scholarly journals Thermal Optimisation of Longitudinal Ribs in Variable Geometry Ducts

1997 ◽  
Author(s):  
S. Naik ◽  
S. D. Probert
Keyword(s):  
Heat Transfer ◽  
Gas Turbine ◽  
Structural Integrity ◽  
Turbine Blades ◽  
Variable Geometry ◽  
Maximum Heat ◽  
Operational Conditions ◽  
Longitudinal Ribs ◽  
Maximum Heat Transfer ◽  
Wide Range

Augmenting the heat transfer rates in the internal flow passages of several components of a gas turbine, such as the turbine blades, vanes and combustor walls is an important pre-requisite for maintaining their structural integrity. This is particularly paramount when higher turbine inlet temperatures and pressure ratios are utilised for enhancing the thermal efficiencies of the gas turbine plant. In this study, the heat transfer enhancement, which can be achieved by longitudinal ribs in a variable geometry duct, has been examined. With the base of the ribs maintained at a constant temperature, it was observed that the optimal rib spacing, which corresponded to the maximum heat transfer from the ribs, was a strong function of the rib height to length ratio and the Reynolds number but relatively insensitive to the amount of clearance above the ribs. A design correlation is proposed which shows the distribution of this optimal rib spacing for a wide range of rib geometrical and operational conditions. Comparisons of the longitudinal ribs with pin fin arrays indicated that at rib height to length ratios of ≥ 0.24, higher heat transfers can be achieved with the longitudinal ribs. The frictional characteristics of the longitudinal ribs is comparable to those of circular pin fins. Measurements of the local heat transfer coefficient for the rib surfaces indicate that it is highly non-uniform along the rib height and length and also significantly influenced by the amount of clearance above the ribs. For all the cases examined, it was observed that developing flow conditions (thermally and hydrodynamically) were prevalent within the longitudinal rib channels.

scholarly journals Investigation of the novelty of latent functionally thermal fluids as alternative to nanofluids in natural convective flows

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Zoubida Haddad ◽  
Farida Iachachene ◽  
Eiyad Abu-Nada ◽  
Ioan Pop
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Transfer Enhancement ◽  
Volume Fraction ◽  
Heat Of Fusion ◽  
Transfer Enhancement ◽  
Maximum Heat ◽  
Thermal Fluids ◽  
Maximum Heat Transfer ◽  
Wide Range

AbstractThis paper presents a detailed comparison between the latent functionally thermal fluids (LFTFs) and nanofluids in terms of heat transfer enhancement. The problem used to carry the comparison is natural convection in a differentially heated cavity where LFTFs and nanofluids are considered the working fluids. The nanofluid mixture consists of Al2O3 nanoparticles and water, whereas the LFTF mixture consists of a suspension of nanoencapsulated phase change material (NEPCMs) in water. The thermophysical properties of the LFTFs are derived from available experimental data in literature. The NEPCMs consist of n-nonadecane as PCM and poly(styrene-co-methacrylic acid) as shell material for the encapsulation. Finite volume method is used to solve the governing equations of the LFTFs and the nanofluid. The computations covered a wide range of Rayleigh number, 104 ≤ Ra ≤ 107, and nanoparticle volume fraction ranging between 0 and 1.69%. It was found that the LFTFs give substantial heat transfer enhancement compared to nanofluids, where the maximum heat transfer enhancement of 13% was observed over nanofluids. Though the thermal conductivity of LFTFs was 15 times smaller than that of the base fluid, a significant enhancement in thermal conductivity was observed. This enhancement was attributed to the high latent heat of fusion of the LFTFs which increased the energy transport within the cavity and accordingly the thermal conductivity of the LFTFs.

