Outlet Water Research Articles

Extremum seeking control for real-time optimization of high temperature heat pump systems incorporating vapor injection

In order to minimize the power consumption of a vapor-injected high temperature heat pump system with R245fa as refrigerant, a control strategy, namely Extremum seeking control, is proposed. It can implement real-time model-free optimization control of plants with concave and convex properties. Modelica-based dynamic simulation model of the proposed system is developed. The Newton-based Extremum seeking control is used to optimize the intermediate pressure of the proposed system to obtain the minimum power consumption of the compressor at a fixed heating capacity (200 kW). The adopted ESC strategy requires four measured quantities, namely, injection pressure, condenser outlet water temperature, evaporator outlet superheat and compressor power consumption, to achieve optimal control of the system in real time. Two operation scenarios are simulated: stable and freely variable heat source temperature. For both scenarios, the condenser outlet water temperature was set to 140 °C. The simulation results show that at stable heat source temperature, the power consumption is reduced by 5.2% and the COP is increased by 7.7% compared to a fixed initial intermediate pressure. Under the free-variable heat source condition, the power consumption can be reduced by up to 5 kW compared to a constant input. A total of 283 kWh of power was saved during the 48 h simulation. Thus, the Newton-based extremum seeking control strategy can optimize the intermediate pressure to achieve the minimum power consumption while maintaining excellent transient performance, and demonstrate the superiority of the ESC strategy for real-time optimization..

Experimental and economic analysis of optimization potential for annual operating characteristics of air source transcritical CO2 heat pump system

In this study, an experimental system of air source transcritical CO2 heat pump system was established for investigating annual operating characteristics. A new operating strategy was proposed based on experimental results, and the economic analysis was studied based on different operating strategies. The results showed that the ambient temperatures had the slight effect on the system performance for summer and transition seasons conditions, which had the greater influence on that for winter conditions. When the ambient temperatures are lower, there were the obvious variations of the system heating capacity. The coefficient of performance decreases with the rise of water outlet temperatures. The annual operating expenses significantly reduced from 659.71 Chinese yuan to 514.72 Chinese yuan, which accounted for approximately 78% of the before-optimization cost. The optimized cycle was verified to be preferable, and the presented discussion could provide a promising solution for optimizing transcritical CO2 system.

CFD analysis of Part-Load operation of an Open-Circuit Induced-Draft cooling tower

Evaporative towers are the most widely used systems for cooling water in industrial processes. These systems, however, are characterized by high energy and water consumptions. Therefore, technologies and operating strategies for optimization of these devices are highly recommended. The heat exchange, which takes place inside an evaporative tower is very complex and not easy to model. In this work, an induced-draft evaporative tower is modelled by means of computational fluid dynamics (CFD), which is relatively new in this field of application. A numerical model, based on the adoption of sub-models for the heat exchange between the water droplets and humid air in the filling region, is developed and validated with experimental data, laying the foundation for further analysis in the future. The achieved results can be considered reliable and accurate as the numerical uncertainty is approximately 4 %. The study aims at evaluating and analyzing the thermo-fluid-dynamic quantities that characterize the heat exchange, with reference to water outlet temperature, cooling capacity, and evaporated water flow rate. In particular, partial load operation are analyzed. The conditions refer to the simultaneous reduction of water and air flow rates. The study shows that both at full load operation and by reducing water and air flow rates to 60 % of the design value while maintaining a constant water/air ratio, the tower process parameters are kept very close to the design ones. Under these conditions, the evaporated water is halved (∼0.05 kg/s instead of ∼ 0.1 kg/s maintaining air flow at full load). Moreover, by adopting lower water and air flow rates a significant reduction of the electric power requested by the fan, from 15 kW at full load to about 8 kW at part load, is achieved.

