scholarly journals Numerical Investigation of Heat Transfer Rate in Helically Coiled Pipe Using Al2O3/Water Nanofluid

2020 ◽  
Vol 13 (4) ◽  
pp. 27-36
Author(s):  
Ahmed F. Hasan
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Pure Water ◽  
Outer Wall ◽  
Reynolds Numbers ◽  
Nano Fluid ◽  
High Reynolds ◽  
Better Than

Nanofluid materials play an important role in the industry nowadays, which has drawn the attention of researchers to enhance the characteristics of the heat transfer of the fluids in the coiled shape heat exchangers. The effect of using Al2O3/water Nano fluid on the characteristic of the heat transfer rate inside the helically coiled pipe was numerically studied at different Reynolds numbers. Moreover, fluid flow analyses were investigated numerically in terms of pressure and velocity profile. The heat transfer enhancement using this Nano fluid has been studied and then compared to pure water at Reynolds number values of 200, 600, and 1500 respectively. The results showed that a reduction in the temperature of the outer wall pipe when Al2O3/water Nano fluid was applied particularly at a low Reynolds number compared to pure water. Generally speaking, it has been seen that the reduction in the temperature profile is much better than the high Reynolds number.

Optimal Ratio of Heat Removal Rate to Pumping Power for PCM Emulsion Fluids: Low Reynolds Number Limits

2006 ◽  
Author(s):  
P. Maloji ◽  
Y.-X. Tao
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Phase Change ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Removal Rate ◽  
Pure Water ◽  
Heat Removal ◽  
Pumping Power ◽  
Optimal Ratio

There are many applications where high heat transfer removal rate in a limited tight space are required. The applications include mini and micro-scale channels flows in compact heat exchangers. The increase in heat transfer rate often requires the significant increase in fluid velocity and therefore the increase in the pumping power. One option is to utilize Phase Change Materials (PCM). This study contributes to the further understanding of performance enhancement of an improved heat transfer fluid by studying the optimal ratio of heat removal rate to the fluid pumping power. PCMs have the unique characteristics that can increase the thermal capacity of heat transfer fluids by providing latent heat capacity at a temperature different than the melting point of the carrier fluid. The ratio of heat transfer rate (Q) to fluid pumping power (P) is about twice as that for using pure water without PCM particles. The effectiveness factor (compared to water without PCM) is also doubled. It has been observed that as Re decreases the effective factor increases and Q/P ratio increases, which is also true if the concentration of PCM increases. In this experimental study focuses are on the heat transfer enhancement effects for very low Reynolds number (Re < 180 of pure water velocity) and PCM concentration slurry flow of 10% to 20%. Experimental investigations relevant to PCM slurry flows are carried out. Experimental results indicate that PCM slurry's heat transfer coefficient and apparent specific heat are affected significantly by the phase change process and the slurry mass fraction. It is found that the Q/P ratio primarily is a function of Reynolds number.

Thermal Performance Assessment of Turbulent Flow Through Dimpled Tubes

2010 ◽  
Author(s):  
Pornchai Nivesrangsan ◽  
Somsak Pethkool ◽  
Kwanchai Nanan ◽  
Monsak Pimsarn ◽  
Smith Eiamsa-ard
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Friction Factor ◽  
Heat Transfer Rate ◽  
Thermal Performance ◽  
Transfer Rate ◽  
Staggered Arrangement ◽  
Plain Tube ◽  
Pitch Ratio ◽  
Surface Patterns