Entropy Generation in Laminar and Turbulent Natural Convection Heat Transfer From Vertical Cylinder With Annular Fins

2017 ◽  
Vol 139 (4) ◽  
Author(s):  
Jnana Ranjan Senapati ◽  
Sukanta Kumar Dash ◽  
Subhransu Roy
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Entropy Generation ◽  
Vertical Cylinder ◽  
Turbulent Regime ◽  
Maximum Heat ◽  
Turbulent Natural Convection ◽  
Maximum Heat Transfer ◽  
Wide Range ◽  
Annular Fins

Entropy generation due to natural convection has been calculated for a wide range of Rayleigh number (Ra) in both laminar (104 ≤ Ra ≤ 108) and turbulent (1010 ≤ Ra ≤ 1012) flow regimes, for diameter ratio of 2 ≤ D/d ≤ 5, for an isothermal vertical cylinder fitted with annular fins. In the laminar regime, the entropy generation was predominantly caused by heat transfer (conduction and convection) and the viscous contribution was negligible with respect to heat transfer. But in the turbulent regime, entropy generation due to fluid friction is significant enough although heat transfer entropy generation is still dominant. The results demonstrate that the degree of irreversibility is higher in case of finned configuration when compared with unfinned one. With the deployment of a merit function combining the first and second laws of thermodynamics, we have tried to delineate the thermodynamic performance of finned cylinder with natural convection. So, we have defined the ratio (I/Q)finned/(I/Q)unfinned. The ratio (I/Q)finned/(I/Q)unfinned gets its minimum value at optimum fin spacing where maximum heat transfer occurs in turbulent flow, whereas in laminar flow the ratio (I/Q)finned/(I/Q)unfinned decreases continuously with the increase in number of fins.

Determination of Optimal Row Spacing for a Staggered Cross-Pin Array in a Turbine Blade Cooling Passage

1998 ◽  
Author(s):  
E. E. Donahoo ◽  
A. K. Kulkarni ◽  
A. D. Belegundu ◽  
C. Camci
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Total Pressure ◽  
Reynolds Numbers ◽  
Steady Increase ◽  
Maximum Heat ◽  
High Heat Transfer ◽  
Maximum Heat Transfer ◽  
Wide Range ◽  
Cooling Passage

Crosspin configurations are of interest in turbine blade design due to the enhanced cooling they provide. In addition, crosspins which extend from the walls of hollow blades provide structural integrity and stiffness to the blade itself. Numerous crosspin shapes and arrangements are possible, but only certain combinations offer high heat transfer capability while maintaining low overall total pressure loss. This study presents results from 2-D numerical simulations of coolant airflow through a turbine blade internal cooling passage. The simulations model viscous flow and heat transfer over circular pins in a staggered arrangement of varying pin spacing. Preliminary analysis over a wide range of Reynolds numbers indicates existence of an optimal spacing for which maximum heat transfer and minimum total pressure drop occurs. Pareto plots, which graphically identify the optimum data points with multiple optimization parameters, were obtained for a range of Reynolds numbers and streamwise soarings in a staggered crosspin arrangement. There is a steady increase in crosspin heat transfer up to a certain number of rows, then a gradual decrease in heat transfer in subsequent rows. Knowledge obtained from such findings can be used to determine the number of crosspins used, as well as the ultimate pin arrangement.

scholarly journals Heat Transfer and Hydrodynamic Properties Using Different Metal-Oxide Nanostructures in Horizontal Concentric Annular Tube: An Optimization Study

Nanomaterials ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 1979
Author(s):  
Omer A. Alawi ◽  
Ali H. Abdelrazek ◽  
Mohammed Suleman Aldlemy ◽  
Waqar Ahmed ◽  
Omar A. Hussein ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Three Dimensional ◽  
Flux Ratio ◽  
Hydrodynamic Properties ◽  
Maximum Heat ◽  
Aspect Ratios ◽  
Maximum Heat Transfer ◽  
Optimization Study ◽  
Wide Range ◽  
Metal Oxide Nanostructures

