Improve Heat Transfer Efficiency Research Articles

Molecular dynamics simulation of enhanced heat transfer through conical Al/Cu nanostructures

The aim of this study is to investigate the improvement of heat transfer efficiency of the Al and Cu substances by modifying the surfaces with conical nanostructures. The natural evaporation is simulated using the molecular dynamics method for a thin layer of Ar atoms on the solid surface. Moreover, a comparison of heat transfer behavior of the Ar atoms is presented for different substances through a comprehensive investigation. The investigated configurations include smooth Al and Cu surfaces, as well as the surfaces modified by conical Al/Cu nanostructures. Also, the distribution of Al/Cu nanostructures on surfaces is investigated. The results indicate that using Cu surface rather than the Al surface improves the heat transfer efficiency by 16.67%. In comparison with the smooth Al surface, employing conical Al and Cu nanostructures can enhance the heat transfer by 38.89% and 44.44%, respectively. Additionally, it is observed that featuring the Cu surface with Al and Cu nanostructures leads to improvement of heat transfer capability of the surface by and 39.81% and 47.59%, respectively. Furthermore, the effect of conically shaped Cu/Al nanostructures with different distribution but the same contact area to be used on the Al/Cu smooth surface on the heat transfer enhancement is studied. Based on the results, for all the structures in which Cu is considered as the base substance, the fluid temperature reaches the solid temperature faster, compared to Al as the base substance. Also, by embedding the nanostructures on Al and Cu smooth surfaces, the fluid temperature reaches the solid temperature faster in the case of Al/Cu smooth surfaces. Additionally, it is observed that employing the Cu nanostructure instead of the Al on Cu smooth surface is more effective for improving the heat transfer performance.

Performance of Vapor Compression Refrigeration System using Nanoparticles – Based Mineral Oil Lubricant

In general, mineral oil and polyester oil are used as lubricants in a refrigeration system compressor. The present work focuses mainly on the mineral oil based lubricant based on MWCNT nanoparticles. The different characterization of the multi-wall carbon nanotube (MWCNT) was performed using different methods such as Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), and Transmission Electron Microscopy (TEM), which will result in size, structure and morphology of the CNT nanoparticle. First prepare the Nano-lubricants by adding nanoparticles in mineral oil with different concentrations of 0.05, 0.075 and 0.1wt% with the help of an ultrasonicator which will give the homogeneous mixture of Nanolubricant. Nanoparticles mixed with mineral oil used in a refrigeration system work safely and normally. The experiment were conducted on refrigeration system for different concentration, namely 0.05, 0.075 and 0.1wt% which will mixed with mineral oil and without nanoparticles in mineral oil. The result shows that 0.1wt% Nanolubricant which will give higher improvement in heat transfer efficiency and increase in the Coefficient of Performance (COP) by 37%. And energy savings is 9.6%.

A novel flexible seal technology and its application in heat transfer of rotary air preheater

The leakage of rotary air preheater (RAPH) greatly affects its heat transfer efficiency in energy conversion. Non-contact rigid seal usually produce large leakage. Contact flexible seal can reduce the leakage of RAPH. However, the friction due to the contact is lack of attentions. In this paper, the heat transfer efficiency of RAPH with flexible seals are studied. Firstly, a herringbone contact flexible seal (HCFS) is provided to reduce the leakage. Then the friction force of HCFS was calculated according to finite element method (FEM). Next, the friction powers on the axial, radial and bypass directions for different interference are examined by theoretical analysis. In the end, the friction power of RAPH with HCFSs is compared with that from the experimental data and shows a good consistency. The results implied that the whole heat transfer efficiency of RAPH increased after installing appropriate HCFSs. The HCFS technology is beneficial to reduce leakages, improve heat transfer efficiency and optimize RAPH.

Development of the Oxygen-Enriched Burner Using Self-Induced Oscillation

We have developed the novel oxygen-enriched burner using the self-induced oscillating phenomenon of jet flow which has excellent radiation heat transfer characteristics. We revealed that the flame property suitable for radiation heat transfer is obtained by extending the oscillation cycle. By optimizing the connecting tube length and diameter, we got the stable oscillating flame in 1 s-oscillation period. At this time, the relationship between the burner structure including the connecting tube and the oscillation period can be easily evaluated by the dimensionless tube length and Strouhal number. In addition, combining multi-staged combustion technology, the burner can improve heat transfer efficiency by 9.1% compared with the conventional oxygen-enriched burner. We confirmed that the burner has a low NOx emission level below 55 ppm.

