Temperature Tw Research Articles

Droplet evaporation on a heated structured wall

Evaporation of water droplets on a structured surface is studied experimentally. With an increase in the wall temperature Tw from 28-70°С the exponent n increases from 1-1.37 in the evaporation law (j = dm/dt ~ R0n, where m is the droplet mass and R0 is the droplet radius). Usually, researchers simulating droplet evaporation consider a linear relationship between the evaporation rate, j, and the droplet radius, R0 (n = 1). This paper shows an increase of the exponent, n, with a growth of the wall temperature, Tw. The diffusion vapor layer on the droplet interface and the boundary air layer on the surface of the heated cylinder with a diameter exceeding the droplet’s one are formed. A neglect of free convection more than five times underestimates calculation results compared with experimental data. At droplet evaporation it is necessary to take into account convection in a vapor-gas medium and wall roughness.

Evaporation of layers of salt solutions

Nonisothermal evaporation of layers of water and aqueous salts solutions of H2O/LiBr, H2O/CaCl2 and H2O/LiCl was studied experimentally. The liquid layer was placed on a horizontal heated wall. The initial concentration of salt C0 was 10 %. The wall temperature Tw = 75 °C and ambient air pressure was 1 bar. It was shown that the heat flux q increases for water for the final evaporation stage and falls for salt solutions due to the increase in salt concentration C and due to a significant drop in the equilibrium partial pressure of water vapor.

Fluid flow and thermal characteristics in inclined tubes with transcritical carbon dioxide as working fluid

In this research work, the fluid flow and thermal characteristics in inclined tubes with transcritical carbon dioxide as working fluid were examined numerically in details. To investigate the drastic thermophysical variations of CO2 near the critical point, the predictions with temperature-dependent thermophysical properties were presented. It was done in inclined tubes with CO2 pressure being 8.0MPa, the inlet temperature (To) 300K and the wall temperature (Tw) 330K with various inclined tube angles ranging from 90° (vertical upward flow) to −90° (vertical downward flow). The velocity and temperature distributions, secondary flow, and friction factor coefficient were presented in detail. Predicted results showed that the effects of temperature-dependent thermophysical properties on the thermal and fluid flow characteristics in inclined tubes with transcritical carbon dioxide as working fluid are significant. Near the entrance, the CfReo behaves significant changes. For the vertical upward flow, the fluid near tube wall is lighter thus the buoyancy force is upward, decreasing the downward flow velocity in the core region but increasing the fluid velocity and its gradient near the wall. For the vertical downward flow, the downward buoyancy force accelerates the fluid velocities in the core region but decreases the fluid velocities near the wall, yielding the smallest CfReo among various negative inclination angles.

Polarimetric Radar and Surface-Based Precipitation-Type Observations of Ice Pellet to Freezing Rain Transitions

Abstract Recent studies document a polarimetric radar signature of refreezing. The signature is characterized by a low-level enhancement in differential reflectivity ZDR and a decrease in the copolar correlation coefficient ρhv within a region of decreasing radar reflectivity factor at horizontal polarization ZH toward the ground, called the refreezing layer (RFL). The evolution of the signature is examined during three winter storms in which the surface precipitation-type transitions from ice pellets to freezing rain. A modified quasi-vertical profile (QVP) technique is developed, which creates inverse-distance-weighted profiles using all available polarimetric data within a specified range from the radar location. Using this new technique reveals that the RFL descends in time prior to the transition from ice pellets to freezing rain and intersects the ground at the approximate transition time. Transition times are estimated using both crowdsourced and automated precipitation-type reports within a specified domain around the radar. These radar-estimated transition times are compared to a recently developed precipitation-classification algorithm based on Rapid Refresh (RAP) model wet-bulb temperature Tw profiles to explore potential benefits of analyzing QVPs during transition events. The descent of the RFL in the cases analyzed herein is related to low-level warm-air advection (WAA). A simple method for forecasting the transition time using QVPs is presented for cases of constant WAA. The repeatability of the refreezing signature’s descent in ice pellet to freezing rain transition events suggests the potential for its use in operational settings to create or modify short-term forecasts.

Genetic programming-based mathematical modeling of influence of weather parameters in BOD5 removal by Lemna minor.

