Maximum Effective Thermal Conductivity Research Articles

Experimental study on solar wall by considering parametric sensitivity analysis to enhance heat transfer and energy grade using compound parabolic concentrator and pulsating heat pipe

Enhancing high-grade and rapid thermal storage for solar energy utilization is of paramount importance in reducing building energy consumption. Therefore, this study combines the Compound Parabolic Concentrator (CPC) and Pulsating Heat Pipe (PHP) to propose an integrated CPC-PHP solar wall (CPC-PHP-SW) that can enhance solar energy grade and rapid thermal storage. The mixed working fluid for CPC-PHP-SW is developed to reduce the dependence on solar radiation intensity and facilitate PHP startup. Furthermore, the operating characteristics and heat transfer performances of the CPC-PHP-SW are studied experimentally under various factors, including solar radiation intensity, working fluid, and cooling temperature. Sensitivity analyses of these three factors on heat transfer performances are conducted using Multi-factor analysis of variance. Results highlight that solar radiation intensity is the most influential factor on heat transfer performance, followed by cooling temperature, and working fluid. Moreover, employing a CPC with a concentration ratio of 2 reduces thermal resistance by up to 56.46 %, while the maximum effective thermal conductivity increases by up to 129.65 %. A recommended methanol to water ratio is 1:3, which effectively copes with a wide range of solar radiation intensity. These findings provide valuable references for the design and application of CPC-PHP-SW in building envelopes.

Effect of Working Fluid, Orientation, and Cooling Mode on Thermal Performance of Miniature Flat Heat Pipe

Abstract Flat heat pipes (FHPs) are commonly used as a passive cooling system in portable electronic gadgets due to their compact profile. The present study investigates the effect of different working fluids on the thermal performance of a miniature FHP under different orientations and condenser cooling mechanisms and the start-up performance of FHP. Deionized water, acetone, ethanol, and methanol are chosen as working fluids in the FHP. Five different inclinations (0 deg (horizontal), 30 deg, 45 deg, 60 deg, and 90 deg (vertical)) and two different condenser cooling methods (natural convection and forced convection with fan cooling) are considered in this experimental study. The FHP thermal performance is quantified in terms of overall temperature difference, thermal resistance, and effective thermal conductivity. The results indicate that comparatively higher effective thermal conductivity values are obtained for methanol and acetone heat pipes at low heat loads and under natural convection. At higher heat loads, the ethanol heat pipe had higher effective thermal conductivity values for the same condenser cooling method. For the case of the forced convection cooling mode, the methanol heat pipe had enhanced thermal performance as compared to the other three fluids for all heat load ranges and different inclinations. Due to the higher boiling point of water, as a working fluid water is not suitable in most of the experimental trials except at high heat load under forced convection cooling and in a horizontal orientation. The maximum effective thermal conductivity of 7846 W/mK is obtained for FHP filled with methanol at 24 W heat load and 90 deg orientation under forced convection condenser cooling.

Experimental study on the effect of graphene and Al2O3 nanofluids in a miniature flat heat pipe

The miniature flat heat pipe (mFHP) is a promising cooling technique for the thermal control of portable electronic appliances. The thermal behavior of miniature flat heat pipe (mFHP) with graphene-DI water and Al2O3-DI water-based nanofluid is experimentally investigated. The copper-made mFHP has dimensions of 200 mm in length, 10 mm in breadth, and 3 mm in thickness. The effect of nanofluid, tilt angle (0˚, 30˚, 45˚, 60˚ and 90˚), condenser cooling mode (natural convection and forced convection with fan cooling), and heat load on the effective thermal conductivity of mFHP are analyzed in this present work. The results reveal that the mFHP filled with nanofluid as working fluids shows better thermal performance as compared to those with the base fluid alone. The FHP filled with Al2O3-DI water nanofluid achieves the maximum effective thermal conductivity of 6271 W/mK under a heat load of 14 W and 60˚ orientation with natural convection condenser cooling. A heat pipe's wettability and capillary pressure are both enhanced by using nanofluid as the working fluid. As the optimum orientation of mFHP varies based on the combined effect of the type of nanofluid used in FHP, the heat load range, and the method of condenser cooling; hence it is very difficult to obtain its value analytically. Therefore, the experimental findings help in selecting the design parameters of mFHP for suitable applications.

