Cold Drop Research Articles

Numerical Study of Heat Transfer During Oblique Impact of a Cold Drop on a Heated Liquid Film

Abstract A three-dimensional study of a cold droplet impacting obliquely on a heated solid flat surface covered with a hot liquid layer has been performed. The drop Weber number, liquid film thickness, and drop impact angle are set to a range from 100 to 800, 0.1 to 0.4, and 0 deg to 60 deg, respectively. The interface evolution and thermal behavior of the drop impingement is well captured using coupled level set and volume of the fluid method (CLSVOF). The code is validated against previously published results both qualitatively and quantitatively. The results show that in the case of oblique drop impact, the crown dynamics and wall heat flux distribution exhibit an asymmetric pattern, with secondary droplets generated solely on the downstream side, as opposed to normal drop impact in which the secondary drops generated around the circumference of the crown. Based on heat flux values, two distinct region within the liquid film exist: (i) impact region around the impact point and (ii) undisturbed region far from the impact region characterized by the impact dynamics. A parametric analysis further reveals that for a moderate Weber number, asymmetric behavior increases as the drop impact angle increases, resulting in a reduction in heat transfer from the solid surface. However, for a drop impacting at an angle of 28 deg, increased asymmetry due to a increase in the Weber number results in significant cooling of the impact region. Furthermore, it is also found that a thinner liquid film promotes higher heat transfer from the solid surface, resulting in a higher wall heat flux.

Effects of die-casting defects on the blister formation in high-pressure die-casting aluminum structural components

The following work aims to present the casting defects effect in AlSi10MnMg alloy structural components on the blister’s possibility. Structural components must exhibit high mechanical properties, specifically high ductility. That requires the heat treatment process. However, the component’s exposure to high temperatures can cause blistering on the surface, which is unacceptable in the final product.For microstructure studies, the samples were cut from regions close to the gating system (hot areas) and those away from it (cold areas). For comparison, the paper studied castings in the as-cast state and after T7 heat treatment. The results suggest that the blistering process begins at casting defects, which create microstructural discontinuities. If gases are present in a discontinuity, they expand during solution treatment, forming surface blisters. The largest blisters form on cold flakes, mainly in casting areas near the gating system.However, smaller blisters form on porosity - both gas and shrinkage. The last casting defects that act as blistering sites are cold drops, cold shots, and thin oxide films occurring mainly in areas away from the gating system.

Circulation weather types as a key factor on runoff initiation and sediment detachment in Mediterranean shrublands

In this research, the circulation weather types (CWTs) associated with individual surface pressure data at different atmospheric heights were used to correlate and quantify soil erosion events collecting soil loss (g m-2), runoff (l m-2) and sediment concentration (g L-1) using field plots and sediment collectors. Representative Mediterranean shrubland, located at Sierra de Enguera (Eastern Spain), was used as a case study where 213 rainfall episodes and related soil loss events were recorded for the 2010-2014 period. Average annual precipitation of 544 mm was registered, summarizing a total of 2,720.1 mm for the five years of the research period. A total of 34.4% of the registered precipitation events ranged from 10 to 29.9 mm, 23.5% from 30 to 49.9 mm, and 15.9% from 50 to 99.9 mm. The dynamic low-pressure with fronts (DLp+f) CWT was found to generate the highest precipitation amount reaching 60.6% of the total precipitation (105 of the 213 events). Over a third (35%) of the precipitation events occurred during Eastern CWT, which accounted for 48% of the total precipitation with average values of 17.6 mm per event. From the total runoff, 65.6% was related to the combined Eastern and cold drops (CD) CWT. The DLp+f CWT was found to produce 48.9% of sediment mobilization, of which 73.5% of this amount was generated by Eastern CWT. The highest sediment concentration event was found for the southern CWT under thermal low-pressure (TLp) reaching 51.65 g L-1, followed by A (anticyclones) with the Eastern CWT (42.23 g L-1). As a whole, the southern is the CWT generating the highest average sediment concentration (28.66 g L-1), followed by Easter CWT. Our findings suggest that CWTs contribute to foreseeing the periods with the highest soil losses and may help to prevent them. We discuss the need to analyse the changes in soil erosion rates due to CWT to better characterize the soil erosion process and assess the soil erosion rates, improve the current soil erosion models and investigate how climate change is changing the role CWT plays in runoff initiation and sediment delivery.

