Initial Water Temperature Research Articles

Impact of operation strategies on performance of integrated kang-floor heating system in severe cold areas

Efficiently and cost-effectively meeting the heating requirements of residents in severely cold regions by utilizing solar energy is currently a pressing need. Therefore, a solar heating system that integrated Kang-floor heating was established and tested for a passive solar house in Gan-nan Tibetan. This study reveals the effects of adjusting the flow/intermittent time periods and implementing variable flow rate operations on performance of system, to improve energy efficiency and optimize sleeping comfort. Findings indicated decreasing flow/intermittent time to 15/15 min had strengthened the average heat transfer from the water side, and mitigated the influence of returning water on internal water temperature of the tank, ultimately enhancing heat supply. The heating period was divided into three stage (18–24, 0–4, 4–8 o'clock), with a specific flow rate assigned to each stage. Under five flow rate configurations(A-E) with identical initial conditions: during constant flow rate, the greater the initial supply water temperature of the system, the more heat was transferred to room, and the higher heating efficiency was achieved, however, under variable flow rate, the effect of the water temperature on heating efficiency was significantly less evident. Mode B (low-to-high flow rate) had the highest heating efficiency and heat supply. The heating rate and cooling rate of Kang surface, temperature variations were notably less compared to the other four modes. Shortening the flow/intermittent periods and implementing variable flow method could improve the system's heat supply and sleep comfort with limited capital and resource investment.

Study on saline-alkali water distillation system by reflection enhanced solar heating

A saline-alkali water distillation system by reflection enhanced solar heating is proposed to treat the saline-alkali soil washing water. In this system, the heat concentration collector employs heat collecting plate to receive solar radiation energy, and converges to small-area steam generating tube through efficiently heat transfer. Without expensive optical tracking equipment, the system also employs an external reflector to reflect the solar radiation to the surface of the heat concentration collector. Thereby the energy flow density is further increased, and the useful energy and vaporization intensity is promoted. The latent heat of the steam is reused by heat recovery to enhance the energy utilization efficiency. The optimal inclination angles of reflector in different seasons and system performance were theoretically calculated. In the spring equinox, summer solstice, autumn equinox, and winter solstice, the optimal inclination angles of the reflector were 30°, 45°, 30°, and 15°, respectively. The freshwater production, useful energy, and heat recovery efficiency of the system were investigated by experiments. The daily freshwater production of the system was 17.04 kg, and the maximum production rate was 3.44 kg/h. The reflector increased the useful energy and freshwater production of the system by 33.68% and 35%, respectively. With heat recovery, the initial temperature of the saline-alkali water was increased to 53.8 °C and the freshwater production was increased by 13.16%.

The use of CO2 for the treatment of alkaline tunnel construction wastewater: Efficiency and influencing factors

Alkaline wastewater from tunnel construction can cause environmental problems when draining into water streams like rivers and lakes. Research interest in the neutralization of alkaline wastewater using CO2 based on the carbon utilization concept has been increasing. In this study, the effects of key parameters such as the flow rate (FR) of CO2, initial water temperature (T), pH, and turbidity (TURB) on CO2 neutralization of alkaline wastewater were investigated through laboratory experiments and field tests using alkaline wastewater collected from the Yunnan Dianzhong Water Diversion Engineering, China. Results revealed that 1.5 L min−1 was the optimal flow rate for CO2 gas. The water pH (p < 0.001) and TURB (p < 0.001) significantly affected the neutralization performance of CO2. The pH, TURB, electrical conductivity and total dissolved solids of alkaline wastewater can be effectively reduced by CO2. The least time required for the treatment was noted at a T, pH, and TURB of 20 °C, 10.5, and 80 NTU, respectively. Laboratory and field stability experiments have shown CO2 to be effective in reducing the pH of alkaline wastewater and consistently maintaining its pH within the discharge standard compliance range (6–9). A cost saving of $0.26 per 1 m3 of water was achieved comparing with neutralization of alkaline wastewater using citric acid. In summary, this study for the first time explored the efficiency and potential influencing factors for the treatment of alkaline tunnel construction wastewater using CO2. It proves the effectiveness and economic benefits of the proposed technology.