Heat transfer characteristics and operational visualization of two-phase loop thermosyphon

The advantages of high-efficiency and pumpless long-distance heat transport make the two-phase loop thermosyphon (TPLT) a promising candidate for various energy- and thermal-related applications. In this work, the simultaneous temperature/pressure measurement and high-speed visualization observation were conducted to compare and evaluate the heat transfer performance and two-phase flow characteristics of a vertical-positioned TPLT having an inner diameter of 10 mm. R141b was used as the working fluid at volumetric filling ratios of 35–50 %. The TPLT functioned well and had high heat transfer capacity at relatively high filling ratios (⩾ 40 %), while it failed to operate at a low filling ratio of 35 % under the power inputs greater than 250 W due to the local dry-out. A maximum effective thermal conductivity of 2.0 × 105 W/(m·K) was achieved at the optimal filling ratio of 40 %. Further, a flow regime map was developed to identify the combination effect of filling ratio and heat power on the flow pattern evaluation and two-phase flow instability. The geyser boiling usually manifests itself as an alternation of two or even three flow patterns, and tends to occur at the combination conditions of relatively low filling ratios (35 % and 40 %) and low heat powers or a moderate filling ratio (50 %) and relatively high heat powers. Additionally, the white mist phenomena caused by the flash vaporization was observed in the riser at relatively higher power inputs. The liquid-vapor mixture flow in the riser would partially degrade the TPLT performance due to the inhibition of vapor condensation in the condenser region. This study provides new insight into the operation characteristics of TPLT and gives guidelines for proper design and applications.

Experimental investigation of a serial-parallel configuration helium pulsating heat pipe

Cryogenic pulsating heat pipe with the features of exceptional heat transfer performance and easy manufacturing is a good candidate to effectively transfer the cooling power energy in the conduction-cooled superconducting magnet system. In this work, a new type of serial-parallel 24-turn configuration pulsating heat pipe with helium as working fluid has been investigated experimentally under various working conditions by changing heat loads, inclination angles, and filling ratios. Experimental results demonstrate that for this pulsating heat pipe, working in vertical orientation is more appropriate. Additionally, the optimum filling ratio changes with the heat load input. The maximum effective thermal conductivity is 12357 W/(m∙K), obtained at the inclination angle of 90° and the filling ratio of 66.1%. The new configuration demonstrates high thermal performance well above the critical point of helium. At the filling ratio of 94.2% and the vertical position, this pulsating heat pipe can transport up to 25 W heat load without reaching dry-out occurrence. The influences of the number of turns and tube structure are discussed by comparing the serial-parallel 24-turn helium pulsating heat pipe with the 4-turn helium pulsating heat pipe and the serial 24-turn helium pulsating heat pipe with the same dimensions we tested previously. The result shows that the serial-parallel 24-turn helium pulsating heat pipe is more efficient concerning heat transfer capacity and thermal resistance. Increasing the number of turns can reduce the temperature gradient of the helium pulsating heat pipe, and changing the tube structure from series to series–parallel can greatly improve the heat transfer limit of the helium pulsating heat pipe. Moreover, another novel parallel 24-turn helium pulsating heat pipe is proposed. According to the theoretical analysis, The parallel 24-turn helium pulsating heat pipe could reach a higher maximum effective thermal conductivity, whereas the serial-parallel 24-turn helium pulsating heat pipe is outstanding in heat transfer capacity.

