High Heat Transfer Performance Research Articles

JATROPHA OIL WITH IRON NANOPARTICLES APPLICATION IN DRILLING PROCESSES

A performance of heat transfer fluids has a substantial influence on the size, weight and cost of heat transfer systems, therefore, a high-performance heat transfer fluid is very important in many industries. Over the last decades, nanofluids have been developed. According to many researchers and publications on nanofluids, it is evident that nanofluids have a high thermal conductivity. The aim of this experimental study was to investigate the change of the workpiece temperature during drilling using Jatropha oil with iron nanoparticles and water with iron nanoparticles as lubricating and cooling fluids. These experiments were carried out with samples of nanofluid with different nanoparticles volume ratio, such as samples JN1, JN5 and JN10 of iron nanoparticles in the base Jatropha oil with a nanoparticle volume fraction of 1 %, 5% and 10% respectively and samples WN1, WN5 and WN10 of iron nanoparticles in the base water with a nanoparticle volume fraction of 1 %, 5% and 10% respectively.

Falling-droplet-enhanced filmwise condensation in the presence of non-condensable gas

Enhancing condensation heat transfer in the presence of non-condensable gas (NCG) is of fundamental importance for a wide range of energy-intensive industrial applications. Heat transfer performance of vapor condensation in the presence of NCG is dominated by the initial nucleation and mass transfer of vapor molecules in the diffusion layer near the condensing surface. Most of the approaches based on accelerating condensate liquid removal cannot effectively improve the nucleation and vapor transport, which makes it challenging to enhance vapor condensation in the presence of NCG. Here, we present a hydrophilic copper surface with interval fluorocarbon-coated hydrophobic bumps to enable falling-droplet-enhanced filmwise condensation in the presence of NCG. Benefiting from the reduced nucleation energy barrier on the hydrophilic surface, water vapor can rapidly nucleate and form a thin liquid film on the surface. Such condensate film can be periodically removed from the interval hydrophobic bumps to prevent the thickness growth of liquid film along the vertical surface, which is attributed to the surface adhesion reduction of condensate liquid on the hydrophobic bumps. More importantly, the removed condensate liquid departing from the hydrophobic bumps can fall off in the form of droplets to strongly disturb the NCG diffusion boundary layer. Numerical calculations and visualization experiments quantitatively reveal that the falling droplets can significantly improve water vapor transport from the bulk vapor to condensing surface for droplet growth. High-performance heat transfer of the enhanced filmwise condensation in the presence of NCG is experimentally demonstrated to be better than both the conventional filmwise and dropwise condensation while avoiding the durability issues of ultra-thin hydrophobic coatings by utilizing durable fluorocarbon-coated bumps.

Baffle orientation and geometry effects on turbulent heat transfer of a constant property incompressible fluid flow inside a rectangular channel

Purpose A computational fluid dynamics (CFD) analysis has been carried out on the aerodynamic and thermal behavior of an incompressible Newtonian fluid having a constant property and flowing turbulently through a two-dimensional horizontal high-performance heat transfer channel with a rectangular cross section. The top surface of the channel was kept at a constant temperature, while it was made sure to maintain the adiabatic condition of the bottom surface. Two obstacles, with different shapes, i.e. flat rectangular and V-shaped, were inserted into the channel; they were fixed to the top and bottom surfaces of the channel in a periodically staggered manner to force vortices to improve the mixing and consequently the heat transfer. The first fin-type obstacle is placed on the heated top channel surface, and the second baffle-type one is placed on the insulated bottom surface. Five different obstacle situations were considered in this study, which are referred as cases FF (flat fin and flat baffle), FVD (flat fin and V-downstream baffle), FVU (flat fin and V-upstream baffle), VVD (V-downstream fin and V-downstream baffle) and VVU (V-Upstream fin and V-upstream baffle). Design/methodology/approach The flow model is governed by Reynolds-averaged Navier–Stokes equations with the k-epsilon turbulence model and the energy equation. These governing equations are discretized by the finite volume method, in two dimensions, using the commercial CFD software FLUENT software with the Semi Implicit Method for Pressure Linked Equations (SIMPLE) algorithm for handling the pressure-velocity coupling. Air is the test fluid with the flow rate in terms of Reynolds numbers ranging from 12,000 to 32,000. Findings Important deformations and large recirculation regions were observed in the flow field. A vortex causes a rotary motion inside the flow field, which enhances the mixing by bringing the packets of fluid from the near-wall region of the channel to the bulk and the other way around. The largest value of the axial variations of the Nusselt number and skin friction coefficient is found in the region facing the baffle, while the smallest value is in the region near the fin, for all cases. The thermal enhancement factor (TEF) was also introduced and discussed to assess the performance of the channel for various obstacle situations. It is found that the TEF values are 1.273-1.368, 1.377-1.573, 1.444-1.833, 1.398-1.565 and 1.348-1.592 for FF, FVD, FVU, VVD and VVU respectively, depending on the Re values. In all cases, the TEF was found to be much larger than unity; its maximum value was around 1.833 for FVU at the highest Reynolds number. Therefore, the FVU may be considered as the best geometrical configuration when using the obstacles to improve the heat transfer efficiency inside the channel. Originality/value This study can be a real application in the field of shell-and-tube heat exchangers and flat plate solar air collectors.

