Bulk Water Temperature Research Articles

Fabrication of NBI Ion Source Back Plate and its High Heat Flux Experiment

The back plate is an important component of the ion source because of its multiple roles including heat load removal during beam operation. The main components of the back plate are (1) a Type 304L stainless steel (SS304L) magnet positioning plate that holds samarium cobalt permanent magnets required for the confinement of ion source plasma, (2) an oxygen-free electronic copper cooling plate with 35 inner and 8 outer cooling channel grooves (each of which is 4 × 1.8 mm2) that is vacuum brazed with a SS304L magnet positioning plate, and (3) a SS304L magnet cover plate. In this paper, the back plate is successfully fabricated, and a high heat flux experiment is done at the High Heat Flux Test Facility Center with an electron beam power of 200 kW for 458 s. The uniform incident heat flux is 2.5 MW/m2. Demineralized water at 34°C is supplied at the rate of 1 kg/s to the cooling plate at inlet pressure of 8.2 bars to remove the high heat load. The surface temperature of the copper plate is measured by an infrared camera, and three temperature regions are observed. The measured average surface temperature of the cooling plate is ~152°C. The bulk water temperature rise ΔTw is ~39.42°C. The estimated absorbed heat flux is ~2.04 MW/m2, and the heat absorption coefficient is 81.6%. The measured leak rate after the heat flux test is 1.6 × 10−8 mbars∙L/s. These High Heat Flux Test experimental results will be useful to study the thermomechanical performance of the back plate and to understand the effect of increasing the beam pulse length.

Hydrovoltaic Electricity Generation from Potato Carbon Cake: Using an Interconnected Porous Solar Steam Generator

AbstractIntegrating two advanced techniques, such as solar thermal evaporation (STE) for freshwater production and hydrovoltaic (HV) for electricity generation, makes a considerable attempt to attain basic energy needs. Here in this work, a crisscross porous carbonized ethanol‐treated potato cake as a hydrovoltaic device (CHV) is fabricated. CHV device is a highly stable, portable, eco‐friendly device with a maximum output voltage of 0.23 V and current of 5 µA under ambient conditions. This is further raised to 0.5 V when exposing 1 sun illumination (1 kW m2). Voltage studies are done by varying the wind flow, relative humidity, and bulk water temperature to confirm the device's HV property and dependent factors. The potential application of the device is tested by glowing an LED light connected with 5 CHV devices in series. It is continuously delivered output till the bulk water is dry. The shelf‐life ability of CHV is also analyzed after 1 year of usage and provided nearly the same outcome. Therefore, this single device with dual‐energy harvesting gives a significant solution to society's energy and water crisis for a better tomorrow.

Formation, evolution, and enhancement mechanisms of mixed temperature gradient during interfacial solar vapor generation

The solar evaporator, which generates a mixed temperature gradient (MTG) in the process of solar-driven interfacial water evaporation (SIWE), has shown great application potential in clean water production. It is also expected to provide a more comprehensive understanding to shed light on the formation, evolution, and enhancement mechanisms of the MTG. Herein, the space-time evolution of the solar absorber temperature and the evaporation performance in the column solar absorber are studied through a three-dimensional and multi-physical model coupling heat transfer and water transport. The results will demonstrate not only the temperature distribution during the SIWE process but the interface between positive temperature gradient (PTG) and negative temperature gradient (NTG). Moreover, the relationship between evaporation rate and light intensity, bulk water temperature, and environment humidity will be investigated. Importantly, the contributions of solar heating, PTG, NTG, and environment heating to the total evaporation rate will be quantitatively analyzed. Finally, based on the above results, the formation conditions, evolution characteristics, and enhancement mechanisms of MTG will be revealed. This paper will provide theoretical guidance for the successful construction and operation of an MTG evaporator for SIWE acceleration.

