Cooling Water Mass Research Articles

Performance Evaluation of a Solar Humidification – Dehumidification Desalination Unit

This paper is to investigate the use of solarenergy in desalination by humidification and dehumid-ification process (HD). Here, a proposal for the desalinationunit has been come out with cylindrical shape containing the evaporator in the middle and surrounded by the condenser.The hot feed water coming from the solar thermal system issprayed at the top of the evaporator where the air flowsfrom the bottom. In the evaporator the air is humidified until it gets out saturated, then introduced to the condenser,where it is dehumidified to obtain the fresh water andcirculated back to the evaporator. Practically there aremany parameters influence on the performance of thisdesalination unit, which are environmental, design and operational. In the current study these parameters are takenin consideration to formulate mathematical models whichgovern the performance of the main components of this unit,which are the evaporator, the condenser and the solarthermal system. The deduced mathematical models have been interpreted in many programs in visual basic languageas a computer software. This software contains many pageswhich help in introducing and analyzing the most influentialparameters. In this case many operational parameters havebeen studied such as feed water temperature, mass flow rate and salinity, in addition to cooling water mass flow rate andinlet temperature, as well as quantity of solar irradiancewith others. At these inputs many outputs have beenobtained which are related to the performance of thedesalination unit such as fresh water productivity, energy consumption, humidifier volume, recovery ratio and gainoutput ratio.

Research on Off-Design Characteristics and Control of an Innovative S-CO2 Power Cycle Driven by the Flue Gas Waste Heat

Recently, supercritical CO2 (S-CO2) has been extensively applied for the recovery of waste heat from flue gas. Although various cycle configurations have been proposed, existing studies predominantly focus on the steady analysis and optimization of different S-CO2 structures under design conditions, and there is a noticeable deficiency in off-design research, especially for the innovative S-CO2 cycles. Thus, in this work aimed at the proposed novel S-CO2 power cycle, off-design characteristics and corresponding control strategies are investigated for the waste heat recovery. Based on the design parameters of the S-CO2 cycle, structural dimensions of printed circuit heat exchangers (PCHEs) and shell-and-tube heat exchangers are determined, and design values of turbines and compressors are specified. On this basis, off-design models for these key components are formulated. By manipulating variables such as cooling water inlet temperature, cooling water mass flow rate, flue gas inlet temperature and flue gas mass flow rate, cycle performances of the system are analyzed under off-design conditions. The simulation results show that when the inlet temperature and the mass flow rate of cooling water vary separately, the thermal efficiency both can reach the maximum value of 28.43% at the design point. For the changes in heat source parameters, the optimum point is slightly deviated from the design condition. Amidst the fluctuations in flue gas inlet temperature, the thermal efficiency optimizes to a peak of 28.56% at 530 °C. In the case of variation in the flue gas mass flow rate, the highest thermal efficiency 28.75% can be obtained. Furthermore, to maintain the efficient and stable operation of the S-CO2 power cycle, the corresponding control strategy of the cooling water mass flow rate is proposed for the cooling water inlet temperature variation. Generally, when the inlet temperature of cooling water increases from 23 °C to 27 °C, the cooling water mass flow should increase from 82.3% to 132.7% of the design value to keep the system running as much as possible at design conditions.

Influence of Cooling Water Parameters on the Thermal Performance of the Secondary Circuit System of a Modular High-Temperature Gas-Cooled Reactor Nuclear Power Plant

This study quantitatively analysed the influence of cooling water parameters on the performance of a modular high-temperature gas-cooled reactor (MHTGR) nuclear power plant (NPP). The secondary circuit system and cold-end system were modelled using EBSILON software, version 16.0. The influence of cooling water inlet temperature and mass flow rate on the thermal performance of the secondary circuit system was analysed over the full power range with the goal of optimising net power. Under 100% rated condition, for each 1 °C increase in cooling water inlet temperature between 10 and 33 °C, the net power and cycle efficiency decreased by 0.67 MW and 0.14%, respectively, whereas the heat consumption rate increased by 28.72 kJ/(kW·h). The optimal cooling water mass flow rates corresponding to cooling water inlet temperatures of 16 °C and 33 °C were obtained. The optimal cooling water mass flow rate decreased nonlinearly with decreasing power levels. At a cooling water inlet temperature of 33 °C, an increase in cooling water mass flow rate from the designed value (7697.61 kg/s) to the optimal value (10,922.14 kg/s) resulted in a 1.03 MW increase in net power. These findings provide guidelines for MHTGR NPP operation optimisation and economic improvement, especially under high-temperature weather conditions.