A novel ultra-thin vapor chamber with composite wick for portable electronics cooling

With the development of integrated and ultra-thin portable electronics, the ultimate heat dissipation power in extremely narrow spaces (<1 mm) is increasing year by year. However, the current critical power of ultra-thin vapor chamber (UTVC) is still at a low level, which hinders the development of high-power portable electronic products. In this study, novel UTVCs with a thickness of only 0.5 mm are prepared by utilizing the composite capillary wick. Different from the traditional multi-layer 2D copper mesh wick, the composite (CA/CB) wick is composed of multi-layer 2D copper mesh and 3D spiral woven mesh. UTVCs prepared from three different wicks, referred as to 2D-UTVC, CA-UTVC, CB-UTVC, were compared. Under different working conditions, the CA/CB-UTVC has better heat transfer performance than 2D-UTVC. In the horizontal state, the maximum effective thermal conductivity (Keff) of CA-UTVC and CB-UTVC is significantly improved by 86.8% and 60.2% compared to that of reference 2D-UTVC. The CA design is recommended for low heating power within 40 W, while the CB design is the optimal choice for high heating power above 40 W. The maximum critical power of CB-UTVC is up to 60 W with gravity support. Even at 50 W under anti-gravity condition, the thermal conductivity of CB-UTVC is still up to 11817.1 W/(m K), which is 29.5 times that of copper. The improved heat dissipation is due to the enhanced capillary force of the composite wick. This positive effect is facilitated by the combination of multiple 3D spiral woven meshes in the CB design. The optimized UTVC effectively reduces the maximum temperature by 14.3 °C compared to copper sheet under natural convection at 10 W heating power. The novel UTVC could provide a guarantee for the heat dissipation of high-power integrated portable electronic devices in the future.

Experimental investigation of the thermal characteristics of a novel pure-metal-based flexible ultrathin vapour chamber

The rapid development of high-performance flexible electronics requires novel metal-based flexible ultrathin vapour chamber (FUTVC) with higher heat transfer capacity to meet their heat dissipation needs. Although many works on flexible vapour chambers have been published, there are few works on metal-based flexible vapour chambers. Therefore, in this paper, a novel pure-metal-based FUTVC was proposed. Three kinds of FUTVCs were fabricated by brazing process and laser welding process, which were cost-effective processes suitable for mass production. The effect of manufacturing process, test direction and bending condition on the heat transfer performance of FUTVC was clarified, and the thermal mechanism of the FUTVC under bending conditions was theoretically analyzed. Results indicated that both laser welding and brazing can effectively seal the FUTVC. Wick sintered on the cover plate can effectively improve the thermal performance of the FUTVC. The maximum heat transfer capacity of the FUTVC in gravity state, horizontal state and anti-gravity state were 19 W, 16 W and 14 W, respectively. Furthermore, the maximum heat transfer capacity of the FUTVC with bending of 15°, 30°, 60° and 90° were 11 W, 10 W, 9 W and 8 W, respectively. The maximum effective thermal conductivity of the FUTVC was over 26000 W/(m•K) in horizontal state and over 10000 W/(m•K) under different bending conditions, which were approximately 65 times and 25 times higher than that of pure copper, respectively. The proposed novel FUTVC is promising for solving the heat dissipation problem of high performance ultra-thin flexible electronics.

Investigation of the role of electrohydrodynamic forces on the heat transfer enhancement and solid extraction during melting of paraffin wax under constant temperature boundary conditions

The melting enhancement of paraffin wax is studied experimentally under the effect of electrohydrodynamic (EHD). Paraffin wax was melted under constant temperature boundary conditions with different applied DC voltage magnitudes and polarities, and different temperature gradients. The role of EHD forces was investigated by applying DC and AC square waves with different frequencies and offset values.It was found that the melting enhancement rises nonlinearly with increasing the voltage magnitudes. The maximum effective thermal conductivity under -10 kV was found to be 0.95 W/m-K in comparison with the value of 0.2 W/m-K for the pure liquid paraffin wax, with an enhancement ratio of 4.75.The EHD solid extraction phenomenon investigation showed that the extraction was detected for all the applied DC voltages. Small dendrites were observed to be pulled out from the mushy zone melt front and rise upwards in a rotational manner. It is concluded that the Coulomb force is the primary force for extraction while the formation of electroconvection cells is the main driving mechanism for the motion of the suspended dendrites in the liquid bulk. In addition, the AC studies revealed that the dielectrophoretic force is negligible in this study.

