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This paper aims to investigate the transient behavior of a salinity gradient solar pond(SGSP) under Mediterranean climate. For this propose, a 2D numerical model is developed in which the absorption of solar radiation by different layers of saline water, the wind effect at free surface, the heat losses and the development of the double-diffusive convection in the lower and upper convective zones are considered. The governing equations of continuity, momentum, thermal energy and diffusion are solved using the finite volume method with SIMPLE algorithm. The validity of the numerical model developed in Fortran95 is achieved through the comparisons of the results computed with the available numerical and experimental results obtained by literature studies. Results show that the developed numerical model can predict transient behavior of the SGSPs with a good accuracy. As an application of this model, temperature, salt concentration, energy stored and storage efficiency variations of a proposed SGSP are analyzed under Mediterranean climate. The results show that the lower convective zone(LCZ) temperature increases from 15 °C to around 95 °C whereas the temperature of the upper convective zone(UCZ) varies sinusoidally depending on that of the ambient air. Furthermore, the salt concentration of the LCZ decreases from 250kg/m3 to around 248kg/m3 while that of the UCZ increases from50 kg/m3 to about 52kg/m3. Additionally, the thermal energy stored is around 135MJ with an efficiency of about 38% which confirms the capacity of the SGSP to store thermal energy as sensible heat.

Owing to the high storage capacity of the latent heat energy storage unit (LHSU), it is preferred among other types of thermal energy storage to overcome the mismatch between energy supply and demand. The orientation of the LHSU affects the melting process of the phase change material (PCM), and this effect could vary according to the fin shape of the LHSU. Thus, the present study aims to numerically examine the impact of vertical and horizontal orientations on the longitudinal, spiral, and annular finned shell and tube LHSUs. The computational fluid dynamics simulation solved the time-dependent conservation equations of mass, momentum, and energy in the three-dimensional domain. The enthalpy-porosity and the Boussinesq approximation were used respectively to simulate the PCM phase change and the change in density. The results show that the LHSUs have completely different behavior in the vertical orientation than in the horizontal orientation due to the various obstructions to the natural convection flow induced by the fins, depending on the fin shape, and the direction of natural convection flow. In the vertical orientation, the annular finned LHSU has a faster melting rate than the longitudinal finned LHSU by 25.6%. In contrast, in the horizontal orientation, the longitudinal finned LHSU melted more rapidly than the annular finned LHSU by 52.5%. The spiral finned LHSU performance was moderate between the two other finned LHSUs in both orientations due to its spiral shape that lies between the shape of the annular and longitudinal fins.

Corrosion course is an elective subject in Department of Chemical Engineering at College of Engineering of the University of Diyala (Iraq). It is also adopted in other departments at College of Engineering of the University of Diyala, such as, civil, mechanical and material engineering. The relation between corrosion course in the chemical engineering department and peer corrosion courses in other departments is not clear to the students. Furthermore, corrosion courses are often concentrated on electrochemistry without clear relation with some main chemical engineering courses. The present work is an attempt in the direction of connecting corrosion subject with the other major subjects of chemical engineering program. Some topics of chemical reaction kinetics and thermodynamics principles are applied to corrosion course. The corrosion inhibition behavior of mild steel in hydrochloric acid in the absence and the presence of potassium iodide as a corrosion inhibitor were selected as a case study. The influence of temperature, time and inhibitor concentration was studied using weight loss technique. Theoretical and scientific principles, experimental work, and interpretations were well clarified for the students. The interaction of students with the results was highly impressive and significantly affects the teaching outcomes. The students’ performance during exams was enhanced by 15 ± 5 %. A questionnaire was constructed to interpret the results of current work.

