Mechanism Of Heat Transfer Enhancement Research Articles

Experimental investigation on the heat transfer enhancement of wall modification inside a piston cooling gallery

ABSTRACT Combined with visualization experiments, a square cavity reciprocating oscillation system is built based on CA6110 diesel engine to study heat transfer enhancement mechanism and explore a more efficient cooling method. Influences of liquid fill ratio, engine speed, and surface property on flow pattern and heat transfer characteristics are studied. Four surfaces are prepared. Results show that heat transfer performs the best with 50% liquid fill ratio and it is improved with increasing engine speed. Polished surface performs the worst, then super-hydrophilic surface and microstructure surface perform better, and microstructure super-hydrophilic surface performs the best with an 66% increase of average heat transfer coefficient.

Performance evaluation and heat transfer mechanism for battery thermal management of autonomous underwater vehicles based on phase change material cooling

Battery thermal management is of great significance to enhance the comprehensive performance of autonomous underwater vehicles(AUVs). However, few relevant studies have been conducted on the AUV’s battery thermal management (BTM). In this work, the phase change material (PCM) cooling was proposed for AUV’s BTM with taking into account natural convection. The temperature behavior of the battery and the melting behavior of PCM were studied under different parameters including thickness of PCM and eccentricity between PCM and battery. In addition, the enhanced heat transfer mechanism of the PCM melting process was further revealed based on the temperature deviation index. More importantly, the dimensionless temperature control rate (TCR) factor and the dimensionless heat storage rate (HSR) factor were introduced to quantitatively evaluate and optimize the eccentricity on the enhancement performance. The results show that PCMs have an excellent performance in the battery thermal management of AUVs. Unlike the traditional view, the whole PCM melting process was further subdivided into three stages according to the thermal energy storage mode or heat transfer types. Increasing the eccentricity can accelerate the melting of the PCM, while the reduced time of complete PCM melting was not linearly correlated with the eccentricity. The optimal eccentricity between PCM and battery was 10 mm, i.e., the eccentricity ratio ε = 0.625. The temperature control performance rate and heat storage performance rate were enhanced by 29.4 % and 5.7 % at e = 10 mm, respectively. These findings can provide guidelines for accurate design of the PCM cooling system for the AUV’s battery thermal management.

Review of surface modification in pool boiling application: Coating manufacturing process and heat transfer enhancement mechanism

• The surface modification methods of coatings commonly used in pool boiling are summarized and evaluated. • The influence mechanisms commonly used for pool boiling are summarized and analyzed. • The influence mechanisms under different heat fluxes are reviewed, including strengthening and weakening. • The CHF prediction models that can be used for coating structure are summarized and prospected. With the development of science and technology, the operating power of equipment is getting higher and higher, and the demand for heat dissipation is also increasing. Therefore, thermal management has become a hot topic in recent years. Boiling heat transfer has been considered as a effective solution for heat dissipation. The effect of boiling heat transfer can be enhanced by increasing the surface microstructure and nanocoating. This is the so-called surface modification technology. This paper divides the coating modification methods into two types: physical methods and chemical methods, for sorting and evaluation. For example, common physical methods include spin coating, magnetron sputtering, and chemical methods include chemical vapor deposition, electrochemical cathode and anode methods. In addition, in order to better predict the heat transfer effects of different structures at different stages, this review summarizes the common boiling strengthening mechanisms, evaluates the surface modification methods applied to pool boiling. Finally, critical heat flux (CHF) prediction models that can be used for nanostructured coatings are summarized.

Rotating thermal flow of water near its density inversion point in a vertical annulus: flow regime transition and heat transfer enhancement

Three-dimensional simulations are performed to identify the flow regimes of the rotating thermal flow of cold water near its density inversion point within a vertical annulus and evaluate the commensurate heat transfer abilities. The development of flow regimes and the variation in heat transfer behaviors in the special case with the density inversion parameter Θm=0.5 are explored over a wide range of parameters, with the Rayleigh number 104≤Ra≤106 and the Reynolds number Re≤150. The convection flow is radially separated into two layers by the density-maximum isosurface, with the inner and outer layers dominated by a positive and negative radial density gradient, respectively. Three axisymmetric and four non-axisymmetric basic flow regimes with different generation mechanisms are defined to describe the double-layer convection flow. Eleven flow regimes are identified, each of which consists of one, two or three basic flow regimes. The spatio-temporal features of the flow regimes depend on Ra and Re. The mixed convection parameter is demonstrated to be capable of qualitatively measuring the relative strength of the flow between the inner and outer layers in certain ranges of Ra. The mechanisms of both the flow regime transitions and the mode transitions between steady and oscillatory states are explored in terms of the combined action of density inversion effect, centrifugal effect and buoyancy effect. The heat transfer behaviors depend on the spatio-temporal features of flow regimes. The mechanism of heat transfer enhancement and that for the non-monotonic variation of heat transfer ability are revealed. The limitation of the axisymmetric assumption is quantified.

