Heat Loss Mechanisms Research Articles

Frostbite on Denali: a case series and review of treatment options.

Frostbite, defined as tissue freezing due to cold weather exposure, is a major risk associated with mountaineering in cold climates. It represents a significant source of morbidity in the climbing population. In 2021, three individuals were evaluated at a single institution after developing frostbite while climbing Denali, Alaska, US. The affected patients were healthy men in the third to sixth decade of their lives, and all experienced frostbite injuries involving the fingers. Among the patients, one individual was unable to descend from the mountain due to the severity of his condition and required medical evacuation. The other men were able to descend without significant difficulty. After leaving the mountain, the patients were treated with thrombolysis, pentoxifylline, hyperbaric oxygen therapy, and/or regional sympathetic blockade. Exposure to cold weather, ascent to high altitudes, and increased mechanisms of heat loss were likely potential risk factors for frostbite injury in these patients. Psychological factors related to the COVID-19 pandemic may have also impacted these individuals' risk for frostbite injury. Prevention is the most effective way to avoid frostbite, and knowledge and understanding of the risks associated with the development of this condition may reduce future occurrences among mountaineers. Since frostbite is not a common diagnosis encountered in patients treated in outpatient wound centres, physicians should maintain awareness of the pathophysiology and treatment options for this condition.

Life cycle cost approach involving steam transport model for insulation thickness optimization of steam pipes

Efficient steam pipe insulation is critical for minimizing heat loss during transportation, ensuring the economic viability of thermal processes or end-user applications. Unlike water-based systems, steam heat loss mechanisms are intricate, predominantly influenced by the transition of steam to condensate which introduces latent heat, thus significantly impacting overall heat loss. This study employs a life-cycle cost approach, integrating a comprehensive steam transport model to evaluate the optimal insulation thickness under varying temperature, flow rates and composite insulation schemes. The steam transport model incorporates a drainage energy loss term, providing a detailed depiction of the energy balance along the steam pipe. Results from the steam transportation simulation conducted on a single long pipe demonstrate a ∼4.6 % deviation between simulated and measured heat loss values. Furthermore, Life cycle cost analysis highlights the economically advantageous insulation configuration, comprising an aerogel blanket as the inner layer and glass wool as the outer layer. With increasing temperature, augmenting the proportion of aerogel blanket yields economic benefit, with the optimum thickness exhibiting a linear growth trend. Conversely, as the flow rate increases, the optimum insulation thickness remains constant.

Thermoregulatory pathway underlying the pyrogenic effects of prostaglandin E2 in the lateral parabrachial nucleus of male rats.

It has been shown that prostaglandin (PG) E2 synthesized in the lateral parabrachial nucleus (LPBN) is involved in lipopolysaccharide-induced fever. But the neural mechanisms of how intra-LPBN PGE2 induces fever remain unclear. In this study, we investigated whether the LPBN-preoptic area (POA) pathway, the thermoafferent pathway for feed-forward thermoregulatory responses, mediates fever induced by intra-LPBN PGE2 in male rats. The core temperature (Tcore) was monitored using a temperature radiotelemetry transponder implanted in rat abdomen. We showed that microinjection of PGE2 (0.28 nmol) into the LPBN significantly enhanced the density of c-Fos-positive neurons in the median preoptic area (MnPO). The chemical lesioning of MnPO with ibotenate or selective genetic lesioning or inhibition of the LPBN-MnPO pathway significantly attenuated fever induced by intra-LPBN injection of PGE2. We demonstrated that EP3 receptor was a pivotal receptor for PGE2-induced fever, since microinjection of EP3 receptor agonist sulprostone (0.2 nmol) or EP3 receptor antagonist L-798106 (2 nmol) into the LPBN mimicked or weakened the pyrogenic action of LPBN PGE2, respectively, but this was not the case for EP4 and EP1 receptors. Whole-cell recording from acute LPBN slices revealed that the majority of MnPO-projecting neurons originating from the external lateral (el) and dorsal (d) LPBN were excited and inhibited, respectively, by PGE2 perfusion, initiating heat-gain and heat-loss mechanisms. The amplitude but not the frequency of spontaneous and miniature glutamatergic excitatory postsynaptic currents (sEPSCs and mEPSCs) in MnPO-projecting LPBel neurons increased after perfusion with PGE2; whereas the frequency and amplitude of spontaneous inhibitory postsynaptic currents (sIPSCs) and the A-type potassium (IA) current density did not change. In MnPO-projecting LPBd neurons, neither sEPSCs nor sIPSCs responded to PGE2; however, the IA current density was significantly increased by PGE2 perfusion. These electrophysiological responses and the thermoeffector reactions to intra-LPBN PGE2 injection, including increased brown adipose tissue thermogenesis, shivering, and decreased heat dissipation, were all abolished by L-798106, and mimicked by sulprostone. These results suggest that the pyrogenic effects of intra-LPBN PGE2 are mediated by both the inhibition of the LPBd-POA pathway through the EP3 receptor-mediated activation of IA currents and the activation of the LPBel-POA pathway through the selective enhancement of glutamatergic synaptic transmission via EP3 receptors.