Heat transfer performance of sintered Cu microchannels produced by a novel method

Microchannels have many thermal management applications due to their high heat transfer performance. In this paper, sintered Cu microchannels with well controlled channel diameters of 450 µm, 390 µm and 290 µm, and volume fractions of channels of 0.1, 0.2, 0.3 and 0.4, were manufactured by a new method and their pressure drops and heat transfer coefficients were compared with conventional machined Cu microchannel and porous Cu manufactured by Lost Carbonate Sintering (LCS). The pressure drops of the sintered Cu microchannels were higher than a conventional machined microchannel, but significantly lower than LCS porous Cu samples. The sintered Cu microchannels achieved a similar range of heat transfer coefficients as the LCS porous Cu, with much lower volume fractions of channels. They had higher heat transfer coefficients than the conventional machined microchannel, mainly due to the introduction of multilayers of channels in the metal matrix. Darcy-Weisbach and Sieder-Tate equations with the introduction of appropriate correcting factors can be used to estimate the pressure drop and heat transfer coefficient of the sintered Cu microchannels. There exists a strong correlation between heat transfer coefficient and pumping power.

Experimental Investigation of Oscillating Heat Pipe With Hybrid Fluids of Liquid Metal and Water

A new oscillating heat pipe (OHP) charged with hybrid fluids can improve thermal performance. The key difference in this OHP is that it uses room temperature liquid metal (Galinstan consisting of gallium, indium, and tin) and water as the working fluid. The OHP was fabricated on a copper plate with six turns and a 3 × 3 mm2 cross section. The OHP with hybrid fluids as the working fluid was investigated through visual observation and thermal measurement. Liquid metal was successfully driven to flow through the OHP by the pressure difference between the evaporator and the condenser without external force. Experimental results show that while added liquid metal can increase the heat transport capability, liquid metal oscillation amplitude decreases as the filling ratio of liquid metal increases. Visualization of experimental results show that liquid metal oscillation position and velocity increase as the heat input increases. Oscillating motion of liquid metal in the OHP significantly increases the heat transfer performance at high heat input. The lowest thermal resistance of 0.076 °C/W was achieved in the hybrid fluids-filled OHP with a heat input of 420 W. We experimentally demonstrated a 13% higher heat transfer performance using liquid metal as the working fluid compared to an OHP charged with pure water.

Investigation of Thermophysical Properties of Nanofluids and Effects of MHD

Heat transfer through a fluid; It is an important parameter in many engineering fields such as heat exchangers, solar collectors, refrigerators, automobiles, cooling of electronic devices, power plants. The increasing demand for energy has made it necessary to use energy more efficiently. For this purpose, it is necessary to design compact, low-cost systems with high thermal conductivity and high-performance heat transfer fluids. Researchers for the use of nanofluids as advanced heat transfer fluid compared to conventional fluids used in heat transfer applications have been aimed at improving the thermophysical properties of nanofluids on magneto fields. Therefore, many parameters such as the size, concentration, shape, base fluid, pH effect and operating temperature of the nano particles used were examined. In this study, information is given about the studies in the literature related to magneto hydrodynamic and the effects of thermophysical properties of the nanofluids on heat and flow characteristics are exemplified by a numerical study. Keywords: Heat transfer, nanofluid, thermophysical properties, heat exchanger, CFD, MHD DOI : 10.7176/JETP/9-4-03 Publication date : April 30 th 2019

Entropy Generation and Heat Transfer Performance in Microchannel Cooling.

