Thermal Performance Enhancement Factor Research Articles

The effect of two main vortexes generator on heat transfer enhancement in mini rectangular ducts of airborne thermoelectric conversion system

To enhance the heat transfer process of supercritical pressure fluid in rectangular channels of the airborne thermoelectric conversion system, the combined effect of the Reynolds stress, properties variation and longitudinal fins on convective heat transfer process in ducts under supercritical pressure is investigated. Then, a method to induce the two main vortexes structure in rectangular ducts is proposed. Results show that, in smooth ducts, the two main vortexes structure is formed due to the effect of density variation. By comparing the flow and heat transfer process in the smooth duct and ridged duct with trapezoidal fins attached on the lower wall, it is found that, due to the effect of new vortexes induced by trapezoidal fins, the two main vortexes structure is inhibited, which makes local wall temperature increases about 50 K. Accordingly, the thermal performance enhancement factor of rectangular duct with trapezoidal fins is lower than 1. To enhance the two main vortexes structure, a method that using triangular fins to induce two main vortexes structure is proposed, and the duct with one triangular longitudinal fin attached on the upper wall is designed, which has better thermal performance than ducts with trapezoidal fins. Due to the effect of triangular fins, the dominant distance of two main vortexes structure increases by 416%. Accordingly, in ducts with triangular fins, local heat transfer coefficient is enhanced about 23.5%, and the maximum of thermal performance enhancement factor is about 1.29.

Thermal Performance and Turbulence Modeling of Combined Multiple Shell-Pass Shell and Tube Heat Exchanger

Abstract This paper investigates the adaptability of different Reynolds-averaged Navier-Stokes (RANS)-based turbulence models for flow behavior and thermal performance of combined multiple shell-pass shell and tube heat exchanger (CMSP-STHE) with unilateral ladder-type helical baffle (ULHB). The presence of ULHB in the outer shell pass of the heat exchanger leads to a complex flow configuration and makes it quite challenging to deal with its computational analysis. The computational fluid dynamic method compares the CMSP-STHE with ULHB with the traditional shell and tube heat exchanger with segmental baffles (SG-STHE). The performance of four turbulence models, namely, realizable k–ɛ, standard k–ɛ, standard k–ω and RNG k–ɛ models are compared with the correlation data. It is observed that the standard k–ω turbulence model more accurately predicts the heat transfer and pressure drop compared to other models. The logarithmic mean temperature difference (LMTD) results for various mass flowrates and thermal performance enhancement factor (TPEF) corresponding to various values of Re are also presented. It is concluded that the TPEF of CMSP (ULHB)-STHE is higher than that of the conventional STHE. The average enhancement is approximately 28% for ULHB STHE than the conventional one. Further, variations in velocity, turbulence kinetic energy, and local Nusselt number along the tube length are examined to understand the thermal performance behavior with CMSP (ULHB)-STHE. It is clear from the results that the CMSP (ULHB)-STHE is a better alternative to the traditional SG-STHEs.

Hydrothermal parameters enhancement of a DTHEX with simultaneous V-cut twisted tape turbulator and air/CuO-water flow usage

Numerous studies have been conducted to assess the effect of using a V-cut twisted tape turbulator, bubble injection method, and CuO-water nanofluid as a working fluid separately on the hydrothermal parameters. For the first time, the current study aimed to comprehensively evaluate the effect of the simultaneous use of these three methods on the effectiveness, friction factor, and thermal performance enhancement factor of a double-tube heat exchanger. Experiments were conducted with Reynolds numbers ranging from 7200 to 14500. Air was injected into the working fluid with a flow rate of 2 to 6 L/min. A turbulator with different geometry was also inserted in the inner tube. The results showed that using the methods separately increased effectiveness by up to 81%, while their simultaneous use increased the effectiveness to 2.36 times that of the plain tube. The friction factor in the presence of these three methods is up to 1.11 to 14.36 times that of a plain tube heat exchanger, respectively. In addition, the results showed that combining these three methods significantly affected thermal performance enhancement factor (TEF), increasing it to 1.46.

