Particle Volume Concentration Research Articles

ENHANCED EFFECTIVENESS AND THERMAL PERFORMANCE FACTOR OF NICKEL NANOFLUID FLOW IN A PLATE HEAT EXCHANGER

The effectiveness, number of transfer units, and carbondioxide (CO2) emissions of water based nickel nanofluids flow in a plate heat exchanger were discussed in this paper. Additionally, thermo-physical properties, heat transfer, and friction factor were also estimated. The water based nickel nanofluids were prepared and experiments performedat various Reynolds number (300 to 1000) and particle volume concentrations (0.1% to 0.6%). At, 60 oC and ϕ = 0.6% nanofluid, the thermal conductivity and viscosity increase are 33.92% and 67.45% respectively. At the same concentration with a Reynolds number of 707 the effectiveness, number of transfer units, and thermal performance factor were enhanced by 21.33%, 38.6%, and 19.8% while the convective heat transfer coefficient is enhanced by 57.35% over water alone data. At ϕ = 0.6%, the maximum total embodied energy is decreased to 556.13 MJ at, whereas for water, it is 675 MJ with the cost of plate heat exchange getting dropped by 17.39% at ϕ = 0.6% of nanofluid. The environmental CO2 emissions released by the stainless steel material used in the plate heat exchanger is lowered to 21.87 kg of CO2 at ϕ = 0.6% of nanofluid while it is 26.55 kg of CO2 for base fluid.

An experimental study of thermal and hydraulic performance in vehicle cooling system tube with hybrid nanofluids

The aim of work is to observe and analyze the effect of hybrid alumina – oxide and copper oxide nanofluids on the performance with water-based fluid in compact tube. The hybrid nanofluids was synthesized at different volume concentration (0.0 %, 0.40 %, 0.60 % 0.80 %) and Reynolds numbers existing between 4000 and 8000 at 40 °C to 70 °C. The present study helps in analysing the influence of hybrid nanofluids on heat transfer characteristics and finding the effects on heat transfer enhancement as compared to base fluid. Minimum heat transfer coefficient value 310 W/m2K was observed at 0.02 % volume concentration and the Reynolds number was 4000. Pressure drop completely depends upon properties like viscosity, specific heat, thermal conductivity, and Reynolds number. The pressure drop rises with rise in the Reynolds number and increasing volume concentration (v/v) of alumina oxide particles.

Characteristics of Diesel/N-Butanol Blend on a Common Rail Diesel Engine with Exhaust Gas Recirculation

20% n-butanol is blended in diesel by volume (noted as D80B20) and experiment has been carried out to study the effect on the combustion and emission characteristics based on a common rail diesel engine with exhaust gas recirculation (EGR) system. The results reveal that D80B20 has longer ignition delay, shorter combustion duration and higher maximum in-cylinder temperature than pure diesel (noted as D100). Further, the number concentration and volume concentration of ultrafine particles decrease significantly while NOX emissions increase a little with the addition of n-butanol. When the exhaust gas is induced into cylinder, NOX emissions significantly decrease and ultrafine particles emissions increase. The number geometric mean diameters and volume geometric mean diameters of ultrafine particles increase with EGR ratio. Compared to D100 without EGR, D80B20 with 20% EGR ratio can reduce both NOX and ultrafine particles emissions at 0.14 MPa BMEP and 0.56 MPa BMEP.

