• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.22 no.5
• /
• pp.584-595
• /
• 1998

An investigation was carried out to determine experimentally the thermal conductivities of non-Newtonian fluids in a shear field. Both time independent purely viscous and viscoelastic fluids were considered. A coaxial cylinder apparatus with a rotating outer cylinder was used to establish the velocity field in the test fluid. First, the thermal conductivity of distilled water measured to validate the instrument. The experimental water data agreed within 1% of literature values and there was no effect of outer cylinder rotation (shear field). However, for non-Newtonian fluids such as aqueous CMC and Separan solutions, there were significant increases in thermal conductivities of up to 70% for CMC and 50% for Separan depending on the shear rate, polymer concentration and temperature. Considering the shear rate dependent thermal conductivity in the study of heat transfer in non-Newtonian fluids could be important. As in natural convection, the momentum and energy equations could no longer be solved separately but would have to be solved simultaneously.

• Journal of the Korean Society for Precision Engineering
• /
• v.28 no.1
• /
• pp.96-101
• /
• 2011

Under extreme test or operation condition, refrigerator endures complicated stresses state and thermal bowing deformation arises on the sidewall. Shelf rails designed in the inner case provide increased surface area to permit expansion without bowing, and also increase structural rigidity to resist bowing. In this study, we designed six different shelf patterns of refrigerator model and studied the bead on refrigerator deformation using finite element method (FEM). Analysis result shows that increasing the numbers of beads properly in refrigerator is more helpful to reduce thermal bowing deformation. In addition, the beads would decrease stress on refrigerator sidewall. However, vertical beads have no effect to reduce thermal deformation of the bowing.

• Polymer(Korea)
• /
• v.29 no.5
• /
• pp.481-485
• /
• 2005

In this work, the thermal and mechanical properties of vapor grown carbon nanofibers (VGCNFs)-reinforced difunctional epoxy (EP) composites were investigated in the presence of the 0, 0.1, 0.5, 1.0, and $2wt\%$ VGCNFs. The thermal properties of the VGCNFs/EP composites were studied by thermo-mechanical analysis (TMA) and dynamic mechanical analysis (DMA). The mechanical properties of the VGCNFs/EP composites were also examined by universal testing machine (UTM), falling impact test, and the friction and wear tests. From experimental results, the thermal and mechanical properties of the VGCNFs/EP composites were improved with increasing the VGCNFs contents. This was due to the increase of crosslinking structure of the composites, resulting in improving the mechanical interlockings between VGCNFs and epoxy resins in the present composite system.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.26 no.3
• /
• pp.479-486
• /
• 2002

In this study, the progressive inelastic deformation, so called, thermal ratchet phenomenon which can occur in high temperature structures of liquid metal reactor was simulated with thermal ratchet structural test facility and 316L stainless steel test cylinder. The thermal ratchet deformation at the reactor baffle cylinder of the liquid metal reactor can occur due to the moving temperature distribution along the axial direction as the sodium free surface moves up and down under the cyclic heat-up and cool-down transients. The ratchet deformation was measured with the laser displacement sensor and LVDTs after cooling the structural specimen which is heated up to 55$0^{\circ}C$ with steep temperature gradients along the axial direction. The temperature distribution of the test cylinder along the axial direction was measured with 28 channels of thermocouples and was used for the ratchet analysis. The thermal ratchet deformation was analyzed with the constitutive equation of nonlinear combined hardening model which was implemented as ABAQUS user subroutine and the analysis results were compared with those of the test. Thermal ratchet load was applied 9 times and the residual displacement after 9 cycles of thermal load was measured to be 1.79mm. The ratcheting deformation shapes obtained by the analysis with the combined hardening model were in reasonable agreement with those of the structural tests.

• Journal of Energy Engineering
• /
• v.21 no.1
• /
• pp.26-32
• /
• 2012

This study has been performed Thermal Shock test for analyze the cause of Power drop in PV(Photovoltaic) Module. Thermal Shock test condition was performed with temperature range from $-40^{\circ}C{\sim}85^{\circ}C$. One cycle time is 30min. which are consist of low and high temperature 15min. each other. The test was performed with total 500cycles. EL, I-V were conducted every 100cycle up to 500cycles. Mono Cell resulted in 8% Power drop rates in Bare Cell and 9% in Solar Cell. In the case of Multi Cell resulted in 6% Power drop rates in Bare Cell and 13% in Solar Cell. After Thermal Shock test, Solar Cell's Power drop resulted from surface damages, but in the case of Bare Cell's Power drop had no surface damages. Therefore, Bare Cell's Power drop was confirmed as according to leakage current increase by analysis of Fill Factor after Thermal Shock test. Also, Solar Cell's Power drop rates are higher than that of Bare Cell because of surface damages and consuming electric power increase. From now on, it should be considered that analyzed the reasons of Fill Factor decrease and irregular Power drop in PV module and Cell level using cross section, various conditions and test methods.

