Analysis of Flow and Heat Transfer Enhancement in a Horizontal Pipe with PTT and V-cut Twisted Tape

Gas turbine blade tips encounter large heat load as they are exposed to the high temperature gas. A common way to cool the blade and its tip is to design serpentine passages with 180-deg turns under the blade tip-cap inside the turbine blade. Improved internal convective cooling is therefore required to increase the blade tip life time. This paper presents numerical predictions of turbulent fluid flow and heat transfer through two-pass channels with and without guide vanes placed in the turn regions using RANS turbulence modeling. The effects of adding guide vanes on the tip-wall heat transfer enhancement and the channel pressure loss were analyzed. The guide vanes have a height identical to that of the channel. The inlet Reynolds numbers are ranging from 100,000 to 600,000. The detailed three-dimensional fluid flow and heat transfer over the tip-walls are presented. The overall performances of several two-pass channels are also evaluated and compared. It is found that the tip heat transfer coefficients of the channels with guide vanes are 10∼60% higher than that of a channel without guide vanes, while the pressure loss might be reduced when the guide vanes are properly designed and located, otherwise the pressure loss is expected to be increased severely. It is suggested that the usage of proper guide vanes is a suitable way to augment the blade tip heat transfer and improve the flow structure, but is not the most effective way compared to the augmentation by surface modifications imposed on the tip-wall directly.

Download Full-text

CFD simulation of heat transfer enhancement in circular tube with twisted tape insert by using nanofluids

Materials Today Proceedings ◽

10.1016/j.matpr.2019.06.717 ◽

2020 ◽

Vol 21 ◽

pp. 572-577 ◽

Cited By ~ 2

Author(s):

A. Natarajan ◽

R. Venkatesh ◽

S. Gobinath ◽

L. Devakumar ◽

K. Gopalakrishnan

Keyword(s):

Heat Transfer ◽

Heat Transfer Enhancement ◽

Cfd Simulation ◽

Circular Tube ◽

Twisted Tape ◽

Transfer Enhancement

Download Full-text

Convective Heat Transfer of Ethanol/Polyalphaolefin Nanoemulsion in Mini- and Microchannel Heat Exchangers for High Heat Flux Electronics Cooling

10.5772/intechopen.96015 ◽

2021 ◽

Author(s):

Jaime Rios ◽

Mehdi Kabirnajafi ◽

Takele Gameda ◽

Raid Mohammed ◽

Jiajun Xu

Keyword(s):

Heat Transfer ◽

Convective Heat Transfer ◽

Heat Transfer Enhancement ◽

Convective Heat ◽

Phase Flow ◽

Transfer Performance ◽

Transfer Enhancement ◽

Heat Transfer Characteristics ◽

Two Phase ◽

Flow And Heat Transfer

The present study experimentally and numerically investigates the flow and heat transfer characteristics of a novel nanostructured heat transfer fluid, namely, ethanol/polyalphaolefin nanoemulsion, inside a conventionally manufactured minichannel of circular cross section and a microchannel heat exchanger of rectangular cross section manufactured additively using the Direct Metal Laser Sintering (DMLS) process. The experiments were conducted for single-phase flow of pure polyalphaolefin (PAO) and ethanol/PAO nanoemulsion fluids with two ethanol concentrations of 4 wt% and 8 wt% as well as for two-phase flow boiling of nanoemulsion fluids to study the effect of ethanol nanodroplets on the convective flow and heat transfer characteristics. Furthermore, the effects of flow regime of the working fluids on the heat transfer performance for both the minichannel and microchannel heat exchangers were examined within the laminar and transitional flow regimes. It was found that the ethanol/PAO nanoemulsion fluids can improve convective heat transfer compared to that of the pure PAO base fluid under both single- and two-phase flow regimes. While the concentration of nanoemulsion fluids did not reflect a remarkable distinction in single-phase heat transfer performance within the laminar regime, a significant heat transfer enhancement was observed using the nanoemulsion fluids upon entering the transitional flow regime. The heat transfer enhancement at higher concentrations of nanoemulsion within the transitional regime is mainly attributed to the enhanced interaction and interfacial thermal transport between ethanol nanodroplets and PAO base fluid. For two-phase flow boiling, heat transfer coefficients of ethanol/PAO nanoemulsion fluids were further enhanced when the ethanol nanodroplets underwent phase change. A comparative study on the flow and heat transfer characteristics was also implemented between the traditionally fabricated minichannel and additively manufactured microchannel of similar dimensions using the same working fluid of pure PAO and the same operating conditions. The results revealed that although the DMLS fabricated microchannel posed a higher pressure loss, a substantial heat transfer enhancement was achieved as compared to the minichannel heat exchanger tested under the same conditions. The non-post processed surface of the DMLS manufactured microchannel is likely to be the main contributor to the augmented heat transfer performance. Further studies are required to fully appreciate the possible mechanisms behind this phenomenon as well as the convective heat transfer properties of nanoemulsion fluids.

Download Full-text

Flow and heat transfer enhancement in condensing water drops in steam flows

Applied Physics Letters ◽

10.1063/1.4865101 ◽

2014 ◽

Vol 104 (7) ◽

pp. 074101 ◽

Cited By ~ 2

Author(s):

Zhen Yang ◽

Yuan-Yuan Duan ◽

Zhao Zhu ◽

Wei Gong ◽

Xiao-Chen Ma ◽

...

