Heat Transfer and Entropy Generation Analysis of Slit Pillar Array in Microchannels

2020 ◽  
Vol 142 (9) ◽  
Author(s):  
Xiao Cheng ◽  
Huiying Wu
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Pressure Drop ◽  
Entropy Generation ◽  
Heat Transfer Performance ◽  
Three Dimensional ◽  
Thermal Characteristics ◽  
Secondary Flows ◽  
Transfer Performance ◽  
Pillar Array

Abstract The slit pillar allows a small fraction of the mainstream flow through pillar to disturb the pillar wake zone fluid and eventually enhance the local and global heat transfer performances in microchannels. In this study, three-dimensional full-domain numerical simulations on the hydrodynamic and thermal characteristics of slit pillar array in microchannels are performed. Effects of slit angle and height over diameter (H/D) ratio on the fluid flow and heat transfer are studied. Comparisons with the nonslit pillar array are conducted on pressure drop, surface temperature, Nusselt number, and thermal performance index (TPI). Furthermore, the results are analyzed by using the entropy generation. As a result of secondary flows and enhanced convective heat transfer area, all cases at H/D ratio of 0.3 demonstrate enhanced heat transfer performance at an increase of 18.0–34.7% on Nusselt number, while a reduction of 3.4–12.9% on pressure drop in comparison to the criterion case at the same conditions. Among them, slit 15–15 deg shows the best comprehensive heat transfer performance. Due to the improved uniformities of velocity and temperature distributions, all slit pillar array microchannels show decreased entropy generation. The maximum entropy generation reduction can reach up to 15.8%, as compared with the criterion case at the same conditions. The above results fully demonstrate that the novel slit pillar array microchannel heat sink can be used as an effective approach for heat transfer enhancement.

scholarly journals Numerical Simulation of Flow and Heat Transfer in Structured Packed Beds with Smooth or Dimpled Spheres at Low Channel to Particle Diameter Ratio

Energies ◽  
2018 ◽  
Vol 11 (4) ◽  
pp. 937 ◽  
Author(s):  
Shiyang Li ◽  
Lang Zhou ◽  
Jian Yang ◽  
Qiuwang Wang
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Pressure Drop ◽  
Heat Transfer Performance ◽  
Particle Diameter ◽  
Packed Bed ◽  
Packed Beds ◽  
Transfer Performance ◽  
Heat Transfer Characteristics ◽  
Flow And Heat Transfer

Packed beds are widely used in catalytic reactors or nuclear reactors. Reducing the pressure drop and improving the heat transfer performance of a packed bed is a common research aim. The dimpled structure has a complex influence on the flow and heat transfer characteristics. In the present study, the flow and heat transfer characteristics in structured packed beds with smooth or dimpled spheres are numerically investigated, where two different low channel to particle diameter ratios (N = 1.00 and N = 1.15) are considered. The pressure drop and the Nusselt number are obtained. The results show that, for N = 1.00, compared with the structured packed bed with smooth spheres, the structured packed bed with dimpled spheres has a lower pressure drop and little higher Nusselt number at 1500 < ReH < 14,000, exhibiting an improved overall heat transfer performance. However, for N = 1.15, the structured packed bed with dimpled spheres shows a much higher pressure drop, which dominantly affects the overall heat transfer performance, causing it to be weaker. Comparing the different channel to particle diameter ratios, we find that different configurations can result in: (i) completely different drag reduction effect; and (ii) relatively less influence on heat transfer enhancement.

Effect of Bifurcation on Thermal Characteristics of Convergent-Divergent Shaped Microchannel

2018 ◽  
Vol 10 (4) ◽  
Author(s):  
Pankaj Srivastava ◽  
Anupam Dewan
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Pressure Drop ◽  
Boundary Layers ◽  
Average Nusselt Number ◽  
Three Dimensional ◽  
Thermal Characteristics ◽  
Lower Temperature ◽  
Drop Flow ◽  
Thermal Boundary Layers

