MODELING OF HEAT EXCHANGE AT TURBULENT FLOW IN FLAT CHANNELS WITH SYMMETRIC TURBULIZERS ON BOTH PARTIES

Objectives. Mathematical modeling of heat transfer in flat channels with turbulators symmetrically located on both its sides, depending on the cross section of the turbulators.Methods. The calculation was carried out on the basis of a theoretical method based on solving the Reynolds equations factorized by the finite-volume finite-volume method, closed using the Menter shear stress transfer model, and the energy equation on multi-scale intersecting structured grids (FCOM), which was successfully tested in [23].Results. The article results of calculating the intensified heat exchange in flat channels with double turbulators of different cross sections (square, rectangular, semicircular, triangular) depending on the determining parameters were quite satisfactorily consistent with the existing experimental material, but having an indisputable advantage over the latter, since the assumptions made in their derivation cover a much wider range of defining parameters than the limitations found in the experiments (Pr=0.7÷100, Re=103÷106, h/dE =0.005÷0.2, t/h=1÷200).Conclusion. According to the results of calculations on the basis of the developed model, it is possible to optimize heat transfer intensification in flat channels with double turbulators of different cross sections, as well as control the heat transfer intensification process. As shown by the calculated data, with the intensification of heat transfer in the flat channels, symmetrical protrusions of square, rectangular and triangular cross sections, i.e. relatively sharp outlines, in the vortices up to the protrusions and behind them the production of turbulence is comparable to energy dissipation, which leads to increased hydraulic losses; for flat channels with protrusions of a semicircular cross section, i.e. relatively smooth outlines, the energy dissipation is much smaller, therefore, the hydraulic resistance in such channels is less. A detailed analysis of the structure of the vortex zones (main, angular, secondary, etc.) between periodic surface flow turbulators of square, semicircular, triangular and rectangular cross sections depending on the geometric and regime parameters of the coolant flow was carried out, the effect of the above vortex zones heat transfer and hydraulic resistance of the channel; additionally confirmed the optimality of application to abrutized turbulators, where hydraulic losses are much smaller than for sharp turbulators, which is directly or indirectly verified by existing experimental material [1—6].

Download Full-text

Low-Reynolds Simulation of Heat Transfer in Turbulent Flow in a Flat Channel with Symmetrically Arranged Turbulators on Both Sides of the Channel

Journal of Chemistry Education Research and Practice ◽

10.33140/jcerp.04.01.04 ◽

2020 ◽

Vol 4 (1) ◽

Keyword(s):

Heat Transfer ◽

Heat Exchange ◽

Cross Section ◽

Heat Exchangers ◽

Thermal Loading ◽

Flat Channel ◽

Heat Transfer Intensification ◽

Heat Flows ◽

Heat Exchange Surface ◽

Exchange Surface

Widespread use in modern heat exchangers and apparatus received heat exchangers, where the channels have a cross-section, different from the round tubes, in a particular case, flat channels, where heat is not produced by means of a full surface to be washed. The thermal loading of a flat channel can be asymmetric, since the heat flows on different surfaces can be unequal, namely: flat channels with one-way heating or with two-way heating with unequal heat flows. In order to ensure the compactness of heat exchange devices and heat exchange apparatuses, heat transfer intensification is used, which in flat channels is achievable by two main methods: the development of the heat exchange surface and turbulence of the flow in the channels.

Download Full-text

The Effect of Regulating Elements on Convective Heat Transfer along Shaped Heat Exchange Surfaces

Chemical and Process Engineering ◽

10.2478/cpe-2013-0002 ◽

2013 ◽

Vol 34 (1) ◽

pp. 5-16 ◽

Cited By ~ 3

Author(s):

Jozef Cernecky ◽

Jan Koniar ◽

Zuzana Brodnianska

Keyword(s):

Heat Transfer ◽

Heat Exchange ◽

Cfd Simulation ◽

Local Heat Transfer ◽

Local Heat ◽

Temperature Fields ◽

Transfer Coefficients ◽

Heat Transfer Intensification ◽

Heat Transfer Coefficients ◽

Forced Air

Abstract The paper deals with a study of the effect of regulating elements on local values of heat transfer coefficients along shaped heat exchange surfaces with forced air convection. The use of combined methods of heat transfer intensification, i.e. a combination of regulating elements with appropriately shaped heat exchange areas seems to be highly effective. The study focused on the analysis of local values of heat transfer coefficients in indicated cuts, in distances expressed as a ratio x/s for 0; 0.33; 0.66 and 1. As can be seen from our findings, in given conditions the regulating elements can increase the values of local heat transfer coefficients along shaped heat exchange surfaces. An optical method of holographic interferometry was used for the experimental research into temperature fields in the vicinity of heat exchange surfaces. The obtained values correspond very well with those of local heat transfer coefficients αx, recorded in a CFD simulation.