Effect of optimum process parameters in rotational-magnetorheological poppet valve polishing

ABSTRACT Poppet valves are commonly used as relief valves, pressure regulators, selectors, and inlet and exhaust valves in automobile internal combustion (IC) engines. Nanofinishing of ridge profiles of the poppet valve is a challenging task due to its narrowness. This article presents the precise finishing of narrow ridge profiles of poppet valves at optimum process parameters in the rotational-magnetorheological fluid-based finishing (R-MRFF) process using a novel magnet fixture. Statistical analysis is used to determine the impact of each process parameter. Further, simulation of finishing forces in the R-MRFF process is performed using software that applies the finite element technique. Investigation of finishing forces assists in controlling the process precisely. An analytical model is formulated for calculating the number of abrasive particles acting on nickel–aluminum–bronze alloy poppet profiles to anticipate final material dislodgement. The significant process parameters for surface roughness are abrasive volume concentration, poppet rpm, poppet vertical feed rate, and carbonyl iron particle (CIP) volume concentration. The minimum obtained surface roughness (Ra) at poppet valve profiles is 23.5 nm. The final finished poppet valve may have a longer service life and improved wear and corrosion resistance at maximum temperature and pressure.

Development and Implementation of Energy-Efficient Magnetorheological Fluid Bypass Damper for Prosthetics Limbs Using a Fuzzy-Logic Controller

Walking behaviour in amputees with lower-limb loss is absent from shock-absorbing properties. A damper can be used to reduce the impact of ground reaction force (GRF) during heel strikes. Magnetorheological fluid (MRF) damper is deemed the best option for this application as it includes the advantages of both passive and active dampers. An enhanced MRF damper is essential in supplying the appropriate current and damping force levels. Therefore, an energy-efficient design is required to prolong the battery life used by MRF dampers in prosthetic limbs. This paper investigates two fluids of different properties and magnetic particle volume content. A bypass damper was used to observe the response of both fluids. The findings highlighted that an MRF with a higher percentage of solid weight could produce a more significant damping force with a lesser amount of applied current. This work presents a simulation study on implementing the energy-efficient MRF damper utilizing a Fuzzy-PID controller in a prosthetic limb.

Numerical and Experimental Study of Hydraulic Performance and Wear Characteristics of a Slurry Pump

The slurry pump is widely used in ore mining, metal smelting, petrochemical, and other industries, mainly to transport fluid media containing large solid particles. Importantly, it is easy to damage the impeller of a slurry pump in the operation process, which greatly affects the performance of the pump. In this paper, a 25 MZ slurry pump was selected as the research object, and the Euler–Euler multiphase flow model was employed to analyze the internal flow characteristics of the slurry pump under the conditions of clear water and solid–liquid two-phase flow. Additionally, the flow characteristics of each part under different flow conditions were studied, and the effects of different particle volume concentrations, particle sizes, and pump speeds on the impeller’s wear characteristics and hydraulic performance were analyzed. In order to verify the reliability and accuracy of the numerical simulation results, clean water and solid–liquid two-phase flow wear tests of the slurry pump were carried out, and the results showed that a high solid volume fraction and solid–phase slip velocity were generated at the junction of the blade leading edge and the rear cover plate, thus leading to easier wear of the blade. Therefore, enhancing the strength of the junction between the blade leading edge and the rear cover plate is beneficial for improving service life and should be considered in the design of slurry pumps.

Innovative experimental method for particle bridging behaviors in natural fractures

Lost circulation is a major challenge in drilling naturally fractured formations. The most common solution for this problem is to add particulate lost circulation materials (LCM) in the drilling fluid to plug the fracture loss zones. A successful plugging depends on whether the LCM particles can form an effective bridging and seal the complex loss zones. Therefore, an investigation on the bridging behavior of particles in natural fractures is needed. In this study, a combination of three-dimensional scanning and numerical control mechanical engraving technology is employed to demonstrate a complex transparent model fracture (TMF) which can accurately analyze the internal spatial characteristics of the natural fractures. A series of visualization experiments for different particle size, particle volume concentration, and differential pressure were conducted by injecting regular particles into the TMF. The migration and bridging behavior of the particles in the TMF were recorded using a high-speed camera. Results showed that the particle bridging structures and their distribution in natural fractures are affected by the concentration, size, differential pressure, and the local aperture distribution of the fracture. Two bridging structures, namely, single-particle bridging (SB) and double-particle bridging (DB) were observed at the entrance or inside of the TMF. The type of bridging structure which plays a dominant role in the process of fracture plugging is mainly determined by the particle concentration. SB dominates at particle concentrations of 0.5 vol%, 1 vol% or 2 vol%, whereas DB dominates at concentration of 5%. The visualization experimental results help to better understand the bridging mechanism of the particulate LCMs in natural fractures. The results indicate that irregularity of the natural fracture aperture, which is usually neglected by conventional experiments, has a crucial effect on the structure and position of particle bridging.

