Numerical Analysis of Flow Structure and Heat Transfer Characteristics in Dimpled Channels With Secondary Protrusions

2015 ◽  
Vol 138 (3) ◽  
Author(s):  
Yonghui Xie ◽  
Zhongyang Shen ◽  
Di Zhang ◽  
Phillip Ligrani
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Numerical Analysis ◽  
Thermal Performance ◽  
The Other ◽  
Combination Effect ◽  
Enhancement Ratio ◽  
Heat Transfer Characteristics ◽  
Transfer Rates ◽  
Heat Transfer Augmentation

Dimple structure is an effective heat transfer augmentation approach on coolant channel due to its advantage on pressure penalty. The implication of secondary protrusion, which indicates protrusion with smaller dimension than dimple, will intensify the Nusselt number Nu inside dimple cavity without obvious extra pressure penalty. The objective of this study is to numerically analyze the combination effect of dimples and secondary protrusion. Different protrusion–dimple configurations including protrusion print-diameter Dp, protrusion–dimple gap P, and staggered angle α are investigated. From the results, it is concluded that the implication of secondary protrusion will considerably increase the heat transfer rates inside dimple cavity. Cases 4 and 6 possess the highest Nusselt number enhancement ratio Nu/Nu0 reaching up to 2.1–2.2. The additional pressure penalty brought by the protrusion is within 15% resulting in total friction ratio f/f0 among the range of 1.9–2.1. Dimpled channels with secondary protrusions possess higher thermal performance factor TP, defined as (Nu/Nu0)/(f/f0)1/3, among which cases 4 and 6 are the optimal structures. Besides this, the TP of protrusion–dimple channels are comparable to the other typical heat transfer devices, and higher TP can be speculated after a more optimal dimple shape or combination with ribs and fins.

Maximizing Heat Transfer Through Joint Fin Systems

2005 ◽  
Vol 128 (2) ◽  
pp. 203-206 ◽  
Author(s):  
A.-R. A. Khaled
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Thermal Performance ◽  
Critical Length ◽  
The Other ◽  
Rigid Fixation ◽  
Convection Coefficient ◽  
Heat Transfer Characteristics ◽  
Cold Side ◽  
Transfer Characteristics

Heat transfer through joint fins is modeled and analyzed analytically in this work. The terminology “joint fin systems” is used to refer to extending surfaces that are exposed to two different convective media from its both ends. It is found that heat transfer through joint fins is maximized at certain critical lengths of each portion (the receiver fin portion which faces the hot side and the sender fin portion that faces the cold side of the convective media). The critical length of each portion of joint fins is increased as the convection coefficient of the other fin portion increases. At a certain value of the thermal conductivity of the sender fin portion, the critical length for the receiver fin portion may be reduced while heat transfer is maximized. This value depends on the convection coefficient for both fin portions. Thermal performance of joint fins is increased as both thermal conductivity of the sender fin portion or its convection coefficient increases. This work shows that the design of machine components such as bolts, screws, and others can be improved to achieve favorable heat transfer characteristics in addition to its main functions such as rigid fixation properties.

scholarly journals Effect of Conical Strip Inserts and ZrO2/DI-Water Nanofluid on Heat Transfer Augmentation: An Experimental Study

Energies ◽  
2020 ◽  
Vol 13 (17) ◽  
pp. 4554
Author(s):  
Mohamed Iqbal Shajahan ◽  
Jee Joe Michael ◽  
M. Arulprakasajothi ◽  
Sivan Suresh ◽  
Emad Abouel Nasr ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Thermal Performance ◽  
Test Section ◽  
Volume Concentration ◽  
Swirl Flow ◽  
Performance Ratio ◽  
Transfer Rates ◽  
Heat Transfer Augmentation ◽  
Twist Ratio ◽  
Constant Wall Heat Flux

