Browsing by Author "Addali, Abdulmajid"
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Item Open Access Condition Monitoring of Helical Gears Using Acoustic Emission (AE) Technology(Cranfield University, 2013-07) Hamel, Mhmod A. A.; Mba, David; Addali, AbdulmajidTechniques such as vibration monitoring, thermal analysis and oil analysis are well established as means to have been used to improve reliability of gearboxes and extend time-to-failure. In this area Acoustic Emission (AE) technology is still in its infancy but the attention shown by researchers towards this method has increased dramatically because several studies have shown the AE offers the important advantage of improved sensitivity over more conventional monitoring tools for the early detection and prediction of gear failure. Helical gear lubrication is critically important for maintaining the integrity of operating gears and the oil also prevents asperity contact at the gear mesh thereby protecting the gears from a deterioration process and surface failures. In gear systems, there are three types of lubrication regimes: Dry Running, Boundary Lubrication (BL), Hydrodynamic Lubrication (HL) and Elastohydro-dynamic Lubrication (EHL). The last regime is associated with the normal operating running condition of gears. Acoustic emissions were acquired from gears and analysed for different lubrication regimes (dry, BL, HL and EHL regimes at different temperatures), and corresponding specific film thicknesses (λ) levels. The results showed an inverse relationship between AE signal levels and specific film thickness (λ) of the oil. This relation was used to determine the lubrication regime from the measured AE signals. For instance, dry running had the highest AE levels which were attributed to the metal-to-metal contact of the gear mesh. The BL regime had relatively high AE levels which also attributed to the level of asperity contact is greater than the oil film thickness. The HL regime was characterized by the lowest AE levels due to the lubricant oil completely separating the teeth during gear meshing. Finally, the EHL regime showed intermediate AE levels compared to the BL and HL regimes because the oil film was less than for the HL regime but greater than for the BL regime. It is shown that the application of advanced signal processing methods is necessary for monitoring helical gears; Kurtosis and Spectral Kurtosis were used to investigate the AE signatures and found to be effective in de-noising (spectral kurtosis) acquired signals. Acoustic Emission proved to be a powerful tool to detect the oil regime for both defective and non-defective conditions. It is concluded that the experimental findings of this research programme will provide the foundations for significant advancement in the application of AE for the determining the lubrication regime present within a helical gearbox and for the detection of developing gear faults. This should give a new impetus in the field of maintenance and prevention of human and material catastrophes. Several papers presenting the findings of this research have been published in international journals and given at conferences.Item Open Access Defect source location of a natural defect on a high speedrolling element bearing with Acoustic Emission(PHM Society, 2011-09-25) Eftekharnejad, Babak; Addali, Abdulmajid; Mba, DavidThe application of Acoustic Emission (AE) technology for machine health monitoring is gaining ground as powerful tool for health diagnosis of rolling element bearings. The successful application of AE to life prognosis of bearings is very dependent on the ability of the technology to identify and locate a defect at its earliest stage. Determining source locations of AE signals originating in real time from materials under load is one of the major advantages of the technology. This paper presents results which highlight the ability of AE to locate naturally initiated defects on high-speed roller element bearing in-situ. To date such location has only be successfully demonstrated at rotational speeds of less than 100 rpm.Item Open Access Deposition of stainless steel thin films: an electron beam physical vapour deposition approach(MDPI, 2019-02-14) Ali, Naser; Teixeira, Joao Amaral; Addali, Abdulmajid; Saeed, Maryam; Al-Zubi, Feras; Sedaghat, Ahmad; Bahzad, HusainThis study demonstrates an electron beam physical vapour deposition approach as an alternative stainless steel thin films fabrication method with controlled layer thickness and uniform particles distribution capability. The films were fabricated at a range of starting electron beam power percentages of 3–10%, and thickness of 50–150 nm. Surface topography and wettability analysis of the samples were investigated to observe the changes in surface microstructure and the contact angle behaviour of 20 °C to 60 °C deionised waters, of pH 4, pH 7, and pH 9, with the as-prepared surfaces. The results indicated that films fabricated at low controlled deposition rates provided uniform particles distribution and had the closest elemental percentages to stainless steel 316L and that increasing the deposition thickness caused the surface roughness to reduce by 38%. Surface wettability behaviour, in general, showed that the surface hydrophobic nature tends to weaken with the increase in temperature of the three examined fluids.Item