Novel condenser based cryogenic pulsating heat Pipe: Investigations on influence of geometrical parameters

Pulsating heat pipes (PHPs) are becoming popular among passive cooling devices as a possible replacement for the thermal conductive links associated with cryocooler applications. To cool high-temperature superconductors, the need for a large cooling capacity cryocooler is rapidly increasing. The available literature studies show that the heat transfer capability of cryogenic PHP depends on the cryocooler's cooling power. Therefore, findings of a higher heat transport limit and optimal geometrical parameters for a cryogenic PHP remain unsolved. The present paper focuses on developing a novel cylindrical shell-type condenser (CSTC) to provide a high cooling load in a cryogenic PHP. Liquid nitrogen is used as a cryogen. The experiments are performed to study the influence of a number of turns (Single-Turn (ST), Two-Turn (TT)) and adiabatic length (60 mm, 120 mm) designated as ST-60, ST-120, TT-60 and TT-120 PHPs. The inner and outer diameters of PHPs are 1.3 mm and 3.2 mm, respectively. The filling ratio (FR) of cryogen is kept between 38 % and 95 %. The heat load varies from 1 W to 60 W with a bottom heating position. For a case of varying adiabatic length, the lowest thermal resistance increases by 24.78 % for ST-120 PHP compared to ST-60 PHP and 3.23 % for TT-120 PHP compared to TT-60 PHP. For a case of a number of turns, the lowest thermal resistance decreases by 36.57 % for TT-60 PHP compared to ST-60 PHP and 47.5 % for TT-120 PHP compared to ST-120 PHP. The maximum effective thermal conductivity (Keff) of 40,590 W/m-K is observed for an ST-120 PHP. A hybrid cooling technique is proposed with a combination of a novel CSTC and cryocooler to provide a high cooling load with a lower need for cryogen replenishment in the condenser section of a PHP device for an on-ground application.

Effect of heat leakage on the operational characteristics of two-phase loop thermosyphon with a thermal insulation pipe

In this paper, a two-phase loop thermosyphon (TPLT) with a hollow polytetrafluoroethylene (PTFE) thermal insulation pipe (TIP) installed below the evaporator section was fabricated to experimentally investigate the effect of heat leakage on the TPLT performance. The startup and heat transfer characteristics of TPLT were compared and evaluated using HFE-7100 as a working fluid at volumetric filling ratios of 35–55%. Two startup modes, with and without temperature/pressure overshoot, were evidenced for the TPLT, and they were heat load dependent. The startup time of TPLT increased with the filling ratio and decreased with the power input. Owing to the hot-cold fluid interaction and mixing at the lower part of the evaporator characterized by larger temperature differences for them, it caused the evaporator temperature fluctuations, and the temperature oscillation amplitudes aggravated with the increase of filling ratio at lower power inputs. The utilization of a TIP into the TPLT increased both the thermal efficiency and thermal performance at filling ratios of 35 and 45%, while opposite results were obtained at the filling ratio of 55%. At the filling ratio of 35%, a highest thermal efficiency of 87% was achieved for the TPLT with a TIP at the power input of 90 W, which was 7.8% higher than that without a TIP. Accordingly, a maximum effective thermal conductivity of 1.5 × 105 W/(m·K) was obtained and 8.2% higher than that without a TIP. The addition of TIP lowered the heat leakage towards the liquid line, and it provides a cost-effective option to improve energy utilization and conversion efficiency for prospective applications.