This paper presents the heat transfer augmentation and friction factor characteristics by means of dimpled tubes. The experiments were conducted using the dimpled tubes with two different dimpled-surface patterns including aligned arrangement (A-A) and staggered arrangement (S-A), each with two pitch ratios (PR = p/Di = 0.6 and 1.0), for Reynolds number ranging from 9800 to 67,000. The experimental results achieved from the dimpled tubes are compared with those obtained from the plain tube. Evidently, the dimpled tubes with both arrangements offer higher heat transfer rates compared to the plain tube and the dimpled tube with staggered arrangement shows an advantage on the basis of heat transfer enhancement over the dimpled tube with aligned arrangement. The increase in heat transfer rate with reducing pitch ratio is due to the higher turbulent intensity imparted to the flow between the dimple surfaces. The mean heat transfer rate offered by the dimpled tube with staggered arrangement (S-A) at the lowest pitch ratio (PR = 0.6), is higher than those provided by the plain tube and the dimpled tube with aligned arrangement (A-A) at the same PR by around 127% and 8%, respectively. The empirical correlations developed in terms of pitch ratio (PR), Prandtl number (Pr) and Reynolds number, are fitted the experimental data within ±8% and ±2% for Nusselt number (Nu) and friction factor (f), respectively. In addition, the thermal performance factors under an equal pumping power constraint of the dimple tubes for both dimpled-surface arrangements are also determined.

Heat Transfer Investigation of a Tube Partially Wrapped by Metal Porous Layer as a Potential Novel Tube for Air Cooled Heat Exchangers

2018 ◽  
Vol 141 (1) ◽  
Author(s):  
M. Mohammadpour-Ghadikolaie ◽  
M. Saffar-Avval ◽  
Z. Mansoori ◽  
N. Alvandifar ◽  
N. Rahmati
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Heat Transfer Rate ◽  
Porous Layer ◽  
Transfer Rate ◽  
Metal Foam ◽  
Convection Heat Transfer ◽  
Darcy Number ◽  
High Heat Transfer

Laminar forced convection heat transfer from a constant temperature tube wrapped fully or partially by a metal porous layer and subjected to a uniform air cross-flow is studied numerically. The main aim of this study is to consider the thermal performance of some innovative arrangements in which only certain parts of the tube are covered by metal foam. The combination of Navier–Stokes and Darcy–Brinkman–Forchheimer equations is applied to evaluate the flow field. Governing equations are solved using the finite volume SIMPLEC algorithm and the effects of key parameters such as Reynolds number, metal foam thermophysical properties, and porous layer thickness on the Nusselt number are investigated. The results show that using a tube which is fully wrapped by an external porous layer with high thermal conductivity, high Darcy number, and low drag coefficient, can provide a high heat transfer rate in the high Reynolds number laminar flow, increasing the Nusselt number almost as high as 16 times compared to a bare tube. The most important result of thisstudy is that by using some novel arrangements in which the tube is partially covered by the foam layer, the heat transfer rate can be increased at least 20% in comparison to the fully wrapped tube, while the weight and material usage can be considerably reduced.

Wake-Induced Unsteady Stagnation-Region Heat Transfer Measurements

1994 ◽  
Vol 116 (1) ◽  
pp. 29-38 ◽  
Author(s):  
P. J. Magari ◽  
L. E. LaGraff
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Edge Region ◽  
Isentropic Compression ◽  
Stagnation Region ◽  
Stagnation Line ◽  
Wide Range ◽  
Mach Numbers

An experimental investigation of wake-induced unsteady heat transfer in the stagnation region of a cylinder was conducted. The objective of the study was to create a quasi-steady representation of the stator/rotor interaction in a gas turbine using two stationary cylinders in crossflow. In this simulation, a larger cylinder, representing the leading-edge region of a rotor blade, was immersed in the wake of a smaller cylinder, representing the trailing-edge region of a stator vane. Time-averaged and time-resolved heat transfer results were obtained over a wide range of Reynolds number at two Mach numbers: one incompressible and one transonic. The tests were conducted at Reynolds numbers, Mach numbers, and gas-to-wall temperature ratios characteristic of turbine engine conditions in an isentropic compression-heated transient wind tunnel (LICH tube). The augmentation of the heat transfer in the stagnation region due to wake unsteadiness was documented by comparison with isolated cylinder tests. It was found that the time-averaged heat transfer rate at the stagnation line, expressed in terms of the Frossling number (Nu/Re), reached a maximum independent of the Reynolds number. The power spectra and cross-correlation of the heat transfer signals in the stagnation region revealed the importance of large vortical structures shed from the upstream wake generator. These structures caused large positive and negative excursions about the mean heat transfer rate in the stagnation region.