Open Access Diagnosis of low-speed bearing degradation using acoustic emission techniques(Cranfield University, 2017-01) Alshimmeri, Fiasael; Addali, Abdulmajid; Amaral Teixeira, JoaoIt is widely acknowledged that bearing failures are the primary reason for breakdowns in rotating machinery. These failures are extremely costly, particularly in terms of lost production. Roller bearings are widely used in industrial machinery and need to be maintained in good condition to ensure the continuing efficiency, effectiveness, and profitability of the production process. The research presented here is an investigation of the use of acoustic emission (AE) to monitor bearing conditions at low speeds. Many machines, particularly large, expensive machines operate at speeds below 100 rpm, and such machines are important to the industry. However, the overwhelming proportion of studies have investigated the use of AE techniques for condition monitoring of higher-speed machines (typically several hundred rpm, or even higher). Few researchers have investigated the application of these techniques to low-speed machines (<100 rpm), This PhD addressed this omission and has established which, of the available, AE techniques are suitable for the detection of incipient faults and measurement of fault growth in low-speed bearings. The first objective of this research program was to assess the applicability of AE techniques to monitor low-speed bearings. It was found that the measured statistical parameters successfully monitored bearing conditions at low speeds (10-100 rpm). The second objective was to identify which commonly used statistical parameters derived from the AE signal (RMS, kurtosis, amplitude and counts) could identify the onset of a fault in either race. It was found that the change in AE amplitude and AE RMS could identify the presence of a small fault seeded into either the inner or the outer races. However, the severe attenuation of the signal from the inner race meant that, while AE amplitude and RMS could readily identify the incipient fault, kurtosis and the AE counts could not. Thus, more attention needs to be given to analysing the signal from the inner race. The third objective was to identify a measure that would assess the degree of severity of the fault. However, once the defect was established, it was found that of the parameters used only AE RMS was sensitive to defect size. The fourth objective was to assess whether the AE signal is able to detect defects located at either the centre or edge of the outer race of a bearing rotating at low speeds. It is found that all the measured AE parameters had higher values when the defect was seeded in the middle of the outer race, possibly due to the shorter path traversed by the signal between source and sensor which gave a lower attenuation than when the defect was on the edge of the outer race. Moreover, AE can detect the defect at both locations, which confirmed the applicability of the AE to monitor the defects at any location on the outer race.Item Open Access The effect of aluminium nanocoating and water pH value on the wettability behavior of an aluminium surface(Elsevier, 2018-02-27) Ali, Naser; Teixeira, Joao Amaral; Addali, Abdulmajid; Al-Zubi, Feras; Shaban, Ehab; Behbehani, IsmailExperimental investigation was performed to highlight the influence of ionic bounding and surface roughness effects on the surface wettability. Nanocoating technique via e-beam physical vapor deposition process was used to fabricate aluminium (Al) film of 50, 100, and 150 nm on the surface of an Al substrate. Microstructures of the samples before and after deposition were observed using an atomic force microscopy. A goniometer device was later on used to examine the influence of surface topography on deionised water of pH 4, 7 and 9 droplets at a temperature ranging from 10 °C to 60 °C through their contact angles with the substrate surface, for both coated and uncoated samples. It was found that, although the coated layer has reduced the mean surface roughness of the sample from 10.7 nm to 4.23 nm, by filling part of the microstructure gaps with Al nanoparticles, the wettability is believed to be effected by the ionic bounds between the surface and the free anions in the fluid. As the deionised water of pH 4, and 9 gave an increase in the average contact angles with the increase of the coated layer thickness. On the other hand, the deionised water of pH 7 has showed a negative relation with the film thickness, where the contact angle reduced as the thickness of the coated layer was increased. The results from the aforementioned approach had showed that nanocoating can endorse the hydrophobicity (unwitting) nature of the surface when associated with free ions hosted by the liquid.Item Open Access Effect of multi-walled carbon nanotubes-based nanofluids on marine gas turbine intercooler performance(MDPI, 2021-09-04) Almurtaji, Salah; Ali, Naser; Teixeira, Joao Amaral; Addali, AbdulmajidCoolants play a major role in the performance of heat exchanging systems. In a marine gas turbine engine, an intercooler is used to reduce the compressed gas temperature between the compressor stages. The thermophysical properties of the coolant running within the intercooler directly influence the level of enhancement in the performance of the unit. Therefore, employing working fluids