Experimental investigation of heat spreading in a wickless and ultrathin thermal ground plane

A thermal ground plane (TGP) device spreads concentrated heat effectively into a relatively large area. The TGP selected for this study utilizes bubble pumping, instead of wicking, to effectively circulate fluid inside its chamber and keep the hot area wetted. It is thin, light, durable, and its performance is orientation-independent. With a 0.80 mm thick chamber, this TGP can achieve a thermal resistance below 0.2 K/W. Reducing the chamber's thickness by 20% and 50% is shown experimentally to yield a better thermal resistance, as low as 0.15 K/W. The corresponding maximum effective thermal conductivity of the TGP is 1339 W/m-K, 1008 W/m-K, and 821 W/m-K for a chamber thickness of 0.40 mm, 0.64 mm, 0.80 mm, respectively. However, a reduced dryout heat flux is detected with a thinner TGP. This work aims to investigate the effects of the chamber's thickness on the thermal performance of this ultrathin TGP. The performance of the TGP is orientation-independent regardless of thickness and water charging amount in its chamber.

Enhanced Longitudinal Heat Transfer in Oscillatory Channel Flow—A Theoretical Perspective

Abstract Enhanced longitudinal heat transfer in viscous, laminar, single-phase, oscillatory channel flow is investigated in this paper. Kurzweg (ASME J. Heat Transfer-Trans. ASME. 107, 1985) analyzed this case theoretically and derived a correlation for a nondimensionalized effective thermal conductivity in terms of Prandtl and Womersley numbers. The present investigation contributes analysis of limiting cases and physical interpretation to the results of Kurzweg. A simplified model with isothermal walls is proposed, applicable if working fluid and channel wall material exhibit sufficiently large differences in thermal inertia. Examined over a wide range of Womersley numbers, this model reveals six distinct regimes characterized by the Prandtl number of the fluid. The respective thickness of hydrodynamic and thermal boundary layers relative to the channel width is relevant in this context. Maximum effective thermal conductivity is attained when the thermal boundary layer expands over the full channel width. The influence of Womersley number is discussed and explained in terms of the interplay of hydrodynamic and thermal flow characteristics. These patterns reveal either quasi-steady parabolic or oscillating bulk characteristics. The importance of the thermal boundary layer thickness motivates the introduction of a new nondimensional group, making it easier to classify the various regimes of enhanced longitudinal heat transfer.

Thermal performance and flow characteristics in additive manufactured polycarbonate pulsating heat pipes with Novec 7000

• A 3D-printed polycarbonate-based transparent PHP was successfully fabricated. • An aluminum plate bonded to the 3D-printed channel allows for better heat conduction. • The 3D-printed transparent PHP enables flexible channel design and flow visualization. • The maximum effective thermal conductivity of 7.0 × 10 3 W/(m⋅K) was obtained. To improve the performance of electronic devices, incorporating an effective cooling system in their thermal design is important. A pulsating heat pipe (PHP) is a passive cooling device that efficiently transports heat as sensible heat and latent heat from an evaporator section to condenser section via an oscillatory two-phase flow. In recent years, with the progress of additive manufacturing technology the design of PHPs with increased flexibility and wider industrial applicability has been expected. To optimize a plastic PHP flow channel structure for practical uses, the effects of channel geometry and flow regime on appropriate operating conditions need to be clarified at higher input power. The present study focuses on the flow visualization of a plastic-based PHP having a practical channel size and configuration. Using additive manufacturing, a serpentine flow channel of the PHP was fabricated with transparent polycarbonate. The PHP was filled with Novec 7000 as a working fluid, and the effects of the flow channel size and fill ratio of the working fluid on PHP’s heat transport performance were investigated. Based on the flow visualization images, we evaluated the flow pattern and two-phase flow parameters such as vapor-slug lengths, velocity, and passing frequency, and clarified the relationship between the oscillating flow and thermal performance during the PHP operation.

Optimization of Effective Thermal Conductivity of Thermal Interface Materials Based on the Genetic Algorithm-Driven Random Thermal Network Model.

