Fouling and fouling mitigation of calcium compounds on heat exchangers by novel colloids and surface modifications

2020 ◽  
Vol 36 (6) ◽  
pp. 653-685 ◽  
Author(s):  
Salim N. Kazi
Keyword(s):  
Heat Exchanger ◽  
Heat Exchangers ◽  
Whey Proteins ◽  
Natural Fibers ◽  
Cooling Water ◽  
Hard Water ◽  
Mineral Salts ◽  
Salt Crystals ◽  
Mineral Fouling ◽  
Living Organisms

AbstractFouling is the accumulation of unwanted materials on surfaces that causes detrimental effects on its function. The accumulated materials can be composed of living organisms (biofouling), nonliving substances (inorganic and/or organic), or a combination of both of them. Mineral fouling occurs when a process uses cooling water supersaturated with mineral salt crystals (i.e. hard water). Precipitation ensues on heat transfer surfaces whenever the inversely soluble dissolved calcium salt ions are exposed to high temperature. Mineral salts, dirt, waxes, biofilms, whey proteins, etc. are common deposits on the heat exchanger surfaces, and they create thermal resistance and increase pressure drop and maintenance costs of plants. Fouling of dissolved salts and its mitigation have been studied in detail by varying process parameters, surface materials, coatings on surfaces, additives, etc. by many researchers. In the present stage, researchers have considered polymeric additives, environmental friendly nanoparticles, natural fibers, and thermal conductive coatings (metallic and polymeric) in the study of mitigation of fouling. A better understanding of the problem and the mechanisms that lead to the accumulation of deposits on surfaces will provide opportunities to reduce or even eliminate the problem in certain situations. The present review study has focused on fouling phenomena, environment of fouling, heat exchanger fouling in design, and mitigation of fouling. The findings could support in developing the improved heat exchanger material surfaces, retain efficiency of the heat exchangers, and prolong their continuous operation.

Application of Pulsed Spark Discharge for Mitigation of Mineral Fouling in a Heat Exchanger

2010 ◽  
Author(s):  
Yong Yang ◽  
Hyoungsup Kim ◽  
Jin M. Jung ◽  
Alexander Fridman ◽  
Young I. Cho
Keyword(s):  
Heat Exchanger ◽  
Calcium Carbonate ◽  
Pure Water ◽  
Cooling Water ◽  
Calcium Content ◽  
Hard Water ◽  
Spark Discharge ◽  
Mineral Contents ◽  
Mineral Fouling ◽  
Pulsed Spark Discharge

One of the challenges in the production of electricity is the cooling water management because the calcium content in circulating cooling water continues to increase with time as pure water evaporates. Thus, the excessive mineral contents in water circulation systems could cause severe fouling in heat transfer equipment. To avoid the catastrophic failure in condensers, the cooling water is discharged after 3 cycles at a rate of 10 million gallons a day in a 1,000-MW thermoelectric power plant. The present study investigated the effect of pulsed spark discharges on the mitigation of mineral fouling in a concentric counterflow heat exchanger. Artificial hard water with calcium carbonate hardness ranging from 250 to 500 ppm was used with velocity varying over a range of 0.1–0.5 m/s and zero blowdown. Fouling resistances decreased by 50–88% for the plasma treated cases compared with the values for no-treatment cases. SEM photographs showed particle with larger sizes for the plasma treated cases comparing to smaller but more organized particles for the no-treatment cases. The different structures of particles were associated with pulsed spark discharge assisted precipitation of calcium carbonate in oversaturated hard water. X-ray diffraction data showed calcite crystal structures for all cases.

Thermal Analysis Technique for Coolers Operating in Off and Low Load Conditions

2012 ◽  
Author(s):  
Thomas J. Muldoon
Keyword(s):  
Heat Exchanger ◽  
Power Plant ◽  
Heat Exchangers ◽  
Cooling Water ◽  
Control Valve ◽  
Operating Conditions ◽  
Outlet Temperature ◽  
Inlet Valve ◽  
Plant Personnel ◽  
Load Conditions

The most conservatively designed power plant heat exchangers are designed to meet a maximum heat load with minimum fluid temperature differences. When the input temperatures are less than design maximums, the cooler will usually be in a position of over performance. This relationship is especially true when the heat exchanger is a closed Component Cooling Water (CCW) heat exchanger with inlet fluid at ambient conditions. Maintaining a consistent cooling temperature is an important concern in the operation of a power plant. It is important that the cooling needs of the equipment such as the hydrogen coolers are maintained at a set temperature. Overcooling may not be of benefit to the equipment. The component which cools the service water with the local cooling water is a component cooling water heat exchanger (CCW). The two primary methods of controlling the heat rejection performance on these vessels is to throttling the tubeside flow to get a consistent shell outlet temperature with control valves or leave the tubeside flow constant and by-pass a portion of the shellside flow. Estimating the performance of the heat exchanger with given set of inlet conditions and a fixed design point can be accomplished using a the Number Transfer Units (NTU) method. Opening and closing the control valve is based on the estimated performance. This analysis can be used by power plant personnel to gauge the operation of these vessels over varying operating conditions. The analysis can also include the effect of different values of cleanliness and the extent of throttling. As a unit experiences fouling, additional flow is required to meet the thermal requirements. Depending upon the extent of fouling, the inlet valve will be either opened or closed. Plant personnel may observe the cooling water inlet temperature and the extent to which the inlet valve is open, and use that information to determine possible fouling and setup a maintenance schedule. The following analytical approach for evaluating low, critical, or off load conditions is important in the design and operation of these types of power plant heat exchangers, piping and control valve systems.