of exceptional thermal properties is beneficial for improving performance in such applications, compared to conventional fluids. This paper investigates the effect of utilizing nanofluids for enhancing the performance of a marine gas turbine intercooler. Multi-walled carbon nanotubes (MWCNTs)-water with nanofluids at 0.01–0.10 vol % concentration were produced using a two-step controlled-temperature approach ranging from 10 °C to 50 °C. Next, the thermophysical properties of the as-prepared suspensions, such as density, thermal conductivity, specific heat capacity, and viscosity, were characterized. The intercooler performance was then determined by employing the measured data of the MWCNTs-based nanofluids thermophysical properties in theoretical formulae. This includes determining the intercooler effectiveness, heat transfer rate, gas outlet temperature, coolant outlet temperature, and pumping power. Finally, a comparison between a copper-based nanofluid from the literature with the as-prepared MWCNTs-based nanofluid was performed to determine the influence of each of these suspensions on the intercooler performance.Item Open Access Experimental investigation of bubble activity at an early stage using te acoustic emission technique in two-phase flow systems.(2018-01) Alhashan, Taihiret; Addali, Abdulmajid; Teixeira, Joao AmaralThis thesis presents an experimental investigation and identifies the feasibility of the use of AE technology to detect and monitor both early stage bubble occurrence and throughout the boiling process. The research programme also included monitoring of bubble formation/collapse phenomena in ball and globe valves using AE techniques. It was demonstrated that an AE piezoelectric sensor can detect pressure pulses associated with bubble occurrence during pool boiling and cavitation in flow through valves. For the pool boiling test, a dedicated test-rig was used to diagnose and monitor bubble formation. It was concluded that bubble occurrence is detectable with AE techniques and there is a clear relationship between increasing AE levels and bubble formation during the boiling process. For the valve tests, a purpose-built test-rig was used to monitor and detect cavitation phenomena with various flow rates and different valve opening percentages. It was shown that AE will detect incipient cavitation and that there is a clear correlation between AE signal levels and the flow rate through the ball and globe valves at a constant opening percentage. This investigation successfully demonstrated that AE monitoring is capable of early diagnosis and monitoring of bubble formation phenomena in boiling processes and valves. This research developed a methodology and prototype framework for using the AE technique for detection and diagnosis of early bubble formation and collapse, allowing cavitation development to be tracked, and maintenance activity to be planned to maximise equipment life and minimise downtime.Item Open Access Experimental investigation of the influences of different liquid types on acoustic emission energy levels during the bubble formation process(Springer, 2017-09-08) Alhashan, Taihiret; Addali, Abdulmajid; Teixeira, Joao Amaral; Naid, AbdelhamidBubble formation phenomena in a two-phase gas/liquid system occur in many industries that involve boiling; such as desalination stations, nuclear reactors, chemical plants, and fluid piping transportation and processes. Bubble formation phenomena cause problems, such as a decrease in equipment efficiency, vibration, noise, and solid surface erosion. Applications of the acoustic emission (AE) technique for monitoring bubble formation and burst stages in boiling processes are marginal in terms of extension in comparison to other applications of the AE technique. The use of the AE technique in this experimental investigation covers the frequency range between 100 and 1000 kHz, showing that the AE sensor can detect acoustic emissions from an occurrence of bubble formation. Statistically, it was found that the best AE parameter indicator for bubble formation was AE-RMS (root mean square).Item Open Access Exploration of the possibility of acoustic emission technique in detection and diagnosis of bubble formation and collapse in valves(International Organization of Scientific Research, 2016-11-30) Alhashan, Taihiret; Addali, Abdulmajid; Amaral Teixeira, JoaoThe application of acoustic emission (AE) technique in detection and monitoring of bubble formation and collapse in valves are presented in this review. The generation of AE signals and the basic compositions of AE detection system are briefly explained. The applications of AE technique in valves are focused on condition monitoring and detection bubble formation (bubble cavitation), and leakage of water through valves. All results prove that the AE technique works well for detection and diagnosis of failures during valves.Item Open Access Flow structure and heat transfer of jet impingement on a rib-roughened flat plate(MDPI, 2018-06-13) Alenezi, Abdulrahman H.; Almutairi, Abdulrahman; Alhajeri, Hamad M.; Addali, Abdulmajid; Gamil, Abdelaziz A. A.The jet impingement technique is an effective method to achieve a high heat transfer rate and is widely used in industry. Enhancing the heat transfer rate even minimally will improve the performance of many engineering systems and