Effects Of Hole Spacing Research Articles

High quality full ablation cutting and stealth dicing of silica glass using picosecond laser Bessel beam with burst mode

Glass cutting is widely used in many fields, such as aerospace and integrated electronics. To meet requirements of high-quality glass cutting, methods of full ablation cutting and stealth dicing of silica glass using picosecond laser Bessel beam are studied in this paper. Position synchronized output function of laser source and burst mode (BM) can flexibly adjust drilling spacing and the number of sub-pulses during processing. Through experimental research and theoretical analyses, effect of hole spacing, BM, laser power, and defocusing distance on the roughness of the cross-sections of cutting samples are investigated. The optimal combination of full ablation cutting parameters is obtained with the minimum roughness of the cross-section of 355 nm. To expand the application range of Bessel beam glass cutting, stealth dicing process is developed. Process parameters selection strategy of stealth dicing is obtained. Main parameter that affects the effect of stealth dicing is the defocusing distance. Aforementioned methods may provide simple, efficient, and high-quality full ablation cutting and stealth dicing technologies for glass materials.

Effect of Hole Spacing on Deposition of Fine Coal Flyash Near Film Cooling Holes

Particulate deposition experiments were performed in a turbine accelerated deposition facility to examine the nature of flyash deposits near film cooling holes. Deposition on both bare metal and thermal barrier coating (TBC) coupons was studied, with hole spacing (s/d) of 2.25, 3.375, and 4.5. Sub-bituminous coal ash particles (mass mean diameter of 13 μm) were accelerated to a combustor exit flow Mach number of 0.25 and heated to 1183°C before impinging on a target coupon. The particle loading in the 1 h tests was 310 ppmw. Blowing ratios were varied in these experiments from 0 to 4.0 with the density ratio varied approximately from 1.5 to 2.1. Particle surface temperature maps were measured using two-color pyrometry based on the red/gree/blue (RGB) signals from a camera. For similar hole spacing and blowing ratio, the capture efficiency measured for the TBC surface was much higher than for the bare metal coupon due to the increase of surface temperature. Deposits on the TBC coupon were observed to be more tenacious (i.e., hard to remove) than deposits on bare metal coupons. The capture efficiency was shown to be a function of both the hole spacing and the blowing ratio (and hence surface temperature). Temperature seemed to be the dominant factor affecting deposition propensity. The average spanwise temperature downstream of the holes for close hole spacing was only slightly lower than for the large hole spacing. Roughness parameters Ra and Rt decreased monotonically with increased blowing ratio for both hole spacing analyzed. The roughness for s/d=3.375 was lower than that for s/d=4.5, especially at high blowing ratio. It is thought that these data will prove useful for designers of turbines using synfuels.

Absorption of oxygen by aqueous glycerol solutions and squalane

Highly viscous media are used in a number of process industries, such as the chemical, petrochemical, pharmaceutical, and food industries. Design of mass transfer equipment for such media is very difficult because of the rather limited experimental data. Therefore, the absorption of oxygen from air into glycerol—water solutions has been studied under different operating conditions and sieve tray geometries (namely, hole diameter and hole spacing). Furthermore, the results of supplementary absorption experiments of oxygen into squalane (C30H62) show that the results with the system oxygen—glycerol—water are transferable to other systems.Chemical, pharmaceutical, and petrochemical as well as food industries have to deal increasingly with processes where mass transfer in highly viscous media is involved. Design of mass transfer equipment for such media is very difficult because of the rather limited experimental data. Therefore, a study was started to partially fill this gap; in particular, it deals with evaporation of pure cyclohexanol into air [2] as well as absorption of oxygen from air into glycerol—water solutions on a sieve tray [3-6].In this paper the influence of the sieve tray geometry on mass transfer was studied. The following observations were made concerning the effect of hole diameter and hole spacing.1.(1) In the bubble and spray regime (υG < 1 m s−1) for low viscosities there is no effect of the hole diameter on the efficiency.2.(2) At higher viscosities and low gas velocities an increasing hole diameter results in a reduction of mass transfer.3.(3) In the drop regime (υG > 1 m s−1), i.e. for high gas velocities, an improvement in the efficiency is noticed for sieve trays with larger holes.4.(4) In the bubble and spray regimes there is no effect of the hole spacing on mass transfer for low and high viscosities.5.(5) In the drop regime a better efficiency is obtained with higher hole spacing.The experimental results are explained well with the recently developed model based on high-speed photographs, which divides the two-phase fluid on a sieve tray into three distinct zones, as shown in Fig. 2. The droplet formation zone which represents break-up of the bubbles at the fluid surface into liquid laminae and droplets, as well as the mass transfer between the droplets formed and the surrounding gas, plays a dominant role with respect to the total mass transferred.Supplementary absorption experiments of oxygen into squalane have been carried out to indicate the transferability of the results to hydrocarbon systems. A comparison of these results with those of the absorption of oxygen into glycerol—water mixtures shows excellent agreement of the basic trends.

Full-Coverage Film Cooling—Part I: Comparison of Heat Transfer Data for Three Injection Angles

Wind tunnel experiments were carried out at Stanford between 1971 and 1977 to study the heat transfer characteristics of full-coverage film cooled surfaces with three geometries: normal-, 30 deg slant-, and 30 deg × 45 deg compound-angled injection. A flat full-coverage section and downstream recovery section comprised the heat transfer system. The experimental objectives were to determine, for each geometry, the effects on surface heat flux of injection blowing ratio (M), injection temperature ratio (θ), and upstream initial conditions. Spanwise-averaged Stanton numbers were measured for blowing ratios from 0 to 1.3, and for two values of injection temperature at each blowing ratio. The heat transfer coefficient was defined on the basis of a mainstream-to-wall temperature difference. Initial momentum and enthalpy thickness Reynolds numbers were varied from 500 to about 3000. This paper compares the experimental results for the three injection geometries. In addition, the effects of hole spacing and number of rows of holes were examined.