Water Temperature Distribution Research Articles

A study of the temperature distribution in the OTEC cold water pipe using a heat and mass transfer approach

Abstract The difference between sea water temperature at a depth of around 1000 m and sea water temperature at sea level is generally used as a parameter in the design of Ocean Thermal Energy Conversion (OTEC). In practice, electricity generation is determined by the difference between the temperature of the cold seawater coming out of the Cold Water Pipe (CWP) and the temperature of the seawater at the surface. The temperature of cold sea water increases due to heat transfer experienced by cold sea water flowing through the CWP, which comes into contact with surrounding sea water which has a higher temperature. This in turn provides a lower actual temperature difference, and therefore reduces the design power capacity. However, many previous studies did not consider these lower temperature differences. This may be acceptable for cases with practically small heat transfer such as CWP with low thermal conductivity combined with good insulation used in 1000 m CWP vertical floating systems. Unfortunately, this may not be the case for many of OTEC’s proposed alternative sites, which are located on land systems that require CWP lengths of five km or more. This raises the need for careful investigation to determine the temperature of the sea water coming out of the CWP, where it is necessary to calculate the temperature distribution of the cold sea water flowing through the CWP. This paper aims to estimate the temperature distribution of cold sea water flowing through the CWP and the increase in temperature of cold sea water leaving the CWP. Analysis based on the principles of mass and heat transfer was carried out in this research, where modelling was carried out numerically using a finite volume approach. For the case considered, the change in sea water temperature at CWP from depth to the surface occurs 1-3°C, which is the accumulation of each change in sea water depth. The results of this research illustrate that designing an OTEC system with a long CWP must consider the temperature distribution of cold sea water flowing through the CWP to produce a more realistic design.

Equivalent Enthalpy Model and Log-Mean Enthalpy Difference Method for Heat-Mass Transfer in Cooling Towers

Abstract In industrial processes involving both heat and mass transfer, the enthalpy or total energy difference, not the temperature difference, is a more comprehensive driving-force potential for heat exchanger systems, such as a cooling tower. However, the common practice of current enthalpy methods based on Merkel integral requires numerical integration with implied linear distributions of air enthalpy and water temperature. If the cooling range is relatively small, the outcome of the integration may carry little error. But for a large cooling range and a substantially increased temperature, the error involved may be significant. Like log-mean temperature difference, a log-mean enthalpy difference method may require only the inlet and outlet conditions without prior knowledge of the enthalpy distributions of the fluids within the heat exchanger. The known Berman's enthalpy difference method requires correction factors, which was derived based on the linearization of the interfacial enthalpy and the enthalpy difference between the interfacial moist-air enthalpy and the bulk air enthalpy without underlying interpretation to demonstrate that the method could be broadly used. In this paper, an equivalent enthalpy model is proposed, and the log-mean enthalpy difference is derived without any constraints for broad uses. The derived method is compared with the results of Merkel's method from literature with excellent agreement. Thus, the work in this paper would open the possibility for broad uses of the log-mean enthalpy difference method for many industrial processes involving mass transfer.

Thermal conductivity of MX80 powders-granules mixture and its prediction for high-level radioactive waste repository

Bentonite granules and their mixtures with powders are considered to be a preferred sealing material for filling gaps between buffer layer and surrounding rock in high-level radioactive waste (HLW) repository. Due to continuous release of decay heat from nuclides, thermal conductivity of bentonite granules must be assessed. In this study, the effects of water content, dry density, temperature on the thermal conductivity in the directions parallel (λpar) and perpendicular (λperp) to the bedding plane of MX80 powders-granules mixture (PGM) were investigated by thermal probe technique. Test results showed that the thermal conductivity of powdered bentonite (PB) was higher than that of PGM and λpar was higher than λperp. With increasing water content, the difference rate (δPSD) in thermal conductivity between PB and PGM increased, and anisotropy coefficient α (a ratio of λpar to λperp) decreased, while the effects of dry density and temperature on δPSD and α were not obvious. The factor importance was analyzed, and results showed that the effects of water content, dry density, temperature, and particle size distribution decreased successively. A modified geometric mean (MGM) model for predicting thermal conductivity of PGM with temperature is proposed and it predicted thermal conductivity of MX80 PGM well.

