Bundit Krittacom

The Effective Thermal Conductivity (ETC) of Spherical Packed-Bed Porous Media for Modification of the Color Surface as Black Color

The effective thermal conductivity (ETC) of the spherical packed-bed porous media in stagnant fluid case is estimated by modifying the color surface of the porous media as black surface. The Alumina-Cordierite (Al-Co) ceramic balls having average diameter (d) of 5.0 cm is constructed as the porous media and, then, a porosity (f) has 0.398. For development of the porous media as black surface, the Al-Co ceramic balls are painted by black color and then it is composed of 600 °C × 8 hr. The experimental procedure to evaluate the ECT is based on ASTM E1225. A higher temperature (TH) is investigated in the range of 400 to 800 K at the constant power of 350 W. The ETC of three surfaces of the Al-Co ceramics ball, i.e., original surface (λorg), combined black-painted and original surface (λcom) and black surface (λblk), are examined. From experiment, it is found that all ETC of three surfaces decrease with increasing TH. The value of three ETCs are in the range of 6.2 to 27.1 W/(m K). The lblk gives highest for the present research and, exactly, the worst case is obtained by λorg. Thus, the ETC of spherical packed-bed porous media with stagnant fluid can be improved by developing the color surface as black color.

Estimating Correlation of Effective Thermal Conductivity on the Spherical Packed Bed Porous Media

The correlation of an effective thermal conductivity (keff) on spherical packed bed porous media with stagnant fluid was proposed. Alumina-Cordierite ceramic ball (Al-Co) having average diameter (d) of 2.1 cm and porosity (Φ) of 0.468 was examined. The experimental procedure was operated based on ASTM E1225. The tested porous sample was sandwiched by references materials (Solid Brass, 70%Cu, 30%Zn). A higher temperature (TH) on the top of test set was obtained from wire heater with a constant electrical power of 350 W. The water cooling set was installed at the bottom of to generate a lower temperature (TL). Four previous models established from geometrical structure were compared to validate the present correlation. From experiment, it was found that keff decreased with increasing TH. Thus, the relation between keff and TH was appropriately proposed by a correlating linear-equation (keff/kf = 329.2(1-0.1028(TH/100)). Agreement between the present correlation and literature models was satisfied particular.

Energy Balance in Al-Co Open-Celled Foam of Transpiration Cooling

Numerical model of one-dimensional steady-state on Alumina-Cordierite (Al-Co) open-celled foam using in transpiration cooling system have been conducted to investigate the local energy balance (LEB) of gas and solid phase within porous plate. Physical properties, i.e., porosity (f), pores per inch (PPI) and thickness (x), of Al-Co open-cellular porous material were 0.87, 13 and 0.103 m, respectively. Two equations of the conservative energy consisting of the gas and solid phase were analyzed. From study, it was found that heat convection (HVF) balanced with heat transfer between two phases/ energy of interaction (INT) for the gas phase case. In the solid phase, heat transfer between two phases (INT) tended to offset heat radiation (HRS). Remarkably, heat conduction of both phases (HDF and HDS) was not effected to the present cooling system. Thus, characteristic of fluid flow effecting by HVF and heat transfer governed from HRS was strongly efficient to transpiration cooling system.

An experimental Investigation of effectiveness of a closed-end flat heat pipe heat exchanger (CEFHPHE)

The effectiveness of a closed-end flat heat pipe heat exchanger (CEFHPHE) was investigated experimentally. The CEFHPHE consists of three parts, which include the evaporator, adiabatic and condenser sections that the lengths were 300, 100 and 300 mm respectively. The standard copper tube with inner diameter of 8.6 mm and 0.46 mm thick was pressed to reform its cross sectional area for a flat tube, and then bent to many U-shapes, which was closed at both ends. The water was used for working fluid with filling ratios of 45% of internal volume. In experiments, hot air was used for supplying the heat to the evaporator section with different temperatures (105-145oC), and different velocities (0.5-2.0 m/s). Fresh air was used for cooling condenser section with temperature approximately 30oC, and was kept constant velocity at 0.5 m/s. The experimental results indicated that the effectiveness of CEFHPHE increase with the inlet hot air temperature, and decrease with the increase of hot air velocity. In addition, the effectiveness of the CEFHPHE obtained from the experiments varied between 0.35 and 0.74.