Patent Application: US-55427804-A

Abstract:
this invention relates to a method and apparatus for improvement of flow rates and reduction of fouling in process equipment such as for instance heat exchangers where fluids are flowing in single or multiphase . this is obtained by imposing a dc - potential at the walls of the process equipment that exactly opposes the naturally ocurring potential due to interaction between the walls of the process equipment and the fluid flowing inside . an improved flow rate will cause that the heat exchanger becomes more efficient , i . e . a lower deposition rate and a higher removal rate of inorganic agents . the fluid may be a pure fluid , colloidal fluid or contain inclusions in the form of particles .

Description:
the invention will now be described in more detail under reference to a . preferred embodiment of the invention . a preferred embodiment of the invention , when implemented on a shell and tube heat exchanger of is shown schematically in fig1 . the arrows indicate the flow directions . the invention 1 is connected to the heat exchanger 2 by two or more connectors of conventional type ( not shown in the figure ). one connector is connected to a ring 4 in the inlet for the cooling / heating medium 3 which is electrically insulated from the rest of the system . one connector is connected to a ring 7 in the inlet for the process fluid 6 which is also electrically insulated from the rest of the system . a third connector is connected to the heat exchanger itself at the point marked 9 . if the invention is used for flow improvement of the process fluid , the connecting point 9 will be at the outlet for the process fluid 5 . for the improvement of the cooling / heating medium flow , the connecting point 9 will be at outlet 8 . for the flow improvement of the cooling / heating medium , ring 4 is used , and for the process fluid , ring 7 is used . when the invention is switch into measuring / calculator mode , the set point for the regulator is determined , as described in the following : the estimation of the set point is based on capacitance measurements . the capacitance is measured between the ring 4 , or 7 , and the heat exchanger 9 itself by the alternating current method , as a function of the applied dc - potential . its positive and negative ends are connected to 9 and 4 , or 7 , respectively . the potential at which the capacitance shows a minimum value , corresponds to the un - electrified condition of the heat exchanger , and is the particular dc - potential used as set point for the regulator . when the invention is switch into working mode , the electrical dc - generator applies the potential between 4 , or 7 , and 9 , and is controlled by the regulator . in order to verify the ability of the invention to reduce deposition of precipitates , a colloid solution of calcium carbonate and barium sulphate in flowing water were made and experiments performed to investigate the deposition rates on a titanium surface . the calcium carbonate and barium sulphate is dispersed ( colloid state ) in the flowing fluid passing the titanium plate . preparation of the colloid solution of calcium carbonate and barium sulphate : 1 l of 0 . 00025 m bacl 2 and 1 l of 0 . 00025 m cacl 2 is mixed , and then 2 . 5 ml of 1 m na 2 co 3 is added . finally , 25 ml of 0 . 01 m na 2 so 4 is added . in this way a colloid solution of calcium carbonate and barium sulphate is obtained . for fresh solution and room temperature , light scattering measurements performed at different wavelengths give the size calcium carbonate and barium sulphate particles equal to about 50 nanometers . in two - three days these particles reach the size of about 100 nm . further growth of the size leads to the transformation of the colloid into suspension and the precipitation of calcium carbonate and barium sulphate is observed . then the colloid solution is replaced by newly prepared solution . during the experiments carried out at 38 ° c ., the growth of the size of the particles and the precipitation was much faster . therefore , every day a new solution has been used . during the measurements , the content of calcium and barium was controlled by atomic absorption spectroscopy . schematic representation of liquid flow system is presented in fig2 . the tube is in the loop which contains two reservoirs with simulated fluid and the peristaltic pump ( p ). the flow velocity is controlled by the height ( h ), while the temperature of liquid is controlled by a thermo reservoir 2 . this reservoir also serves for avoiding the periodic pressure changes which arise during the work of the peristaltic pump and which can influence the frequency of quartz crystal oscillation . the 5 mhz at - cut 15 mm diameter and 0 . 