Faleh A. Al-Sulaiman

Evaluation of the performance of local fibers in evaporative cooling

A special test setup is designed to evaluate the performance of three natural fibers to be used as wetted pads in evaporative cooling. The chosen fibers are date palm fibers (stem), jute and luffa. As a reference, a widely used commercial wetted pad is chosen. The performance criteria include cooling efficiency, material performance and cooling efficiency degradation. The results show that the average cooling efficiency is highest for jute at 62.1%, compared to 55.1% for luffa fibers, 49.9% for the reference commercial pad and 38.9% for date palm fiber. Material performance tests comprise salt deposition and bio-degradation (mold forming). Jute has the least salt deposition followed by palm and luffa fibers. The commercial type has the highest salt deposits. The highest resistance to mold forming is offered by luffa followed by palm fibers. The commercial type and jute have very poor performance. The results of the cooling efficiency degradation indicate that luffa has an overall advantage over the other fibers. Palm fibers and the commercial type have a significant reduction in the cooling efficiency, while jute has the highest deterioration. The total results indicate that luffa has an overall advantage over the other fibers. However, if the jute surface can be treated to offer higher mold resistance characteristics, it would provide the best alternative.

Mechanical Properties of Date Palm Fiber Reinforced Composites

Mechanical properties of several laminates of date palm leave (DPL) reinforced composites are investigated. Three different processes to construct these composite laminates are assessed. These are wet lay-up with simple vacuum bagging, autoclaving with vacuum bagging and Vulcan press moulding. Several fiber orientation and dimensions are tested. Two types of resins are selected. The first is a high temperature curing Phenolic (phenol formaldehyde) resin. The second is a two-component Bisphenol resin with amine-based slow curing agent. The average tensile strength ranged between 127.4 and 152.3 MPa for long unidirectional fibers and 8.4 to 62.6 MPa for short and medium length fibers respectively (depending on process and resin type). The Bisphenol laminates have better mechanical properties. These laminates have consistently 25 to 50% higher tensile strength than Phenolic laminates. The bending strength ranged between 120.6 and 342.3 MPa (at 500 mm/min loading speed) depending on fiber length. Short fiber Bisphenol laminates have excellent fatigue life characteristics (over 466,000 and 653,000 cycles at 70% and 60% of maximum stress loads respectively). The process parameters and resin types have significant effects on the laminate properties. The water absorption of the laminates ranged between 2.3 to 5.8% for the Phenolic laminates (depending on the test method and manufacturing process used). The water absorption of Bisphenol laminates ranged between 10 and 40%. The produced laminates were very stable to handle all required machining processes as construction panels. They were successfully subjected to several machining processes such as milling, end milling, hack sawing and drilling.

Exergy analysis of major recirculating multi-stage flash desalting plants in Saudi Arabia

A simple and auspicious scheme to estimate exergy losses in multi-stage flash (MSF) plants is discribed. This method is used to evaluate major MSF plants in Saudi Arabia, namely, Al-Khobar II, Al-Jubail II, and Shuaibah. This study presents a quantitative assessment of the exergy losses, exergetic efficiency, and exergy-destruction term for each plant. The effect of these terms on the performance of the three MSF plants when operating at various top brine temperature (load conditions) is also investigated. The results obtained for the three plants show that the three MSF desalting plants are highly irreversible with exergetic efficiencies ranging from 1.12–10.38%. The associated total exergy destruction is found to range from 6.75–26.16% MW, with the exergy-destruction term e ranging from 40.52–77.96 kJ/kg. The exergetic efficiency of brine heaters, when calculated separately, ranges from 72.20–87.98%, with exergy losses of 1.20–5.42 MW. The study concludes that the top brine temperature (TBT) is directly proportional to the exergy losses in the MSF plants.

Prediction of the Thermal Conductivity of the Constituents of Fiber-Reinforced Composite Laminates: Voids Effect

There are inherent difficulties in the direct measurement of the thermal conductivity of fibers. The need to determine the thermal conductivity of fibers for design purposes has been the motivation of the present work. Four empirical formulas are developed to predict the thermal conductivities of fiberreinforced composite laminates (FRCLs) and their constituents. Two of these models utilize the parallel and series thermal models of composite walls in predicting the thermal conductivity of the fibers. The models are tested at different fiber-to-resin volume ratios (30/70, 45/55, 50/50, 60/40, and 75/25) and various fiber-to-resin thermal conductivity ratios (0.5, 1, 2, 3, 4, and 5). These ranges indicate the physically possible fiber to resin volume thermal conductivity ratios including the extreme possible cases. The effect of the air void volume ratio on the thermal conductivity of the composite laminates is investigated. The range of the investigated void fractions also represent the practical ranges. The predicted thermal conductivity of the fiber can be accurately predicted throughout the spectrum via three models. The first model is a first-order formula (R 2 = 0.9148) based on the parallel series structure of the constituents within the composite laminate. The second model is a second-order formula (R 2 = 0.9308) which is also based on the parallel series structure of the constituents. A third model is developed to predict the fiber thermal conductivity as a direct function of the composite thermal conductivity and other composite constituents and volume ratios. This correlation has a coefficient of determination (R 2 = 0.9632). A fourth model is developed to predict the effective thermal conductivity of the laminate. The effective thermal conductivity of the FRCL is predicted with very high accuracy (R 2 = 0.9948). Another use of these models is to determine the fiber to resin volume ratio or air void volume fraction (if all thermal conductivities of fiber, resin, and laminate are known).