Buoyancy effects on film boiling heat transfer from a sphere at low velocities

A theoretical model is developed for the forced convection film boiling phenomenon over a heated sphere moving vertically downwards in the water. Unprecedented compared with the previous analytical studies, this model accounts for the buoyancy effects while solving the momentum and energy equations in the vapour phase to obtain the velocity and the temperature distribution in terms of the vapour boundary layer thickness. To calculate the vapour boundary layer thickness, an energy balance is applied at the vapour–liquid interface. The flow of liquid around the sphere is considered to be governed by potential theory, and the energy equation in liquid is then solved for the known velocity distribution. We find that the vapour boundary layer thickness increases with an increase in the sphere temperature, the bulk water temperature and a decrease in the free stream velocity. This further results in a decrease in the film boiling heat transfer coefficient. The present study concludes that at low free stream velocities ( ${<}0.5\, {\rm m}\,{\rm s}^{-1}$ ) buoyancy becomes significant in delaying the separation, and when the velocity is further reduced the separation angle approaches $180^{\circ}$ .

Sunlight penetration dominates the thermal regime and energetics of a shallow ice-covered lake in arid climate

Abstract. The Mongolian Plateau is characterized by cold and arid winters with very little precipitation (snowfall), strong solar insolation, and dry air, but little is known about the thermal regimes of the ice and ice-covered lakes and their response to the distinct weather and climate in this region. In a typical large, shallow lake, ice and snow processes (cover) and under-ice thermodynamics were monitored for four winters in 2015–2019. Heat transfer at the ice–water interface and lake heat budget were investigated. The results revealed that persistent bare ice of 35–50 cm thickness transmits 20 %–35 % of the incident solar radiation into the water below. This is a dominant source for under-ice energy flows and causes/maintains high water temperature (up to 6–8 ∘C) and high heat flux from water to ice (averages of 20–45 W m−2) in mid-winter, as well as higher heat conduction in the ice interior during freezing. The heat balance shows that the transmitted radiation and the heat flux from water to ice are the dominant and highly correlated heat flows in the lake. Both bulk water temperature and temperature structure are sensitive to solar transmittance and occasional snow events. Under-ice convective mixing does not necessarily occur because of stratification of salinity in the water body. In particular, salt exclusion during freezing changes both the bulk salinity and the salinity profile, which plays a major role in the stability and mixing of the water column in this shallow lake.

Frequency-dependent sonochemical degradation of perfluoroalkyl substances and numerical analysis of cavity dynamics

Ultrasonic breakdown of perfluorooctanoic acid and perfluorooctane sulfonic acid were evaluated at various ultrasonic frequency (575 kHz, 860 kHz, and 1140 kHz), pH (3–12), bulk water temperature (14.5–30 °C), and gases (Helium, Nitrogen, Oxygen, Ozone, Argon). Contrary to the result reported in the literature, we observed an increase in the rate kinetics of PFOA and PFOS decomposition in an air environment (i.e., without sparging any gases), at higher pH, and higher bulk water temperature. The rate kinetics of PFOA degradation in gases follows the order as Helium > Nitrogen > Argon > Oxygen > Ozone. The present work concludes that the presence of known/unknown chemical compounds formed during sonolysis, influence the interaction of PFOA and PFOS with the cavity-water interface. The cavity collapse simulation using Gilmore equation showed that an increase in acoustic pressure increases the compression ratio and bubble radial velocity of the collapsible cavity. This study suggests that the lower degradation rate of PFOS as compared to PFOA, over a range of ultrasound frequencies, is due to the lower number of active cavities collapsing at higher temperatures. The radius of active collapsible cavities, with maximum compression ratio and bubble radial velocity, was 3.2 µm, 2 µm, and 1.7 µm at an ultrasonic frequency of 575 kHz, 860 kHz, and 1140 kHz, respectively.