Theoretical Analysis of Effects of Solution Heat Exchanger on the Performance of Mixed Absorption Refrigeration Cycle

2012 ◽  
Vol 170-173 ◽  
pp. 2521-2524
Author(s):  
Wen Li ◽  
Jun Hua Wan ◽  
Jing Liu ◽  
Zu Yi Zheng ◽  
Wen Ming Xu
Keyword(s):  
Heat Exchanger ◽  
Theoretical Analysis ◽  
Temperature Difference ◽  
Heat Exchangers ◽  
Water Flow Rate ◽  
Cooling Water ◽  
Solution Temperature ◽  
Refrigeration Cycle ◽  
Absorption Refrigeration ◽  
Cooling Water Flow Rate

The model of solution heat exchangers of mixed absorption refrigeration cycle was developed. The effects of strong solution temperature difference between inlet and outlet of solution heat exchanger on the coefficient of performance (COP) and cooling water flow rate of mixed absorption refrigeration cycle were analyzed, at the same time, the effects of temperature difference on the unit heat exchange area of counter-flow and cross-flow solution heat exchangers were analyzed. The theoretical analysis results showed that there was an optimal value for the strong solution temperature difference, for the mixed absorption system, the optimal temperature difference was about 12°C, the corresponding COP was 11.2% higher and the cooling water flow rate was 7.8% less than that of system without heat exchanger.

Experimental Comparison of Thermal Control Strategies in Piping Networks

2003 ◽  
Author(s):  
Walfre Franco ◽  
Mihir Sen ◽  
K. T. Yang ◽  
Rodney L. McClain
Keyword(s):  
Heat Exchanger ◽  
Heat Exchangers ◽  
Thermal Load ◽  
Control Strategies ◽  
Cooling Water ◽  
Thermal Control ◽  
Control Technique ◽  
Experimental Comparison ◽  
Primary Loop ◽  
Heating And Cooling

This manuscript presents an experimental study of three thermal control strategies commonly used in heating and cooling of buildings. The strategies are defined by the variables to be controlled, the hardware used for control and the piping arrangement. The experimental facility includes three heat exchangers within secondary loops that are connected to a primary loop. A different control technique is applied to each secondary loop. A heat exchanger on the primary loop delivers cooling water to the secondaries and receives warm water in return. Chilled water is provided by the building services. The thermal load to the heat exchangers is supplied by two water heaters which are located on a closed heating circuit. PID controllers are used to respond to changes in the thermal load. The temperature difference at the primary loop heat exchanger is used as a criterion for comparison to assess the relative merits and drawbacks of each strategy.

Passive Heat Exchanger Anti-Fouling for Solar DHW Systems

Solar Energy ◽  
2005 ◽  
Author(s):  
Stephen J. Harrison
Keyword(s):  
Heat Exchanger ◽  
Heat Exchangers ◽  
Hot Water ◽  
Normal Operation ◽  
Mineral Deposits ◽  
Accelerated Tests ◽  
Mineral Salts ◽  
Potable Water Supply ◽  
External Power ◽  
User Intervention

The interior surfaces of heat exchangers used in domestic hot water systems are particularly prone to fouling or complete blockage due to the accumulation of sediments, scale and mineral deposits. In many locations, mineral salts and other impurities may be present in the potable water supply and fouling may occur if the heat exchanger is not routinely cleaned or flushed of accumulated matter. In small residential installations, however, this is not practical due to the associated costs. In response to this need, a passive back-flushing system was designed that allows heat exchangers to be routinely back-flushed many times a day. The action is a normal operation of the system and does not require user intervention, external power or controls to function. During back-flushing mineral deposits are washed out of the heat exchanger and flushed from the system. the operation of the device and documents the results of accelerated tests undertaken to verify its operation.

Performance Enhancement of Enhanced Herringbone Wavy-Fin Round Tube Inclined Heat Exchangers With and Without Hydrophilic Coating Using Evaporative Spray and Deluge Cooling

2013 ◽  
Author(s):  
Sahil Popli ◽  
Yunho Hwang ◽  
Reinhard Radermacher
Keyword(s):  
Heat Exchanger ◽  
Pressure Drop ◽  
Heat Exchangers ◽  
Cooling Water ◽  
Ambient Air ◽  
Spray Cooling ◽  
Round Tube ◽  
Capacity Enhancement ◽  
Side Pressure ◽  
Over The Top