Improved green and sintered density of alumina parts fabricated by binder jetting and subsequent slurry infiltration

Additive Manufacturing (AM) of ceramics is a constantly emerging field of interest both in research and in industry. Binder jetting-based AM of ceramics in particular offers the opportunity to produce large ceramic parts with a high wall thickness at a high throughput. One limitation is that it requires flowable powders, which are generally coarse and thus exhibit only limited sintering activity. The resulting low sintered densities impede the commercial binder jetting-based production of dense oxide ceramics. We present an approach to efficiently increase the green density of binder jetted alumina parts by optimized slurry infiltration, which also leads to a significant increase in the sintered density. In a first step, alumina parts were fabricated via binder jetting, using a 20-µm-sized alumina powder, yielding relative green densities of about 47–49%. Initial sintering studies with powder compacts showed that sintering even above 1900 °C is not sufficient to achieve acceptable densification. Therefore, green samples were infiltrated with a highly filled ceramic slurry to fill the remaining pores (about 2–5 µm in size) with smaller particles and thus increase the packing density. Particle volume content (40–50 vol%), particle size (100–180 nm) and the infiltration procedure were adapted for tests on cuboid samples to achieve a high penetration of the green bodies and a high degree of pore filling. In this way, the relative green density could be increased starting from about 47% after binder jetting, to 73.4% after infiltration and drying. After sintering at 1675 °C densities above 90% could be achieved, yielding three-point bending strengths up to 145 MPa. As a conclusion, this approach can be regarded as a promising route for overcoming the drawbacks of the binder jetting process on the way to denser, mechanically more stable sintered alumina parts.

Vertical distributions of aerosol microphysical and optical properties based on aircraft measurements made over the Loess Plateau in China

Aerosol microphysical properties, scattering and absorption characteristics, and in particular, the vertical distributions of these parameters over the eastern Loess Plateau, were analyzed based on aircraft measurements made in 2020 during a summertime aircraft campaign in Shanxi, China. Data from six flights were analyzed. Statistical characteristics and vertical distributions of aerosol concentration, particle size, optical properties, including aerosol scattering coefficient (σsp), backscattering ratio (βsc), Ångström exponent (α), single-scattering albedo (SSA), partially-integrated aerosol optical depth (PAOD), and black carbon concentration (BCc), were obtained and discussed. Mean values of aerosol particle number concentration (Na), particle volume concentration (Va), mass concentration (Ma), surface concentration (Sa), and particle effective diameter (EDa) were 854.92 cm−3, 13.37 μm3 cm−3, 20.06 μg/m3, 170.08 μm3 cm−3, and 0.47 μm, respectively. Mean values of BCc, σsp(450, 525, 635 nm), βsp(525 nm), α(635/450), and SSA were 1791.66 ng m−3, 82.37 Mm−1 at 450 nm, 102.57 Mm−1 at 525 nm, 126.60 Mm−1 at 635 nm, 0.23, 1.47, and 0.92, respectively. Compared with values obtained in 2013, Na decreased by 60% and Ma decreased by 45%, but the scattering coefficients increased in different degrees. In the vertical direction, aerosol concentrations were higher at lower altitudes, decreasing with height. Vertical profiles of σsp, βsp, α(635/450), and BCc measured during the six flights were examined. Two peaks in Na were identified near the top of the boundary layer and between 2000 and 2200 m. Fine particles with EDa smaller than 0.8 μm are dominant in the boundary layer and coarse aerosols existed aloft. Aerosol scattering properties and BCc in the lowest layer of the atmosphere contributed the most to the total aerosol radiative forcing. SSA values were greater than 0.9 below 2500 m, with lower values at higher levels of the atmosphere. On lightly foggy days, SSA values were greater than 0.9, and aerosols played a cooling role in the atmosphere. On hazy days, lower-level SSA values were generally greater than 0.85, with aerosols likely having a warming effect on the atmosphere. 48-hour backward trajectories of air masses during the observation days showed that the majority of aerosol particles in the lower atmosphere originated from local or regional pollution emissions, contributing the most to the total aerosol loading and leading to high values of aerosol concentration and radiative forcing.