Effects of Aloe Vera Compresses Patients with Fever in The GM Hospital

Fever is one of the signs on the body that there is a process in which the body is fighting infection, the temperature of 37.5 ° C can be categorized as Fever caused by the presence of infection and autoimmune diseases, the inability of the mechanism of body heat loss can also occur due to excess production at body temperature.The World Health Organization (WHO) stated that the number of diseases in children with symptoms of fever is 62% with a mortality rate of 33%.The administration of aloevera compresses is one of the non-pharmacological interventions that can lower body temperature.The aim of this study is to find out how Aloevera Compresses affect the decrease in body temperature in fever patients. The design of this study is quasi-experimental with an approach (the one group,pretest posttest design). The sampling technique used in this study is Purposive Sampling, in which the sampler technique is based on the inclusion criteria that have been set to be respondents. The sample that was used for 3 months was 30 respondents. The results of statistical analysis using paired simple t-test obtained p value 0,000 (p<0,05) which means there is an effect of Aolevera Compress on the decrease in body temperature in fever patients. It is hoped that health workers can improve the quality of nursing staff services in improving skills in administering the effect of aloe vera compresses and can be used as information and increase knowledge.

Analysis of heat-loss mechanisms with various gases associated with the surface emissivity of a metal containment vessel in a water-cooled small modular reactor

In various small modular reactor (SMR) designs currently under development, the conventional concrete containment building has been replaced by a metal containment vessel (MCV). In these systems, the gap between the MCV and the reactor pressure vessel is filled with gas or vacuumed weakly, effectively suppressing conduction and convection heat transfer. However, thermal radiation remains the major mode of heat transfer during normal operation. The objective of this study was to investigate the heat-transfer mechanisms in integral pressurized water reactor (IPWR)-type SMRs under various gas-filled conditions using computational fluid dynamics. The use of thermal radiation shielding (TRS) with a much lower emissivity material than the MCV surface was also evaluated. The results showed that thermal radiation was always the dominant contributor to heat loss (48–97%), while the conjugated effects of the gas candidates on natural convection and thermal radiation varied depending on their thermal and radiative properties, including absorption coefficient. The TRS showed an excellent insulation performance, with a reduction in the total heat loss of 56–70% under the relatively low temperatures of the IPWR system, except for carbon dioxide (13%). Consequently, TRS can be utilized to enhance the thermal efficiency of SMR designs by suppressing the heat loss through the MCV.

Neural circuits of long-term thermoregulatory adaptations to cold temperatures and metabolic demands.

The mammalian brain controls heat generation and heat loss mechanisms that regulate body temperature and energy metabolism. Thermoeffectors include brown adipose tissue, cutaneous blood flow and skeletal muscle, and metabolic energy sources include white adipose tissue. Neural and metabolic pathways modulating the activity and functional plasticity of these mechanisms contributenot only to the optimization of function during acute challenges, such as ambient temperature changes, infection and stress, but also to longitudinal adaptations to environmental and internal changes. Exposure of humans to repeated and seasonal cold ambient conditions leads to adaptations in thermoeffectors such as habituation of cutaneous vasoconstriction and shivering. In animals that undergo hibernation and torpor, neurally regulated metabolic and thermoregulatory adaptations enable survival during periods of significant reduction in metabolic rate. In addition, changes in diet can activate accessory neural pathways that alter thermoeffector activity. This knowledge may be harnessed for therapeutic purposes, including treatments for obesity and improved means of therapeutic hypothermia.