The behavior of anodic porous alumina film formed on an aluminum surface by anodizing in chromic acid solutions was optimized using Box–Wilson experimental design. The film thickness was correlated as a function of temperature, acid concentration, applied voltage, and time. A mathematical model was suggested and optimized. Results of coating thickness indicate that both temperature and time play an important role in the anodizing process. The interaction effect of variables on the film thickness is less pronounced compared with the effect of the main variables. Optimum film thickness obtained during the anodizing process was 10.43 µm at the optimum value of temperature (45 °C) and time (68 min). The polarization measurement of anodized aluminum ASA 6061 in chromic acid shows a high corrosion resistance in the presence of coating. The results confirmed by using surface morphology investigations.

1-[(5-Phenyl-1,3, 4-oxadiazol-2-yl)thio] acetone (POTA) was synthesized and tested as a new corrosion inhibitor for low carbon steel in 1 M hydrochloric acid. The diagnosis of POTA was carried out by FTIR and NMR analysis. Inhibitor performance was investigated using mass loss technique. POTA was acted as a moderate corrosion inhibitor for low carbon steel in 1 M hydrochloric acidic solution with efficiency more than 70%. The inhibitor performance was attributed to the formation of an adsorption layer on the low carbon steel surface. The mechanism of inhibitor adsorption on the low carbon steel surface was according to the Langmuir adsorption isotherm. The value of adsorption heat was within the range of chemical adsorption. Quantum chemical studies were adopted as a theoretical tool to clarify the mechanism of inhibition and to support the experimental part.

The research reports the results of the corrosion rate data of mild steel in H3PO4 acid as a function of temperature and inhibitor concentration. Potassium iodide was used as a corrosion inhibitor. The weight loss technique was used to evaluate the corrosion rate data. Mathematical and statistical analyses were used to interpret the results. Descriptive statistical analyses showed the distribution of data deviate from normal distribution, which means that most of corrosion rate data were distributed at higher level of inhibitor concentration and lower level of temperature and this preferable case in pickling process. Three mathematical models were suggested to represent the data with high correlation coefficients.

Enhancing the effectiveness of solar power, including daytime storage for overnight use, is essential to reduce fossil fuel usage. This work explores the melting behaviour of paraffin wax in shell and tube latent heat thermal storage unit (LHSU) in different configurations and orientations. Numerical simulation were carried out and compared with experimental measurements for non-finned and finned configurations arranged vertically during the melting (charging) process. A commercial paraffin wax was used as a phase change material (PCM). The temperature and liquid fraction of the PCM during the course of the melting process in both configurations were used for model validation. When considering the liquid fraction, the numerical results showed excellent qualitative agreement with the experimental images for all the cases being studied. Specifically, the shape and progress of the melting front showed good agreement between the experiments and numerical results. Furthermore, the model predicted well the experimentally measured temperature in the melting PCM, with a maximum average discrepancy of 3.6%. The validated model was then used to investigate different process configurations. The results indicated that the addition of fins enhanced the melting process by an average of 50%. The non-finned tubes had a superior melting rate in the horizontal orientation over the vertical orientation, while orientation was found to have only a minor impact on the melting process with finned tubes.

In the present study, a mass transfer based theoretical model to investigate the rate of corrosion of an alloy of mild steel in a solution of a carbon oxide-wastewater from oilfield with and without acetic acid is presented. Electrochemical polarization data are evaluated using β – model which takes into account the influence of mass transfer on the corrosion process. An algorithm is built, and two software programs are used in evaluating the corrosion kinetics parameters. The effect of correction factor of mass transfer, which depends on β, on the kinetic reaction parameters is evaluated.The average value of β is 0.42 suggesting a mixed control corrosion mechanism. A mass transfer correction factor (λ) is evaluated at different temperatures and speeds of rotation in the absence and presence of the protective film. The values of λ ≈1 at low overpotential and it decrease as over potential increases. The polarization resistance values in the absence of acetic acid are larger (≈0.5 Ω. cm2) than the polarization resistance values in the presence of acetic acid (≈0.1 Ω. cm2), due to the formation of the protective film. The results are further analyzed by dimensionless groups and empirical equations are obtained with high correlation coefficients.

