Reduction In Heat Transfer Efficiency Research Articles

Impact of variation in gap spacing and orientation of split baffles on thermodynamics optimization in naturally convective flow in corrugated enclosure

The fundamental aim of this research work is to examine the effect of heated split baffles and the influence of different corrugation frequencies on steady-state natural convection within a sinusoidal corrugated square cavity. The configuration of the present model maintains a constant temperature of T c for the horizontal wavy boundaries and vertical walls while the inner split baffles are heated at a constant temperature of T h . The finite element method is applied to the discretized equations representing the fluid behavior within the enclosure, with the aim to investigate the inclination angles, variation of space between the baffles, corrugation frequencies, and the impact of Rayleigh number on the fluid motion and heat transfer. The variation in velocity and temperature profile is illustrated through the streamlines and isotherm contours. Moreover, the numerical results are carried out in terms of local and average Nusselt numbers of the heat transfer, which are analyzed for inside space of baffles and line dip-angles of the baffle ( θ = 0 ° , 45 ° , 90 ° ) , and ( φ = 0 ° , 30 ° , 60 ° , 90 ° ) . The key findings indicate that increasing the space l s between the baffles enhanced the convective heat transfer by 8.5 % , moreover, elevating the baffle angle to right angle ( θ = 90 ° ) amplify the heat transfer rate increase by 19.17 % . The augmentation in corrugation frequency leads 7.15 % reduction in heat transfer efficiency. The comparison of the present numerical simulations revealing a satisfactory and reliable match with the literature precedents.

Numerical simulation of flow characteristics of falling-film evaporation of R32/R134a non-azeotropic refrigerant outside a horizontal tube

Horizontal-tube falling-film evaporator is regarded as an effective alternative to full-liquid evaporator because of its higher heat transfer coefficient and lower refrigerant charge. In the process of falling-film evaporation, the thin liquid film thickness (δ) is an important parameter for characterizing the hydrodynamics, and accurate prediction of δ can effectively prevent the reduction in heat transfer efficiency caused by local wall dryout. In this study, non-azeotropic refrigerant R32/R134a was taken as the research object. By incorporating the multi-component phase change model and contact angle model into the governing equations, a two-dimensional numerical model of falling-film evaporation outside a horizontal circular tube was established. The effects of the spray height (H), tube diameter (d), Reynolds number (Re), inlet temperature (Tinlet), and mass fraction of R32 in the liquid-phase mixture (MR32_liquid) on δ were analyzed under sheet flow. The results show that an increase in Tinlet, H, and d is favorable for increasing the average δ (δave), whereas an increase in MR32_liquid and Re leads to a reduction in δave. Besides, the decreasing rate of the δave decreases gradually as H and d increase. When H is 4 mm, the local δ (δlocal) first decreases and then increases as the circumferential angle (Φ) increases. When H ranges from 6 mm to 13 mm, as Φ increases, δlocal first increases slightly, then decreases, and finally increases significantly near the wake region. The δlocal of a larger tube diameter is thicker than that of a smaller tube diameter near the impact region, whereas in the subsequent regions, the δlocal of a larger tube diameter is thinner than that of a smaller tube diameter. The minimum δlocal occurs at Φ between 130° and 140°, and with an increase in H and d, Φ corresponding to the minimum δlocal decreases.

Entropy generation due to nanofluid flow in porous media over radiative permeable exponentially surface with nanoparticle aggregation effect

In recent years, energy scarcity has emerged as a serious problem for manufacturing since most of the power produced is lost as heat during transportation. Due to the irreversible nature of heat transfer processes, it is crucial to minimize the development of entropy during nanofluid flow and heat transmission. Therefore, the purpose of this study is to inquire entropy generation on viscous TiO2−C2H6O2 nanofluid through a permeable exponentially surface with porous media and effect that nanoparticle aggregation with thermal radiation, mixed convective stagnation point flow. The controlling partial differential equations were simplified by using an appropriate similarity transformation, resulting in a set of ordinary differential equations. After that, we used Mathematica's shooting technique and fourth order Runge-Kutta integration to get a numerical answer to these equations. The current study showed that increasing the volume percentage of nanoparticles, the porosity of the nanofluid, the mass suction, and the mixed convection parameters all led to an increase in the skin friction coefficient. The heat transfer rates increased by 6.7021% points when the suction settings were set to values between 2.0 and 2.5 and the nanoparticle volume fraction was set to 1%. The average reduction in heat transfer efficiency for the aggregation model was around 4.249% for the range of 0–1% nanoparticle volume fraction. Since aggregation models may provide more accurate velocity and skin friction profiles, they are often preferred over homogeneous models. The growing use of aggregation models may largely be attributed to their improved profile prediction accuracy. Improving Ω's values is known to lessen the onset of entropy. An increase in Ec is shown to be beneficial to the entropy inception field. Increasing the Brinkman number accelerates the entropy production rate.

