Murat Parlak

Size-dependent thermal properties of multi-walled carbon nanotubes embedded in phase change materials

This study has focused on the systematical investigation of effect of mass fraction and size of multi-walled carbon nanotubes (MWCNTs) doped in phase change material (PCM) on thermal properties such as thermal conductivity, melting/solidification temperatures and latent heats. Thermal conductivity, melting/solidification temperatures and latent heats of MWCNTs/PCM composites with three different diameters and two different lengths, obtained by doping MWCNTs into PCM at the mass fraction of 1–5%, were evaluated according to the criteria such as particle size and mass fraction. The results demonstrated that not only mass fractions but also size of MWCNTs are effective on the thermal properties of the composites. It was concluded that increase in diameter and length of MWCNTs positively affects enhancement of thermal conductivity; on the other hand, it does not cause a significant change at melting/solidification temperatures. In addition to these, a decline was observed at melting/solidification latent heats of MWCNTs/PCM composites, depending on doped mass fractions of MWCNTs.

Heat transfer performance of water based nanofluids containing various types of metal oxide nanoparticles in an air-cooled microchannel heat exchanger

In the present study performance of air-cooled cross flow microchannel heat exchanger is analysed experimentally with various metal oxide type nanofluids. Types of the nanoparticles and their particle size are TiO2 (30 nm, 50 nm), MgO (20 nm, 40 nm), ZnO (10–30 nm, 35–45 nm, 80–200 nm), SiO2 (20–30 nm, 60–70 nm), NiO (10–20 nm) and Fe3O4 (15–20 nm). Zeta potential measurement is employed for the stability evaluation of the dispersions. Among the nanofluids considered, only suspensions containing SiO2 (60–70 nm) and NiO (10–20 nm) nanoparticles give zeta potential above the critical stability value of 30 mV. Strong dependency between relative zeta potential of the suspensions and particle size is observed. The heat transfer characteristic of nanofluids through the cross flow air cooled microchannel heat exchanger is evaluated with the overall heat transfer coefficient under laminar conditions. Experimental results show that, all nanofluids considered, except TiO2/water, deteriorate the heat transfer coefficient of nanofluids depending on the flow rate through heat exchanger. This may be may be explained by the poor nanofluid stability and deposition of nanoparticles to the surface of the channels during the flowing of the nanofluids.

Thermal property investigation of multi walled carbon nanotubes (MWCNTs) embedded Phase Change Materials (PCMs)

In the present study the effect of different size MWCNTs, on the thermal properties such as thermal conductivity, melting/solidification temperatures and latent heats were investigated systematically. Two sizes of MWCNTs that have same diameter but two different lengths as long MWCNTs and short MWCNTs were used at various mass fractions including 1%, 3% and 5% to fabricate MWCNTs/PCM composites. The thermal conductivity, melting/solidification temperatures and latent heats of MWCNTs based composites were evaluated incorporating both particle size and mass concentrations. The experimental results demonstrated that both size and the loading content of the MWCNTs have direct effect on the thermal properties of the samples. The thermal conductivity enhancement of the short MWCNTs was realized to be lower than that of the long MWCNTs. On the other hand, latent heat was measured slightly higher for short MWCNTs than the long MWCNTs.

Electronical packaging of a high power device operating in geo orbit

It is known that thermal design engineers have difficulties in temperature control of GEO (Geostationary Equatorial Orbits) satellites, compared to other systems operating in ground applications due to harsh space environment. Electronic packaging is an essential discipline especially when high thermal loads together with other mechanical requirements need to be optimized. In most of the design, thermal management or cooling methods draw the main design path for the unit. In this study, there are eleven identical PCBs and cold plates in an electronic box. The main focus of this article is the thermal optimization of the cold plates to obtain a light and high conductive cold plate by considering all mechanical design requirements. In order to achieve this goal, the thermal unknowns in the design are reduced by improving mechanical design and production technique as much as possible. Thermal and structural analyses (Power Spectral Density- PSD) have been carried out to decide and check the mechanical requirements. All thermal and structural analyses have been carried out with finite element methods (FEM). The results show that 1.9 kg lighter cold plates can be achieved by using Annealed Pyrolytic Graphite (APG) with the same thermal performance of copper

Thermal management of an electronical device using PCM embedded in a pin fin heat sink

Phase Change Materials (PCM) have high fusion heat capacity so that they can absorb large amounts of energy before melting. The temperature of a PCM remains almost constant during the phase change, a property which is useful for keeping the subject around the PCM at a uniform temperature. Therefore, PCM is a widely used material in the thermal solutions of time-dependent problems. In this study, thermal control of an electronical device has been carried out using organic and inorganic PCMs. Since thermal conductivity of PCM is very low, pin fin heat sink has been used to increase the conductivity and surface area. In the device, heat sources are not in direct contact with PCM.