There is a significant enhancement of the heat transfer rate with the usage of nanofluid. This article describes a study of the combination of using nanofluid with inserts, which has proved itself in attaining higher benefits in a heat exchanger, such as the radiator in automobiles, industries, etc. Nanofluids are emerging as alternative fluids for heat transfer applications due to enhanced thermal properties. In this paper, the thermal hydraulic performance of ZrO2, awater-based nanofluid with various volume concentrations of 0.1%, 0.25%, and 0.5%, and staggered conical strip inserts with three different twist ratios of 2.5, 3.5, and 4.5 in forward and backward flow patterns were experimentally tested under a fully developed laminar flow regime of 0–50 lphthrough a horizontal test pipe section with a length of 1 m with a constant wall heat flux of 280 W as the input boundary condition. The temperatures at equidistant position and across the test section were measured using K-type thermocouples. The pressure drop across the test section was measured using a U-tube manometer. The observed results showed that the use of staggered conical strip inserts improved the heat transfer rates up to that of 130.5%, 102.7%, and 64.52% in the forward arrangement, and similarly 145.03%, 116.57%, and 80.92% in the backward arrangement with the twist ratios of 2.5, 3.5, and 4.5 at the 0.5% volume concentration of ZrO2 nanofluid. It was also seen that the improvement in heat transfer was comparatively lower for the other two volume concentrations considered in this study. The twist ratio generates more swirl flow, disrupting the thermal hydraulic boundary layer. Nanofluids with a higher volume concentration lead to higher heat transfer due to higher effective thermal conductivity of the prepared nanofluid. The thermal performance factor (TPF) with conical strip inserts at all volume concentrations of nanofluids was perceived as greater than 1. A sizable thermal performance ratio of 1.62 was obtained for the backward-arranged conical strip insert with 2.5 as the twist ratio and a volume concentration of 0.5% ZrO2/deionized water nanofluid. Correlations were developed for the Nusselt number and friction factor based on the obtained experimental data with the help of regression analysis.

Heat Transfer Augmentation From Extended Surface Using Dimples

2018 ◽  
Author(s):  
Jay D. Mehta ◽  
Fay N. Colah ◽  
Anurag P. Rao ◽  
Vineeta P. Pendse ◽  
Vyankatesh U. Bagal ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Thermal Performance ◽  
Transfer Rate ◽  
Surface Modifications ◽  
Exposed Surface ◽  
Transfer Rates ◽  
Heat Transfer Augmentation ◽  
Extended Surface ◽  
Extended Surfaces ◽  
Exposed Surface Area

This paper concentrates on comparing dimples to improve the heat transfer rate from extended surfaces under forced convection conditions. Dimples are milled on the surface of the fins while keeping the exposed surface area between the various designs as constant. Spherical dimples, ellipsoidal dimples, cylindrical dimples, and pyramidal dimples are selected as part of the paper. Experimental results are compared with results obtained from simulation. The paper concludes that surface modifications improve the heat transfer rates. The paper also compares the thermal performance of various shapes of dimples.

Theoretical prediction of performance of Single and Double pass solar air heaters with artificial roughened absorber plates

2018 ◽  
Vol 8 (4) ◽  
Author(s):  
S. G. Sam Stanley ◽  
K.Kalidasa Murugavel Kumar Reddy ◽  
M. Blessy Queen Mary
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Theoretical Prediction ◽  
Friction Factor ◽  
The Other ◽  
Solar Air Heater ◽  
Roughness Parameters ◽  
Heat Transfer Characteristics ◽  
Double Pass ◽  
Transfer Characteristics

Investigations are carried out on artificial roughened absorber plates on Solar air heater. The roughness parameters are identified in to five basic profiles A, B, C, D and E. The profiles A, B and C are basic cubical and cylindrical profiles and the profiles D and E are categorized as rod arrangement of inline and staggered nature. Both frictional and heat transfer characteristics have been studied. Optimum results of frictional and heat transfer characteristics have been arrived out. Results show a higher value of frictional factor for the profile E. All reasons of variations have been justified and discussed. The deviation of friction factor from modified Balsius equation is within the limit of 4.32 %. Results also show higher value of Nusselt number for the inline rod arrangement of SAH than the other profiles.

Heat Transfer in Air Enclosures of Aspect Ratio Less than One

1981 ◽  
Vol 103 (4) ◽  
pp. 617-622 ◽  
Author(s):  
V. Sernas ◽  
E. I. Lee
Keyword(s):  
Heat Transfer ◽  
Vertical Wall ◽  
The Other ◽  
Heat Transfer Characteristics ◽  
Number Range ◽  
Transfer Rates ◽  
Aspect Ratios ◽  
Vertical Walls ◽  
Adiabatic Boundary Condition ◽  
Better Than

The heat transfer rates inside rectangular air enclosures of aspect ratios between 0.1 and 1.0 were investigated interferometrically for a Grashof number range between 2.64 × 106 and 5.45 × 106. The enclosures were composed of dissimilar temperature vertical walls and two types of ceilings and floors. One type was made from constant temperature plates kept at the vertical wall temperatures, and the other type was made of low thermal conductivity polyurethane foam rubber. The heat transfer characteristics and flow patterns within these two types of enclosures were found to be significantly different. For aspect ratios between 0.4 and 1.0 the isothermal ceiling and floor approximate an adiabatic boundary condition much better than foam because much less heat was interchanged between the floor (or ceiling) and the air in the enclosure.