Investigation of molten salts incorporated with anodic aluminum oxide as thermal energy storage fluid on heat transfer efficiency

The aim of this research is to investigate mass and heat transfer of anodic aluminum oxide in packed-bed thermocline vessel with molten salt system (5% Lithium, 20% sodium, 50% potassium and 25% calcium). According to the computational fluid dynamic simulation, the ceramic ball that is packed inside the vessel does not have a significant impact on the mass transfer of anodic aluminum oxide in the molten salt system. Heat storage performance testing was conducted in a thermocline vessel (packed-bed zone 0.7 m in length and 0.3 m diameter) and molten salt flow rate between the ranges of 0.5–0.7 m3/h. Two different molten salt systems were studied including a normal molten salt system and a molten salt system with 0.5 wt% anodic aluminum oxide. An increase in molten salt flow rate have a positive impact on heat transfer inside the vessel due to the increase in turbulence of the flow. A decrease in charging time from 3.75 h to 3.5 h was observed for molten salt with 0.5 wt% anodic aluminum oxide. A seven-cycle charge/discharge test revealed that addition of 0.5 wt% anodic aluminum oxide resulted in a smaller reduction in heat transfer efficiency and actual energy storage. Heat storage decreased from 20.42 to 19.54 MJ corresponding heat transfer efficiency of only 87 to 85% for molten salt system consisting of anodic aluminum oxide.

Study on the deposition migration and heat transfer characteristics in the reactor core based on OpenFOAM

Corrosion deposition in heat exchangers may lead to a reduction in heat transfer efficiency, and even can affect equipment operational safety. Traditional CFD deposition heat transfer analysis methods are limited by model size, making it difficult to obtain global, long-term deposition heat transfer characteristics for complex heat exchange equipment. In this paper, a corrosion product deposition prediction and heat transfer model based on sub-channel analysis is proposed. By integrating it into the nuclear reactor core thermal–hydraulic characteristics analysis code CorTAF, which is developed on the OpenFOAM platform, the corrosion deposition and heat transfer calculation for the entire reactor is achieved. A numerical simulation of the deposition and heat transfer of the AP1000 reactor core during a 300-day operation is conducted. The calculation results clearly show the distribution of corrosion products in the reactor core and the temperature changes of the fuel cladding with the deposition days: the maximum deposition thickness on the core cladding surface is 38.3 μm, and the highest temperature increase is 11.0 K. The deposition and cladding temperature rise distribution is not linear with operation time but is closely related to the core power distribution. The modeling method successfully obtains the corrosion deposition and heat transfer characteristics of the entire reactor core, and has potential implications for the prediction of corrosion deposition distribution and thermal effect calculations in other large-scale heat exchange equipment.

State of art bio-materials as scale inhibitors in recirculating cooling water system: a review article.

During the operation of the circulating cooling water system, inorganic scale deposition may cause technical problems, such as reduction of heat transfer efficiency in cooling systems and obstruction of pipes. In the industry, chemicals are often used as scale inhibitors in scale deposition control, antiscalants popular in industry are generally phosphorus and nitrogen-containing chemicals, which may lead to eutrophication. However, increasing environmental concern and discharge limitations have guided antiscalants to move toward biodegradability, nontoxicity and cost-effectiveness. This paper reviews current research on the application of using bio-materials as scale inhibitors, including proteins and amino acids, polysaccharides, plant extracts, microbial reagents, and microbiological products. The non-bioaccumulation, low cost, readily biodegradability and sustainably available characters promote the development of green-scale inhibitor chemistry.