A microchannel heat sink with convergent-divergent (CD) shape and bifurcation is presented, and flow and heat transfer characteristics are analyzed for Re ranging from 120 to 900. The three-dimensional governing equations for the conjugate heat transfer with temperature-dependent solid and fluid properties are solved using the finite volume method. Comparisons are carried out for four cases, namely, rectangular shape with and without bifurcation and CD shape with and without bifurcation. The pressure drop, flow structure, and average Nusselt number are analyzed in detail, and the thermal resistance and overall performance are compared. It is shown that the CD shape with bifurcation has more uniform and lower temperature at the bottom wall and better heat transfer performance compared to other geometries. The heat transfer augmentation in the CD shaped microchannel with bifurcation can be attributed not only to the accelerated and redirected flow toward the constant cross section segment but also to periodically interrupted and redeveloped thermal boundary-layers due to bifurcation. It is also shown that increasing Re leads to thinning of thermal boundary-layers resulting in an enhanced heat transfer in terms of an increased average Nusselt number from 38% to 74%. However, there is an increased pressure drop due to channel shape and obstacle in fluid flow. Further, due to a high pressure drop penalty at high Re, CD shaped microchannel with bifurcation loses its heat transfer effectiveness.

scholarly journals FORCED CONVECTION HEAT TRANSFER PERFORMANCE OF AN INTERNALLY FINNED TUBE

1970 ◽  
Vol 40 (1) ◽  
pp. 54-62 ◽  
Author(s):  
Asharful Islam ◽  
A. K. Mozumder
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Friction Factor ◽  
Heat Transfer Performance ◽  
Finned Tube ◽  
Transfer Performance

Heat transfer performance of T-section internal fins in a circular tube has been experimentally investigated. The T-finned tube was heated by electricity and was cooled by fully developed turbulent air. Inside wall temperatures and pressure drop along the axial distance of the test section at steady state condition were measured for different flows having Reynolds number ranging from 2x104 to 5x104 for both smooth and finned tubes. From the measured data, heat transfer coefficient, Nusselt number and friction factor were calculated. From the measured and calculated values, heat transfer characteristics and fluid flow characteristics of the finned tube are explained; the performance of the finned tube is also evaluated. For finned tube, friction factor on an average was 5 times higher and heat transfer coefficient was 2 times higher than those for smooth tube for similar flow conditions. The finned tube, however, produces significant heat transfer enhancement. Key Words: Heat Transfer, Internal Fin, Reynolds Number, Nusselt Number, Pressure Drop. doi: 10.3329/jme.v40i1.3473 Journal of Mechanical Engineering, Vol. ME40, No. 1, June 2009 54-62

scholarly journals Air-side heat transfer enhancement by self-agitators

2019 ◽  
Author(s):  
◽  
Kuojiang Li
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Heat Exchanger ◽  
Pressure Drop ◽  
Working Conditions ◽  
Heat Transfer Performance ◽  
Transfer Performance ◽  
Transfer Enhancement ◽  
Flow Mixing

Airfoil-based self-agitators (AFAs), bio-inspired rectangular-shaped self-agitators (RSAs), and caudal-fin inspired hourglass-shaped self-agitators (CHSAs) were installed inside plate-fin heat exchanger. The heat transfer enhancement and pressure drop characteristics of these AFAs, RSAs, CHSAs design were experimentally investigated and compared with the clean channel case. We found that the self-agitators vibrate periodically and generate vortices, which enhance flow mixing and thus heat transfer performance. For the chosen heat sink and assigned working conditions, the best heat transfer performance was obtained with four rows AFAs, which caused an 80% increase in overall Nusselt Number over the clean channel at same Reynolds Number, and a 50% rejected heat increase at the same pumping power due to the strong longitudinal vortices generated by the presence of the AFAs. Experiments were conducted at a wide range of Reynolds numbers from 400 to 10000, which covered laminar-transitional-turbulent regime with CHSAs. Experimental correlations of the pressure drop as a function of dimension parameter and friction factor and Nusselt number as functions of dimensionless ones have been proposed. Mutual coupling motions and effects of multiple-row flapping CHSAs in parallel and tandem configurations were studied by using a high-speed camera. A stereo Particle Image Velocimetry (PIV) system was used to conduct detailed flow field measurements to quantify the flow mixing level. For the chosen plate-fin heat exchanger and assigned working conditions, the best heat transfer performance was obtained with six-row CHSAs with a pitch of 25mm, which caused a 200% increase in the Nusselt number over the clean channel at the same Reynolds number. However, the best overall performance was obtained with twelve-row CHSAs with a pitch of 12.5mm, which caused a 68% enhancement in thermal-hydraulic characteristic compared to the clean channel at the same Reynolds number.

