scholarly journals Experimental and numerical investigations on heat transfer in fused filament fabrication 3D-printed specimens

2021 ◽  
Author(s):  
Nathalie Ramos ◽  
Christoph Mittermeier ◽  
Josef Kiendl
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer Coefficient ◽  
Numerical Data ◽  
Fused Filament Fabrication ◽  
Thermal Boundary Conditions ◽  
Thermal Measurements ◽  
Stress Prediction ◽  
3D Printed ◽  
Air Void

AbstractA good understanding of the heat transfer in fused filament fabrication is crucial for an accurate stress prediction and subsequently for repetitive, high-quality printing. This work focuses on two challenges that have been presented when it comes to the accuracy and efficiency in simulating the heat transfer in the fused filament fabrication process. With the prospect of choosing correct thermal boundary conditions expressing the natural convection between printed material and its environment, values for the convective heat transfer coefficient and ambient temperature were calibrated through numerical data fitting of experimental thermal measurements. Furthermore, modeling simplifications were proposed for an efficient numerical discretization of infill structures. Samples were printed with varying infill characteristics, such as varying air void size, infill densities and infill patterns. Thermal measurements were performed to investigate the role of these parameters on the heat transfer and based on these observations, possible modeling simplifications were studied in the numerical simulations.

Experimental Evidence of Temperature Ratio Effect on Turbine Blade Tip Heat Transfer

2018 ◽  
Vol 140 (12) ◽  
Author(s):  
H. Jiang ◽  
Q. Zhang ◽  
L. He ◽  
S. Lu ◽  
L. Wang ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Boundary Conditions ◽  
Transfer Coefficient ◽  
Experimental Evidence ◽  
Turbine Blade ◽  
Tip Clearance ◽  
Temperature Ratio ◽  
Thermal Boundary Conditions ◽  
Thermal Measurements

Determination of a scalable Nusselt number (based on “adiabatic heat transfer coefficient”) has been the primary objective of the most existing heat transfer experimental studies. Based on the assumption that the wall thermal boundary conditions do not affect the flow field, the thermal measurements were mostly carried out at near adiabatic condition without matching the engine realistic wall-to-gas temperature ratio (TR). Recent numerical studies raised a question on the validity of this conventional practice in some applications, especially for turbine blade. Due to the relatively low thermal inertia of the over-tip-leakage (OTL) flow within the thin clearance, the fluids' transport properties vary greatly with different wall thermal boundary conditions and the two-way coupling between OTL aerodynamics and heat transfer cannot be neglected. The issue could become more severe when the gas turbine manufacturers are making effort to achieve much tighter clearance. However, there has been no experimental evidence to back up these numerical findings. In this study, transient thermal measurements were conducted in a high-temperature linear cascade rig for a range of tip clearance ratio (G/S) (0.3%, 0.4%, 0.6%, and 1%). Surface temperature history was captured by infrared thermography at a range of wall-to-gas TRs. Heat transfer coefficient (HTC) distributions were obtained based on a conventional data processing technique. The profound influence of tip surface thermal boundary condition on heat transfer and OTL flow was revealed by the first-of-its-kind experimental data obtained in the present experimental study.

Natural Convective Heat Transfer of Water-in-FC72 Nanoemulsion Fluids

2008 ◽  
Author(s):  
Zenghu Han ◽  
Bao Yang
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Hydrodynamic Interaction ◽  
Convective Heat Transfer Coefficient ◽  
Relative Viscosity ◽  
Solid Particles ◽  
Water Loading

The use of SOLID-particles has long been a common way of increasing fluid thermal conductivity. In this paper, nanoemulsion fluids—dispersions of LIQUID-nanodroplets—are proposed. As an example, water-in-FC72 nanoemulsion fluids are developed, and their thermophysical properties and impact on natural convective heat transfer are investigated experimentally. A significant increase in thermal conductivity—up to 52% for 12vol% of water nanodroplets (or 7.1 wt%)—is observed in the fluids. The enhancement in conductivity and viscosity of the fluids is found to be nonlinear with water loading, indicating an important role of the hydrodynamic interaction and aggregation of nanodroplets. However, the relative viscosity is found to be about two times the relative conductivity if compared at the same water loading. The presence of water nanodroplets is found to systematically increase the natural convective heat transfer coefficient in these fluids, in contrast to the observation in several conventional nanofluids containing solid nanoparticles.

Predicting the effect of build orientation and process temperatures on the performance of parts made by fused filament fabrication

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Fernando Moura Duarte ◽  
José António Covas ◽  
Sidonie Fernandes da Costa
Keyword(s):  
Molecular Diffusion ◽  
Operating Conditions ◽  
Fused Filament Fabrication ◽  
Content Type ◽  
Build Orientation ◽  
Thermal Boundary Conditions ◽  
Chamber Temperature ◽  
3D Printed ◽  
Time Required

Purpose The performance of the parts obtained by fused filament fabrication (FFF) is strongly dependent on the extent of bonding between adjacent filaments developing during the deposition stage. Bonding depends on the properties of the polymer material and is controlled by the temperature of the filaments when they come into contact, as well as by the time required for molecular diffusion. In turn, the temperature of the filaments is influenced by the set of operating conditions being used for printing. This paper aims at predicting the degree of bonding of realistic 3D printed parts, taking into consideration the various contacts arising during its fabrication, and the printing conditions selected. Design/methodology/approach A computational thermal model of filament cooling and bonding that was previously developed by the authors is extended here, to be able to predict the influence of the build orientation of 3D printed parts on bonding. The quality of a part taken as a case study is then assessed in terms of the degree of bonding, i.e. the percentage of volume exhibiting satisfactory bonding between contiguous filaments. Findings The complexity of the heat transfer arising from the changes in the thermal boundary conditions during deposition and cooling is well demonstrated for a case study involving a realistic 3D part. Both extrusion and build chamber temperature are major process parameters. Originality/value The results obtained can be used as practical guidance towards defining printing strategies for 3D printing using FFF. Also, the model developed could be directly applied for the selection of adequate printing conditions.

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