Classification of set-net fish catch volumes in Iwate Prefecture, Japan using machine learning with water temperature and current distribution images at migration depth

Efficient management of set-net fisheries can be achieved by predicting fish catches in advance. We aimed to estimate fish catch volumes using machine learning based on the data obtained from past set-net fisheries. We also suggested that the estimation can be conducted without the installation of special sensors, such as fish finders, sonars, and cameras, in the set nets. Therefore, a special feature of this study is the construction of a machine learning model using marine environmental images around the set net. In particular, the distribution images of water temperature and current at a certain water depth were applied to the model. In set-nets where migratory fish are caught, ocean data related to migration routes can be useful for estimation. The images used in this study included the water temperature at a depth of 100 m, absolute velocity at a depth of 50 m, and sea surface temperature for comparison. We then classified the fish catch into three classes as follows: chum salmon, yellowtail, and Japanese common squid in Iwate Prefecture, Japan. Consequently, our results achieved an accuracy of approximately 70–80% compared with the validation and test dataset with the water temperature at depths of 100 m. They showed higher accuracy than the sea surface temperature and absolute velocity at a depth of 50 m. This study indicates the usefulness of image-based classification for predicting the volumes of fish caught by set nets.

Coupled heat and water transfer in heterogeneous and deformable soils: Numerical model using mixed finite element method

We present a generic model framework for coupled heat and water transfer (CHWT) in deformable (non-rigid) soils with spatial variations of soil properties. The model backbone is a mixed finite element method (FEM), which solves the Philip and de Vries (1957) CHWT model and achieves conservation of mass and energy on both local and global scales. Spatial variations occur in soil hydraulic and thermal properties due to transient water content and temperature distributions. Based on the mixed FEM scheme, a gradient measure and a clustering model (“k-means”) are proposed to trace the regions with large spatial variations of soil properties, and an adaptive mesh refinement technique is developed to improve the spatial resolution and simulation accuracy. Deformation perturbates local soil topography and alters transient soil water and temperature regimes in the deformed regions. A quasi-static deformation model is presented, and the deformation effects are incorporated into the mixed FEM scheme. When external load exists, soil deformation is simulated with an updated Lagrangian formulation, and the local water content and temperature variations due to soil volume changes are also updated in the CHWT model. Numerical examples, including thermally induced soil water transfer and water infiltration, illustrate the model ability to provide plausible CHWT results, especially the refined solutions near the wetting fronts and the water content and temperature distributions when the soil is deformable. In conclusion, the proposed model framework provides an effective pipeline to incorporate and process the spatial variations of soil properties and soil deformation in CHWT simulations.

Abundance and Distribution of Blue Swimmer Crab in Response to Environmental Variation Across Two Contrasting Estuaries

Portunid crabs are an iconic, high value species in NSW, but catches are highly variable in space and time. Substantial variation in biomass is observed in both exploited and unfished populations, and environmental effects on distribution and abundance are an important factor contributing to this variability. Predicting and responding to this variability is a challenge for management and sustainability of exploited populations. We examine spatial and temporal variation in Blue Swimmer Crab (Portunus armatus) populations, over a 2.5 year trapping survey in two temperate estuaries that differ in tidal flow and riverine input. Specifically, monthly catch rates and distribution throughout the estuary are examined alongside variation in temperature and conductivity. In Wallis Lake, the shallower estuary with a restricted entrance, both water temperature and conductivity impacted abundance and distribution of crabs but there was no evidence that pulses of freshwater flow had a major impact. For a 10 °C increase in temperature the population on average shifted ~ 700 m closer to the ocean. Males were consistently located slightly further into the estuary compared to females, but there was no convincing evidence of estuarine egression in response to lower salinity. In Port Stephens, the deeper, tidal estuary, water temperature and conductivity also impacted abundance, but while males were more dispersed than females, the distribution of crabs within the estuary did not appear to be influenced by temperature, conductivity or flow. These results highlight the links between nuanced environmental relationships and estuarine geomorphology for Blue Swimmer Crab.