Thermal, hydraulic, exergitic and economic evaluation of a flat tube heat exchanger equipped with a plain and modified conical turbulator

Increasing use of fossil fuels has led to serious consequences on the environment including global warming, pollution, and increased costs of heating systems. This indicates the importance of improving the efficiency of devices used in heating and air conditioning systems such as heat exchangers. In this study, it was tried to enhance the performance of the heat exchanger by simultaneous use of a flat tube as a central tube of the heat exchanger and dual conic turbulator. In addition to plain conical turbulator, the influence of the conical turbulator with aerodynamic geometry was investigated on the heat transfer and pressure drop. Finally, economic evaluation of the studied cases was done based on the thermal performance enhancement factor (TEF) and the net profit of unit transferred heat load (ηp). Tests were conducted in the hot water flow rate ranging 0.033–0.0678 L/s while cold water flow rate was kept constant at 0.166 L/s. The results indicated that the heat transfers and exergy loss of the flat tube heat exchanger with a dual modified conical turbulator was up to 33% and 30% higher than the plain tube heat exchanger, respectively. Also, a heat exchanger with a modified dual turbulator with convergent embellishment (case B) selected as the economic case and has the highest TEF and ηp . It was revealed that the application of enhanced conical turbulator would lead in the increment of ηp up to 1.26 times.

Influence of a novel serrated wire coil insert on thermal characteristics and air flow behavior in a tubular heat exchanger

The application of wire coil as a turbulent generator to enhance the heat transfer in heat exchangers is constantly being studied and presented. In this work, a novel wire coil turbulator was developed to have characteristics that are different from those previously proposed. It is based on the concept of a combination of a coiled wire structure with a continuous V–shaped rib turbulator, which was referred to as a serrated wire coil (SWC). In the paper, the turbulent air flow behavior and heat transfer characteristics in a tube heat exchanger with SWC insert was investigated experimentally under isothermal–flux condition. Ambient air was used as a working fluid in a turbulent flow regime with Reynolds numbers (Re) ranging from 5114 to 14,752. The SWCs were inserted into test tubes with three different coil diameters (DC) of 34.4, 41.2 and 47.9 mm (or diameter ratio, DR = DC/DT = 0.68, 0.81 and 0.94) and four different pitch lengths (PC) of 10, 20, 30 and 40 mm (or pitch ratio, PR=PC/DT = 0.1969, 0.3937, 0.5906 and 0.7874). The experimental results of heat transfer and friction loss were presented as dimensionless parameters, Nusselt number (Nu) and friction factors (f), respectively. It was observed that the Nu increased with a decrease in pitch length and an increase in coil diameter. While the f decreased with an increase in both pitch length and coil diameter. Under the scope of this study, it was found that the insertion of the coils increased the Nu and f above the smooth tubes by approximately 1.75–2.46 times and 3.31–8.16 times, respectively. The empirical correlations of Nu and f for tubular heat exchanger inserted with SWC under the scope of this study were developed and showed error within ±4 % for Nu and ±12 % for f. The maximum thermal performance enhancement factor (η) for this work was about 1.41 for the SWC with DC = 47.9 mm and PC = 10 mm at Re = 5114. In addition, the Nu, f and η obtained in the optimal conditions of this work were compared with previous work.

Experimentally validated 3D simulation and performance optimization of a solar air duct with modified conical vortex generators

Providing flow-disturbing components on the effective heat transfer area of the absorber plate is the most efficient thermohydraulic performance enhancement technique employed in a solar air heater. The present investigation aims at finding the optimal set of geometrical parameters for a solar air heater with modified conical vortex generators. Optimization approach is adopted considering the thermohydraulic performance of the proposed design of the solar air heater. Experimentally validated numerical simulations for different parameters of the vortex generators like relative pitch ratio of 8 to 15, relative vortex generator height ratio of 0.17 to 0.34 and Reynolds number range of 3000 to 16,000 are optimized using Grey relational analysis and Overall evaluation criteria. Performance of solar air heater under different investigated parameters is analysed using performance indices like Nusselt number, friction factor, thermal performance enhancement factor, friction enhancement factor and thermo-hydraulic enhancement factor. A maximum Nusselt number of 142.4 is observed for relative pitch ratio of 8 and relative vortex generator height ratio of 0.34. Optimized geometrical parameters are predicted for different percentage weightage set on thermal and hydraulic performances. Correlation equations for Nusselt number and friction factor are developed for the overall range of investigated parameters.

