Abd. Rahim Abu Talib

Aerogels in Aerospace: An Overview

Aerogels are highly porous structures prepared via a sol-gel process and supercritical drying technology. Among the classes of aerogels, silica aerogel exhibits the most remarkable physical properties, possessing lower density, thermal conductivity, refractive index, and dielectric constant than any solids. Its acoustical property is such that it can absorb the sound waves reducing speed to 100 m/s compared to 332 m/s for air. However, when it comes to commercialization, the result is not as expected. It seems that mass production, particularly in the aerospace industry, has dawdled behind. This paper highlights the evolution of aerogels in general and discusses the functions and significances of silica aerogel in previous astronautical applications. Future outer-space applications have been proposed as per the current research trend. Finally, the implementation of conventional silica aerogel in aeronautics is argued with an alternative known as Maerogel.

Tailoring Aerogel for Thermal Spray Applications in Aero-Engines: A Screening Study

Irregular silica aerogel particles had been tailored to a regular spherical shape within the proper granulometric size range for thermal spraying. Silica aerogel is an ultralow dense and highly porous nanomaterial with its thermal conductivity being the lowest than any solids. Although silica aerogels possess fascinating physical properties, their implementation is limited to aerogel-doped blankets in the aerospace industry. Due to space constraints, these heat insulative and fireproof blankets are not encouraged by aero-engine manufacturers, and hence, alternatives are being sought. Although it was thought that an aerogel-based thermally sprayed coating may be applicable, aerogel powders are extremely challenging to be injected and deposited by thermal spray guns because of their inappropriate granulometric and morphological properties. Consequently, this study intends to tailor the aerogel powders accordingly. Aerogel-based slurries with yttria-stabilized zirconia as a secondary ceramic were prepared and spray-dried according to a modified Taguchi experimental design in order to appreciate the effect of both the slurry formulation and drying conditions such as the solid content, the ratio of yttria-stabilized zirconia : aerogel added, the amount of dispersant and binder, inlet temperature, atomization pressure, and feeding rate on the aforementioned characteristics of the resulting spray-dried powder. Uniformity was found to be the most influenced one (F-ratio = 62.40) by the overall spray-drying process. Solid content had the most significant effect on median particle size ( value = 0.035) and volume fraction ( value = 0.010) but did not affect uniformity significantly ( value = 0.065). Furthermore, a strong positive and significant correlation existed (Pearson’s r = 0.930) between median particle size and volume fraction. Based on the derived relationships, an optimised condition to achieve the maximum median particle size was then predicted and verified experimentally. The optimised aerogel-based spray-dried powder had a median particle size, volume fraction, and uniformity of 28.93 ± 0.726 μm, 64.45 ± 0.535, and 0.475 ± 0.002, respectively. Finally, the morphology of the optimised powder was noticed to have been changed from irregular shapes to spherical or donut-like granules which made them within the frame of thermally sprayable. However, when the optimised spray-dried powder was weighed, the quantity was found to be 10% only from the total weight of ceramics within the slurry prior to spray-drying, which makes it uneconomically reasonable for subsequent thermal spraying.

Evaluation of hardness and density properties of sintered Inconel 718 using palm oil-based binder

This paper investigates the effect of palm oil-based binder on hardness and density of sintered Inconel718. Palm stearin (PS) is the palm oil derivative, which has been formulated and evaluated as possible alternative binder system. The variety of PS contents can be an advantage during debinding process as it can be removed gradually to maintain the shape of the debound part. At different heating temperatures, each binder contents melts, leaving different impurities. The remaining impurities help to form capillary holes for the removal of the binder material. The PS binder system is compared with conventional binder system based on the physical and mechanical properties of Inconel718 sintered parts. It was found that the PS binder systems proved to enhance the properties and improve the microstructure behaviour. Result shows that the sintered properties from palm oil binder system can be achieved in accordance to the Metal Powder Industries Federation standard.

Malaysian aviation technologist promotion to managerial role: an empirical overview

The Malaysian aviation industry has continued to march forward. With a turnover of RM23.7 billion in 2013, it is expected to grow higher especially after the Malaysian national aerospace blueprint was launched in 2015. The aviation related organizations currently have a workforce of approximately 13500. These organizations need to be managed by competent managers who have a strong background of technologist. Aviation technologist is one of the key components in the aviation maintenance industry as they are the future managers charged with the responsibility to ensure continuation of the organizations objectives and culture. The technologist role and managers role are somehow different. The promotion of technologist to managerial roles is quite common but whether the technologist is able to take up managerial role effectively is yet to be fully understood. It is quite common that there was insufficient training for the technologist before being promoted to take up management roles. The purpose of this paper is to give an overview of the role of technologists and managers in professional services industries such as MRO and to understand that there is a need within the industry to re-look into the perspective of a proper training to prepare them to take up management roles effectively.

Effect of multiple jet impingement plate configurations on Reynolds Number in a pipe

Experimental investigations were carried out to study the effect of varying multiple jet impingement plate configurations on Reynolds Number (Re) in a closed conduit. Air was considered as the working fluid. There were six multiple impingement plates used for this experiment where each plate has a different hole configurations that include the hole diameter, hole orientation, pitch in x-direction and pitch in y-direction. Four sets of orifice plate with diameter of 0.02, 0.03, 0.04, and 0.05 m were used to get the mass flow rate in the pipe. Air was sucked through the impingement plate for five different settings of suction fan with an interval of 10Hz from 10 to 50Hz. By taking the data for constant suction fan setting at 50Hz, it was found that the impingement hole orientation for both in-line and staggered does not give any effect on the Re obtained since the differences was considerably small and fell within the accepted errors. Meanwhile, impingement hole diameter was found to be directly proportional with the Re obtained. It was also found that the different pitch in multiple hole impingement plate resulted in changes of Re. The results show that the Re was decreasing with higher pitch. The uncertainty analyses for the Re were also presented.

Flame Temperature Distribution from ISO2685 Standard Propane-Air Burner using CFD

This analysis considers the computational simulations of the temperature distribution of a propane-air customary flame combusted from an aeronautical fire-certification set according to the ISO2685standard. The numerical codes have been executed in Computational Fluid Dyanmics using the k-ω SST turbulence model coupled with eddy-dissipation. The resultshowsthat the maximum predicted temperature using the standard flame settings exceeds the required temperature for evaluation of a fire-resistive material. The mole fractions of the by-products, carbon dioxide and water have also been predicted.

Numerical Simulation of Plain Fin‐and‐Round Tube Heat Exchanger under Frost Condition

Three‐dimensional numerical simulations are carried out to investigate the amount of heat transfer of a plain fin‐and‐four staggered layout and round tube rows for different fin pitch namely 25.4, 12.7, 6.35 and 4.23 mm. The simulations were conducted for two different frost thermal conductivity of 0.1 and 0.3 W/m‐1K‐1 using FLUENT 6.3 CFD code. The amount of heat transfer of the plain fin‐and‐round tube heat exchanger under frost condition (0, 1, 2, and 3 mm frost thickness) was investigated. Fluid flow and heat transfer are simulated and results calculated using two turbulence models (k‐epsilon, and Transitional SST k‐omega), with steady‐state solver. Model validation was carried out by comparing the pressure drop of simulated case to experimental results from the literature. Reasonable agreement was found between the present simulations compared to existing numerical study and experimental data.