Transient cooling performance of R134a flash-evaporation spray enhanced by cold air jet: A novel heat transfer enhancement method in laser dermatology

Nevus of Ota is a dermal hyperplastic pigmented disease with a morbidity rate of 0.1–0.6% in the Asian population. Laser surgery with the assistance of cryogen spray cooling (CSC) is a potential clinical treatment for nevus of Ota. However, for Asians with high melanin content, it is necessary to enhance cooling capability without the increment of refrigerant amount. In this study, a R134a flash-evaporation cryogen spray cooling coupled with cold air jet (CSC-CAJ) was developed to improve the cooling capacity. Epoxy resin was employed as a skin phantom to investigate the heat transfer characteristics of CSC-CAJ with different air jet parameters. Air jet parameters of CSC-CAJ are recommended to be Ta = -7 ℃, Va = 3 m3/h Za = 10 mm and Φa = 30°. Compared to CSC, CSC-CAJ could reduce the minimum surface temperature from -39 to -42.1 ℃, and the average value of convective heat transfer coefficient (h) of CSC-CAJ could increase from 8 to 12.9 W/(m2·k) or 61.3% for the recommended parameters. The liquid film residence time (τ) decreases from 301 to 234 ms or 23.3%. In addition, based on the visualization observation and surface heat transfer measurement, the frost formation phenomenon on the surface and the heat transfer enhancement mechanisms are well understood. Four modes, including Leidonfrost mode, no runoff mode, runoff mode and evaporation mode, are proposed to describe the four stages of CSC-CAJ. A non-dimensional correlation of normalized Nusselt number (Nu*) and time (t*) is summarized. The primary heat transfer enhancement mechanism of CSC-CAJ is found to be the increase in cryogen evaporation rate and the ratio of heat removal from the phantom surface to phase change latent heat.

Numerical investigation on thermal–hydraulic characteristics of the helically corrugated tube in intermediate heat exchangers for very-high-temperature gas-cooled reactors

A three-dimensional numerical simulation is conducted to investigate the flow and heat transfer characteristics of the helically corrugated tube (HCT) intermediate heat exchanger (IHX) for very-high-temperature gas-cooled reactors (VHTRs). Helium is the working fluid with Reynolds number (Re) ranging from 10,000 to 20,000 and Prandtl numbers of 0.66. The heat transfer enhancement mechanism is analyzed in detail with the use of the ANSYS Fluent 18.0 computational fluid dynamics program. The results show that the helical corrugation disrupts the boundary layer development, strengthens the secondary flow intensity, and improves the synergy between the velocity vector field and temperature gradient vector field, thus enhancing the heat transfer. Moreover, the effect of geometric parameters characterized by dimensionless corrugation height e/d (0.02, 0.04, and 0.06) and dimensionless corrugation pitch p/d (0.5, 1.0, and 1.5) on the thermal–hydraulic performance are examined. The results indicate that increasing e/d and reducing p/d can enhance heat transfer. The Nusselt number of HCTs is increased by 17.25 %-81.46 % compared to a smooth tube, while the friction factor is also increased by 38.01 %-361.69 %. The comprehensive performance represented by the performance evaluation criterion is improved by 3.26 %–11.84 %. In the present study, e/d = 0.04 and p/d = 0.5 are the optimal HCT structures to obtain better comprehensive performance for the IHX design.