Keyword(s):

Heat Transfer ◽

Heat Transfer Enhancement ◽

Transfer Enhancement ◽

Flow And Heat Transfer ◽

Water Drops

Download Full-text

Heat transfer enhancement in microchannels using ribs and secondary flows

International Journal of Numerical Methods for Heat &amp Fluid Flow ◽

10.1108/hff-04-2021-0253 ◽

2021 ◽

Vol ahead-of-print (ahead-of-print) ◽

Author(s):

Karthikeyan Paramanandam ◽

Venkatachalapathy S. ◽

Balamurugan Srinivasan

Keyword(s):

Heat Transfer ◽

Temperature Distribution ◽

Heat Transfer Enhancement ◽

Heat Transfer Rate ◽

Transfer Rate ◽

Secondary Flows ◽

Transfer Enhancement ◽

Heat Transfer Characteristics ◽

Content Type ◽

Flow And Heat Transfer

Purpose The purpose of this paper is to study the flow and heat transfer characteristics of microchannel heatsinks with ribs, cavities and secondary channels. The influence of length and width of the ribs on heat transfer enhancement, secondary flows, flow distribution and temperature distribution are examined at different Reynolds numbers. The effectiveness of each heatsink is evaluated using the performance factor. Design/methodology/approach A three-dimensional solid-fluid conjugate heat transfer numerical model is used to study the flow and heat transfer characteristics in microchannels. One symmetrical channel is adopted for the simulation to reduce the computational cost and time. Flow inside the channels is assumed to be single-phase and laminar. The governing equations are solved using finite volume method. Findings The numerical results are analyzed in terms of average Nusselt number ratio, average base temperature, friction factor ratio, pressure variation inside the channel, temperature distribution, velocity distribution inside the channel, mass flow rate distribution inside the secondary channels and performance factor of each microchannels. Results indicate that impact of rib width is higher in enhancing the heat transfer when compared with its length but with a penalty on the pressure drop. The combined effects of secondary channels, ribs and cavities helps to lower the temperature of the microchannel heat sink and enhances the heat transfer rate. Practical implications The fabrication of microchannels are complex, but recent advancements in the additive manufacturing techniques makes the fabrication of the design considered in this numerical study feasible. Originality/value The proposed microchannel heatsink can be used in practical applications to reduce the thermal resistance, and it augments the heat transfer rate when compared with the baseline design.

Download Full-text

Experimental investigation on heat transfer enhancement with twisted tape having various V-cut configurations

Applied Thermal Engineering ◽

10.1016/j.applthermaleng.2020.115148 ◽

2020 ◽

Vol 172 ◽

pp. 115148 ◽

Cited By ~ 3

Author(s):

Wen-Xiao Chu ◽

Ching-An Tsai ◽

Bing-Hung Lee ◽

Kai-Yueh Cheng ◽

Chi-Chuan Wang

Keyword(s):

Heat Transfer ◽

Experimental Investigation ◽

Heat Transfer Enhancement ◽

Twisted Tape ◽

Transfer Enhancement

Download Full-text

Convective Heat Transfer Enhancement in a Circular Tube Using Twisted Tape

Journal of Heat Transfer ◽

10.1115/1.3122778 ◽

2009 ◽

Vol 131 (8) ◽

Cited By ~ 10

Author(s):

Zhi-Min Lin ◽

Liang-Bi Wang

Keyword(s):

Heat Transfer ◽

Nusselt Number ◽

Convective Heat Transfer ◽

Heat Transfer Enhancement ◽

Secondary Flow ◽

Convective Heat ◽

Tube Wall ◽

Twisted Tape ◽

Transfer Enhancement ◽

Thermal Boundary Conditions

The secondary flow has been used frequently to enhance the convective heat transfer, and at the same flow condition, the intensity of convective heat transfer closely depends on the thermal boundary conditions. Thus far, there is less reported information about the sensitivity of heat transfer enhancement to thermal boundary conditions by using secondary flow. To account for this sensitivity, the laminar convective heat transfer in a circular tube fitted with twisted tape was investigated numerically. The effects of conduction in the tape on the Nusselt number, the relationship between the absolute vorticity flux and the Nusselt number, the sensitivity of heat transfer enhancement to the thermal boundary conditions by using secondary flow, and the effects of secondary flow on the flow boundary layer were discussed. The results reveal that (1) for fully developed laminar heat convective transfer, different tube wall thermal boundaries lead to different effects of conduction in the tape on heat transfer characteristics; (2) the Nusselt number is closely dependent on the absolute vorticity flux; (3) the efficiency of heat transfer enhancement is dependent on both the tube wall thermal boundaries and the intensity of secondary flow, and the ratio of Nusselt number with twisted tape to its counterpart with straight tape decreases with increasing twist ratio while it increases with increasing Reynolds number for both uniform wall temperature (UWT) and uniform heat flux (UHF) conditions; (4) the difference in the ratio between UWT and UHF conditions is also strongly dependent on the conduction in the tape and the intensity of the secondary flow; and (5) the twist ratio ranging from 4.0 to 6.0 does not necessarily change the main flow velocity boundary layer near tube wall, while Reynolds number has effects on the shape of the main flow velocity boundary layer near tube wall only in small regions.

Download Full-text