applications. In this numerical study, the convective heat transfer process between orthogonal air jet impingement on a smooth, horizontal surface and a roughened uniformly heated flat plate is studied. The roughness element takes the form of a circular rib of square cross-section positioned at different radii around the stagnation point. At each location, the effect of the roughness element on heat transfer rate was simulated for six different heights and the optimum rib location and rib dimension determined. The average Nusselt number has been evaluated within and beyond the stagnation region to better quantify the heat transfer advantages of ribbed surfaces over smooth surfaces. The results showed both flow and heat transfer features vary significantly with rib dimension and location on the heated surface. This variation in the streamwise direction included both augmentation and decrease in heat transfer rate when compared to the baseline no-rib case. The enhancement in normalized averaged Nusselt number obtained by placing the rib at the most optimum radial location R/D = 2 was 15.6% compared to the baseline case. It was also found that the maximum average Nusselt number for each location was achieved when the rib height was close to the corresponding boundary layer thickness of the smooth surface at the same rib position.Item Open Access Heat removal in axial flow high pressure gas turbine(Cranfield University, 2016) Alhajeri, Hamad; Amaral Teixeira, Joao; Addali, AbdulmajidThe demand for high power in aircraft gas turbine engines as well as industrial gas turbine prime mover promotes increasing the turbine entry temperature, the mass flow rate and the overall pressure ratio. High turbine entry temperature is however the most convenient way to increase the thrust without requiring a large change in the engine size. This research is focused on improving the internal cooling of high pressure turbine blade by investigating a range of solutions that can contribute to the more effective removal of heat when compared with existing configuration. The role played by the shape of the internal blade passages is investigated with numerical methods. In addition, the application of mist air as a means of enhanced heat removal is studied. The research covers three main area of investigation. The first one is concerned with the supply of mist on to the coolant flow as a mean to enhancing heat transfer. The second area of investigation is the manipulation of the secondary flow through cross-section variation as a means to augment heat transfer. Lastly a combination of a number of geometrical features in the passage is investigated. A promising technique to significantly improve heat transfer is to inject liquid droplets into the coolant flow. The droplets which will evaporate after travelling a certain distance, act as a cooling sink which consequently promote added heat removal. Due to the promising results of mist cooling in the literature, this research investigated its effect on a roughened cooling passage with five levels of mist mass percentages. In order to validate the numerical model, two stages were carried out. First, one single-phase flow case was validated against experimental results available in the open literature. Analysing the effect of the rotational force, on both flow physics and heat transfer, on the ribbed channel was the main concern of this investigation. Furthermore, the computational results using mist injection were also validated against the experimental results available in the literature. Injection of mist in the coolant flow helped achieve up to a 300% increase in the average flow temperature of the stream, therefore in extracting significantly more heat from the wall. The Nusselt number increased by 97% for the rotating leading edge at 5% mist injection. In the case of air only, the heat transfers decrease in the second passage, while in the mist case, the heat transfer tends to increase in the second passage. Heat transfer increases quasi linearly with the increase of the mist percentage when there is no rotation. However, in the presence of rotation, the heat transfers increase with an increase in mist content up to 4%, thereafter the heat transfer whilst still rising does so more gradually. The second part of this research studies the effect of non-uniform cross- section on the secondary flow and heat transfer in order to identify a preferential design for the blade cooling internal passage. Four different cross-sections were investigated. All cases start with square cross-section which then change all the way until it reaches the 180 degree turn before it changes back to square cross-section at the outlet. All cases were simulated at four different speeds. At low speeds the rectangle and trapezoidal cross-section achieved high heat transfer. At high speed the pentagonal and rectangular cross-sections achieved high heat transfer. Pressure loss is accounted for while making use of the thermal performance factor parameter which accounts for both heat transfer and pressure loss. The pentagonal cross-section showed high potential in terms of the thermal performance factor with a value over 0.8 and higher by 33% when compared to the rectangular case. In the final section multiple enhancement techniques are combined in the sudden expansion case, such as, ribs, slots and ribbed