Numerical and experimental thermal performance analysis of two different types of air cooled electronic chassis developed for military aviation platform

Because of exposing challenging environmental conditions such as extreme ambient temperatures, high humidity, salt fog and dust, electronic units in military systems have substantially different design constraints than others. Hence it should be taken serious precautions to prevent electronics and mechanics from these environmental threats. This study is aimed to provide numerical approach to tackle the extreme environmental conditions and obtain high cooling performance for an electronical device. In accordance with the purpose, two different chassis design alternatives have been proposed. First, cold plate fin (heat sink) design is carried out with several fin type iterations considering the temperature and pressure drop values and it gives rise to a compact product with high cooling rate. Second, using the exactly the same fin configuration, the chassis is externally cooled where corrugated plain fin (air to air HX) is used to make the unit as bright as possible with easy production. In mechanical aspect, both designs are very different from each other but they serve the same purpose using the same electronic components, cold plates and cooling fan. All numerical analysis have been carried out by using ANSYS Fluent ® software and prototypes are tested in the laboratory by measuring the temperature at critical points. Besides, in terms of engineering point view, advantages and disadvantages of both designs are discussed in detail.

Experimental investigation of transient thermal response of phase change material embedded by Graphene nanoparticles in energy storage module

Here, an experimental study has been conducted to evaluate thermal performance and energy storage capabilities of organic paraffin wax with melting point of 95 °C embedded at various loadings of Graphene nanoplatelets (0, 1, 3, 5, 7, 10 wt. %). All experiments were carried out in a cubical aluminium box with the dimensions of 40×40×40 in mm. Temperature measurements were carried out at different locations within the module by using J type thermocouples. Due to the low thermal conductivity of pure paraffin wax, temperature variations among the measured locations are relatively high. On the other hand as the loading of Graphene nanoplatelets within the paraffin wax is increased, temperature differences within the thermal energy storage (TES) module is decreased significantly and almost reach uniform at the highest mass fraction used, 10 wt. %. The results obtained from experiments indicate that a Graphene/paraffin wax composite is an effective method for the thermal management of devices that operates transiently.

Cooling of high power active phased array antenna using axially grooved heat pipe for a space application

An engineering model of a phased array antenna, cooled using axially grooved heat pipes (AGHP) is presented. Solid state power amplifiers (SSPA) located inside the satellite are wave transmitted to the reflector through waveguides. This integration technique is preferred to minimise electrical losses. However, usually when designing waveguides, minimising antenna losses takes precedence, which leads to an un-optimised design for thermal performance. Because of this situation, a thermal solution has become a challenging problem on this project. With a total heat load of 578 W, it is essential that the waste heat is transferred to the radiator of the satellite which is designed to operate in GEO orbit. This work presents a thermal solution being developed for a satellite phased array antenna that incorporates 4 AGHPs to carry the heat from the SSPA to the radiator. Thermal design work for the antenna and heat pipes completed for the specific boundary conditions for the application, using Icepack® computational fluid dynamics (CFD) thermal software is presented. It is crucial in this pre-development phase to identify problems which can arise from electronic performance loss or thermal issues in advance, both by theoretical design and ground testing.

An Investigation Into Performance Characteristics of an Axial Flow Fan Using CFD for Electronic Devices

Rotating fans are widely utilized in thermal management applications and their accurate characterization has recently become even a more critical issue for thermofluids engineers. The present study investigates the characterization of an axial fan computationally and experimentally. Using the three-dimensional CAD models of the fan, a series of computational fluid dynamics (CFD) simulations were performed to determine the flow and pressure fields produced by the axial mover over a range of flow rates. In order to validate the computational model findings, experiments were conducted to obtain the pressure drop values at different flow rates in an AMCA (Air Movement and Control Association) standard 210-99, 1999 wind tunnel. These data sets were also compared with the fan vendor’s published testing data. A reasonably good agreement was obtained among the data from these three separate sources. Furthermore, an attempt was made to understand the overall fan efficiency as a function of the volumetric flow rate. It was determined that the maximum overall fan efficiency was less than 27% correlating well with the computational results.Copyright

Thermal Solution of High Flux Phased Radar Antenna for Military Application

In military applications, cooling of high heat flux antenna is a challenging problem considering the thermal, mechanical and limited space requirements. In addition to system cooling, thermal uniformity among the high power amplifiers is one of the main issues that should be taken into account for electrical performance requirements. Cold plate is the main mechanical part of the radar antenna structure where it serves as a cooler and a carrier. Liquid path and fin pattern are critical parts of the cold plate design that needs to be carefully studied. These topics are comprehensively discussed in this work. Finite element method software has been used for CFD and thermal analysis. Although cold plate is designed to cool high heat flux, it is known that there is liquid flow in it which applies some amount of hydraulic pressure. Some precautions are taken to withstand high pressure inside the cold plate. The system solution together with manifold design is examined in this study. The internal pressure drop in cold plate has a direct relation with the manifold design. All these topics are discussed in this work.Copyright