This study, through extensive experiments and mathematical modeling, reveals that other than retention time and wastewater temperature (Tw), atmospheric parameters also play important role in the effective functioning of aquatic macrophyte-based treatment system. Duckweed species Lemna minor is considered in this study. It is observed that the combined effect of atmospheric temperature (Tatm), wind speed (Uw), and relative humidity (RH) can be reflected through one parameter, namely the "apparent temperature" (Ta). A total of eight different models are considered based on the combination of input parameters and the best mathematical model is arrived at which is validated through a new experimental set-up outside the modeling period. The validation results are highly encouraging. Genetic programming (GP)-based models are found to reveal deeper understandings of the wetland process.

Investigation spatial distribution of droplets and the percentage of surface coverage during dropwise condensation

The aim of this research is to develop an algorithm to simulate droplets nucleation and growth during dropwise condensation in order to study the droplets spatial distribution. The proposed algorithm starts with droplets distributed based on the Poisson point process and investigates the spatial distribution of droplets using Ripley's L function method. Also, the effects of substrate temperature (Tw) and initial density (ND) on the percentage of area occupied by droplets (ϕ) are studied. Good agreement between model predictions and experimental data for the rate of growth and changes in droplets density (Nt) as well as spatial distribution of droplets verifies the validity of the simulating model.

Transfer-free growth of polymer-derived graphene on dielectric substrate from mobile hot-wire-assisted dual heating system

Chemical vapor deposition (CVD) is the most promising, relatively inexpensive approach for the growth of high quality graphene. However, the need to transfer the graphene to dielectric substrates limits its usage in electronic applications. Here, we demonstrate transfer-free growth of graphene on dielectric substrates via mobile hot-wire (MHW) assisted dual heating system (DHS). MHW is utilized as independent heat source over polymer/Ni/SiO2/Si, which is placed on a bottom heater. The hot-wire scan speed (Vw, 0.01–40 mm/min) and temperature (Tw) are varied to control the diffusion kinetics and amount of carbon source into nickel by changing the cooling rate of hot zone where nucleation and growth of graphene occurs between Ni and SiO2. The optimum growth condition for single-layer graphene is further verified through controlling the substrate temperature (Tsub, 430–630 °C). We also improve coverage of graphene by changing polymers as a function of thermal stability. The results show that thermal decomposition temperature determines the amount of the carbon dissolved into nickel for graphene growth. Through our synthesis, we can obtain nearly full-coverage of single-layer graphene. We believe our simple method of growing graphene is potentially scalable and advances the possibility of various electrical and optical applications.

IDEAL DESIGN OF LOW-HEAD COILED-TUBE IRRIGATION

In low-head tube irrigation, water is applied to the soil surface as a little stream, typically from a small-diameter tube without filtration. The objective of this study were coiling the tube to overcome its lengths problems and developing mathematical model to design the lateral of low-head coiled-tube irrigation with full water application uniformity. Constructing the model include input data under determined operating conditions to get the optimum design. The design model was developed to identify lateral length (Ll), coiled-tube lengths (Cl) and pressure heads (Ch). by using the input data of lateral inside diameter (LID), coiled-tube inside diameter (CID) and discharge (Cq), tube interval distances (Cs), soil surface slope (%), and water temperature (Tw). The optimum design example was presented to three coiled-tube diameters of 3.8, 5.2 and 6.8 mm under upstream low-head pressure (Lh.a) of 0.5, 1.0 and 1.5m for predetermined tube discharges. The results show that the effect of each parameter in the design output.

Can spatial statistical river temperature models be transferred between catchments?

Abstract. There has been increasing use of spatial statistical models to understand and predict river temperature (Tw) from landscape covariates. However, it is not financially or logistically feasible to monitor all rivers and the transferability of such models has not been explored. This paper uses Tw data from four river catchments collected in August 2015 to assess how well spatial regression models predict the maximum 7-day rolling mean of daily maximum Tw (Twmax) within and between catchments. Models were fitted for each catchment separately using (1) landscape covariates only (LS models) and (2) landscape covariates and an air temperature (Ta) metric (LS_Ta models). All the LS models included upstream catchment area and three included a river network smoother (RNS) that accounted for unexplained spatial structure. The LS models transferred reasonably to other catchments, at least when predicting relative levels of Twmax. However, the predictions were biased when mean Twmax differed between catchments. The RNS was needed to characterise and predict finer-scale spatially correlated variation. Because the RNS was unique to each catchment and thus non-transferable, predictions were better within catchments than between catchments. A single model fitted to all catchments found no interactions between the landscape covariates and catchment, suggesting that the landscape relationships were transferable. The LS_Ta models transferred less well, with particularly poor performance when the relationship with the Ta metric was physically implausible or required extrapolation outside the range of the data. A single model fitted to all catchments found catchment-specific relationships between Twmax and the Ta metric, indicating that the Ta metric was not transferable. These findings improve our understanding of the transferability of spatial statistical river temperature models and provide a foundation for developing new approaches for predicting Tw at unmonitored locations across multiple catchments and larger spatial scales.