slot. The maximum heat enhancement is achieved once all previous techniques are used together. Under these circumstances the Nusselt number increased by 60% in the proposed new design.Item Open Access Heat removal in high pressure turbine seal segments(Cranfield University, 2017-02) Alenezi, Abdulrahman H.; Amaral Teixeira, Joao; Addali, AbdulmajidAn important parameter for turbomachinery designers is “clearance control”, because the clearances between interfaces must be set to optimum values to maximize power output, operational life and efficiency. Leakage of hot gas result- ing from excessive clearance, can lead to flow instabilities, components overheat- ing, lower cycle efficiency and a dramatic increase in specific fuel consumption (SFC). Seal segments are used to reduce blade tip leakage, maintain coolant air flow and the stability of rotor-dynamic systems, helping to maximize blade perfor- mance. Seal segments in the High-Pressure Turbine (HPT) stages are one of the hottest components as they face the hot gases coming from the combustion chamber with temperatures which can reach 1700 0 C and which makes them sub- ject to oxidation, erosion, and creep. Thus, seal segments need to be protected. They are currently cooled using jet impingement techniques, passing cooling air (supplied by the high-pressure stage of the compressor) through channels to di- rectly impinge on the hot surfaces. The focus of this research was to improve the jet impingement cooling of the seal segments in HPTs by investigating methods that provide more effective heat removal. The role played by configurations of ribs (surface roughness using be- spoke turbulators), custom-made seal-segments, and surface features such as contouring, both in isolation and combination, were investigated using numerical methods. A set of 174 simulations were carried including the use of uniform and non-uniform roughness elements with different shapes and heights. Firstly, three different uniform roughness elements were tested, a square cross-sectional continuous rib, a hemi-spherical pin-fin and a cubical pin-fin for three jet impingement angles of α=90°, 60° and 45°. Each roughness element was also tested for six different heights (e) between 0.25 mm and 1.5 mm in increments of 0.25 mm. Results are presented in the form of average Nusselt number within and beyond the stagnation region. Secondly, the effect of using a roughness element with a square cross section in the shape of a circle, on the average Nu was investigated for four different radial locations (R), three jet angles (α) and six rib heights (e). Finally, the roughness element used was continuous, of square cross-sec- tion, in the shape of tear drops and reversed tear drops. This meant the rib did not act as a total barrier to flow in either the uphill or downhill direction.Item Open Access Identifying bubble occurance during pool boiling employing acoustic emission technique(Elsevier, 2017-12-11) Alhashan, Taihiret; Addali, Abdulmajid; Teixeira, Joao Amaral; Elhashan, SaidThis paper reports the results of a study for the early detection of bubble formation during the boiling process using acoustic emission. The feasibility of using AE technology to detect and monitor early bubble formation during pool boiling is assessed, and the results show that AE technology is an affective tool for this purpose. There is a clear correlation between the AE signal levels and height of the water level above the heated surface during the boiling process. The different types of heated fluid influence AE energy levels during the bubble formation process. Statistically, it was found that the best AE parameters to indicate bubble formation were AE-RMS, AE-Energy and AE-Amplitude.Item Open Access Investigation of the influence of flow rate on bubble formation and collapse in ball values at various opening percentages using an AE technique(The British Institute of Non-Destructive Testing, 2018-06-01) Alhashan, Taihiret; Addali, Abdulmajid; Teixeira, Joao AmaralBall valves are popularly used in many different industrial processes and hydraulic systems because of their light weight and simple structure. However, they are susceptible to cavitation phenomena and the growth and collapse of the bubbles formed lead to erosion and pitting of the metal surfaces. This paper presents the monitoring and detection of bubble formation at an early stage in a ball valve using acoustic emission (AE). It is shown that AE will detect incipient cavitation and that there is a clear correlation between AE signal level and the flow rate through the ball valve at a constant opening percentage.Item Open Access Investigation on the performance of nanofluids due to preparation effects and operational conditions.