Monitoring sedimentary areas from mine waste products with Sentinel‐2 satellite images: A case study in theSEof Spain

AbstractTorrential rainfall regimes, among others, are the origin of accelerated soil erosion. The Spanish southeastern Mediterranean region is characterised by an arid climate regime affected by extreme erosion episodes with an important loss of sediments. Soil erosion effects are even more noticeable in areas where soil has been anthropically degraded, as in the mining district ofSierra Minera de Cartagena. The present research focuses on monitoring and mapping the changes in the sediment distribution of iron oxides and hydroxyl (OH−) bearing minerals caused by a cold drop known in Spanish as 'DANA' in September 2019 on theRambla del Beal. This shortramblais fed by sediments from its drainage basin and by mining residues, irrigating a wide agricultural area. When discharges overflow theramblachannel, residues spread over its floodplain and reach the ecological protected coastal lagoonMar Menor. The objective of the study was mapping the mineral distribution of the mining materials eroded from the source areas and sedimented inRambla del Bealduring a DANA. The study was carried out using a pre‐ and a post‐DANA image from the Sentinel‐2 satellite. After masking vegetation, urban areas and water bodies, different band ratios (B4/B3, B11/B12, B8A/B6) and a Spectral Angle Mapper (SAM) classification were applied. Sediment deposits were identified in wider areas after the DANA. Iron oxides increased their extension by 11.08% in the central area (B3/B4 with R2of 0.84) and hydroxyl‐bearing minerals increased by 8.95% in theRambla del Beal's headwaters (B11/B12 withR2of 0.71). The SAM classification (with a 0.1 rad threshold and an overall accuracy of 87.33%) allowed the differentiation and classification of two ferric iron oxides (haematite and goethite) and one iron hydrous sulphate mineral (jarosite). Additionally, band ratio images were spatially overlaid with the soil land uses map layer of the cadastre in order to plot the land uses most affected by the transported sediments during the DANA. These results highlighted agricultural land as the areas (land uses) most affected by iron oxides deposition, as oxidation processes occur more rapidly in these areas. However, grassland and scrubland were the areas with the highest content of hydroxyl‐bearing minerals, as water is accumulated in these places, which favours hydrolysis reactions.HighlightsTorrential events can relocate large volumes of contaminated sediments from former mining areas.Sentinel‐2 allows monitoring mine waste iron‐sulphate changes caused by weathering alteration.Spatial mineralogical pattern in sediments is controlled by geomorphology and flood dynamics.The proposed digital image analysis allows mapping short‐term evolution of mine waste sediments.

Datasets for the manuscript "Cold Drops from Mid-Latitudes and Atmospheric Rivers from the tropics triggered the Middle East's Severe Dust Storms in Spring 2022"

Datasets for the manuscript "Cold Drops from Mid-Latitudes and Atmospheric Rivers from the tropics triggered the Middle East's Severe Dust Storms in Spring 2022"

Datasets for the publication "Cold Drops from Mid-Latitudes and Atmospheric Rivers from the tropics triggered the Middle East's Severe Dust Storms in Spring 2022"

Datasets for the publication "Cold Drops from Mid-Latitudes and Atmospheric Rivers from the tropics triggered the Middle East's Severe Dust Storms in Spring 2022"

Flood Hazards in Flat Coastal Areas of the Eastern Iberian Peninsula: A Case Study in Oliva (Valencia, Spain)

Enhancing resilience against flooding events is of great importance. Eastern Iberian Peninsula coastal areas are well known for high intensity rainfalls known as DANA or “cold drop”. Extreme records in 24 h can exceed the annual average of the historical series. This phenomenon occurs normally in autumn due to convective storms generated by the existence of cold air in the upper layers of the atmosphere combined with warm winds coming from the Mediterranean Sea. In many coastal areas of the Eastern Iberian Peninsula, their flat topography, sometimes of a marsh nature, and the natural (e.g., dune ridges) and man-made (e.g., infrastructures) factors, result in devastating flooding events of great potential damage and risk for urban and rural areas. In this context, this paper presents the case study of the town of Oliva (Valencia, Spain) and how in a flooding event the flow tends to spread and accumulate along the flat coastal strip of this populated area, causing great potential damage. From that point, the paper discusses the particular issues that flood studies should consider in such flat and heavy rainy areas in terms of the hydrological and hydraulic models to be conducted to serve as the key tool of a correct risk assessment. This includes the correct statistical simulation of rainfalls, the hydrological model dependency on the return period and the correct geometry definition of all possible water barriers. An analysis of the disturbance that climatic change effects may introduce in future flooding events is also performed.