Experimental study on condensate heat transfer coefficient of multi-channel cylinder dryer integrated with Bayesian-optimized machine learning prediction

The condensation heat transfer coefficient of the multi-channel dryer, one of the key component of paper-making machine, directly determines the efficiency of heat energy utilization. However, the prediction of condensation heat transfer coefficient remains a challenge because the heat transfer characteristics in multi-channel dryer is a complex fundamental issue involving the thermal behavior of two-phase fluid systems. Herein, we successfully developed the four supervised machine learning models to predict the heat transfer coefficient of a multi-channel cylinder dryer under different working conditions. The multi-channel cylinder dryer experiments under different steam mass flux and cooling water mass flow rates were performed and the measured data is used as the input data for training. Interestingly, the four trained Bayesian-optimized machine models present the excellent capability of prediction for condensation heat transfer coefficient of multi-channel cylinder dryer, where the values of R 2 for tested Bayesian-optimized-based SVR, ANN, linear SVR, and RF are 0.983, 0.997, 0.996, and 0.953, respectively. In addition, the feature importance of descriptors is quantified based on a random forest algorithm. Our study suggests that machine learning models can effectively predict the condensate heat transfer coefficient of two-phase fluid systems, which not only would be beneficial to optimizing the structures and operation parameters of multi-channel cylinder dryer in the industry but to develop a reasonable correlation of heat transfer coefficient in fundamental research.

High performance vapor chamber enabled by leaf-vein-inspired wick structure for high-power electronics cooling

The boom of the advanced technologies, such as microprocessors, 5G, and big data, has led the thermal management to be a crucial factor in determining the operating speed, reliability, and efficiency as well as lifetime of electronic devices. As passive heat transfer devices utilizing the liquid–vapor phase change, vapor chambers are greatly attractive due to the high thermal conductivity and passive operation. Here, we present a novel vapor chamber with leaf-vein-inspired wick structure, which could effectively facilitate the condensate to flow back to the evaporation region. Besides, the capillary wick functioned as the supporting structure instead of traditional solid supporting columns to withdraw the deformation of the vapor chamber. The heat transfer performance of the proposed vapor chamber was experimentally investigated under forced water cooling condition, and the effects of the cooling water temperature and mass flow rate were analyzed systematically. The results showed that the vapor chamber could effectively tolerate a wide heat load range from 20 W to 500 W with no noticeable performance degradation, and a minimum thermal resistance of 0.029 °C/W was attained at 200 W. Additionally, increasing the cooling water temperature and decreasing the cooling water mass flow rate could lead to the increase of the total thermal resistance at all heat loads. Finally, compared to other reported works, the vapor chamber featured a lowest thickness and vapor chamber thermal resistance, demonstrating a promising solution for cooling high-power and miniaturized electronics.

Performance analysis of nuclear powered desalination unit based on MED-TVC: a case study for Saudi Arabia

Abstract Nuclear desalination has been identified as an alternative option with much lower carbon dioxide emissions to provide fresh water by driving high capacity desalination plants. This work considers a theoretical analysis of using nuclear desalination to provide fresh water in three selected Saudi Arabian cities. It presents a theoretical model that integrates the characteristics of nuclear reactor, power cycle and desalination blocks. The power block includes three steam turbines and five feed water heaters. It is coupled via low pressure turbine to a multiple effect desalination unit integrated with a thermal vapor compressor encompassing eight effects, seven feed preheaters and a down condenser. The output includes work generated as function of fuel mass and reactor type, enrichment percentage, power and water production with different nuclear reactor type. Desalination performance indicators such as the fresh water production rate, gain output ratio (GOR), specific energy consumption (SEC) and specific cooling water mass flow rate have been evaluated and analyzed as function of sea water temperature for three specific Saudi cities. It was found that these indicators reflect better performance along a year for Jizan city than for Jubail and Tabuk. The case of Jizan city gives over the whole year more uniform values of water production rates, gain output ratio, specific energy consumption and cooling water mass flow rates.