Heat Transfer Enhancement and Vortex Flow Structure in the Spirally Fluted Tubes

The turbulence kinetic energy and heat transfer performance of air in spirally fluted tube were numerically studied at a constant wall temperature with Reynolds number (Re) between 5000 and 45 000. Furthermore, the flow dynamics and heat transfer performance of spirally fluted tubes with five different geometric parameters as well as the effects of separation vortex and swirling wake flow on heat transfer and flow resistance were analyzed. According to the results, heat transfer is enhanced mainly because the fluid hit the windward side of the flute, thus generating a strong turbulence kinetic energy to further reconstruct the boundary layer. The second reason is that the formation of the recirculation zone between the flutes disturbs the boundary layer caused by the flow separation. With the increase of flute depth ratio (Ld/D), the separation vortex will become stronger and larger on the leeward side of flute. The separation vortex will break the boundary layer and improve the heat transfer capacity which is accompanied with the increase of fluid resistance. As the flute pitch length ratio (Lp/D) decreases, the spiral flow is strengthened, and meanwhile more wake flow is generated. The spiral flow causes little impact on enhancing heat transfer but inhibits the development of the separation vortex and fluid pulsation; in addition, the fluid resistance is reduced at the same time. The maximum value of the average Nusselt number appears when Re=5000, Ld/D=0.25 and Lp/D=1.00, which is 2.53 times the value of smooth tube. In view of the whole range of Reynolds number, the thermal performance enhancement factor indicates that Ld/D=0.15 and Lp/D=1.00 are the optimal geometric design parameters.

Experimental investigation for thermal performance of inclined spherical ball roughened solar air duct

This work deals with determination of thermal efficiency of spherical ball roughened collector aligned inclined to flow direction. Roughened collector produces more heat transfer compared to smooth ones but heat transfer augmentation comes at the cost of increased frictional losses. Lesser thermal efficiency of solar air heater has necessitated researchers to focus on its improvement by providing artificial flow modification techniques in the flow field. Laminar sublayer beneath the absorber plate will get disturbed and this helps to increase turbulence level of air. Present work discusses the influence of inclined spherical ball shaped roughness element and improving its thermal performance. Design considerations, geometries used viz. relative roughness pitch 9–18, relative roughness height 0.024–0.040, height-diameter ratio 0.5–2, angle of attack 35°-75°, flow conditions and their influence on turbulence viz. Reynolds no 2500–18500, heat transfer rate, absorber temperature and thermal performance enhancement factor have been thoroughly discussed. Finally concluding remarks and future scope for additional enhancement in performance of solar air heater is proposed. Maximum thermal efficiency for roughened ducts was found as 81% compared to 38% for smooth duct at parameters viz. ‘relative roughness pitch = 12, ‘relative roughness height’ = 0.036, ‘height-diameter ratio’ = 1 and ‘angle of attack’ = 55֠ at mass flow rate = 0.0319 kg/s.

Augmented heat transfer in tubular heat exchanger fitted with V-baffled tapes

Effects of insertion of a straight tape mounted with double-sided V-baffles used as a longitudinal vortex generator (LVG) on turbulent convection heat transfer behaviors in a constant heat-fluxed tube in the Reynolds number (Re) range of 4120 to 25,800 are experimentally and numerically investigated. In the present experiment, the V-baffles at a fixed attack angle (α = 30°) were placed on the tape with two arrangements: V-apex pointing downstream and upstream (hereinafter called “V-down” and “V-up”). The V-down and up tapes with three baffle height ratios, (RB = b/D = 0.20, 0.15, 0.10) and pitch ratios, (RP = P/D = 1.5, 1.0, 0.5) were tested. Data of the current smooth or plain tube were also examined for comparison. The experimental results have shown that the employ of the V-down tape generally yields higher heat transfer, friction loss and thermal performance than that of the V-up one. A new derived thermal-performance enhancement factor (TEF) is proposed. The maximum TEF of the V-down tape is around 2.07 at RB = 0.15, RP = 1.0 and is, in average, about 1.4% higher than the V-up one having its peak of 2.04. A 3D numerical V-baffled-tube flow model was also simulated to examine the fluid flow and heat transfer patterns. The numerical validation was seen in close agreement with available experimental data. Numerical heat transfer contours and flow structures were also reported.