Deposition characteristics of particles in inclined heat exchange channel with surface ribs

Ash particles in flue gas flow would deposit on the heat recovery exchanger in the waste heat recovery system (WHRS), which may lead to the reduction of heat transfer efficiency and service life. Understanding of ash particle deposition in the heat exchange channel is crucial for the safe operation of WHRS. In this study, deposition characteristics of ash particles in an inclined heat exchange channel with surface ribs were investigated by using Reynolds stress model combined with discrete phase model. The turbulent fluctuation correction and particle rebound model were developed by using UDF program to improve the prediction accuracy. After grid sensitivity analysis and numerical verification, the flue gas thermal-fluid fields, the 3D particle deposition patterns and deposition efficiency on each ribbed channel surface were obtained and analyzed. Parameter study on the deposition characteristics was conducted by considering flue gas flow velocity, particle size and inclination angle of the ribbed channel. The results showed that significant secondary flow eddies can be observed near the rib windward surfaces and high-value turbulent intensity area appears near the rib crest. The windward surfaces and the crests of the ribs are the main deposition locations in the inclined heat exchange channel. The deposition efficiency in the ribbed channel is obviously changed by the particle diameter and flue gas flow velocity. The inclination angle has little influence on deposition efficiency for small particles (dp<5μm) but great effect on deposition efficiency for large particles (dp>10μm).

Experimental and numerical approach to resolve particle deposition on dimpled heat transfer surfaces locally and temporally

When optimizing the performance of heat exchangers, it can be advantageous to introduce structures, such as dimples or ribs on the surface. One especially advantageous solution in terms of thermo-hydraulic efficiency is to use surfaces with spherical dimples, where heat transfer is increased at an only minor pressure loss increase. However, this surface structuring also influences the deposition of particles in aqueous suspensions. The resulting fouling is a serious problem for the design and operation of heat exchangers and can cause significant economic and ecological damage. Despite the knowledge of the importance of fouling and the resulting disadvantages, this knowledge has not been incorporated systematically into the design process, and the criteria of maximizing heat transfer and reducing hydraulic losses remain in the foreground during the design of heat exchangers.In this study, dimpled surfaces with a depth to diameter ration of 0.18,0.26 and 0.35 were evaluated by measuring and comparing their heat transfer ability and pressure loss with and without the occurrence of particulate fouling from aqueous suspensions. The fouling resistance is used to assess the reduction in heat transfer efficiency due to particulate depositions, both local and time resolved. For the first time, a row of dimples is quantitatively assessed regarding its heat transfer efficiency under fouling conditions, and the thermo-hydraulic efficiency is determined experimentally. The results are matched against numerical investigations. The interactions of turbulent flow structures, heat transfer and particulate fouling in aqueous suspension are determined for dimpled surfaces.

Simulation and experiment of adsorption behavior of calcite, aragonite and vaterite on alpha-Fe2O3 surface

The service life of the equipment can be seriously shortened by corrosion, and the heat resistance of the heat exchange surface will increase sharply due to scaling adhesion, which leads to the reduction of heat transfer efficiency. Simultaneously, scaling adhesion and surface corrosion are not simply isolated. Based on the molecular dynamics, the adsorption of different phase calcium carbonate on the alpha-Fe2O3(0 0 1) surface was studied. Results demonstrate that the atoms of the corrosion interface have a greater impact on the adsorption of aragonite-phase calcium carbonate, and the vaterite-phase calcium carbonate is unstable on the corroded surface. With the increase of temperature, diffusion coefficients of calcite, aragonite and vaterite increase correspondingly, and the diffusion coefficient change of calcite is relatively stable. The concentrations of the surface in a descending order are aragonite, calcite and vaterite in turn. The initial densities of adsorbate atoms on the alpha-Fe2O3(0 0 1) surface are 8.03, 8.44 and 9.10 g/cm, respectively. Additionally, the deposition of various crystalline calcium carbonate molecules can be reinforced by the strong intermolecular interaction under high temperature to a certain extent. Further experiment proves that the scaling is prone to deposit on the severely corroded surface and corrosion products can further accelerate the deposition rate of scaling. The amount of aragonite on the mild steel surface is more than that of calcite. And the corroded surface has selectivity to the nucleation of calcium carbonate scaling.

