Heat Exchanger Surfaces Research Articles

Exploration of KCl deposition dynamics for the formation of coarse and fine layer deposits

In biomass and waste combustion, the release of KCl into the gas phase results in its deposition on heat exchanger surfaces, enhancing their stickiness and accelerating deposit buildup from incoming ash particles. Despite this, the mechanisms governing KCl deposition remain inadequately explored. KCl has been observed to form either a fine, powdery layer through thermophoresis of nucleated KCl particles or a crystal-like, coarse layer through heterogeneous condensation of KCl vapor. However, the quantitative assessment of coarse and fine layer formation has never been performed. In this study, an entrained flow reactor and mechanistic model were employed to analyze KCl deposition behavior, examining the effect of probe temperature and exposure time. Quantification of both the coarse and fine deposit layers was accomplished. Probe temperature was found to have no influence on the deposition in the range from 300 °C – 595 °C. For coarse layer formation, the critical factor was the development of a fine layer upon which the crystal-like structure of the coarse layer grows. Lower probe temperatures accelerate initial layer formation, initiating the coarse section sooner. Additionally, it slightly increases nucleation and condensation, however, nucleation is increased stronger resulting in a lower ratio of coarse to fine deposit. The quantification of the coarse mass, in conjunction with the simulation, provides a first estimation of the critical mass required to initiate heterogeneous condensation on a steel tube. In this study, a critical mass of 1.26e-3 g/cm2 was determined.

Frost measurement of air source heat pump heat exchangers based on image recognition processing technology

In order to understand the application of frost measurement of air source heat pump heat exchanger, a research on frost measurement of air source heat pump heat exchanger based on image recognition processing technology is put forward. In this paper, the scheme design of defrosting control system based on image processing technology is introduced, and the frost degree coefficient of outdoor heat exchanger fin surface is introduced to characterize the frost degree of fin surface. Secondly, the experimental environment room was built, and the conventional defrosting control method of the existing heat pump unit was tested on the spot. It was found that in the air temperature of -6~0?C and the air relative humidity of 86~92%, the unit appeared the phenomenon of ?defrosting in time? and ?defrosting without frost?. Finally, the change of frost layer on the surface of the outdoor heat exchanger fin during defrosting is analyzed, and the coefficient of frost degree on the surface of the fin is calculated and analyzed. At the beginning of defrosting, due to the large degree of frost, the P-value of the frost degree coefficient on the surface of the fin is close to 1, when the defrosting is carried out for 125 seconds, the P-value of the frost degree coefficient on the surface of the fin decreases sharply to 0.09, when the defrosting is completed, the P-value of the frost degree coefficient on the surface of the outdoor heat exchanger is maintained at about 0.04. The defrosting control method of air source heat pump based on image processing technology is proposed in this paper, and its technical feasibility and effect are verified by experimental tests, which lays a foundation for future popularization and application.

Energy-efficient chamber dryer with combined heating heat transfer

Chamber dryers are widely used in the processing of vegetables and fruits in Ukraine, the USA, China, France, etc. They are intended for drying lumpy (artificial) products (bread, chopped vegetables and fruits, etc.). A chamber dryer is a connection of one or more dryer cabinets in location mode. In a 2-zone chamber dryer, it is possible to dry large volumes of raw materials, which consumes less energy compared to the power that the entire drying cabinet has when it is operated separately. But high energy costs for the process of drying materials with high prices for the second encourage to solve the task of increasing energy efficiency when creating new chamber dryers using electronic heaters of the coolant. The Institute of Technical Thermal Physics of the National Academy of Sciences of Ukraine suggests using steam heat generators in the operation of a multi-zone tunnel dryer, which, in comparison with organic fuel heat generators, make it possible to save heat consumption by 1.7-2.3 times compared to existing analogues. Energy consumption of heat in the tunnel dryer is 3800 kJ/kg of evaporated moisture. To reduce energy costs, solar tunnel dryers with an increase in the heat exchange surface due to the maximum separation of pallets with raw materials at different angles have become widespread. Due to the influence of solar energy, the temperature of the drying agent can reach 70 °С. The main direction of the development of drying plant materials is the combination of existing technologies with renewable energy sources, in particular the use of solar energy, heat pumps, as well as microwave, infrared and sublimation drying. Combined drying technology is the combination of two or more different drying processes that can provide a synergistic effect, resulting in reduced energy requirements and reduced drying time while maintaining most of the quality characteristics, such as taste, nutrients, color, aroma, texture, etc. Different methods of combined drying are considered, such as: solar-infrared, convective-infrared, infrared-microwave, convective-microwave and multifunctional, which combines microwave-sublimation drying under vacuum. The comparison of the combined methods showed a significant decrease in the duration of drying and a reduction in energy consumption, which can be used in the design of tunnel energy-efficient dryers.