Statistical stream temperature modelling with SSN and INLA: an introduction for conservation practitioners

Statistical stream temperature models predicting the fine-scale spatial distribution of water temperatures (i.e., “thermalscape”) can guide aquatic species recovery and habitat restoration efforts. However, stream temperature modelling is complicated by spatial autocorrelation arising from non-independence of sampling sites within dendritic networks. We used August mean temperature data from miniature sensors deployed in Canadian Rocky Mountain streams to demonstrate two statistical stream temperature modelling techniques that account for spatial autocorrelation. The first was a spatial steam network (SSN) model specifically developed to account for spatial autocorrelation in dendritic stream networks. The second was an integrated nested Laplace approximation (INLA) model that accounts for spatial autocorrelation but was not designed to address anisotropic stream network data. We evaluated the best-fitting SSN and INLA models using leave-one-out cross-validation. Relative to INLA, SSN models had lower RMSE (1.23 vs. 1.45 C) and higher r2 (0.71 vs. 0.61); however, the SSN models required more preprocessing steps before incorporating spatially correlated random errors. We provide practical advice, an open-access r-script, and data to help non-experts develop statistical stream temperature models.

NUMERICAL AND EXPERIMENTAL INVESTIGATIONOF STEAM FILM CONDENSATION ON A VERTICAL TUBE

NUMERICAL AND EXPERIMENTAL INVESTIGATIONOF STEAM FILM CONDENSATION ON A VERTICAL TUBE

Optimising thermal design for cross flow heat exchanger in fan coil units

ABSTRACT Analytical and numerical solutions for determining the dimensions of a cross-flow heat exchanger under different conditions have been developed in this study. The analytical solution using the ε-NTU method is used to find the initial dimensions of the cross-flow heat exchanger. The numerical solution is used to validate the analytical solution and optimise the cooling coil dimensions. The ε-NTU design results show the effect of water mass flow rate, air inlet velocity, and the outer tube diameter of the cooling coil. The distribution of air and water temperatures through the heat exchanger can be predicted by solving the basic Navier-Stokes equation and energy equation using numerical methods.

Distribution analysis of adult and larval Calopteryx japonica using unmanned aerial vehicle acquired water temperature distribution

AbstractIn rivers, water temperature has a significant impact on aquatic organisms. Thermal infrared sensors mounted on unmanned aerial vehicles (UAVs), which can measure surface temperatures over an area with high spatial resolution, provide new ways to investigate river water temperatures. Therefore, we analyzed the high‐spatial‐resolution water temperature distribution acquired by UAV as an environmental factor affecting Calopteryx japonica inhabiting the river. The study site was a 9‐km section of the Sasayama River in the Kako River system, Japan. Adult and larval C. japonicas were counted walking along the water's edge. The water temperature distribution was determined by taking UAV photographs in August, when river temperatures were estimated to be the highest of the year, and in February, when river temperatures were estimated to be the lowest in the study area. The number of adult and larval C. japonicas were used as the objective variable, and water temperature, vegetation, and water area classification were used as variables in RandomForest analysis. These findings are consistent with existing research on C. japonica ecology. The analysis revealed that the water temperature distribution acquired by UAV can be used as an environmental factor in the analysis of aquatic organisms. This method has the potential to be applied to the analysis of other aquatic organisms.

Anti-Freezing Study of High-Level Water-Collecting Natural Draft Wet-Cooling Tower Based on Its Water Temperature Distribution Characteristics

Thermal power units play a crucial role in the deep peak regulation of power generation. During deep peak regulation, the load of the unit changes significantly, causing fluctuations in the inlet water temperature of the cooling tower and the water temperature in the filler. Therefore, in cold regions in winter, cooling towers have a high risk of freezing, which threatens the economic and safe operation of the unit. This paper establishes a three-dimensional numerical model based on constant heat dissipation and explores the average and minimum water temperatures at the bottom of filler under different water distribution methods, crosswind velocities, and ambient temperatures. The results show that the water distribution method has a significant impact on the water temperature at the filler bottom. Reducing the water distribution area can significantly increase the minimum water temperature at the filler bottom and reduce the risk of freezing. Although the presence of crosswind is not conducive to the cooling performance of the cooling tower, the higher the crosswind velocity, the higher the minimum outlet water temperature at the filler bottom and the lower the risk of freezing. The minimum water temperature at the filler bottom is approximately linearly related to the ambient temperature and is less affected by the unit load at the same temperature.