Effect of ten different physical parameters on solar still productivity: Theoretical modeling

AbstractSolar distillation using solar stills is widely recognized as a clean and cost‐effective method for producing freshwater. However, due to its straightforward design, solar still performance is greatly influenced by various physical characteristics. Many researches have evaluated solar still parameters, while only a few articles have concerned physical ones. Therefore, this article aims to investigate the effect of different physical parameters on solar still productivity through thermal modeling. The theoretical results were validated with those of a previous experimental model, showing a good agreement with each other. The results reveal that daily productivity experiences significant improvement with an increase in plate emissivity or insulation thickness. Conversely, an increase in water mass, glass absorptivity or insulation thermal conductivity leads to a substantial reduction in productivity. Notably, water transmissivity and plate absorptivity do not affect productivity. Modest enhancements in productivity can be achieved by reducing the effective emissivity between water and glass. While the initial temperature of water has a minor impact on productivity at low water mass, it exhibits a substantial improvement effect at high water mass. These results can be a good guidance for the designers and manufacturers to develop more efficient designs that maximize the production of clean water.

Simulation and parameter determination of the net sorption of phenanthrene by sediment particles

The distribution of polycyclic aromatic hydrocarbons (PAHs) in the ocean is affected by the sorption-desorption process of sediment particles. This process is determined by the concentration of PAHs in seawater, water temperature, and organic matter content of sediment particles. Quantitative relationships between the net sorption rates (=the difference of sorption and desorption rates) and these factors have not been established yet and used in PAH transport models. In this study, phenanthrene was chosen as the representative of PAHs. Three groups of experimental data were collected to address the dependence of the net sorption processes on the initial concentration, water temperature, and organic carbon content representing organic matter content. One-site and two-compartment mass-transfer models were tested to represent the experimental data using various parameters. The results showed that the two-compartment mass-transfer model performed better than the one-site mass-transfer model. The parameters of the two-compartment mass-transfer model include the sorption rate coefficients kafand kas (L g−1 min−1), and the desorption rate coefficients kdf and kds (min−1). The parameters at different temperatures and organic carbon contents were obtained by numerical simulations. Linear relationships were obtained between the parameters and water temperature, as well as organic carbon content. kaf, kas and kdf decreased linearly, while kds increased linearly with temperature. kaf, kas and kdf increased linearly, while kds decreased linearly with organic carbon content. The r2 values between the simulation results based on the relationships and the experimental results reached 0.96–0.99, which supports the application of the model to simulate sorption-desorption processes at different water temperatures and organic carbon contents in a realistic ocean.

Heat Transfer Analysis of Insulation Material for the Reserve Hot Water Tank

A domestic hot water tank represents a significant potential demand-side management asset in energy systems. The selection of insulation materials is crucial for maintaining the temperature of the hot water tank and preventing massive heat loss from the tank. This study aims to analyze the different combinations of insulation material for the reserve hot water tank. Several materials, such as plywood, white bricks, red bricks, plasticine, aluminum foil, styrofoam, fine sand, and glass, were used as the insulation layer in experiments. Seven combinations of insulation layers were made to insulate the mini reserve water tank in the experiment. The insulation layers covered the surface of the water tank, and the initial and final temperature of the hot water was measured. The heat loss from the hot water tank and the thermal resistivity of the insulators were also studied. The experimental results revealed that the combination of plastic, plasticines, styrofoam, and timber yields the lowest heat loss for the hot water tank. This finding indicated that the material with low thermal conductivity is the best insulator for preventing heat loss from the thermal system. Thus, this study is useful in designing and selecting the insulation materials for the reserve hot water tank for domestic and industrial use.