Study on the heat transfer performance of heat exchange surfaces and flow channels under negative pressure

This paper presents a theoretical analysis and simulation study on heat transfer characteristics under negative pressure. The results can provide guidance for the design and optimization of heat transfer equipment under negative pressure.

Helium pool boiling critical heat flux under various magnetically controlled gravity levels

The characterization of Critical Heat Flux (CHF) under magnetic compensation of gravity in liquid helium (LHe) is particularly important for the design of the future very high magnetic field superconducting magnets. Through a series of experimental sessions, the critical heat flux in LHe pool boiling has been determined under various gravity conditions ranging from 0.03g to 2.2g using magnetic forces. It is the largest range of gravity variation, from reduced to hyper-gravity, ever studied in a single facility so far. The study was conducted in a very high magnetic field up to 30 T. The magnetic compensation of gravity does not allow for perfect resulting gravity homogeneity. Nevertheless, for the first time, the magnetic field configuration is considered in the experimental results analysis. The relative resulting gravity inclination with respect to the heat exchange surface is also taken into account. The experimental results are compared with the well-known CHF correlation in LHe pool-boiling and show a very good behavior agreement. For our experimental gravity level, the CHF is ranging from 3000 W/m2 to 12000 W/m2.

Erosion wear analysis of heat exchange surfaces in a falling particle-based concentrating solar power system

Next generation concentrating solar power (CSP) plants that use solid particles as the heat transfer and storage medium provide opportunities for higher temperature operation, higher efficiency, and lower levelized cost. However, falling particles over component material surfaces can cause significant erosion, severely limiting the performance and operational service life of the components. An understanding of the particle erosion wear of heat transfer surfaces is imperative for designing components and operating conditions to minimize wear. Considering a shell-and-tube heat exchanger configuration, this study presents a computational analysis coupling falling particle flow around heat exchanger tubes and particle-scale erosion of the tube surfaces governed by the Finnie model. Several tube arrangements, particle flow and geometric parameters, and tube material parameters are systematically investigated for their effects on the erosion rate spatially and with time. Parameters that influence the erosion depth, the cumulative mass loss rate and the maximum erosion rate are elucidated. The results of the study may be used to help identify locations that experience the most erosion and devise ways for targeted erosion mitigation.

Prospects for the Use of Metal Surfaces Modified by Nanosecond Laser Radiation for Energy Applications

Laser technologies for processing metals used as heat exchange surfaces are unrivaled to solve a number of problems in the energy industry. This is explained by the fact that after laser radiation treatment, metal surfaces gain unique surface functional properties (extreme wettability properties, high resistance to corrosion in contact with traditional coolants, high abrasive and cavitation resistance). The study of the processes of evaporation, boiling, and condensation on such surfaces is hampered by one of the unsolved problems, which is the lack of the ability to predict the configuration of microtextures, for example, in the form of micropillars and microchannels with predetermined sizes. In this work, a graphic–analytical technique based on the use of ablation spot sizes for the formation of a given configuration and microtexture dimensions on traditional structural materials of heat exchange surfaces is developed. Based on experimental data, regime maps were constructed for the formation of microtextures on the surfaces of aluminum alloy AlMg6 and steel AISI 310. The prospects for using metal surfaces with a given microtexture formed by laser radiation to intensify the phase transition of coolants and control convective flows in a droplet lying on a heated surface were assessed. The obtained results can be used in the development of spray (drip) irrigation systems to provide thermal protection for heat-stressed equipment.

Hybrid Polymer Salogels for Reversible Entrapment of Salt-Hydrate-Based Thermal Energy Storage Materials.

