Cooling Water Temperature Research Articles

Analysis of a Thermal Energy Storage Tank in a Large District Cooling System: A Case Study

This study’s primary goal is to evaluate the performance of a large thermal energy storage tank installed in a Gas District Cooling (GDC) plant. The performance parameters considered in this study include thermocline thickness (WTc), Cumulated Charge (Qcum), and Half Figure of Merit (½ FOM). The operation sensor data of a large Thermal Energy Storage (TES) tank was acquired for this analysis. The recorded temperature sensor from the 1st to 7th January and from 12th to 17th October 2019 was considered in this research. GraphPad prism computer software was deployed for analyses, and the temperature distribution data were analyzed to determine the four temperature parameters (hot water temperature (Th), cool water temperature (Tc), cool water depth (C), and slope gradient (S)) using a non-linear regression curve fitting technique and sigmoid Dose Responses function as integrated with the software. At the end of this research, the relationship between the growth of the determined performance parameter with charging hours was analyzed and presented. The research results proved the ability of GraphPad Prism software to assess the temperature distribution in the TES tank and also the corresponding effects on the overall Tank performance. The software offers better advantages in evaluating the performance parameter of the TES tank accurately.

Modeling of geothermal power system equipped with absorption refrigeration and solar energy using multilayer perceptron neural network optimized with imperialist competitive algorithm

For geothermal energy system, the low geothermal well operating lifetime and temperature is one of the main obstacles. Also, finding the optimum design parameters and operating conditions requires many experimental tests and intricate mathematical models. Besides, improving the energy efficiency and lacking technical feasibility of the combined geothermal systems are other challenges concerning geothermal systems. To cover the mentioned challenges, in the current study, a hybrid geothermal/absorption refrigeration system (ARS) incorporated with solar thermal collector, desalination unit and hydrogen storage system is designed and assessed. The proposed system is investigated by developing two methods of artificial intelligence (AI) as well as thermodynamic model. The intelligent methods are multilayer perceptron (MLP) neural network optimized with imperialist competitive algorithm (ICA), MLP-ICA, and MLP optimized with genetic algorithm (GA), MLP-GA. These methods are manufactured based on the solar irradiance, cooling water temperature difference, ambient temperature, pinch-point temperature, evaporating and condensing temperatures as independent parameters. These parameters are utilized to obtain the power generation, coefficient of performance of the ARS (COPchiller), heat exchanger area of the ARS, and cycle thermal efficiency.The obtained results show that simulation of the system by MLP-ICA was successfully carried out and this model operates substantially better than the MLP-GA for simulating the behavior of the system. Also, the payback time for the proposed system (with the interest rate of 3%) was obtained around 8 years.

Development of the thermal performance model using temperature gradient analysis for optimized design of steam surface condenser

This paper presents a new method of evaluating the thermal performance of a steam condenser based on the temperature gradient between steam and cooling water. With reference to the experimental results, the pressure transition temperature (PTT), defined as the limiting cooling water temperature initiating insufficient heat removal over the applied heat load, was identified. An analytical methodology was developed to estimate the PTT for given geometrical and thermal-hydraulic conditions of the condenser system. The methodology was extended to a temperature gradient analysis (TGA) model for the performance evaluation of power plant-scale condensers by considering the effects of condensate inundation, tube loading pattern, steam shear, and fouling resistance. The assessment results of the TGA model showed good agreement with existing numerical and lumped-volume models, as well as measurement data of existing power-plant condenser systems. Its simplicity and strong capability to elucidate most of the design variables of the condenser make the TGA model suitable for executing many iterative calculations required when designing and optimizing the new condenser system.

Effect of pipe-cooling system on thermal-mechanical behaviour of PC box bridge girders at hydration age

