Copper Spreader Research Articles

A critical review on renewable battery thermal management system using heat pipes.

The critical review presented here exclusively covers the studies on battery thermal management systems (BTMSs), which utilize heat pipes of different structural designs and operating parameters as a cooling medium. The review paper is divided into five major parts, and each part addresses the role of heat pipes in BTMS categorically. Experimental studies, numerical analyses, combined experimental and numerical investigations, optimum utilization of a phase-change material (PCM) with a heat pipe (HP), oscillating heat pipe (OHP), and micro heat pipes combined with PCM for Li-ion BTMS using heat pipes are presented. The usage of HP's and PCM can keep the temperature of the battery system in the desirable limit for a longer duration compared to other traditional and passive methods. More emphasis is made on how one can achieve a suitable cooling system design and structure, which may tend to enhance the energy density of the batteries, improve thermal performance at maximum and minimum temperature range. Arrangement of battery cells in a pack or module, type of cooling fluid used, heat pipe configuration, type of PCM used, working fluid in a heat pipe, and surrounding environmental conditions are reviewed. According to the study, the battery's effectiveness is significantly influenced by temperature. The usage of flat HPs and heat sink proves to be the best cooling method for keeping the battery working temperature below 50°C and reduces the heat sink thermal resistance by 30%. With an intake temperature of 25°C and a discharge rate of 1 L per minute, an HP that uses water as a coolant is also effective at regulating battery cell temperature and maintaining it below the permissible 55°C range. Using beeswax as a PCM in HPs reduces the temperature of BTMS by up to 26.62°C, while the usage of RT44 in HPs reduces the temperature of BTMS by 33.42°C. The use of fins along with copper spreaders drastically decreases the temperature capability of HPTMS by 11°C. MHPA shows excellent performance in controlling the battery temperature within 40°C. The effective thermal management can be done by incorporating heat pipe alone or by coupling with liquid cooling or metal plate. However, extensive and extended research is required to improve thermal management to safely and effectively use the battery for day-to-day applications.

Intra-Lid Multi-Core Vapor Chamber Architecture for Heterogeneous Electronic Packages: Technology Concept to Prototype Evaluation

Thermal management of future heterogeneous electronic packages with extreme heat fluxes relies on effective spreading of heat in the package lid. Intra-lid integration of vapor chambers is a promising strategy for simultaneous dissipation of large total heat loads and localized high-flux hot spots. However, conventional vapor chambers comprising a single vapor core require relatively thick evaporator wicks to prevent dry out at high total heat loads, thereby imposing a large temperature drop across the wick at the hot spot location. We recently proposed a cascaded multi-core vapor chamber (CMVC) architecture comprising a single-core vapor chamber stacked on an array of smaller footprint vapor cores having relatively thinner wicks. The multi-core array is designed to spread heat from arbitrarily distributed high-flux hot spots before they enter the top vapor chamber having a thicker wick. Then, the top vapor chamber spreads the high total heat loads to the base of the mounted heat sink. To evaluate the proposed CMVC technology, we make a weighted decision to identify an appropriate minimum viable prototype for subsequent design and testing. A reduced-order model is used to determine the dimensions and properties of the wick and vapor core that minimize the temperature drop across the down-selected multi-core vapor chamber architecture for a given power map, considering manufacturing process constraints. Finite element analysis (FEA) simulations are employed to decide a condenser wall thickness that avoids permanent deformation in the vapor chamber architecture under a mechanical load. A prototype is manufactured by a commercial vendor following these parameters and manufacturing constraints. As predicted by the thermal model, experimental characterization of this first-reported multi-core vapor chamber array prototype offers a notable reduction in temperature drop relative to a benchmark solid copper spreader, owing to attenuation of hot spots at a low temperature difference.