Experimental and numerical heat transfer study of turbulent tube flow through discrete V-winglets

The article presents an experimental and numerical investigation on heat transfer augmentation in a tubular heat exchanger inserted with discrete-V-winglet (DW) tape. Air entered the DW-inserted tube having a uniform wall heat flux in a turbulent flow regime, Reynolds number from 4200 to 25,800. Two arrangements of DWs: V-tip pointing upstream (V-up) and downstream (V-down) were introduced with three relative winglet heights (RB=b/D = 0.1, 0.15 and 0.2) and four relative winglet-pitches (RP=P/D = 0.5, 1.0, 1.5 and 2.0), all at a single angle of attack, α = 30°. Effects of those parameters on the heat transfer/Nusselt number (Nu) and friction factor (f) were examined. Also, a novel thermal-performance enhancement factor (TEF) was put forward. The experimental result has shown that at a given RB, the smallest pitch length (RP=0.5) yields the highest f and Nu. The DW with RB=0.2 and RP=0.5 has the maximum Nu and f of about 3.8 times and 18.8 times, respectively whereas the one with RB=0.15 and RP=1.0 gives the highest TEF of about 1.99 and 2.02 for the V-up and V-down, respectively. Moreover, the DW provides higher TEF than the typical V-winglet as expected. To explore the mechanism of heat transfer, a numerical model of the inserted-tube flow was carried out and the numerical result was validated and found in favorable agreement with available measurement. Flow structures and heat transfer patterns from the simulation such as temperature contours and streamlines including the Nusselt number contours were also proposed.

Numerical study of heat transfer and friction factor in a tube with groove and rib on the wall

AbstractHeat transfer and friction factor in a tube with turbulator internally grooved and rib are studied using numerical simulation. Two different turbulator geometries, including only groove and both groove and rib, on the tube wall are investigated. The study is developed for different parameters of turbulator including pitch ratio (PR), groove and rib height (DR), and Reynolds number in the range of 10 000 to 38 000. The results revealed that the best Nusselt number is achieved for GR turbulator and for the tube wall with PR = 2 and DR = 1. Furthermore, for a specific turbulator parameter, Nusselt number is improved by 46% compared with the experimental result. The results show that the friction factor decreases by increase of both step and height ratios. For example, based on Reynolds number, 21% to 69% reduction in the friction factor was observed for PR = 7 and DR = 3. In addition, the correlations for Nusselt number and friction factor with acceptable deviation are presented for the studied turbulators. Finally, thermal performance enhancement factor is defined to be a good criterion for selection of the optimum turbulator and their parameters.

Enhanced heat transfer in rectangular duct with punched winglets

Abstract Thermal performance of a heat exchanger duct with punched winglets (PWs) mounted on the upper duct wall has been examined for Reynolds number (Re) ranging from 4100 to 25,500. In the present experiment, two types of PWs: punched delta- and elliptical-winglets (P-DW and P-EW) with four punched-hole sizes were tested at a fixed attack angle, optimal relative pitch and height. Also, data of solid delta- and elliptical-winglets (DW and EW) were included for comparison. The investigation has shown that the P-DW yields higher thermal-performance enhancement factor (η) than the P-EW. Although the solid DW and EW with no punch have the highest heat transfer and friction loss, the PWs yield better η than the solid ones. For PWs, the P-DW with smaller hole size has the peak heat transfer and friction loss around 5.7 and 40 times over the smooth duct, respectively but the optimum η of 2.17 is seen for the one with a certain hole size. The PWs provide η at about 5%–8% above the solid winglets.

Thermo-hydraulic performance in heat exchanger tube with V-shaped winglet vortex generator

This article presents the influence of V-shaped winglet vortex generators (V-WVGs) inserted into a constant heat-fluxed tube on thermal characteristics. In the present experiment, two V-WVG types: V-shaped rectangular- and delta-winglets (V-RW and V-DW) were mounted periodically on both sides of a straight tape before insertion into the tube with four relative winglet pitches (PR = P/D = 0.5, 1.0, 1.5 and 2.0) and three winglet blockage ratios (BR = b/D = 0.1, 0.15 and 0.2) at a fixed attack angle (α = 45°). Effects of geometric parameters of both V-WVGs on thermal performance enhancement were studied using air as tested fluid in a turbulence condition, Reynolds number (Re) ranging between 4130 and 25,900. The measured result has been shown that the V-RW performs higher rate of heat transfer as well as friction loss than the V-DW and the rise in BR results in higher increase of the heat transfer rate and friction loss while the increment in PR yields the reversing tendency for both V-WVG types. A new thermal-performance enhancement factor (TEF) has been introduced and it reveals that the V-DW has TEF in a range of 1.82–2.0 or around 3% above the V-RW where its peak regarded as the optimal point is at BR = 0.15 and PR = 1.0. Empirical correlations for the Nusselt number and friction factor to assess the real merits of a heat exchanger tube with V-WVGs are determined.