Prestressed concrete (PC) box bridge girders on the pier top is prone to generate thermal cracks due to large inner-outer temperature difference at hydration age. This paper presents an approach for investigating behaviour of PC box bridge girders at early age of curing. First, based on measured data from a typical PC box bridge girder, an inverse analysis method for adiabatic temperature rise function of concrete hydration heat is proposed using genetic algorithm and thermal analysis. Then, a thermo-hydro-mechanical coupling model is established, using the computer program ANSYS incorporating time-dependent wind speed and ambient temperature, to analyse thermal mechanical behaviour of PC box bridge girders considering pipe-cooling system. Subsequently, parametric studies are carried out to evaluate influence of cooling time, cooling water flow rate, cooling water temperature and cooling period on temperature and stress of PC box bridge girders during curing. Results from analysis show that the principal tensile stress generated in the vicinity of pipe increases more rapidly during cooling, while the temperature and principal tensile stress can be significantly reduced when cooling is terminated. Increasing cooling time, cooling water flow rate or decreasing cooling water temperature can reduce the highest temperature. However, unreasonable value of these cooling parameters will cause PC box bridge girders cracking due to excessive principal tensile stress around pipe. Both one-stage and two-stage cooling are effective measures to minimize the adverse effects of hydration heat in PC box bridge girders.

Experimental analysis of a CO2 heat pump for instantaneous domestic hot water production

The performance of a CO2 (R744) heat pump (HP) depends strongly on the application and on the environmental operating conditions. In particular, the CO2 HP becomes competitive compared to traditional heat pumps using halogenated refrigerants in applications characterized by a high hot water demand (hospitals, sport centres, etc.). This paper deals with the experimental analysis of an air-to-water commercial R744 HP tested in ENEA laboratories for instantaneous production of domestic hot water (DHW). The results show that HP efficiency is strongly affected by the inlet water temperature at the gas cooler. A test equipment capable of maintaining the ambient temperature at a desired value (between -10 °C and +20 °C), and managing water flow and water temperature (between 15 °C and 45 °C) is used to evaluate the machine COP as a function of the boundary conditions (inlet gas cooler water temperature, water flow rate, external ambient temperature). The analysis shows the considerable potential of R744 heat pumps for the instantaneous production of DHW, combining a high performance and relevant energy saving. As well, it points out that, to maximize the COP it is necessary to combine the HP with a high stratification storage system, which ensures a suited inlet water temperature, and with a correct value of water flow.

Energy, exergy, economic analysis and optimization of single-effect absorption chiller network

This study is aimed to conduct energy, exergy and economic analysis on a network of single-effect absorption chillers. First, the network was analyzed parametrically and then optimized to minimize exergy destruction and annual cost. Multi-objective optimization was performed by implementing a particle swarm optimization algorithm. The case study was conducted on the absorption chiller network in Iranian Marun Petrochemical Company. The results indicated the greatest effects of the solution heat exchanger efficiency and network inlet cooling water temperature on energy and exergy performance coefficients and annual cost. Accordingly, decreasing the network inlet cooling water temperature from 35 to 25 °C increased energy and exergy performance coefficients by 5.3 and 6.2%, respectively, and reduced annual cost by $70,000.00. Besides, increasing solution heat exchanger efficiency from 60 to 80% increased energy and exergy performance coefficients by 5.9 and 2.1%, respectively, and decreased the annual cost by $60,000.00. According to the optimization results, the economic function of the network saved 9.95%, so that if the network works in optimized thermodynamics and economic conditions, the cost decreases by 3.24% compared to the typical manner.

Experimental performance of membrane water absorption in LiBr solution with and without cooling

The operation of a microchannel membrane-based absorber using LiBr-water as absorbent-refrigerant pair is presented. The absorber is a stainless-steel plate structure, provided with microchannels coupled with a membrane which separates the water vapor and the solution. The same device is experimentally tested in two modes of operation. In one, water is used to cool the absorption process (as occurs in conventional absorbers) circulating through channels separated from the solution by a thin plate. In the second mode, no water circulates, and the absorption is adiabatic. The absorption rates obtained using both configurations are compared, evaluating the influence of the solution mass flux. The absorption ratio (absorbed vapor to solution mass flow rate) is studied as a function of the cooling water temperature and its effect on solution temperature and pressure potential. The mass transfer coefficient is inferred from the measurements. Also, the measured pressure drop along the channels shows the viability for the operation of this type of absorber.