Hypothalamic Neuromodulation of Hypothermia in Domestic Animals

When an organism detects decreases in their core body temperature, the hypothalamus, the main thermoregulatory center, triggers compensatory responses. These responses include vasomotor changes to prevent heat loss and physiological mechanisms (e.g., shivering and non-shivering thermogenesis) for heat production. Both types of changes require the participation of peripheral thermoreceptors, afferent signaling to the spinal cord and hypothalamus, and efferent pathways to motor and/or sympathetic neurons. The present review aims to analyze the scientific evidence of the hypothalamic control of hypothermia and the central and peripheral changes that are triggered in domestic animals.

Surviving heat: Resilience of Nellore bulls to solar radiation exposure

Surviving heat: Resilience of Nellore bulls to solar radiation exposure

Numerical study on a nuclear-powered Stirling system for space power generation

The use of nuclear-powered Stirling systems for planetary and deep space exploration applications has drawn increasing attention in recent decades. As the critical energy conversion unit in the system, the free-piston Stirling engine (FPSE) is characterized by high efficiency, low mass, compact configuration, robustness, and long lifetime, but difficult to accurately model and analyze. A self-developed numerical model of the whole system, coupled with a third-order model of the FPSE, was proposed for the first time, and a nuclear-powered Stirling system comprising eight 1 kW FPSEs was designed. The methodology for designing a system with high efficiency, high specific power, and compact structure was proposed. Furthermore, the internal heat transfer and loss mechanisms were analyzed. The results revealed that the engines’ performance could be improved by increasing the temperature ratio of the hot end to the cold end. However, this leads to a corresponding increase in the size and mass of the heat exchangers. It was shown that the optimum hot-end temperatures for maximizing the system efficiency exist at different cold-end temperatures due to the radiation heat loss of heat pipes. When the hot-end and cold-end temperatures are respectively 1050 K and 450 K, a maximum system efficiency of 25.64% could be obtained. Moreover, the system efficiency and specific power could be increased by optimizing the FPSEs’ parameters and enhancing the heat exchangers’ heat transfer capabilities, and the adverse effect of the heat sink fluctuation could be inhibited accordingly. The distribution of the exergy losses changes greatly with the operating temperatures, and the primary parameter to be optimized also changes accordingly.

Finite Element Analysis of Underwater Wet Welding: The Implementation of Bubble Configuration

To reasonably characterize the features of underwater wet welding, especially the bubble effect engendered from a high concentration of heat, a three-dimensional (3D) numerical model considering the interaction of bubble dynamics with the boundary layer was developed. A semi-empirical method assessing the bubble growth process was incorporated into the model as boundary conditions to account for the heat loss mechanism. It was proven that consideration of the bubble configuration can improve prediction accuracy, and the predicted weld profile was in good agreement with the experimental results. To reveal the contribution of the bubble configuration while maintaining processing variables consistency, the influences of the equivalent contact radius of the bubble and its floating frequency on the temperature field evolution were evaluated. The results showed that low floating frequency and/ or a high equivalent contact radius tend to depress the heat losses to a water environment, prolong the t8/5 time, and enhance the weld width and joint penetration, which render the role of optimized bubble dynamics beneficial. Under otherwise identical conditions, the equivalent contact radius of the bubble plays a much better role than the bubble floating frequency in promoting weld pool dimensions. Based on the quantified data, suggestions concerning the matching strategy of bubble configuration and heat input for underwater wet welding may be provided.