Present work reports the results of the corrosion current density of mild steel in acidic solution as a function of acid concentration, inhibitor concentration, and temperature. Phenylthiourea was used as concentration a corrosion inhibitor. The work is focused on estimating the optimum mathematical equation and the ANN architecture. Corrosion rate (corrosion current density) was the response or the dependent variable, while inhibitor concentration (0.1, 0.75, and 1 g/l), acid concentrations (1, 3, and 5 M), and different temperatures (303, 313, 323, and 333 K) were the factors or the independent variables of the models. Five mathematical equations and five ANN architectures were suggested. Models were developed and estimated with the aid of a computer program. Linear, Linear – Logarithmic, Logarithmic – Linear, polynomial – individual effect, and polynomial – interaction effect model were estimated. Results show that the polynomial – interaction effect equation was able to accurately predict the measured data with acceptable correlation coefficient (R2 = 0.9803). Linear Model, Multi-Layer Perceptrons, and Radial Basis Function were trained and tested. Multi-Layer Perceptrons with three inputs—multi hidden layers—three outputs (MLP 3:3-6-1:1) was the best ANN with significant performance (R2 = 0.9529). Sensitivity analysis was carried out to study the effect of unavailability of each variable. Both mathematical and ANN analyses showed that the temperature has the most significant influence on the corrosion current density than the other two variables. The temperature individual effect coefficient was 840.6 as compared with 88.5 and − 170.5 for acid concentration and inhibitor concentration, respectively. Interaction effects between variables were also addressed.

The corrosion inhibition of cupronickel alloy in 5% hydrochloric acid (HCl) was investigated in the absence and presence of diethylenetriamine (DETA) and ethylenediamine (EDA) as organic corrosion inhibitors. The effects of inhibitor concentration and temperature were investigated using mass loss method. The results obtained show that EDA act as an anticorrosion material for cupronickel alloy in hydrochloric acid with a maximum performance of 66.7%, while DETA was a poor inhibitor with maximum efficiency of 34.7%. The inhibition performance was found to increase with increase in inhibitor concentration and decrease with increase in temperature. The adsorption of both inhibitors on surface of metal was found to obey Freundlich isotherm. The values of the free energy of adsorption were below − 20 kJ/mol that is indicative of physisorption (physical adsorption). The proposed mechanism of the inhibition process suggests an adsorption of amine groups on metal surface. Mathematical models were also suggested to correlate the dissolution rate data as a function of temperature and inhibitor concentration. High correlation coefficients were obtained between experimental and predicted data. The mean value of residual between the experimental and predicted data was 0.457.

A study on the corrosion inhibition of N80 steel in 0.5 M HCl acid with (S)‑6‑Phenyl‑2,3,5,6‑tetrahydroimidazo[2,1‑b] thiazole was undertaken by conducting electrochemical, weight loss, surface morphology, and FTIR measurements. The inhibition efficiency was found to exceed 95%. An excellent inhibitor performance was attained when a spontaneous layer was formed and adsorbed chemically on the surface of steel. The adsorption of inhibitor followed Langmuir adsorption isotherm. Meanwhile, the inhibitor was categorized as a mixed – type one. FTIR and surface morphology analysis was conducted to validate the results, whereas quantum chemical calculation was applied for justifying the inhibition process.

The photovoltaic/thermal (PVT) system is developed to combine the two separate systems to reduce the located area and cost, improve the efficiency and save lots of materials. However, different PVT designs and configurations had been proposed with air, water, nanofluid, phase change materials (PCM) and mix of these cooling methods. In this paper, a mathematical model was proposed for the new nanofluid/nano-PCM PVT system. Experiments had been conducted to validate the mathematical model results. The comparison confirmed the ability of the proposed mathematical model to satisfactory simulate and match the experimental results. The experimental and mathematical model results show that electrical and thermal efficiencies are 13.7%, 13.2% and 72%, 71.3% respectively. However, it is found that the maximum temperature registered in glass, PV cell, wax, and nanofluid are 41.2, 39.92, 38.8 and 36.5, respectively. The proposed mathematical model accuracy compared and validated with experiment results and shows a good consistent and agreement.

