the TM-BTC active site structure, we have successfully reproduced the experimental trend of ORR activity on the TM-BTC systems: Mn-BTC > Fe-BTC > Cu-BTC. We also show that the unusual ORR activity trend from experiments for Mn and Fe systems is originated from the strength of OH adsorption on these systems. Mn-BTC system has better ORR activity than the Fe-BTC system because it has weaker OH adsorption. A very strong OH adsorption makes the final OH reduction step become more sluggish, and hence hindering the ORR process

Hydrazine (N2H4) adsorption on Ni(1 0 0) - Density functional theory investigation

A theoretical study on the structure and adsorption mechanism of hydrazine (N2H4) on Ni(1 0 0) are presented. The hydrazine molecule was found to adsorb on the surface through one of its nitrogen atom in its anti-conformation. The charge transfer from hydrazine lone pair orbitals played a key role in the formation of the bonding. The mechanism involved in the bonding was found to reduce the necessity of hyper-conjugation interaction, that reduces the gauche effect found in hydrazine at the gas-phase. Upon adsorption to the surface, the reduced interaction resulted in the promotion of a more favored conformation through its anti-conformation

Theoretical study of hydrazine adsorption on Pt(111): Anti or cis?

Hydrazine (N2H4) adsorption on metal surface is important due to its application in the direct hydrazine fuel cell technology. First principles DFT calculations have been carried out to understand the structure and mechanism of hydrazine adsorption on Pt(111). Calculations revealed that configuration with hydrazine adsorbed on its anti-conformation yields the largest adsorption energy suggesting it to be the most stable structure on Pt(111). This result was found to be in disagreement with available XPS results which favor the adsorption on cis-conformation as the most stable configuration. However, by taking into account the energy cost for orbital re-hybridization and internal rotation involves in the adsorption, it was found that the interaction strength between adsorbate and substrate is comparably equal for adsorption on both anti and cis-conformations that indicates the feasibility of the adsorption in cis-conformation to occur. Charge transfers from lone-pair orbitals belong to the highest occupied molecular orbital (HOMO) and second highest occupied molecular orbital (S-HOMO) were found to be important in the formation of the bonding. The π-anti-bonding HOMO lone-pair transfers its charge to the surface which stabilizes the internal structure of the molecule and responsible for the stable anti-conformation adsorption structure. The interaction of the π-bonding S-HOMO lone pair with the surface was found to be dative type and plays an important role in the stabilization of cis-conformation adsorption structure. © 2011 Elsevier B.V. All rights reserved

Mekanisme Hidrogenasi CO2 pada Klaster Subnanometer Ni7 yang Disangga pada Graphene

We study the mechanism of carbon dioxide (CO2) hydrogenation to carbon monoxide (CO) and formic acid (HCOOH) on a graphene-supported subnanometer Ni7 cluster by means of density functional theory calculations. We find that this system has similar activation energies for the first CO2 hydrogenation step for the formate and RWGS pathways. However, the second hydrogenation step for these pathways has very distinct profiles. The HCOOH formation on the formate pathway has very large activation energy, while the CO formation on the RWGS pathway has negligible activation energy. We conclude that the CO2 hydrogenation process on this system is more selective towards the RWGS pathway to produce CO