Pilot Evaluation of DSA Anode Electrochemical Scaling Applied in a Cooling Water Circulation System

Scale deposition in circulate cooling water system is a terrible problem which could result in the reduction of heat transfer efficiency and increasing of operational consumption. In this paper, based on the Lab scale experiment, the DSA electrodes was evaluated in cooling water scaling by pilot experiment. The experimental results indicated that, the hardness removal rate appeared approximately linear relationship with the current density, and the hardness removal rate increased rapidly with the increasing of the residence time and then tends to be stable. According to the scaling requirement and economic consumption in practical application, under the experimental condition, current density of 25.56A/m2 and the residence time of 4min was the best working condition with the hardness removal rate of 22.87%. The research results could provide important practical basis for the development, design and commissioning of electrochemical equipment in the future.

(Industrial Electrochemistry and Electrochemical Engineering Division Student Achievement Award Address) Mathematical Modeling of Transport and Corrosion Phenomenon inside High-Temperature Molten Salt Systems for Next Generation Concentrated Solar Power Systems

Concentrated solar power system, more commonly referred to as CSP, is unique among renewable energy generators because even though it is variable, like solar photovoltaic and wind, it can be easily coupled with thermal energy storage as well as conventional fuels, making it highly dispatchable. In these systems molten salts, specifically molten halides, are widely applied as the heat transfer medium due to their good thermal conductivity and relatively good chemical inertness [1]. However, the molten halide salts are highly corrosive, especially at high temperatures (700-1000 °C) [2]. Although superalloys have been developed for high-temperature applications, they are not able to meet both the high-temperature strength and the high-temperature corrosion resistance simultaneously. As a result, the challenge with CSP systems is the potential corrosion of the superalloys in the receivers and heat exchangers at high-temperature operational conditions, which leads to a reduction of heat transfer efficiency and impacts the systems durability [3]. In this work a comprehensive mathematical model has been developed to predict the rates and mechanisms for the corrosion of superalloys that are in contact with a molten salt heat transfer system. Coupled with computational fluid dynamics (CFD), the local electrochemical environment and corrosion rates in a high temperature molten salt system can be predicted. The corrosion model has been designed and benchmarked against a thermosiphon reactor. This thermosiphon reactor exposed alloy coupons to the non-isothermal conditions expected in CSP plants. Cathodic protection was also added to the model as a mitigation strategy for corrosion of metal surfaces. The model compared the corrosion rates for the cases with and without cathodic protection under different operating conditions for different superalloys. Results were in good agreement with the experimental values for the cases with and without the cathodic protection and at isothermal and non-isothermal conditions. Acknowledgements The authors gratefully acknowledge the financial support for this work from the DOE EERE SunShot Initiative (DE-AC36-08GO28308) under a subcontract from SRNL to the University of South Carolina. The authors also thank the University of South Carolina Center for Fuel Cells and the CD-adapco group for their support.

The Effect of Nickel Alloy Corrosion Under Cathodic Protection inside High Temperature Molten Salt Systems

One way to potentially reduce the costs of concentrated solar power (CSP) central receiver systems is to operate the central receiver at high temperatures that allow for more efficient thermodynamic power conversion cycles. Molten salts are one potential heat transfer fluid at that can operate efficiently at these temperatures, but their use will introduce other technological challenges, such as corrosion and mass transfer reactions. The corrosion of alloys at high-temperature (700-1000°C) in the receivers and heat exchangers cause a reduction in heat transfer efficiency and durability. Cathodic protection may mitigate corrosion of metal surfaces by shifting the potential of the alloy below its oxidation potential. The behavior of molten salt cooled concentrated solar power (CSP) systems under cathodic protection can be obtained by developing a 3-D model. A simplified model was designed for and benchmarked against a thermosiphon reactor. This thermosiphon reactor exposed alloy coupons to non-isothermal conditions expected in concentrated solar power (CSP) plants. When the cathodic current density is equal to the protection current density and the potential is a protective, the model calculates the corrosion rate and the corrosion potential. Magnesium was used as a sacrificial anode. The rate of Mg consumption, the corrosion potential, and the corrosion current are dependent on several studied variables. Kinetic parameters were obtained from experimental coupon exposures conducted between 700-1000 °C in molten salt in the thermosiphon reactor. Results were in good agreement with experimental values at different conditions. Fig. 1 shows a comparison of the model prediction of corrosion rate distribution, i (A/cm2) at coupon surfaces for both Hot-Zone and Cold- Zone without (a) and with (b) cathodic protection. Acknowledgements The authors gratefully acknowledge the financial support for this work from the DOE EERE SunShot Initiative (DE-AC36-08GO28308) under a subcontract from SRNL to the University of South Carolina. The authors also thank the University of South Carolina Center for Fuel Cells and the CD-adapco group for their support. Figure 1