Experimental and numerical investigation on the flow and heat transfer characteristics of the tube with an integrated internal longitudinal fin

The flow and heat transfer characteristics of a tube with an integrated internal longitudinal fin were studied by experiment and numerical simulation. The effects of inscribed circle diameter and fin included angle on the thermal performance were investigated by numerical simulation. The numerical results were in good agreement with the experimental data. The results indicated that the tube-IILF was superior to the ST. For the experiment, the α of the T30D10 was 3.2–4.0 times higher than that of the ST when 5177 ≤ Re ≤ 9432. In general, the f of the T30D10 was higher than that of the ST. In the work, both the α and f decreased with the increase of the dins, while increased with the decrease of the θ. The (α/α0)/(f/f0)1/3 values of the tubes-IILF were more than 1. It is demonstrated that the tube-IILF has a significant heat transfer enhancement. Besides, the velocity, pressure, and temperature distributions were obtained to discern the mechanisms of heat transfer enhancement.

An experimental investigation on performance of microencapsulated phase change material slurry in ground heat exchanger

As a promising alternative to conventional heat transfer fluids, microencapsulated phase change material slurry (MPCS) was applied in ground heat exchanger (GHE) in this paper. A sandbox system embedded with horizontal serpentine GHE was installed and MPCS using N-eicosane (C20H42) as phase change material is prepared. To explore the merits of MPCS, a comparison study between performance of water and MPCS was conducted. In addition, the enhanced heat transfer mechanism of MPCS were studied by comparing performance of MPCS with different inlet temperature and particle concentration. The experimental results indicate that the heat transfer rate and pumping consumption of 25 wt% MPCS with inlet temperature of 30 °C are 10.5 and 2.8 times that of water, respectively. The heat load-to-pumping consumption ratio has an enhancement of 3.73 times in comparison to water. Obviously, considering the phase transition process, MPCS can efficiently improve thermal performance of GHE. However, in the non-phase transition temperature range, the performance of MPCS is even worse than that of water. The comprehensive performance factor of 15 wt% MPCS and 25 wt% MPCS with inlet temperature of 38 °C declined by 45.6% and 36.9% in comparison with pure water.

Study of pool boiling heat transfer of nanofluid in the PCD electrical fields

Nanofluids with excellent thermal properties can be used for a coolant and the heat exchange. Actually, the heat transfer between the nanoparticles and working medium benefits from the nanoparticles movement, which could be controlled actively by the electrical field with periodically changed direction (PCD electrical field). Therefore, the coupled effect of nanofluid and switching period and the prediction model were investigated. Concretely, the boiling heat transfer coefficient (BHTC) and the critical heat flux (CHF) with various switching periods of the electrical field were compared. Meanwhile, the mechanism of heat transfer enhancement was discussed. Besides, the predicted model was developed. The present study finds that the BHTC and the CHF will be further strengthened due to the coupled effect of the PCD electrical field and nanofluid. However, this enhancement has an optimal concentration. Moreover, the heat transfer performance enhancement is attributed to the continuous heat transfer by nanoparticle and the further decrease of surface tension. The prediction curves mostly coincide with experimental data, and the prediction models are proposed by considering the influence of the switching period, the nanoparticles movement, the gas-liquid interface surface tension and the dynamic thermal conductivity.

Numerical study on the enhanced heat transfer characteristics of steam generator with axial economizer

The heat transfer enhancement of heat exchangers is vital to improve energy utilization efficiency in industrial fields. The axial economizer used in steam generator is a typical enhanced heat transfer device. In this paper, the mechanism of heat transfer enhancement in steam generator with axial economizer was studied and the key thermal hydraulic parameters in steam generator were analyzed. The effects of divider plate heights and flow distribution on the heat transfer characteristics were also investigated. Results show that the axial economizer can effectively increase the heat exchange up by 2% and the steam production up by 3%. Within a certain range (0–2.2 m), the increase of divider plate height is beneficial for heat transfer enhancement. The flow distribution on the hot and cold sides would affect the heat transfer obviously. The influence of flow distribution on the heat transfer in steam generator is mainly concentrated in the cold side region. The conclusions can provide references for the design and operation of a new steam generator with the axial economizer, and are also meaningful for the enhancing heat transfer research in other industrial fields involving shell-and-tube heat exchangers.