Early succession of biofilm bacterial communities in newly built drinking water pipelines via multi-area analysis

Biofilms inhabiting pipeline walls are critical to drinking water quality and safety. With massive pipeline replacement underway, however, biofilm formation process in newly built pipes and its effects on water quality are unclear. Moreover, differences and connections between biofilms in newly built and old pipes are unknown. In this study, early succession (≤ 120days) of biofilm bacterial communities (abundance and diversity) in upper, middle and bottom areas of a newly built cement-lined ductile iron pipeline were evaluated using improved Propella™ biofilm reactor and multi-area analysis. A comparison with old pipelines (grey cast iron, 10years) was performed. In the newly built pipeline, the abundance of biofilm bacteria did not change significantly between 40 and 80days, but increased significantly between 80 and 120days. The biofilm bacterial abundance (per unit area) in the bottom area was always higher than that in the upper and middle areas. Based on alpha diversity index and PCoA results, biofilm bacterial community richness, diversity and composition did not change significantly during the 120-day operation. Besides, biofilm shedding from the walls of newly built pipeline significantly increased bacterial abundance in the outlet water. Opportunistic pathogen-containing genera, such as Burkholderia, Acinetobacter and Legionella, were identified in both water and biofilm samples from newly built pipelines. The comparison between new and old pipelines suggested a higher bacterial abundance per unit area at the middle and bottom areas in old pipelines. Moreover, the bacterial community composition of biofilms in old pipelines was similar to that of newly built pipelines. These results contribute to accurate prediction and management of biofilm microbial communities in drinking water pipelines, ensuring the biosafety of drinking water. KEY POINTS: • Biofilm bacterial communities in different areas of pipe wall were revealed. • The abundance of biofilm bacteria increased significantly between 80 and 120days. • Biofilm bacterial community compositions of newly built and old pipes were similar.

Performance evaluation of delta-nabla channel configuration in a solar absorber with thermal energy storage

A novel configuration of solar absorber containing water channels of triangular cross-section in a delta-nabla arrangement, has been experimentally investigated. Traditionally, the triangular channeled solar absorbers are in use for space heating, but their effectiveness in solar water heating systems is yet to be explored. In addition to the performance investigation of the absorber, the effect of an integrated phase change material (PCM) based thermal energy storage (TES) has also been examined under solar and off-solar conditions. The highest temperature of 80 °C is obtained on the right side of the absorber containing hot water outlet in contrast to the left side where the cold-water inlet is located. Moreover, the average temperature gradient exists along the surface normal from the channel contours to the outside glazing. Integration of paraffin-based TES provides 62 L of water above 30 °C during off solar conditions. The efficiency of TES increases with smaller delays after charging and for higher flow rates because of reduced heat losses from the storage to the atmosphere. A delta-nabla configuration comparison with a conventional flat plate type solar absorber shows a prominent improvement in the overall performance.

Study on performance of a gas engine-driven heat pump system with R410A for heating and domestic hot water applications

Traditional gas engine-driven heat pump (GHP) systems were switched off in the transitional season, and the engine waste heat could no longer be used for producing domestic hot water. Most studies on GHP systems used piston compressors with low efficiency, and the refrigerants used were R134a or R407C. This paper presents an innovative GHP system using open scroll compressors with R410A which can be used throughout the year. The novel GHP system can be switched freely between heating mode-H, which produced heating water combined with domestic hot water, and heating mode-D which only produced domestic hot water. In these two heating modes, the effects of different condenser water outlet temperatures (tw,out1), domestic hot water outlet temperatures (tw,out2), engine speeds (Neng), and total domestic hot water outlet temperatures (tw,out3) on performance of the GHP system for heating and domestic hot water applications were experimentally investigated. The results show that tw,out1 and tw,out3 have greater effect on primary energy ratio (PER), Neng has significantly larger effect on heating capacity and the recovered waste heat, whereas tw,out2 has little effect on the comprehensive performance. The change between heating mode-H and heating mode-D hardly affects the system heating performance. For the experiments, the waste heat recovery rates are between 42.05 % and 61.08 %. The total PER of the GHP system ranges from 1.179 to 1.453 without waste heat recovery, while it ranges from 1.521 to 1.834 when the engine waste heat is recovered. It indicates that the total PER can be significantly improved by recovering the engine waste heat.