Features of weather types involving heavy rainfall along the southern Spanish Mediterranean

Heavy rainfall events in the Mediterranean can be of high intensity, commonly exceeding 100 mm day-1, and have irregular spatio-temporal distribution. Such events can have significant impacts both on soils and human structures. The aim of this paper is to highlight a systematic comparison of synoptic conditions with heavy rainfall events in Mediterranean Southern Spain, assessing the weather types responsible for meteorological risk in specific locations of this mountainous region. To do this, we analyzed the maximum intensity of rainfall in observational periods ranging from 10 min to 24 h using a database from 132 rain gauge stations across the study area since 1943; then, the heavy rain has been associated with the weather type which triggers it. This analysis identified a pattern of heavy rainfall which differs from that previously reported in the Mediterranean area. Thus, in this research, the maximum number of heavy rainfall events uses to come from a dominant pattern of low pressures associated to front systems and East-Northeast winds; but the maximum volumes use to be associated to Cold Drops and the same winds; in addition, there are differences throughout the territory, showing several patterns and seasonal incidence when analyzing sub-zones, which may be related with different erosive conditions according to its position with respect to Atlantic or Mediterranean sea, and the entity of its relief.

Single and Double Drop Impingement on a Heated Plate CFD and Experimental Investigation

A drop impingement on a hot surface is known as an effective way for heat removal. The present work uses a VOF (volume of fluid) model to simulate the flow behavior and temperature distribution on a 50 °C heated plate while relatively cold water drop is impinging. The temperature distribution at the impingement zone is used to examine the transient heat transfer coefficients using a single drop and double drops conditions. The spreading factor is tested in both cases. A test rig is built to verify the temperature distribution and a heat balance method is introduced to find the experimental heat coefficients on the heated. The CFD solution and its flow results gives a good agreement for single drop previous results. The results for the double drop condition show a high tendency for rebound and splash of the drop leaving the central zone without water drop coverage which way causes a burn out in case of high heat fluxes. The single drop condition show a symmetrical temperature and heat transfer coefficients distribution while the double drop impingement gives lower value of coefficients with non-uniform and unsymmetrical distribution specially at the bigger drop to plate distances. The experimental average heat coefficients gives relatively low error of only 5% in case of double drop when compared to the single drop values.

Distinct coalescence behaviors of hot and cold drops in the presence of a surrounding viscous liquid

Coalescence of a millimeter-sized drop initially touching a pool of the same liquid in the presence of another surrounding viscous liquid is studied in this work, wherein the drop may be hotter or colder than its surroundings. Moreover, the effect of the outer fluid viscosity on the coalescence dynamics and thermal convection is examined. An axisymmetric numerical model is employed to investigate the drop merger dynamics, wherein the drop and pool are modeled as water fluid, and the surroundings are modeled as silicone oils of different viscosities. The coalescence behaviors of hot and cold drops are found to be significantly different, especially at higher temperature differences. An otherwise partial coalescence for an isothermal system turns into a case of total coalescence when the drop is made colder than its surroundings, whereas the behavior in the case of a hot drop does not depart qualitatively from that of a corresponding isothermal system. Thermal convection has been examined in terms of the penetration depth of hot or cold fluid into the pool. Hot drops are found to have a greater penetration depth as compared to cold drops for higher viscosities of the surrounding fluid. The penetration depth is also related to the size of the leading vortex ring and the maximum vorticity magnitude.