Comparative analysis of ground thermal conductivity and thermal resistance of borehole heat exchanger in different geological layered sequence

Borehole heat exchanger usually passes through many geological layers of the different thermo-physical properties from one layer to another in practical project of ground-coupled heat pump system. Considering the effect of heterogeneity in geological structures on heat transfer of borehole heat exchanger, it is necessary for in-situ thermal response test analysis to investigate the effect of geological layered sequence on ground thermal conductivity and borehole thermal resistance. Firstly, based on the validated numerical layered borehole heat exchanger model and numerical homogenous borehole heat exchanger model, the simulated distributions of water temperatures in U-pipe and heat flux along the depth in thermal response test are respectively compared and analysed. Then, the effective thermal conductivity and effective borehole thermal resistance estimated by the infinite line source model are respectively obtained based on the simulated thermal response tests carried out in the borehole heat exchanger installed in the six types of geological layered structures. The borehole thermal resistances in the two numerical model were respectively calculated by integrating the local thermal resistance along the depth. Finally, the ground thermal conductivities and borehole thermal resistances are compared in six types of geological layered structures. The results show that the maximum relative error of 7 % between the effective thermal conductivity and the thickness-weighted thermal conductivity in the numerical layered borehole heat exchanger model is located in the sequence of S-L-C due to BOTTOM 60m-thickness clay with lowest thermal conductivity. The relative error between effective borehole thermal resistance and borehole thermal resistance in the numerical layered borehole heat exchanger model are 3.5 %∼7.9 % in the six types of layered geological structures, and the maximum relative error between the two borehole thermal resistances corresponding to the two numerical models is only 1.1 %, which proves that effect of geological layered sequence on the deviation is limited in the two numerical models.

Energy and economic analysis of flue gas heat recovery systems improving the energy efficiency of gas cogeneration units

This paper presents the results of energy and economic analyses of a gas-fired CHP plant. The analyses were carried out for three variants of technical solutions to improve the thermal efficiency of the CHP plant. The fuel combustion process involves the generation of a large amount of heat. In addition, the heat is dissipated to the surroundings through the exhaust gas with a high temperature of 300÷350 °C. Therefore, to limit heat loss, a heat recovery system is used, which removes heat from the engine body and from the hot exhaust gases through a heat exchanger, allowing the exhaust gases to be cooled to a temperature of 100÷120 °C. In addition, heat is recovered from the oil cooling process and intercoolers. The recovered heat is usually supplied to the heating water in the district heating network. For the calculations, the temperature distribution of the return water from the district heating network during the year was assumed. First, the benefits of adding an additional economizer to pre-heat district heating water were analysed, Next, a heat recovery system was simulated to cool the flue gases to lower temperatures using an absorption heat pump or a compressor heat pump.

Coupling dynamic response of saturated soil with anisotropic thermal conductivity under fractional order thermoelastic theory.

In this paper, a two-dimensional (2D) thermo-hydro-mechanical dynamic (THMD) coupling analysis in the presence of a half-space medium is studied using Ezzat's fractional order generalized theory of thermoelasticity. Using normal mode analysis (NMA), the influence of the anisotropy of the thermal conduction coefficient, fractional derivatives, and frequency on the THMD response of anisotropy, fully saturated, and poroelastic subgrade is then analyzed with a time-harmonic load including mechanical load and thermal source subjected to the surface. The general relationships among the dimensionless physical variables such as the vertical displacement, excess pore water pressure, vertical stress, and temperature distribution are graphically illustrated. The NMA method does not require the integration and inverse transformation, increases the decoupling speed, and eliminates the limitation of numerical inverse transformation. The obtained results can guide the geotechnical engineering construction according to different values of load frequency, fractional order coefficient, and anisotropy of thermal conduction coefficient. This improves the subgrade stability and enriches the theoretical studies on thermo-hydro-mechanical coupling.