Coupled thermal model for geothermal exploitation via recycling of supercritical CO2 in a fracture–wells system

Geothermal exploitation via recycling of supercritical CO2 (CO2–EGS) in a fracture–wells system is a new method, which can reduce the injection pressure, and improve heat transfer efficiency. In this study, a coupled thermal model for this system is proposed, considering the coupling effects of the temperature and pressure on the CO2 flow and heat transfer. The simulation results show that the thermal breakthrough time is approximately 40 d when the well separation distance is 230 m. After thermal breakthrough, the fracture outlet temperature decreases from 260 °C to 100 °C, and the heat mining rate decreases from 4.6 MW to 3.0 MW over the following 2 months. However, as the deep formation continues to replenish energy into the wellbores and fracture, the decreasing trend in the temperature gradually slows down, and it reaches a quasi-equilibrium state after one year. Owing to the low heat conduction rate of the formation, thermal utilization depth is only approximately 15 m from the wellbore, and 50 m from the fracture after 20 y. Comprehensive analysis shows that the heat mining rate reaches a maximum at an injection rate of 36 kg/s in this case. This model can provide an accurate evaluation and design optimization method for CO2–EGS in a fracture–wells system.

Controlled assembly and alignment of CNTs in ferrofluid: Application in tunable heat transfer

Abstract Nanofluids are new generation of heat transfer fluids with enhanced thermal properties. When using nanofluids, one of the major problems is aggregation of nanoparticles. In this study, in order to benefit from controlled aggregation of nanoparticles by application of magnetic field, we used magnetic nanoparticles (MNPs) as one of the most useful nanoparticles in recent energy and biomedical researches. To achieve a more precise insight about behavior of MNPs under magnetic field, a water-based nanofluid of Fe3O4/MWNTs was studied. Due to the importance of thermal conductivity (TC) of nanofluids, it was investigated for the mentioned nanofluid. Taking advantage of magnetic properties of magnetite nanoparticles besides high thermal conductivity of multi-wall carbon nanotubes, a water-based nanofluid of 0.1 wt% Fe3O4/MWNT was prepared and its thermal conductivity was measured for the situations in which temperature gradient and magnetic field were either parallel or perpendicular. The findings suggested that TC was increased by 52% and 11.9% at H = 0.14 T for the two situations, respectively. This finding proved the anisotropic behavior of magnetic nanofluid. Formation of chain-like structures of MNPs was demonstrated through a novel approach. This phenomenon was found to be the reason of thermal conductivity enhancement. Our findings show that employing Fe3O4/MWNT is a promising approach for improving heat transfer efficiency of heat carriers.

Study on Optimization of Pressure Ratio Distribution in Multistage Compressed Air Energy Storage System

In this study, the round trip efficiency of a multistage adiabatic compressed air energy storage (A-CAES) system was optimized by differential evolution (DE) algorithm, and decision variables were the pressure ratio of each compressor/expander. The variation of the pressure ratio of each compressor/expander leads to different inlet air temperatures of the heat exchanger. Thus, this optimization method provides more heat energy recovery from compression to increase the inlet air temperature of expanders. Results indicate that the optimization method is effective for the pressure ratio allocation, improving the system efficiency by ∼1% and exergy efficiency of the heat storage process by 5.3% to the maximum compared with an equal pressure ratio distribution A-CAES system. Besides, a uniformity factor of temperature difference (UFTD) of multistage heat exchangers is proposed to analyze the temperature uniformity of the multistage heat exchangers, which indicates that decreasing the UFTD contributes to an increased uniformity of the temperature field and an improvement in heat transfer efficiency. The study is extended onto optimal off-design system configuration and the recommendations are proposed, which provides a guidance for A-CAES system design.

CFD analysis of fluid flow and particle-to-fluid heat transfer in packed bed with radial layered configuration

The channeling effect at the container wall results in difficulties for heat transfer in the central part of packed beds with small tube-to-particle diameter ratios. To overcome this shortcoming, a new kind of packed bed is developed with radial layered configuration: a fluid-penetrable wire mesh is used to divide the container into two parts in the radial direction, which allows particles of different sizes for regional loading. Therefore, following the general rule of fluid flow distribution in packed beds, small particles could be filled in the zone at the container wall to restrain the channeling effect and large particles in the center to promote local heat transfer capacity. In the present work, to facilitate the proper functionality of new equipment using the novel method, a CFD simulation combined with the DEM method for random packing generation is conducted to study the characteristics of the new packed bed on the packing structure, fluid flow, and particles-to-fluid convective heat transfer under a high fluid velocity regime (Re ∼ 104). It finds that the new packing method could exhibit a much regular structure than the conventional packed beds. And outstanding performance is observed in pressure drop reduction and heat transfer efficiency improvement. Moreover, the well-known equations for pressure drop and convective heat transfer predictions are found not applicable to the new bed and distinctive features of fluid velocity and temperature distribution are identified. These findings are helpful for the design of high efficiency reactors.