Impacts of Weather Types on Soil Erosion Rates in Vineyards at “Celler Del Roure” Experimental Research in Eastern Spain

To understand soil erosion processes, it is vital to know how the weather types and atmospheric situations, and their distribution throughout the year, affect the soil erosion rates. This will allow for the development of efficient land management practices to mitigate water-induced soil losses. Vineyards are one of the cultivated areas susceptible to high soil erosion rates. However, there is a lack of studies that link weather types and atmospheric conditions to soil erosion responses in viticultural areas. Thus, the main aim of this research is to assess the impacts of weather types and atmospheric conditions on soil erosion processes in a conventional vineyard with tillage in eastern Spain. To achieve this goal, rainfall events from 2006 to 2017 were monitored and the associated runoff and soil loss were collected from experimental plots. Our results showed that the highest volume of runoff and soil erosion is linked to rainfall associated with the eastern winds that accounted for 59.7% of runoff and 63.9% of soil loss, while cold drops in the atmospheric situation classifications emerged as the highest contributor of 40.9% in runoff and 44.1% in soil loss. This paper provides new insights into the development of soil erosion control measures that help to mitigate the negative impact of extreme rainfall and runoff considering atmospheric conditions.

Consequences of being phenotypically mismatched with the environment: no evidence of oxidative stress in cold- and warm-acclimated birds facing a cold spell.

Seasonal changes in maximal thermogenic capacity (Msum) in wild black-capped chickadees suggests that adjustments in metabolic performance are slow and begin to take place before winter peaks. However, when mean minimal ambient temperature (Ta) reaches -10°C, the chickadee phenotype appears to provide enough spare capacity to endure days with colder Ta, down to -20°C or below. This suggests that birds could also maintain a higher antioxidant capacity as part of their cold-acclimated phenotype to deal with sudden decreases in temperature. Here, we tested how environmental mismatch affected oxidative stress by comparing cold-acclimated (-5°C) and transition (20°C) phenotypes in chickadees exposed to an acute 15°C drop in temperature with that of control individuals. We measured superoxide dismutase, catalase and glutathione peroxidase activities, as well as lipid peroxidation damage and antioxidant scavenging capacity in pectoralis muscle, brain, intestine and liver. We generally found differences between seasonal phenotypes and across tissues, but no differences with respect to an acute cold drop treatment. Our data suggest oxidative stress is closely matched to whole-animal physiology in cold-acclimated birds compared with transition birds, implying that changes to the oxidative stress system happen slowly.

Droplet evaporation on a structured surface: The role of near wall vortexes in heat and mass transfer

Experimental studies on the evaporation of a drop located on a horizontal hot wall with cavities of different diameters of 0.5–2.5 mm were carried out. The wall temperature Tw was constant (74 °C and 83 °C). The evaporation behavior on a structured surface was compared with that on a smooth wall. Instantaneous velocity profiles have been obtained over a single cavity and in the vicinity of several cavities using the Micro Particle Image Velocity method (Micro PIV). It has been established that a hotter liquid is periodically ejected from the cavity, which increases convection inside the drop. The strongest intensification of mass transfer is specific for the largest cavities with a diameter of 2.5 mm. The behavior of the droplet evaporation on a smooth wall coincides with that on a structured surface with a cavity diameter of 0.5 mm. Until now, there have been no data that would link the convection in the drop with the vortexes in the cavity at non-isothermal evaporation and at high heat fluxes. The strongest influence of cavities is manifested in the initial period of evaporation, when a cold drop is placed on a hot wall. Over time, the evaporation rate on a structured wall approaches evaporation on a smooth (unstructured) surface. The article considers the influence of several key factors on the convection in a drop.

Sentinel-2 Satellites Provide Near-Real Time Evaluation of Catastrophic Floods in the West Mediterranean

Flooding is among the most common natural disasters in our planet and one of the main causes of economic and human life loss worldwide. Evidence suggests the increase of floods at European scale with the Mediterranean coast being critically vulnerable to this risk. The devastating event in the West Mediterranean during the second week of September 2019 is a clear case of this risk crystallization, when a record-breaking flood (locally called the “Cold Drop” (Gota Fría)) has swollen into a catastrophe to the southeast of Spain surpassing previous all-time records. By using a straightforward approach with the Sentinel-2 twin satellites from the Copernicus Programme and the ACOLITE atmospheric correction processor, an initial approximation of the delineated flooded zones, including agriculture and urban areas, was accomplished in quasi-real time. The robust and flexible approach requires no ancillary data for rapid implementation. A composite of pre- and post-flood images was obtained to identify change detection and mask water pixels. Sentinel-2 identifies not only impacts on land but also on water ecosystem and its services, providing information on water quality deterioration and concentration of suspended matter in highly sensitive environments. Subsequent water quality deterioration occurred in large portions of Mar Menor, the largest coastal lagoon in the Mediterranean. The present study demonstrates the potentials brought by the free and open-data policy of Sentinel-2, a valuable source of rapid synoptic spatio-temporal information at the local or regional scale to support scientists, managers, stakeholders, and society in general during and after the emergency.