Heat Transfer Characteristics of the Single-Phase, Elbow Thermosyphon

1993 ◽  
Vol 115 (1) ◽  
pp. 173-177 ◽  
Author(s):  
G. S. H. Lock ◽  
D. Ladoon
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Rayleigh Number ◽  
Thermal Performance ◽  
Single Phase ◽  
Flow Model ◽  
Flow Patterns ◽  
Heat Transfer Characteristics ◽  
Heated Section ◽  
Rayleigh Numbers

This paper describes the results of single-phase experiments on a right-angled, or elbow, thermosyphon with the cooled section upright and the heated section horizontal. For diameter-based Rayleigh numbers less than 107.6, the data indicate the existence of two flow regimes: fully mixed and impeded. A flow model is used to suggest how the cooled section and heated section flow patterns are coupled together. This model satisfactorily explains the effect of geometry on heat transfer, as revealed in the usual plots of Nusselt number versus Rayleigh number. Thermal performance was found to be comparable to that of the linear thermosyphon.

Heat Transfer Augmentation in a Divergent Duct with Angled Ribs

2017 ◽  
Vol 25 (01) ◽  
pp. 1750008
Author(s):  
SooWhan Ahn ◽  
MyungSung Lee
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Cross Section ◽  
Test Section ◽  
Average Nusselt Number ◽  
Rectangular Duct ◽  
Heat Transfer Characteristics ◽  
Cross Sectional ◽  
Circular Duct ◽  
Heat Transfer Augmentation

Heat transfer characteristics in the rectangular divergent duct with parallel angled ribs are experimentally compared with the straight smooth circular duct. The ribs with four different parallel angles ([Formula: see text], 45[Formula: see text], 60[Formula: see text], and 90[Formula: see text]) are glued on the duct’s two opposite walls as well as on the duct’s one sided wall only, respectively. The 0.72[Formula: see text]-inclined walls are installed at the two opposite walls of the rectangular divergent duct. The test section of 1000[Formula: see text]mm long has the cross section of [Formula: see text][Formula: see text]mm2 at inlet and [Formula: see text][Formula: see text]mm2 at exit. The ribbed walls are manufactured with a rib height [Formula: see text][Formula: see text]mm and the ratio of rib spacing ([Formula: see text]) to height([Formula: see text]) [Formula: see text] 10. The main findings are summarized that the increase in the dimensionless Nusselt number for the flow attack angles can be seen in the order of 90[Formula: see text], 30[Formula: see text], 60[Formula: see text], and 45[Formula: see text] at the two opposite ribbed divergent wall ducts, in addition, the average Nusselt number in the divergent rectangular duct with two opposite ribbed walls is somewhat greater than in the ribbed straight cross-sectional rectangular duct.

Analysis of heat transfer enhancement in microchannel by varying the height of pin fins at upstream and downstream region

2021 ◽  
pp. 095440892199297
Author(s):  
Mohammad Nawaz Khan ◽  
Munawwar Nawab Karimi
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Numerical Analysis ◽  
Pressure Drop ◽  
Thermal Performance ◽  
Full Length ◽  
Transfer Enhancement ◽  
Rectangular Microchannel ◽  
Pin Fins ◽  
Reynold’S Number

In this study, a numerical analysis of a microchannel with the different configuration of varying height of pin fins entrenched at the bottom of the channel base wall has been carried out. Five different configurations of pin fins arrangement which are considered in this study are, Case 1(Full length fins in complete microchannel), Case 2(Full length fins at the upstream), Case 3(Full length fins at the downstream), Case 4(Full length fin at the center of microchannel), Case 5(Full length fins at the inlet and exit of microchannel) and the results of these five cases are compared with the plain rectangular microchannel. In this investigation, deionized ultra-filtered water is used and Reynold’s number is ranging from 150 to 350. Results reveals that the highest Nusselt number is achieved by case 2 at a lesser value of Reynold’s number while by case 5 at higher Reynold’s number and the lowest pressure drop is occurring in case 4. The overall thermal performance of case 2 beats the corresponding cases.