Polymer-based thermal interface materials (TIMs) are indispensable for reducing the thermal contact resistance of high-power electronic devices. Owing to the low thermal conductivity of polymers, adding multiscale dispersed particles with high thermal conductivity is a common approach to enhance the effective thermal conductivity. However, optimizing multiscale particle matching, including particle size distribution and volume fraction, for improving the effective thermal conductivity has not been achieved. In this study, three kinds of filler-loaded samples were prepared, and the effective thermal conductivity and average particle size of the samples were tested. The finite element model (FEM) and the random thermal network model (RTNM) were applied to predict the effective thermal conductivity of TIMs. Compared with the FEM, the RTNM achieves higher accuracy with an error less than 5% and higher computational efficiency in predicting the effective thermal conductivity of TIMs. Combining the abovementioned advantages, we designed a set of procedures for an RTNM driven by the genetic algorithm (GA). The procedure can find multiscale particle-matching ways to achieve the maximum effective thermal conductivity under a given filler load. The results show that the samples with 40 vol %, 50 vol %, and 60 vol % filler loading have similar particle size distribution and volume fractions when the effective thermal conductivity reaches the highest. It should be emphasized that the optimized effective thermal conductivity can be improved obviously with the increase in the volume fraction of the filler loading. The high efficiency and accuracy of the procedure show great potential for the future design of high-efficiency TIMs.

On the design of Phase Change Materials based thermal management systems for electronics cooling

This work aims at explaining the effect of the operating conditions on the performance of passive electronic thermal management systems based on Phase Change Materials. The low thermal conductivity of the Phase Change Materials is usually felt as one of their major limitations that hinders the effective heat transfer capability of the whole passive system. However, the present study experimentally demonstrates that the real improvement due to the use of enhanced heat transfer surfaces depends upon the operating conditions. The experimental tests were run on a latent thermal management system based on a paraffin wax with a 70 °C phase change temperature embedded in two different samples: an aluminum 3D pyramidal periodic structure having a porosity of 0.95 and a cell dimension of 10 mm realized via additive manufacturing, and an empty sample used as reference. The system was experimentally tested under several working conditions to simulate the real operation of an electronic device, including complete melting/solidification cycle and intermittent operations at different ambient temperatures, in natural and forced convection. The main outcome of the present study is that, when considering the junction temperature, the use of the enhanced surface does not always lead to an improvement of the heat transfer performance especially during fast intermittent operations and thus the maximum effective thermal conductivity cannot be always considered the main design objective. A novel integrated design approach should include the properties of the Phase Change Material, the system requirements and the real operating conditions.

Experimental investigations on two-turn cryogenic pulsating heat pipe with cylindrical shell-type condenser

• Cryogenic Pulsating Heat Pipe is experimentally investigated. • A cylindrical shell-type condenser is proposed for Liquid nitrogen-based Cryogenic PHP. • The influence of heat input and Filling Ratio (FR) on the performance of Cryogenic PHP is studied. • Fast Fourier Transform (FFT) analysis is carried out to comprehend the Cryogenic PHP system. Pulsating heat pipe (PHP) is a two-phase passive cooling device and has become an efficient heat transport system to replace bulky conductive straps in cryogenics applications. A two-turn cryogenic PHP is experimentally investigated with liquid nitrogen as working fluid in the present paper. A cylindrical shell-type condenser is proposed that provides a high cooling load with easy refilling of liquid nitrogen. The inner diameter of the capillary tube is 1.3 mm, and the outer diameter is 3.2 mm. The filling ratios are kept as 38%, 57%, 76%, and 95%. Heat input is varied in the range of 1 W-80 W. The maximum heat transport capacity of a two-turn cryogenic PHP with cylindrical shell-type condenser is observed 70 W before dry out. The maximum effective thermal conductivity ( K eff ) of 16350 W/m-K is observed at an optimum filling ratio of 76%. Fast Fourier Transform (FFT) analysis showed cryogenic PHP's deterministic behaviour at the optimal stage with a frequency range of 0.62–1.56 Hz.