scholarly journals Optimization of heat transfer and pressure drop of the channel flow with baffle

2021 ◽  
Vol 40 (1) ◽  
pp. 286-299
Author(s):  
Behzad Ghobadi ◽  
Farshad Kowsary ◽  
Farzad Veysi
Keyword(s):  
Heat Transfer ◽  
Boundary Condition ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Pressure Drop ◽  
Friction Factor ◽  
Heat Transfer Performance ◽  
Transfer Performance ◽  
Maximum Heat ◽  
Maximum Heat Transfer

Abstract In this article, the numerical analysis has been carried out to optimize heat transfer and pressure drop in the horizontal channel in the presence of a rectangular baffle and constant temperature in two-dimension. For this aim, the governing differential equation has been solved by computational fluid dynamics software. The Reynolds numbers are in the range of 2,000 < Re < 10,000 and the working fluid is water. While the periodic boundary condition has been applied at the inlet, outlet, and the channel wall, axisymmetric boundary condition has been used for channel axis. For modeling and optimizing the turbulence, k–ω SST model and genetic algorithm have been applied, respectively. The results illustrate that adding a rectangular baffle to the channel enhances heat transfer and pressure drop. Hence, the heat transfer performance factor along with maximum heat transfer and minimum pressure drop has been investigated and the effective geometrical parameters have been introduced. As can be seen, there is an inverse relationship between baffle step and both heat transfer and pressure drop so that for p/d equal to 0.5, 1, and 1.25, the percentage of increase in Nusselt number is 141, 124, and 120% comparing to a simple channel and the increase in friction factor is 5.5, 5, and 4.25 times, respectively. The results of modeling confirm the increase in heat transfer performance and friction factor in the baffle with more height. For instance, when the Reynolds number and height are 5,000 and 3 mm, the Nusselt number and friction factor have been increased by 35% and 2.5 times, respectively. However, for baffle with 4 mm height, the increase in the Nusselt number and friction factor is 68% and 5.57 times, respectively. It is also demonstrated that by increasing Reynolds number, the maximum heat transfer performance has been decreased which is proportional to the increase in p/d and h/d. Moreover, the maximum heat transfer performance in 2,000 Reynolds number is 1.5 proportional to p/d of 0.61 and h/d of 0.36, while for 10,000 Reynolds number, its value is 1.19 in high p/d of 0.93 and h/d of 0.15. The approaches of the present study can be used for optimizing heat transfer performance where geometrical dimensions are not accessible or the rectangular baffle has been applied for heat transfer enhancement.

Heat Transfer Enhancement in a Rectangular (AR = 3:1) Channel With V-Shaped Dimples

2012 ◽  
Vol 135 (1) ◽  
Author(s):  
C. Neil Jordan ◽  
Lesley M. Wright
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Liquid Crystal ◽  
Pressure Drop ◽  
Heat Transfer Enhancement ◽  
Thermal Performance ◽  
Secondary Flows ◽  
Transfer Enhancement ◽  
Reduced Pressure