Control of galvanic corrosion of steel–brass couples in petroleum waste water solution by Curcuma longa was studied at different temperatures, inhibitor concentrations, and velocities using the electrochemical polarization technique. Inhibition efficiency was increased with the increase in inhibitor concentration and decreased with both rises in temperature and solution velocity. Maximum inhibitor efficiency was 94.9% in static solution, higher level of inhibitor concentration and lower level of temperature. The adsorption of Curcuma longa obeyed a Langmuir adsorption isotherm by formation of spontaneous physical layer on the metal surface. Scanning electron microscopy of the metal surface revealed that damage was lower in the presence of Curcuma longa. Activation studied via Arrhenius equation showed that the adsorb layer on the surface increases the energy barrier for corrosive dissolution which is also supported by the higher values of activation energy. Mathematical and statistical analyses were also used as a successful tool to correlate the corrosion rate data with operating conditions.

This study investigates the temperature distribution of a liquid-liquid-vapour three-phase direct contact heat exchanger, both experimentally and theoretically. The experimental investigation was conducted using a Perspex column with an internal diameter of 10 cm and 100 cm height. Liquid pentane at its saturation temperature and warm water were used in the dispersed phase and continuous phase respectively. Various dispersed phase flow rates ( 10 , 15 & 20 L / h ) and continuous phase flow rates ( 10 , 20 , 30 & 40 L / h ) were tested using three different sparger configurations ( 7 , 19 & 36 nozzles ) and two different nozzle diameters (1 & 1.25 mm). The results showed that the temperature of the continuous phase decreased with the height of the heat exchanger from its inlet at the top towards its outlet at the bottom. This behaviour was entirely opposite to the dispersed phase that flows counter currently with the continuous phase in the heat exchanger. For the same sparger and constant continuous phase flow rate ( Q c ) , the outlet temperature of the continuous phase was inversely affected by the dispersed phase flow rate ( Q d ) ; while decreasing the nozzle numbers in the sparger led to a decrease in the outlet temperature of the continuous phase. Furthermore, the initial temperature of the continuous phase in terms of the Jakobs number ( Ja ) was found to have a significant positive impact on outlet temperature: the higher the Ja , the higher the outlet temperature. The analytical model had an acceptable agreement with the experimental measurements.

Citrus Aurantium extract consists of many compounds such as Alpha terpineol (AT), Linalool (LI), Linalyl acetate (LA), and Monoterpene hydrocarbons (MH) that suggested as corrosion inhibitors in the ground and protonated states. The current study included treatment of the corrosion process caused by the aggressive ions and/or Acidithiobacillus ferrooxidans bacteria (A. ferrooxidans) through Density Function Theory (DFT). The autodock process was carried out by the Molecular Graphic Laboratory (MGL) and Discovery Studio Visualizer (DSV) software. The bond length, angles, and dihedral were measured to present the adsorption sites of molecules. Also, the HOMO, LUMO, dipole moment, energy gap, and more parameters were used to compare the efficiency of the inhibitors. Total Electron Density (TED) and Electrostatic Surface Potential (ESP) were used to show the sites of adsorption according to electron density. Fukui function used to present the ability of atoms to donate and receipt electrons. Binding energy (Eb) was used to test the inhibition ability of A. ferrooxidans by docking calculations. DFT showed that the order of corrosion inhibition was MH > LI > LA > AT, while bio-corrosion inhibition of A. ferrooxidans was AT > MH > LA > LI. Statistical analysis was used to correlate quantum chemical parameters with inhibition efficiency. A significant model was obtained with a 0.98 correlation coefficient. The calculated inhibition efficiency was compared with the experimental one.

