The subject of heat transfer enhancement has significant interest to develop the compact heat exchangers in order to obtain a high efficiency, low cost, light weight, and size as small as possible. Therefore, energy cost and environmental considerations are going on to encourage attempts to invent better performance over the existence designs. Streamwise vortices can be generated using small flow manipulators or protrusions such as wings and winglets configurations. Single-pair, single row, or two dimensional array of vortex generators (VGs) can be punched, mounted, attached or embedded in the boundary layer of flow channel. VGs generate longitudinal and transverse vortices, while longitudinal vortices are more efficient for heat transfer enhancement than transverse vortices. A dramatic augmentation in thermal performance of the thermal system can be achieved but pressure drop penalty is existed. Several parameters have been overviewed in this paper, which have pronounced effect on the convective heat transfer coefficient and pressure drop penalty. These parameters are: attack angle of VG, geometry of VG, standard and novel types of VG, spacing between the VG tips, number of pairs of VGs in the flow direction, rectangular or circular array arrangement of VGs, common-flow upper (CFU) or common-flow down (CFD) configuration of VG, pointing up (PU) or pointing down (PD) arrangement of VG with flow direction, Re number, channel aspect ratio, number of tubes of fin-tube heat exchanges (HE), circular or oval tubes of fin-tube HE, and location of VG respect to the tube of HE or from leading edge of the channel. This paper gives an overview about the early studies done in order to improve the performance of thermal systems with minimal pressure losses to derive systems with less negative impact on the environment and high level of energy economic. This study also provides an outlook for future work using nanofluids with vortex generators. This article is also summarizes the recent experimental and numerical developments on the thermal conductivity measurements of nanofluids, thermal conductivity enhancement, convection and conduction heat transfer, some applications, main problems and suggestions for future works.

An overview on heat transfer augmentation using vortex generators and nanofluids: Approaches and applications

Optimization of heat exchangers with vortex-generator fin by Taguchi method

Enhancement of heat transfer in a fin-tube heat exchanger using rectangular winglet type vortex generators

This paper summarizes the current state of the art related to improvement of the heat exchanger surfaces using streamwise longitudinal vortices Primarily, the improvements related to fin-tube cross-flow heat exchangers and the plate-fin heat exchangers have been addressed Protrusions in certain forms, such as delta wings or winglet pairs, act as vortex generators, which can enhance the rate of heat transfer from the heat-exchanger surfaces that may be flat or louvered The strategically placed vortex generators create longitudinal vortices, which disrupt the growth of the thermal boundary layer, promote mixing between fluid layers, and hence lead to augmentation in heat transfer The flow fields are dominated by swirling motion associated with modest pressure penalty Heat transfer is augmented substantially for all the proposed configurations of the longitudinal vortex generators, such as delta wings, rectangular winglet pairs, and delta winglet pairs, with varying degree of pressure penalty Both comp

Augmentation of Heat Transfer by Creation of Streamwise Longitudinal Vortices Using Vortex Generators

Effect of geometric size of curved delta winglet vortex generators and tube pitch on heat transfer characteristics of fin-tube heat exchanger

Numerical study of the relationship between heat transfer enhancement and absolute vorticity flux along main flow direction in a channel formed by a flat tube bank fin with vortex generators

Numerical study of laminar flow and heat transfer characteristics in the fin side of the intermittent wavy finned flat tube heat exchanger

Secondary flow intensity determines Nusselt number on the fin surfaces of circle tube bank fin heat exchanger

In real application, once the pattern of fin is determined, fin spacing of tube bank fin heat exchanger can be adjusted in a small region, and air flow velocity in the front of the heat exchanger is not all the same. Therefore, the effects of fin spacing on heat transfer performance of such heat exchanger are needed. This paper numerically studied the optimal fin spacing regarding the different front flow velocities of a circular tube bank fin heat exchanger with vortex generators. To screen the optimal fin spacing, an appropriate evaluation criterion JF was used. The results show that when front velocity is 1.75 m/s, the optimal fin spacing is 2.25 mm, when front velocity is 2.5 m/s, the optimal fin spacing is 2 mm, and when front velocity is higher than 2.5 m/s, the optimal fin spacing is 1.75 mm.

The optimum fin spacing of circular tube bank fin heat exchanger with vortex generators

The invention discloses a flat tube-fin heat exchanger with a double-side vortex generator, which belongs to the technical field of flat tube-fin heat exchangers and comprises flat tubes arranged along the direction of air flow and fins sleeved on the flat tubes. The fins are provided with holes used for sleeving the flat tubes, two pairs of vortex generators facing upwards and two pairs of vortex generators facing downwards are stamped respectively by the upper side and the lower side of each hole, and corresponding small holes are left on the fins; and the front edge points of the first pair of the vortex generators facing upwards are located at front-end tangent lines of the holes used for sleeving the flat tubes, and the front edge points of the second pair of the vortex generators facing upwards are located at middle perpendicular lines of the holes used for sleeving the flat tubes. Compared with a traditional single-side fin for stamping the vortex generators, two sides of the fins disclosed by the invention are simultaneously turned over to stamp out the vortex generators, thereby the heat exchange capability of the fins can be improved, and the flow resistance of an air side can be simultaneously reduced. Moreover, the compactedness of a heat exchange device is increased, the power of a pump is reduced, and the energy sources are saved under an identical heat load.

Limin Chang

Papers

Numerical study of the relationship between heat transfer enhancement and absolute vorticity flux along main flow direction in a channel formed by a flat tube bank fin with vortex generators

Numerical study of laminar flow and heat transfer characteristics in the fin side of the intermittent wavy finned flat tube heat exchanger

Secondary flow intensity determines Nusselt number on the fin surfaces of circle tube bank fin heat exchanger

The optimum fin spacing of circular tube bank fin heat exchanger with vortex generators

Flat tube-fin heat exchanger with double-side vortex generator