An alternative to ribs for internal heat transfer enhancement of gas turbine airfoils is dimpled depressions. Relative to ribs, dimples incur a reduced pressure drop, which can increase the overall thermal performance of the channel. This experimental investigation measures detailed Nusselt number ratio distributions obtained from an array of V-shaped dimples (δ/D = 0.30). Although the V-shaped dimple array is derived from a traditional hemispherical dimple array, the V-shaped dimples are arranged in an in-line pattern. The resulting spacing of the V-shaped dimples is 3.2D in both the streamwise and spanwise directions. A single wide wall of a rectangular channel (AR = 3:1) is lined with V-shaped dimples. The channel Reynolds number ranges from 10,000–40,000. Detailed Nusselt number ratios are obtained using both a transient liquid crystal technique and a newly developed transient temperature sensitive paint (TSP) technique. Therefore, the TSP technique is not only validated against a baseline geometry (smooth channel), but it is also validated against a more established technique. Measurements indicate that the proposed V-shaped dimple design is a promising alternative to traditional ribs or hemispherical dimples. At lower Reynolds numbers, the V-shaped dimples display heat transfer and friction behavior similar to traditional dimples. However, as the Reynolds number increases to 30,000 and 40,000, secondary flows developed in the V-shaped concavities further enhance the heat transfer from the dimpled surface (similar to angled and V-shaped rib induced secondary flows). This additional enhancement is obtained with only a marginal increase in the pressure drop. Therefore, as the Reynolds number within the channel increases, the thermal performance also increases. While this trend has been confirmed with both the transient TSP and liquid crystal techniques, TSP is shown to have limited capabilities when acquiring highly resolved detailed heat transfer coefficient distributions.

Heat Transfer Performance of Different Nanofluids Flows in a Helically Coiled Heat Exchanger

2013 ◽  
Vol 832 ◽  
pp. 160-165 ◽  
Author(s):  
Mohammad Alam Khairul ◽  
Rahman Saidur ◽  
Altab Hossain ◽  
Mohammad Abdul Alim ◽  
Islam Mohammed Mahbubul
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Heat Exchanger ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Friction Factor ◽  
Heat Exchangers ◽  
Heat Transfer Performance ◽  
Volume Concentration ◽  
Transfer Performance

Helically coiled heat exchangers are globally used in various industrial applications for their high heat transfer performance and compact size. Nanofluids can provide excellent thermal performance of this type of heat exchangers. In the present study, the effect of different nanofluids on the heat transfer performance in a helically coiled heat exchanger is examined. Four different types of nanofluids CuO/water, Al2O3/water, SiO2/water, and ZnO/water with volume fractions 1 vol.% to 4 vol.% was used throughout this analysis and volume flow rate was remained constant at 3 LPM. Results show that the heat transfer coefficient is high for higher particle volume concentration of CuO/water, Al2O3/water and ZnO/water nanofluids, while the values of the friction factor and pressure drop significantly increase with the increase of nanoparticle volume concentration. On the contrary, low heat transfer coefficient was found in higher concentration of SiO2/water nanofluids. The highest enhancement of heat transfer coefficient and lowest friction factor occurred for CuO/water nanofluids among the four nanofluids. However, highest friction factor and lowest heat transfer coefficient were found for SiO2/water nanofluids. The results reveal that, CuO/water nanofluids indicate significant heat transfer performance for helically coiled heat exchanger systems though this nanofluids exhibits higher pressure drop.

A Study on Flow Boiling in Microchannel With Piranha Pin Fin

2015 ◽  
Author(s):  
X. Yu ◽  
C. Woodcock ◽  
Y. Wang ◽  
J. Plawsky ◽  
Y. Peles
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Fluid Flow ◽  
Pressure Drop ◽  
Heat Transfer Performance ◽  
Flow Boiling ◽  
Transfer Performance ◽  
Flow Conditions ◽  
Pin Fin ◽  
Flow And Heat Transfer

In this paper we reported an advanced structure, the Piranha Pin Fin (PPF), for microchannel flow boiling. Fluid flow and heat transfer performance were evaluated in detail with HFE7000 as working fluid. Surface temperature, pressure drop, heat transfer coefficient and critical heat flux (CHF) were experimentally obtained and discussed. Furthermore, microchannels with different PPF geometrical configurations were investigated. At the same time, tests for different flow conditions were conducted and analyzed. It turned out that microchannel with PPF can realize high-heat flux dissipation with reasonable pressure drop. Both flow conditions and PPF configuration played important roles for both fluid flow and heat transfer performance. This study provided useful reference for further PPF design in microchannel for flow boiling.

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