Owing to its relatively high heat transfer performance and simple configurations, liquid cooling remains the preferred choice for electronic cooling and other applications. In this cooling approach, channel design plays an important role in dictating the cooling performance of the heat sink. Most cooling channel studies evaluate the performance in view of the first thermodynamics aspect. This study is conducted to investigate flow behaviour and heat transfer performance of an incompressible fluid in a cooling channel with oblique fins with regards to first law and second law of thermodynamics. The effect of oblique fin angle and inlet Reynolds number are investigated. In addition, the performance of the cooling channels for different heat fluxes is evaluated. The results indicate that the oblique fin channel with 20° angle yields the highest figure of merit, especially at higher Re (250–1000). The entropy generation is found to be lowest for an oblique fin channel with 90° angle, which is about twice than that of a conventional parallel channel. Increasing Re decreases the entropy generation, while increasing heat flux increases the entropy generation.

Effects of Graphene Ethylene Glycol/Water Nanofluids on the Performance of a Brazed Plate Heat Exchanger

Effects of graphene ethylene glycol/water nanofluids as the hot side fluid on heat transfer and pressure drop characteristics in a brazed plate heat exchanger (BPHE) were experimentally investigated. Nanofluid properties, especially thermal conductivity and viscosity of the graphene nanofluids were measured at various graphene concentrations (0.01 to 1.0% wt.) and temperatures (10 to 60 °C). Dimensionless Nusselt number and friction factors were used to compare the performances of the BPHE with and without graphene addition. Experimental analysis showed that the heat transfer performance is improved by an increase in Reynolds number and flow velocity and with a decrease in nanofluid concentration. The graphene nanofluids at 0.01 to 0.1% wt. brings an acceptable pressure drop penalty, but with a higher heat transfer performance than the base fluid in the BPHE. At a fixed flow velocity, the graphene nanofluids with proper concentrations give an increase about 4% to 7% in the heat transfer coefficients, which reveals that the graphene nanofluids can be a useful working medium in the BPHE. The increase in pressure drop is moderate under these experimental conditions which favours graphene nanofluids to be used in BPHEs for thermal systems. (Less)

Heat transfer and pressure loss of turbulent flow in channels with miniature structured ribs on one wall

This paper presents an experimental and numerical study of turbulent flow heat transfer and pressure loss in channels with structured miniature ribs on one wall with the aim to improve the internal cooling performance of gas turbine blades and combustor liners. Miniature transverse, angled, V-shaped and W-shaped ribs are investigated respectively in the study, and the aspect ratio of the channels is kept to be 6:1, and the rib pitch to height ratio is 10 and the rib height to mean hydraulic diameter ratio is 0.029. The experiments were carried out at the Reynolds numbers ranging from 10,000 to 60,000, and a low-Reynolds number k-ε turbulence model was also adopted to simulate the turbulent flow and heat transfer in the channels. Both experimental and numerical results have shown that the shapes of miniature ribs have appreciable influences on the heat transfer and pressure loss performance in the channels. The experiments showed that the W ribs have the highest heat transfer and pressure loss performance in the channel, and the angled ribs have the lowest heat transfer and pressure loss performance in the channel. The W-ribbed channel shows respectively the globally averaged Nusselt numbers and overall Nusselt numbers of 2.2–2.6 and 2.9–3.3 times those of a smooth channel, and the friction factors of 2.5–3.7 times those of the smooth channel, which are higher than those of the V-ribbed channel and the transverse-ribbed channel. The miniature structured ribs show appreciable higher thermal performance than the conventional sized ribs. Furthermore, the numerical simulations show different vortex flow structures near the wall induced by the structured miniature ribs on the wall, which are responsible for the high-performance heat transfer enhancement.