Numerical study and experimental validation of a solar powered humidification-dehumidification desalination system with integrated air and water collectors in the humidifier

This paper presents a numerical study and experimental validation of humidification-dehumidification solar desalination unit. This unit consists of a solar evaporator and a tubular condenser. The design particularity of the evaporator is the integration of the humidifier in the solar air and water collectors. A mathematical model based on the heat and mass balances has been developed in the desalination unit. The finite difference method is adopted for discretization of the equations and the resolution is done by MATLAB software. Numerical results are compared with literature and experimental results. An acceptable agreement is observed. A parametric study was conducted to test the influence of the different operating parameters on the unit production and the Gained output ratio GOR. The production of the desalination system increases with air and water temperatures of the water in the evaporator and the inlet humid air temperature at the dehumidifier. It should be noted that the production reaches its maximum value for a feed water mass flow rate in the humidifier of 5.5 kg/h and a cooling water mass flow rate in the dehumidifier of 0.2 kg/s.

Optimization of the circulating cooling water mass flow in indirect dry cooling system of thermal power unit using artificial neural network based on genetic algorithm

The power consumption of circulating pumps can be effectively reduced by optimizing the circulating cooling water mass flow rate in indirect dry cooling system of a thermal power unit. The coupling algorithm of the artificial neural network optimized by genetic algorithm and the heat transfer model of the condenser and the air-cooled heat exchanger was established to obtain the air mass flow rate into the natural draft dry cooling tower (NDDCT). Assuming that the steam turbine back pressure is constant, the optimal mass flow rate of the circulating cooling water corresponding to the ambient temperature and the ambient temperature range in which the mass flow rate can be adjusted were obtained when the output power load was constant by using the heat transfer model of the condenser and the air-cooled heat exchanger. Calculation results show that the optimal mass flow rate of the circulating cooling water corresponding to ambient temperature gradually increased with the increase in the output power load and the decrease in the minimum inlet temperature of circulating cooling water in the NDDCT. Moreover, the ambient temperature range in which the mass flow rate of the circulating cooling water can be adjusted gradually decreased. Meanwhile, the ambient temperature range gradually decreased with the increase in the minimum outlet temperature of the circulating cooling water in the NDDCT, but the optimal mass flow rate corresponding to the ambient temperature remained unchanged. Taking the operating state of the unit on a certain day as an example, at least 16,515 kWh circulating pump power consumption can be saved by adjusting the circulating cooling water mass flow rate to the optimum value.

Experimental analysis of a transcritical heat pump system with CO2 refrigerant

Today, it is seen that increasing environmental pollution is getting ahead of the increasing energy need. Therefore, more environmentally friendly and more economical refrigerants are needed. In this context, carbon dioxide appears as a natural refrigerant in cooling systems and heat pump (HP) systems, and it has been widely used in recent years. In this study, a single-stage heat pump system with a CO2 refrigerant, with a transcritical cycle, has been experimentally studied. The system is designed as a water-to-water heat pump. The performance of the system has been determined experimentally. In the system, capillary pipes with a diameter of 2.00 mm and two different lengths are used. It is aimed to create different evaporation pressures with two capillary tubes. The first capillary tube is 2.40 m long and the second is 1.20 m long. Gas cooler pressures, gas cooler and evaporator cooling water mass flow rates were kept the same for both cases. A certain gas charge was made and measurements were made for both cases. Thermodynamic analysis and comparison of the system were made. In the short capillary tube system, it was observed that the COPHP value was 7.2% higher, the CO2 mass flow rate increased by 9.1% to achieve the same gas refrigerant pressure value, and the power consumption in the compressor decreased by 1.8%. In addition, the gas cooler outlet temperature, the evaporator outlet temperature and the change in ambient temperatures, as well as the exergetic destruction and exergetic efficiencies in the system and system components are presented in figures with EES.