Implementation and validation of boundary conditions between a chemical reactor and ambient air

This work is dedicated to the development and validation of boundary conditions for a hot object cooled in a colder environment due to natural convection, radiation and evaporation. The main background of this research is to present boundary conditions for a hot reactor in cold ambient air, where the reactor walls are not thermally insulated. Water cooling in a standard small paper cup (coffee cup) was selected as a validation test. The experimental data comprise time histories of the cup’s side wall temperature measured using three thermoelements. The initial water temperature was set to 94 °C. The ambient air temperature was fixed at 25 °C and the air humidity at 20%. The computational model is based on unsteady laminar flow Navier–Stokes equations coupled with the heat transfer equation. The water density and all water transport properties (i.e., thermal conductivity, molecular viscosity, and specific heat capacity) are temperature-dependent. Numerical simulations in two-dimensional (2D) axisymmetry aligned well with the results from experiments. Including evaporative cooling on the top water surface proved essential to accurately determine the temperature profile. The boundary conditions are implemented into the Ansys Fluent 2022R2 computational fluid dynamics (CFD) commercial solver using user-defined functions (UDFs). The model equations can be used as a boundary condition for fixed beds and adsorption columns to improve the prediction of thermal profiles in both lab-scale and industrial-scale units.

Study of hydrothermal characteristics of large‐scale water conveyance trunk canals in seasonally frozen ground regions under the influence of different initial water contents

AbstractIn seasonal frozen soil, freezing and thawing can change the physical and mechanical properties and affect slope stability. There are complex moisture conditions in the main water transfer canal. A study of the hydrothermal evolution of canals with different initial water contents under the action of freezing and thawing is of great importance for the prevention and control of canal slope slides. Hydrothermal coupling models are the key to revealing the canal's hydrothermal evolution. As some of the modeling parameters in the current hydrothermal coupling model are based on empirical values, particularly those in the van Genuchten equation, which are not necessarily related to soil properties, they are not suitable for analyzing the hydrothermal evolution of canals. This paper determines the soil‐water characteristic curve from the cumulative curve of particle gradation in the subsoil, and then determines the hydraulic parameters of the subsoil using the VG model, which then corrects the hydrothermal coupling model. The method of modifying the hydrothermal coupling model is original, which makes the model more realistically reflect drainage soil characteristics. During freezing and thawing of channel slopes with different initial water contents (21%, 25%, 29%, 33%, 37%, and 41%), temperature field, water field, and ice content distributions were investigated. Using the V‐G model, the optimal parameters for canal subsoil were a = 0.06, n = 1.2, and m = 0.17, and temperature distribution trends between canals with different water contents were basically similar. Water will accumulate at the bottom as the liquid water content increases at the canal boundary.

Experimental investigation of air step cooling by the combination of spray and chord grid for mine cooling

To address the issues of heat and humidity hazards, as well as insufficient air volume in deep mining operations, a novel cooling method combining spray and chord grid is proposed. To investigate the cooling dynamics, an experimental platform integrating both spray and chord grid components is independently developed. Field boundary conditions are simulated to conduct orthogonal experimental research. Under the experimental parameters of an inlet air temperature of 32 °C, relative humidity of 88 %, and initial spray water temperature of 26 °C, the effects of water-air ratio, nozzle distance, and other parameters on inlet and outlet temperature, as well as moisture content, are quantified. These influencing factors are analyzed through range analysis. Results demonstrate that the water-air ratio has a greater impact on cooling compared to the nozzle distance. Notably, when the water-air ratio and nozzle distance reach critical values of 0.6 and 70 cm respectively, the cooling rate begins to plateau. Furthermore, comparative analysis of the cooling and dehumidification effects of single spray versus spray + chord grid reveals that the cooling capacity of single spray systems can be surpassed by incorporating a chord grid. Specifically, the combination of spray + chord grid achieves superior cooling effects with lower water consumption.