Numerical studies were performed to estimate the heat transfer and hydrodynamic properties of a forced convection turbulent flow using three-dimensional horizontal concentric annuli. This paper applied the standard k–ε turbulence model for the flow range 1 × 104 ≤ Re ≥ 24 × 103. A wide range of parameters like different nanomaterials (Al2O3, CuO, SiO2 and ZnO), different particle nanoshapes (spherical, cylindrical, blades, platelets and bricks), different heat flux ratio (HFR) (0, 0.5, 1 and 2) and different aspect ratios (AR) (1.5, 2, 2.5 and 3) were examined. Also, the effect of inner cylinder rotation was discussed. An experiment was conducted out using a field-emission scanning electron microscope (FE-SEM) to characterize metallic oxides in spherical morphologies. Nano-platelet particles showed the best enhancements in heat transfer properties, followed by nano-cylinders, nano-bricks, nano-blades, and nano-spheres. The maximum heat transfer enhancement was found in SiO2, followed by ZnO, CuO, and Al2O3, in that order. Meanwhile, the effect of the HFR parameter was insignificant. At Re = 24,000, the inner wall rotation enhanced the heat transfer about 47.94%, 43.03%, 42.06% and 39.79% for SiO2, ZnO, CuO and Al2O3, respectively. Moreover, the AR of 2.5 presented the higher heat transfer improvement followed by 3, 2, and 1.5.

Numerical Modeling of Buoyancy Induced Convection in Finned Heat Sinks in Presence of Unheated and Heated Shrouds

2005 ◽  
Author(s):  
S. S. Bahga ◽  
A. Bhattacharya ◽  
Roop L. Mahajan
Keyword(s):  
Heat Transfer ◽  
Thermal Performance ◽  
Heat Sink ◽  
Numerical Study ◽  
Numerical Results ◽  
Heat Sinks ◽  
Maximum Heat ◽  
Maximum Heat Transfer ◽  
Wide Range ◽  
The Impact

This paper investigates the effects of the presence of unheated and heated shrouds on the thermal performance of longitudinal finned heat sinks. A comprehensive numerical study was conducted to determine the impact of the shroud clearance from the tip of the fins and shroud heating. The first part of the study deals with the effects of an unheated shroud on finned heat sinks of different fin height, fin pitch and length in an attempt to cover a wide range of geometry. The numerical results reveal an optimum clearance for maximum heat transfer. For all heat sinks studied the unheated shroud improved the performance by as much as 15% until the shroud was very close when the performance decreased by as much as 10%. In the second part of the paper, the effects of heating of the shroud were considered. In these numerical runs, an isothermal boundary condition was imposed on the shroud. For the heating levels considered, it was found that heating of the shrouds can increase or lower the thermal performance of the heat sink depending on the heat sink geometry and shroud clearance. Finally, the numerical results also revealed a systematic dependence of the normalized Nusselt number on the Rayleigh number for a given heat sink geometry.

Impingement Cooling Performance in Gas Turbine Airfoils Including Effects of Leading Edge Sharpness

1972 ◽  
Vol 94 (3) ◽  
pp. 219-225 ◽  
Author(s):  
D. E. Metzger ◽  
R. T. Baltzer ◽  
C. W. Jenkins
Keyword(s):  
Heat Transfer ◽  
Gas Turbine ◽  
Leading Edge ◽  
Maximum Heat ◽  
Turbine Engine ◽  
Transfer Rates ◽  
Maximum Heat Transfer ◽  
Circular Jets ◽  
Edge Sharpness ◽  
Turbine Airfoils

An experimental study of the heat transfer characteristics of impingement into cavities which model the cooled leading edges of gas turbine engine airfoils is presented. The study includes both two-dimensional slot jets and single lines of evenly-spaced circular jets. For broad cylindrical cavities correlations are given for the maximum heat transfer rates attainable with optimum positioning of the jet nozzle with respect to the cooled surface. For elongated narrow cavities heat transfer rates relative to these maximum values are presented for a variety of cavity shapes.

scholarly journals A MCDM Methodology to Determine the Most Critical Variables in the Pressure Drop and Heat Transfer in Minichannels