Thermal performance and stress analysis of heat spreaders for immersion cooling applications

This paper numerically investigates the thermal performance and stress analysis of enhanced Copper (Cu) spreaders for nucleate boiling immersion cooling of high-power electronic chips. The proposed spreaders take advantage of the remarkably high thermal conductivity of Cu (low thermal spreading resistance) and enhanced nucleate boiling heat transfer of dielectric liquid PF-5060 on Microporous Cu (MPC) coating. The spreaders topmost surfaces are smooth (Ra = 0.21 μm), roughened (Ra = 1.44 μm), and coated with an 80-μm thick MPC layer. The spreader thicknesses (δCu) varied between 1.6 and 3.2 mm, the chip side length (LC) between 10 and 30 mm, and chip thickness (δC) between 200 and 500 μm. The numerical results show that MPC spreaders remove the most significant quantity of thermal power (58–270 W) dissipated by underlying chips compared to plane (smooth and roughened) Cu spreaders (28–210 W). The MPC spreaders have the least total thermal resistance, and the corresponding maximum chip temperature (Tc,max) is low (67 °C) and in a considerable safe margin from the temperature limits set by the high-power chip industry (85–120 °C). The maximum Von-Mises stress (70 MPa) on the underlying chips cooled by MPC spreaders is 1/100 of the allowable yield strength of silicon (7 GPa) but much higher than those cooled by plane Cu spreaders (40–44 MPa). The total displacement or deformation due to the temperature gradient is 22 μm and 4 μm at the top face of the spreader and at the chip-spreader interface, respectively, for MPC spreaders cooling 500 μm thick 10 × 10 mm underlying chips. The total displacement is much less (<0.5 μm) for all chips cooled by plane Cu spreaders or larger footprint area underlying chips (LC = 20–30 mm) cooled by MPC spreaders. These numerical results demonstrate the capability of MPC spreaders for immersion cooling by nucleate boiling of dielectric liquid PF-5060 of high-power electronic chips.

Experimental investigation of a vapour chamber heat spreader with hybrid wick structure

The vapour chamber is a two-phase heat transfer device that is able to effectively spread heat from concentrated heat sources to much larger heat sinks. This paper presents an experimental investigation into a copper-water vapour chamber heat spreader with hybrid wick structures. The vapour chamber had sintered powder and screen mesh wicks on the evaporator, and a screen mesh wick on the condenser. Its overall dimensions were 123 mm × 140 mm × 3 mm. The spreading resistance of the vapour chamber was explored for a non-central heating scenario. It was determined that spreading resistance of 0.08 K/W could be achieved with this vapour chamber, which was around half what would be achieved with an equivalent copper heat spreader. At low heat inputs, the vapour chamber experienced start-up difficulties. Furthermore, temperature drops through the vapour chamber and copper spreader were explored and some weaknesses of current vapour chamber designs were highlighted. Even with these weaknesses, the hybrid wick vapour chamber was able to spread heat more effectively than a copper spreader.

An Investigation into the Effective Thermal Conductivity of Vapour Chamber Heat Spreaders

Abstract Vapour chambers are a promising solution to thermal spreading issues associated with high heat flux devices. This paper presents a numerical investigation into vapour chamber heat spreaders using the concept of effective thermal conductivity. A 2D axisymmetric model was built and thermal performance was analysed through variation in effective thermal conductivity. The vapour chamber had more even temperature distributions and lower spreading resistances than an equivalent copper spreader. At a larger radius the superiority over copper was less distinct as only a 7% reduction in spreading resistance was observed compared to 20% reduction at a smaller radius. The effective thermal conductivity was identified as the limiting factor for this case and thus further advances are required to improve the spreading performance of vapour chambers.

Experimental study of a closed loop flat plate pulsating heat pipe under a varying gravity force

This paper reports on an experimental study of a closed loop Flat Plate Pulsating Heat Pipe (FPPHP) tested on ground and on board of an aircraft during the 60th ESA parabolic flight campaign, during which hyper- and microgravity conditions were reproduced. The tested FPPHP consists of two brazed copper plates, into one of which a continuous rectangular channel (1.6 × 1.7 mm2) with 12 bends in the evaporator is machined. The channel is filled with FC-72 as working fluid with a volumetric filling ratio of 50%. Tests have been conducted with the FPPHP positioned both horizontally and vertically (bottom-heated). The FPPHP presents an innovative design, involving the milling of grooves between the channels. Experimental results on the ground show that the thermal device can transfer more than 180 W in both inclinations, and that the horizontal operation is characterized by repeated stop-and-start phases and lower thermal performance. The FPPHP can operate under microgravity conditions and with a transient gravity force, with global thermal resistance reaching 50% and 25% of that of the empty plate (or around 66% and 35% of a full copper spreader of same overall dimensions), in horizontal and vertical orientation respectively. The temperature homogeneity remains within 10 K in the evaporator section and 3 K in the condenser section with thermal power transfer up to 180 W. Minimum thermal resistance of 0.12 K W−1 was recorded, with its value rising as heating grew more powerful. A parabolic flight test demonstrated that the FPPHP in vertical inclination is rapidly influenced by variation of gravity field, even if, due to the novel geometry, it continues to operate under microgravity. In horizontal inclination, on the other hand, there was no observable parameter change during gravity field variations.