Temperature Control of Blow-Down, Supersonic Tunnels

1956 ◽  
Vol 60 (541) ◽  
pp. 67-70
Author(s):  
T. A. Thomson
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Reynolds Number ◽  
Mach Number ◽  
Reynolds Numbers ◽  
Stagnation Temperature ◽  
Blow Down ◽  
High Reynolds Numbers ◽  
Experimental Errors ◽  
High Reynolds

The blow-down type of intermittent, supersonic tunnel is attractive because of its simplicity and because relatively high Reynolds numbers can be obtained for a given size of test section. An adverse characteristic, however, is the fall of stagnation temperature during runs, which can affect experiments in several ways. The Reynolds number varies and the absolute velocity is not constant, even if the Mach number and pressure are; heat-transfer cannot be studied under controlled conditions and the experimental errors arising from the effect of heat-transfer on the boundary layer vary in time. These effects can become significant in quantitative experiments if the tunnel is large and the variation of temperature very rapid; the expense required to eliminate them might then be justified.

scholarly journals Effect of Reynolds Number and Property Variation on Fluid Flow and Heat Transfer in the Entrance Region of a Turbine Blade Internal-Cooling Channel

2005 ◽  
Vol 2005 (1) ◽  
pp. 36-44 ◽  
Author(s):  
R. Ben-Mansour ◽  
L. Al-Hadhrami
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Mass Flow Rate ◽  
Heat Transfer Rate ◽  
Turbine Blade ◽  
Flow Rate ◽  
Transfer Rate ◽  
Internal Cooling ◽  
Cooling Channel ◽  
Flow And Heat Transfer

Internal cooling is one of the effective techniques to cool turbine blades from inside. This internal cooling is achieved by pumping a relatively cold fluid through the internal-cooling channels. These channels are fed through short channels placed at the root of the turbine blade, usually called entrance region channels. The entrance region at the root of the turbine blade usually has a different geometry than the internal-cooling channel of the blade. This study investigates numerically the fluid flow and heat transfer in one-pass smooth isothermally heated channel using the RNGk−εmodel. The effect of Reynolds number on the flow and heat transfer characteristics has been studied for two mass flow rate ratios (1/1and1/2) for the same cooling channel. The Reynolds number was varied between10 000and50 000. The study has shown that the cooling channel goes through hydrodynamic and thermal development which necessitates a detailed flow and heat transfer study to evaluate the pressure drop and heat transfer rates. For the case of unbalanced mass flow rate ratio, a maximum difference of8.9% in the heat transfer rate between the top and bottom surfaces occurs atRe=10 000while the total heat transfer rate from both surfaces is the same for the balanced mass flow rate case. The effect of temperature-dependent property variation showed a small change in the heat transfer rates when all properties were allowed to vary with temperature. However, individual effects can be significant such as the effect of density variation, which resulted in as much as9.6% reduction in the heat transfer rate.

Flow Visualization and Conjugate Heat Transfer Study From Shower Head Impinging Jets

2011 ◽  
Author(s):  
Rajesh Kumar Panda ◽  
B. V. S. S. S. Prasad
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Flow Visualization ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Nodal Point ◽  
Weighted Average ◽  
Bottom Surface ◽  
Separation Flow ◽  
Flow Topology

Computational and experimental investigations on a flat circular disk are reported with a constant heat flux imposed on its bottom surface and a shower head of air jets impinging on the top surface. The shower head consists of a central jet surrounded by four neighboring perimeter jets. Lamp black flow visualization technique and computations using shear stress transport (SST) κ-ω turbulence model are employed to describe the complex interaction of the wall jets and the associated flow structure. Thermochromic liquid crystal measurement technique is used for surface temperature measurement. The formations of saddle point, nodal point of attachment, nodal point of separation, flow separation line and the up-wash flow are identified. It is observed that the flow topology is practically independent of Reynolds number within the investigated range but is significantly altered with the spacing between the jet orifice and the target surface. A strong correlation between the Nusselt number and the pressure distribution is noticed. Local variation of heat transfer rate with varying plate spacing to jet diameter ratio is significant but its effect on the area weighted average heat transfer rate is small. When compared with a single jet of equal mass flow rate and Reynolds number, the shower head jets provide higher heat transfer rate but require more power for pumping.