Comparison of water vapour condensation in vertically oriented pipes of condensers with internal and external heat rejection

This paper deals with the intensification of water vapour condensation in vertical pipes. Two configurations of vertical condensers are compared. A standard configuration and a novel configuration with cooling water at the inner pipe wall in direct contact with the condensing vapour. For this configuration, a detailed mathematical model of heat transfer is made using empirical relationships to describe the behaviour of the liquid film and vapour. The focus is placed on a detailed description of the processes at the vapour-liquid interface. The results of the mathematical model are compared with an experimental study in which the real condensing power was assessed depending on the vapour mass flow rate, the cooling water temperature at the pipe inlet, and the volumetric flow rate of the cooling water. This paper presents specific mean heat transfer coefficients useable for design calculations. The results show that the heat transfer coefficient is proportional to the liquid film temperature as well as the vapour flow rate. The condensers are compared with the same vapour flow rate and cooling water temperature. The novel configuration rejects the same amount of condensation heat as the standard configuration, but only requires a third of the amount of cooling water.

Impact of climate change on fossil fuel power-plant efficiency and water use

Thermoelectric plants consume large amounts of water for electricity generation, mainly for cooling purposes. The performance and cooling capacity of power plants is thus strongly dependent on rising ambient temperatures. This study investigates the effect of rising ambient temperatures on power-plant performance and water use. A natural gas combined-cycle and a coal power plant, using both recirculating and once-through cooling systems, have been analyzed under increasing cooling water temperature and increasing ambient air temperature. Higher ambient temperatures lead to higher pressure at the steam turbine outlet, decreasing power-plant performance. The efficiency of the power plants is found to be more sensitive to ambient temperature variations when a recirculating cooling system is used, as opposed to once-through cooling. For example, a 10 °C temperature increase leads to an efficiency decrease in coal plants of 0.5–0.7 percentage points, when they are equipped with recirculating systems, versus a 0.3–0.4 percentage-point decrease, when they are equipped with once-through systems. The cooling-water mass flow is also found to be more sensitive to temperature increases in plants with recirculating cooling than in plants with once-through cooling. When comparing coal to natural gas plants, it is seen that the cooling water quantity of coal-fired plants is more sensitive to temperature changes. On the other hand, the efficiency of natural gas plants is more sensitive to temperature changes overall. This is related to higher losses in gas turbine systems caused by increased ambient temperatures and to the fact that the gas turbine system delivers approximately two-thirds of the total power output in the natural gas plants.

Transient thermal–hydraulic analysis of SCO2-cooled reactor system with modified RELAP5

The SCO2-Cooled Reactor System (SCRS) has good prospects in Gen-IV reactors. The SCO2 makes SCRS safe, compact and efficient. However, the variations of SCO2 thermophysical properties cause complex operation characteristics of SCRS. Transient simulation has great significance for SCRS safety analysis and its control system design. In this paper, the RELAP5 was modified and benchmarked by typical design. Transient conditions including reactor power step reduction, loss of electrical load and cooling water temperature disturbance were simulated without the intervention of control or auxiliary systems to study the natural responses of SCRS. The results demonstrated that the first two transients had great influence on turbomachinery. And control and auxiliary systems were necessary to respond quickly to ensure the normal operation of turbine. Moreover, the influences of cooling water temperature disturbance with temperature increase of 1 K on the change of main compressor operation condition and the weakening of circulation efficiency were acceptable.

디젤(CRDI)차량 프리히터 과열등에 의한 발화연구

To prevent the fire due to the overheating of coolant and the insulation deterioration, pre-heater parts are installed to improve indoor heating of winter diesel vehicles. The preheater operation method is divided into two types: a heating plug type that generates heat by electric energy and a combustion type that heats with fuel combustion heat. The experiment was focused on the heating plug method that is currently widely used. As a result of analyzing national fire statistics for the past five years, it was found that 235 (54.3%) occurred in winter (November to March) out of 432 vehicle fires in SantaFe. It is judged that this is not irrelevant to the seasonal effect of the heater rod operating under the preheater cooling water temperature of 75℃ or less, and through reproducibility experiments ➀part corrosion due to cooling water oxidation, ➁coolant overheating due to ECU defect (150℃), ➂insulation of distribution lines It was concluded that it could be ignited by deterioration. In addition, the actual vehicle fire in the preheater area was conducted to describe the combustion pattern and fire detection method of the vehicle.

Assessment of thermal behavior of a cooling system to reduce thermal fatigue cracks in aluminum injection molds

The present article aimed to test changes in cooling water temperatures of males, present in aluminum injection molds, to reduce failures due to thermal fatigue. In order to carry out this work, cooling systems were studied, including their geometries, thermal gradients and the expected theoretical durability in relation to fatigue failure. The cooling system tests were developed with the aid of simulations in the ANSYS software and with fatigue calculations, using the method of Goodman. The study of the cooling system included its geometries, flow and temperature of this fluid. The results pointed to a significant increase in fatigue life of the mold component for the thermal conditions that were proposed, with a significant increase in the number of cycles, to happen failures due to thermal fatigue.