Response surface methods based in artificial intelligence for superstructure thermoeconomic optimization of waste heat recovery systems in a large internal combustion engine

In a large internal combustion diesel engine, less than half of the fuel energy is converted into useful energy, while the remaining energy is lost, mainly by the exhaust gases and cooling water. Thus, the implementation of waste heat recovery (WHR) systems has been one of the main research areas for increasing power, and reducing specific fuel consumption and pollutant emissions, which favors the improvement of these engines. Currently, there are two important challenges regarding the use of WHR systems in internal combustion diesel engines: (i) identifying the best technology, or combination of technologies, for the WHR in an internal combustion diesel engine from an economic point of view; and (ii) determining the ideal configuration and the best design parameters for the most suitable system. This paper proposes an optimization procedure for automatic selection of the most economically suitable WHR technology for a large internal combustion diesel engine, as well as the definition of its optimal configuration and ideal design parameters. For this, superstructures composed by the Organic Rankine Cycle (ORC), Kalina Cycle (KC), and Conventional Rankine Cycle (CRC) are modeled and optimized using a genetic algorithm. For the formulation of the thermoeconomic optimization problem—Mixed Integer Nonlinear Programming (MINLP)—the economic model of each component of the superstructures is evaluated and the objective function is proposed based on the specific cost. However, due to the complexity of the superstructure optimization problem, the use of the response surface method to solve this problem can become more attractive than the original modelling optimization. The superstructure optimization problem, as well as its thermodynamic modeling, economic modeling and response surfaces based on radial base function and artificial neural network, were solved using the programs Engineering Equation Solver (EES) and Octave. The results show that for a medium-sized superstructure (384 variables and 17 decision variables), despite the high computational effort, the use of the response surface method in the optimization problem proved to be more efficient than the original modelling optimization, and for a large superstructure (944 variables and 45 decision variables) it is only possible to solve the optimization problem using the response surface method. Furthermore, after the superstructure’s optimizations, the additional net power is produced by ORC through of the recovery waste heat from the exhaust gases mass flow and the cooling water mass flow provided by the diesel engine. The additional net power represents around 7% of the nominal net power.

Enhancement of Heat Transfer Performance of a Heat Pipe by Using Calcium Magnesium Carbonate-Ethylene Glycol/Water Nanofluid with Sodium Dodecylbenzene Sulfonate

In this paper, the effect of using CaMg(CO3)2/Ethylene Glycol-water (50:50%) as a working fluid on the thermal performance of thermosyphon heat pipe was experimentally studied. Nanofluid was prepared by two-step method using 2% concentration of CaMg(CO3)2 nanoparticle and 0.05% surfactant (Sodium dodecylbenzene sulfonate). For the experimental set-up, a straight copper pipe of one-meter length was used. The inner diameter of the pipe is 13 mm, and the outer diameter is 15 mm. Experiments were conducted at three different cooling water mass flow rates (5, 7.5, and 10 g/s) and different heating powers (200, 300, 400 W) to test heat pipe performance. It was observed that the CaMg(CO3)2 nanofluid reduced the average wall temperature of the heat pipe according to the base fluid. Furthermore, the efficiency and thermal resistance of the heat pipe were investigated separately for EG/water and CaMg(CO3)2 nanofluid. The maximum heat transfer enhancement was obtained as 9.55% under 400 W heating power and 10 g/s cooling water mass flow rate conditions and the maximum improvement in thermal resistance was observed as 21% at 200 W and 10 g/s cooling mass flow rate. Viscosity and specific heat of base fluid and CaMg(CO3)2 nanofluid were also determined and compared to each other.