Experimental and theoretical investigation into effectiveness of ZnO based transparent heat mirror covers in mitigating thermal losses in volumetric absorption based solar thermal systems

The present study investigates efficacy of ZnO based transparent heat mirror covers as thermal loss mitigators in 'direct volumetrically absorbing' solar thermal platforms. Comprehensive experimental and theoretical modeling frameworks have been developed to understand and quantify the heat loss mechanisms. Detailed analysis reveals that performance characteristics are strong functions of the 'side' of the glass that has been coated (i.e. whether 'receiver facing' (RF) or 'sky facing' (SF) sides of the cover has been coated). Results show that employing ZnO based heat mirror as a cover significantly reduces the thermal losses relative to uncoated glass cover (27.72% and 21.44% reduction for RF and SF side coated heat mirrors respectively). Moreover, fundamental performance limits of ideal heat mirrors have also been determined for both RF and SF side coated cover configurations. Relative to the uncoated glass covers, ideal heat mirror covers (viz., RF and SF side coated) promise 47.42% and 36.07% thermal loss reduction respectively (@ 400 °C receiver surface temperature and 1.5 μm cut-off wavelength). Overall, the present work represents a significant step in improving the existing volumetric absorpion based solar thermal systems; particularly aiming at intermediate temperature applications (viz. industrial and domestical heating/cooling).

Acute stress and restricted diet reduce bill-mediated heat dissipation in the song sparrow (Melospiza melodia): implications for optimal thermoregulation.

We used thermal imaging to show that two environmental factors - acute stress and diet - influence thermoregulatory performance of a known thermal window, the avian bill. The bill plays important roles in thermoregulation and water balance. Given that heat loss through the bill is adjustable through vasoconstriction and vasodilation, and acute stress can cause vasoconstriction in peripheral body surfaces, we hypothesized that stress may influence the bill's role as a thermal window. We further hypothesized that diet influences heat dissipation from the bill, given that body condition influences the surface temperature of another body region (the eye region). We measured the surface temperature of the bills of song sparrows (Melospiza melodia) before, during and after handling by an observer at 37°C ambient temperature. We fed five birds a restricted diet intended to maintain body mass typical of wild birds, and we fed six birds an unrestricted diet for 5months prior to experiments. Acute stress caused a decrease in the surface temperature of the bill, resulting in a 32.4% decrease in heat dissipation immediately following acute stress, before recovering over approximately 2.3 min. The initial reduction and subsequent recovery provide partial support for the hemoprotective and thermoprotective hypotheses, which predict a reduction or increase in peripheral blood flow, respectively. Birds with unrestricted diets had larger bills and dissipated more heat, indicating that diet and body condition influence bill-mediated heat dissipation and thermoregulation. These results indicate that stress-induced vascular changes and diet can influence mechanisms of heat loss and potentially inhibit optimal thermoregulation.

PMON118 Cerebral Palsy Resulting in Hypothalamus Volume Loss and Temperature Dysregulation

Abstract Background Cerebral palsy is a syndrome caused by a non-progressive brain injury or malformation during early brain development, which can lead to severe physical disability. However, there is limited data on the consequences of cerebral palsy on other crucial brain functions such as hypothalamus and pituitary gland. We report a case of hypothalamic-pituitary involvement in a cerebral palsy patient. Clinical case A 28-year-old man with history of quadriplegic cerebral palsy, severe cognitive delay and seizure disorder presented to our clinic with temperature dysregulation for 2 years. He is wheel-chair-bound and non-verbal. His core temperature generally ranges from 96.8o to 97.2oF but occasionally he has had fluctuations as high as 102oF and as low as 88oF associated with extremes in surrounding temperature. At the time of initial evaluation, his temperature was 96.8oF (36°C) and his skin was cool and mottled. He was on levothyroxine replacement for hypothyroidism and thyroid hormone levels were within the normal range (Free T4 of 1.33 ng/dL and Total T3 of 153 ng/dL). Head CT revealed extensive encephalomalacia involving the frontal and temporal lobes, diffuse thinning of the parenchyma of the parietal and occipital lobes with secondary lateral ventricle enlargement, and volume loss in the deep gray nuclei including the hypothalamus. Further evaluation revealed a borderline response to Cortrosyn (16.9 ug/dL at 60 min) but associated with an adequate baseline cortisol of 13.7 ug/dL. IGF-1 and prolactin levels were normal (IGF-1 of 117 ng/mL and prolactin of 7.9 ng/mL), but testosterone was 175 ng/dL associated with an LH of 3.1 mIU/mL and FSH of 10.7 mIU/mL consistent with central hypogonadism. The family was advised to carefully regulate and monitor ambient temperature, and maintain dress appropriate for the surrounding temperature. Conclusion Although periventricular white matter lesions are most commonly associated with cerebral palsy resulting in motor dysfunction, deep gray matter lesions are also occasionally documented. These lesions should be recognized, as they could be detrimental to the body. The hypothalamus, with the preoptic area as its main thermoregulatory locus, plays an important role in temperature regulation. It integrates all information from the surface thermoreceptors and local brain temperature then initiates heat production or heat loss mechanisms to help maintain homeostasis. Therefore, volume loss of the hypothalamus can lead to serious consequences such as poikilothermia that can lead to life-threatening hypothermia or hyperthermia. Keywords: Cerebral palsy, hypothalamus, temperature dysregulation, poikilothermia Presentation: Monday, June 13, 2022 12:30 p.m. - 2:30 p.m.

