Improving heat transfer is a critical subject for energy conservation systems which directly affects economic efficiency of these systems. There are active and passive methods which can be employed to enhance the rate of heat transfer without reducing the general efficiency of the energy conservation systems. Among these methods, passive techniques are more cost-effective and reliable in comparison with active ones as they have no moving parts. To achieve further improvements in heat transfer performances, some researchers combined passive techniques. This article performs a review of the literature on the area of heat transfer improvement employing a combination of nanofluid and inserts. Inserts are baffles, twisted tape, vortex generators, and wire coil inserts. The progress made and the current challenges for each combined system are discussed, and some conclusions and suggestions are made for future research.

Combination of nanofluid and inserts for heat transfer enhancement

Heat transfer performance of TiO2–SiO2 nanofluids in a tube with wire coil inserts

Numerical investigation of rectangular-cut twisted tape insert on performance improvement of heat exchangers

Energy saving in thermal energy systems using dimpled surface technology – A review on mechanisms and applications

Combining corrugated surfaces and nanofluids technologies have a significant advantage to develop compact heat exchangers in order to produce more efficient and reliable thermal systems. In this paper, the employment of alumina oxide (Al2O3) in water nanofluid for heat transfer enhancement with corrugation is performed numerically and experimentally over Reynolds number ranges of 10,000–30,000. Three corrugated channels, semicircle (SCC), trapezoidal (TCC), and straight (SC) are fabricated and tested with nanofluid Al2O3 volume fractions of 0%, 1%, and 2%. Thermophysical properties of the prepared nanofluid are measured experimentally. Numerically, the governing equations are solved in the computational domain using the finite volume method, and the results are presented in terms of velocity and isotherms contours. The findings clarified that the corrugation profile has a significant impact on heat transfer enhancement compared to the straight profile. Furthermore, heat transfer enhancement increases with increasing the volume fraction of nanoparticles. The new style of trapezoidal corrugated channel has the best heat transfer enhancement. This result may clarify the best use of corrugated channels in heat exchange devices to obtain the required thermal improvement. The numerical results are compared with the corresponding experimental data, and the results are in a good agreement.

Experimental and numerical investigations of convection heat transfer in corrugated channels using alumina nanofluid under a turbulent flow regime

Numerical investigation on heat transfer performance and flow characteristics in circular tubes with dimpled twisted tapes using Al2O3-water nanofluid

Flow characteristics and heat transfer performance in the circular and annular microchannels with dimples/protrusions are studied numerically. The effects of Reynolds number (Re), dimple/protrusion size, combinations of dimples or protrusions, and arrangement pattern are examined. The results show that in circular microchannels, dimple cases show the poor heat transfer capacity and the staggered dimple case provides no significant difference. The aligned protrusion cases provide excellent heat transfer performance, which is further improved with the increase in protrusion size or Re, and the staggered protrusion case shows the worse heat transfer performance. In annular microchannels, the outer protrusion shows the better heat transfer effect superior to the inner protrusion. In protrusion microchannel, it will be helpful in avoiding the excessive additional flow resistance when dimples are fixed on the opposite wall. The arrangement has no significant effect on the heat transfer and friction characteristic, and the flow separation on the dimple (protrusion) side is suppressed when the protrusion (dimple) is fixed on the opposite wall. From the view point of energy saving, in circular microchannels, the protrusion cases provide the high effectiveness, and the staggered case possesses the lower effectiveness especially in the protrusion case.

Thermal performance of dimpled/protruded circular and annular microchannel tube heat sink

Numerical investigation on heat transfer and flow characteristics in helically coiled mini-tubes equipped with dimples

Numerical investigation on heat transfer performance and flow characteristics in a rectangular air cooling channel (AR=2) with ridged dimples

Nanofluid has great potentials in heat transfer enhancement and entropy generation decrease as an effective cooling medium. Effects of Al2O3-water nanofluid flow on entropy generation and heat transfer performance in a rectangular conventional channel are numerically investigated in this study. Four different volume fractions are considered and the boundary condition with a constant heat flux is adopted. The flow Reynolds number covers laminar flow, transitional flow and turbulent flow. The influences of the flow regime and nanofluid volume fraction are examined. Furthermore, dimples and protrusions are employed, and the impacts on heat transfer characteristic and entropy generation are acquired. It is found that the average heat transfer entropy generation rate descends and the average friction entropy generation rate rises with an increasing nanofluid volume fraction. The effect of nanofluid on average heat transfer entropy generation rate declines when Reynolds number ascends, which is inverse for average friction entropy generation rate. The average wall temperature and temperature uniformity both drop accompanied with increasing pumping power with the growth in nanofluid volume fraction. The employment of dimples and protrusions significantly decreases the average entropy generation rate and improve the heat transfer performance. The effect of dimple-case shows great difference with that of protrusion-case.

https://www.mdpi.com/1099-4300/18/4/148/pdf

Lu Zheng

Papers

Numerical investigation on heat transfer performance and flow characteristics in circular tubes with dimpled twisted tapes using Al2O3-water nanofluid

Thermal performance of dimpled/protruded circular and annular microchannel tube heat sink

Numerical investigation on heat transfer and flow characteristics in helically coiled mini-tubes equipped with dimples

Numerical investigation on heat transfer performance and flow characteristics in a rectangular air cooling channel (AR=2) with ridged dimples

Entropy Generation and Heat Transfer Performances of Al2O3-Water Nanofluid Transitional Flow in Rectangular Channels with Dimples and Protrusions