Calcareous nannofossil biostratigraphy and paleogeographic significance in the lower Maastrichtian of the Miechów Trough (southern Poland)

Biostratigraphic analysis of calcareous nannofossils from the Pełczyska section in the Miechów Trough (southern Poland) has revealed that the entire section covers the lowermost Maastrichtian. The UC16bTP Tethyan subzone is designated based on the presence of Broinsonia parca constricta Hattner, Wind and Wise, 1980, reworked remains of Uniplanarius trifidus (Stradner) Hattner and Wise in Wind and Wise, 1983 and the simultaneous lack of Eiffellithus eximius (Stover) Perch-Nielsen, 1968. The studied section spans also the interval between the LO of Zeugrhabdotus praesigmoides Burnett, 1997 and the FO of Prediscosphaera mgayae Lees, 2007 (UC16 S3 Boreal subzone). Quantitative analysis of nannofossil assemblages has shown the dominance of cold water species (up to 50%), e.g., Micula decussata Vekshina, 1959, Prediscosphaera spp., Arkhangelskiella spp., Calculites obscurus (Deflandre) Prins and Sissingh in Sissingh, 1977 and Lucianorhabdus cayeuxii Deflandre, 1959. In the early Maastrichtian, the studied area was more influenced by cool water masses from the Boreal Province rather than by warm water from the Tethyan Province. The significant predominance of cold water taxa and the elevated presence of Prediscosphaera cretacea (Arkhangelsky) Gartner, 1968 also supports the hypothesis of climate cooling in the early Maastrichtian.

Thermodynamic Analysis of Steam Cooling Process in Marine Power Plant by Using Desuperheater

Thermodynamic (energy and exergy) analysis of steam cooling process in the marine steam propulsion plant is presented in this research. Steam cooling is performed by using Desuperheater which inject water in the superheated steam to obtain wet steam. Wet steam is used in auxiliary heaters for various heating purposes inside the marine steam propulsion system. Auxiliary heaters require wet steam due to safety reasons and for easier steam condensation after heat transfer. Analysis of steam cooling process is performed for a variety of steam system loads. Mass flow rates of cooling water and superheated steam in a properly balanced cooling process should have the same trends at different system loads - deviations from this conclusion is expected only for a notable change in any fluid temperature. Reduction in steam temperature is dependable on the superheated steam temperature (at Desuperheater inlet) because the temperature of wet steam (at Desuperheater outlet) is intended to be almost constant at all steam system loads. Energy losses of steam cooling process for all observed system loads are low and in range between 10–30 kW, while exergy losses are lower in comparison to energy losses (between 5–15 kW) for all loads except three the highest ones. At the highest system loads exergy losses strongly increase and are higher than 20 kW (up to 40 kW). The energy efficiency of a steam cooling process is very high (around 99% or higher), while exergy efficiency is slightly lower than energy efficiency (around 98% or higher) for all loads except the highest ones. At the highest steam system loads, due to a notable increase in cooling water mass flow rate and high temperature reduction, steam cooling process exergy efficiency significantly decreases, but still remains acceptably high (between 95% and 97%). Observation of both energy and exergy losses and efficiencies leads to conclusion that exergy analysis consider notable increase in mass flow rate of cooling water which thermodynamic properties (especially specific exergies) strongly differs in comparison to steam. Such element cannot be seen in the energy analysis of the same system.

Comparative Numerical Study on Global Heat Transfer Process in Micro-Channel Gas Coolers with Different Structures

A numerical simulation of global heat transfer process in three types of micro-channel heat exchangers was investigated in this paper: spiral double-pipe micro-channel heat exchanger (DPHE), cross-plate micro-channel heat exchanger (CPHE), and shell and tube micro-channel heat exchanger (STHE). The inner tubes of all three heat exchangers have a diameter of 1 mm and are charged with CO2 as refrigerant. A detailed analysis of the heat exchanger's global heat transfer process was carried out, which is entirely different for different structures. The heat transfer characteristics of supercritical CO2 were analyzed by considering the operating pressure, the refrigerant mass flux, the cooling water mass flux, and the heat exchanger refrigerant inlet temperature. The relationship between the CO2 heat transfer coefficient (hCO2) and CO2 bulk temperature (Tb,CO2) was analyzed in detail. The pseudo-critical temperature (Tpc) mainly determines where the peak CO2 heat transfer coefficient occurs. When Tb,CO2 < Tpc , the rise in Tb,CO2 is accompanied by an increase in the heat transfer coefficient, which reaches a maximum when Tb,CO2 is a little bit higher than the pseudo-critical temperature, the heat transfer coefficient curve begins to decline as Tb,CO2 continues to rise. Higher peak heat transfer coefficients can be achieved at higher pressures. Increased refrigerant mass flux always results in larger heat transfer coefficients. The influence of the refrigerant inlet temperature of the heat exchanger in the Tb,CO2 < Tpc region on the heat transfer coefficient is more significant than expected. In this study, different flow patterns on heat transfer due to different structures were compared. The best heat transfer was achieved using a spiral double-pipe micro-channel heat exchanger (DPHE). It consistently reaches the highest heat transfer and the lowest outlet temperature under the same operating conditions‎.