Download Full-text

Thermo-Hydraulic Performance of U-Tube Borehole Heat Exchanger with Different Cross-Sections

Sustainability ◽

10.3390/su13063255 ◽

2021 ◽

Vol 13 (6) ◽

pp. 3255

Author(s):

Aizhao Zhou ◽

Xianwen Huang ◽

Wei Wang ◽

Pengming Jiang ◽

Xinwei Li

Keyword(s):

Heat Transfer ◽

Heat Exchange ◽

Heat Resistance ◽

Cross Sections ◽

Three Dimensional ◽

Thermal Response ◽

Transfer Efficiency ◽

Cross Sectional ◽

Heat Transfer Efficiency ◽

Oval Tube

For reducing the initial GSHP investment, the heat transfer efficiency of the borehole heat exchange (BHE) system can be enhanced to reduce the number or depth of drilling. This paper proposes a novel and simple BHE design by changing the cross-sectional shape of the U-tube to increase the heat transfer efficiency of BHEs. Specifically, in this study, we (1) verified the reliability of the three-dimensional numerical model based on the thermal response test (TRT) and (2) compared the inlet and outlet temperatures of the different U-tubes at 48 h under the premise of constant leg distance and fluid area. Referent to the circular tube, the increases in the heat exchange efficiencies of the curved oval tube, flat oval tube, semicircle tube, and sector tube were 13.0%, 19.1%, 9.4%, and 14.8%, respectively. (3) The heat flux heterogeneity of the tubes on the inlet and outlet sides of the BHE, in decreasing order, is flat oval, semicircle, curved oval, sector, and circle shapes. (4) The temperature heterogeneity of the borehole wall in the BHE in decreasing order is circle, sector, curved oval, flat oval, and semicircle shapes. (5) Under the premise of maximum leg distance, referent to the heat resistance of the tube with a circle shape at 48 h, the heat exchange efficiency of the curved oval, flat oval, semicircle, and sector tubes increased 12.6%, 17.7%, 10.3%, and 7.8%, respectively. (6) We found that the adjustments of the leg distance and the tube shape affect the heat resistance by about 25% and 12%, respectively. (7) The flat-oval-shaped tube at the maximum leg distance was found to be the best tube design for BHEs.

Download Full-text

Effect of liquid cooling on PCR performance with the parametric study of cross-section shapes of microchannels

Scientific Reports ◽

10.1038/s41598-021-95446-0 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Yousef Alihosseini ◽

Mohammad Reza Azaddel ◽

Sahel Moslemi ◽

Mehdi Mohammadi ◽

Ali Pormohammad ◽

...

Keyword(s):

Heat Transfer ◽

Cross Section ◽

Cross Sections ◽

Heat Sink ◽

Evaluation Criteria ◽

Circular Cross Section ◽

Microchannel Heat Sink ◽

Liquid Cooling ◽

Maximum Heat ◽

Maximum Heat Transfer

AbstractIn recent years, PCR-based methods as a rapid and high accurate technique in the industry and medical fields have been expanded rapidly. Where we are faced with the COVID-19 pandemic, the necessity of a rapid diagnosis has felt more than ever. In the current interdisciplinary study, we have proposed, developed, and characterized a state-of-the-art liquid cooling design to accelerate the PCR procedure. A numerical simulation approach is utilized to evaluate 15 different cross-sections of the microchannel heat sink and select the best shape to achieve this goal. Also, crucial heat sink parameters are characterized, e.g., heat transfer coefficient, pressure drop, performance evaluation criteria, and fluid flow. The achieved result showed that the circular cross-section is the most efficient shape for the microchannel heat sink, which has a maximum heat transfer enhancement of 25% compared to the square shape at the Reynolds number of 1150. In the next phase of the study, the circular cross-section microchannel is located below the PCR device to evaluate the cooling rate of the PCR. Also, the results demonstrate that it takes 16.5 s to cool saliva samples in the PCR well, which saves up to 157.5 s for the whole amplification procedure compared to the conventional air fans. Another advantage of using the microchannel heat sink is that it takes up a little space compared to other common cooling methods.