Case study of variable speed photovoltaic direct-driven ice-storage air conditioning system in Wuhu

In order to meet the contradiction between the growing demand for refrigeration and energy scarcity, this paper proposes a novel photovoltaic ice storage air conditioning system. The system is directly driven by a photovoltaic array. The performance of the system was studied through experiments, and a mathematical model was constructed for comparative verification. The experimental results show that the daytime cooling COP of the system is 1.18, the photovoltaic conversion efficiency is 6.29 %, and the nighttime cooling time is 9 h, which basically meets the cooling needs. Through simulation, the performance of the system was optimized, and the results showed that an increase in the initial water volume and temperature of the ice storage tank would increase the cooling COP; the spacing between evaporator pipes increased from 45 mm to 60 mm, resulting in a 7.11% increase in COP; the optimal spacing between evaporator fins is 9 mm, which improves performance by 9.11 %.

Multiple Heat Recovery System for an Industrial Thermal Peeling Press Machine—Experimental Study with Energy and Economic Analyses

The enhancement of energy systems in industrial zones is attracting the attention of researchers from all over the world. At the same time, optimization and advancement in heat recovery systems are now generating major interest in the energy sector. In this context, the present study suggests a new multiple heat recovery system should be applied to an industrial thermal peeling press machine. The new system consists of multiple sources of energy: the heat excess in the chimney, the exhaust gas of the chimney, and the exhaust gas of the boiler. To proceed with testing the potential of the suggested system, a hydraulic thermal peel press machine in the wood industry undergoes different tests to achieve the best configuration that will enable this machine to reach its operational temperature when heating. Five test configurations are proposed, designed, and applied experimentally on this machine. Many parameters were effective during the experimental tests, such as water flow rate, ambient air temperature, and initial water temperature. It was found that the application of the multiple heat recovery system increases the rate of heating from around 7 °C/min to around 13 °C/min. In terms of energy and economy, the “chimney + boiler only” configuration proved to be the best system to apply during the fall and winter seasons.

Models for Considering the Thermo-Hydro-Mechanical-Chemo Effects on Soil–Water Characteristic Curves

The soil–water characteristic curve (SWCC) is widely used as a tool in geotechnical, geo-environmental, hydrology, and soil science fields for predicting and interpreting hydro-mechanical behaviors of unsaturated soils. Several previous studies focused on investigating the influence of initial water content, stress history, temperature, and salt content on the SWCC behavior. However, there is still limited understanding to be gained from the literature on how we can systematically incorporate the influence of complex thermo-hydro-mechanical-chemo (THMC) effects into interpreting and predicting the behavior of unsaturated soils. To address that knowledge gap, in this study, the coupled influence of temperature, initial stress state, initial density, soil structure, and chemical solution effects was modeled using established SWCC equations from the literature. The methodology for incorporating the coupled effects of these influential factors is presented herein. Furthermore, we evaluated the SWCC models proposed in this study, enabling us to provide a comprehensive discussion of their strengths and limitations, using the published SWCC data from the literature. The developments outlined in this paper contribute toward facilitating a rigorous approach for analyzing the THMC behaviors of unsaturated soils.

Performance prediction of a solar hot water system with change of circulating pump efficiency in solar collectors

In this study a mathematical model was developed to predict operating performance of the solar collector under specified weather conditions at Jeju Island, Korea. The optimum mass flow rate through collector based on the relationship between the useful heat gain of solar collector and the electricity consumption of solar pump is investigated. Besides, the effect of various parameters such as solar collector area, initial water temperature and volume of storage tank is analyzed. The results of the simulation show that the system performance increased about 1.33% at m = 0 . 442 kg/s with the new coefficient K c = 0 . 17 . Furthermore the system performance is affected strongly by the change of collector area, initial water temperature and volume of storage tank It should give concise information on the aims, the methods, the results and the conclusions of the paper. Its length should not exceed 200 words.