Design of a prototypical natural circulation water-based reactor cavity cooling system (RCCS) for a pebble-bed generic FHR

A prototypical natural circulation water-based reactor cavity cooling system (RCCS) for the UC Berkeley Mark-1 pebble-bed gFHR is designed based on one-dimensional thermal hydraulics modeling and optimization implemented in an in-house MATLAB code. The model employs a lumped core consisting of fuel pebble and graphite pebble regions, while the graphite reflector, vessel, and RCCS are represented as separate but energy-coupled regions. The model is derived based on steady state energy balance equations accounting for conductive heat transfer from the lumped core to the vessel and subsequent radiative heat transfer to the RCCS and convective heat transfer in the water. Mass flow rate is calculated based on momentum and thermal energy balance in the RCCS. Starting with ANL’s water NSTF as baseline, effects of RCCS design parameters such as size of the plate between pipes, pipe diameter, source-to-sink distance, surface emissivity, and pitch from the core are examined in an integral effects framework which accounts for subsequent variation of the mass flow rate, number of pipes, convection coefficient, mean region and surface temperatures, radiative view factors, and water outlet temperature. The importance of including a prototypical reactor design in RCCS design calculations is emphasized as the calculations show that temperature drops from the core to the RCCS fluid to transfer the heat tend to be the limitation not the heat removal capacity of the fluid. A closed-loop design is obtained with capability to safely remove up to 0.72% of the nominal reactor power at maximum estimated peak conditions and 0.40% at shutdown. The design is based on physics calculations and does not account for economic optimization.

Implementation of electrocoagulation for reduction of Zn in an outlet stream from waste incineration plant

The paper is focusing on the full-scale operation of electrocoagulation for Zn removal from wastewater with origin in a municipal incineration plant. The process was custom designed for continuous full-scale operation. Total capacity of the process varied between 1200 and 1400L/h. This was achieved by two simultaneous electrocoagulation cells operated in parallel. Residual concentrations of Zn in the treated water were consistently lower than 0.5 mg/L during the testing period. Residual concentrations of Zn and other accompanying contaminants were reduced below the desired limits (current limit for Zn in outlet water is 1.5 mg/L). The process cost was critically assessed. The electricity consumption for the operation of electrocoagulation cells is 0.75–1.1 kWh/m3 of purified water. A more significant expense is the consumption of electrode cartridges. The service life of electrode cartridges with a plate thickness of 5 mm is about 1 200 m3 of water/electrode pack, which represents a cost of around 0.6–1 EUR/m3 out of total 1.6 EUR/m3 of purified water. Waste incineration plants usually produce their own electricity therefore technologies like electrocoagulation become affordable and competitive.

Thermal, exergy and economic analysis of a cascaded packed-bed tank with multiple phase change materials for district cooling system

In Singapore's industry, the required temperature of a district cooling system's outlet and return water are 5 °C and 12 °C, respectively. Thus far, few researches have been reported on the cascaded phase change material (PCM) tank focusing on this temperature duration. In this study, a cascaded packed-bed tank for a district cooling system is proposed to improve heat transfer efficiency and decrease tank cost with the same cold energy capacity. The cascaded PCM system, employing PCM-1 and PCM-2 (volume ratio 50%–50% and 30%–70% tetradecane-hexadecane mixtures), is designed, modeled, and validated through experimental data. Key results revealed that the PCM-1 tank performs poorly during its charging phase, while the PCM-2 tank performs poorly in discharging phase. However, the proposed cascaded packed-bed tank that simultaneously PCM-1 and PCM-2 can achieve high average exergy efficiencies during the charging and discharging phases. Additionally, the cascaded system incorporating 0.42 of PCM-1 and 0.18 of PCM-2 demonstrates higher exergy efficiency and tank volume but incurs higher construction costs than other tank designs. Comparatively, the same cold energy capacity tank with 0.18 of PCM-1 and 0.42 of PCM-2 reduces construction cost by 6.8%, with a depreciation of exergy efficiency by 14.1% during the discharging phase.