Parametric Study on Thermo-Hydraulic Performance of NACA Airfoil Fin PCHEs Channels

In this work, a discontinuous airfoil fin printed circuit heat exchanger (PCHE) was used as a recuperator in a micro gas turbine system. The effects of the airfoil fin geometry parameters (arc height, maximum arc height position, and airfoil thickness) and the airfoil fin arrangements (horizontal and vertical spacings) on the PCHE channel’s thermo-hydraulic performance were extensively examined by a numerical parametric study. The flow features, local heat transfer coefficient, and wall shear stress were examined in detail to obtain an enhanced heat transfer mechanism for a better PCHE design. The results show that the heat transfer and flow resistance were mainly increased at the airfoil leading edge owing to a flow jet, whereas the airfoil trailing edge had little effect on the thermo-hydraulic performance. The airfoil thickness was the most significant while the arc height and the vertical spacing were moderately significant to the performance. Moreover, only the airfoil thickness had a significant effect on the PCHE compactness. Based on a comprehensive investigation, two solutions NACA-6230 and -3220 were selected owing to their better thermal performance and smaller pressure drop, respectively, with horizontal spacings of 2 mm and vertical spacings of 2 or 3 mm.

Heat-transfer performance of twisted tubes for highly viscous food waste slurry from biogas plants

BackgroundThe use of food waste as feedstock shows high production of biogas via anaerobic digestion, but requires efficient heat transfer in food waste slurry at heating and cooling processes. The lack of rheological properties hampered the research on the heat-transfer process for food waste slurry. Referentially, the twisted hexagonal and elliptical rubes have been proved as the optimal enhanced geometry for heat transfer of medium viscous slurries with non-Newtonian behavior and Newtonian fluids, respectively. It remains unknown whether improvements can be achieved by using twisted geometries in combination with food waste slurry in processes including heating and cooling.ResultsFood waste slurry was observed to exhibit highly viscous, significant temperature-dependence, and strongly shear-thinning rheological characteristics. Experiments confirmed the heat-transfer enhancement of twisted hexagonal tubes for food waste slurry and validated the computational fluid dynamics-based simulations with an average deviation of 14.2%. Twisted hexagonal tubes were observed to be more effective at low-temperature differences and possess an enhancement factor of up to 2.75; while twisted elliptical tubes only exhibited limited heat-transfer enhancement at high Reynolds numbers. The heat-transfer enhancement achieved by twisted hexagonal tubes was attributed to the low dynamic viscosity in the boundary layer induced by the strong and continuous shear effect near the walls of the tube.ConclusionsThis study determined the rheological properties of food waste slurry, confirmed the heat-transfer enhancement of the twisted hexagonal tubes experimentally and numerically, and revealed the mechanism of heat-transfer enhancement based on shear rate distributions.

Numerical investigation on flow and heat transfer characteristics of U-shaped channels with side-wall column ribs

For improving the cooling performance of U-shaped channels in the blade mid-chord region both in static and rotating states, this paper introduces the column rib spoiler structure on the side wall, putting forward the arrangement of column ribs along the radial direction in sequenced and staggered ways, as well as the vertical and inclined column ribs. The flow and cooling characteristics of this new channel (AR = 1:1) with different column rib structures and arrangements are studied in detail, considering rotational numbers varying from 0 to 0.4 at a typical Reynolds number of 10,000. The enhanced heat transfer mechanism of vertical and inclined column ribs in both arrangement modes and the coupling mechanism combined with the rotation effect are emphatically analyzed. The cooling performance of the two channels is compared in many aspects and the optimized size and layout of side-wall column ribs are obtained. Results show that the cooling method proposed can significantly improve the cooling effect of the U-shaped channel by 37.9% and 41.6% in the static state and rotating state, respectively. This study will provide important reference data for the development of high-efficient mid-chord cooling technology in gas turbine blades.

Time-dependent heat transfer analysis of ellipsoidal protruded microchannel with multiple pulsating jets

Comparing with continuous jets inside microchannel, the heat removal capacity is enhanced by introducing protrusions or pulsating jets individually. Therefore, the preferred heat transfer enhancement and satisfactory thermal performance are investigated after taking both advantages of unsteady properties and ellipsoid protrusions simultaneously in this work. Especially, phase difference, Δφ, as a pivotal parameter, is applied in multiple pulsating jets. The total mass flow rate in microchannel, temperature fluctuation on heated wall, thermal and flow resistance are therefore varied. The largest fluctuation of mass flow rate is achieved when the phase difference between each adjacent jet inlets at Δφ = 0∙π, while the smallest at 0.75∙π, and the temperature distribution of the target wall correspondingly fluctuates. The heat transfer enhancement is most prominent at 0.75∙π. The increment in heat transfer is close to that of flow resistance at Δφ = 0.50∙π, 0.75∙π and 1∙π. The thermal performance TP firstly increases and then decreases with Δφ, and reaches the maximum value at 0.75∙π. Furthermore, due to the phase difference, each jet becomes the one with the highest velocity among all jets periodically, weakening adverse effect of cross flow and suppressing the drift phenomenon effectively. This is exactly the mechanism for heat transfer enhancement of unsteady multiple jets with velocity phase difference in ellipsoid protrusion microchannel.