Novel key parameter for eutectic nitrates based nanofluids selection for concentrating solar power (CSP) systems

A high-performance heat transfer fluid (HTF) plays a crucial role in the overall performance and efficiency of concentrating solar power (CSP) systems for utilizing solar energy. Molten salt-based nanofluids, which may offer a promising solution to help reduce the size and cost of CSP systems, have attracted increasing attention. However, there is still no comprehensive assessment strategy that considers the conflictive effects of adding nanoparticles in HTFs, such as the compromise between energy storage capacity increase and pumping cost increase. In this work, a methodology for nanofluids screening and selection is proposed and a novel parameter (R) is determined to assess the conflictive effect. The parameter (R) considers the ratio between the relative pumping power and the relative energy stored of the nanofluid compared to its base fluid. Three promising eutectics nitrate based nanofluids (NaNO3–KNO3, LiNO3–NaNO3–KNO3, LiNO3–NaNO3–KNO3–Ca(NO3)2) doped with 0.5 wt.% and 1 wt.% silica nanoparticles were selected and evaluated by the proposed methodology. As a result, adding nanoparticles into binary salts always present a negative effect (R = 1.03–1.22) when considering the ratio between the relative pumping cost and the relative energy stored. For ternary salt, adding 1 wt.% silica nanoparticles would be more preferable with a decrease of the parameter (R = 0.89–0.97, R < 1). In terms of quaternary, adding nanoparticles into quaternary does not change the parameter significantly (R = 0.96–1.04).

Heat Transfer Enhancement of Double-Tube-Type Heat Exchanger by Petal-Shaped Tube (Study on Optimum Tube Shape)

Abstract Heat exchangers are used widely in many fields, and various kinds of exchanger have been developed according to the requirement of the practical applications. Recently, heat exchangers that are highly efficient or compact have become more desirable from the viewpoint of energy conservation, and several new types have been developed, such as a compact fin tube type and a double tube type having an inner pipe with a special geometry. In this study, the flow and heat transfer characteristics of a petal-shaped double tube with a large wetted perimeter of six and five petals and five shallow petals and the effect of tube shape on the heat transfer and heat transfer efficiency were examined experimentally. The heat transfer of the double tube with a petal-shaped inner tube was increased because of the large wetted perimeter, but the pressure loss by friction increased. The optimal shape of the petal-shaped double tube with a high heat transfer performance and the greatest efficiency is discussed.

Suggestion of a Scale Factor to Design Spiral-Coil-Type Horizontal Ground Heat Exchangers

Spiral-coil-type horizontal ground heat exchangers (GHEs) have been increasingly used in ground source heat pump (GSHP) systems due to their higher heat transfer performance. Many attempts have been made to investigate the heat transfer mechanism and establish design methods for the spiral-coil-type ground heat exchangers. Nevertheless, a universal design method for horizontal GHEs has not been reported due to its complexity. In contrast to the spiral-coil-type horizontal GHEs, straight-line-type horizontal GHEs have been widely adopted since they are easy to design for use in industry. In this study, a scale factor model, which could be used to design the coil-type exchanger based on the design length of a straight-line-type heat exchanger, was presented. The ratio of the mean thermal transfer energy between the straight-line-type and spiral-coil-type heat exchangers was numerically investigated by considering weather condition, configuration of GHE, and thermal properties of the ground. Using the numerical results for a total of 108 cases, artificial neural network and linear regression methods were employed for the model development. The proposed model of the scale factor may provide an alternative way to design the spiral-coil-type horizontal GHEs.

Performance analysis of a solar thermoelectric generation (STEG) system with spray cooling

Use of an efficient cooling system is critical from the performance viewpoint of solar thermoelectric generation (STEG) systems. This study proposes the use of spray cooling as an effective technique for use in applications involving STEG systems. A mathematical model has been established to analyze STEG systems from the perspective of net generating efficiency and output power. Results demonstrate that compared to water-cooling, use of the spray-cooling technique results in enhanced generating efficiency, especially under high concentration ratios, owing to inherent advantages, such as high heat transfer performance, low power consumption, and no contact resistance. At a concentration ratio of roughly 200, the net generating efficiency when using spray cooling was observed to be 31.3% higher compared to that achieved when using water cooling. Under conditions of fixed module parameters and structure, there exist optimum values of the spray flow rate and concentration ratio that result in maximization of the net generating efficiency of STEG systems. This maximum efficiency of 13.203% occurs at a concentration ratio of 165 and corresponding flow rate of 0.35 L·min−1, at ZT = 1. Additionally, the net generating efficiency can be further enhanced by reducing the temperature of cooling water. The structural parameter γ is proposed to characterize the geometry of the thermoelectric module. As observed, there exists an optimum value of γ as well that tends to maximize the net generating efficiency of the system. Moreover, this optimum value of γ gradually increases with increase in concentration ratio. Results also demonstrate that optimum values of the spray flow rate and concentration ratio follow an approximately linear increase with increase in the ZT value of STEG modules.