Laboratory studies of suspended particle volume concentration in atmosphere using a smartphone

The article presents the results of laboratory studies of the effect of volume concentration of suspended particles in contrast to the luminous slits image obtained by smartphone cameras of SAMSUNG Galaxy A3 and Honor 8 Lite. Experimentally it was found that a pattern of change in contrast to the luminous slits image from the volumetric concentration of suspended particles appears under ambient light. The pattern of contrast change can be expressed by an exponential function. The correlation coefficient is 0.97. Cigarette smoke was used as suspended particles.

Variability in Oceanic Particle Size Distributions and Estimation of Size Class Contributions Using a Non-parametric Approach.

A dataset of nearly 400 measurements of the particle size distribution (PSD) compiled from the Pacific, Atlantic, and Arctic Oceans is used to examine variability in the magnitude and shape of the PSD, and to characterize the partitioning of particle number, cross‐sectional area, and volume concentration among defined size intervals. The results indicate that the relative contributions of three size classes based upon the pico‐, nano‐, and microplankton size range exhibit substantial changes among measures of particle size and between oceanic environments. The single‐slope power law model commonly employed to characterize the PSD in aquatic studies is demonstrated to have significant limitations in capturing the complexity of PSD shapes observed for natural particle assemblages, and in consequence poorly predicts the relative contributions of these different size intervals. We show that specific percentile diameters derived from the cumulative distributions of particle size are strongly correlated with the contributions of these three size classes, and that these non‐parametric descriptors of the cumulative distribution provide superior performance for estimating their contributions while requiring no assumption of underlying PSD shape. A comparison of these predictive relationships with independent field measurements suggests that this approach is generally robust for particle assemblages representing a wide diversity of marine environments.

Variability of scattering and backscattering of marine particles in relation to particle concentration, size distribution, and composition off the eastern hainan coast in the south China sea

The light scattering and backscattering coefficients of particles (bp(λ) and bbp(λ)) and their association with particle concentration, size distribution, and composition off the eastern Hainan coast in the South China Sea (SCS) were analyzed between August and September 2013. Variations in bp(532) and bbp(532) were correlated to changes in the LISST-based total cross-sectional area and volume concentration of particles (AC and VC). Two significantly different covariations between bbp(λ) and bp(λ) and chlorophyll a concentration (Chla) were observed, and all samples were clearly separated into two groups (Group A and Group B) using the threshold relationship between bbp and Chla. Samples in Group B, most of which were collected in the nepheloid layer, showed higher bp/AC and bbp/AC than those in Group A. This indicates the presence of inorganic particles with higher np in Group B than in Group A. The relationship between bbp and Chla for Group A could be well fitted by a published model involving a constant backscattering background independent of Chla. A significant relationship (R2 = 0.85) was observed between bbp and Chla in the Chla maximum layer, which was different from that in other layers. This finding might imply that both an increase in the micro-phytoplankton community and a decrease in the contribution of background backscattering to bbp at the Chla maximum layer. Understanding this variability of beam-scattering properties off the eastern Hainan coast can improve our understanding of marine biogeochemical processes at a regional scale, and can also promote the application of these regional bio-optical relationships for ocean color.