Перспективы и преимущества использования металлосетчатых каталитических реакторов для газовых отопительных систем и бытовых нагревательных приборов

This article aims to acquaint as many specialists in the field of heat engineering and thermal power engineering as possible with the possibilities and advantages of metal-mesh catalytic heaters developed at the Institute of Catalysis SB RAS. They are shown to be fundamentally different from catalytic heaters in which ceramic or glass-fiber structures are used as carriers of oxidation catalysts. Practical examples of the implementation of this technology on the example of a hot water boiler, infrared heaters and other small-sized household appliances are given. It was shown experimentally that the supplied gas is oxidized completely, and the efficiency of the laboratory, even unoptimized sample of hot water boiler determined by the inlet and outlet water temperature is not lower than 85 % in the range from 15 to 100 % of nominal capacity and 93 % in the low-power mode. The presented technology enables smooth regulation of the heater output within the whole range from 1.5 to 10 kW with power overlap factor of about 7.

Long-term warming modulates diversity, vertical structuring of microbial communities, and sulfate reduction in coastal Baltic Sea sediments.

Coastal waters such as those found in the Baltic Sea already suffer from anthropogenic related problems including increased algal blooming and hypoxia while ongoing and future climate change will likely worsen these effects. Microbial communities in sediments play a crucial role in the marine energy- and nutrient cycling, and how they are affected by climate change and shape the environment in the future is of great interest. The aims of this study were to investigate potential effects of prolonged warming on microbial community composition and nutrient cycling including sulfate reduction in surface (∼0.5 cm) to deeper sediments (∼ 24 cm). To investigate this, 16S rRNA gene amplicon sequencing was performed, and sulfate concentrations were measured and compared between sediments in a heated bay (which has been used as a cooling water outlet from a nearby nuclear power plant for approximately 50 years) and a nearby but unaffected control bay. The results showed variation in overall microbial diversity according to sediment depth and higher sulfate flux in the heated bay compared to the control bay. A difference in vertical community structure reflected increased relative abundances of sulfur oxidizing- and sulfate reducing bacteria along with a higher proportion of archaea, such as Bathyarchaeota, in the heated compared to the control bay. This was particularly evident closer to the sediment surface, indicating a compression of geochemical zones in the heated bay. These results corroborate findings in previous studies and additionally point to an amplified effect of prolonged warming deeper in the sediment, which could result in elevated concentrations of toxic compounds and greenhouse gases closer to the sediment surface.

Effect of novel phase change material (PCM) encapsulated design on thermal performance of solar collector

Solar energy is one of the renewable energy sources that has a great potential for water heating system applications. In this work, the effect of the PCM on the outlet water temperature was studied. The solar energy is collected in the phase change material (PCM) by the storage unit during the higher radiation hours. The collected thermal energy then used to heat the water during the lower radiation hour. In this work, the effect of the PCM on the outlet water temperature was studied. Furthermore, the performance of consecutive two years (2018 and 2019) of thermal solar collector was investigated. The compound parabolic concentrator (CPC) was positioned on the upper surface of the thermal collector. Moreover, a thin layer of PCM was positioned under the absorber plate as a back layer for the storage of the collected latent heat. A constant flow rate was obtained at maximum outlet water temperature for those consecutive years. Additionally, a relatively steadier decrease of solar efficiency at lower solar radiation was also evident on the PCM system compared to that of the system without PCM thin film. The efficiency of solar collector depends on the design of solar collector and our proposed design was able to extract a prospective thermal efficiency for two consecutive years of observation. These outputs are satisfactory and acceptable for long-term applications for both domestic and industrial purposes.

Experimental investigation of thermal storage integrated indirect solar cooker with and without reflectors

Environmental degradation, harmful gas emissions, and the increase in prices of fuel and electricity are the main driving forces behind the need for more effective utilization of renewable energy. In the present study, indirect solar cooking system with a flat plate collector integrated with a phase change material was designed, constructed and experimentally tested. Comparative study was conducted on the performance of the solar cooker with and without reflectors. Four plane reflectors on each side of the collector were used to enhance the solar insolation falling on the collector while stearic acid is used as PCM in the thermal storage unit. Daily average enhancement of 42.3% on the reflected solar radiation was found with four reflectors. The result showed that the maximum average absorber plate temperature, maximum outlet water temperature, maximum energy and exergy efficiency of FPC with and without reflectors are found to be 130 °C, 103.65 °C , 79%, and 48% and 92 °C, 71 °C, 63%, and 42% respectively.The overall system efficiency of the indirect solar cooker was found to be 19.04%. The utilization efficiency and characteristic boiling time of the cooker was found to be 22.3% and 15.7 min/kg.