Experimental investigation of an R600a two-phase loop thermosiphon to cool a motorized spindle shaft

This paper has presented a novel method for cooling a motorized spindle shaft based on two-phase loop thermosiphons (TPLTs) which have a high heat transfer performance and work without external power. The evaporator section and the condenser section of the TPLT were on the same pipeline due to the thermal conduction of the shaft in the process of exporting the heat inside the shaft. An experimental investigation of a copper TPLT was carried out using R600a as the working fluid, under the special heating and cooling conditions in a stationary. Then the heat transfer performance of an R600a TPLT was compared with that of an N-pentane TPLT. According to the experimental results, the cooling effect on the shaft was numerically calculated. The results showed that the TPLT worked well and the average equivalent thermal conductivity was 3712–8048 W·m−1·K−1 under the special cooling and heating conditions, which was higher than that of an N-pentane TPLT when the temperature of the evaporation section was below 387 K. The optimum liquid filling ratio of the R600a TPLT was 40%–60%, in this filling ratio range the R600a TPLT had a growing thermal conductivity and a falling heat transfer limit. The maximum temperature rise of the motorized spindle shaft was reduced by 44%, from 55 K to 31 K after using the R600a TPLTs cooling structure.

Investigation of Operating Conditions for Development of an Ultra-Micro Steam Injector

A steam injector (SI) works as a passive jet pump and has high heat transfer performance due to direct contact condensation between steam flow and subcooled water jet. The objective of the present study is to clarify heat transfer and flow characteristics of an ultra-micro steam injector (UMSI) with throat diameter of 1.0 mm. To this end, internal flow was visualized by a high-speed video camera. Pressure and temperature were measured with the visualization simultaneously. The main parameters were inlet steam pressure, inlet water flow rate and inlet water temperature. As a result, the formation of the water jet was confirmed. In that case, it was verified that discharged pressure became higher than the inlet pressure. The UMSI was successfully operated by achieving simultaneous maintenance of water jet and boosting pressure. In addition, water cooling capacity and steam heating power were evaluated. The operable region was suggested to exist in the large water cooling capacity condition.

Nanofluids Application in the Drilling Process

A high performance of heat transfer fluid has a great influence on the size, weight and cost of heat transfer systems, therefore a high-performance heat transfer fluid is very important in many industries. Over the last decades nanofluids have been developed. According to many researchers and publications on nanofluids its evident that nanofluids are found to exhibit enhance thermal conductivity. The aim of this experiment was to investigate the change of workpiece temperature during drilling using Jatropha oil with nanoparticle and water with iron nanoparticle as lubricating and cooling fluids. These experiments were carried out with samples of nanofluid with different volume ratio. Samples JN1, JN5 and JN10 of iron nanoparticles in the base Jatropha oil with iron volume fraction 1%, 5% and 10% respectively. Samples WN1, WN5 and WN10 of iron nanoparticles in the base water with iron volume fraction 1%, 5% and 10% respectively. The work arises from the projects which were realized at University J. E. Purkyně, Faculty of Mechanical Engineering, in cooperation with Namibia University of Science and technology, department of Mechanical Engineering.

Liquid metal gallium laden organic phase change material for energy storage: An experimental study

This paper presents the experimental study on the thermophysical behavior, thermal cyclic characteristics and energy storage performance of liquid metal (LM) laden in organic solid-liquid phase change material (PCM) for energy storage. In this view, Gallium (Ga) is added into D-Mannitol (DM) with a weight fraction of 0.1% and 0.5% by dispersion technique using a ball mill. Repeated melting/freezing cycle was carried out for 350 cycles and the samples were characterized using Differential Scanning Calorimetry (DSC), Thermogravimetry Analysis (TGA) and Fourier Transform Infrared (FTIR). The DM/Ga composite PCM showed enhanced thermal conductivity of ∼8.4%, ∼27.8% for 0.1 and 0.5 wt % Ga as compared to pure DM. XRD studies reveal that the pure DM exhibited β polymorphic phase while TGA and FTIR analysis confirm the thermal reliability and chemical stability of composites in the temperature range of 50–200 °C. Non isothermal crystal kinetic study proved that the addition of Ga increased the crystallization rate due to heterogeneous nucleation effect and leads to the reduction in subcooling temperature of the PCM. The experimental setup results to test the charging and discharging performance of the composite PCM revealed that the total time for one complete cycle reduced from 97.48 min for pure DM to 84.73 min and 63.92 min for DM-Ga composite with 0.1 wt % and 0.5 wt % respectively. Based on the results obtained, D-Mannitol based composites could be recommended as potential PCM candidates for solar heat and industrial waste heat recovery application due to its high energy density capacity, thermal/chemical stability and good heat transfer performance.