Evidence for a very thick Kaapvaal craton root: Implications for equilibrium fossil geotherms in the early continental lithosphere

The presence of diamonds of Archaean age within the cratonic lithosphere is surprising because their formation implies a cool early mantle lithosphere despite the early Earth's hotter state. There remains a widely (albeit not exclusively) held concept that the prevailing geothermal gradient within Archaean cratons was not much different from today. This ‘Archaean paradox’ is supported by pressure and/or temperature (PT) estimates of potentially ancient diamond inclusion (DI) falling close to modern cratonic geotherms. Solutions to the paradox include more effective Archaean heat loss mechanisms (e.g. heat pipes), deeper lithospheric mantle roots or the early lithosphere forming in a disequilibrium state.Here we demonstrate the effects of a thermally evolving Earth on equilibrium geotherms within the Kaapvaal craton of South Africa. We modelled geotherms from the present-day conditions backward in time to 3.0 Ga at thermal equilibrium in the lithosphere by adjusting three dominant variables: (i) time-corrected crustal heat production; (ii) a secularly cooling mantle potential temperature (Tp) in the underlying convecting mantle; and, for illustrative purposes, (iii) variable depth of the lithosphere-asthenosphere boundary (LAB) or variable heat flow at the LAB. Computed model geotherms were compared to DI PT data from the Kaapvaal craton, as well as PT conditions recorded in mantle xenoliths of variable age. It is demonstrated that equilibrium geotherms in the lithosphere cannot be reconciled with PT conditions recorded in Kaapvaal craton DI nor with those recorded in Proterozoic xenoliths if either the lithosphere has remained of constant thickness or held a constant basal heat flux since 3.0 Ga. Rather, provided that PT conditions recorded by DI from the Kaapvaal craton reflect equilibration along fossil ancient equilibrium geotherms, it is required that the early lithosphere was substantially thicker than what is preserved today. The inferred former thickness of Kaapvaal craton could have reached up to ∼350 km if the prevailing mantle Tp at the time of diamond encapsulation was high and they are of Archaean age. If, however, the Archaean asthenosphere Tp was more modest or if the diamonds formed later than the Archaean the inferred LAB depths are shallower (∼250-275 km), but still substantially deeper than at the present day.Although only the Kaapvaal craton has the necessary DI PT constraints for this exercise, the fundamental nature of radioactive heat production rate and mantle cooling mean that our findings could imply that Earth's continental lithosphere in general attained its maximal vertical extent early in the Archaean and that cratons have been variably eroded and weakened since that time.

Numerical and experimental studies on a pressurized hybrid tubular and cavity solar air receiver using a Scheffler reflector