Analysis of the effect of ultrasonic vibration on nanofluid as coolant in engine radiator

The paper discusses the combined methods of increasing heat transfer, effects of adding nanofluids and ultrasonic vibration in the radiator using radiator coolant (RC) as a base fluid. The aim of the study is to determine the effect of nanoparticles in fluids (nanofluid) and ultrasonic vibration on the overall heat transfer coefficient in the radiator. Aluminum oxide nanoparticles of 20–50 nm in size produced by Zhejiang Ultrafine powder & Chemical Co, Ltd China were used, and the volume concentration of the nanoparticles varied from 0.25 %, 0.30 % and 0.35 %. By adjusting the fluid flow temperature of the radiator from 60 °C to 80 °C, the fluid flow rate varies from 7 to 11 lpm. The results showed that the addition of nanoparticles and ultrasonic vibration to the radiator coolant increases the overall heat transfer coefficient by 62.7 % at a flow rate of 10 liter per minute and temperature of 80 °C for 0.30 % particles volume concentration compared to pure RC without vibration. The effect of ultrasonic vibration on pure radiator coolant without vibration increases the overall heat transfer coefficient by 9.8 % from 385.3 W/m2·°C to 423.3 W/m2·°C at a flow rate of 9 liter per minute at a temperature of 70 °C. The presence of particles in the cooling fluid improves the overall heat transfer coefficient due to the effect of ultrasonic vibrations, nanofluids with a volume concentration of 0.25 % and 0.30 % increased about 10.1 % and 15.7 %, respectively, compared to no vibration. While, the effect of nanoparticles on pure radiator coolant at 70 °C enhanced the overall heat transfer coefficient by about 39.6 % at a particle volume concentration of 0.35 % compared to RC, which is 390.4 W/m2·°C to 545.1 W/m2·°C at 70 °C at a flow rate of 10 liter per minute

CFD simulation of laminar free convection flows of nanofluids in a cubical enclosure

Understanding the physics behind heat transfer within an enclosure especially in the natural convection domain has many important applications. The heat transfer performance of nanofluids inside a cubical enclosure with an internal heat source fixed on the side-wall of the enclosure will be investigated under natural convection flow condition in this paper. A three-dimensional two-phase mixture model will be developed and validated for this investigation. Computational fluid dynamic (CFD) simulations will be undergone using an in-house solver developed on simplified marker and cell (SMAC) algorithm within a collocated grid by finite difference method. The time dependent flow and characteristics of heat transfer for nanofluids will be investigated with pure water as the base fluid dispersed with different nanoparticles. In addition, parametric studies will also be performed by varying the particle volume concentrations (0%≤Φ ≤ 3%), particle diameters (25 nm ≤ Dp ≤ 50 nm) and Grashof numbers (103 ≤ Gr ≤ 106). The particle volume concentration when increased in a nanofluid gives more affinity to heat absorption. Velocity increase of particles leads to the efficient mixing of nanofluid and so an increase in Grashof number also leads to heat transfer enhancement. Decrease in particle diameter is the final parameter which shows a heat transfer increase.

Experimental studies of combustion and emission characteristics of diesel engine fueled with diesel/cyclopentanone blend

Cyclopentanone from lignocelluloses is a promising renewable biofuel and can be used as diesel alternative fuel. Cyclopentanone has excellent fuel properties and high intramolecular oxygen content, which has the potential in promoting combustion and reducing emissions. In this study, the effects of blending cyclopentanone with diesel on the combustion and emission of common rail diesel engine were investigated. The novelty of this study is to figure out which blending ratio is the most promising for diesel engine. Cyclopentanone is blended with diesel with 10% and 20% ratio by vol., noted as C10 and C20, respectively. Double injection strategy (pre-injection and main-injection) was adopted in this study. Compared with pure diesel, blending cyclopentanone can prolong the ignition delay, increase the peak heat release rate and increase the peak in-cylinder temperature. The emission tests indicate that blending cyclopentanone can effectively reduce the particle number concentrations (PNC) and particle volume concentrations (PVC) compared to diesel. Further, the number geometric mean diameters (NGMD) of cyclopentanone diesel blend fuels are lower than those of diesel and the reduction increases with cyclopentanone blending ratio. However, a little increase in NOx emission is observed. With the increase of EGR ratio, the NOx emissions of all test fuels decrease obviously, the PNCs and PVCs of diesel and C10 increase. PNCs and PVCs of C20 almost remain unchanged when the EGR ratio is no higher than 8%. Consequently, with 8% EGR ratio, C20 has the best effect in reducing both particle and NOx emissions and it has great potential for application on diesel vehicles.