Simulation of the Temperature of a Shielding Induction Motor of the Nuclear Main Pump under Different Turbulence Models

Thermal design and the choice of turbulence models are crucial for motors. In this project, the geometrical model of the vertical shielding induction motor for a small nuclear main pump was established by SolidWorks software and the finite volume method was adopted to investigate the temperature of the motor, especially the temperatures of bearings lubricated water. To make the numerical simulation of flow and heat transfer in the rotating clearance of the shielding induction motor more accurate, the effects of four types of different two equation turbulence models on the temperature field of the shielding induction motor were studied. The results showed that different choices of turbulence models had little effect on the temperature of the winding insulation but influenced the temperature of the lower guide bearing lubricating water and the secondary cooling water outlet. The SST k-ω model showed the lowest relative error result of the temperature of the winding insulation and the bearing lubricating water in the primary loop system of the shielding induction motor. The temperature of the clearance water, the spiral tube water and the spiral groove water increased approximately linearly along the axial direction.

Performance analysis of a novel PV/T hybrid system based on spectral beam splitting

Photovoltaic/thermal (PV/T) hybrid utilization is a promising method for efficient solar energy harvesting. However, a low operating temperature is required for photovoltaic (PV) conversion to make PV efficiency at a high level, while a relatively high operating temperature is preferred for photothermal (PT) conversion to improve the quality of collected heat, which causes a temperature conflict and induces certain limitations on the efficiency and scale promotion of PV/T. Herein, a novel PV/T system is proposed based on the spectral beam splitting and serial thermal circuit to decouple the power generation and heat collection, which aims to reduce the intrinsic temperature conflict and improve efficiency. A combined thermal-electrical model of the PV/T system is developed and parametric analysis is performed. Predicted results show that the temperature of the solar cells is 7.7 °C lower than the outlet water temperature in the novel PV/T system, demonstrating the temperature-decouple effect. Compared with the traditional PV/T system, the outlet water temperature is 3.9 °C higher and the solar cell temperature is 9.4 °C lower in the proposed system, showing a comprehensive efficiency improvement of 17.9%. In summary, this work provides an alternative way for efficient PV/T utilization by decoupling the operating temperature of PV and PT processes.

Numerical study of different micro-channel structures on fluid flow and heat transfer performance

This research mainly proposed three new types of micro-channel heat sink structures. Numerical simulations and simulation calculations were carried out on the heat sink structure. The three groups of inlet flow rates were used as the main variables to analyse the three new types of heat sinks, model flow characteristics and heat transfer performance. In addition, it was compared with the traditional rectangular micro-channel heat sink (RT-MCHS). Based on and compared with RT-MCHS, three new microchannel heat sinks, reverse concave microchannel heat sink (RC-MCHS), co-directional concave microchannel heat sink (CC-MCHS) and convex reverse concave microchannel heat sink (CRC-MCHS), were designed and studied numerically. The comparative analysis of MCHS design performance includes fluid flow characteristics, fluid heat transfer performance and heat transfer efficiency. The effects of inlet velocity on the Darcy friction coefficient, pressure drop, Nusselt number, average outlet temperatures and efficiency factors were studied numerically as inlet velocity from 1 m·s-1 to 5 m·s-1. The results show that the optimal strategy in the new design is the CRC-MCHS, which can hinder the flow of fluid and enable sufficient heat exchange between the liquid and the substrate. In addition, at the optimal inlet flow rate of 3 m·s-1, the outlet water temperature of CC-MCHS is the lowest, indicating the heat transfer performance of the electronic components is the best.

