An Investigation of Local Heat Transfer during Grinding Process—Effects of Porosity of Grinding Wheel

1979 ◽  
Vol 101 (2) ◽  
pp. 97-103 ◽  
Author(s):  
Y. Saito ◽  
N. Nishiwaki ◽  
Y. Ito
Keyword(s):  
Heat Transfer ◽  
Boundary Condition ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Thermal Boundary Condition ◽  
Grinding Wheel ◽  
Grinding Process ◽  
Workpiece Surface

The thermal boundary condition around the workpiece surface is one of important factors to analyze the thermal deformation of a workpiece, which is in close relation to the machining, accuracy of grinding. The heat dissipation from the workpiece surface which is influenced by the flow pattern, may govern this thermal boundary condition. In consequence, it is necessary to clarify the convection heat transfer coefficient and the flow pattern of air and/or grinding fluid around surroundings of a rotating grinding wheel and of a workpiece. Here experiments were carried out in a surface grinding process to measure the flow velocity, wall pressure and local heat transfer by changing the porosity of the grinding wheel. The air blowing out from the grinding wheel which is effected by the porosity may be considered to have large influences on the local heat transfer coefficient, which is found to be neither symmetric nor uniform over the workpiece surface.

Local Heat Transfer Dependency on Thermal Boundary Condition in Ribbed Cooling Channel Geometries

2013 ◽  
Vol 135 (10) ◽  
Author(s):  
Beni Cukurel ◽  
Tony Arts
Keyword(s):  
Heat Transfer ◽  
Boundary Condition ◽  
Heat Flux ◽  
Local Heat ◽  
Thermal Boundary Condition ◽  
Heat Extraction ◽  
Condition Dependence ◽  
Thermal Conductivity Ratio ◽  
Uniform Heat Flux ◽  
Cooling Channel

The present study is geared toward quantifying the effects of imposed thermal boundary condition in cooling channel applications. In this regard, tests are conducted in a generic passage, with evenly distributed rib type perturbators at 90 deg, with a 30% passage blockage ratio and pitch-to-height ratio of 10. Uniform heat-flux is imposed on the external side of the slab which provides Biot number and solid-to-fluid thermal conductivity ratio around 1 and 600, respectively. Through infrared thermometry measurements over the wetted surface and via an energy balance within the solid, conjugate heat transfer coefficients are calculated over a single rib-pitch. The local heat extraction is demonstrated to be a strong function of the conduction effects, observed more dominantly in the rib vicinity. Moreover, the aero-thermal effects are investigated by comparing the findings with analogous aerodynamic literature, enabling heat transfer distributions to be associated with distinct flow structures. Furthermore, the results are contrasted with the iso-heat-flux wetted boundary condition test case. Neglecting the thermal boundary condition dependence, and thus the true thermal history of the boundary layer, is demonstrated to produce large errors in heat transfer predictions.

Full Surface Local Heat Transfer Coefficient Measurements in a Model of an Integrally Cast Impingement Cooling Geometry

1998 ◽  
Vol 120 (1) ◽  
pp. 92-99 ◽  
Author(s):  
D. R. H. Gillespie ◽  
Z. Wang ◽  
P. T. Ireland ◽  
S. T. Kohler
Keyword(s):  
Heat Transfer ◽  
Boundary Condition ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Local Heat Transfer Coefficient ◽  
Target Plate ◽  
Impingement Cooling ◽  
Impingement Plate

Cast impingement cooling geometries offer the gas turbine designer higher structural integrity and improved convective cooling when compared to traditional impingement cooling systems, which rely on plate inserts. In this paper, it is shown that the surface that forms the jets contributes significantly to the total cooling. Local heat transfer coefficient distributions have been measured in a model of an engine wall cooling geometry using the transient heat transfer technique. The method employs temperature-sensitive liquid crystals to measure the surface temperature of large-scale perspex models during transient experiments. Full distributions of local Nusselt number on both surfaces of the impingement plate, and on the impingement target plate, are presented at engine representative Reynolds numbers. The relative effects of the impingement plate thermal boundary condition and the coolant supply temperature on the target plate heat transfer have been determined by maintaining an isothermal boundary condition at the impingement plate during the transient tests. The results are discussed in terms of the interpreted flow field.