A novel truncated cone helix energy pile: Numerical and laboratory investigations of thermal performance

As for the cylinder helix energy pile (CyHEP), in order to reduce thermal interference and improve heat transfer efficiency, a novel truncated cone helix energy pile (CoHEP) was proposed in this paper. A 3-D numerical model both considering the dynamic surface condition and the initial soil temperature distribution was developed to investigate its thermal performance, and three main influencing factors (inlet water temperature, water flow rate, cone angle) were studied by the established model. In addition, the laboratory investigation was carried out to verify the accuracy of the numerical model. The results indicate that the heat flux per unit pipe length of the 20° cone angle CoHEP is 6.16% larger than the traditional CyHEP. The whole pipe of CoHEP can be divided into four stages along the flow direction of the pipe length: the entrance stage → the thermal short circuit stage → the small temperature difference stage → the exit stage. During the design of CoHEP, the proportion of the thermal short circuit stage and the small temperature difference stage should be reduced to ensure the overall heat transfer capability. Heat flux per unit pipe length of the CoHEP increases linearly with the inlet water temperature. Increasing the water flow rate can increase the heat flux per unit pipe length of the CoHEP, but it can also reduce the flow time in the pipe, resulting in insufficient heat exchange. As for the cone angle, increasing the cone angle can effectively reduce the radial thermal interference at the upper part of CoHEP and the axial thermal interference. When the system running time is 12 h, as the cone angle increases from 0° to 10° to 20°, the growth rates of heat flux per unit pipe length are 2.54% and 3.53% respectively. Moreover, there must be an allowable maximum cone angle considering the minimum spiral radius of PE pipe, for example, the allowable optimal cone angle is 21° for the model built in the paper.

Bubble growth, departure and rising of ethane at nucleate pool boiling condition

Boiling heat transfer exists in many industrial heat exchangers such as the evaporator of the refrigerator and the air conditioner, the reboiler of the chemical equipment and steam generator of the nuclear reactor. In the process of boiling, bubble movement can speed up the heat transfer between liquid and solid, leading to the improvement in heat transfer efficiency. Traditional refrigerants used in the industrial facilities have serious environmental problems, therefore, new substitutes are needed. Hydrocarbons are good alternatives. Ethane was suggested as one component of a mixed- refrigerant for its zero ozone depletion potential, low global warming potential and high thermodynamic properties. Therefore, it is important to investigate the bubble behavior of ethane in saturated nucleate pool boiling to design and optimize the industrial equipment like evaporator, improve natural gas liquefaction technology, and research characteristics of heat transfer and multiphase flow as well. Although there are a lot of researches on the heat transfer characteristics of pool boiling, the research on the bubble behavior in ethane is still lacking. In this paper, visualization experiments on the pool boiling heat transfer characteristics of ethane were carried out at 0.2 MPa. The heat fluxes varied from 14.65 kW m−2 to 80.79 kW m−2. Boiling occurred on the upward facing side of a smooth vertical copper cylinder with 20 mm diameter, connected to a DC power supply to control the heat flux on the surface. The measured roughness of the surface was 68.1 nm (root mean square average of the height deviations) and 50.7 nm (the arithmetic average of the absolute values of the surface height deviations). Acquisition of the temperature and pressure was accomplished by using a Keithley 2700 and six thermocouples. The experimental apparatus has a steel ruler inside the pool as the reference length to measure the bubble sizes and the maximum uncertainty for length measurement is 0.060 mm. Some conclusions can be drawn. (1) According to the change of diameter with time, the growth process was divided into three stages. The bubble growth process has obvious segmentation characteristics, and piecewise prediction models are recommended. (2) The bubbles in boiling pool exhibit the characteristics of axial symmetry and uneven distribution; the shape of separation of ethane bubbles has ellipsoidal and irregular shapes relative to normal temperature liquids. (3) There were trail changes and additional movements of large bubbles. Compared to normal temperature liquids, the trail changes were relatively simple; and the bubbles are bubbly and slug flow of two flow regimes. (4) System pressure, heating wall properties like surface roughness, liquid properties like contact angle and surface tension have an important influence on bubble behavior. This paper suggests that the heat transfer prediction equation should consider them.