Performance Analysis of a Large-Scale Steam Condenser Used in a Steam Power Plant

This paper summarizes performance analysis of large-scale seawater-cooled box type condenser in a 660 MW steam power plant. Effect of seawater temperature and steam mass flow rate are investigated on the key performance parameters of steam condenser. Results indicated that improvement in the cooling water temperature generally is found favorable on the performance indicators of condenser. On the other hand, in the case of steam flow rate changing, effectiveness and overall heat transfer coefficient almost remain constant. Effectiveness of condenser isn’t found as a function of steam flow variation. Moreover, steam power plant heat rate is investigated as a function of cooling water of condenser and thus it is seen to be decreased in the result of improvement of cooling water temperature. Conversely, power plant overall thermal efficiency decreases due to reduction of power generation.

Pilot-scale study on flue gas moisture recovery in a coal-fired power plant

The exhaust gas from coal-fired power plants installed with desulfurization tower contains a large amount of water vapor, recovering water from flue gas for recycling is of great significance in water saving and sustainable development. In this work, a transport membrane condenser was assembled by using the 1 μm pore-sized ceramic membrane, and experimental research was performed on a coal-fired power plant. The influence of longitudinal tube spacing on the water recovery and total heat transfer coefficient of the membrane condenser under the condition of high cooling water temperature (greater than 30 °C) was analyzed. The results show that for three different longitudinal spacings of 8, 5, and 3 cm, the amount of reclaimed water first decreases slowly by increasing the cooling water temperature. When the temperature reaches about 36 °C, the amount of reclaimed water decreases significantly. Among the three longitudinal spacings, the membrane module with a spacing of 8 cm has the best water recovery performance. The maximum water flux and maximum total heat transfer coefficient can reach 22.23 kg/(m2•h) and 1068.2 W/(m2•K). The findings from the pilot-scale investigation provide important insights for optimizing large scale water and heat recovery systems.

Investigation of copper-water loop heat pipe for different filling ratios

The present work reported here involves the experimental investigation and performance evaluation of loop heat pipe (LHP) with flat evaporator and wick made up of stainless-steel mesh. The experiment is conducted for different fill ratio such as 40%, 50%, 60% and different heat loads of 20 W, 40 W, 60 W, 80 W and 100 W using De-Ionized water as fluid for electronic cooling applications. And evaluated operating performance of loop heat pipes for both steady and transient state. The evaporator, condenser, liquid line and vapour line are made up of copper and are placed in horizontal orientation. The results show Under forced water-cooling condition with the cooling water temperature of 25 °C, the LHP can transfer a maximum heat load of 100 W with the evaporator temperature of 92°C and a minimum thermal resistance of 0.5332 °C/W.

Experimental Investigation of Microbial Fouling and Heat Mass Transfer Characteristics on Ni-P Modified Surface of Heat Exchanger

Fouling deposition problem on heat transfer surface is widely distributed in the field of energy and chemical industry, and microbial fouling is a common fouling type in heat exchanger. In this article, the surface modification was used for inhibiting or mitigating the microbial fouling deposition on heat exchange surface. Firstly, the experimental system for real-time monitoring the fouling deposition process was built, and then the Ni-P modified surface was prepared. Further, the slime forming bacteria (SFB) microbial fouling characteristics and corresponding influencing factors on Ni-P modified surface were investigated experimentally. The results indicated that Ni-P modified surface had an excellent fouling inhibition property. Comparing with carbon steel, Ni-P modified surface reduced the fouling heat resistance by 80%. Accordingly, the influencing factors of microbial fouling deposition including temperature, flow rate and microbial concentrations were discussed. With cooling water temperature increasing given in the experiment arrangement, the microbial fouling resistance was increased first and then decreased, while with bacteria concentration and flow rate increasing, the fouling resistance was increased and decreased separately. The work can provide experimental reference for the fouling inhibition surface development and fouling inhibition mechanism study.