Development and Characterization of Optimum Heat Sink for 30 W Chip on Board LED Down-Light

An optimum heat sink for a 30 W chip on board (COB) LED down-light is designed, fabricated, and characterized. By using the SolidWorks Flow simulator and thermal analysis software, the thermal characteristics of the optimum heat sink is analyzed. Four different types of heat sink are simulated and an optimum structure of the heat sink is found. The simulated temperature of the heat sink when operating the LED down-light is <TEX>$55.9^{\circ}C$</TEX>, which is only a difference of <TEX>$2^{\circ}C$</TEX> from the measured temperature. In order to reduce the temperature further, a copper spreader is introduced to the heat sink. The temperature of the heat sink with the copper spreader is <TEX>$3^{\circ}C$</TEX> lower than without the copper spreader.

Heat Transport Capability and Fluid Flow Neutron Radiography of Three-Dimensional Oscillating Heat Pipes.

An experimental investigation into the parameters affecting heat transport in two three-dimensional oscillating heat pipes (OHPs) was implemented. A three-dimensional OHP is one in which the center axis of the circular channels containing the internal working fluid do not lie in the same plane. This novel design allows for more turns in a more compact size. The OHPs in the current investigation is made of copper tubings (3.175 mm outside diameter, 1.65 mm inside diameter) wrapped in a three-dimensional fashion around two copper spreaders that act as the evaporator and condenser. The two OHPs have 10 and 20 turns in both the evaporator and condenser. The 20-turn OHP was filled to 50% of the total volume with a high performance liquid chromatography grade water. Transient and steady state temperature data were recorded at different locations for various parameters. Parameters such as heat input, operating temperature, and filling ratio were varied to determine its effect on the overall heat transport. Neutron radiography was simultaneously implemented to create images of the internal working fluid flow at a rate of 30 frames per second. Results show the average temperature drop from the evaporator to condenser decreases at higher heat inputs due to an increase in temperature throughout the condenser region due to greater oscillations. These large oscillations were visually observed using neutron radiography. As the operating temperature is increased, the thermal resistance is reduced. A decrease in filling ratio tends to create more steady fluid motion; however, the heat transfer performance is reduced.

Efficient spreaders for cooling high-power computer chips

Investigated is the performance of composite spreaders, consisting of a top layer of porous graphite (⩾0.4 mm), for enhanced cooling by nucleate boiling of FC-72 dielectric liquid, and a copper substrate (⩽1.6 mm), for efficient spreading of the dissipated thermal power by the underling 10 × 10 mm or 15 × 15 mm high-power computer chips. The analysis assumes uniform thermal power dissipation by the chips and calculates the square surface area of the spreader, along with the spreading, boiling and total thermal resistances, the maximum chip temperature, and the removed thermal power from the spreader surface by saturation or subcooled nucleate boiling of FC-72 liquid. These performance parameters are determined as functions of the thickness of the copper substrate and the size of the underlying chip. When compared with those of copper and porous graphite spreaders of the same total thickness, 2.0 mm, the performance of the composite spreaders is superior for cooling high-power computer chips. When cooled by nucleate boiling of 30 K subcooled FC-72 liquid, the composite spreader removes 160.3 W and 98.4 W of dissipated thermal power by the underlying 10 × 10 mm and 15 × 15 mm chips, at total thermal resistances of 0.29 and 0.48 °C/W. When the same spreader is cooled by saturation boiling of FC-72, the removed thermal power decreases to 85.6 W and 53.4 W, and the total thermal resistances also decrease to 0.12 and 0.20 °C/W, respectively. Although the calculated surface temperatures of the chips are not uniform, the maximum temperatures are <71 °C and the temperature differential across the chips is <8 °C. For the same cooling condition, the calculated surface area of the copper spreaders, the total thermal resistance, and the maximum chip temperature are much higher, but the removed thermal powers from the surface of spreaders are much lower than with composite spreaders. The calculated surface areas of the porous graphite spreaders are smaller, the thermal powers removed from surface of these spreaders are much lower and both the total thermal resistance and the maximum chip temperature are higher than those with composite spreaders.