Experimental study of energy conversion on pure water static flashing evaporation considering the gravity

Energy conversion of pure water during the static flash evaporation is analysed with water static pressure taken into consideration.The experiment is conducted by varying the initial temperature and height of water in the range of 50 ℃ to 80 ℃ and 3 mm to 60 mm, respectively. The enthalpy difference is the main driving force of the flashing and the superheat can represents the enthalpy difference at the macro level which can be calculated by measuring the temperature of the water. The results indicates that the the gravity has a great effect on the energy conversion during the flashing. According to the evolution of the NEF, the flashing can be divided into rapid evaporation stage(RES) and gradual evaporation stage(GES) and the heat and mass transfer obviously show differences at the two stages. The NEFtp and τtp are introduced as evaluation index to express the completeness of the flashing during the RES and the duration of RES. The initial height of water can increase NEFtp and τtp and the superheat show different effect on the NEFtp. The gravity restrains the growth of the bubbles and extend the the duration of RES. The initial height and superheat positively increase the evaporated mass and mass flow rate during the flashing. It is clear that the gravity can not be ignore when the flashing is studied.

Features of heat transfer and phase-change on a pinned surface at pulse heat release

An experimental study was conducted of the boiling characteristics of water subcooled to the saturation temperature during pulsed heating on a smooth surface with a technical roughness of up to 5 μm and on a modified surface with cylindrical pins 200 μm in height and diameter, located at the nodes of a rectangular grid with a step of 400 μm, with an upward flow with a pressure of 0.29 MPa and an average flow velocity of 0.52 m/s. It was found that at an initial water temperature of 110°C for a modified surface, the rate of increase in the heater temperature is lower, and the onset time of nucleation is the same as for a smooth surface. For an initial water temperature of 80°C and an average temperature increase rate of about 5000 K/s, it was experimentally shown that the bubbles on the modified surface are larger, but their number and the share of the area occupied by them are significantly lower than on a smooth surface.

Simulation of cooling of aboveground water pipeline with heat insulation

Aboveground water pipelines are often more preferred in the organization of water supply systems in permafrost and low ambient temperatures conditions. If the water movement in such pipeline stops, there is a risk of cooling and subsequent freezing of the liquid. The purpose of this work is to study the dynamics of the cooling process of an aboveground water pipeline with heat insulation and to calculate the cooling time of water to the freezing temperature. To build a mathematical model of the cooling process, the method of averaging the equations of hydrodynamics and thermal conductivity is used. The model equations do not contain any assumptions about the nature of the water movement in the pipeline during the cooling process. The possibility of using the equations of the model in a quasi-stationary form is justified. The range of task parameter values at which this approximation applies is determined. The possibilities of applying different boundary conditions on the surface of the water pipeline are also considered. In the quasi-stationary approximation, a dependence on the time of the average water temperature in the pipeline was found. An explicit formula is also obtained for calculating the cooling time of water to the freezing temperature. The criteria for the applicability of the obtained formulas have been established. For a wide range of parameters, water cooling time is calculated from the specified initial temperature to the freezing temperature. Ranges of values of parameters at which increase of thickness of heat insulator layer and increase of initial water temperature lead to significant increase of water cooling time in pipeline are determined.

Optimization mathematical model of a contact air cooler for a mine turbocompressor

Purpose. Establishing the dependencies of rational parameters of turbocompressor contact air coolers on the operating mode and initial conditions. Methodology. The methods of analytical research, mathematical modeling, physical modeling, and mathematical statistics were used in the study. Findings. As a result of the research, an optimization mathematical model of the mine turbocompressor air cooler was developed, which allows establishing its rational parameters depending on the initial conditions and operating modes of the turbocompressor. The adequacy of the theoretical studies was proved on a specially designed experimental setup. The obtained dependences make it possible to minimize the theoretical flow rate at the inlet to the uncooled section of the turbocompressor, which reduces the specific energy consumption for the compressed air production. Originality. For the the first time, a method has been developed for determining the rational parameters of contact air coolers when the initial temperature of water, air, and air pressure changes, which allows developing a methodology for the constructive calculation of the contact cooling system of mine turbocompressors. Practical value. Compressed air is widely used in all industries. It is one of the most common energy carriers in industrial enterprises, and the devices associated with its distribution and processing are an energy-intensive complex industrial energy system; the level of its perfection depends on the performance of technological processes that use compressed air. Compressed air is widely used in the mining industry (ore mining and fuel production). Compressed air is produced by turbocompressors. To increase the efficiency of the compressor, compressed air coolers are used. A significant weakness of the standard compressor cooling system is the rapid contamination of the heat exchange surfaces of air coolers with scale layers, which leads to a decrease in their efficiency and an increase in the specific energy consumption for compressed air production. This disadvantage is not found in the Venturi tube – centered droplet separator contact air coolers. As a result of the study, the dependencies were obtained and used to develop a methodology for the constructive calculation of contact air coolers for a mine turbocompressor.