(2019-10) Alsayegh, Naser; Teixeira, Joao Amaral; Pilidis, Pericles; Addali, AbdulmajidNanofluids are advanced type of fluids that are produced by dispersing nanoparticles within a non-dissolving liquid. In heat transfer applications, these suspensions have shown to be superior to conventional heat transfer fluids in terms of thermal performance because of their enhanced effective thermal properties. The effective thermal conductivity of nanofluid depends on several factors, such as the preparation method employed, particles concentration, colloidal stability, thermal conductivities of both basefluid and solid particles used, … etc. Furthermore, the suspension effective thermal conductivity can only have a value within the range of the added nanoparticles (highest) and the hosting fluid (lowest) thermal conductivities. Thus, to obtain an optimum effective thermal conductivity for a certain mixture with minimum degradation in the aforementioned property, the nanofluid needs to be homogeneously dispersed while sustaining its short and long-term stability. This is one of the main challenges seen today with such type of advanced fluids. Moreover, the nanofouling effect associated with these suspensions in operational conditions is another important factor that needs to be focused on, as it tends to change the surface wettability behaviour depending on the fluid and deposited surface properties, and hence can increase or decrease the heat transfer performance of the system. To address the previous challenges, the thesis at hand investigates the effect of nanofluid fabrication approach on its stability and pH value, and explores the influence of deposited particles of similar surface materials on the wettability behaviour of the surface. In order to achieve this, a two-step controlled temperature approach was used to fabricate the nanofluids at different set of fixed temperatures using a bath type ultrasonicator. The as- prepared suspensions were then characterised in terms of changes in pH value and stability using a pH meter and the sedimentation photograph capturing method, respectively. In addition, an electron beam physical vapour deposition technique was used to form nanoscaled layers on surfaces of similar materials to the evaporant source, so that a reflection of the nanofouling build-up on surfaces can be obtained, after which the wettability was examined, through a goniometer device, by varying the extracted liquid conditions. The results have shown that increasing the nanoparticles concentration had caused the fluid alkalinity level to increase, while the rise in nanofluid sonication temperature had led to a decrease in its pH value, and vice versa. Furthermore, a general correlation was developed to predict the changes in pH value for similar fabricated suspensions, which illustrated an overall accuracy of ~92% in its prediction capability. The shelving-life evaluation of aluminium – water dispersion has showed that the nanofluids fabricated via the two-step controlled temperature approach at 30ᴼC had better short and long-term stabilities than the ones produced by the conventional method. Moreover, the wettability behaviour of aluminium surfaces was seen to depend on the deposited aluminium film thickness, surface characteristics, and water properties; but in general, the water of pH 7 has demonstrated a tendency to enhance the hydrophilicity of the surface, while water of lower and higher pH values were seen to have the opposite outcome. On the other hand, the wettability behaviour of copper or stainless steel surfaces has shown to greatly depend on the surface topographical structure compared to the attached liquid properties.Item Open Access Monitoring Gas Void Fraction In Two-Phase Flow With Acoustic Emission(Cranfield University, 2010-04) Addali, Abdulmajid; Mba, DavidThe two-phase gas/liquid flow phenomenon can be encountered over a range of gas and liquid flow rates in the chemical engineering industry, particularly in oil and gas production transportation pipelines. Monitoring and measurement of their characteristics, such as the gas void fraction, are necessary to minimise the disruption of downstream process facilities. Thus, over the last decade, the investigation, development and use of multiphase flow metering system have been a major focus for the industry worldwide. However, these meters suffer from several limitations in some flow conditions such as Slug flow regime. This research presents experimental results correlating Acoustic Emission measurements with Gas Void Fraction (GVF) in a two-phase air / water flow. A unique experimental facility was modified to accommodate an investigation into the applicability of the Acoustic Emission (AE) technology in monitoring two-phase gas\liquid flow. The testing facility allowed for investigations over a range of superficial liquid velocities (0.3 to 2.0 ms-1) and superficial gas velocities (0.2 to 1.4 ms-1). The influence of several variables such as temperature, viscosity and surface roughness were also investigated. Measurements of AE for varying gas void fractions were compared to conductive probe measurements and results showed a direct correlation between the AE energy and the gas void fraction. It is concluded that the GVF can be determined by measurement of Acoustic Emission and this forms the major contribution of this thesis.Item Open Access New pH correlations for stainless steel 316L, alumina, and copper(I) oxide nanofluids fabricated at controlled sonication temperatures(Trans Tech Publications, 2019-06-19) Ali, Naser; Amaral Teixeira, Joao; Addali, AbdulmajidThis research investigates the pH value of stainless steel (SS) 316L/ deionised water (DIW), alumina (Al2O3)/DIW, and copper (I) oxide (Cu2O)/DIW nanofluids prepared using a two-step controlled sonication temperature approach of 10°C to 60°C. The nanoparticles volumetric concentration of each family of as-prepared nanofluid ranged from 0.1 to 1.0 vol%, using as-received