One of the challenges preventing wide use of inorganic salt hydrate phase change materials (PCMs) is their low viscosity above their melting point, leading to leakage, phase segregation, and separation from heat exchanger surfaces in thermal management applications. The development of a broad strategy for using polymers that provide tunable, temperature-reversible shape stabilization of a variety of salt hydrates by using the lowest possible polymer concentrations is hindered by differences in solubility and gelation behavior of polymers with change in the type of ion. This work addressed the challenge of creating robust, temperature-responsive shape-stabilizing polymer gels (i.e., salogels) using a low cost PCM, calcium chloride hexahydrate (CaCl2·6H2O, CCH). Due to the extremely high (9 M) concentration of chloride ions and the tendency to salting-out polymer chains, the previous strategy of using single-polymer salogels was not successful. Thus, this work introduced a strategy of using two polymers, poly(vinyl alcohol) and ultrahigh molecular weight polyacrylamide (PVA and PAAm, respectively), along with borax as a cross-linker to achieve temperature-reversible, shape-stable salogels. This system resulted in robust salogels whose gel-to-sol transition temperature (Tgel) was tunable within an application-relevant range of gelation temperature (30-80 °C). This behavior was enabled by a synergistic combination of dynamic covalent cross-links between PVA units and entanglements of PAAm chains which were combined into a single hybrid network. The hybrid salogels had <5 wt % polymer content, maintaining ∼95% of the heat of fusion of the pure PCM. Importantly, the noncovalent nature of gelation supported thermo-reversibility of gelation, shape stability, and retention of thermal properties over 50 melting/crystallization cycles.

Study on the influence of circumferential shape on the performance of cross wavy primary surface heat exchanger channel

The primary surface heat exchanger can be described as a compact and highly efficient heat exchanger. In contrast, the cross wavy primary surface heat exchangers are suitable for microturbines. Based on the study of circular cross wavy channel, this study innovatively proposed the triangular cross wavy channel to improve the fluid flow conditions and the rectangular cross wavy channel to increase the overall heat exchange of the channel. The applicability domain of the three types of channels is summarized by numerical simulation. The circular cross wavy channels have the smallest irreversible loss, the triangular cross wavy channels have the highest efficiency and the rectangular channels have the largest total heat transfer. Moreover, the correlations of Nusselt number and friction factor are proposed. The correlations for the Nusselt number and friction coefficient have been validated, and the average absolute errors are 2.71 % and 7.85 % respectively. The results show that the correlation formulas can effectively predict the resistance and heat transfer performance of the cross wavy heat exchange channel.

Environmental Risk Assessment of Hydrocarbon-Rich Sludge of a Gas Refinery Using the Integrated Approach of PMBOK Standard Risk Management and FMEA Technique: A Case Study

Background: The present study aimed to assess the potential hazards of hydrocarbon-rich gas refinery sludge from the South Pars Gas Complex-First Refinery, Iran, and to analyze how these risks could impact the project goals based on the Project Management Body of Knowledge (PMBOK) guidelines. Methods: Statistical population of this analytical, cross-sectional survey was 31 health, safety, and environment (HSE) experts from the study refinery selected by purposeful sampling. Environmental, health, safety, and technical risks were categorized and identified using the PMBOK guidelines. Delphi method and 5-point Likert scale questionnaire were employed to assess the significance of each risk. Priority one risks within each category were determined using Primavera Risk Analysis version 8.7 software. Results: Following three Delphi steps, 17 out of 77 primary risks were identified and finalized. The first rank with the highest weight corresponded to time and cost group (the risk of soil contamination via sludge stored in the burn pit due to aliphatic and aromatic hydrocarbons), human resources group (radioactive materials accumulated on the inner surfaces of pipes, valves, pumps, heat exchangers, tanks, boilers and other equipment and the risk of these materials being hazardous for human health), and quality group (failure to supply equipment and quality control systems and personal protective equipment). Conclusion: The research findings pinpointed 17 risks within various domains, encompassing time and cost, human resources, quality, contract, scope, and communication. These identified risks necessitate a comprehensive, integrated approach to risk management for effective mitigation and resolution.

