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Effects of flow attack angles of the V-wavy plate on flow and heat transfer in a square channel heat exchanger are investigated numerically. The V-wavy plates with V-tips pointing downstream and upstream called V-Downstream and V-Upstream, respectively, are examined for the Reynolds number in the range of 3000–10,000. The finite volume method with SIMPLE algorithm is selected to solve the present problem. The numerical results are presented in terms of flow and heat transfer visualization. The thermal performance analysis is also concluded in the form of Nusselt number ratio (Nu/Nu_{0}), friction factor ratio (

Heat exchanger is important equipment for various industries. The thermal improvement of heat exchanger can help to save production cost and energy. The thermal improvement in the heat exchanger is separated into two methods: active and passive methods. The active method requires additional power to enhance heat transfer rate of the system. The passive method is done by installing turbulators or vortex generators in the heating/cooling system. The flow created by the vortex generators will disturb the thermal boundary layer on the heat transfer surface which is the reason for heat transfer augmentation. The passive method is worthy way to improve thermal performance in the heat exchanger when compared with active method.

The thermal performance improvement of the heat exchanger with passive method had been performed by many researchers. The V-shaped baffle/rib is a type of vortex generator which gives high effectiveness. The investigations on flow and heat transfer in heat exchanger with V-shaped baffle/rib had been presented. For examples, Kumar et al. [

Another interesting vortex generator is wavy surface. The wavy surface always selects improving heat transfer rate and thermal performance in fin-and-tube heat exchanger. The wavy surface can increase the strength of the flow in the heat exchanger. The combinations between wavy fin and the other types of the turbulators in the fin-and-tube heat exchanger had been reported by many researchers [

Boonloi and Jedsadaratanachai [

As [

The wavy plate with square profile

Square channel heat exchanger inserted with V-wavy plate and computational domain.

The square channel walls are set with uniform heat flux around 600 W/m^{2}, while the wavy plate is assumed as adiabatic wall (insulator). The inlet and outlet of the computational domain for the square channel inserted with wavy plate are set with periodic boundary. No slip wall condition is imposed for all surfaces of the numerical model.

The tested fluid is air that keeps the thermal properties at the average bulk mean temperature. The flow and heat transfer are steady in three dimensions. The flow is turbulent and incompressible. The natural convection, radiation, viscous dissipation, and body force are not considered.

The turbulent model is realizable

The SOU numerical scheme is selected for all governing equations, decoupling with the SIMPLE algorithm using a finite volume method (FLUENT commercial code). The solutions are considered to be converged when the normalized residual is less than 10^{−9} and 10^{−5} for the energy equation and the other variables, respectively.

The important parameters are Reynolds number (Re), friction factor (

The Reynolds number is computed from

The pressure loss in the heating channel is presented as friction factor. The friction factor can be calculated

The heat transfer rate in the tested section is shown in terms of Nusselt number.

The local Nusselt number is computed by

The average Nusselt number can be printed by

Thermal performance is presented in the form of thermal enhancement factor (TEF).

The TEF is defined as the ratio of the heat transfer coefficient of an augmented surface,

Numerical results for the present problem are separated into three parts: verification of the computational domain, mechanisms in the test section, and thermal performance analysis.

Hexahedral mesh is selected for the numerical domain. The different numbers of grids for the computational domain (

Grid independence for (a) Nusselt number and (b) friction factor of 45° V-wavy plate for V-Downstream.

The heat transfer rate and pressure loss in the smooth channel heat exchanger for the current problem are compared with the values from the correlations as in Figure

Verification of the smooth channel on Nusselt number and friction factor.

From the preliminary study, it can be concluded that the computational domain of the present study has reliability to predict flow and heat transfer in the square channel heat exchanger inserted with various flow attack angles of the V-wavy plate.

Figures

Tangential velocity vector in transverse planes of the square channel heat exchanger inserted with 45° V-wavy plate at Re = 3000 for (a) V-Downstream and (b) V-Upstream.

Streamline in transverse planes for the square channel heat exchanger inserted with 20° V-wavy plate at Re = 3000.

Figures

Longitudinal vortex flow of the square channel heat exchanger inserted with 45° V-wavy plate at Re = 3000 for (a) V-Downstream and (b) V-Upstream.

Figures

Impinging jet on the channel wall of the square channel heat exchanger inserted with 45° V-wavy plate at Re = 3000 for (a) V-Downstream and (b) V-Upstream.

Temperature distribution in transverse planes for the square channel heat exchanger inserted with 45° wavy plate at Re = 3000 for V-Downstream.

Figures

Local Nusselt number distribution on the wall surface of the square channel heat exchanger inserted with 45° V-wavy plate at Re = 3000 for (a) V-Downstream and (b) V-Upstream.

Figures _{0} and flow attack angle of the square channel inserted with wavy plate for V-Downstream and V-Upstream, respectively. In general, the addition of the wavy plate in the test section can improve the heat transfer rate higher than the smooth channel in all cases (Nu/Nu_{0} > 1). Nu/Nu_{0} increases when increasing the Reynolds number. For V-Downstream, 15° ≤ _{0} is detected at the flow attack angle of 35° and 30° wavy plate for V-Downstream and V-Upstream, respectively. In range studies, the Nusselt number is around 3–6.5 and 2.8–6 times above the smooth channel with no wavy plate for V-Downstream and V-Upstream, respectively.

Nu/Nu_{0} versus

The variation of the

Figures

TEF versus

Numerical prediction on flow and heat transfer mechanisms in the square channel inserted with V-wavy plate is presented. The influences of the flow attack angles (

The addition of the wavy plate in the test section leads to producing the vortex flow or swirling flow through the test section. The vortex flow is an important factor for heat transfer improvement in the heating section because the vortex flow disturbs the thermal boundary layer on the channel walls. The insertion of the wavy plate not only increases in heat transfer rate, but also enhances the pressure loss.

The maximum heat transfer rate is detected at the flow attack angle around 35° and 30° of the wavy plate for V-Downstream and V-Upstream, respectively. The wavy plate with V-Downstream and V-Upstream performs the heat transfer rate higher than the smooth channel around 3–6.5 and 2.8–6 times, respectively, for

The friction loss of the square channel inserted with the wavy plate is found to be maximum at the flow attack angle around 45°, while the flow attack angle of 15° performs the opposite result for both cases. In range studies, the friction loss is higher than the smooth channel around 11–44 times.

The optimum TEF is found at 20° wavy plate to be about 2.02 and 2.09, respectively, for V-Downstream and V-Upstream.

The manufacture and installation of the V-wavy plate is more convenient than other types of the turbulators such as V-baffle placed on the channel wall.

The optimum flow attack angles of the wavy surface in the heat exchanger channel for laminar [

Friction factor

Channel height

Convective heat transfer coefficient (W/

Thermal conductivity (W/m K)

Nusselt number

Static pressure (Pa)

Prandtl number

Reynolds number

Temperature (K)

Thermal enhancement factor

Velocity in

Mean velocity in channel (m/s)

Cartesian coordinates.

Flow attack angle, degree

Dynamic viscosity (Pa s)

Density (kg/

Thermal diffusivity.

Inlet

Wall

Smooth tube.

The authors declare that there are no conflicts of interest regarding the publication of this article.

The funding of this work is supported by King Mongkut’s Institute of Technology Ladkrabang research funds (Contract no. KREF046006). The authors would like to thank Associate Professor Dr. Pongjet Promvonge, KMITL, for suggestions.