A 500-year flood history of the arid environments of southeastern Spain. The case of the Almanzora River

Abstract The study of flood events, especially analyses of flood magnitude and flood frequency, is crucial for the planning and management of settlements and infrastructure located near river channels. This work studies the historical floods of the Almanzora catchment, in southeastern Spain, one of the driest regions in Europe. We compile, describe and statistically process flood data that extend back to the year 1500 CE. The data were collected from historical sources held in both local and regional archives. The analysis of the flood record shows that the most destructive events occurred in 1550, 1729, 1879 and 1973, the last of these being the most catastrophic event on record. The synoptic configurations of the four most destructive floods in the time-series were explored and found to present the same type of pattern (cold drop). Historical flood discharges were estimated by calibrating historical flood magnitudes with instrumental data. This assessment was undertaken using a cumulative function applied to flood episodes that exceeded the threshold of magnitudes ≥3. The flood frequency analysis performed by combining instrumental and historical data shows that catastrophic events, such as the 1973 flood with a discharge of 5600 m3 s−1, occur with a return period of

Study and analysis of plate type heat exchanger

With the emerging trend in technology heat transfer dissipation from those device which required certain temperature for their efficient operation in the major problem. In this regards high technology is required to cool such devices. As far as heat exchanger is the major solution of such problem. Plate heat exchanger are the exchangers having a number of plates combined together having different corrugation for transfer the heat between the two fluid. An experimental investigation are done on the plate type heat exchanger to estimate the value of heat transfer characteristics by changing the mass flow rate and study the pressure drop. And from the experiment estimate the value of heat transfer characteristics for hot and cold fluid, nusselt number, pressure drop and effectiveness. It is shown that Nusselt number, pressure drop and effectiveness are depends on the mass flow rate. This paper is concerned with the plate type heat exchanger and investigation is carried out by considering the different works published in the field of heat exchangers.

Study case of aluminium die-cast parts with different gating conditions tested in fatigue

Aluminium die-castings whose performance needed to be evaluated against the baseline were subjected to fatigue testing. The results showed lower than expected fatigue life and incorrect Weibull distribution of the data, as well changes in the failure location and fracture morphology. This was a clear indication that the casting parameters were inadequate. In addition, the microstructure analysis revealed the presence of flow-induced segregation patterns, entrapped oxide films, gas porosity, microshrinkage and dross. Die-cast parts typically exhibit some of these microstructural inconsistencies; however, in this case, the presence of atypical casting defects such as the numerous internal cold drops and cold shuts in the fracture surface pointed towards incorrect casting parameters and design as root cause. Further investigation determined that a different gating system, more prone to cold shut development – all other parameters being equal, was used to produce these parts. After improvements were made to the gating system, the evaluated castings achieved the desired quality of the baseline parts.

Meteocean Influence on Inland and Coastal Floods in the East of Spain

ABSTRACT Diez, J.J.; Esteban, M.D.; Lopez-Gutierrez, J.S., and Negro, V., 2013. Meteocean influence on inland and coastal floods in the east of Spain. The Santa Irene flood, at the end of October 1982, is one of the most dramatically and widely reported flood events in Spain. Its renown is mainly attributable to the collapse of the Tous dam, but its main message is to be the paradigm of the incidence of the maritime/littoral weather and its temporal sea-level rise on the coastal plains inland floods. The Santa Irene flood was attributable to a meteorological phenomenon known as gota fria (cold drop), a relatively frequent and intense rainy phenomenon on the Iberian Peninsula, particularly on the Spanish E to SE inlands and coasts. There are some circumstances that can easily come together to unleash the cold drop there: cold and dry polar air masses coming onto the whole Iberian Peninsula and the north of Africa, high sea-water temperatures, and low atmospheric pressure (cyclone) areas in the western Medi...