3 mm thick quartz crystals were used . both sides of crystals were coated with titanium by cathodic sputtering . the decrease in frequency change is linearly related with an increase of electrode mass . the fundamental frequency of quartz crystal ( 5 mhz ) and the geometric area of a circular titanium region in the centre of the crystal ( 0 . 2 cm − 2 ) give the eqcm mass sensitivity equal to 25 ° 10 − 9 g hz − 1 cm − 2 = 25 ng hz − 1 cm − 1 . these coated working quartz crystals ( qcm 1 , qcm 2 and qcm 3 , see fig3 and 4 ) were glued into cylindrical holders , which were affixed to the tube in three different ways , see fig3 . one side of the crystals were exposed to the solution in the tube and served as working electrodes ( qcm 1 , qcm 2 and qcm 3 , see fig3 and 4 ). another side of these crystals faced the air . the working quartz electrodes were inserted into three separately controlled oscillators — qcm drivers ( fig4 ) configuration of which allows the working electrodes to be grounded . home - made voltammetric and frequency measurement system was used ( fig4 ). in this system , a high precision frequency counter performs a measurement with accuracy in 0 . 1 - 0 . 2 hz for about 5 mhz frequency in 3 ms . during the measurements , the same potential was applied simultaneously to all three electrodes and the changes of the frequency of these quartz supported electrodes with time were separately recorded for 600 s . then the same experiment was repeated for another potential . in such a way , the potential range from 1 v to − 1 v vs . the standard hydrogen electrode ( from 0 . 8 v to − 1 . 2 v vs . the silver / silver chloride / saturated kcl electrode ) with 0 . 1 v increments was investigated . 1 . measurements in colloid solution at flow rate 3 l / min ( re = 1300 ) and room temperature ( 22 ° c .) the results of these measurements are depicted in fig5 - 9 . low rates observed in fresh colloid solution at the most positive potentials ( fig5 ) can be explained by very small size of the particles ( less than 50 nm ). during the measurements they were growing ( growing was followed by the light scattering technique ). that could be the reason for the rate growth when the potential is changed in negative direction but still remains in positive region . when the experiments were repeated next day and on the third day in the same solution , in positive region the potential influence on the mass deposition rate is smaller ( fig8 and 9 ). in the negative potential region , the clear potential influence is observed — mass deposition rate is noticeably decreased ( fig5 and 9 ) fig8 — the same solution and the same conditions of the measurements as given in fig5 but the measurements were performed the next day after the experiments , the results of which are presented in fig7 . the size of particles is approximately 100 nm and still growing , though much slower . the data presented in fig8 show the influence of the potential ( growth effects are small ). fig9 — solution turned to be more opalescent , the size of particles is larger than 100 nm and solution turned to be more opalescent ( white colour of the solution is visually observed ). the rates of mass deposition onto these electrodes were very small and similar for the first two days ( fig6 and 7 ). the measurements , repeated on the third day ( the data for bottom electrode are presented in fig9 ) revealed some similarity to the behaviour of bottom electrode , though the absolute values of the rates are noticeably smaller . 2 . measurements in colloid solution at increased flow rate 4 l / min ( re = 1700 ) and room temperature ( 22 ° c .) the results of these measurements are depicted in fig1 - 12 . decrease in deposition rates , observed at higher flow rates ( fig1 and 11 ), may be related with “ washing ” of particles from the electrode surface . both experiments 1 and 2 are carried out at laminar flow ( the reynolds numbers are 1300 and 1700 , respectively ). at laminar flow , the friction factor decreases with increasing reynolds number . the decrease in deposition rates , observed at higher flow rates ( fig9 and 10 ), may be related with lower friction factor . the results show that the deposition rate of calcium carbonate and barium sulphate on an electrode surface depends on the applied electrical dc - potential within the range of 0 . 8 - 1 . 0 v ( ag / agcl 2 reference electrode ). within certain ranges a decrease in the deposition rate is observed , while an increase is observed in other ranges . the results show that the deposition rate decreases with higher flow rates , which indicates that the effect , maybe , is related with lower friction factor . 2 ) evaluation of the prinsiples of magnetic water treatment . american petroleum institute , washington d . c ., 1985 . 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