A comprehensive statistical approach for determining the effect of two non-ionic surfactants on thermal conductivity and density of Al2O3–water-based nanofluids

The purpose of this study was to evaluate the effect of surfactants on the density and thermal conductivity values of water, as well as to separately evaluate the variations in these values due to particle–surfactant interaction. To this end, Al2O3–water-based nanofluids with different particle volume concentrations (0.3–1.1%) were prepared, as were Tween 80 and Tergitol NP-10 surfactants at different weight ratios (0.2–0.8%). Density and thermal conductivity of obtained nanofluids were then measured at temperatures ranging from 298 to 338 K. Statistical evaluation was carried out to determine the effects of surfactant type, temperature, particle concentration, and surfactant concentration on density and thermal conductivity. Additionally, the sedimentation method, zeta potential, and particle size analysis were utilized to estimate the stability of nanofluids. Results showed that when base fluid (water and surfactant) density was determined, the use of surfactants had no additional impact on the density of the nanofluids. The highest observed improvement in thermal conductivity was 7.5%, obtained using 0.2 wt% Tween 80 and 1.1 vol% Al2O3 at 338 K. Although particle concentration was the most influential factor and surfactant type was not statistically significant for density ratio, the thermal conductivity ratio was affected by other factors in addition to particle concentration.

Analysis of minimum specific energy consumption and optimal transport concentration of slurry pipeline transport systems

Slurry pipeline transport is widely used in several industrial processes. Calculating the specific power consumption (SPC) and determining the best working conditions are important for the design and operation of transportation systems. Based on the Shanghai Jiao Tong University high-concentration multi-sized slurry pressure drop (SJTU-HMSPD) pipeline-resistance-calculation model, the SJTU-SPC model for calculating the power required to transport a unit volume of solid materials over a unit pipeline length is established for a slurry transport system. The said system demonstrates a uniformity coefficient in the 1.26–7.98 range, median particle size of 0.075–4 mm, particle volume concentration of 10–60%, and pipeline diameter of 0.203–0.8 m. The results obtained were successfully verified against existing experimental data. The influence of parameters, such as particle-gradation uniformity coefficient, median particle size, pipe diameter, and particle volume concentration, on the SPC were analysed. The results revealed that the greater is the uniformity coefficient, the smaller is the minimum specific energy consumption and the larger the optimal transport concentration for a constant, median particle size slurry. As observed, the optimal transport concentration for broad-graded sand equalled approximately 48%. These results supplement the conclusions of existing research, indicating that the optimal transport concentration is approximately 30% and provides theoretical support for high concentration transportation of broad graded slurry.

Vertical assessment of the mineral dust optical and microphysical properties as retrieved from the synergy between polarized micro-pulse lidar and sun/sky photometer observations using GRASP code