Analyzing competing effects between heat transfer area and natural convection to enhance heat transfer in latent heat storage

Phase change materials (PCMs) are effective means of storing thermal energy and to balance temporal supply-demand mismatch. To enhance heat transfer within the PCM, internal fins are often employed to increase the heat exchange area, but they usually suppress simultaneously natural convection reducing the performance of the PCM storage. To better understand these two conflicting effects and to find a better trade-off between the different heat transfer means, a comprehensive numerical study of PCM storage with different fin shapes (straight and sinusoidal wavy fins) and surface areas, but with equivalent volume fraction, was accomplished. The results show that increasing the surface area of sinusoidal fins improves only marginally the heat transfer, mainly because the flow velocity of natural convection along the normal direction of the solid interface is inhibited. The velocity normal to the solid interface was found to be the most critical factors to the overall heat transfer efficiency of the system and to the time needed to complete the phase change in the PCM container. The study clearly shows that to enhance the heat transfer in PCM, the effects from natural convection (direction and strength) play a more important role than the heat exchange surface area. To improve the thermal performance and efficiency of PCM storage systems both factors need to be combined in an optimal way.

Theoretical and numerical study on new evaluation criteria for longitudinal vortex enhanced heat transfer

The enhancement of heat transfer caused by longitudinal vortex phenomena has been a widely studied topic for a significant period in fluid mechanics and heat transfer. However, despite extensive efforts, the current understanding of longitudinal vortex flow and the involved physical mechanisms leading to enhanced heat transfer remains qualitative in nature. To unveil the physical mechanisms underlying the enhancement of convective heat transfer by longitudinal vortices, further quantitative research and in-depth discussions are necessary. By performing detailed derivations and proofs of the equations, this study aims to further understand the relationship between local vortex variations and heat transfer performance. The results indicate that the presence of longitudinal vortices alters the gradient of the convective term and ultimately leads to enhanced heat transfer performance. Based on the derived results, corresponding metrics have been proposed to quantitatively analyze the degree of heat transfer enhancement due to longitudinal vortices. This proposed quantitative analysis metric has been applied to evaluate the heat transfer performance of a cross-wavy primary surface heat exchanger, validating the reliability of the metrics. The research content and conclusions provide valuable insights for both theoretical investigations and practical engineering applications in the field of enhanced heat transfer.

An Experimental Examination into the Efficiency of a Shell-and-Tube Heat Exchanger for an EGR Cooler

The increasing concerns over environmental pollution and stringent regulations on emission have led to the widespread adoption of exhaust gas recirculation (EGR) systems in interna combustion engines. EGR systems help reduce nitrogen oxide (NOx) emissions by recirculating a portion of exhaust gaes back into the combustion chamber. Howerver, the elevated temperature of exhaust gases poses challenges related to thermal management, necessitating the use of exhaust gas recirculation cooler. The experimental setup allows for the controlled circulation of exhaust gases and cooling fluids, thereby facilitating the measurement of heat transfer rates, pressure drops and overall thermal efficiency. These parameters encompass the inlet and outlet temperatures of both the exhaust gases and the cooling fluids flow rates for both fluids resulting pressure drops. By systematically altering these factors, the intricate, interplay between the various parameters and their inputs on the heat exchangers thermal performances are comprehensively explored. Addition, the research develops into critical aspects often overshadowed in EGR cooler studies on fouling. Overtime, the accumulation of deposits in the heat exchanger surface can led to reduced heat transfer efficiency. The outcomes of this study are instrumental for the advancement of EGR cooler technologies fostering more sustainable and environmentally friendly and automotive engines.

Thermal management system design for a series hybrid-electric propulsion architecture

Abstract The current paper is focused on the conceptual design of a thermal management system with a liquid working medium for a commuter hybrid-electric aircraft, featuring a series propulsion configuration. Regarding the system’s architecture, parametric analyses are conducted, by altering the number of heat exchangers. To clarify, a centralised and a decentralised thermal management system architecture are examined. Furthermore, a computational model calculates the temperatures during the system’s operation and the required coolant mass flows to sufficiently cool all the compartments. Subsequently, the required heat exchanger surface is determined and the weight of each compartment that comprises the thermal management system can be calculated. It is worth noting, that the compartments’ cold plate weight is integrated. The results indicate that the decentralised configuration results in lower temperature fields for all components compared to the centralised configuration. However, the latter weighs 32.2% lower at 158.22kg while the decentralised configuration weighs 233.48kg.

