The effect of using staggered and partially tilted perforated baffles on heat transfer and flow characteristics in a rectangular channel

2022 ◽  
Vol 174 ◽  
pp. 107422
Mohamed A. El Habet ◽  
Saeed A. Ahmed ◽  
Mohamed A. Saleh
2000 ◽  
M. Singh ◽  
P. K. Panigrahi ◽  
G. Biswas

Abstract A numerical study of rib augmented cooling of turbine blades is reported in this paper. The time-dependent velocity field around a pair of symmetrically placed ribs on the walls of a three-dimensional rectangular channel was studied by use of a modified version of Marker-And-Cell algorithm to solve the unsteady incompressible Navier-Stokes and energy equations. The flow structures are presented with the help of instantaneous velocity vector and vorticity fields, FFT and time averaged and rms values of components of velocity. The spanwise averaged Nusselt number is found to increase at the locations of reattachment. The numerical results are compared with available numerical and experimental results. The presence of ribs leads to complex flow fields with regions of flow separation before and after the ribs. Each interruption in the flow field due to the surface mounted rib enables the velocity distribution to be more homogeneous and a new boundary layer starts developing downstream of the rib. The heat transfer is primarily enhanced due to the decrease in the thermal resistance owing to the thinner boundary layers on the interrupted surfaces. Another reason for heat transfer enhancement can be attributed to the mixing induced by large-scale structures present downstream of the separation point.

2021 ◽  
Vol 8 (3) ◽  
pp. 386-392
Ahmed Hashim Yousif ◽  
Hakim T. Kadhim ◽  
Kadhim K. Idan Al-Chlaihawi

In this paper, a numerical simulation is performed to study the effect of two types of concave vortex generators (VGs), arranged as fish-tail locomotion in a rectangular channel. The heat transfer and fluid flow characteristics with and without VGs are examined over the Reynolds number range 200≤Re≤2200.The two proposed types of the VGs are selected based on the speed of the fish movement which is arranged in different distances between them (d/H=0.6, 1, 1.3). The results show that the use of VGs can significantly enhance the heat transfer rate, but also increases the friction factor. The heat transfer performance is enhanced by (4-21.1%) reaching the maximum value by using the first type of the VGs at (d/H=1.3) due to better mixing of secondary flow and the new arrangement of the VGs which lead to decreasing the friction factor with an easy flow of fluid.

2021 ◽  
Syaiful ◽  
M. Kurnia Lutfi

The high thermal resistance of the airside of the compact heat exchanger results in a low heat transfer rate. Vortex generator (VG) is one of the effective passive methods to increase convection heat transfer by generating longitudinal vortex (LV), which results in an increase in fluid mixing. Therefore, this study aims to analyze the convection heat transfer characteristics and the pressure drop of airflow in a rectangular channel in the presence of a concave rectangular winglet VG on a heated plate. Numerical calculations were performed on rectangular winglet pairs vortex generators (RWP VGs) and concave rectangular winglet pairs vortex generators (CRWP VGs) with a 45° angle of attack and one, two, and three pairs of VGs with and without holes. The simulation results show that the decrease in the value of convection heat transfer coefficient and pressure drop on CRWP with three perforated VG configuration is 4.63% and 3.28%, respectively, of the three pairs of CRWP VG without holes at an airflow velocity of 2 m/s.