Full Surface Local Heat Transfer Coefficient Measurements in a Model of an Integrally Cast Impingement Cooling Geometry

1996 ◽  
Author(s):  
David R. H. Gillespie ◽  
Zuolan Wang ◽  
Peter T. Ireland ◽  
S. Toby Kohler
Keyword(s):  
Heat Transfer ◽  
Boundary Condition ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Local Heat Transfer Coefficient ◽  
Target Plate ◽  
Impingement Cooling ◽  
Impingement Plate

Cast impingement cooling geometries offer the gas turbine designer higher structural integrity and improved convective cooling when compared to traditional impingement cooling systems which rely on plate inserts. In this paper, it is shown that the surface which forms the jets contributes significantly to the total cooling. Local heat transfer coefficient distributions have been measured in a model of an engine wall cooling geometry using the transient heat transfer technique. The method employs temperature sensitive liquid crystals to measure the surface temperature of large scale perspex models during transient experiments. Full distributions of local Nusselt number on both surfaces of the impingement plate, and on the impingement target plate are presented at engine representative Reynolds numbers. The relative effects of the impingement plate thermal boundary condition and the coolant supply temperature on the target plate heat transfer has been determined by maintaining an isothermal boundary condition at the impingement plate during the transient tests. The results are discussed in terms of the interpreted flow field.

Shape Optimization of Partly Removed Straight Ribs in Turbine Internal Rectangular Cooling Channel With 45 Degree Ribs

2018 ◽  
Author(s):  
Jiangnan Zhu ◽  
Xiying Wang ◽  
Changxian Zhang ◽  
Hui Miao
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Friction Factor ◽  
Response Surface ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Friction Loss ◽  
Cooling Channel ◽  
Number Ratio ◽  
Ansys Workbench

Angled ribs have been widely used in the rectangular internal cooling channel of gas turbine to enhance heat convection strength and the optimal rib parameters have been shown in the former investigations. However, the heat transfer strength of the wall near the terminal of angled ribs is less enhanced by the rib and the local Nusselt number ratio may be lower than 1, which means that the local heat transfer strength of the ribbed wall is lower than that of smooth wall. At the same time, the ribs also generate large friction loss. As a result, a part of ribs which provides little heat transfer enhancement effect are removed in order to both reduce friction loss and maintain or enhance local heat transfer strength. In order to find out the optimal geometry parameters of the removed part of the rib, the optimization study are conducted in this paper based on the ANSYS Workbench software. The channel width to height ratio is 1 and 4. The rib attack angle is 45 degrees. The length of removed part, the transverse location of the removed part and the angle between the flow direction and the incision edge are chosen as the design variables. The area-averaged Nusselt number ratio and temperature on the ribbed wall, the friction factor ratio of the channel and the thermal performance factor are chosen as the objectives. The samples are generated by Latin Hypercube Sampling method and the CFD calculation is conducted by ANSYS CFX module using SST turbulence model. The response surface is obtained by Kriging model based on the CFD results and the Pareto optimal solution of this multi-objective problem is conducted by Multi-Objective Genetic Algorithm (MOGA) in the Response Surface Optimization module of ANSYS Workbench. The results show that the removed part of rib could both maintain or slightly enhance the overall Nusselt number ratio and obviously reduce the friction factor at the same time. Furthermore, the Nusselt number ratio in the terminal region of original ribs is also largely enhanced.