An optimization of acquiring geothermal energy from a deep geothermal well by downhole coaxial open loop (DCOL)

As one of the methods to extract geothermal energy, downhole coaxial heat exchanger is widely concerned because of its high heat extraction rate and no need of re injection. However, there are few studies on the extraction of open-loop heat from a single deep geothermal shaft, and there is a lack of detailed inlet and outlet transient temperature data. In this study, the downhole coaxial open-loop heat collector is improved, and the slotted liner at the bottom of the well is used to form a free open space to improve the heat exchange. Using the improved experimental device design, the field thermal recovery test was carried out in deep geothermal well of Shengli Oilfield, Dongying, China. According to the field test results, the control equation was established, and the influence of parameters on the thermal recovery rate was studied. It is found that the improved heat output is greater than the reported value of the downhole heat exchanger with the traditional structure. After about eight days, the heat extraction rate reached a gradually stable stage. After 15 days of continuous operation, the heat output is stable at 200 kW, and the water temperature at the water outlet is 34.6 °C.

Numerical investigation of a shell-and-tube thermochemical reactor with thermal bridges: Structurale optimization and performance evaluation

Thermochemical heat storage is a key technology to solve the mismatch between supply and demand of renewable energy and realize long-term energy storage. This work is concerned about a shell-and-tube thermochemical energy storage reactor and its aim is to address a challenge associated the low reaction rate from the tube centre of the reactor due to low thermal conductivity of the storage material. We proposed the integration of porous copper thermal bridges into the reactor and examined the performance enhancement with a validated mathematical model. By optimizing the structural parameters (numbers, thickness, and porosity) of the thermal bridge, the discharging rate and water temperature of the reactor can be maximized while the fan's electricity consumption is reduced. The results show that, with the addition of the thermal bridges with optimal structural parameters, the total heat release and water peak temperature lift can be increased by 11.33% and 39.75%, respectively, with the peak outlet water temperature reaching 59.02 °C. Reducing air velocity from 0.428 m/s to 0.107 m/s, the fan's electricity consumption can be reduced by 85.07% and 91.72% in the charging and discharging processes, which can be reduced by another 62.34% and 16.55%, respectively, after adding the thermal bridge.

Multi-Domain Modeling and Analysis of Marine Steam Power System Based on Digital Twin

The marine steam power system includes a large amount of thermal equipment; meanwhile, the marine environment is harsh and the working conditions change frequently. Operation management involves many disciplines, such as heat, machinery, control, electricity, etc. It is a complex multi-discipline physical system with typical nonlinear, multi-parameter, strong coupling characteristics. In order to realize the health management of a marine steam power system, based on digital twin technology combined with the Modelica language, modular modeling, etc., this paper conducts in-depth research on the multi-domain modeling of the marine steam power system, characteristic analysis of variable working conditions, fault simulation, etc. The analysis results show that the dynamic response trend of the model is consistent with the actual operation, the error of the main steam flow at 1800 s is the largest and is −4.9%, and the error of the main steam flow, steam turbine output power, cooling water outlet temperature and other key parameters is within ±5%. Virtual reality mapping between the digital model and the physical equipment is realized, which lays a foundation for mastering the dynamic characteristics of the marine steam power system.

Research on The Performance of A Novel Compact Electrostatic Separator: From Laboratory Experiment to Oilfield Test

ABSTRACT Water cut of oil well stream becomes high and crude oil emulsions are more stable and complex as most oilfields are in middle and late exploitation stage. It is difficult to meet the outlet oil quality requirement by using conventional electric dehydrator with bulky tank configuration in crude oil dehydration process. In this paper, we developed a novel compact electrostatic separator (CES) which combines the effect of electric field, centrifugal field and gravitational field. We firstly investigated the variations of oil content at the water outlet of CES under different working conditions in laboratory experiment. Then dehydration performance of the engineering prototype with two-stage CES were studied in the oilfield test. Oilfield test results showed the CES could effectively demulsify water-oil emulsions with water cut as high as 80%. Electric frequency has more significant influence on dehydration performance than electric voltage. Water content at the oil outlet and oil content at the water outlet of CES could be as low as 3.3% and 302.1 ppm, respectively. The laboratory experiment and oilfield test both have demonstrated good dehydration performance of CES. Results in this study can lay a solid foundation for further optimization and engineering application of compact electrostatic separator.