Becoming Tecciztecatl

Becoming Tecciztecatl Jill Kolongowski (bio) When we dream of snails, we are dreaming about ourselves, according to Carl Jung. Snails represent home and self spiraled into one. When I was young, I was fascinated by snails—their tiny, gelatinous bodies supporting their shells. How slowly they went, carrying all that was precious. Whenever it drizzled, I went out to look for snails. I bent down to the gravel driveway and traced their glistening trails with my fingers. Their tracks crisscrossed the driveway and I followed them until they had disappeared under the raspberry bushes. But I could never find the snails that had left the tracks. I wanted to pick one up and pull it out of its shell. I would put them back in, I thought, I only wanted to see the inside of their shells, to see what their homes looked like. It must be some kind of magic, I thought, to make the snail's house good enough to carry with him always. I thought the point of home was to stay in one place. When the drizzle turned into a downpour, I ran inside my house to escape the thick, cold drops of spring rain, giving up my quest to mutilate gastropods. In the kitchen, I stood at the windows and pressed my nose to the mildewed glass. Steam from my quick breaths fogged the glass while I stared at the driveway. Snails move at an average pace of 1 millimeter per second. I waited and waited for one to appear, to explain what they carried. I don't remember the apartment I was born in and lived in until I was two, but I do remember the red Oldsmobile. Or was it a Taurus? Everything was red; the chipped paint on the outside, the upholstered seats that left static shocks in my hair, the plastic console. After my parents moved to the first house I remember, the red car disappeared. My mother tells me that as a baby, I cried because of constant ear infections and an upset stomach. Nothing worked to comfort me—not [End Page 37] a bottle, not a crib, not her arms folded into a cradle, not her whispered words, not her tears—I cried, still. As a last resort, to escape the walls of the apartment, my mom carried me down to the red car and strapped me, still screaming, into my car seat, and drove in the dark. And then, I slept. Maybe the red car was my first home, the first place where I felt safe and happy enough to fall asleep. When I moved into my first apartment, I took my bed from the home I grew up in for my boyfriend Charlie and me to share. My dad helped hoist the bed up the stairs and into the new bedroom. It was an island in the middle of the beige carpet. We didn't move the bed from that spot. The mattress was uneven, with a depression from years of my body on the right side of the bed. On the first night, Charlie rolled into the depression, his body taking up the space where mine used to lie. I didn't mind, but gravity pulled me toward him, toward my impression, and our arms and legs tangled and I didn't know what was mine and what was his. My dad filled up the space in my old bedroom with the loveseat and a flat-screen TV mounted so high on the wall that you had to tip your head up to watch it. I never had a TV in my room. I never really decorated my room, either. My sister ripped the covers off Rolling Stone to tack up on her wall, even though the eyelined rockers' eyes scared her during the night. Maybe I was lacking, I worried. Shouldn't I have wanted to express myself with quotes cut out from magazines and books, shining celebrity bodies, poetry, and black and white photos? I wanted to, but something kept the walls blank. Maybe putting too much of myself into the room would make it harder to leave. But my room never felt empty...

Influence of initial fixation protocol on the appearance of primary cilia on the rabbit corneal endothelial cell apical surface as assessed by scanning electron microscopy

The objective was to examine primary cilia at the apical surface of corneal endothelial cells after using different fixatives. Female albino rabbits (2 kg) were euthanised at 15:00 h and the corneas fixed immediately (usually with an isotonic 2% glutaraldehyde-cacodylate fixative) either after dissection, by application fixative at 4 degrees C, by immersion of the eyeball in fixative at room temperature (RT), or by application of an isotonic or a hypertonic (Karnovsky-type) fixative at RT. Images at 2000x were taken from the central corneal region, and number and length of primary cilia assessed. The length was the same regardless of method (overall average of 1.67+/-0.70 microm), but the incidence of primary cilia was hypertonic fixative (87% of cells) >cold drop fixation (71%), >whole globe immersion (68%) >dissect then fix methods (67%) >RT drop fixation (34%). The first four methods however yielded cells with unacceptable artefacts (especially distortion). More details should be provided of the primary fixation method used.