The heat transfer enhancement in terms of temperature of a vertical helically coiled tube heat exchanger is carried out experimentally. The experiments were achieved in a heat exchanger with a 50 cm height and 15 cm internal diameter under four different cold and three hot water mass flow rates and four different airflow rates. At the same time, the temperature difference was taken invariant (ΔT=20°C). To avoid some uncertainties, the hot side temperature of the heat exchanger was measured via k-type thermocouples. The results showed that the increase of air injection flow rate improved heat transfer from the hot stream flowing in the coil to the shell’s cold stream. An intimate thermal mixing when air injected is clearly observed, which could be responsible for the heat exchanger’s thermal enhancement. Finally, the injected air pressure was noticed to be having only a minor effect on thermal performance improvement.

In the present work, graphene oxide quantum dots (GOQDs) prepared via electrochemical method was used as a liquid phase corrosion inhibitor. The structure and compositions of GOQDs were characterized by Fourier transform infra-red (FTIR) and X-ray photoelectron spectroscopy (XPS). The corrosion behavior of Q235 steel in 1 M hydrochloric acid solution in the absence and presence of different concentrations of GOQDs at different temperatures was investigated using weight loss and electrochemical measurements. The steel surface morphology was investigated with the implementation of XPS, scanning electron microscopy (SEM), and atomic force microscopy (AFM). It was found that the prepared GOQDs presented the best inhibition efficiency over 94%. The characterization studies revealed that prepared GOQDs contains functional groups such as carboxyl, hydroxyl, and aldehyde groups, which can spontaneously self-assembles on the metal surface to form adsorbed film, the adsorption isotherm showed that the adsorption process obeyed the Langmuir equation. The electrochemical polarization measurements demonstrated that GOQDs served as a mixed type inhibitor with the primarily inhibitive performance on anodic reaction, which is in well agreement with the adsorption free energy results.

Thermal energy storage plays an essential role in energy systems to reduce the mismatch between the energy supply and demand. Phase change materials are widely used in different technologies but suffer from low heat transfer performance. This numerical study aims to investigate the enhancement in the melting thermal characteristics of lauric acid as a phase change material by using Ansys-Fluent. Three inner tubes of heat transfer fluid were employed with four different arrangements: inline-central array (normal case, Case A), downward and upward triangle arrays (Case B and C) and an arc array at the shell bottom (Case D). Results revealed that the arc array and downward triangle configurations reduced the melting time by about 76% and 72%, respectively. However, the upward triangle tube arrangements increased the melting time by about 10% compared with the normal case.

A neutron beam has been used to measure the volume fraction of crude oil in water of non- flow two-phase mixture experimentally.241Am-Be neutron source were used with an activity of 3.7x104 MBq. The volume fraction was simulated by using small plastic tubes filled with oil and immersed in non-flow water tube. The results show that it is feasible to measure the volume fraction of crude oil in a crude oil-water mixture.

An experimental investigation of the volumetric heat transfer coefficient in a three-phase direct contact condenser was carried out. A 75-cm long cylindrical Perspex column with a 4 cm diameter was used. Only 48 cm of the column was utilised as the active direct contact condensation height. Pentane vapour at three different initial temperatures (40°C, 43.5°C and 47.5°C), with differing mass flow rates, and tap water at a constant initial temperature (19°C) with five different mass flow rates were employed as the dispersed phase and the continuous phases, respectively. The results showed that the volumetric heat transfer coefficient increased with increasing mass flow rate ratio (variable dispersed phase mass flow rate per constant continuous phase mass flow rate), the continuous phase mass flow rate and holdup ratio. An optimal value of the continuous phase mass flow rate is shown for an individual dispersed phase mass flow rates. This value increases with increasing vapour (dispersed) phase mass flow rate. Furthermore, it was observed that the initial driving temperature difference had no effect on the volumetric heat transfer coefficient. While, the temperature gained by the continuous phase has a considerable effect.

The emphasis of this current study is to perform a numerical simulation of the solidification behaviour of phase change material for the latent heat thermal storage unit has shell and tube design in order to improve the thermal performance of the latent heat storage unit. A comparison has been carried out for the storage unit using two different alignment, essentially, horizontal and vertical for two configurations plane one (non-finned) and finned one. The outcome results were compared with the experimental results in order to validate the model. Moreover, the transit temperature profile was also presented in this study to get a better understanding for this particular process. The predicated results were shown a good agreement with experimental data that used. The results indicated that when fins is installed solidification process time enhanced with an average percentage of 60% the effect of alignment during solidification process is insignificant for both cases of finned and plane LHSU. It is worth to mention that this study can be used to improve the understanding the thermal performance of the phase change material and to reduce the efforts of the experiential trails in the future investigations.