Typical patterns of the water temperature distribution in the upper mixed layer of the Bering Sea in winter season

Typical patterns of the water temperature distribution in the upper mixed layer of the Bering Sea in winter are determined on all available oceanographic data obtainedby research institutions of Russia, Japan, USA, and China. Previously [Luchin, 2023], the data were sorted to two sets presenting «cold» and «warm» winters. The proper set includes 2,492 oceanographic stations and the latter one – 2,130 stations. Spatial distribution of the temperature has some common patterns for both sets: the highest values (3–4 to 5–6 оC) are observed at the central and eastern passages between Aleutian Islands, primarily reflecting the Pacific waters invasion to the sea, then these waters are involved into the large-scale cyclonic gyre over the deep-water basin and transported along the continental slope that is indicated by 3оC isotherm. However, different types of the temperature distribution are well distinguished by prominent difference of its values that is amounted in 1.0–1.5о, up to 3–4о at the northwestern coast including the western part of the eastern Bering Sea slope. A wide set of potential predictors for interannual variability of thermal and dynamic conditions in the Bering Sea are examined using correlation analysis,including the global and regional climatic indices. There is concluded that the winter temperature fields are formed by several key factors, as the warm Pacific waters advection, the basin-scale cyclonic circulation, the vertical and lateral water mixing in the Aleutian sounds and at the continental slope, and fall-winter cooling of the surface layer driven by air–sea heat exchange.

Evaluation of Changes in the Scale and Direction of Thermal Pollution Flows in the Kalinin NPP Cooling Lakes From 1985 to 2020

The article evaluates the change in the scale and direction of thermal pollution flows of the cooling lakes of the Kalinin NPP from 1985 to 2020 based on the use of Earth remote sensing data. A retrospective analysis was carried out using satellite images obtained by the sensors of the Landsat series satellites. An analysis of the distribution of surface water temperature over the water area of NPP cooling lakes has been carried out. The change in the structure of thermal pollution after the increase in the capacity of the Kalinin NPP is determined. The temperature of the cooling lakes of the Kalinin NPP was estimated relative to the background indicators in the lakes-analogues, which were used as nearby Lake Navolok and Lake Kezadra. The study identified five stages of transformation of the water mass circulation system in the cooling lakes of the Kalinin NPP.

Performance Enhancement of Falling Film Dehumidifier by Variation Number and Width Ratio Rectangular Cylinder Based on CFD Simulation

The implementation of computational fluid dynamics (CFD) technologies has grown popular in various engineering fields to solve problems because it has high efficiency, affordable cost, and requires a relatively short time. This study examines the effect of adding a rectangular cylinder to a falling film dehumidifier with modifications to the geometry of the width ratio and the number of rectangular cylinders. Model without rectangular cylinder variations and three width ratio variations of 0.1D; 0.5D; D with two variations of the number of rectangular cylinders will be simulated under isothermal conditions for the process of mass transfer, distribution of water vapor mass fraction, pressure drop, turbulence intensity, temperature, and dehumidifier performance. The RNG k-ε turbulence model is used to simulate fluid flow with the addition of a user-defined function (UDF). Significant results can be seen in the distribution of water vapor mass fraction in the geometry modification with the addition of a rectangular cylinder with mass transfer enhancement of 12.4 – 13.4% compared to no geometry modification. High Wa,in with variation C is more effective in minimizing the pressure drop of moist airflow. Vortex flow is formed behind the rectangular cylinder, which increases the mass transfer around the flow. The turbulence intensity appears near the liquid desiccant solution and the rectangular cylinder with a value of 33%. The best geometry variation design shows a dehumidification effectiveness value of 36.8%, 3.3 – 3.8% greater than the design without geometry variations.

Evolution of Morphology and Distribution of Salt Crystals on a Photothermal Layer during Solar Interfacial Evaporation.