A useful formulas to describe the performance of a steam condenser in off-design conditions

The article presents relations for determining the performance of a steam condenser in off-design operating conditions. To determine some steam condenser characteristics that are simplified, but useful for analyzing steam cycles of a power unit, a model validated on the basis of factory characteristics and measurement data was used. Formulas presented in the article-for given values of cooling water temperature at the condenser inlet, the cooling water mass flow rate, the inlet steam mass flow rate and reference data-determine the cooling water temperature at the outlet and the pressure in the steam condenser. The model can be used to analyze the operation of cooling systems in off-design conditions and to optimize the way the condenser works with the low-pressure (LP) part of the turbine and all steam cycles. The two proposed relations make it possible to determine the condenser performance easily and with acceptable accuracy. The correctness of the proposed relations was verified on the basis of data obtained from the condenser simulator, measurements obtained from the Distributed Control System (DCS), and data provided in the literature.

Improved Solar Operation Control for a Solar Cooling System of an IT Center

In this contribution, a model predictive control algorithm is developed, which allows an increase of the solar operating hours of a solar cooling system without a negative impact on the auxiliary electricity demand, e.g., for heat rejection in a dry cooler. An improved method of the characteristic equations for single-effect H 2 O / LiBr absorption chillers is used in combination with a simple dry-cooler model to describe the part load behavior of both components. The aim of the control strategy is to find a cut-in and a cut-off condition for the solar heat operation (SHO) of an absorption chiller cooling assembly (i.e., including all the supply pumps and the dry cooler) under the constraint that the specific electricity demand during SHO is lower than the electricity demand of a reference cooling technology (e.g., a compression chiller cooling assembly). Especially for the cut-in condition, the model predictive control algorithm calculates a minimum driving temperature, which has to be reached by the solar collector and storage in order to cover the cooling load with a low cooling water temperature but restricted auxiliary electricity demand. Measurements at a solar cooling system for an IT center were used for the testing and a first evaluation of the control algorithm.

Multi-objective optimization and off-design evaluation of organic rankine cycle (ORC) for low-grade waste heat recovery

Organic Rankine Cycle (ORC) is a technically feasible way for low temperature waste heat recovery. Multi-objective optimization of the ORC using R245fa is conducted considering both thermodynamic performance and economic factors simultaneously, by means of Non-dominated sorting genetic algorithm-Ⅱ. The optimum operating parameters were achieved by sorting the Pareto-optimal solutions using the technique for order preference by similarity to ideal situation. A comprehensive analysis on the off-design performance of the optimized ORC system is examined. Rls is defined as the ratio of latent heat to sensible heat of the input heat to investigate the relation between the distribution of the input heat and the system performance. The effects of hot water temperature and mass flow rate, cooling water temperature and mass flow rate, superheated degree, subcooling degree and working pump rotational speed, on thermal efficiency, exergy efficiency, net power output, investment cost per unit power and Rls were investigated. The fitted correlations between Rls and the system performance indexes were derived. The novelties of the present paper are the multi-objective optimization for the further off-design behavior analysis and the quantitative relation investigation between Rls and system performance indexes. It is indicated that the direction of system optimization is to reduce Rls.

Experimental evaluation of two consecutive air-gap membrane distillation modules with heat recovery

Abstract Two rectangular modules with a total interior membrane surface area of 13.53 m2 were consecutively combined to evaluate the use of heat recovery in an air-gap membrane distillation (AGMD) system. Several operating inlet parameters including feed water temperature, mass water flow rate and salinity were investigated. The experimental results revealed that the performance of the system was improved by virtue of efficient heat recovery resulting from combining two AGMD membrane modules in series. Under optimal inlet operating parameters of cooling water temperature of 20 °C, salinity of 0.05% and flow rate of 3 l/min, the system productivity (Pp) increased up to 192.9%, 179.3%, 176.5% and 179.2%, and the thermal efficiency (ηth) by 261.5%, 232.6%, 239.4% and 227.3% at feed water temperatures of 45 °C, 55 °C, 65 °C and 75 °C, respectively. Concurrently, the specific waste heat input (Ew.h.i) decreased by 6.7%, 4.7%, 5.6% and 2.7% due to the efficient heat recovery. The results confirmed that heat recovery is an important factor affecting the AGMD system that could be improved by designing one of the two AGMD modules with polytetrafluoroethylene (PTFE) hollow fibers with a flow length shorter than the other one having a salt rejection rate of 99%.