Flow Regimes and Transitions for Two-Phase Flow of R152a During Condensation in a Circular Minichannel

Two-phase flow regimes were experimentally investigated during the entire condensation process of refrigerant R152a in a circular glass minichannel. The inner and outer diameters of the test minichannel were 0.75 and 1.50 mm. The channel was 500 mm long to allow observation of all the two-phase flow regimes during the condensation process. The experiments used saturation temperatures from 30 to 50°C, a mass flux of 150 kg/(m2·s) and vapor qualities from 0 to 1. The annular, intermittent and bubbly flow regimes were observed for the experimental conditions in the study. The absence of the stratified flow regime shows that the gravitational effect is no longer dominant in the minichannel for these conditions. Vapor-liquid interfacial waves, liquid bridge formation and vapor core breakage were observed in the minichannel. Quantitative measurements of flow regime transition locations were carried out in the present study. The experiments also showed the effects of the saturation temperature and the cooling water mass flow rate on flow regime transitions. The results show that the annular flow range decreases and the intermittent and bubbly flow ranges change little with increasing saturation temperature. The cooling water mass flow rate ranging from 38.3 kg/h to 113.8 kg/h had little effect on the flow regime transitions.

4E analysis and multiobjective optimization of a PEMFC-based CCHP system with dehumidification

This paper proposes a novel PEMFC-based combined cooling, heating and power (CCHP) system with independent control of refrigeration and dehumidification, which is used in data centers with strict requirements on temperature and humidity. The effects of operating parameters of PEMFC (current density, hydrogen and oxygen pressure) and refrigeration system (hot water distribution ratio, mass flow of cooling water and chilled water) on the 4E (energy, exergy, economy and environment) are investigated. Meanwhile, multiobjective optimization of the above parameters is carried out. The results show that a high inlet pressure is beneficial to improve system efficiency and reduce annual greenhouse gas (GHG) emissions. An increase in the chilled water mass flow increases system efficiency and reduces annual GHG emissions, while an increase in the cooling water mass flow yields the opposite results. Moreover, an increase in the proportion of hot water entering the adsorption chiller causes system efficiency and the annual GHG reduction to initially decrease and then increase. Compared with the unoptimized system, the energy efficiency, exergy efficiency, system cost, GHG emission reduction, electric power, cooling power, heating power and dehumidification rate of the system increase by 5.5%, 0.77%, 10%, 21.27%, 12.87%, 5.37%, 45.73% and 1.53%, respectively.

Performance investigation of a counterflow packing tower for flue gas waste heat recovery

Direct emission of flue gas waste heat into the environment causes a great waste of energy. In order to recover the waste heat of the flue gas efficiently, a counterflow packing tower for flue gas waste heat recovery is presented. In this paper, the mathematical model of the counterflow packing tower is established and experiments were conducted for model validation. A Genetic Algorithm based approach was proposed to obtain the correlation equations of the heat and mass transfer coefficient between the flue gas and cooling water. The performance of the counterflow packing tower under different operational conditions is studied with the mathematical model. Results indicate that: (1) For different packing heights, the relative position of the maximum diffusion flux remains unchanged, which is 0.2 in this study. (2) The effectiveness of CFPT of the counterflow packing tower is positively correlated with the flue gas inlet temperature, the flue gas inlet humidity ratio, the cooling water mass flow rate and the packing height. When the flue gas inlet temperature is 75–95 °C, the cooling water inlet temperature is 20–26 °C, the effectiveness of CFPT is about 50–67%.