Inhibitory effect of glutamic acid on the scale formation process using electrochemical methods

ABSTRACTThe formation of calcium carbonate CaCO3 in water has some important implications in geoscience researches, ocean chemistry studies, CO2 emission issues and biology. In industry, the scaling phenomenon may cause technical problems, such as reduction in heat transfer efficiency in cooling systems and obstruction of pipes. This paper focuses on the study of the glutamic acid (GA) for reducing CaCO3 scale formation on metallic surfaces in the water of Bir Aissa region. The anti-scaling properties of glutamic acid (GA), used as a complexing agent of Ca2+ ions, have been evaluated by the chronoamperometry and electrochemical impedance spectroscopy methods in conjunction with a microscopic examination. Chemical and electrochemical study of this water shows a high calcium concentration. The characterization using X-ray diffraction reveals that while the CaCO3 scale formed chemically is a mixture of calcite, aragonite and vaterite, the one deposited electrochemically is a pure calcite. The effect of temperature on the efficiency of the inhibitor was investigated. At 30 and 40°C, a complete scaling inhibition was obtained at a GA concentration of 18 mg/L with 90.2% efficiency rate. However, the efficiency of GA decreased at 50 and 60°C.

Multidimensional Modeling of Nickel Alloy Corrosion inside High Temperature Molten Salt Systems

One challenge with concentrated solar power (CSP) systems is the potential corrosion of the alloys in the receivers and heat exchangers at high-temperature (700–1000°C), which leads to a reduction of heat transfer efficiency and influences the systems durability. In this work, a corrosion model has been developed to predict the rates and mechanisms for corrosion of a nickel-based alloy that is in contact with a molten salt heat transfer system. In addition to accounting for heat and mass transfer effects on the corrosion, the model takes into account the electrochemical kinetics. Coupled with computational fluid dynamics (CFD), the local electrochemical environment and corrosion rates in a high-temperature molten salt system can be predicted. The kinetic, heat and mass transfer parameters used in the model are based on experimental studies conducted in a thermosiphon. The immersion cell was designed to expose coupons to the molten salt at isothermal or non-isothermal conditions between 700–1000°C. The model can predict the effect of thermal gradients between the top and the bottom of the reactor which induce natural convection of the molten salt. The model has been validated against experimental results at different isothermal and non-isothermal conditions and good agreement has been achieved between the model predictions of the corrosion rates and corrosion potentials with the experimental observations.

Multidimensional Modeling of Nickel Alloy Corrosion inside High Temperature Molten Salt Systems