Theoretical simulation and experimental validation of a new design tube-bundle latent-heat thermal storage (LHTS) working under solar-thermal application conditions was performed. A laboratory-scale experimental test rig was designed and tested for charging and discharging processes by using lauric acid and water as a phase-change material (PCM) and heat-transfer fluid (HTF), respectively. Six equal size tubes with 2 cm diameter and 45 cm length were clamped together with a central diameter tube for carrying the HTF. The temperature of the PCM during charging and discharging in the tubes in the bundle was measured radially. A 3D numerical model using ANSYS FLUENT was developed to simulate the time-dependent liquid fraction, temperature, and stored power of the PCM. The simulation was conducted after the successful validation with the experimental results at different HTF inlet temperatures (70 °C, 75 °C, and 80 °C) and (10 °C, 15 °C, and 20 °C) for charging and discharging processes, respectively, as well as with different Reynolds numbers (750, 1250, and 1750) for both processes. Although the design of the proposed LHTS was very simple, the results revealed that it has a superior thermal performance and fast charging and discharging period when compared to a double-pipe LHTS. Accordingly, the time was shortened by about 85.3% and 82.5% for charging and discharging processes, respectively.

This study examines an innovative design to enhance the natural convection in a rectangular latent heat energy storage unit (LHSU). The new design divides the rectangular plane into different small partitions (1, 2, 4, 8, 16 and 32) to trap the melted phase change material (PCM) and create several melting fronts which accelerate the melting process than with a normal 1-partition LHSU. The number of these partitions was varied by changing the PCM cavity aspect ratio with values 2, 1, 0.5, 0.25, 0.125 and 0.0625 taken. To validate the numerical model developed herein, LHSUs with one and two partitions were tested experimentally. The numerical model using the ANSYS FLUENT, extended the analysis to other partition numbers. Results showed that the natural convection was significantly strengthened by partitioning the LHSU, which shortens the time required for PCM melting. However, an optimal number of partitions were obtained after which improvement ratio was declined. An LHSU with 8 partitions (0.25 aspect ratio partitions) was found as an optimum. In addition, the comparison with a normal 1-partition LHSU found that the PCM melting process was enhanced by 31.2%, 53.6%, 65% and 68% for the LHSUs with 2, 4, 8, and 16 partitions, respectively.

The average volumetric heat transfer coefficient in a spray column liquid–liquid–vapour direct contact evaporator has been experimentally investigated. The experiments were carried out utilising a cylindrical Perspex tube of diameter 10 cm and height and 150 cm. Saturated liquid n-pentane and warm water at 45 °C were used as the dispersed and continuous phases, respectively. Three different dispersed flow rates (10, 15 and 20 L/h) and four different continuous phase flow rates (10, 20, 30 and 40 L/h) were used in the study. The effect of different parameters, such as the initial drop size, continuous and dispersed phase flow rates and sparger configuration, on the average volumetric heat transfer coefficient in the evaporator was studied. The results showed that the average volumetric heat transfer coefficient was reduced as the initial drop size increased. Also, both the continuous phase and the dispersed phase flow rates have a significant positive impact on the average volumetric heat transfer coefficient.

Thermal energy storage plays an important role to control the intermittent nature of renewable energy. This paper presents a numerical study to the enhancement of the melting and solidification rates of phase change material (PCM) mounted in the annulus of a double pipe latent heat storage unit (LHSU). The enhancement is achieved by using the natural inspired fins (branch shape fins). One and two bifurcations branch fins were designed and their effect on the thermal performance of the LHSU was studied and compared with the longitudinal-finned. The result shows that the melting and solidification processes of the branch shape fins contributed to the improvement by about 44% and 46% respectively.

