Heat Dissipation Measurements Research Articles

Applying wash coating techniques for swelling-induced stress reduction and thermal improvement in metal hydrides

The storage of hydrogen in metal alloys as an alternative to hydrogen storage in pressurized or liquid form has the advantage of high volumetric storage capacity and less complex storage systems due to lower pressure and moderate temperature conditions. The later leads to an improved safety and reduced cost of the storage vessel. However, when considering their utilization in hydrogen storage tanks, swelling-induced stress and heat management are challenges that still require to be addressed. Several strategies have been published in the past to address these problems, however it can be challenging to scale them up. In this work, we propose an easily scalable approach to overcome these drawbacks. The commercially available AB2 room-temperature metal alloy Hydralloy C5 was modified by applying a wash coating-like methodology. The surface of the metal alloy was coated with a mixture of a conductive material like expanded natural graphite (ENG) or aluminum and the elastomeric ethylene-vinyl acetate copolymer (EVA). The performance of this modified metal alloy was investigated by in situ measurement of hydrogen capacity, heat dissipation and swelling-induced stress during 50 hydrogenation/dehydrogenation cycles. The coated metal alloy maintained a satisfactory hydrogen capacity with slightly improved heat dissipation. The swelling-induced stress behavior of the treated material was greatly improved. Especially the addition of a mixture of 10 wt% ENG and 10 wt% EVA allowed to completely compensate for the swelling-induced stress during hydrogenation.

Measurement of Heat Dissipation and Thermal-Stability of Power Modules on DBC Substrates with Various Ceramics by SiC Micro-Heater Chip System and Ag Sinter Joining.

This study introduced the SiC micro-heater chip as a novel thermal evaluation device for next-generation power modules and to evaluate the heat resistant performance of direct bonded copper (DBC) substrate with aluminum nitride (AlN-DBC), aluminum oxide (DBC-Al2O3) and silicon nitride (Si3N4-DBC) ceramics middle layer. The SiC micro-heater chips were structurally sound bonded on the two types of DBC substrates by Ag sinter paste and Au wire was used to interconnect the SiC and DBC substrate. The SiC micro-heater chip power modules were fixed on a water-cooling plate by a thermal interface material (TIM), a steady-state thermal resistance measurement and a power cycling test were successfully conducted. As a result, the thermal resistance of the SiC micro-heater chip power modules on the DBC-Al2O3 substrate at power over 200 W was about twice higher than DBC-Si3N4 and also higher than DBC-AlN. In addition, during the power cycle test, DBC-Al2O3 was stopped after 1000 cycles due to Pt heater pattern line was partially broken induced by the excessive rise in thermal resistance, but DBC-Si3N4 and DBC-AlN specimens were subjected to more than 20,000 cycles and not noticeable physical failure was found in both of the SiC chip and DBC substrates by a x-ray observation. The results indicated that AlN-DBC can be as an optimization substrate for the best heat dissipation/durability in wide band-gap (WBG) power devices. Our results provide an important index for industries demanding higher power and temperature power electronics.

Energy use efficiency of root growth – a theoretical bioenergetics framework

ABSTRACTMetabolic efficiency of root growth is a crucial physiological parameter, contributing to the amount of photosynthate that plants need to invest into soil exploration. Common measurements of metabolic efficiency usually rely on CO2 respiration measurements with the underlying assumption that all metabolic processes are taking place under aerobic conditions. In this conceptual paper, we introduce energy use efficiency based on the quantification of heat dissipation and energy fluxes as an alternative metric to quantify the metabolic efficiency of root growth. In a theoretical framework, we adopted recently published heat dissipation data from wheat seedlings and show that energy use efficiency decreases in response to (i) soil hypoxia and (ii) increased soil penetration resistance. In contrast to traditional CO2 respiration measurements, heat dissipation measurements account for both aerobic as well as anaerobic respiration in growing roots. Hence, we advocate that the quantification of heat dissipation provides a more complete picture of the metabolic efficiency of root growth than CO2 respiration measurements alone. We therefore propose that energy use efficiency should be included in future studies assessing the metabolic efficiency of root growth.