Experimental investigation on thermal-hydraulic performance of a novel shell-and-tube heat exchanger with unilateral ladder type helical baffles

A novel structure of the shell-and-tube heat exchanger with unilateral ladder type helical baffles (STHX-ULHB) is proposed. Compared with the shell-and-tube heat exchanger with segmental baffles (STHX-SB), the heat transfer and pressure drop performances of the STHX-ULHB are experimentally investigated. The experimental results show that both the shell-side heat transfer coefficient hs and the overall heat transfer coefficient K of the STHX-ULHB are dramatically increased with the increasing of the mass flow rate, which are 109.3–125.5% and 105.2–122.5% higher than that of the STHX-SB, respectively. The pressure drop of the STHX-ULHB is decreased by 12.1–45.9% than that of the STHX-SB. Two criteria, i.e., the heat transfer coefficient per unit pressure drop and the thermal performance enhancement factor (TEF), are introduced to evaluate the comprehensive performance of the STHX-ULHB. Overall, the shell-side heat transfer coefficient per unit pressure drop of STHX-ULHB is 151.9%–176.4% higher than that of the STHX-SB. The values of the TEF of the STHX-ULHB increase by 161.3–178.9%, with an average value of 171.2%. Both of the results illustrate that the comprehensive performance of the STHX-ULHB is superior to that of the STHX-SB.

Numerical Study on Heat Transfer Enhancement in a Rectangular Duct with V-Shaped Ribs

This research aims to study the numerical investigation of heat transfer and fluid flow characteristics of multiple cylinder v-rib with combined staggered rib in a rectangular duct. The conventional heat exchangers were usually used as flat plate rib shape leading to increase pressure drop from obstructive flow. Therefore, the inclined cylinder V-shaped rib was modified to use in this work. The cylinder shape rib increases pressure drop (less than flat plate rib) because of the rounded shape of cylinder v-rib creating the smooth flow of the fluid. The heat transfer and the pressure drop are represented in term of Nusselt number (Nu) Friction factor (f), respectively. The relation of Nu with f values was analysed to obtain the Thermal performance enhancement factor (TEF). The velocity vector and temperature contours were examined by the Computational Fluid Dynamics (CFD). The data was compared with the experimental result. The channel size was simulated at the rectangular duct height (H) of 30 mm and width (W) of 300 mm with rib-to channel-height ratios (e/H) at 0.1, 0.2, 0.3 and the angle of attack (α) at 30°. Air was used as the test fluid. Reynolds number (Re) was varied from 12,681 to 35,000 with constant heat flux on the bottom wall of the tested section. Simulation results represented the velocity vectors and temperature contours. It was found that the increasing of e/H leading to provide high co-rotating of the flow. The highest TEF (TEF = 2.05) was observed at 30(, e/H 0.3 and Re 12,618.

Numerical investigation of thermohydraulic performance of air to water double-pipe heat exchanger with helical fins

In this work, the thermohydraulic performance of a proposed design of an air-to-water double pipe heat exchanger with helical fins on the annulus gas side, is numerically studied. Three-dimensional computational fluid dynamics (CFD) simulations are performed, using the FLUENT software in order to investigate the gas side fluid flow, turbulence, heat transfer, and power consumption for different configurations of the heat exchanger. CFD performance analysis is conducted under turbulent flow conditions for configurations with helical fin spacings in the range of 0.05–0.2m. The numerical model is first verified against experimental data available in the literature, for a double-pipe heat exchanger with longitudinal fins. Then, longitudinal fins are considered asa reference configuration and a comparative analysis of the thermohydraulic performances of the different helical fin configurations and the reference configuration is conducted. The flow field characteristics of the helical fin configurations are clearly demonstrated and discussed. Key design parameters such as the heat transfer coefficient, pressure drop, and thermal performance enhancement factor are evaluated to predict the overall performance of the heat exchangers. Results show that the use of helical fins significantly enhances the heat transfer rate for the same unit weight, but it also increases the pressure drop. The overall compactness and performance of the heat exchanger improve through the use of helical fins, and within the scope of the present investigation, the helical fin configuration with a fin spacing of 0.1m provides the optimal thermohydraulic performance. Therefore, the present study helps to reveal and expand the potential of helical fins in providing an enhanced overall performance of this type of heat exchanger as well as in limiting its material cost for design engineers and manufacturers.