The inhibition action of the Portulaca grandiflora leaf (PGL) extract against corrosion on N80 carbon steel was tested under 0.5 M HCl acidic conditions at variable temperatures and inhibitor concentrations. The performance behaviour of PGL was evaluated by weight loss and electrochemical techniques including polarisation measurement, open circuit potential, and electrochemical impedance spectroscopy. The analysis results of Fourier transform infrared spectroscopy, ultraviolet spectra, and surface morphology strongly support the corrosion rates results. The obtained outcomes show that the inhibitor can effectively inhibit the corrosion of carbon steel in acidic media with a maximum inhibition efficiency of 95% at high levels of temperature (60 °C) and inhibitor concentration (20 mL/L). The adsorption of PGL on the steel surface followed that according to the Langmuir isotherm model. The heat of adsorption values increased from -17.71 kJ mol-1 to -22.03 kJ mol-1 as the temperature increased from 30 to 60°C suggests a mixed-mode of adsorption on the metal surface.

An experimental study on the melting behavior of paraffin wax used as a phase change material (PCM) in a conical coil latent heat energy storage unit (LHSU) was performed. The experiments were conducted concurrently for conical coil and normal coil LHSUs to compare their thermal performances. The effect of heat transfer fluid (HTF) inlet temperature was examined. The evolution of the temperature during charging, the spatial variation in temperatures and captured images of the melting PCM in both LHSUs were compared. The results indicated that the melting rate in the conical coil LHSU was enhanced by 20.97%, 22.13% and 28.32% in comparison with that of normal coil LHSU at HTF inlet temperature of 70 °C, 75 °C and 80 °C respectively. Moreover, the rate of energy stored in the conical coil LHSU was a notably faster than that of the normal coil LHSU. The HTF inlet temperature has a similar effect on both LHSUs by substantially decreasing their melting time.

It has previously been proven that fins can significantly enhance the thermal performance of latent heat thermal energy storage (LHTS) units. Nevertheless, the magnitude of improvement, especially in a horizontal LHTS, is still less than that required to address some of the existing challenges in solar energy applications. The tendency of the phase change material (PCM) at the bottom of the horizontal storage to remain solid because of the absence of convection currents to promote heat transfer must be tackled practically for this technology to be viable in different thermal applications. Thus, the fin configuration around the circumference of the horizontal storage must be optimised to enhance the melting rate and therefore improving efficiency. In the present paper, the thermal performance during the melting process for PCM (RT-50) in a horizontal LHTS unit was studied numerically with a view to optimizing the fin configuration. The baseline case of bare heat transfer fluid (HTF) tubes was compared with finned surfaces with four different fin angles ( θ = 72 o , 60 o , 45 o and 30 o ) with four different heights (0.2, 0.4, 0.6 and 0.8 of the hydraulic radius of the annulus (Rh)). The average temperature of the PCM, its liquid fraction, and velocity distribution during the melting process were investigated. The numerical results showed that increasing fin height (using a fixed fin configuration: θ = 72 o ) significantly improved the thermal performance of the horizontal LHTS. When the fin height was varied from 0 (bare HTF tube) to 0.8 of Rh, a shortening of the total melting time by approximately 50% was observed. For this fin height 0.8 Rh, it was shown that having a smaller angle between the fins, with all of them mounted below the horizontal axis of the LHTS unit, led to significant enhancement in the thermal performance of the storage. This is because the enhanced heat transfer surfaces are targeted to the regions of the LHTS unit where heat transfer is poorest in the bare tube configuration, as mentioned above. Thus, the total PCM melting time was reduced by 6.7%, 14.3%, 16.7% and 10.0% when the fin angle was changed respectively from 72o to 60o, from 60o to 45o, from 45o to 30o, and finally from 30o to 15o.