An experimental study has been conducted to evaluate the performance of two herringbone wavy-fin round tube compact heat exchangers working as coolers, with frontal areas of approximately 0.24 m2 each in both dry and wet conditions. Heat exchanger capacity and air-side pressure drop were measured with the heat exchanger angle set at 20° from vertical. Deluge water cooling was achieved by incorporating a water distributor on top of the heat exchanger from which wetting water overflows as thin film over the top leading edge of the heat exchanger fins. A hollow cone nozzle was used for spray cooling. Water was used as a refrigerant, and enters the heat exchanger tubes at 43°C temperature. Ambient air, deluge and spray cooling water were maintained at 28°C temperature, and frontal air velocity was varied from 1.5 m/s to 3.0 m/s. Capacity was significantly enhanced for all heat exchangers using both deluge and spray cooling. However, the air-side pressure drop penalty ratio was much higher for deluge cooling. Furthermore, heat exchanger with hydrophilic coated fins achieved higher capacity enhancement ratios. This study contributes 8 dry cases and 48 wet cases experimental data points of wavy-fin heat exchanger performance. Future studies would aim at obtaining higher capacity enhancement ratios for spray cooling while maintaining air-side pressure drop penalty ratio of 1.0.

Mineral Fouling Control by Underwater Plasma Discharge in a Heat Exchanger

2011 ◽  
Vol 133 (5) ◽  
Author(s):  
Yong Yang ◽  
Hyoungsup Kim ◽  
Alexander Fridman ◽  
Young I. Cho
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Hard Water ◽  
Plasma Discharge ◽  
Mineral Contents ◽  
Fouling Control ◽  
Spark Discharges ◽  
Mineral Fouling ◽  
Pulsed Spark Discharge ◽  
Heat Exchanger Surface

The excessive mineral contents in water circulation systems could cause severe fouling in heat transfer equipment. The present study investigated the effect of underwater pulsed spark discharges on the mitigation of mineral fouling in a concentric counterflow heat exchanger. Artificial hard water with calcium carbonate hardness of 250 mg/L was used with velocity ranging from 0.1 m/s to 0.5 m/s and zero blowdown. Fouling resistances decreased by 50–72% for the plasma treated cases compared with the values for no-treatment cases, indicating that the pulsed spark discharge could significantly mitigate the mineral fouling on the heat exchanger surface.

scholarly journals TEMPERATURES OPTIMIZATION OF TWO-CIRCUIT CLOSED COOLING SYSTEM OF SHIP'S POWER PLANT

2020 ◽  
pp. 175-183
Author(s):  
Konstantin Yu. Fedorovskiy ◽  
Nadezhda K. Fedorovskaya
Keyword(s):  
Heat Exchanger ◽  
Power Plant ◽  
Heat Exchangers ◽  
Closed Loop ◽  
Cooling System ◽  
Cooling Water ◽  
Cooling Systems ◽  
Additional Heat ◽  
Temperature Head ◽  
Optimal Value

    The issues of creating environmentally friendly highly reliable closed-loop cooling systems are considered in the paper. The achievement of these qualities is ensured by the rejection of cooling water intake. The analysis of various coolants of the power installation requiring cooling is carried out. It is shown that for the cooling of a number of coolants it is advisable to create double-circuit cooling systems. This requires the introduction of an additional heat exchanger and the separation of the temperature head between the cooled coolant and seawater. The authors suggest an approach that makes it possible to distribute this temperature head between the circuits optimally. This procedure involves comparing various heat exchangers based on their reduced area. A nomogram is presented to determine the optimal value of the temperature head.

Analysis of the Thermal Stress at the Tubesheet in Floating-Head or U-Tube Heat Exchangers

2017 ◽  
Vol 139 (2) ◽  
Author(s):  
Jiuyi Liu ◽  
Caifu Qian ◽  
Huifang Li
Keyword(s):  
Thermal Stress ◽  
Heat Exchanger ◽  
Temperature Difference ◽  
Heat Exchangers ◽  
Influence Factors ◽  
Area Ratio ◽  
Shell Side ◽  
Tube Heat Exchanger ◽  
Numerical Tests ◽  
Hole Area

Thermal stress is an important factor influencing the strength of a heat exchanger tubesheet. Some studies have indicated that, even in floating-head or U-tube heat exchangers, the thermal stress at the tubesheet is significant in magnitude. For exploring the value, distribution, and the influence factors of the thermal stress at the tubesheet of these kind heat exchangers, a tubesheet and triangle arranged tubes with the tube diameter of 25 mm were numerically analyzed. Specifically, the thermal stress at the tubesheet center is concentrated and analyzed with changing different parameters of the tubesheet, such as the temperature difference between tube-side and shell-side fluids, tubesheet diameter, thickness, and the tube-hole area ratio. It is found that the thermal stress of the tubesheet of floating-head or U-tube heat exchanger was comparable in magnitude with that produced by pressures, and the distribution of the thermal stress depends on the tube-hole area and the temperature inside the tubes. The thermal stress at the center of the tubesheet surface is high when tube-hole area ratio is very low. And with increasing the tube-hole area ratio, the stress first decreases rapidly and then increases linearly. A formula was numerically fitted for calculating the thermal stress at the tubesheet surface center which may be useful for the strength design of the tubesheet of floating-head or U-tube heat exchangers when considering the thermal stress. Numerical tests show that the fitted formula can meet the accuracy requirements for engineering applications.

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