Rozli Zulkifli

Characterization of a Bifacial Photovoltaic Panel Integrated with External Diffuse and Semimirror Type Reflectors

Silicon wafer accounts for almost one-half the cost of a photovoltaic (PV) panel. A bifacial silicon solar cell is attractive due to its potential of enhancing power generation from the same silicon wafer in comparison with a conventional monofacial solar cell. The bifacial PV cell is able to capture solar radiation by back surface. This ability requires a suitable reflector appropriately oriented and separated from the cell’s rear surface. In order to optimize the bifacial solar cell performance with respect to an external back surface reflector, diffuse and semimirror reflectors were investigated at various angles and separations from the back surface. A simple bifacial solar panel, consisting of four monocrystalline Si solar cells, was designed and built. Reflection from the rear surface was provided by an extended semimirror and a white-painted diffuse reflector. Maximum power generation was observed at 30° with respect to ground for the semimirror reflector and 10° for diffuse reflector at an optimized reflector-panel separation of 115 mm. Output power enhancement of 20% and 15% from semimirror and diffuse reflectors, respectively, were observed. This loss from diffuse reflector is attributed to scattering of light beyond the rear surface capture cross-section of the bifacial solar panel.

Failure characterisation in polymer matrix composite for un-notched and notched (open-hole) specimens under tension condition

This paper presents an investigation of the influences causing failure in the materials comprising polymer matrix composites. Structures with differences in stacking sequences and design configuration are analysed. The objective of this study is to investigate and evaluate the reasons for the failure of composite lamination structures in terms of stress, strength, strain, and Young modulus within a morphology observation of composite materials. The materials selected for the study were a chopped strand mat (CSM) and a woven roving (WR) fabric. These materials are used as reinforcement and are produced by the hand lay-up technique using epoxy and polyester matrix resin. The experiment was performed using specimens made of notched (open-hole; OH) tension and un-notched (UN) shapes. The characteristics of different shapes, materials, and lamination structures are studied in this research. The results showed the failure phenomenon in the structure of the polymer matrix composite is dependent on the characteristics of the material used and the design configuration of both structures.

An investigation into mode II failure mechanisms in carbon fibre reinforced PEEK

Abstracts are not published in this journal

Steady state characterization of bifacial solar cells at different configurations of air-based photovoltaic thermal solar panels

This paper examines the first and second law efficiency of bifacial photovoltaic thermal (PVT) solar collectors. A mathematical model was developed to evaluate the system performance. Four air-based bifacial photovoltaic thermal panels were also designed based on the bifacial PV cell requirement. Most of the existing PVT designs contain an absorber plate, which in this research is replaced by a reflector to avoid blocking the rear aperture of bifacial cells. The following four air-based panel configurations were considered: single-path; double-path, parallel; double-path, counter flow; and double-path, returning flow. All four panel designs evaluated based on the first law and second law of thermodynamic, at steady state mode. Energy and exergy efficiencies of aforementioned designs strongly depend on packing factor and air mass flow rate. From an energy point of view (first law), the bifacial photovoltaic thermal panel with two parallel air streams exhibited the best efficiency (51%–67%) compared with th...

EFFECT OF PULSE JET FREQUENCY ON IMPINGEMENT HEAT TRANSFER

An experimental investigation was carried out to study the effect of flow pulsation frequency on the local and average heat transfer characteristics of a heated air jet. The experiments were performed for steady jets and for pulsating jets at frequencies from 10 to 80 Hz. The nozzle to plate spacing, x/D was fixed at 4 and Reynolds number was set at 16 000, 23 300 and 32 000. The duty cycle of the pulse air flow was 33%. Pulsation of the air jet was produced by a rotating cylinder valve mechanism. The investigation showed that the average pulsed jet Nusselt number was equal or higher than the steady jet Nusselt number at the same Reynolds number for all values of frequencies except at 50Hz. In contrast, the stagnation point heat transfer of the pulsed jet was lower than that of steady jets for all the frequencies tested. The higher average Nusselt numbers for pulse flow compared to steady flow resulted from significant enhancement of the heat transfer at distances greater than about 1 nozzle diameter away from the stagnation point. This increase is believed to be caused by enhanced turbulence intensity due to pulsing the jet. The degradation in heat transfer at the stagnation point is believed to be due to the small turbulent intensity at this position.

Development of Pulsating Twin Jets Mechanism for Mixing Flow Heat Transfer Analysis

Pulsating twin jets mechanism (PTJM) was developed in the present work to study the effect of pulsating twin jets mixing region on the enhancement of heat transfer. Controllable characteristics twin pulsed jets were the main objective of our design. The variable nozzle-nozzle distance was considered to study the effect of two jets interaction at the mixing region. Also, the phase change between the frequencies of twin jets was taken into account to develop PTJM. All of these factors in addition to the ability of producing high velocity pulsed jet led to more appropriate design for a comprehensive study of multijet impingement heat transfer problems. The performance of PTJM was verified by measuring the pulse profile at frequency of 20 Hz, where equal velocity peak of around 64 m/s for both jets was obtained. Moreover, the jet velocity profile at different pulsation frequencies was tested to verify system performance, so the results revealed reasonable velocity profile configuration. Furthermore, the effect of pulsation frequency on surface temperature of flat hot plate in the midpoint between twin jets was studied experimentally. Noticeable enhancement in heat transfer was obtained with the increasing of pulsation frequency.