Download Full-text

Numerical Simulating Open-Channel Flows with Regular and Irregular Cross-Section Shapes Based on Finite Volume Godunov-Type Scheme

International Journal of Computational Methods ◽

10.1142/s0219876220500474 ◽

2020 ◽

pp. 2050047

Author(s):

Xiaokang Xin ◽

Fengpeng Bai ◽

Kefeng Li

Keyword(s):

Finite Volume ◽

Cross Section ◽

Cross Sections ◽

Open Channel ◽

Arbitrary Cross Section ◽

Second Order ◽

Cross Sectional ◽

Shallow Flows ◽

Natural Streams ◽

Saint Venant Equations

A numerical model based on the Saint-Venant equations (one-dimensional shallow water equations) is proposed to simulate shallow flows in an open channel with regular and irregular cross-section shapes. The Saint-Venant equations are solved by the finite-volume method based on Godunov-type framework with a modified Harten, Lax, and van Leer (HLL) approximate Riemann solver. Cross-sectional area is replaced by water surface level as one of primitive variables. Two numerical integral algorithms, compound trapezoidal and Gauss–Legendre integrations, are used to compute the hydrostatic pressure thrust term for natural streams with arbitrary and irregular cross-sections. The Monotonic Upstream-Centered Scheme for Conservation Laws (MUSCL) and second-order Runge–Kutta methods is adopted to achieve second-order accuracy in space and time, respectively. The performance of the resulting scheme is evaluated by application in rectangular channels, trapezoidal channels, and a natural mountain river. The results are compared with analytical solutions and experimental or measured data. It is demonstrated that the numerical scheme can simulate shallow flows with arbitrary cross-section shapes in practical conditions.

Download Full-text

Heat Transfer Characteristics of Various Gun Barrels Under Different Operating Conditions

Volume 8: Heat Transfer and Thermal Engineering ◽

10.1115/imece2019-12083 ◽

2019 ◽

Author(s):

Mohamed Gadalla ◽

Muhammad Jasim ◽

Omar Ahmad

Keyword(s):

Heat Transfer ◽

Thermal Management ◽

Cross Section ◽

Wall Temperature ◽

Circular Cross Section ◽

Typical Case ◽

Operating Conditions ◽

Firing Process ◽

Transfer Model ◽

Gun Barrel

Abstract The thermal stability parameter is an important parameter for predicting the lifespan of structures. In this paper, a two-dimensional transient heat transfer model of machine gun barrels undergoing continuous firing developed and analyzed for different geometries and thermal properties. The model for the transient thermal analysis is based on the forced convection heat transfer at the inner surface of the gun barrel. Finite element simulations were performed to predict the interior and exterior barrel temperature profiles and temperature contours after continuous firing process. The incomplete Cholesky Conjugate Gradient (ICCG) solver was adopted in solving unsymmetrical thermal transient analyses. The material thermal behavior studied for the basic circular cross section of gun barrels showed that the lowest inner wall temperature was for high rounds was achieved in steel barrels due to the rapid conducted and convective heat transfer to the environment. While the highest inner wall temperature was recorded for ceramic STK4 barrels and an increase of inner wall temperature by 17% was observed as compared to the typical case of circular cross section steel barrel. In general, a higher inner temperature in the gun barrel is undesirable and harm due to the possibility of reaching the cook-off scenario at earlier rounds. Results concluded that non-circular geometries with constrained cross section areas of typical case improve thermal management and the hexagonal geometry had the best thermal management and could provide more rounds for users. In addition, titanium barrels would have a weight drop of 41% while the overall barrel’s temperature increases by 49%.

Download Full-text

A Variational Method for Fully Developed Laminar Heat Transfer in Ducts

Journal of Heat Transfer ◽

10.1115/1.4008164 ◽

1959 ◽

Vol 81 (2) ◽

pp. 157-164 ◽

Cited By ~ 36

Author(s):

E. M. Sparrow ◽

R. Siegel

Keyword(s):

Heat Transfer ◽

Laminar Flow ◽

Variational Method ◽

Cross Section ◽

Cross Sections ◽

Axial Direction ◽

Circular Sector ◽

Thermal Boundary Conditions ◽

Temperature Distributions ◽

Good Agreement

A variational method is presented for determining fully developed velocity and temperature distributions for laminar flow in noncircular ducts. The heat addition to the fluid is taken to be uniform in the axial direction, but a variety of thermal boundary conditions are considered around the periphery of the duct cross section. Several illustrative examples are given, and comparisons are made which show good agreement with available exact solutions. These examples include ducts of rectangular and circular-sector cross sections.

Download Full-text