Numerical simulation of nitrogen vapor condensation on microstructure surface

• A three-dimensional model of condensation on micro fin is established. • Micro fin surface area exhibits different functionalities. • Micro fin curvature radius affects the driving force of liquid film movement. • An optimal micro fin structure for best performance is proposed. The mechanism of the condensation heat transfer enhancement on the microstructure surface has not been deeply explored, which restricts the full play of microstructure strengthening ability. In this study, a three-dimensional numerical simulation of the condensation on the micro fin surface revealed the liquid film flow behavior and the heat transfer performance, and the model is in good agreement with the experimental and theoretical results. The internal flow field on the curved surface shows that the liquid film is redistributed, and it proves that the surface tension plays a leading role in promoting the transverse movement of the liquid film. The micro fin surface area exhibits different functionalities, the excellent mass transfer region is located at the fin top, and its local heat transfer coefficient can reach 25 k W · m - 2 · K - 1 , which is one order of magnitude higher than Nusselt's theoretical value. The fin bottom is the condensate collection area, where the condensate discharge velocity is increased by 2–3 times. The simulation results of the different micro fins indicate that the curvature radius of the micro fin could affect the condensate flow process, and the aspect ratio of the micro fin determines the local heat transfer enhancement degree and the strengthening area ratio. This study finally pointed out that the high-efficiency micro structure should have a large area of the fin top for enhancing heat transfer, as well as a large volume of the fin bottom for the liquid drainage.

Flow boiling heat transfer characteristics on micro-pin-finned surfaces in a horizontal narrow microchannel

In this paper, an experimental investigation of flow boiling in a horizontal narrow microchannel with hydraulic diameter of Dh = 952 μm was conducted. Flow boiling heat transfer characteristics of micro-pin-finned surfaces were evaluated over the mass fluxes range from 200 - 500 kg/m2s (corresponding flow velocity: 0.2 - 0.5 m/s), using deionized water as the working fluid with different inlet temperatures Tin = 30 - 50 °C. The outlet pressure of the microchannel was about 1 atm. The boiling curves, heat transfer coefficients, bubble behaviors and heat transfer enhancement mechanism were discussed with the variation of heat flux, mass flux and inlet temperature. The results indicated that the micro-pin-finned surfaces could improve the critical heat flux (CHF) and heat transfer coefficient (HTC) greatly due to numerous nucleate sites and large heat transfer area enhancement ratio. The CHF up to 360 W/cm2 has been demonstrated at a mass flux of 500 kg/m2s. Compared with a smooth surface, a 240% higher heat transfer coefficient (18.4 W/cm2K) on the S30-120 surface has been achieved at a mass flux of 500 kg/m2s with an inlet temperature of 30 °C. The boiling curves of the micro-pin-finned surfaces presented an obvious “hook back” phenomenon after reaching the onset of the nucleate boiling (ONB) and then the wall temperature had a slight rise with the increase of the heat flux. Moreover, the intensive micro-pin-finned arrangements showed a significant wicking effect and promoted liquid replenishment, which could destroy the liquid boundary and enhance turbulence. The bubble behaviors were also captured to explain the heat transfer enhancement mechanism in a horizontal narrow microchannel.

Experimental and numerical studies on heat transfer enhancement in the silicothermic reduction process

Currently, the silicon thermal method is the main process to produce primary magnesium, which is controlled by chemical reaction kinetics and the heat transfer process in the retort. However, the unbelievably low thermal conductivity and point contact thermal resistance of the pellets greatly reduce the heat transfer efficiency, resulting in low magnesium production efficiency. To increase productivity, the enhanced heat transfer mechanism was studied in detail by experiments in this paper. The results show that temperature rise may not accurately reflect the enhanced heat transfer effect, thus a synthetical valuation method which took total heat transfer, effective heat transfer ratio and temperature rise into account is proposed. On this basis, a new recycling technique which uses high temperature silicon carbide particles to enhance the heat transfer in the retort is developed. Then a three-dimensional unsteady numerical model incorporating the chemical reaction kinetics and heat transfer was established and used to prove the superiority of this new technique in terms of heat transfer efficiency, magnesium production rate and production cycle. Numerical results show that when the initial temperature of silicon carbide is 1373 K, the instantaneous magnesium production rate can reach 13.2 kg/h within 30 min of heating, which is three times that of the traditional silicothermic process. The production cycle could also be shortened to 240 min, which is half of the original, and the production efficiency can be doubled. This new technique can significantly improve heat transfer efficiency, shorten the production cycle and reduce the production cost.