Gota Suga ◽  
Tetsuaki Takeda

Abstract A Very High Temperature Reactor (VHTR) is one of the next generation nuclear systems. From a view point of safety characteristics, a passive cooling system should be designed as the best way of a reactor vessel cooling system (VCS) in the VHTR. Therefore, the gas cooling system with natural circulation is considered as a candidate for the VCS of the VHTR. Japan Atomic Energy Agency (JAEA) is advancing the technology development of the VHTR and is now pursuing design and development of commercial systems such as the 300MWe gas turbine high temperature reactor GTHTR300C (Gas Turbine High Temperature Reactor 300 for Cogeneration). In the VCS of the GTHTR300C, many rectangular flow channels are formed around the reactor pressure vessel (RPV), and a cooling panel utilizing natural convection of air has been proposed. In order to apply the proposed panel to the VCS of the GTHTR300C, it is necessary to clarify the heat transfer and flow characteristics of the proposed channel in the cooling panel. Thus, we carried out an experiment to investigate heat transfer and fluid flow characteristics by natural convection in a vertical rectangular channel heated on one side. Experiments were also carried out to investigate the heat transfer and fluid flow characteristics by natural convection when a porous material with high porosity is inserted into the channel. An experimental apparatus is a vertical rectangular flow channel with a square cross section in which one surface is heated by a rubber heater. Dimensions of the experimental apparatus is 600 mm in height and 50 mm on one side of the square cross section. Air was used as a working fluid and fine copper wire (diameter: 0.5 mm) was used as a porous material. The temperature of the wall surface and gas in the channel were measured by K type thermocouples. We measured the outlet flow rate by hot-wire anemometer which is an omnidirectional spherical probe of diameter 2.5mm. The experiment has been carried out under the condition that a copper wire with a scourer model and a cubic lattice model were inserting into the channel.

Takumi Shigematsu ◽  
Tetsuaki Takeda ◽  
Shumpei Funatani

The Very High Temperature Reactor (VHTR) is a next generation nuclear reactor system. The passive cooling system should be designed for the VHTR as the best way of reactor vessel cooling system (VCS). Therefore, the gas cooling system with natural circulation is considered as a candidate for the VCS of the VHTR. Furthermore, we examined the heat transfer of rectangular vertical channel using “Spandrel” panel. “Spandrel” is the metallic plate having grooved patterns. The reason is that we can set it at low cost to the VCS because it is a kind of general construction materials. The objective of this study is to examine heat transfer characteristics of one side heated vertical rectangular channel with natural circulation and application of spandrel panel to the VCS of VHTR in order to construct the passive cooling system of the VHTR. We have performed an experiment and a numerical analysis. On experiment, we set the panel to adiabatic wall and supplied 100–400W/m2 heat flux to the panel. In order to obtain the heat transfer and fluid flow characteristics of a vertical channel inserting porous material, we have also carried out a numerical analysis using the commercial CFD code as the first step. From the results obtained in the analysis, it was found that the amount of heat removal was increased for 1–21% by inserting copper wires as porous material. This paper describes a thermal performance of the one-side heated vertical rectangular channel inserting copper wire with high porosity. From the view point of the economical and safety characteristic, the passive cooling system should be designed for the VTHR as the best way of the system. So, the gas cooling system by natural convection is the one of candidate system.

Andallib Tariq ◽  
P. K. Panigrahi

The present investigation is an experimental study of convective heat transfer in the entrance region of a rectangular channel with a single surface mounted slit rib. The open area ratios of the slit rib set during the experiment are equal to 10, 20, 30, 40 and 50%. Hotwire anemometry (HWA) and resistance thermometry (RTD) have been used for velocity and temperature measurement respectively. Both mean and turbulent statistics of the velocity and temperature fluctuations have been reported. Smoke visualization has also been carried out to obtain a qualitative picture of the flow field behind the rib. The surface Nusselt number has been determined from liquid crystal thermography (LCT). The Reynolds number based on the hydraulic diameter of the channel has been set at Re = 32,100. The nature of the flow through the slit and its interaction with the shear layer from the top of the rib depend on the size of the slit. For the slit rib with higher open area ratio (β = 40 and 50%), the bottom part of the slit rib behaves like an independent small rib with its own reattachment region. At smaller open area ratio (β = 10, 20 and 30%), the flow through the slit manipulates the reattaching shear layer from the top of the rib. The size of the slit and its location from the bottom channel surface are the primary parameters responsible for the modification and manipulation of the flow behavior of a slit rib in comparison to the solid rib.

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