• Transactions of Materials Processing
• /
• v.11 no.1
• /
• pp.61-68
• /
• 2002

The thermal shock and thermal fatigue test has been carried out to analyze the thermal characteristics of tool steels for hot forging and the effects of mechanical properties on this study have been investigated. The resistance to thermal shock is first of all a matter of good toughness and ductility. Therefore, a proper hot-work tool steel should be characterized by high fracture strength and high temperature toughness. Based on these results, some critical temperature($T_{fracture}$) at which fracture occur can be measured to characterize the thermal resistance of the materials. During thermal fatigue tests, the thermal fatigue cracks occur because of the repetitive heating and cooling of the die surface and the thermal fatigue damage was evaluated by analyzing different number of cycles to failure. The results showed that the resistance to thermal shock and thermal fatigue were found to be favoured by high hot tensile strength and high hot hardness, and thermal resistance of SKD61 was superior to that of ESC, SKT4 and this was caused by higher mechanical properties of SKD61.

• Advances in concrete construction
• /
• v.12 no.5
• /
• pp.439-450
• /
• 2021

In recent years, nano-reinforcing materials are widely utilized in cement composites due to their unique multifunctional properties. This study incorporated multi-walled carbon nanotubes (MWCNTs) into the cementitious composites at ratios of 0.1%, 0.3%, and 0.5%, and investigated their influence on the flowability, mechanical strength, and hydration heat properties. The addition of MWCNTs enhanced the compressive and split tensile strengths approximately by 18-51%. In the semi-adiabatic temperature rise test, the internal hydration heat of the composites reduced by 5%, 9%, and 12% with the increase of MWCNTs in 0.1%, 0.3%, and 0.5%. This study further performed hydration heat analysis and estimated the adiabatic temperature rise, thermal stress, and thermal crack index. The internal hydration heat of the concrete decreased by 5%, 10%, and 13% with the increase of MWCNTs. The thermal stress of the concrete decreased with increase in the addition of MWCNTs, and the obtained temperature crack index was effective in controlling the thermal cracks.

• Journal of Power System Engineering
• /
• v.1 no.1
• /
• pp.70-79
• /
• 1997

Ni-base self-fluxing alloy powder particles were flame sprayed onto the SS400 mild steel substrate surface. The effects of both substrate temperature and spraying distance on the splat behavior of sprayed particles were examined. The results obtained are summarized as follows: 1) In the splat behavior of Ni-base self-fulxing alloy particles sprayed onto the SS400 mild steel substrate, splashing was observed under the room temperature condition. On the contrary, it showed circular plate pattern in the substrate temperature range over 373K. 2) It was cleared that there was close relationship between mechanical properties of coating layer and splat behavior of sprayed particles. 3) From the experimental results, optimum spraying conditions showed excellent mechanical properties in the case of Ni-base self fluxing alloy sprayed onto the SS400 mild substrate were 473K of substrate temperature and 250mm of spraying distance.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.17 no.1
• /
• pp.103-115
• /
• 2013

Durability testing method trends of the thermal barrier coating(TBC) for the combustion chamber of the liquid-propellant rocket engine have been investigated. Many types of the durability testing method such as the mechanical tests to measure surface cohesion force, the thermal fatigue tests with laser, furnace, burner or plasma, the small scale combustion tests using injectors, and the thermo-mechanical fatigue tests were observed. The TBC with sufficient durability can be selected for the use of combustion chamber through such specimen-level tests and the durability can be verified by the tests using the real scale combustion chambers.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.13 no.5
• /
• pp.82-89
• /
• 2014

In this paper, fire resistance test was carried out to obtain class H-120 thermal insulation of fire dampers according to a hydrocarbon fire conditions. Specimens were fabricated three different types according to the change of the insulation system applied to damper blade and coaming which were measured surface temperature by performing the fire resistance test. As a test result, specimen-1, 2 of an uninsulated damper blade were exceeded thermal insulation acceptance criteria at 21 minutes, 46 minutes respectively, but specimen-3 of an insulated damper blade was satisfied thermal insulation acceptance criteria during 120 minutes. The test results showed that the insulation of the damper blade was an important factor in the fireproof performance of fire dampers concerning the coaming length minimum 500 mm on the unexposed side as specified test standard.