Solar interfacial evaporation (SIE) by leveraging photothermal conversion could be a clean and sustainable solution to the scarcity of fresh water, decontamination of wastewater, and steam sterilization. However, the process of salt crystallization on photothermal materials used in SIE, especially from saltwater evaporation, has not been completely understood. We report the temporal and spatial evolution of salt crystals on the photothermal layer during SIE. By using a typical oil lamp evaporator, we found that salt crystallization always initiates from the edge of the evaporation surface of the photothermal layer due to the local fast flux of the vapor to the surroundings. Interestingly, the salt crystals exhibit either compact or loose morphology, depending on the location and evaporation duration. By employing a suite of complementary analytical techniques of Raman and infrared spectroscopy and temperature mapping, we followed the evolution and spatial distribution of salt crystals, interfacial water, and surface temperature during evaporation. Our results suggested that the compact crystal structure may emerge from the recrystallization of salt in an initially porous structure, driven by continuous water evaporation from the porous and loose crystals. The holistic view provided in this study may lay the foundation for effective strategies for mitigation of the negative impact of salt crystallization in solar evaporation.

Computational fluid dynamics analysis of the effects of total weight and food on the water temperature distribution and flow in a pot during cooking

AbstractUniform quality of cooked foods regardless of its position in the pot is desirable. However, there are no research about the effect of cooking scale on the flow and water temperature distribution. This study investigated the effects of the weight and the presence of food on the water temperature distribution and flow during cooking. Using nylon cylinders with thermophysical properties similar to those of root vegetables, the water temperature near the inner surface of the pot was measured. The water temperature and flow were simulated with 2D models based on the finite element method. The water temperature was highly uniform at a total weight of 20 kg than at 3 kg due to the greater convection and faster flow velocity. The water flow velocity was lower with nylon cylinders than in its absence and decreases with decreasing sample size. This study demonstrates the usefulness of combining simulations with nylon cylinders.Practical applicationsThe evaluation of temperature distribution and water flow during cooking is important for ensuring uniform quality of products in a pot. Particularly, it is important to evaluate the effect of cooking scale, presence of food and ingredient size. However, the experimental verification of large‐scale cooking is costly and time‐consuming. This study shows the usefulness of combining computational fluid dynamics (CFD) simulation with the nylon cylinders having thermophysical properties similar to those of root vegetables as food analogs. The CFD analysis revealed that increasing cooking scale increases the water flow velocity and uniformity of water temperature. This result should be considered in the actual large‐scale cooking of prototypes, which are tested at small scale, for example, in laboratories. Furthermore, small‐sized foods hinder the flow and cause uneven water temperature distribution. The findings suggest that sample size affects the temperature and uniformity in quality of cooked products in a pot.

Experimental and numerical study of tomatoes drying kinetics using solar dryer equipped with PVT air collector

The present work aims to develop a 3D numerical simulation that describes fresh tomatoes' heat- and mass-transfer characteristics using software COMSOL Multiphysics. Besides, a numerical study of the effect of drying parameters (drying temperature, Velocity of air drying and thickness of the slice) on the moisture content elimination from the tomato slice was realized. Also, an experimental study of the effect of the continuity and the discontinuity of the drying process on the water content vaporization is carried out. In contrast, the numerical simulation developed is validated by comparing the experimental data with the numerical results of the temperature distribution and mass transfer inside the tomato slice. The results show that the numerical simulation is agrees with the experimental tests. In addition, the results show that bacteria contamination appears in the tomato slice when the drying temperature decreases under 50 °C. The discontinuity of the drying process harms the quality of the dried product. Furthermore, the results show that the water evaporation rate in the thin slice was faster compared to the thick slice. Consequently, the drying time was reduced by 39 h when the thickness of the product was decreased from 33 mm to 10 mm. Also, the numerical simulation shows that moisture elimination is faster at higher drying air temperatures and increasing the drying air velocity leads to decrease drying time. The results show that the numerical simulation developed in this paper can accurately simulate the drying process characteristics of the agro-food product, especially Tomato, and that it provides a high spatial resolution of the distribution of water content and temperature inside the slice of tomatoes during the drying process.