The potential of the synergetic use of both polarized Micro-Pulse Lidar (P-MPL) and Sun/sky photometer observations by using the GRASP (Generalized Retrieval of Atmosphere and Surface Properties) code for retrieving dust properties has been analysed in this work. Both the columnar and height-resolved variables have been evaluated in comparison, respectively, with AERONET data and vertical P-MPL-derived profiles of the dust optical and microphysical properties over a mid-latitude site. The linear regression analysis together with the mean fractional bias values and relative differences between datasets have been used as the statistical proxies for assessing the degree of agreement by examining 24 selected dust cases. Regarding columnar variables, the microphysical properties (both the particle volume concentration and effective radius) presented a high confidence level between GRASP and AERONET retrievals by taking into account all the proxies. In addition, the single scattering albedo and the real refractive index presented a good confidence level at all the wavelengths, as well, unlike the imaginary refractive index, which was confident at 440 nm only. By analysing the height-resolved properties of the total particle backscatter coefficient and the total volume concentration, the degree of agreement shows a high confidence between GRASP retrievals and P-MPL-derived variables, which were retrieved by using an alternative, well-validated, polarization-based methodology. Indeed, these results can be essential for application with no-polarized systems (e.g., ceilometers, lidars …). Overall, the synergy between P-MPL and Sun/sky photometer measurements regarding the usual co-location of both MPLNET and AERONET networks in combination with GRASP code represent an improved approach to derive the height-resolved optical and microphysical properties for mineral dust particles with a high degree of confidence.

Poly(l-lactic acid)/lithium ferrite composites: Electrical properties

Composites of lithium ferrite, LiFe5O8 (LFO) particles, dispersed in the biopolymer poly (l-lactic acid) (PLLA) were prepared by solvent casting in concentrations from 0 to 19.5 wt%, which were characterized by thermal analysis (TGA/DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy and impedance spectroscopy (IS). As neat PLLA, all obtained composites are semi-crystalline, but the crystallinity decreasing with percentage LFO increase. Moreover, a good dispersion of LFO particles was found, with no interactions with the polymeric matrix. For the lower LFO content (3.5 wt%), dynamical relaxation processes were probed by IS, allowing to disclose subtle differences relative to the neat matrix. Above that concentration, the conductivity dominates and follows the percolation law above a quite low volume concentration of conductive particles (5.45%v/v). Therefore, depending on the LFO content different applications can be envisaged: energy storage for low concentrations and electromagnetic radiation shielding for concentrations above the percolation threshold.

Optical Properties and Biochemical Indices of Marine Particles in the Open Mediterranean Sea: The R/V Maria S. Merian Cruise, March 2018

A rich data set on particulate matter optical properties and parameters (beam attenuation coefficient, volume concentration, particle size and PSD slope), accompanied by measurements of biochemical indices (particulate organic carbon, particulate nitrogen and their stable isotopic composition) was obtained from the surface to deep waters across the Mediterranean Sea, in March-April 2018. A decrease of beam attenuation coefficients, total particle volume concentrations, particulate organic carbon and nitrogen concentrations was noted towards the eastern Mediterranean Sea (EMed) in comparison to the western Mediterranean Sea (WMed). LISST-derived optical properties were significantly correlated with water mass characteristics. Overall, the most turbid water mass identified in the Mediterranean Sea was the Surface Atlantic water (AW), and the most transparent was the Transitional Mediterranean Water (TMW) in the Cretan Sea, whereas a general decrease in particulate matter concentration is observed from the WMed towards the EMed. Relatively depleted δ13C-POC values in the particle pool of the open Mediterranean Sea can be attributed to contribution from terrestrial inputs, mainly via atmospheric deposition. Throughout the entire water column, a significant positive correlation between particle beam attenuation coefficient and particulate organic carbon concentration is observed in the open Mediterranean Sea. Such relationship suggests the predominance of organic particles with biogenic origin. POC concentration and particle median diameter D50 are significantly and negatively correlated both in the WMed and the EMed Sea, confirming that small particles are POC-rich. At depth, a prominent decrease of most measured parameters was observed, with the exception of particle median diameter that increased substantially in the EMed towards the deep sea, suggesting potentially enhanced aggregation processes. The low particle size distribution slope ξ observed in the EMed, corresponding to larger particle populations, supports the above notion. Basin-wide Rayleigh-type isotopic fractionation in vertical profiles of δ15N-PN across the Mediterranean Sea, underlines the differences in the trophic characters of the two sub-basins and highlights the role of circulation changes on biogeochemical parameters and the redistribution of particulate matter as a source of nutrients in the water column.