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[en] A numerical study on the heat exchanger design process has been conducted in order to propose a more effective method for the preliminary design of highly efficient and compact heat exchanger. The ε-NTU based performance prediction program and the heat exchanger database having performance correlations of various fin-type heat exchanger were developed. Numerical characteristics of the genetic, pattern search, and simulated annealing algorithms for the heat exchanger sizing were compared in terms of the accuracy and the computational speed. The effect of margins in design requirements were examined through the size ranking and the response surface analysis. The usefulness of the entropy generation minimization was appraised by comparing to the case when the objective function was the volume of the heat exchanger
[en] The thermal process of wastes with higher calorific value by pyrolysis is reviewed to recover the value added three by-products; a pyrolytic char, a pyrolytic oil, and a non-condensable gas. These by-products from pyrolysis of the waste is converted for electricity power and thermal energy thru gasification process as well as waste heat recovery process. The energy resource and several processes in the integrated pyrolysis gasification combined cycle for waste treatment are investigated with the conceptual design in using the obtained operation data from the pyrolysis pilot, demonstration and commercial plant.
[en] The characteristics of a three-dimensional hemispherical droplet on a heterogeneous surface were studied using the Lattice Boltzmann method (LBM). The hydrophilic surface has a hydrophobic part at the center. The hemispherical droplets are located at the center of the heterogeneous surface. According to the contact angles of hydrophilic and hydrophobic bottom surfaces, the droplet either separates or reaches a new equilibrium state. The separation time varies according to the change in droplet size, and it affects the status of droplet separation. The droplet separation behavior was investigated by analyzing the velocity vector around the phase boundary line. The shape and separation time of a droplet are determined by the contact angle of each surface. The speed of droplet separation increases as the difference in contact angle increases between the hydrophobic surface and hydrophilic surface. The separation status and the separation time of a droplet are also determined by the change of the droplet size. As the size of the droplet decreases, the effect of surface tension decreases, and the separation time of the droplet also decreases. On the other hand, as the droplet becomes larger, the effect of surface tension increases and the time required for the droplet to separate also increases.
[en] A numerical study was carried out using a molecular dynamics program to examine the wetting characteristics of nano-sized water droplets on surfaces with various pillar surface fractions under different conditions. Square-shaped pillars had surface fractions that increased from 11.1 % to 69.4 %. The pillars had 4 different heights and 3 different surface energies. When the pillar surface fraction changed, the contact angle of a water droplet also changed due to the attraction between the droplet and the pillar surface or the inner attraction of the water molecules. The pillar height also has different effects on the water droplet depending on the magnitude of surface energy
[en] The present study investigated the two-phase immiscible Couette flow in which a lower smooth or rough plate is stationary and an upper plate is moving, using the hybrid method which combines the simulation using the lattice Boltzmann method in the bulk region with the molecular dynamics simulation near the lower smooth or rough surface. The computational time required using the hybrid method was compared with that using the full molecular dynamics simulation, showing big savings in the computational time required by using the hybrid method. The boundary conditions formed on the lower surface depend on the surface energy, viscosity ratio and the geometry of the lower plate, resulting in the slip, no-slip and locking boundary conditions. The results corresponding to the case of the rough surface were compared with those for the smooth surface in order to investigate the effect of the roughness on the flow behavior on the lower plate.