Concentrated solar power (CSP) systems in the presence of high operating temperature heat transfer fluids for power production processes has attracted more attention in recent years. The challenge with these systems is the corrosion of alloys at high-temperature (700-1000°C) in receivers and heat exchangers causing a reduction in heat transfer efficiency and influencing the apparent durability [1-3]. In this work, a corrosion model that includes thermal gradients and fluid flow is developed to predict corrosion rates and mechanisms observed in a nickel base alloy in contact with a molten salt heat transfer system. The model takes into account the electrochemical kinetics in addition to mass transfer-limited corrosion coupled with a computational fluid dynamic (CFD) model that can predict the local electrochemical environment and corrosion rates in a system with temperature and fluid flows. The kinetic and mass transfer parameters used in the model are based on the experimental coupon studies were conducted between 700-1000 °C within molten salt in a thermosiphon reactor that designed to allow exposure the coupons to the non-isothermal condition. The thermal gradients between top and bottom of the reactor could induce natural convection of the salts [4-5]. Fig. 1 shows an example of the model prediction of corrosion rate distribution, i (A/cm2) at coupon surfaces at both hot and cold zones in addition to the temperature gradient near the wall and streamlines that show the flow pattern of molten salt inside the thermosiphon. the This corrosion model accounts for the effects of different operational conditions such as temperature and component concentrations in addition to the alloy surface properties on the corrosion rate. Acknowledgements The authors gratefully acknowledge the financial support for this work from the DOE EERE SunShot Initiative (DE-AC36-08GO28308) under a subcontract from SRNL to the University of Alabama and to the University of South Carolina. The authors also thank the University of South Carolina Center for Fuel Cells and the CD-adapco group for their support. R eferences C. Forsberg, P.F. Peterson, and H.H. Zhao, J. Sol. Energy Eng. Trans.-ASME, 129, 141-146, 2007.C. Forsberg, Progress in Nuclear Energy, 47, 32-43, 2005.D. Ludwig, L. Olson, K. Sridahran, M. Anderson, and T. Allen, Corrosion Engineering Science and Technology, 46, 360-364, 2011.B. L. Garcia-Diaz, L. Olson, M. Martinez-Rodriguez, R. Fuentens, J. Gray. paper #741, 2014 ECS and SMEQ Joint International Meeting, Cancun, Mexico, Oct. 08, 2014.R. Fuentens, L. Olson, M. Martinez-Rodriguez, J. Gray, B. L. Garcia-Diaz. paper #743, 2014 ECS and SMEQ Joint International Meeting, Cancun, Mexico, Oct. 08, 2014. Figure 1. Corrosion rate distribution, i (A/cm2) at coupon surfaces at both hot and cold zones in addition to the temperature gradient near the wall and streamlines inside the thermosiphon. Figure 1

Mini-review: Inhibition of biofouling by marine microorganisms

Any natural or artificial substratum exposed to seawater is quickly fouled by marine microorganisms and later by macrofouling species. Microfouling organisms on the surface of a substratum form heterogenic biofilms, which are composed of multiple species of heterotrophic bacteria, cyanobacteria, diatoms, protozoa and fungi. Biofilms on artificial structures create serious problems for industries worldwide, with effects including an increase in drag force and metal corrosion as well as a reduction in heat transfer efficiency. Additionally, microorganisms produce chemical compounds that may induce or inhibit settlement and growth of other fouling organisms. Since the last review by the first author on inhibition of biofouling by marine microbes in 2006, significant progress has been made in the field. Several antimicrobial, antialgal and antilarval compounds have been isolated from heterotrophic marine bacteria, cyanobacteria and fungi. Some of these compounds have multiple bioactivities. Microorganisms are able to disrupt biofilms by inhibition of bacterial signalling and production of enzymes that degrade bacterial signals and polymers. Epibiotic microorganisms associated with marine algae and invertebrates have a high antifouling (AF) potential, which can be used to solve biofouling problems in industry. However, more information about the production of AF compounds by marine microorganisms in situ and their mechanisms of action needs to be obtained. This review focuses on the AF activity of marine heterotrophic bacteria, cyanobacteria and fungi and covers publications from 2006 up to the end of 2012.

Numerical method for heat transfer and fouling analysis of a shell and tube heat exchanger using statistical analysis

Through proper monitoring, problems can be identified and isolated well before the economics of the process are threatened. In contrast to most conventional methods, fouling can be detected when the heat exchanger operates in transient states. Statistical analysis is used to develop a fouling growth model of a heat exchanger subjected to fouling. The statistical analysis was considered for four different types of distributions out of which the lognormal distribution was found to be most suitable. Experiments were conducted with a single pass shell and tube heat exchanger with water both as the hot and cold fluids. The results show that the proposed tool is very effective in detecting critical fouling in a heat exchanger, which can be utilized for predicting the optimal maintenance schedule. Hence, the results of this work can find application in predicting the reduction in heat transfer efficiency due to fouling in heat exchangers that are in operation and assist the exchanger operators to plan cleaning schedules.