Structurally tuning microwave absorption of core/shell structured CNT/polyaniline catalysts for energy efficient saccharide-HMF conversion

Microwave absorption and catalytic activity have been synergistically integrated into a core/shell structured CNT/polyaniline (PANI) hybrid catalyst that enables localized heating on the catalyst surface and uplifts energy efficiency in the dehydration reaction of saccharides to 5-hydroxymethylfurfural (HMF). Results reveal that the integration of CNT and polyaniline significantly improves the overall saccharide conversion and HMF yield. The PANI shell thickness and morphology are controlled by both reactant feeding ratio and polymerization reaction rate. A thinner and rougher PANI shell is favourable to enhance the overall microwave absorption, improve heat transfer efficiency to catalyst surface and thus reaction efficiency. The highest energy efficiency of 7.6mmolkJ−1L−1 is reached in 10min with CNT/PANI catalyst (30wt% CNTs) and 19W input power. Moreover, the packing of polyaniline shell on CNT core facilitates its separation from reaction mixture and effectively prevents catalyst loss. These catalysts show excellent recyclability that the catalyst activity can be completely recovered by a simple re-doping process in 1.0M sulfuric acid. This work opens up a new window in microwave responsive catalyst design that enhances energy efficiency in saccharide-HMF conversion reactions and promotes the economic feasibility of such reactions in practice.

Molten waste plastic pyrolysis in a vertical falling film reactor and the influence of temperature on the pyrolysis products

Abstract Molten plastics are characterised with high viscosity and low thermal conductivity. Applying falling film pyrolysis reactor to deal with waste plastics can not only improve heat transfer efficiency, but also solve the flow problem. In this work, the pyrolysis process of molten polypropylene (PP) in a vertical falling film reactor is experimentally studied, and the influence of heating temperature on pyrolysis products is discussed. It has been found that with the temperature increases from 550 °C to 625 °C, the yield of pyrolysis oil decreases from 74.4 wt% (± 2.2 wt%) to 53.5 wt% (± 1.3 wt%). The major compositions of the pyrolysis oil are C 9 , C 12 and C 18 , and β-scission reactions are predominant. The content of the light fraction C 6 –C 12 of pyrolysis oil is 69.7 wt%. Compared with other pyrolysis reactors, the yield of oil from vertical falling film pyrolysis reactor is slightly higher than that from tubular reactor, equal to that from rotary kiln reactor, and slightly lower than that in medium fluidised-bed reactor.

Parametric Thermal and Flow Analysis of ITER Diagnostic Shield Module

As part of the diagnostic port plug assembly, the ITER Diagnostic Shield Module (DSM) is designed to provide mechanical support and the plasma shielding while allowing access to plasma diagnostics. Thermal and hydraulic analysis of the DSM was performed using a conjugate heat transfer approach, in which heat transfer was resolved in both solid and liquid parts, and simultaneously, fluid dynamics analysis was performed only in the liquid part. ITER Diagnostic First Wall (DFW) and cooling tubing were also included in the analysis. This allowed direct modeling of the interface between DSM and DFW, and also direct assessment of the coolant flow distribution between the parts of DSM and DFW to ensure DSM design meets the DFW cooling requirements. Design of the DSM included voids filled with Boron Carbide pellets, allowing weight reduction while keeping shielding capability of the DSM. These voids were modeled as a continuous solid with smeared material properties using analytical relation for thermal conductivity. Results of the analysis lead to design modifications improving heat transfer efficiency of the DSM. Effect of design modifications on thermal performance as well as effect of Boron Carbide will be presented.

Optimization of the tube in tube counter-flow heat exchanger in a 4.5 K hybrid J-T cryocooler to be used in space