Numerical Solution of N-S Equations in the case of Unsteady Axisymmetric Stagnation-point Flow on a Vertical Circular Cylinder with Mixed Convection Heat Transfer

The unsteady problem of impulsive stagnation-point flow on a vertical circular cylinder along with mixed convection heat transfer is solved numerically for the first time. This is because of limitations of similarity solution techniques when we encounter various physical conditions such as time-dependent states. Initially, the fluid is considered to be at rest and with a uniform temperature . At t=0 this fluid starts flowing toward a vertical cylinder at the strength rate of and the cylinder surface's temperature rises to Tw, simultaneously. The Navier-Stokes and energy equations in cylindrical coordinate system have been descritized and solved in a 2-D domain by using a SIMPLE based algorithm. The solution has been obtained in three cases. Firstly, when cylinder's wall temperature Tw is constant. Secondly, when Tw varies linearly along cylinder's axis. And thirdly, when it has parabolic variations. Considering a sample case of incompressible flow with Re=1 and , the results of Nusselt number, wall shear- stress and dimensionless velocity and temperature have been obtained at different states of cylinder's wall temperature and for some selected values of Grashof numbers. An entropy generation analysis for the case of constant wall temperature is performed which is also for the first time in this subject.

Friction spot welding between porous TC4 titanium alloy and ultra high molecular weight polyethylene

Due to the advantages of light-weight, excellent integrated physical/chemical properties and design flexibility, metal/polymer hybrid structures have been increasingly used in automotive, aerospace and biomedical industries, which calls for effective method for joining metal and polymer. In this study, biomedical 3D-printed porous TC4 titanium alloy plate and ultra high molecular weight polyethylene (UHMWPE) plate were successfully joined by friction spot welding (FSpW) technology. The unique welding temperature (Tw) - z-axis force (Fz) evolution at the TC4 plate/UHMWPE plate interface were characterized. During dwell stage, Tw and Fz were identified to be coupled. An arch-shaped embedded zone (EZ) which characterized by the embedment of UHMWPE into porous TC4 formed under non-uniformly distributed Tw at the interface, which provided the most effective bonding mechanism. The porous structure of TC4 plate is critical for the mechanical interfacial bonding formation. As a result, TC4/UHMWPE joints of high lap shear strength can be obtained by forming large EZ. Failure occurred at either TC4 or UHMWPE base plates rather than the TC4 plate/UHMWPE plate interface.

Warming Water in Arctic Terrestrial Rivers under Climate Change

Abstract Recent years have seen an obvious warming trend in the Arctic. Streamflow and water temperature Tw are important parameters representing the changes of Arctic rivers under climate change. However, few quantitative assessments of changes in river Tw have been conducted at the pan-Arctic scale. To carry out such an assessment, this study used a modeling framework combining a land process model [the coupled hydrological and biogeochemical model (CHANGE)] with models of river discharge Q, ice cover, and Tw dynamics. The Tw model was improved by incorporating heat exchange at the air–water interface and heat advection from upstream through the channel network. The model was applied to pan-Arctic terrestrial rivers flowing into the Arctic Ocean over the period 1979–2013 and quantitatively assessed trends of Tw at regional and pan-Arctic scales. The simulated Tw values were consistent with observations at the mouths of major pan-Arctic rivers. The model simulations indicated a warming trend of Tw by 0.16°C decade−1 at the outlets of the pan-Arctic rivers, including widespread spatial warming consistent with increased air temperature Ta. The strong impact of Ta on Tw was verified by model sensitivity analysis based on various scenarios involving changes in the Ta and Q forcings. Finally, this study demonstrated the warming of Tw in Arctic rivers induced by Ta warming, suggesting the potential for warming Tw of Arctic rivers under future climate change scenarios.