Three-Dimensional Printing of Abrasive, Hard, and Thermally Conductive Synthetic Microdiamond–Polymer Composite Using Low-Cost Fused Deposition Modeling Printer

A relative lack of printable materials with tailored functional properties limits the applicability of three-dimensional (3D) printing. In this work, a diamond-acrylonitrile butadiene styrene (ABS) composite filament for use in 3D printing was created through incorporation of high-pressure and high-temperature (HPHT) synthetic microdiamonds as a filler. Homogenously distributed diamond composite filaments, containing either 37.5 or 60 wt % microdiamonds, were formed through preblending the diamond powder with ABS, followed by subsequent multiple fiber extrusions. The thermal conductivity of the ABS base material increased from 0.17 to 0.94 W/(m·K), more than five-fold following incorporation of the microdiamonds. The elastic modulus for the 60 wt % microdiamond containing composite material increased by 41.9% with respect to pure ABS, from 1050 to 1490 MPa. The hydrophilicity also increased by 32%. A low-cost fused deposition modeling printer was customized to handle the highly abrasive composite filament by replacing the conventional (stainless-steel) filament feeding gear with a harder titanium gear. To demonstrate improved thermal performance of 3D printed devices using the new composite filament, a number of composite heat sinks were printed and characterized. Heat dissipation measurements demonstrated that 3D printed heat sinks containing 60 wt % diamond increased the thermal dissipation by 42%.

The influence of carbon dioxide-induced water acidification on the osmotic and metabolic responses of the Baltic amphipod Gammarus oceanicus

The aim of this study was to investigate the effect of CO2-induced water acidification (pH values: 8.1 − control, 7.5 and 7.0) on the hemolymph osmolality and total metabolic rate of amphipod Gammarus oceanicus under short-term exposure. The hemolymph osmolality was measured using a vapor pressure osmometer. The metabolic rate was determined based on the heat dissipation measurements using a Calvet-type isothermal twin calorimeter. The hemolymph osmolality remained unchanged after exposure to pH 7.5 and it increased in the lowest treatment. Acidification did not significantly affect the resting or active metabolic rate. The observed results indicate that high osmolality maintained during hypercapnia did not generate additional physiological costs. It may therefore be concluded that the studied species is preadapted for this factor. The long-term adaptation to hypoosmotic conditions in the brackish Baltic Sea might also have preadapted it to hypercapnia because similar physiological mechanisms are responsible for the resistance to both factors.

Measurement of electronic heat dissipation in highly disordered graphene

We have measured the electronic heat dissipation of hot electrons in highly disordered millimeter scale graphene at temperatures $T=0.3\text{--}3$ K. Disorder was introduced by hydrogenation of graphene, bringing low-temperature electron conduction below the Ioffe-Regel criterion for metallic conduction. Resistive thermometry was employed to determine the dependence of electron temperature on applied electrical power. The relation between heat flow and electron temperature was found to be well described by a power law with an exponent $\ensuremath{\beta}\ensuremath{\sim}3.7\text{--}3.9$ and a coupling coefficient $\mathrm{\ensuremath{\Sigma}}\ensuremath{\sim}1\phantom{\rule{0.28em}{0ex}}\mathrm{mW}/{\mathrm{m}}^{2}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{\beta}}$. Our observations are similar to electronic heat dissipation of a two-dimensional electron gas in the hydrodynamic limit of electron-phonon coupling, corresponding to acoustic phonon emission into the substrate.

The Effect of CO2-Induced Seawater Acidification on the Behaviour and Metabolic Rate of the Baltic ClamMacoma balthica

The aim of this study was to investigate the effect of CO2-induced seawater acidification (pH 8.1; control pH 7.0 and 6.0) on the survival, behaviour and metabolic rate of the Baltic clam Macoma balthica during short- (36 hours) and long-term (14 days) exposures. Total metabolic rate and gaping behaviour (shell opening and closing) were determined based on heat dissipation measurements using an isothermal twin calorimeter of the Calvet type. The survival and burrowing behaviour during long-term exposure were observed every day. Short-term exposure to reduced pH did not significantly affect the resting or active metabolic rate. Neither were there any significant changes in gaping behaviour. However, long-term exposure significantly affected burrowing behaviour. In the lowest-pH treatment, both resting and active metabolic rates were also significantly higher than in the control.