Hybrid J-T cryocooler is commonly employed in space detective missions requiring liquid helium temperature. In fact, nearly all the space applications of mechanical cryocoolers working at 4.5 K, having been launched or under development are hybrid J-T cryocoolers. For instance, mechanical cryocoolers used in Planck, JWST, SMILES, SPICA and so on, are all J-T cryocoolers precooled by adsorption cryocooler, Stirling cooler or pulse tube cooler. But there is hard any research on space hybrid 4.5 K J-T cryocooler in China. Key Laboratory of Space Energy Conversion Technologies in Technical Institute of Physics and Chemistry has developed a 4.5 K J-T cooler precooled by three stages of pulse tube cryocooler. Base on this cryocooler, design optimization is carried out on the tube-in-tube counter flow heat exchanger to improve its performance. Counter flow heat exchanger is one of the key components of the 4.5 K hybrid J-T cryocooler. Spiral tube-in-tube heat exchanger is widely used in 4 K class hybrid J-T cryocooler because of its advantages of light weight and small size. The impact of tube-in-tube heat exchanger on J-T cycle is analyzed. And J-T cycle is able to provide more cooling capacity and needs less precooling power as the efficiency of the counter flow heat exchanger increases. Then, for the purpose of improving heat transfer efficiency of the counter flow heat exchanger, design optimization is carried out on the basis of theoretical analysis. The main heat transfer resistance of the counter flow heat exchanger is the convection heat transfer between return gas and the outer wall of inner tube. Thus, smaller tube is used to decrease the main heat transfer resistance. Besides, the centrifugal force of the moving helium flow in the spiral pipe brings about secondary flow. The development of secondary flow results in enhancement of heat transfer of the counter-flow heat exchanger. So heat transfer coefficient of the heat exchanger increases with decreasing diameters of the tubes and the spiral diameter. On the other hand, when the efficiency of the counter flow heat exchanger rises, the high pressure flow will be precooled much more fully, which means less precooling power from the precooling cooler will be consumed. As a result, the power consumption of the whole hybrid J-T cooler will decrease and its efficiency will be improved. Then, experimental research is conducted and the experimental results agree well with theoretical analysis. The temperature before throttling decreases as the efficiency of the counter flow heat exchanger increases. At the same time, the cooling capacity increases while the precooling power decreases. However, the cooling capacity and precooling power are smaller than theoretical analysis which attributes to the mass flow rate of calculation is much larger than measured one. Consequently, the benefit of improving heat transfer efficiency is verified. As the efficiency of the counter-flow heat exchanger increases, the cooling capacity of the J-T cooler is improved while the precooling power is cut down. Eventually, the cooling capacity of the hybrid J-T refrigerator at 4.7 K is improved from 15 to 32 mW.

Experimental Study on R245fa Condensation Heat Transfer Properties in Horizontal Tube

Abstract The condenser is widely used in the field of HVAC&R, thermal energy and petrochemical engineering. The improvement of heat transfer efficiency can lead to the overall system energy efficiency increase, so the operating cost is reduced. This study focuses on condensation heat transfer process of R245fa with 4.38 mm horizontal tube. It is shown from test results that the changing rate of heat transfer coefficient for R245fa is normally same in the different condensation temperature. The peak of heat transfer coefficient exists with the quality increasing at the large mass flow condition. And heat transfer coefficient increases with quality increasing at small mass flow conditions. High efficiency of condenser can be designed by the experiment results. In addition, the enhancement of the heat transfer can also reduce the required heat transfer area. And consequently, the initial cost is decreasing.

Analytical and experimental studies for power-law fluids in a double-pass parallel-plate heat exchanger under asymmetric isotherm conditions

The double-pass parallel-plate heat exchanger under asymmetric isotherm conditions referred to conjugated Graetz problem was proposed to enhance the thermal performance and investigated theoretically and experimentally. The analytical solutions were obtained using the separation of variables, superposition principle and an orthogonal expansion technique in terms of power series. The dependence of the average Nusselt number on the Graetz number and power-law index was formulated in a simplified expression. The theoretical predictions show that the power-law fluids in such a double-pass operation come up with the considerable heat-transfer efficiency improvement as compared with those in an open conduit (without an impermeable resistless sheet inserted), especially when the double-pass device was operated in larger Graetz numbers. This work shows that the good agreement was obtained between the experimental results and theoretical predictions. The effects of the ratio of asymmetric wall temperatures, impermeable-sheet position and power-law index on both the device performance enhancement and power consumption increment have also been presented.

Assessment of differences between products obtained in conventional and vacuum spray dryer

In this work, an experimental unit of a vacuum spray dryer was built. This prototype attempted to combine the advantages of freeze-drying (drying at low temperatures due to vacuum) and spray drying (increase of surface area aiming the improvement of heat transfer efficiency). Maltodextrin solutions were dried in the vacuum operated equipment and in conventional spray dryer. The vacuum spray dryer system allowed obtaining powder at low temperatures due to the lowering of pressure conditions (2-5 kPa) inside the drying chamber. The products obtained in the two systems were characterized and compared for particle size distribution, moisture content, water activity, bulk density and solubility in water. The processes yields were also evaluated and compared. The vacuum spray dryer system allowed the production of larger, more soluble and less dense particles than those obtained in the conventional configuration of the equipment, resulting in drier and, therefore, with lower water activity particles. Thus, the use of the vacuum spray dryer as a drying technique may be an alternative for the production of powder rich in thermosensitive compounds.