Thermodynamic evaluation and particle migration of hybrid nanofluids flowing through a complex microchannel with porous fins

A compound method is established by adding Al2O3-TiO2/Water (W) nanofluids and porous media in a microchannel to reduce pressure drop and enhance heat transfer in the limited heat dissipated area. Effects of porosity and hybrid nanofluids are numerically investigated in the laminar region. Pressure drop, Nusselt number, velocity and temperature fields are used as indicators to evaluate the characteristics of flow and heat transfer. Furthermore, the analytical methods including thermodynamic evaluation and nanoparticle migration were performed to reveal the essential mechanism of heat transfer enhancement. Compared with non-porous microchannels, the maximum reduction of porous microchannels is 9.73% (ε = 0.5), 8.3% (ε = 0.6) and 6.8% (ε = 0.7) for pressure drop, while the maximum agument is 23.53% (ε = 0.5), 20.59% (ε = 0.6) and 16.67% (ε = 0.7) for Nusselt number. The permeability of fluid reduces pressure drop and enhances heat transfer in the porous region. The maximum heat transfer irreversibility reduces up to 64%, and exergy efficiency reaches 88% by adding nanofluids and porous media. Nanoparticle migration originating from thermophoresis affects the concentration distribution near the wall, and cold-hot fluids fully mix in the porous region, thereby increasing heat transfer. The effect of thermophoretic diffusion of dilute nanofluids in micro-scale convective heat transfer is higher than that in the macro-scale one.

Influence of key geometry parameters on heat transfer and flow resistance properties of toothed internal spiral piece cracking furnace tube

Strengthening the heat transfer technology of the furnace tube in the radiant section of the cracking furnace is very important in the field of energy-saving and environmental protection. This research proposes a new type of open-tooth spiral to enhance heat transfer and increase ethylene productivity. The mathematical computation has been conducted to evaluate the thermal-hydraulic performance with an open-tooth spiral. The classical Ordinary tube was also investigated for comparison. At the same time, the vortex identification method based on the Q criterion reveals the enhanced heat transfer mechanism of the open-toothed spiral tube. Then use the field synergy principle to qualitatively judge the heat transfer performance, combined with the comprehensive heat transfer evaluation factor (PEC) to quantitatively evaluate the comprehensive heat transfer performance of the open-tooth spiral tube. The results show that although the Nusselt number of the open-tooth spiral is 8%-10% lower than that of the ordinary screw, the friction resistance coefficient of the spiral tube with an opening angle of 15° can be reduced by 33%∼43%. Its PEC value is between 1.15 and 1.25, with excellent comprehensive heat transfer performance. It can effectively improve key products, such as ethylene, propylene, etc.

Vibration-Enhanced Heat Transfer of Helical Tube with Different Number of Tubes

Based on a two-way fluid/solid coupling model, the heat transfer enhancement mechanism of a helical elastic coiled tube (HECT) by fluid-induced vibration (FIV) was numerically studied. The field synergy principle was used to compare and analyze the shell-side convective heat transfer of the HECT. The field synergy angle, Nusselt number, and comprehensive enhanced heat transfer performance were quantitatively studied from the overall and local perspectives. The influences of the Reynolds number and the number of tubes on heat transfer performance and vibration-enhanced heat transfer performance were analyzed. Numerical results show that the field synergy level and the oscillation relative velocity near the tube are two important factors for fluid-induced tube vibration to enhance heat transfer. The average Nusselt number of coiled tubes decreases when the number of tubes increases and increases when the Reynolds number increases. The comprehensive heat transfer enhancement capability of the heat exchanger with different numbers of tubes of 2, 4, and 8 gradually decreases as the number of tubes increases, and the average performance evaluation criteria of the heat exchanger are 1.043, 1.023, and 1.004, respectively, for the three typical cases. The tubes on the upper and lower sides have a better heat transfer enhancement effect by the FIV.