A new method suitable for calculating accurately wetting temperature over a wide range of conditions: Based on the adaptation of continuation algorithm to classical DFT

A new scheme is put forward to determine the wetting temperature (Tw) by utilizing the adaptation of arc-length continuation algorithm to classical density functional theory (DFT) used originally by Frink and Salinger, and its advantages are summarized into four points: (i) the new scheme is applicable whether the wetting occurs near a planar or a non-planar surface, whereas a zero contact angle method is considered only applicable to a perfectly flat solid surface, as demonstrated previously and in this work, and essentially not fit for non-planar surface. (ii) The new scheme is devoid of an uncertainty, which plagues a pre-wetting extrapolation method and originates from an unattainability of the infinitely thick film in the theoretical calculation. (iii) The new scheme can be similarly and easily applied to extreme instances characterized by lower temperatures and/or higher surface attraction force field, which, however, can not be dealt with by the pre-wetting extrapolation method because of the pre-wetting transition being mixed with many layering transitions and the difficulty in differentiating varieties of the surface phase transitions. (iv) The new scheme still works in instance wherein the wetting transition occurs close to the bulk critical temperature; however, this case completely can not be managed by the pre-wetting extrapolation method because near the bulk critical temperature the pre-wetting region is extremely narrow, and no enough pre-wetting data are available for use of the extrapolation procedure.

Performance study of humidification–dehumidification system operating on the principle of an airlift pump with tunable height

Abstract A new experimental set up for humidification–dehumidification operating on the principle of an air lift pump was experimented. Experimental work investigates the main operating parameters of a proposed desalination process working with an air humidification–dehumidification method. The principal objective of this investigation was the determination of the humid air behavior through single stage of an airlift humidification–dehumidification system. The experimental work studied the influence of the operating conditions such as the water temperature, the submerged ratio and the airflow rate on the performance of the setup. The experimental results show that the production rate of the system increases with the both increase of the brackish water temperature and the airflow rate. The productivity of the system is strongly affected by the brackish water temperature, airflow rate and slightly affected by the submerged ratio. Within the studied ranges, the maximum productivity of the system reached to 4.035 kg/h, at water temperature (Tw) = 85 °C and m ˙ a = 5 kg/h. A good agreement was achieved with productivity calculations.

Effect of phase change material on concentric circular tubular solar still-Integration meets enhancement

In this work, a compound parabolic concentrator (CPC)-concentric circular tubular solar still (CCTSS) with phase change material (PCM) is presented. The experiment is conducted with and without PCM in the CCTSS. The PCM is loaded (450g of paraffin wax/tube) in the specially designed circular trough of the tubular solar still. The water temperature (Tw), air temperature (Tair), outer cover temperature (Toc) and fresh water production are measured in frequent intervals of time. The results showed that the fresh water production of CPC-CCTSS with and without PCM integration were 5779ml/m2/day and 5330ml/m2/day. Therefore, the PCM enhanced the fresh water productivity by 8%.

Lessons learned deploying an oyster farm monitoring auto-sustainable wireless sensor network and trial of a temperature and relative humidity–based transmission power control scheme

We present challenges faced deploying a solar-powered wireless sensor network base station and nodes, at a remote oyster farm. It involved installing the base station system and a data server at the shore of a shallow bay, where there is no electrical power available. To solve the problem, we set up a photovoltaic array with an energy monitoring node, from which performance metrics were recorded and plotted. At the water, we deployed two wireless sensor nodes on a raft, a kilometre away from the base station. One node was configured for sea water pH and water temperature ( Tw) measurements. The other node was configured for salinity and Tw measurements. Furthermore, both nodes measured air temperature and relative humidity, for a more complete characterization. At the salinity node, temperature and relative humidity knowledge was crucial to determine a gain factor for doing a trial of a transmission power control scheme, using a novel temperature and relative humidity algorithm. To enable a fair comparison, the pH nodes transmitter was configured with a fixed power level. The nodes performances were measured locally at the base station, recording metrics such as received signal strength indicator and packet received rates.