Experimental Study on Local Heat Transfer in a Rotating, Two-Pass Cooling Channel With Dense Array of Turbulence Promoters With Naphthalene Sublimation Method

2014 ◽  
Author(s):  
Tomoko Hagari ◽  
Katsuhiko Ishida ◽  
Kenichiro Takeishi ◽  
Masaharu Komiyama ◽  
Yutaka Oda
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Surface Area ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Cooling Channel ◽  
Overall Heat Transfer Coefficient ◽  
Rib Turbulators

Detailed heat transfer coefficient distributions in a rotating, two-pass, square channel with densely arranged rib turbulators on the leading and trailing walls are investigated. Rib turbulators have been used in a cooling channel of turbine airfoils. The dense arrangement of the ribs is one of the potential candidates to improve heat transfer performance because of its surface area enlargement effect. The ribs are arranged with a rib height to channel hydraulic diameter ratio (e/Dh) of 0.13, angles of attack to the mainstream of 60 and 90deg, and rib pitch-to-height ratios (P/e) of 3, 6 and 10. Both rib and floor surfaces are coated with naphthalene to measure their local mass transfer rate, which is correlated with heat transfer coefficient through heat/mass transfer analogy. Combination of a laser displacement sensor and a precision auto-traverse system enables detailed measurement of local heat transfer distribution on the floor surface between the ribs. Overall heat transfer coefficient including the effect of the rib is obtained by measuring the decrease in weight of the naphthalene test piece. Reynolds number is set at 50,000 and rotation numbers are up to 0.05. The results show that the effect of rotation on local heat transfer behavior depends on the rib spacing and orientation. Compared the overall heat transfer coefficients with the local ones on the floor surface, they showed different trend in some cases. This suggests that variation of rib heat transfer characteristics due to rotation might determine the overall heat transfer coefficient. Such tendency would be stronger for smaller rib spacing because surface area of the rib has large portion of the total heat transfer area. Further investigation on this effect is expected by measuring heat transfer of rib itself under rotating condition.

Influence of Non-Uniform Sinusoidal Periodic Bottom Boundary Condition on Natural Convection in an Isotropic Porous Enclosure

2011 ◽  
Vol 110-116 ◽  
pp. 1576-1581 ◽  
Author(s):  
Manish Kr. Khandelwal ◽  
P. Bera
Keyword(s):  
Heat Transfer ◽  
Boundary Condition ◽  
Fluid Flow ◽  
Natural Convection ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Bottom Wall ◽  
Isotropic Case ◽  
Material Derivative ◽  
Porous Enclosure

A comprehensive numerical investigation on the natural convection in an isotropic porous enclosure is presented. All the walls of the enclosure are adiabatic except the bottom wall which is partially heated and cooled by sinusoidal temperature profile. The governing equations were written under assumption of Brinkman-extended non-Darcy model, including material derivative, and then solved by numerically using spectral element method (SEM). The heat transfer and fluid flow mechanisms in isotropic case are governed by periodicity parameter (N) Rayleigh Number (Ra), Darcy number (Da), aspect ratio (A), Prandtl number (Pr) and media permeability (K). The main emphasize is given on effect of N on local heat transfer as well as mechanism of heat transfer and fluid flow in enclosure. The results shows that, as the periodicity is decreased on increasing N the absolute value of Nux at the bottom left corner point increases. For odd values of N, the local heat transfer profile is symmetric about the line x=0.5, which is consequence of symmetric boundary condition at the bottom wall of the enclosure. The entire flow is governed by two type convective cells: (i) rotating clockwise (ii) rotating anticlockwise. Furthermore for even values of N cells rotating anticlockwise are dominated and covered the entire domain. In particular the present analysis shows that, different periodicity of temperature boundary condition has the significant effect on the flow mechanism and consequently on the heat transfer rate.