A Preliminary Study on the Sound Absorption of Date Palm Fibers

In this study sound absorption properties of a single layer date palm fiber has been investigated. Experimental measurements were carried out using impedance tube at the acoustic lab, Faculty of Engineering, Universiti Kebangsaan Malaysia. A constant thickness sample was considered in this study.The results show that the values of absorption coefficient are small at low frequencies, rising with increasing frequency but exhibiting a significant peak. The low density of the sample is reflected in the overall sound absorption performance of the date palm fiber. An improvement in the sound absorption in the lower frequency range was achieved by backing the sample with air gap of different thicknesses of 10 mm, 20 mm and 30 mm. The increase in the air gap thickness moved the peaks toward lower frequencies and improved the low frequencies absorption. However, that increase coincided with reduction of absorption in medium frequency range and reduction in the absorption peak. A linear relationship was found between sound absorption peaks and the air gap thickness. The performance of the date palm fiber can be improved by increasing the density of the sample, using different sample thicknesses and adding perforated plates to the date palm fiber panel.

A practical acoustical absorption analysis of coir fiber based on rigid frame modeling

An analytical study based on rigid frame model is demonstrated to evaluate the acoustic absorption of coir fiber. Effects of different conditions such as combination of air gap and perforated plate (PP) are studied in this work. Materials used here are treated as rigid rather than elastic, since the flow resistivity of coir fiber is very low. The well-known rigid frame Johnson-Allard equivalent-fluid model is applied to obtain the acoustic impedance of single layer coir fiber. Atalla and Sgard model is employed to estimate the surface impedance of PP. Acoustic transmission approach (ATA) is utilized for adding various consecutive layers in multilayer structure. Models are examined in different conditions such as single layer coir fiber, coir fiber backed with air gap, single layer PP in combination with coir fiber and air gap. Experiments are conducted in impedance tube on normal incidence sound absorption to validate the results. Results from the measurement are found to be in well agreement with the theoretical absorption coefficients. The performance of the rigid frame modeling method is checked more specifically in all conditions, by the mean prediction error rate of normal incidence sound absorption coefficients. Comparison between the measured absorption coefficients and predicted by rigid frame method shows discrepancy lower than 20 and 15% for most of the conditions in the frequency range of 0.2–1.5 and 1.5–5 kHz, respectively. Moreover, acoustic absorption of various single and multilayer structures is compared with the simpler empirical methods such as Delany-Bazley and Miki model; and complicated method such as Biot-Allard Model and Allard Transfer Function (TF) method. Comparisons show that the presented method offers a better accuracy of the results than the empirical models. Subsequently, it can provide almost same absorption plot with Biot-Allard model (single layer combination) and TF method (multilayer combination) proving it to be a comprehensively easy and general analytical tool. Therefore, the rigid frame model can be implemented relatively easier than other similar models to analyze the acoustic absorption of coir fiber in most of the conditions.

Energy Absorption Capability of Axially Compressed Woven Natural Ramie/Green Epoxy Square Composite Tubes

This study focuses on failure response and energy absorption of woven ramie epoxy square composite tubes when exposed to the axial quasi-static compression test. Hand lay-up technique was used to prepare the rectangular composite tubes composed of 12 layers of ramie fabric with a thickness of 1.7 mm and 50-, 80-, and 120-mm-long tubes. The measured parameters were specific energy absorption, energy absorption, and peak load. The total energy absorption increased with the increase in the length of the tubes. The failure mode of the tested tubes was examined, and the mid-length and local buckling were considered as the main sources of failure. The woven natural ramie was used in the textiles for years. However, the results of this paper can be significant because of the limited research employing woven ramie as reinforcement for composites.

Recycled Paper Fibres as Sound Absorbing Material

Noise pollution is a workplace hazard which causes loss of hearing, depending on the sound pressure level and duration of exposure. Because duration of exposure is usually uncontrollable, sound absorbers are used to reduce the value of sound pressure level. A common method to reduce noise is to use porous sound absorbers made out of mineral wools or glass fibres. However, these materials pose health risks and are non-recyclable. This project aimed to fabricate a sound absorber using recycled paper which is in the form of egg cartons as an alternative to the abovementioned fibres. Paper fibres posses high fibre porosity and can be manufactured in a manner which the properties can be easily controlled, making them ideal to be made into sound absorbers. Furthermore, they are biodegradable, do not pose health risks and can be manufactured into different shapes easily. Recycled paper was first turned into pulp, blended and poured into moulds. Different amounts of pulp was compressed until the sample size was approximately 20 mm thick and then dried in a furnace dryer at 600C for 12 hours. The samples were tested using a two-microphone, transfer function impedance tubes according to the ISO 10534-2 standard. Its porosity was determined using a modified wash basin method. The results indicate that the optimum panel has an average noise reduction coefficient, (NRC) of 0.50, which qualifies it to be used as a sound absorbing material. It also encounters its maximum value of 0.98 which occurred at the 1575-1675 Hz range. When compared to other materials, recycled paper has similar properties as coir fibre and is quite comparable to other commercial sound absorbers at the same thickness.