Numerical analysis of die wear characteristics in hot forging of titanium alloy turbine blade

This paper provides a simple and effective numerical modeling procedure to determine the thermal effects of initial workpiece temperature (Tw) and preheated die temperature (Td) on the die wear behavior in turbine blade forging. In particular, a local 3D finite element (FE) approach embedded with the modified Archard wear model is developed for the numerical modeling and subsequently validated by comparing the simulated average contact pressure to the analytical one, as well as the experiment from literature. Then, the wear evolution and distribution of blade forging dies are characterized numerically. Further, the thermal effects of both initial workpiece and preheated die temperatures on the die wear characteristics are assessed, and the strategies for decreasing the die wear volume are consequently suggested. The results show that the die wear depth distribution is uneven and the wear volume is more influenced by the preheated die temperature in hot forging process of the blade.

Surface ozone characterization at Larsemann Hills and Maitri, Antarctica.

Data are analyzed in terms of daily average ozone, its diurnal variation and its relation with meteorological parameters like dry bulb temperature (T), wet bulb temperature (Tw), atmospheric pressure and wind speed based on measurement of these parameters at two Indian Antarctic stations (Larsemann Hills, and Maitri) during 28th Indian Scientific Expedition of Antarctica (ISEA) organized during Antarctic summer of the year 2008-09. The work has been carried out to investigate summer time ozone level and its day-to-day and diurnal variability at these coastal locations and to highlight possible mechanism of ozone production and destruction. The result of the analysis indicates that daily average ozone concentration at Larsemann Hills varied from ~13 and ~20ppb with overall average value of ~16ppb and at Maitri, it varied from ~16 and ~21ppb with overall average value of ~18ppb. Photochemistry is found to partially contribute occasionally to the surface layer ozone at both the stations. Lower concentration of ozone at Maitri during beginning of the observational days may be due to destruction of ozone through activated halogens, whereas higher ozone on latter days may be due to photochemistry and advective transport from east to south-east areas. Ozone concentration during blizzard episodes at both the stations is reduced due to slow photochemical production of ozone, its photochemical removal and removal through deposition of ozone molecules on precipitation particles. Diurnal variation of ozone at Larsemann Hills and Maitri has been found to be absent.

Long-term trends in river water temperature: a case study of the Raba River (Polish Carpathians)

This study analyses potential trends in river water temperature (Tw) over a period of 50 years (1960–2009). The study area is located in the Raba catchment in the Polish Carpathians. The aim of the study was to evaluate long-term trends in daily Tw for each season of the year as well as to compare the direction of these trends for sites located some distance upstream and downstream from the Dobczyce Reservoir (DR), built in 1986 on the Raba River. For autumn and winter, increases in mean, median, and minimum Tw are significant for the downstream site (39 km from the DR), with a rate of change of 0.18–0.26 C per decade. Contrasting results were obtained for the spring and summer seasons; significant increases (0.22–0.47 C per decade) in mean, median, and maximum Tw were found for the upstream site, in concordance with seasonal air temperature trends, but a significant decrease in maximum Tw (–0.42 and –0.35 C per decade, respectively) was identified for the downstream site. The revealed discrepancies in the direction of seasonal trends for the upstream and downstream sites studied suggest an anthropogenic impact on Tw downstream from the DR. Overall, a significant increase in summer Tw suggest the need for appropriate flowing water management that would mitigate adverse effects of climate warming on the fluvial environment.

Gas Transfer Velocity of CH4 at Extremely Low Wind Speeds

Thin boundary theory equation (TBL) is widely used to determine gas fluxes across water-air interfaces, and the gas transfer velocity (k600) is the key environmental factor in the equation. A monthly field campaign was carried out during one year to measure CH4 flux and to probe its exchange rate across the air-water interface in a drinking reservoir and 5 adjacent ponds. The ranges of wind speed and surface water temperature were 0-0.75 m·s-1 and 6.3-30.9℃respectively, and their average values were 0.19 m·s-1 and 19.3℃ respectively. The gas transfer velocity of CH4 varied from 0.20 to 1.99 cm·h-1 with an average of 0.50 cm·h-1. Correlation functions between the gas transfer velocity and the wind speed at 10 m height (U10) and surface water temperature (Tw) were given here to quantify k600. There were significant correlations between the fitted values and actual values both for original and bin-averaged data.