High Rotation Number Effect on Heat Transfer in a Leading Edge Cooling Channel With Three Channel Orientations

2012 ◽  
Author(s):  
Szu-Chi Huang ◽  
Yao-Hsien Liu
Keyword(s):  
Heat Transfer ◽  
Leading Edge ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Cooling Channel ◽  
Height Ratio ◽  
Triangular Channel ◽  
Rotation Numbers ◽  
Channel Orientation

Heat transfer in a leading edge, triangular shaped cooling channel with three channel orientations under high rotation numbers is experimentally studied. Continuous ribs and V-shaped ribs, both at 45° rib angle of attack, are applied on the leading and trailing surfaces. For each rib case, three channel orientations (90°, 67.5°, and 45°) with respect to the plane of rotation are tested. The rib height to hydraulic diameter ratio (e/Dh) is 0.085 and the rib pitch to height ratio (P/e) is 9. Reynolds numbers are from 15000 to 25000, and the rotation numbers are from 0 to 0.65. Results show that the heat transfer variation is influenced by the combined effects of rib configuration and channel orientation. Effect of channel orientation influences local heat transfer distribution inside this triangular channel, and heat transfer is enhanced gradually on the leading surface when the channel orientation varies from 90° to 45° for both ribbed cases in this study.

Numerical Study on Local Heat Transfer in a Rotating Cooling Channel

2018 ◽  
Author(s):  
Min Ren ◽  
Xueying Li ◽  
Jing Ren ◽  
Hongde Jiang
Keyword(s):  
Heat Transfer ◽  
Rotation Number ◽  
Numerical Study ◽  
Density Ratio ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Hydraulic Diameter ◽  
Internal Cooling ◽  
Cooling Channel ◽  
Channel Diameter

Effect of rotation on turbine blade internal cooling is an important factor in gas turbine cooling systems. To obtain the distribution of the heat transfer and the flow field in a rotating cooling channel, a series of computational simulations using the realizable k-ε model are utilized. The channel Reynolds number based on the channel diameter is 25000. The rotation number ranges from 0 to 0.20. The investigated density ratio Δρ/ρ ranges from 0.05 to 0.33 and the range of radius-to-passage hydraulic diameter r/D is from 10 to 40. The results show that the heat transfer on the trailing side shows an overall augmentation while that on the leading side decreases in the cooling channel. When the channel is stationary, the density ratio has little effect on the thermal performance. And for the rotating channel, the heat transfer on the trailing side and leading side both increases when the density ratio increases. The heat transfer both on the trailing side and leading side decreases when the radius-to-passage hydraulic diameter (r/D) increase. And the radius has a greater effect when the rotation number is higher.

Investigation on Heat Transfer Characteristics of a Cooling Channel With Dense Array of Angled Rib Turbulators

2012 ◽  
Author(s):  
Tomoko Hagari ◽  
Katsuhiko Ishida ◽  
Ken-ichiro Takeishi ◽  
Yutaka Oda ◽  
Hiroki Kitada
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Navier Stokes ◽  
Cooling Channel ◽  
Heat Transfer Characteristics ◽  
Test Channel ◽  
Transfer Characteristics ◽  
Experimental Heat ◽  
Rib Turbulators

Heat transfer characteristics of a cooling channel with densely arranged, angled rib turbulators were investigated experimentally and numerically. The dense arrangement of the ribs is one of the potential candidates to improve heat transfer performance because of its surface area enlargement effect. The square test channel consisted of six square ribs, which were placed on one side. The ribs were arranged with a rib height to channel hydraulic diameter ratio (e/Dh) of 0.13, an angle of attack to the mainstream of 60deg, and rib pitch-to-height ratios (P/e) of 3, 6 and 10. Local heat transfer distribution on all surfaces of the rib and the floor surface between the ribs were measured by the naphthalene sublimation method. Channel Reynolds number ranges from 30,000 to 70,000. Measured data showed that the P/e of 3 provided the largest total heat transfer. It was found that 60% of heat flux was transferred through the rib surface. Numerical simulations using a Reynolds-Averaged Navier-Stokes (RANS) method and a Large Eddy Simulation (LES) were carried out for the above test cases. The RANS underestimated the experimental heat transfer data by 40–50% for all rib surfaces with close rib arrangement. On the other hand, time-averaged heat transfer distribution obtained by LES showed better agreement with experimental data. Moreover, the LES predicted the periodic large vortex structure ranging over several rib pitches. Further investigation is expected on the periodic secondary flow and the application of LES to the prediction of heat transfer in the near future.

Sign in / Sign up

Export Citation Format

Share Document