Labrador Slope Water connects the subarctic with the Gulf Stream

Labrador Slope Water (LSLW) is a relatively fresh and cool water mass that originates from the Labrador Current in the subarctic and is known to occur in the Eastern Slope Sea on the US-Canadian shelf-slope north of the Gulf Stream. It has potential densities of 27.4–27.65 kg m−3. Using ocean observations, we show here that the LSLW penetrates as a boundary current deeply into the Western Slope Sea (west of 66°W) as a salinity minimum between 400 and 600 m, bringing it into close proximity with the Gulf Stream. The LSLW at Line W (near 69°W) also spreads across, and brings fresher and thicker waters to, the Slope Sea north of the Gulf Stream. A high-resolution ocean model simulation shows that the spreading of the LSLW occurs throughout the entire Slope Sea through the extrusion of fine-scale filaments from the boundary current following interaction with Gulf Stream meanders and eddies. At Line W, the LSLW is also found to be fresher and thicker between 2003 and 2008, when the Atlantic Meridional Overturning Circulation (AMOC) at 26°N is higher (by 3 Sv), and the Shelf Slope Front is further south (by 0.7°), compared to AMOC low conditions in 2009–2014. The thicker LSLW causes lighter isopycnals to rise over the shelf slope, and through increasing the lateral density gradient contributes an additional 1.3 Sv to the Gulf Stream transport. These changes to the LSLW and the Shelf Slope Front are likely to result from an enhanced flow of the Labrador Current into the Slope Sea, caused by changes in the wind stress in the subpolar gyre. The transport of the LSLW (as opposed to the deeper Labrador Sea Water) thereby offers a potential new mechanism for decadal variability in the Atlantic climate system, through connecting changes in the subarctic with subsequent variability in the Gulf Stream and AMOC.

An investigation of the second law performance for a condenser used in 210 MW thermal power station

This work presents a case study of thermodynamic performance of a condenser used in a 210 MW thermal power station at Mejia in West Bengal, India. The analysis involves an improvement of actual overall heat transfer coefficient by varying tube materials and fouling resistance. Exergy Destruction Factor (EDF) is introduced to quantify the percentage of exergy loss from the condenser wall. From this study, it is revealed that the second law performance of the condenser increases with the increase in thermal conductivity of the tube materials, decreases with the increase in fouling resistance and decreases with the increase in condenser pressure at the turbine outlet. The actual overall heat transfer coefficient can be increased up to 6% by selecting better conducting tube materials. While the EDF decreases with the increase in cooling water temperature rise and increases with the increase in cooling water inlet temperature, EDF is found to decrease with the increased cooling water mass flow rate.

Optimization of the cooling water mass flow rate under variable load of a power unit

• Optimization of the cooling water mass flow rate for a power unit was performed. • The cooling water mass flow rate should be reduced for load below 60% of rated power. • The power unit model in off-design conditions was developed in Ebsilon software. As the contribution of renewable energy sources in the energy balance is increasing, traditional thermal power units have to be more flexible over a full and thus extended range of load conditions, among other requirements. Furthermore, the efficiency of power units should not significantly decrease under lower load conditions which will often occur. The paper analyzes the process of determining the cooling water mass flow rate under the power unit load varying between 100% and 40% with the aim of achieving the maximum efficiency and power output. A mathematical model of a 225-MW power unit was developed using Ebsilon software and validated based on measurement data. The efficiency characteristics of the boiler, turbine and cooling water pump in off-design conditions as a function of load were entered in Ebsilon. As part of the calculations, the optimal cooling water mass flow rates were determined. The analysis shows that reducing the cooling water mass flow rate may seem reasonable in the case of power units operating at less than 60% load. Assuming that the power unit operates under 40% load for 1000 h per annum, if the cooling water flow rate is reduced from the nominal value down to the optimal one, the 225-MW power unit would produce an additional net power output of about 137 MWh.