Stabilization of Fluidic Silty Sands with Cement and Steel Slag

Fluidic silty sand is often difficult to use directly in engineering construction because of its low strength and plasticity index. This study employed steel slag to replace part of the cement in silty sand stabilization to broaden the feasibility of resource recycling and to reduce the construction cost and carbon emissions in engineering practices. A series of indoor tests investigated the influences of the cement/steel slag ratio, initial water content, curing age, and temperature on the compressive strength of cement- and steel slag-stabilized fluidic silty sands (CSFSSs). Their stabilization mechanism was discussed via microstructural observation and spectral analysis. The results showed that the most economical cement/steel slag ratio could be 9:6, saving 40% of cement and not changing with the initial water content. The compressive strength of the CSFSSs decreased with the initial water content and increased rapidly and then slowly over the curing age. The curing temperature had a positive impact on their strength growth. The microstructure characteristics and spectral analysis showed that adding steel slag indeed affected the formation of gels in the cement-stabilized fluidic silty sands. This study could reference the application of CSFSSs in engineering practices.

Flash evaporation method for improved desalination and cooling applications: An experimental study

The present study involves the experimental analysis of flash evaporation when sudden depressurization is created into a vertical cylindrical tube having a water volume range of 120 to 180 ml. During experiments, low water pool volumes are used to prevent the impact of gravity on the change of saturation temperature. The investigation is carried out by varying the initial water temperature and back pressure of the vacuum tank in the range of 65 to 80 ∘C and 11.32 to 41.32 kPa, respectively. It is observed that the evaporation rate and cooling rate are both enhanced by increasing the initial pool temperature and decreased by increasing the back pressure. It is reported that the evaporation rate is improved by 29.7 % with an increase in initial water temperature of 5 ∘C and decreases by 152 % with an increase in the back pressure of 10 kPa. It is also found that the cooling rate is improved by 21.6 % with an increase in initial water temperature of 5 ∘C and decreased by 59.2 % with an increase of water volume of 30 ml. It is clear from the visualization procedure that the degree of superheat plays a vital role in flash evaporation.

Calorimetric determination of wet snow liquid water content: The effect of test conditions on the calorimeter constant and its impact on the measurement uncertainty

The liquid water content (lwc) of wet snow is a fundamental parameter in determining snow properties like its strength and adhesion force to surfaces. Among the different methods available for the measurement of the lwc, this paper focuses on melting calorimetry: known masses of hot water and snow are mixed into a thermally insulated container, and the lwc is obtained from the difference between the initial hot water temperature and the final mixing temperature; it is a fast and easy to implement method that requires little equipment, making it suitable for both laboratory and field measurements. Tests with “equivalent” wet snow samples whose liquid water content was known in advance were carried out to assess the method, showing that the liquid water content was overestimated by a variable amount that seemed to depend on the test parameters. To account for the heat capacity of the calorimeter, which was found not to be negligible, a constant in terms of equivalent hot water mass (E) was introduced. However, its value also depended on the test conditions. Hence, a correlation between E and the test parameters was found, and the measurements were repeated using a container of a different material, showing a similar behavior. Eventually, a discussion about the effects of choosing different hot water masses and hot water-to-snow mass ratios on measurement accuracy is provided.