Experimental investigation on thermal stratification induced by steam direct contact condensation with non-condensable gas

Thermal stratification induced by steam direct contact condensation is a significant technical concern to consider in the energy industry. Thirty experiments have been performed to investigate the effect of steam mass flux, bulk water temperature and air mass fraction on temperature distribution in the water pool. The condensation behavior and time evolution of temperature distribution are recorded and analyzed. Two condensation regimes of chugging and bubbling are observed. Three flow patterns, namely chugging-induced synthetic jets, steam-driven negative buoyancy jets and plume, are discussed. Three thermal patterns of mixing, stratification and re-mixing are identified. A small amount of air (1–2%) could make stratification pattern occur earlier and severer. The maximum vertical temperature difference is about 30 °C in pure steam experiments and 60 °C in mixture gas experiments. Re-mixing pattern occurs when the bulk water temperature is close to 80 °C. In addition, thermal penetration depth, the velocity of thermocline moving down and the thickness of thermocline are estimated through temperature data.

Investigation on transient thermal hydraulics of reduced scale passive residual heat removal heat exchanger in tank

In advanced nuclear power plant AP1000, the passive residual heat removal heat exchanger (PRHR HX) is a key part of the passive safety system. It can transfer decay heat from the reactor core to the water in the in-containment refueling water storage tank (IRWST) during the accidents. The secure operation of the C-shaped PRHR HX has a great impact on the reactor safety. In the present work, the heat transfer performance of a reduced scale PRHR HX was investigated by experiments and numerical simulations. A system including a 6 × 7 C-shaped tube bundle and a rectangular tank was studied. A three-dimensional numerical model using porous media method was developed to explore the transient single phase thermal hydraulic characteristics of the PRHR HX. The distributed resistances caused by the C-shaped tube bundle were calculated by empirical correlations. Both the heat transfer coefficients from the hot fluid in the tube to the inside surface of tube and that from the outer tube surface to the water in the IRWST were calculated by empirical correlations published in literatures. Tests were performed on the 6 × 7 C-shaped tube bundle installed in the middle of the tank. The outer wall temperature and bulk water temperature in the tank were measured by thermocouples. The numerical methods were validated by the experimental results. The calculated results of the local temperature distribution and heat transfer rate were both well consistent with the experimental values. The deviation of the heat transfer rate was smaller than 5%.

Solar Photothermal Electrodes for Highly Efficient Microbial Energy Harvesting at Low Ambient Temperatures.

Temperature is an important parameter for the performance of bioelectrochemical systems (BESs). Energy-intensive bulk water heating has been usually employed to maintain a desired temperature for the BESs. This study concerns a proof-of-concept of a light-to-heat photothermal electrode for solar heating of a local electroactive biofilm in a BES for efficient microbial energy harvesting at low temperatures as a replacement for bulk water heating approaches. The photothermal electrode was prepared by coating Ti3 C2 Tx MXene sunlight absorber onto carbon felt. The as-prepared photothermal electrode could efficiently raise the local temperature of the bioelectrode to approximately 30 °C from low bulk water temperatures (i.e., 10, 15, and 20 °C) under simulated sunlight illumination. As a result, highly efficient microbial energy could be harvested from the low-temperature BES equipped with a photothermal electrode without bulk water heating. This study represents a new avenue for the design and fabrication of electrodes for temperature-sensitive electrochemical and biological systems.

Commercially Available Activated Carbon Fiber Felt Enables Efficient Solar Steam Generation.

Sun-driven steam generation is now possible and has the potential to help meet future energy needs. Current technologies often use solar condensers to increase solar irradiance. More recently, a technology for solar steam generation that uses heated surface water and low optical concentration is reported. In this work, a commercially available activated carbon fiber felt is used to generate steam efficiently under one sun illumination. The evaporation rate and solar conversion efficiency reach 1.22 kg m-2 h-1 and 79.4%, respectively. The local temperature of the evaporator with a floating activated carbon fiber felt reaches 48 °C. Apart from the high absorptivity (about 94%) of the material, the evaporation performance is enhanced thanks to the well-developed pores for improved water supply and steam escape and the low thermal conductivity, which enables reduced bulk water temperature increase. This study helps to find a promising material for solar steam generation using a water evaporator that can be produced economically (∼6 $/m2) with long-term stability.