Experimental study on the heat transport capability of micro-grooved oscillating heat pipe

This paper presents an experimental study to investigate the heat transfer limit of a micro-grooved OHP at the vertical bottom heat mode. The internal hydraulic diameter of the micro-grooved OHP is about 2.0 mm, and deionized water was used as a working fluid at volumetric filling ratios (FRs) ranging from 30% to 60%. Experimental results demonstrated that the micro-grooved OHP could significantly enhance the allowable maximum input heat flux before the occurrence of dry-out owing to the capillary action provided by micro-grooved structures to facilitate condensate backflow to the evaporator. The OHP obtained a maximum effective thermal conductivity of 41.8 kW/(m·°C) at 40% FR, corresponding to a dry-out heat flux of 36.9 W/cm2 with respect to the heat transfer limit. The allowable maximum input heat flux was found to be greater than 80 W/cm2 for 50% and 60% FRs, and could be further increased by increasing the OHP turn number. This study provides a promising option to address thermal management demand for high-density power devices.

Performance Tests on a Novel Un-Finned Thermosyphon Heat Exchanger Requiring a Single Charge

A novel design of an unfinned thermosyphon HPHX having a continuous closed tube loop which requires only a single charge is proposed for industrial waste heat recovery. The HPHX consists of 9×17 straight copper tubes in a staggered arrangement connected by 144 U bends. Without fins, not only are the pressure drops of the cooling air flow limited, but the cost, weight and maintenance effort can be greatly reduced. The thermal performance of this novel thermosyphon HPHX was tested with water at a filling ratio of 40%. The evaporator section is immersed in hot silicone oil, while the condenser section is cooled by air flow. The heat transfer rate (Q) reaches 6.65 kW at a heating pool temperature of 150 °C and a cooling air flow rate (F) of 1600 CMH, when the HPHX attains maximum effective thermal conductivity of 12,798 W/m-K. An ε-NTU theoretical model for single-tube thermosyphons was formulated with the boiling and film condensation modelled by empirical correlations. This model predicts the total resistance Rtot of the HPHX, which decreases with Q and F, with a total error of less than ±10%.

Effects of micro heat pipe arrays on thermal management performance enhancement of cylindrical lithium‐ion battery cells

The performance of lithium-ion (Li-ion) batteries in a battery module is significantly affected by the operating temperature. Temperatures above 40°C can speed up the battery aging and shorten the lifespan and may even lead to thermal runaway. Besides, the maximum temperature deviation between the cells inside the battery module is normally expected to be less than 5°C. Among various cooling strategies used in thermal management of Li-ion batteries, application of micro heat pipe arrays (MHPAs) has received little attention. Hence, in the present study, a feasibility study has been conducted to assess the thermal performance of such a thermal link in controlling both the maximum temperature and temperature dispersion within the desired range. The MHPA-assisted cooling system was tested under various rates of heat generations (10-25 W total) and degrees of inclination (−90° to +90°). Experimental results have revealed a significant influence of the MHPA angle of inclination on the temperature of the evaporating section of the heat pipe. The best thermal performance was found to be at an angle of inclination of −15° where the condenser is located above the evaporating section. Performance degradation was observed for all the MHPA orientations where the condenser is located below the evaporating section. The thermal performance of the MHPA-assisted cooling system is also influenced by the rate of generated heat. The maximum effective thermal conductivity for the MHPA was measured to be about 75 000 W/m2 °C. A dimensional figure of merit is defined for the MHPA-assisted cooling system.

Product design: An optimization-based approach for targeting of particulate composite microstructure

The microstructure of a particulate composite with given ingredients has enormous influence on its physicochemical properties. An optimization-based approach is presented for determining the target of two-component particulate composite microstructure. The dominant physicochemical phenomena are captured by the relevant gradient-based transport equations. Particles of different size, shape, and orientation are placed in the composite to maximize a desired physicochemical property. The formulated problem is readily solved via mixed-integer non-linear programming. A case study is performed on the design of a die attach adhesive the objective of which is to obtain the maximum effective thermal conductivity at different loadings of the nano filler particles.