Metabolic activity and behavior of the invasive amphipod Dikerogammarus villosus and two common Central European gammarid species (Gammarus fossarum, Gammarus roeselii): Low metabolic rates may favor the invader

The Ponto-Caspian amphipod Dikerogammarus villosus is one of the most successful invaders in Central European rivers. Contrary to studies on its ecology, ecophysiological studies comparing the species' physiological traits are scarce. In this context, in particular the metabolic activity of the invasive species has rarely been considered and, moreover, the few existing studies on this species report strongly deviating results. The purpose of this study was to assess the metabolic activity and behavior of D. villosus and other common European amphipod species (Gammarus fossarum, Gammarus roeselii) in relation to temperatures covering the thermal regime of the invaded habitats. Based on direct calorimetric measurements of metabolic heat dissipation at three temperature levels (5°C, 15°C and 25°C), we found the routine metabolic rate of D. villosus to be significantly lower than that of the other studied gammarid species at the medium temperature level. The estimated resting metabolic rate indicated a similar trend. At 5°C and 25°C, both routine and resting metabolic rate did not differ between species. Compared to G. fossarum and G. roeselii, D. villosus exhibited lower locomotor activity at the low and medium temperatures (5°C and 15°C). In contrast, its locomotor activity increased at the high experimental temperature (25°C). G. fossarum and G. roeselii were apparently more active than D. villosus at all studied temperatures. We conclude that D. villosus has both physiological and behavioral adaptations that lead to a reduction in metabolic energy expenditure, which is assumed to be beneficial and might contribute to its invasive success.

Measuring the mechanical efficiency of a working cardiac muscle sample at body temperature using a flow-through calorimeter.

We have developed a new `work-loop calorimeter' that is capable of measuring, simultaneously, the work-done and heat production of isolated cardiac muscle samples at body temperature. Through the innovative use of thermoelectric modules as temperature sensors, the development of a low-noise fluid-flow system, and implementation of precise temperature control, the heat resolution of this device is 10 nW, an improvement by a factor of ten over previous designs. These advances have allowed us to conduct the first flow-through measurements of work output and heat dissipation from cardiac tissue at body temperature. The mechanical efficiency is found to vary with peak stress, and reaches a peak value of approximately 15 %, a figure similar to that observed in cardiac muscle at lower temperatures.

Metabolic rate and activity of blue mussel Mytilus edulis trossulus under short-term exposure to carbon dioxide-induced water acidification and oxygen deficiency

This work investigated the effect of carbon dioxide-induced decreased water pH (8.1 – control, 7.5 and 7.0), oxygen saturation (~100% and ~20%) and the combination of both factors on the behaviour (gaping activity) and the total metabolic rate of blue mussel Mytilus edulis trossulus from the southern Baltic Sea. Heat dissipation measurements were carried out in a Calvet-type isothermal twin calorimeter equipped with a flow-through system. The resting metabolic rate was not significantly (p > 0.05) affected by pH or oxygen saturation. Neither was there significant (p > 0.05) effect of the interaction of both factors on this process. The high inter-individual variability in behaviour affected the value of maximal recorded activity and duration of activity peaks connected with shell gaping behaviour. In some mussels, they were short and appeared periodically, and other individuals were inactive or exhibited temporal activity terms of different duration. The lowered oxygen saturation significantly (p < 0.05) affected the time spent on activity. However, there was no effect (p > 0.05) of lowered pH on this parameter, which indicates that oxygen deficiency may affect the Baltic population of M. edulis trossulus more seriously than acidification.