Heat Transfer and Anti-Fouling of Liquid-Solid Two-Phase Flow in Cooling Water Pipes of Staves

To solve the hard problem that the reduction of heat transfer efficiency on the cooling stave of blast furnace due to fouling deposition, solid particles have been added into the cooling water pipes, forming liquid-solid two-phase flow, which can change the heat transfer and anti-fouling capacities of the cooling water pipes. Under the different solid phase volume scores, the heat transfer and anti-fouling capacities of the liquid-solid two-phase flow in the cooling water pipes are studies. The results indicates that because of the perturbation and shearing effect of solid phase particles, not only can the heat transfer coefficient and heat transfer capacity of the cooling water pipes be enhanced, but also the anti-fouling capacity be increased. Thus the highly effective running time of the equipment is greatly extended, realizing the long-term highly effective running of the cooling staves. The blast furnace cooling stave as heat exchange equipment, its heat transfer effects has the very important influence to blast furnace's life. In order to enhance cools wall's cooling capacity, the domestic and foreign scholars around material quality [1], structure optimization [2-4], dirt cleaning of water pipe [5], heat-transfer property [1] of the cooling wall and so on to do the massive fruitful research work. At present, the fouling cleaning of blast furnace stave cooling water pipe wall is still a difficult problem. The high-pressure water washing and sand washing methods are commonly used in industrial practice, these are "doctors after the disease first" and low efficiency methods. The effect removing dirty stuff is not very ideal. The cleaning effect of on-line chemical cleaning is difficult to guarantee. Liquid-solid fluidization cleaning technology can be used in the blast furnace to cool the cooling water pipe wall. It can on-line clean fouling and strengthen heat transfer. Its anti-fouling performance has been studied experimentally.

Use of C-factor for monitoring of fouling in a shell and tube heat exchanger

Heat exchangers operating in process industries are fouled during operations and results in decrease in the thermal efficiency of a heat exchanger. Once the thermal efficiency decreases to a minimum acceptable level, cleaning of the equipment becomes necessary to restore the performance. This paper uses C-factor as a tool for investigation of the performance of a heat exchanger due to fouling which consequently gives information regarding the extent of fouling developed on the heat transfer surfaces. The fouling parameters are predicted by measurements of flow rate and pressure drop. In contrast to most conventional methods, the extent of fouling can be detected considering the flow rate and pressure drop when the heat exchanger operates in transient states. The C-Factor is first calculated through out cleaning period and then compared with the clean and the design value. The results show that the proposed tool is very effective in detecting the fouling developed and the corresponding degradation in heat transfer efficiency of a heat exchanger. Hence the results of this work can find applications in predicting the reduction in heat transfer efficiency due to fouling in heat exchangers that are in operation and assist the exchanger operators to plan cleaning schedules.

Corrosion of carbon steel and Monel-400 in EDTA based steam generator cleaning formulations

Corrosion products and the scale forming impurities foul the steam generators of Pressurized Water Reactors (PWR) and Pressurized Heavy Water Reactors (PHWR). The impurities from the make-up water, the condenser leaks and the corrosion product oxides leached from the feed train structural materials are carried along with the feed water and concentrate in the steam generators. These impurities deposit/precipitate over the steam generator surfaces and cause several problems such as reduction in heat transfer efficiency, under deposit attack, tube failures and production loss. In order to solve this problem, the power utilities are resorting increasingly to chemical cleaning of the steam generators. The chemical formulation selected for cleaning should be able to dissolve the accumulated corrosion products/sludge and at the same time should be compatible with the steam generator structural materials. Of the various chemical-cleaning formulations, the EDTA based formulations are more popular and have been used in the chemical cleaning of many nuclear steam generators. Its corrosion compatibility with the structural-materials of the steam generators needs a thorough evaluation. In this work, the effect of various additives added to the EDTA such as pH additive, reducing agent, oxidizing agent and corrosion inhibitors have been investigated. Increase in the concentration of hydrazine has been found to increase the corrosion rate of carbon steel. The variation in corrosion release from carbon steel with time was found to fit a second order equation. The variation in corrosion rate with time was attributed entirely to the increase in surface area caused by roughening of the surface. Presence of dissolved oxygen in EDTA based iron formulation enhanced the corrosion rate of carbon steel and pitted the Monel-400. The study indicated the need for strict oxygen control and the necessity of using a suitable corrosion inhibitor during the iron removal step. The role of copper in the corrosion of carbon steel during chemical cleaning has also been studied. Problems encountered in the use of oxygen as an oxidant for copper removal in steam generators having Monel-400 as tube material have been investigated. The results of experiments to investigate the corrosion behavior of Monel-400 tubes, that has seen ten years of operation and has already undergone intergranular attack, in EDTA based formulation has also been discussed.