nanopowders, of 18 – 80 nm average particles size. Furthermore, the pH measuring apparatus and the measurement procedure were validated by determining the pH of commercially supplied calibration fluids, of pH 4, 7, and 10. Following the validation, pH correlations were obtained from the experimental measurements of the 0.1, 0.5, and 1.0 vol% nanofluids in terms of varied sonication bath temperatures and volumetric concentrations. Those correlations were then combined into one robust pHnf correlation and validated using the pH data of the 0.3 and 0.7 vol% nanofluids. The new proposed correlation was found to have a 2.18%, 0.92%, and 0.63%, average deviation from the experimental pH measurements of SS 316L, Al2O3, and Cu2O nanofluids, respectively, with an overall prediction accuracy of ~ 92%.Item Open Access On the role of nanofluids in thermal-hydraulic performance of heat exchangers - a review(MDPI, 2020-04-11) Almurtaji, Salah; Ali, Naser; Teixeira, Joao Amaral; Addali, AbdulmajidHeat exchangers are key components in many of the devices seen in our everyday life. They are employed in many applications such as land vehicles, power plants, marine gas turbines, oil refineries, air-conditioning, and domestic water heating. Their operating mechanism depends on providing a flow of thermal energy between two or more mediums of different temperatures. The thermo-economics considerations of such devices have set the need for developing this equipment further, which is very challenging when taking into account the complexity of the operational conditions and expansion limitation of the technology. For such reasons, this work provides a systematic review of the state-of-the-art heat exchanger technology and the progress towards using nanofluids for enhancing their thermal-hydraulic performance. Firstly, the general operational theory of heat exchangers is presented. Then, an in-depth focus on different types of heat exchangers, plate-frame and plate-fin heat exchangers, is presented. Moreover, an introduction to nanofluids developments, thermophysical properties, and their influence on the thermal-hydraulic performance of heat exchangers are also discussed. Thus, the primary purpose of this work is not only to describe the previously published literature, but also to emphasize the important role of nanofluids and how this category of advanced fluids can significantly increase the thermal efficiency of heat exchangers for possible future applications.Item Open Access A review on nanofluids: Fabrication, stability, and thermophysical properties(Hindawi, 2018-06-04) Ali, Naser; Teixeira, Joao Amaral; Addali, AbdulmajidNanofluids have been receiving great attention in recent years due to their potential usage, not only as an enhanced thermophysical heat transfer fluid but also because of their great importance in applications such as drug delivery and oil recovery. Nevertheless, there are some challenges that need to be solved before nanofluids can become commercially acceptable. The main challenges of nanofluids are their stability and operational performance. Nanofluids stability is significantly important in order to maintain their thermophysical properties after fabrication for a long period of time. Therefore, enhancing nanofluids stability and understanding nanofluid behaviour are part of the chain needed to commercialise such type of advanced fluids. In this context, the aim of this article is to summarise the current progress on the study of nanofluids, such as the fabrication procedures, stability evaluation mechanism, stability enhancement procedures, nanofluids thermophysical properties, and current commercialisation challenges. Finally, the article identifies some possible opportunities for future research that can bridge the gap between in-lab research and commercialisation of nanofluids.Item Open Access Slug Velocity Measurement and Flow Regime Recognition Using Acoustic Emission Technology(Cranfield University, 2013-07) Alssayh, Muammer Ali Ahmed; Mba, David; Addali, AbdulmajidSlug velocity measurement and flow regime recognition using acoustic emission technology are presented. Two non-intrusive and three intrusive methods were employed to detect the slug regime and measure its velocity using AE sensors. For the non-intrusive methods, AE sensors were placed directly on the exterior of the steel pipe section of the test rig with and without clamps. The intrusive method involved using different waveguide configurations with the AE sensors flush with the inner wall of the pipe. The experimental study presented investigated the application of Acoustic Emission (AE) technology for detecting slug velocity in addition to differentiating flow regime in two-phase (gas/liquid) flow in horizontal pipes. It is concluded that the slug velocity can be determined with acoustic emission (AE) sensors. The results were compared to slug velocities measured using high speed camera (HSC) and Ultrasound Transit Time (UST) techniques with good agreement between the three techniques at low gas void fraction (GVF). However, at high GVF (up to 95%) where the UST technique has limitations in application, the AE and HSC offered a good agreement. Flow regimes were also differentiated by using a combination of AE technology and Kolmogorov–Smirnov test technique. Stratified, slug and bubble regimes were recognised differentiated.