Age-Related Decrements in Heat Dissipation during Physical Activity Occur as Early as the Age of 40

Older adults typically experience greater levels of thermal strain during physical efforts in the heat compared to young individuals. While this may be related to an age-dependent reduction in whole-body sweating, no study has clearly delineated at what age this occurs. In the present study, we report direct measurements of human heat dissipation during physical activity in the heat in males ranging in age from 20–70 years. Eighty-five males performed four 15-min bouts of cycling separated by 15-min rest periods, in a calorimeter regulated to 35°C and 20% relative humidity. Direct calorimetry was used to measure total heat loss (whole-body evaporative heat loss and dry heat exchange). We also used indirect calorimetry as a continuous measure of metabolic heat production. Body heat storage was calculated as the temporal summation of heat production and total heat loss over the experimental session. Whole-body sweat rate (WBSR) was calculated from measurements of evaporative heat loss. Males were divided into five age categories for the analysis of WBSR and body heat storage: 20–31 years (n = 18), 40–44 years (n = 15), 45–49 years (n = 15), 50–55 years (n = 21) and 56–70 years (n = 16). Relative to young males, WBSR was reduced in males aged 56–70 during each exercise (all P<0.05), in males aged 50–55 during the second (P = 0.031) and third exercises (P = 0.028) and in males aged 45–49 during the final exercise bout (P = 0.046). Although not significantly different, 40–44 years old males also had a lower rate of heat loss compared to younger males. Over the sum of two hours, the change in body heat content was greater in males 40–70 years compared to young males (all P<0.05). Our findings suggest that middle-aged and older adults have impairments in heat dissipation when doing physical activity in the heat, thus possibly increasing their risk of heat-related illness under such conditions.

Direct calorimetry exposes inadequacies of respirometry in the measurement of resting metabolic rate

Resting metabolic rate (RMR) in animals is frequently estimated by respirometry, but the dependence of this method upon untested or untestable assumptions (such as negligible anaerobic metabolism, simultaneously measured or negligible protein oxidation, and no substrate inter‐conversion) render respirometry inappropriate or inadequate for examining novel genetically‐manipulated animal models. A Seebeck‐style direct calorimeter apparatus was constructed to allow simultaneous measurement of total heat dissipation and respirometry gasses from unrestrained mice. Double‐transgenic “sRA” mice exhibit elevated brain renin‐angiotensin system activity by expression of human renin via the synapsin promoter and human angiotensinogen via its own promoter. Respirometry underestimated the RMR in sRA mice by 16% (n=6, male, 11.0±0.6 wks, 20.97±0.68 g; 0.889±0.036 vs 1.057±0.034 kcal/100g lean/hr, P=0.008), and by 14% in control littermates and C57Bl/6J mice (n=10, male, 11.6±0.5 wks, 27.02±0.60 g; 0.712±0.025 vs 0.828±0.018 kcal/100g lean/hr, P=0.005). While respirometry faithfully detected the 26% increase in sRA RMR vs control (P&lt;0.001 by both methods), the magnitude of RMR estimation error by respirometry was similar (~15%). Reanalysis of various other genetically‐manipulated models by direct calorimetry may therefore uncover previously unappreciated physiological regulators of RMR.

Heat dissipation measurements in low stress cyclic loading of metallic materials: From internal friction to micro-plasticity

The present paper deals with a procedure to measure the very small quantities of heat generated during the very first cycles of mechanical loading on metallic specimens. A dedicated procedure is presented to reach the required sensitivity in terms of heat sources with some original features with respect to the present state of the art, assuming that the heat sources are uniformly distributed within the specimen as such low strain levels. Then steel (cold rolled and annealed) and aluminium specimens were tested at two different aspect ratios ( R σ = 0.1 and R σ = - 1 ). It was shown that for small stress levels, the heat generated was more or less constant with cycle number. This energy was associated to visco-elastic behaviour (internal friction) and it was shown that the same energy could be measured with the two stress ratios when plotted against strain rate (stress amplitude at constant frequency, here 15 Hz). Then, after a certain stress level, an initial outburst of energy was evidenced over about 10–15 cycles before a constant level was reached again. This was associated to micro-plastic adaptation. This procedure provides an advanced tool to tackle the problem of very early fatigue damage detection and is aimed at providing some physical justification to the procedures of rapid fatigue limit detection by self-heating tests.