Experimental study of Large-scale cryogenic Pulsating Heat Pipe

Pulsating Heat Pipes (PHP) are passive two-phase heat transfer devices consisting of a long capillary tube bent into many U-turns connecting the condenser part to the evaporator part. They are thermally driven by an oscillatory flow of liquid slugs and vapor plugs coming from phase changes and pressure differences along the tube. The coupling of hydrodynamic and thermodynamic effects allows high heat transfer performances. Three closed-loop pulsating heat pipes have been developed by the DACM (Department of Accelerators, Cryogenics and Magnetism) of CEA Paris-Saclay, France. Each PHP measures 3.7 meters long (0.35 m for the condenser and the evaporator and 3 m for the adiabatic part), being almost 20 times longer than the longest cryogenic PHP tested. These PHPs have 36, 22 and 12 parallel channels. Numerous tests have been performed in horizontal position (the closest configuration to non-gravity) using nitrogen as working fluid, operating between 75 and 90 K. The inner and outer diameters of the stainless steel capillary tubes are 1.5 and 2 mm respectively. The PHPs were operated at different filling ratios (20 to 90 %), heat input powers (3 to 20 W) and evaporator and condenser temperatures (75 to 90 K). As a result, the PHP with 36 parallel channels achieves a certain level of stability during more than thirty minutes with an effective thermal conductivity up to 200 kW/m.K at 10 W heat load and during forty minutes with an effective thermal conductivity close to 300 kW/m.K at 5 W heat load.

PIV measurement of flow structures in a circular heat exchange tube with central slant rod inserts

In this paper, we use a Stereoscopic Particle Image Velocimetry (SPIV) system to measure the flow field of a circular tube fitted with central slant rods inserts for heat transfer enhancement. In addition, numerical simulation has been carried out to investigate the characteristics of heat transfer and flow structure. The length of inserts used in experiments is equal to that used in the numerical model, and the experiment and simulation are carried out at Re = 480, 1000 and 1750. Afterwards, the uncertainty of the flow field has been analyzed and the results indicate that the maximum relative errors for velocity in x-direction, y-direction and z-direction are about 3%, 6% and 1.5%, respectively. Experimental results show that three pairs of vortexes are created by central slant rods and the vortex strength increase with the increase of Reynolds numbers. Moreover, quantitative comparison of vortexes and z-velocity distribution between experimental and numerical simulation data has been performed and the results show that the deviations of vorticity and z-velocity distribution between experimental and numerical results are within 8% and 5%, respectively. Therefore, the experimental results suggest that the numerical simulation has a reasonable accuracy. Accordingly, we believe that the high overall heat transfer performance in tube fitted with central slant rod inserts obtained from numerical simulation is reasonable and credible.

An experimental and numerical study on the laminar heat transfer and flow characteristics of a circular tube fitted with multiple conical strips inserts

In this work, numerical simulations on the flow structures and heat transfer enhancement of laminar flow in a heat exchanger tube fitted with multiple conical strips inserts have been carried out. And stereoscopic particle image velocimetry (SPIV) measurements on the flow structures have been conducted to verify the numerical results. Both the experimental and numerical results show that multiple longitudinal vortexes are generated in tube, and the flow structures obtained by simulations agreed well with those of the PIV measurements. Numerical results show that heat transfer and friction factor were respectively enhanced by approximately 2.54–7.63 and 2.40–28.74 times compared to the plain tube, and the overall heat transfer performance (performance ratio R3) was located in the range of 1.23–6.05. Moreover, effects of the number of conical strips (n), central angle (α), slant angle (θ) and the pitch (p) have been investigated. It is found that both the heat transfer rate and flow resistance increase with the increasing number of conical strips, central angle and the decreasing pitch, and they both increase first and then decrease with the increase of slant angle. Compared with the previous published works, the tube with multiple conical strips inserts can obtain a moderate heat transfer and low flow resistance, and thus achieve a high overall heat transfer performance.