Study the effect of axially perforated twisted tapes on the thermal performance enhancement factor of a double tube heat exchanger

The main objective of this numerical study is to investigate the ways to reduce the pressure drop and consequently increase thermal performance enhancement factor (TEF) of a heat exchanger equipped with twisted tapes. For this purpose, axial perforated twisted tapes (PTTs) with various hole diameters are used instead of simple twisted tapes (STTs). Moreover, the variations of the effectiveness with number of transfer units (NTU) for different heat capacity ratios (Cr) were presented. The numerical model was well validated with the available experimental results. The results indicated that the use of perforated twisted tape leads to a reduction in pressure drop and heat transfer rate, subsequently; a significant increase in TEF was seen compared to simple twisted tapes. In addition, some correlations were formulated to present the numerical results.

Performance characteristics of heat exchanger with internal turbulence generators under various blade configurations and operating conditions

In this study, turbulence generators with rectangular geometry were designed to be fixed inside the tube of an oil cooler for the hydraulic steering of automobiles and their performance characteristics in the heat exchanger were investigated. The heat transfer rates, heat transfer coefficients, the coefficient of the pressure drop values, and friction factors were measured in accordance to the flow rates and inlet temperature of the oil. The resulting Nusselt numbers (Nu) increased when the angle of the turbulence generator wings was increased up to 45–65° but decreased when the angle was increased further up to 75°. On the hand, the friction factor (f) continued to increase as the angle configuration was increased. The highest value of the thermal performance enhancement factor (TEF), which was 6.46, was obtained from the turbulence generator angle of 45°, which could be considered as the optimum angle configuration. Lastly, the empirical correlations that were developed for the Nu and the f had good agreement with the experimental values and both had conservative error range of ±20%.

Experimental and numerical study on heat transfer enhancement in a channel with Z-shaped baffles

The influence of baffle turbulators on heat transfer augmentation in a rectangular channel has been investigated experimentally and numerically. In the experiment, the baffles are placed in a zigzag shape (Z-shaped baffle) aligned in series on the isothermal-fluxed top wall, similar to the absorber plate of a solar air heater channel. The aim at using the Z-baffles is to create co-rotating vortex flows having a significant influence on the flow turbulence intensity leading to higher heat transfer enhancement in the tested channel. Effects of the Z-baffle height and pitch spacing length are examined to find the optimum thermal performance for the Reynolds number from 4400 to 20,400. The Z-baffles inclined to 45° relative to the main flow direction are characterized at three baffle- to channel-height ratios (e/H=0.1, 0.2 and 0.3) and baffle pitch ratios (P/H=1.5, 2 and 3). The experimental results show a significant effect of the presence of the Z-baffle on the heat transfer rate and friction loss over the smooth channel with no baffle. The Nusselt number, friction factor and thermal performance enhancement factor for the in-phase 45° Z-baffles are found to be considerably higher than those for the out-phase 45° Z-baffle at a similar operating condition. The in-phase 45° Z-baffle with larger e/H provides higher heat transfer and friction loss than the one with smaller e/H while the shorter pitch length yields the higher Nu, f and TEF than the larger one. The numerical work is also conducted to investigate the flow friction and heat transfer behaviors in the channel mounted with the 45° Z-baffles, and the numerical results are found in good agreement with experimental data.

Numerical Study of Laminar Heat Transfer in Baffled Square Channel with Various Pitches

Abstract The article presents a numerical analysis of laminar periodic flow and heat transfer characteristics in a constant temperature-surfaced square channel mounted with 30° angled baffles of various pitches. The computations were based on a finite volume method and the SIMPLE algorithm implemented. The fluid flow and heat transfer characteristics are presented for Reynolds number based on the channel hydraulic diameter ranging from 100 to 2000. The angled baffles were placed repeatedly on the lower and upper channel walls with in–line arrangement to generate a pair of streamwise counter–rotating vortex flows. Effects of different pitch ratios (PR = P/H) with a single baffle height ratio of 0.2 on heat transfer and pressure loss in the channel were examined. The baffled channel flow showed a fully developed periodic flow profile at about x/D≈7. The computation revealed that the pair of vortex flows created by the baffles exists and induces impingement/attachment flows on a side and the upper and lower walls leading to substantial increase in heat transfer rate over the test channel. The decrease in the PR led to the rise of friction factor only. The result showed that the optimum thermal performance enhancement factor of about 3.78 is found at PR = 2.5.