Leaf Chlorophyll Fluorescence Parameters and Huanglongbing

Chlorophyll fluorescence and photochemical and nonphotochemical quenching parameters were measured in 20 genotypes of Citrus spp. or relatives grown in the greenhouse and commercial ‘Valencia’ sweet orange (Citrus sinensis) trees at two Florida locations. The purpose was to determine the utility of measurements for early huanglongbing [HLB (Candidatus Liberibacter asiaticus)] detection in asymptomatic trees and to examine the leaf response to HLB infection. Polymerase chain reaction (PCR)-negative healthy and PCR-positive symptomatic, asymptomatic, and distant asymptomatic leaves were used for fluorescence analysis using a portable chlorophyll fluorometer. Greenhouse-grown genotypes were separated into mild, moderate, and severe symptom groups based on leaf mottling, color, and size. In general, mild symptom genotypes were characterized by increased photosystem II (PSII) excitation pressure and unregulated heat dissipation and decreased regulated heat dissipation, whereas moderate and severe symptom genotypes increased loss of photosynthetic efficiency and increased unregulated and regulated heat dissipation. Distant asymptomatic leaves could be distinguished from healthy ones in moderate and severe symptom genotypes by increased total and regulated heat dissipation measurements. In the field, overall photosynthetic efficiency and total regulated heat dissipation measurements could distinguish between healthy and asymptomatic ‘Valencia’ sweet orange leaves at the location with slow or more recent infection, but not at the location where infection appeared to progress faster or was of longer duration. Starch content followed a similar pattern. The results indicate that no single measurement uniquely described the relationship between HLB and the host in asymptomatic and healthy leaves, but accuracy of field-based detection could be strengthened by a combination of total nonphotochemical quenching, overall photosynthetic efficiency, starch content, and PCR analyses. Chlorophyll fluorescence and quenching measurements suggest a PSII-based explanation for, and temperature dependency of, leaf symptom development.

Measurements of heat dissipation from miniaturized vertical rectangular fin arrays under dominant natural convection conditions

Experiments have been conducted to investigate the effects of miniaturizing the base plate dimensions of vertically based straight rectangular fin arrays on the steady-state heat-dissipation performance under dominant natural convection conditions. The miniaturization process was initiated from a square-based array of 49×49 mm2 (maximum base area) and terminated at a square-based array of 25×25 mm2 (minimum base area) with rectangular-based arrays of varying intermediate areas in between. Two inter-fin separation distances of 3 and 11 mm were used. The effect of base plate orientation on the heat-dissipation performance was studied through comparison of present results with those of an earlier work, in which the arrays were miniaturized with the base horizontally oriented. A correlation for miniaturized vertically based straight rectangular fin arrays, which employed the fin length as the prime geometric parameter, has been presented on the basis of the experimental conditions of this investigation.

Measurements of steady-state heat dissipation from miniaturized horizontally-based straight rectangular fin arrays

Measurements of steady-state heat dissipation from miniaturized horizontally-based straight rectangular fin arrays

Measurements of steady-state heat dissipation from miniaturized horizontally-based straight rectangular fin arrays

Experiments have been conducted to investigate the effects of miniaturizing the base plate dimensions of horizontally-based straight rectangular fin arrays on the steady state heat dissipation performance. The variation of the steady-state heat dissipation rates per unit base area and the average heat dissipation coefficients within a limited fin base excess temperature above the ambient temperature (from 20 to 50 °C) have been studied as integral aluminum alloy fin arrays were miniaturized by changing the ratio of the base width to length from 0.51 to 1.96 for two inter-fin spacing distances of 3 mm and 11 mm. The miniaturization process have been initiated from a square-based array of 49 × 49 mm (maximum base area of 24.51 × 10–4m2) and terminated at a square-based array of 25 × 25 mm (minimum base area of 6.25 × 10–4m2) with rectangular-based arrays of varying intermediate areas in between. Relevant non-dimensional parameters formulated by earlier similarity analyses for large fin arrays with comparable inter-fin-spacing distances and fin heights have been found inadequate for generalizing the results. Modifications to correlations proposed for large fin arrays have been made by including the effect of varying the value of the base width to length ratio parameter to correlate the data for miniaturized fin arrays. Two types of correlations for miniaturized horizontally-based straight rectangular fin arrays, one which used the inter-fin separation distance as the prime geometric parameter, and the other, which employed half the fin length, have been presented, on the basis of the experimental conditions of this investigation.

