| In recent years,heat exchangers perform an important function in energy saving of power station with the increasing pressure.The fouling seriously affects the heat exchange performance,that fouling is a particle adhering to the surface of heat exchange equipment in the certain conditions.For preventing,restraining and removing the heat exchanger fouling,it is important that investigate the correlation characteristics among the leading fouling factors,clear the formation principle of fouling particles in cooling water,and obtain rapid fouling judgment variables.It is also a great significance to improve the heat exchange performance and realize energy saving.Cooling water fouling has uncertainty and hysteresis,so the investigation assumes the constant heat exchange parameters.The fouling thermal resistance and typical water quality parameters(conductivity,pH and dissolved oxygen)can be detected and analyzed in different operation parameters.The correlation characteristics are investigated between the fouling thermal resistance and water quality parameters(conductivity,pH and dissolved oxygen)leading to fouling in the alternating magnetic field.It is received the quantitative determination for detecting heat exchanger fouling.Secondly,the correlation characteristics are investigated between parameters of alternating magnetic field and cooling water.The alternating magnetic field parameters control cooling water parameters,indirectly control the fouling thermal resistance.Prediction model is built between the model input and outputs are water parameters leading to fouling and thermal resistance on the heat exchanger in alternating magnetic field.Otherwise,the pure water and CaCO3 solution models are investigated in varies strength of the magnetic field with the molecular dynamics simulation.From a micro perspective,the restraining fouling principle can deeply investigate in the alternating magnetic field.Firstly,the fouling thermal resistance and water quality parameters(conductivity,pH and dissolved oxygen)can be detected in different magnetic field strength by the intelligent detection of fouling resistance experiment platform,which is independently design and built.According to the experiment data,the principle of fouling is analyzed on the heat exchanger surface,simultaneously the calculation method is deduced about the fouling induction period.Base on the experiment research,correlation characteristics are analyzed with mathematical statistical and grey relational,that the correlation are between the fouling thermal resistance and water quality parameters(conductivity,pH and dissolved oxygen)leading to fouling.From the result,it shows that the highest correlation parameter is conductive,followed by pH,and the lowest is dissolved oxygen,that the correlation are between the fouling thermal resistance and cooling water quality parameters.Compared with the pH and dissolved oxygen,the conductive reflection is better for the fouling thermal resistance,and it can be used as the basis for quantitative determination for thermal resistance.Secondly,based on the circulating cooling water dynamic simulation experiment device,the correlation characteristics are investigated with magnetic memory effect time as a target norm,which correlation is between parameters of alternating magnetic field and conductivity of cooling water.The investigation includes the conductive is effected by the magnetic field strength,magnetic field duration action and solution concentration.These parameters perform the range analysis and analysis of variance in the investigation.Prediction model is built through the experiment investigation,which the model input and output are water parameters leading to fouling and thermal resistance on the heat exchanger.Compared with the magnetic field duration action and solution concentration,the magnetic field strength obviously effect to the conductive reflection.So the strength of the alternating magnetic field can indirectly control the fouling thermal resistance on the heat exchange surface,that magnetic field restrains the fouling.Thirdly,the restraining fouling is investigated in varies strength of the alternating magnetic field(0-200Gs)experiment through the intelligent detection of fouling resistance experiment platform.It shows that the longest fouling induction period is 10536 minutes,when the magnetic field strength is 200Gs.It is the best result for restraining fouling.The inputs are typical fouling water parameters(conductivity,pH and dissolved oxygen)in 200Gs,and the output is fouling resistance.According to the inputs and output,the GA-Elman neural network model is built which predicts the fouling thermal resistance and fouling tendency.The prediction result can be used as a quantitative judgment basis which is a tendency fouling or measure the degree of fouling.Finally,the pure water and CaCO3 solution are investigated in varies strength of the alternating magnetic field with the molecular dynamics simulation.According to radial distribution function and mean square displacement in different strength of magnetic field,it shows the trajectory and micro-cluster structure of microscopic particles.From a micro perspective,the restraining fouling principle can deeply investigate in the alternating magnetic field.The motion range become narrow about water molecules in magnetic field,and larger water cluster structure is synthesized through hydrogen bonding among the water molecule.Meanwhile,the magnetic field also increases the probability of the formation of hydrated calcium ions through hydration.The water molecules form a hydrated layer on the surface of calcium ions and tightly wrap calcium ions.It prevents the collision of calcium ions and carbonate ions and generation of calcium carbonate.It achieved the fouling can be retrained.In the thesis,combining the macro experiments with microscopic mechanism analysis,it clarifies the principle of electromagnetic suppression of heat transfer fouling,and establishes an effective heat transfer fouling prediction model. |
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