Investigation of zirconium (Zr) coated heat exchanger surface for the enhancement of heat transfer and retardation of mineral fouling

BackgroundFouling is a major problem in many industrial heat exchangers as in these devices water has been used for heat exchanging purposes. With the commencement of foulants deposition on heat exchanger surface the performance of heat exchangers is deteriorated due to lower thermal conductivity of the deposits formed on the heat exchanger surface. This study investigated the heat transfer and mitigation of CaCO3 fouling by applying zirconium coating layer on heat exchanger surface. MethodsZirconium was chosen as a coating material because of its surface adhesion and one of the best corrosion resistance materials. The Physical Vapor Deposition approach was implemented to develop a coating layer on heat exchanger surface. Heat transfer was investigated at numerous temperatures and flow rates to examine the impact of coating on heat transfer. Fouling experiments were conducted to examine the CaCO3 accumulation on the uncoated SS316L and Zirconium coated surfaces. After the fouling experiments, the coupon was disassembled from the test segment for the investigation of surface texture, after fouling effect and the morphology of deposits was assessed by using Field Emission Scanning Electron Microscopy (FESEM). Significant findingsResults reveal that the Zirconium coated surface declined the fouling deposition and improved the heat transfer.

Experimental and theoretical study on effect of dust deposition on frosting characteristics of fin surface

Since dust accumulates on the fin surface of the outdoor heat exchanger all year round, frost formation inevitably occurs on the fin surface with dust deposition when an air source heat pump is used for heating in winter. However, the effect of dust deposition on frosting characteristics of fin surface has not been clarified. Therefore, visualization experiments were carried out in this paper to study the frosting characteristics on bare and superhydrophobic fin surfaces under different dust deposition levels. Meanwhile, the influence mechanism of dust deposition on frost formation was analyzed theoretically based on phase transition dynamics. The experimental results showed that when the dust deposition on the superhydrophobic fin surface was less than 0.2 g, the dust deposition promoted crystal growth at the initial stage of frost formation, while the frost formation was inhibited when the dust deposition was more than 0.4 g. In the case of bare fin surface, dust deposition always inhibited the frost formation. As the dust deposition mass on the fin surface increased, the thickness and density of the frost layer decreased on both bare and superhydrophobic fin surfaces. In addition, it was worth noting that with the increase of dust deposition, the super hydrophobicity of the superhydrophobic surface was gradually lost. This is not conducive to the practical application of superhydrophobic anti-frosting technology.

Improvement of heat transfer and fouling retardation performance of heat exchanger using green functionalized graphene nanoplatelets additives

BackgroundCalcium carbonate (CaCO3) is one of the main fouling elements of the crystallization fouling that causes critical problems in the operation of industrial heat exchangers. This study presents the retardation of CaCO3 Fouling, and heat transfer enhancement of a tube heat exchanger immersed in a CaCO3 rich solution containing clove treated graphene nano platelets (C-GNP) additives as suspension. MethodsThermo-physical properties of water-based C-GNP additives nanofluid were tested before running the experiment. Experimental investigation was conducted to assess the C-GNP additives performance in the enhancement of heat transfer and reduction of fouling deposition. For the retardation of fouling experiments, the hard water or super saturated fouling solution of 300 ± 20 mgL−1 was prepared. To maintain the hard water concentration until the end of the experiments, a complexometric titration was adopted to monitor the CaCO3 concentration at every 6 h. interval. The FESEM was utilized for the investigation of the morphology of CaCO3 deposition on the heat exchanger surface. Significant findingsThe results of this study demonstrate that the addition of C-GNP enhanced the heat transfer and reduced the foulant deposition without any effect of corrosion. The results also revealed the inverse relationship between the additive concentration and the fouling resistance. The outcomes of this study also support the achievement of United Nation sustainable development goal (SDG) target 7.3.