Energies ◽  
2021 ◽  
Vol 14 (8) ◽  
pp. 2069
Author(s):  
Eloy Hontoria ◽  
Alejandro López-Belchí ◽  
Nolberto Munier ◽  
Francisco Vera-García
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Heat Exchangers ◽  
Saturation Pressure ◽  
Computational Cost ◽  
Urban Systems ◽  
Condensation Process ◽  
Geometrical Parameters ◽  
Maximum Heat ◽  
Maximum Heat Transfer

This paper proposes a methodology aiming at determining the most influent working variables and geometrical parameters over the pressure drop and heat transfer during the condensation process of several refrigerant gases using heat exchangers with pipes mini channels technology. A multi-criteria decision making (MCDM) methodology was used; this MCDM includes a mathematical method called SIMUS (Sequential Interactive Modelling for Urban Systems) that was applied to the results of 2543 tests obtained by using a designed refrigeration rig in which five different refrigerants (R32, R134a, R290, R410A and R1234yf) and two different tube geometries were tested. This methodology allows us to reduce the computational cost compared to the use of neural networks or other model development systems. This research shows six variables out of 39 that better define simultaneously the minimum pressure drop, as well as the maximum heat transfer, saturation pressure fluid entering the condenser being the most important one. Another aim of this research was to highlight a new methodology based on operation research for their application to improve the heat transfer energy efficiency and reduce the CO2 footprint derived of the use of heat exchangers with minichannels.

scholarly journals Significance of Shape Factor in Heat Transfer Performance of Molybdenum-Disulfide Nanofluid in Multiple Flow Situations; A Comparative Fractional Study

Molecules ◽  
2021 ◽  
Vol 26 (12) ◽  
pp. 3711
Author(s):  
Asifa ◽  
Talha Anwar ◽  
Poom Kumam ◽  
Zahir Shah ◽  
Kanokwan Sitthithakerngkiet
Keyword(s):  
Heat Transfer ◽  
Skin Friction ◽  
Molybdenum Disulfide ◽  
Heat Transfer Rate ◽  
Shape Factor ◽  
Transfer Rate ◽  
Maximum Heat ◽  
Left Wall ◽  
Maximum Heat Transfer ◽  
Mos2 Nanoparticles

In this modern era, nanofluids are considered one of the advanced kinds of heat transferring fluids due to their enhanced thermal features. The present study is conducted to investigate that how the suspension of molybdenum-disulfide (MoS2) nanoparticles boosts the thermal performance of a Casson-type fluid. Sodium alginate (NaAlg) based nanofluid is contained inside a vertical channel of width d and it exhibits a flow due to the movement of the left wall. The walls are nested in a permeable medium, and a uniform magnetic field and radiation flux are also involved in determining flow patterns and thermal behavior of the nanofluid. Depending on velocity boundary conditions, the flow phenomenon is examined for three different situations. To evaluate the influence of shape factor, MoS2 nanoparticles of blade, cylinder, platelet, and brick shapes are considered. The mathematical modeling is performed in the form of non-integer order operators, and a double fractional analysis is carried out by separately solving Caputo-Fabrizio and Atangana-Baleanu operators based fractional models. The system of coupled PDEs is converted to ODEs by operating the Laplace transformation, and Zakian’s algorithm is applied to approximate the Laplace inversion numerically. The solutions of flow and energy equations are presented in terms of graphical illustrations and tables to discuss important physical aspects of the observed problem. Moreover, a detailed inspection on shear stress and Nusselt number is carried out to get a deep insight into skin friction and heat transfer mechanisms. It is analyzed that the suspension of MoS2 nanoparticles leads to ameliorating the heat transfer rate up to 9.5%. To serve the purpose of achieving maximum heat transfer rate and reduced skin friction, the Atangana-Baleanu operator based fractional model is more effective. Furthermore, it is perceived that velocity and energy functions of the nanofluid exhibit significant variations because of the different shapes of nanoparticles.

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

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.

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