Vibration analysis of drillstrings with string—borehole interaction

Abstract Drillstring vibration is one of the major causes for a deteriorated drilling performance, and if left untreated may result in a complete failure of the drilling process. Although the variations in the drilling load, stick-slip, and whirling are known to be the primary causes of severe vibrations, they often give rise to excessive flexural deformations and subsequent string—borehole interaction. Drillstring contact-impact interaction with borehole results in high-frequency excitations, which further deteriorate the drilling performance, and may cause damage to the bottomhole assembly. Modelling of impact is crucial to understanding the associated dynamic response, and to providing means for controlling the collision phenomenon. A continuous force—displacement law is introduced to model the impulsive force during the short-lived interval of impact, wherein the material compliance and damping coefficients are determined from energy balance relations. The impact model is integrated to the dynamic model of the whole drillstring; including drillpipes and drillcollars. The dynamic model of the rotating drillstring is formulated using a Lagrangean approach in conjunction with the finite-element method. The model accounts for the torsional-bending inertia coupling and the axial-bending geometric non-linear coupling. In addition, the model accounts for the gyroscopic effect and the effect of the gravitational force field. The generalized eigenvalue problem is solved to determine modal transformations, which are invoked to obtain the reduced-order modal form of the dynamic equations. The developed model is integrated into a computational scheme to calculate time-response of the drillstring system in the presence of string—borehole collisions.

Machinability of Kevlar® 49 Composite Laminates While Using Standard TiN Coated HSS Drills

Abstract This article addresses the machinability of plain weave Kevlar® 49 prepeg composite laminates of different thickness while using 135° split-point TiN coated 6 mm diameter HSS drills. The effect of composite preparation parameters and the drilling conditions on the machinability of the laminates is assessed using the drilling thrust force, cutting torque, and specific cutting energy. The thickness and processing time of the laminates as well as the drilling process parameters were found to influence the maximum value of thrust force and torque as well as the quality of drilled holes. The wear features of the drills used in machining Kevlar composites have been found to be different from the conventional wear patterns that occur during drilling metals and alloys.

Mechanical Properties of Date Palm Leaves

The basic mechanical properties of date palm leaves are investigated. This abundant and cheap fibrous material exhibits very favorable characteristics that can make it an excellent building block in composite structures. The tensile strength (210 MPa) and the specific strength (180 MPa cm3/g) of this fiber are higher than many common building materials (i.e., wood, aluminum and steel). The mechanical properties are dependent on the moisture content of the leaves and the temperature exposure.

Fatigue Life Estimates in Woven Carbon Fabric/Epoxy Composites at Non-Ambient Temperatures

The influence of temperature on fatigue resistance of Plain Weave Woven CFRP isexamined. The 8-ply laminateswere obtained from epoxy resin prepreg fabric layers stacked in two different sequences, producing unidirectional [0]8 and angle plied [0, 0, 45, −45]s orientations. The fatigue tests were carried out at −20, 0, 24, 100 and 150°C. It wasfound that there wasno change in sequence of damage eventsbut duration of each event and hence cumulative damage rateswere different at different temperatures. The fatigue life at elevated temperature was found to decrease with increasing temperature but decreasing temperature below ambient conditions caused an increase in fatigue life for both classes of woven laminates. An analytical model based on stiffness degradation during cyclic loading, which isused in fatigue life prediction of CFRP at ambient temperature conditions has been successfully employed to estimate fatigue lives of WCFRP at non-ambient temperatures. A parameter D critical, which isa function of testing temperature, and represents the least stiffness value in modulus degradation curve, was introduced. Estimates of fatigue lives were compared with experimentally determined fatigue lives. Reasonably good correlation has been obtained between calculated and experimentally determined values of fatigue at all test temperatures considered in the present investigation.

Estimation of monthly average daily and hourly solar radiation impinging on a sloped surface using the isotropic sky model for Dhahran, Saudi Arabia

In this paper the isotropic sky method of Liu and Jordan is used to theoretically estimate the monthly average daily and hourly solar radiation impinging on an unshaded tilted surface in Dhahran, Saudi Arabia. The surface receiving solar radiation is assumed to be fixed at a tilt angle, β, equal to the latitude of Dhahran, O and oriented such that it is facing south with zero azimuth angle, γ. The calculation of total radiation on a sloped surface from measurements on a horizontal surface is discussed. Monthly average daily and hourly solar radiation values are then tabulated. The results obtained can be effectively employed in solar process design calculations.

Actuator placement in lumped parameter systems subjected to disturbance

Abstract This paper is intended to report preliminary results in the area of actuator placement in a lumped parameter system subjected to a disturbance at a known location. A criterion has been established relating the optimal actuator position to the location of the disturbance. Linear time invariant lumped parameter models were chosen to investigate the effect of control actuator locations. The results of the simulations show that the optimal actuator location is the one closest to the source of the unknown disturbance. This work suggests placing the actuator as close as possible to the source of the known disturbance.