Numerical simulation on heat transfer enhancement of phase change thermal storage devices for low-middle temperature

Using Ba(OH)2·8H2O as phase change material (PCM) and water as heat transfer fluid (HTF), we numerically simulated annular finned-tube heat exchangers. In order to measure and analyze the impact of parameters in the heating/cooling process, temperature changes of different monitoring points, fin widths, and fin pitches as key parameters were considered and applied. The experimental results show that the heat exchange process can be divided into three stages within a certain time. The faster heat transfer rate is associated with the greater temperature difference between PCM and HTF. Furthermore, fins width and pitch affect dramatically the heat charging/discharging rate. The large fins width or small fins pitch is beneficial for extending the heat exchange surface, leading to improve heat transfer efficiency.

Developments for Copper-Graphite Composite Thermal Cores for PCBs for High-Reliability and High-Temperature RF Systems

Summary System designs that have only conduction cooling available, that must operate in harsh or challenging environments, present significant challenges to the system thermal engineer. A second thermal design challenge is continued miniaturization of semiconductor devices and increased functionality per square centimeter of semiconductor die, resulting in continued increases in device heat flux. Elimination of packaging materials allows more efficient heat transfer as thermal resistances from one material to another are reduced or designed out. When possible, concurrent elimination of package materials that have low bulk thermal conductivity and replacement with high thermal conductivity materials will improve heat transfer efficiency. Attachment of the resulting unpackaged semiconductor device can then be made directly to the circuit carrier; however, care must be taken regarding increases in potential for damage or failure due to mismatched coefficient of thermal expansion (CTE). Continuing reductions in die size that result in higher heat flux exacerbate this potential failure mechanism at the die-to-substrate level. This is further worsened in harsh environment (i.e., vibration, shock, high moisture, rapid power cycling) and/or high operating temperature conditions. For aerospace, military, geothermal, and other applications where increasingly high heat flux radio frequency (RF), microwave, and processor semiconductors are attached directly (with solders, silver sintering pastes, or other joining materials) to an organic or ceramic printed circuit card, efficient and rapid heat transfer becomes critical. These are frequently also applications where forced convection (air or liquid) may be unavailable to the system design engineer. One solution for thermal management design problems of this type has traditionally been the incorporation of one or more heavy copper layers within a complex multilayer printed circuit board (PCB). This solution, however, has come under increasing scrutiny in recent years due to concerns for weight (especially in airborne and space applications) and the potential for severe CTE mismatch between semiconductor die materials with relatively low thermal expansion values and the relatively very high value of copper. Therefore, development of CTE-matched alternative materials to replace a heavy copper layer has been a focus for development activities. A suitable selection must, however, have a bulk thermal conductivity that is as close to that of copper as is practicable. Recent developments of a copper-graphite composite material in sheet form that can be employed in standardized PCB manufacturing processes are described in this presentation.

Heat transfer model of dropwise condensation and experimental validation for surface with coating and groove at low pressure

It is well known that dropwise condensation corresponds to a high heat transfer coefficient. The high performance enhancement of dropwise condensation in comparison to filmwise condensation is attributed to the ability of non-wetting droplets to be shed from the surface by gravity, therefore reducing the overall thermal resistance. The common treatments to carry out the hydrophobic surface for dropwise condensation are coating and structure. The improvement of heat transfer efficiency by combination of surface treatments with coating and groove structure has been proved compared of surface with single surface treatment by coating or groove structure. Based on this result, in this study presents a model developed to predict the heat transfer efficiency of dropwise condensation for surface with coating and groove structure features. The model is established by heat transfer though a single droplet with the drop size distribution. The heat transfer of single drop is not only analyzed as combination of thermal resistances, but also considered capillary effect of droplet due to groove geometry and properties of surface. In addition, the model results are validated with experimental data which is investigated by varied modification of vapor side metallic surface properties at low absolute pressure. It can be a reference to design industrial condensers of heat exchangers in the future. Further to optimize the surface properties and improve the higher heat transfer performance of dropwise condensation.