The electrochemical behavior of mild steel in phosphoric acidic solutions was investigated in the absence and presence of three heterocyclic tetrazoles derivatives using polarization and electrochemical impedance techniques. The corrosion rate is affected by both acid and inhibitors concentration. Inhibitors reduce the corrosion rate values by suppression of anodic dissolution of steel rather than the cathodic process of hydrogen evolution. Corrosion potential values were shifted to positive direction. Addition of inhibitors did not change the mechanism of corrosion process, which indicates that these compounds act by forming a film on metal surface. Impedance measurements showed that the charge transfer resistance increases and the double layer capacity decreases with addition of inhibitors. Charge transfer resistance increased with time. Maximum inhibitor efficiency was 71.5%, which leads to conclude that the studied inhibitors represent moderate anticorrosion materials. Quantum chemical investigations were also used to optimize the chemical structure of inhibitors.

The transient temperature distribution and volumetric heat transfer coefficient during the 16 inception of flooding in a three-phase bubble type direct contact condenser have been 17 experimentally investigated. The flooding mechanism and the factors affecting the onset of 18 flooding of the three-phase direct contact column are not considered. A short Perspex column 19 of 70 cm total height and 4 cm internal diameter utilising two immiscible fluids was studied. 20 Pentane vapour with initial temperatures of 40°C, 43.5°C and 47.5℃ was the dispersed phase 21 and tap water at a constant temperature (19℃) was the continuous phase. Only 48 cm of the 22 column was used as the active height and different mass flow rates of both phases were used. 23 The experimental results showed that the instantaneous temperature distribution along the 24 direct contact column tends to be uniform when the direct contact column is working under 25 flooding conditions. Furthermore, the volumetric heat transfer coefficient increases as the 26 dispersed mass flow rate is increased towards the flooding limit and remains constant along 27 the column height. In addition, the dispersed phase mass flow rate that leads to flooding 28 increased with increasing mass flow rate of the continuous phase. The initial temperature of 29 the dispersed phase did not have a considerable effect on the flooding inception limit under 30 the present experimental conditions

An analytical model for the convective heat transfer coefficient and the two-phase bubble size of a three-phase direct contact heat exchanger was developed. Until the present, there has only been a theoretical model available that deals with a single two-phase bubble and a bubble train condensation in an immiscible liquid. However, to understand the actual heat transfer process within the three-phase direct contact condenser, characteristic models are required. A quasi - steady energy equation in a spherical coordinate system with a potential flow assumption and a cell model configuration has been simplified and solved analytically. The convective heat transfer in terms of Nu number has been derived, and it was found to be a function to Pe number and a system void fraction. In addition, the two-phase bubble size relates to the system void fraction and has been developed by solving a simple energy balance equation and using the derived convective heat transfer coefficient expression. Furthermore, the model correlates well with previous experimental data and theoretical results.

Low-grade energy cycles for power generation require efficient heat transfer equipment. Using a three-phase direct contact heat exchanger instead of a surface type exchanger, such as a shell and tube heat exchanger, potentially makes the process more efficient and economic. This is because of its ability to work with a very low temperature driving force, as well as its low cost of construction. In this study, an experimental investigation of the heat transfer efficiency, and hence cost, of a three-phase direct contact condenser has been carried out utilising a short Perspex tube of 70 cm total height and 4 cm internal diameter. Only 48 cm was used for the direct contact condensation. Pentane vapour with three different initial temperatures (40℃, 43.5℃ and 47.5℃) was contacted with water with an inlet temperature of 19℃. In line with previous studies, the ratio of the fluid flow rates was shown to have a controlling effect on the exchanger. Specifically, the heat transfer efficiency increased virtually linearly with this ratio, with higher efficiencies also being observed with higher flow 2 rates of the continuous phase. The effect of the initial temperature of the dispersed phase was shown to have a lower order impact than flow rate ratio. The capital cost of the direct contact condenser was estimated and it was found to be less than the corresponding surface condenser (shell and tube condenser) by 30 times. An optimum value of the continuous phase flow rate was observed at which the cost of the condenser is at a minimum. Keywords: Three-phase direct contact condenser, heat transfer efficiency, costing