Warm layer and cool skin corrections for bulk water temperature measurements for air‐sea interaction studies

AbstractThe sea surface temperature (SST) relevant to air‐sea interaction studies is the temperature immediately adjacent to the air, referred to as skin SST. Generally, SST measurements from ships and buoys are taken at depths varies from several centimeters to 5 m below the surface. These measurements, known as bulk SST, can differ from skin SST up to O(1°C). Shipboard bulk and skin SST measurements were made during the Coupled Air‐Sea Processes and Electromagnetic ducting Research east coast field campaign (CASPER‐East). An Infrared SST Autonomous Radiometer (ISAR) recorded skin SST, while R/V Sharp's Surface Mapping System (SMS) provided bulk SST from 1 m water depth. Since the ISAR is sensitive to sea spray and rain, missing skin SST data occurred in these conditions. However, SMS measurement is less affected by adverse weather and provided continuous bulk SST measurements. It is desirable to correct the bulk SST to obtain a good representation of the skin SST, which is the objective of this research. Bulk‐skin SST difference has been examined with respect to meteorological factors associated with cool skin and diurnal warm layers. Strong influences of wind speed, diurnal effects, and net longwave radiation flux on temperature difference are noticed. A three‐step scheme is established to correct for wind effect, diurnal variability, and then for dependency on net longwave radiation flux. Scheme is tested and compared to existing correction schemes. This method is able to effectively compensate for multiple factors acting to modify bulk SST measurements over the range of conditions experienced during CASPER‐East.

Measurements of surface thermal structure, kinematics, and turbulence of a large-scale solitary breaking wave using infrared imaging techniques

The surface temperature fields of large-scale solitary breaking waves are measured using infrared imaging techniques in a laboratory surf and swash zone. The surface velocity fields obtained by cross-correlating the images are decomposed into wave and turbulent motions using two filtering methods in the spatial and temporal domains. The techniques presented here provide new quantitative descriptions for the evolution of the surface thermal structures, kinematics, and turbulence that are induced by unsteady and highly foamy turbulent coastal flows. Novel organized streaks of thermal structures, which exhibit a finger-like shape, are found on the water surface of the crest roller behind the head of the rebounding jet. These thermal streaks evolve with time and become isotropic when returning to the surrounding bulk water temperature. The Froude-scaled maximum flow speed, accelerations, and vorticity are O(1), and the scaled turbulent kinetic energy (TKE) is O(−1); these results are similar to previous findings from numerical results and periodic surf-zone breakers. Significant and concentrated structures of these quantities occur in the moving wave crest during the uprush phase; however, these structures only develop during the late stages of the backwash phase. The TKE increases shoreward from the surf to the swash zones. The ratio of the averaged variance of the turbulent velocity in the wave breaking zone does not agree with the canonical prediction for plane-wake turbulence; however, the ratio is similar to that of boundary-layer turbulence and decreases in the bore region and the swash zone, indicating an increase in the turbulence anisotropy shoreward from the surf to the shallower swash flow.

Investigation of Transport Phenomena in a Vapour Film Formed in Contact Between Hot Metallic Sphere and Water

AbstractContact between hot objects and liquids occurs in many industries, such as nuclear reactors, metal casting industries and paper production. In such cases growth of vapour film leads to steam explosion that may cause human and financial damages. It is obvious that possibility of these phenomena can be judged by comparing vapour film radius growth and pressure inside vapour film. In this paper vapour film growth and pressure inside the vapour film formed, on hot sphere interaction with water, are investigated. The numerical simulation of problem is obtained and then validated using experimental test and other available results. The effects of the variations of different parameters such as hot sphere diameter, temperature, immersion depth into water and bulk water temperature are investigated on the vapour film radius, vapour pressure inside vapour film and the saturation temperature of phase interface surface. Finally, the overall results show that the effect of hot sphere interaction with water would be the same pressure inside vapour film suddenly increases up to 5 times more than initial pressure which would lead to hazard and put the safety of the system at risk.