Energy efficiency analysis and optimization of a pressurized oxy-fuel circulating fluidized bed combustion system

The commercial application of oxy-fuel combustion technology is limited by energy deduction which is caused by addition of air separation unit (ASU) and carbon dioxide compression and purification unit (CPU). Pressurized circulating fluidized bed (CFB) oxy-fuel combustion technology is one option to improve the net electric generation efficiency. In this research, a series of simulations and optimizations were carried out to analyze the energy efficiency of a pressurized oxy-fuel combustion system. The boiler structure and heat exchange surface arrangement under different pressure were calculated. The cross-sectional area of the furnace and tail flue were both reduced up to 10 % of the original size and the floor space of the boiler was considered to be the lowest at 1.1 MPa. The energy efficiency and exergy analysis were used to explore the influence of pressure on the net efficiency and the optimization potential of system. The net electric generation efficiency reached a maximum value of 24.16 % at 1.1 MPa, which is 5.4 % higher than that at atmospheric pressure. Finally, four parameters, i.e. preheat temperature, oxygen concentration, ASU outlet oxygen purity and CPU compressor outlet pressure, were optimized to improve the system net efficiency to 26.67 %, 29.04 %, 25.87 % and 24.36 %, respectively.

Numerical investigation of thermal-hydraulics characteristics of cross-flow corrugated plate heat exchanger for lithium-cooled space nuclear reactor

The utilization of a lithium-cooled nuclear power supply system in conjunction with the He-Xe Brayton power system has great potential for providing power for space exploration missions. This is primarily attributed to its notable characteristics, such as high energy density, substantial output power, long-duration operation cycle, and little vulnerability to environmental factors. One of the salient concerns that necessitates attention is the phenomenon of heat transfer occurring between liquid lithium and a mixture of helium and xenon (He-Xe). The Vertical Cross-Flow Corrugated Plate Heat Exchanger (VC-CPHE) constructed from W-alloy possesses several advantages in space reactor applications compared to other heat exchangers. These include its compact design, which allows for a large heat exchange surface, as well as its ability to shield gamma-ray radiation. This paper investigates the thermal hydraulic properties of the VC-CPHE internal heat transfer medium using Computational Fluid Dynamics (CFD) techniques. The results indicate that, due to the similar flow channel structure of Li and He-Xe, there are similarities in terms of flow direction and periodic distribution of parameters. Nevertheless, due to the distinct thermophysical properties and operational parameters, these materials demonstrate notable disparities in temperature boundary layers, local thermal resistance, and other relevant factors. Furthermore, the optimization of VC-CPHE involves a balancing act between enhancing heat transfer efficacy and minimizing flow resistance. The VC-CPHE demonstrates optimal balanced performance when the inlet cross-angle is set at 45°. In comparison to Li, He-Xe exhibits elevated levels of thermal resistance and pressure loss. Hence, in the investigation of optimizing the corrugation pitch and inlet cross-angle, the optimal balanced size of corrugation pitch is 12 mm and inlet cross-angle is 45° on He-Xe side is used as the final result. An increase in the inlet temperature difference of the heat exchanger leads to a slight decrease in the heat transfer coefficient, but an overall improvement in heat transfer. On the basis of obtaining the flow and heat transfer characteristics inside VC-CPHE, the effects of inlet cross-angle, corrugation pitch, and inlet temperature difference on the performance of VC-CPHE are discussed. The findings derived from the present study provide valuable insights for the future design and optimization of VC-CPHE systems in megawatt-class nuclear power deep space exploration spacecraft, particularly in relation to internal heat transfer.

Evaporation and heat exchange of a thin liquid layer under various heating methods: Advantages of local heating over uniform heating of the wall

Intensification of heat transfer and evaporation is widely used in modern technologies at limited dimensions of heat exchange surfaces and high energy density. To date, stationary heat transfer at uniform wall heating, has been most thoroughly investigated. Meanwhile, there is no comprehensive research providing a comparison of free convection, heat transfer and evaporation with different heating methods. The novelty of the work lies in the comparison of the heat transfer efficiency using one laser beam, two beams and homogeneous heating. When heated by a single laser beam, the average temperature of the layer interface is significantly lower than at homogeneous heating. However, due to the generation of intense Marangoni flow, a small heating spot provides more intense evaporation than homogeneous heating. The effectiveness of heat transfer is analyzed in terms of the total efficiency coefficient. If it is important to take into account power input, it is preferable to use a single laser beam. If it is not decisive, then two laser beams allow achieving maximum heat transfer and evaporation rate. Homogeneous heating is significantly inferior to local non-stationary heating in terms of all key criteria. The simple expressions serve to optimize the total efficiency coefficient.