Wake-Induced Unsteady Stagnation-Region Heat-Transfer Measurements

1992 ◽  
Author(s):  
P. J. Magari ◽  
L. E. LaGraff
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Reynolds Numbers ◽  
Edge Region ◽  
Isentropic Compression ◽  
Stagnation Region ◽  
Stagnation Line ◽  
Wide Range ◽  
Mach Numbers

An experimental investigation of wake-induced unsteady heat transfer in the stagnation region of a cylinder was conducted. The objective of the study was to create a quasi-steady representation of the stator/rotor interaction in a gas turbine using two stationary cylinders in crossflow. In this simulation, a larger cylinder, representing the leading-edge region of a rotor blade, was immersed in the wake of a smaller cylinder, represenung the trailing-edge region of a stator vane. Time-averaged and time-resolved heat-transfer results were obtained over a wide range of Reynolds numbers at two Mach numbers: one incompressible and one transonic. The tests were conducted at Reynolds numbers, Mach numbers and gas-to-wall temperature ratios characteristic of turbine engine conditions in an isentropic compression-heated transient wind tunnel (LICH tube). The augmentation of the heat transfer in the stagnation region due to wake unsteadiness was documented by comparison with isolated cylinder tests. It was found that the time-averaged heat-transfer rate at the stagnation line, expressed in terms of the Frossling number (Nu/√Re), reached a maximum independent of the Reynolds number. The power spectra and cross correlation of the heat-transfer signals in the stagnation region revealed the importance of large vortical structures shed from the upstream wake generator. These structures caused large positive and negative excursions about the mean heat-transfer rate in the stagnation region.

Thermal Fluid Flow Transport Characteristics in Confined Channels With Two-Dimensional Dual Jet Impingement

2011 ◽  
Author(s):  
Caner Senkal ◽  
Shuichi Torii
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Rate ◽  
Inclination Angle ◽  
Transfer Rate ◽  
Velocity Ratio ◽  
Heated Wall ◽  
Outer Diameter ◽  
Stagnation Zone ◽  
Governing Equations

The flow and heat transfer characteristics of laminar dual circular jet impinging on a heating plate with inclined confinement surface has been investigated numerically. Governing equations in steady state are solved by a control volume based finite-difference method. The simulations have been carried out for Reynolds number (250≤Re≤418), the angle of inclination of the confined upper wall (0 ≤ θ ≤ 10), circular jet to annular jet velocity ratio (0≤VR≤2) and jet to target plate distances between 2D and 8D where D is the outer diameter of dual jet.SIMPLE algorithm was used to obtain velocity and temperature fields. Hybrid difference scheme is adopted for the discretized terms in the governing equations. The discretised equations are solved iteratively using the tridiagonal matrix algorithm line solver. Heat transfer performance along the heated wall is amplified with an increase in the velocity ratio and the Reynolds number. On the contrary, a substantial reduction in the heat transfer rate, for VR = 0.0, occurs in the stagnation zone, because the absence of the inner nozzle injection causes the recirculation in the corresponding region. The heat transfer rate in the stagnation zone is attenuated by increasing the jet nozzle to impinging plate distance. In particular, the effect of the inclination angle in the down-stream region, especially at the vicinity of outlet, is major then other effects Nusselt number distribution on the impingement plate is affected by inclined upper wall because inclination of the wall accelerates the exhaust flow. The streamwise reduction in the heat transfer rate for θ = 0° is suppressed by the presence of the inclined confinement surface and its value is intensified by the inclination angle.

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