Effects of Temperature and Dry Density on Hydraulic Conductivity of Silty Clay under Infiltration of Low-Temperature Water

Volumes of low-temperature water present in large reservoirs have increased considerably worldwide during the past decades. One of the most important soil physical properties affected by low-temperature water use is soil saturated hydraulic conductivity. Using a custom-made permeability testing device, we studied the permeability of a silty clay and analyzed the combined influence of bulk density and water temperature on permeability. The results show that when the dry bulk density of the silty clay sample increases from 1.4 to 1.6 g/cm3, the hydraulic conductivity decreases exponentially from 10−4 to 10−5cm/s (at 10, 15, 20 and 25 °C). When the water temperature is 25 °C and the dry bulk density is either 1.4, 1.5 or 1.6 g/cm3, the hydraulic conductivity is more or less three times as high as that when the temperature is 10 °C. When the dry bulk density is 1.4 g/cm3 and the water temperature increases from 10 to 25 °C, the dimensionless permeability factor (k′/k) is close to unity. The same parameter (k′/k) becomes considerably larger than 1 when the dry bulk density are, respectively, 1.5 and 1.6 g/cm3.

Thermo-Hydraulic Behavior of Water Cooling Channel Subjected to Constant Heat Flux during Pressure Reduction Transient in its Cooling System

Heat transfer parameters of concentric heat source cooling channel exposed to pressure reduction transient is studied experimentally and theoretically. The heat source is of constant heat flux cooled by upward flowing water in concentric channel. The heat source is located inside cylindrical shape tube which is fixed in an annular vertical channel. The cooling water pressure reduction transient is ensured by different shape disturbance functions. The theoretical investigation involved a mathematical modeling for axially, symmetric, simultaneously developing laminar water flow in a vertical annulus. The mathematical model is based on one dimensional flow. The boundary conditions of the studied case are based on adiabatic outer wall while the inner wall is subjected to a constant heat flux for upwards flow. The heat & mass balance equation derived for specified element of bulk water within the annulus, is solved to determine the variation of bulk water temperature, heat transfer coefficient, clad surface temperature and the boiling safety factor based on clad surface temperature versus length and time during transient course. The present theoretical work covers heat flux of 46345 W/m 2 , channel inner to outer diameter ratio of 0.8, water sub-cooled degree in the channel inlet ranging (20-30 O C), heat source length of 0.65, water pressure at channel inlet of 1.3 bars and pressure reduction transient according to step, ramp and sinusoidal shape disturbance function (1.3- 1.0) bars. The experimental investigation included a set of experiments carried out to investigate the temperature variation along the heat source for step, ramp and sinusoidal pressure reduction transients in cooling system during and after reaching the steady state condition.

In situ thermal dynamics of shallow water corals is affected by tidal patterns and irradiance

We studied the diel variation of in situ coral temperature, irradiance and photosynthetic performance of hemispherical colonies of Poriteslobata and branching colonies of Poritescylindrica during different bulk water temperature and tidal scenarios on the shallow reef flat of Heron Island, Great Barrier Reef, Australia. Our study presents in situ evidence that coral tissue surface temperatures can exceed that of the surrounding water under environmental conditions typically occurring during low tide in shallow reef or lagoon environments. Such heating may be a regular occurrence on shallow reef flats, triggered by the combined effects of high irradiance and low water flow characteristic of low Spring tides. At these times, solar heating of corals coincides with times of maximum water temperature and high irradiance, where the slow flow and consequent thick boundary layers impede heat exchange between corals and the surrounding water. Despite similar light-absorbing properties, the heating effect was more pronounced for the hemispherical P. lobata than for the branching P. cylindrica. This is consistent with previous laboratory experiments showing the evidence of interspecific variation in coral thermal environment and may result from morphologically influenced variation in convective heat transfer and/or thermal properties of the skeleton. Maximum coral surface warming did not coincide with maximum irradiance, but with maximum water temperature, well into the low-tide period with extremely low water flow in the partially drained reef flat, just prior to flushing by the rising tide. The timing of low tide thus influences the thermal exposure and photophysiological performance of corals, and the timing of tidally driven coral surface warming could potentially have different physiological impacts in the morning or in the afternoon.