Measurements of the material properties of metal nanoparticles by time-resolved spectroscopy

An important aim of nanoparticle research is to understand how the properties of materials depend on their size and shape. In this Invited Article I describe how time-resolved spectroscopy can be used to measure physical properties of nanometre sized objects such as the characteristic time scales for electron–phonon coupling and heat dissipation, and their elastic moduli. The electron–phonon coupling and heat dissipation measurements are important for applications of particles that involve conduction of heat or electricity. On the other hand, the elastic moduli studies provide fundamental information about the properties of nanomaterials. The results of these experiments show that nanometre sized particles can have very different properties compared to the corresponding bulk material. For example, we have recently shown that gold nanorods produced by wet chemical methods have much smaller elastic moduli (an 18% decrease in Young’s modulus) compared to bulk gold.

Direct Measurement of Thermoelastic Properties of Glassy and Rubbery Polymer Brush Nanolayers Grown by “Grafting-from” Approach

We report the results of atomic force microscopy (AFM) based nanoscale probing of thermal and nanomechanical properties of relatively thick (50−90 nm) polymer brush layers from poly(styrene-co-2,3,4,5,6-pentafluorostyrene) (PSF) and polymethylacrylate (PMA). These layers, with a high density of grafting, are synthesized according to a “grafting-from” approach on a silicon surface modified with a reactive self-assembled monolayer. In the dry state, glassy and rubbery brush layers are found to be homogeneous matters with no signs of lateral chain segregation, which is observed for polymer layers with low to moderate grafting densities. We observed that thermal, mechanical, and thermoelastic properties of these polymer brush layers are virtually identical to that for unconfined polymers obtained concurrently via bulk polymerization. Direct measurement of heat dissipation and the thermoelastic response within the PSF brush layer confirms that the glass−rubber transition occurs between 100 and 110 °C as expected for the high-molecular weight polymer. Surface nanomechanical mapping reveals much lower adhesion of the PSF layer, which is glassy at room temperature and contains fluorine-enriched segments, in comparison with the sticky PMA layer containing polar segments. At room temperature, the PSF layer shows a compression elastic modulus of approximately 1 GPa whereas the rubbery PMA layer has an elastic modulus of 50 MPa, typical for the rubbery state. Heating the glassy PSF layer results in a gradual decrease of the elastic modulus caused by the glass transition, and conversion to the rubbery state is completed above 110 °C with an elastic modulus of 15 MPa.

Measurement of uniform and localized heat dissipation induced by cyclic loading

An experimental technique is presented for measuring the heat dissipation and localization during cyclic loading of materials. The temperature field is measured by a number of thermistors and an infrared camera, which scans the specimen surface continuously. The specimen is mounted inside an isothermal chamber. The measured whole-field temperature can be used for detection of damage propagation and localization. The resolution of the technique under various boundary conditions is discussed using a onedimensional model for the heat loss under steady-state conditions. Applications of the technique are demonstrated for specimens made of fiber-reinforced ceramic and polymer matrix composites (PMCs). A methodology is proposed for measuring changes in damping and stiffness properties of viscoelastic polymer matrix composites using the temperature rise of a cyclic loaded specimen. It is demonstrated that for a ceramic matrix composite, where interfacial frictional sliding gives rise to heat dissipation, the temperature resolution can be used for detection of stress-strain hysteresis with an accuracy better than that of the stress-strain data.