scholarly journals Effects of Reynolds number, baffle angle, and baffle distance on three-dimensional turbulent flow and heat transfer in a circular pipe

2015 ◽  
Vol 19 (5) ◽  
pp. 1633-1648 ◽  
Author(s):  
Oguz Turgut ◽  
Erkan Kizilirmak
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Friction Factor ◽  
Thermal Performance ◽  
Three Dimensional ◽  
Circular Pipe ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer

In this study, steady-state three-dimensional turbulent forced convection flow and heat transfer characteristics in a circular pipe with baffles attached inside pipe have been numerically investigated under constant wall heat flux boundary condition. Numerical study has been carried out for Reynolds number Re of 3000-50,000, Prandtl number Pr of 0.71, baffle distances s/D of 1, 2, and 3, and baffle angle a of 30o-150o. Ansys Fluent 12.0.1 software has been used to solve the flow field. It is observed that circular pipe having baffles has a higher Nusselt number and friction factor compared to the smooth circular pipe without baffles. Maximum Nusselt number and friction factor are obtained for the baffle angle of 90o. Nusselt number increases while baffle distance increases in the range of studied; however, friction factor decreases. Periodically fully developed conditions are obtained after a certain module. Thermal performance factor increases with increasing baffle distance in the rage of studied but decreases with increasing Reynolds number; maximum thermal performance factor is obtained for the baffle angle of 150?. Results show that baffle distance, baffle angle, and Reynolds number play important role on both flow and heat transfer characteristics. The accuracy of the results obtained in this study is verified by comparing the results with those available in the literature for smooth circular pipes. All the numerical results are correlated within accuracy of ?10 and ?15% for average Nusselt number and Darcy friction factor, respectively.

scholarly journals Assessment and Evaluation of the Thermal Performance of Various Working Fluids in Parabolic Trough Collectors of Solar Thermal Power Plants under Non-Uniform Heat Flux Distribution Conditions

Energies ◽  
2020 ◽  
Vol 13 (15) ◽  
pp. 3776 ◽  
Author(s):  
Nabeel Abed ◽  
Imran Afgan ◽  
Andrea Cioncolini ◽  
Hector Iacovides ◽  
Adel Nasser
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Molten Salt ◽  
Thermal Performance ◽  
Thermal Efficiency ◽  
Thermal Stresses ◽  
The Other ◽  
Inlet Temperature ◽  
Parabolic Trough ◽  
Pure Fluids

Changing the heat transfer fluid (HTF) is a viable approach to study the corresponding effect on the thermal and hydraulic performances of parabolic trough collectors (PTC). Three categorized-types of pure fluids are used in this study; water, Therminol® VP-1 and molten salt. The parametric comparison between pure fluids is also studied considering the effect of various inlet fluid temperatures and different Reynolds ( R e ) numbers on the thermal performance. Two low-Reynolds turbulence models are used; Launder and Sharma (LS) k-epsilon and Shear Stress Transport (SST) k-omega models. In order to assess the performance of each fluid, a number of parameters are analyzed including average Nusselt ( N u ) number, specific pressure drop distributions, thermal losses, thermal stresses and overall thermal efficiency of the PTC system. Results confirmed that changing the working fluid in the PTC enhances the overall heat transfer thereby improving thermal efficiency. For a temperature-range of (320–500) K, the Therminol® VP-1 performed better than water, resulting in higher N u numbers, lower thermal stresses and higher thermal efficiencies. On the other hand, for the common temperature-range, both Therminol® VP-1 and molten salt preformed more or less the same with Therminol® VP-1 case depicting lower thermal stresses. The molten salt is thus the best choice for high operating temperatures (up to 873 K) as it does not depict any significant reduction in the overall thermal efficiency at high temperatures; this leads to a better performance for the Rankine cycle. For the highest tested Reynolds number for an inlet fluid temperature of 320 K, a comparison of heat transfer performance (Nusselt number) and the overall thermal efficiency between Therminol® VP-1 and water showed that Therminol® VP-1 is the best candidate, whereas the molten salt is the best choice for a higher inlet temperature of 600 K. For example, at an inlet temperature of 320 K, the Nusselt number and overall thermal efficiency of therminol VP-1 were 910 and 49% respectively as opposed to 443 and 38% for water. On the other hand, at the higher inlet temperature of 600 K, these two parameters (Nusselt number and overall thermal efficiency) were recorded as 614 and 41 % for molten salt and 500 and 39 % for Therminol® VP-1.

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