Thermal model for performance prediction of integrated collector storage systems

The result of many years of global research on solar water heating systems has outlined the promising approach of integrated collector storage solar water heaters (ICS-SWHs) in cold climates. This research paper aims to model the field performance of a newly developed ICS-SWH for Scottish weather conditions. Field experiments were performed to investigate the performance of the newly developed ICS-SWH and the parameters affecting it. This was followed by developing a thermal macromodel able to compare the internal temperature variation under differing external weather conditions in order to evaluate the transient performance of the ICS-SWH for field conditions. Through this work, important parameters for modeling field performance of ICS-SWH were established. The innovative modeling tool developed was found to accurately predict the bulk water temperature of the ICS-SWH for any orientation and location in the world with good accuracy.

Heat Transfer and Fluid Flow Characteristics in Supercritical Pressure Water

A series of integral heat transfer measurements in a square annular flow passage was performed for bulk water temperatures of 175–400°C with upward mass velocities of 300 kg/m2 s and 1000 kg/m2 s and heat fluxes of 0, 200 kW/m2, and 440 kW/m2, all at a pressure of 25 MPa. Mean and turbulent velocities measured with a two-component laser Doppler velocimetry system along with simulations using the computational fluid dynamics (CFD) code FLUENT were used to explain the deterioration and enhancement of heat transfer in supercritical pressure water. At low mass velocities, the integral heat transfer measurements exhibited large localized wall temperature spikes that could not be accurately predicted with Nusselt correlations. Detailed mean and turbulent velocities along with FLUENT simulations show that buoyancy effects cause a significant reduction in turbulent quantities at a radial location similar to what is the law of the wall region for isothermal flow. At bulk temperatures near the pseudocritical temperature, high mass velocity integral heat transfer measurements exhibited an enhanced heat transfer with a magnitude dependent on the applied heat flux. Measured mean and turbulent velocities showed no noticeable changes under these conditions. FLUENT simulations show that the integrated effects of specific heat can be used to explain the observed effects. The experimentally measured heat transfer and local velocity data also serve as a database to compare existing CFD models, such as Reynolds-averaged Navier-Stokes (RANS) equations and possibly even large Eddy simulations (LES) and direct numerical simulations (DNS). Ultimately, these measurements will aid in the development of models that can accurately predict heat transfer to supercritical pressure water.

Remote sensing of the Dead Sea surface temperature

The Dead Sea is a unique terminal lake located at the lowest place on Earth's surface. It has the highest surface temperature, salinity, and density among Earth's large water bodies, and its level is currently dropping at a rate of ∼1 m/a. Knowledge of the Dead Sea thermal and saline structure is based on meteorological and hydrological measurements from a single site at a time. In this study, we used satellite and in situ data to characterize the spatial and temporal variations of the Dead Sea sea surface temperature (SST) and to explore the causes for these variations. Sequences of almost continuous individual satellite images were transformed into a time series of parameters representing the spatial distribution of SST. Also used were in situ measured bulk SST, wind speed, solar radiation, and water temperature profiles with depth. Analysis of this data set shows strong diurnal and seasonal variations of the surface and vertical temperature field and the meteorological forcing. The temperature field is heterogeneous after noon, when radiation is high and wind speed is low and thermal layering develops. The temperature field is homogeneous during the nighttime, when solar radiation is absent and the high wind speed vertically mixes the upper layer.

Integrated collector storage solar water heater: Temperature stratification

An analysis of the temperature stratification inside an Integrated Collector Storage Solar Water Heater (ICS-SWH) was carried out. The system takes the form of a rectangular-shaped box incorporating the solar collector and storage tank into a single unit and was optimised for simulation in Scottish weather conditions. A 3-month experimental study on the ICS-SWH was undertaken in order to provide empirical data for comparison with the computed results. Using a previously developed macro model; a number of improvements were made. The initial macro model was able to generate corresponding water bulk temperature in the collector with a given hourly incident solar radiation, ambient temperature and inlet water temperature and therefore able to predict ICS-SWH performance. The new model was able to compute the bulk water temperature variation in different SWH collectors for a given aspect ratio and the water temperature along the height of the collector (temperature stratification). Computed longitudinal temperature stratification results obtained were found to be in close agreement with the experimental data.