• Coupled optical and thermal model of a pressurized tubular and cavity solar air receiver. • Modelled the dynamic variation of concentrated solar radiation input to the receiver cavity surface. • Three-dimensional CFD analysis is performed on the hybrid receiver model. • Validation with on-sun experimental results using a Scheffler dish. • Natural convection and radiation heat loss estimation. In this study, a pressurized tubular and cavity solar air receiver is analyzed numerically, and the results are validated experimentally using a Scheffler fixed focus concentrator. Transient numerical analyses for periods similar to experimental testing duration allows realistic performance prediction of new receiver designs and help in understanding the dominant heat loss mechanisms, thus mitigating or reducing them. A coupled optical and thermal model is developed for analyzing the receiver with a novel method of capturing the spatial and temporal variation in the heat input to the receiver. The concentrated heat flux input to the receiver is defined as the product of two separate functions. The first function defines the incident radiation to the receiver as a spatially resolved flux profile on the cavity inside surface, obtained from the ray tracing algorithm. The second function captures the transience in heat input by curve-fitting the measured direct normal irradiation variation with time corresponding to the experimental testing period. Receiver heat loss modelling involves natural convection heat loss from the inside cavity surface estimated using an existing correlation, while radiation heat loss is estimated by prescribing the surface emissivity and computing the ambient view factor. A three-dimensional transient CFD analysis is performed on the hybrid receiver model under identical heating conditions as experiments to predict the flow heat transfer. The result from the numerical model is subsequently compared with on-sun experimental results obtained using a test rig equipped with a Scheffler dish for heat input and supply of compressed air as the heat transfer fluid through the receiver. The deviation between numerical and experimental results are less than 16 °C for air outlet temperature and less than 9% for the receiver thermal efficiency, thus proving the effectiveness of the coupled optical and thermal model. To account for the transient nature of the receiver heating during the on-sun experiments, the receiver thermal efficiency definition has been modified to include the thermal inertia of the receiver material. It is also observed that natural convection is the dominant heat loss mechanism for the present configuration and can significantly reduce the overall thermal efficiency of a receiver. The present numerical model incorporating an optical model of the solar field and as-measured variation of solar radiation input can be effectively used for optimizing the design of any generic concentrator-receiver system with high-pressure heat transfer fluid, with the objective of minimizing thermal losses.

Modeling heat transfer in humans for body heat harvesting and personal thermal management

The human thermoregulatory system dictates the transfer of heat, produced within organs and skeletal muscles, through body layers and its dissipation to the environment. With the remarkable progress in the field of heat transfer within human beings (bioheat transfer), numerical modeling of the thermal behavior of humans became possible. Such models allow a rough diagnosis of the subject’s health in various clinical conditions (humans undergoing hyperthermia or hypothermia, humans under sleep, newborn infants, etc.) and more accurate estimation of power generated from body heat harvesting devices. In this review, elements that accompany the bioheat transfer models (e.g., heat conduction through body layers, heat generation due to metabolism and blood perfusion, and heat loss mechanisms) are discussed, along with how they have been integrated to develop various numerical methods for estimating the human thermal behavior under different environmental conditions. More importantly, we introduce two representative applications of bioheat transfer models: body heat harvesting and core body temperature measuring devices. The human body is a reliable and continuous heat source that can be used for operating wearable sensors and devices. Accurately determining the amount of heat flowing into the device is crucial for estimating the power output. Furthermore, noninvasive core body temperature sensors based on bioheat transfer mechanisms are explained. Reportedly, the measurements taken with these sensors agree well with the actual core temperatures. This review will be beneficial for heat transfer engineers interested in bioheat transfer as well as for those working in the field of wearable sensors and devices pursuing a reliable energy harvester to operate their sensors.

Study of heat loss mechanism in argon-circulated hydrogen engine combustion chamber wall surface conditions

Hydrogen fuel in internal combustion engine gives a very big advantage to the transportation sector especially in solving the greenhouse emission problem. However, there are only few research discovered the ability of argon as a working gas in hydrogen combustion in internal combustion engine. The high temperature rises from the argon compression tend to result in heat loss problem. This research aims to study the heat loss mechanism on wall surface condition in the combustion chamber. Experiments were conducted to study the effects of different heat flux sensor locations and the effect of ignition delay on heat flux. Local heat flux measurement was collected and images were observed using high speed shadowgraph images. The ignition delay that occurred near the combustion wall will result in larger heat loss throughout the combustion process. Higher ambient pressure results in a bigger amount of heat flux value. Other fundamental characteristics were obtained and discussed, which may help in contributing the local heat loss data of an argon-circulated hydrogen engine in future engine operation.

Discrete particle modelling of buoyant convective particle-laden air flow in solar cavity free-falling particle receivers

A coupled computational fluid dynamics and discrete particle method numerical model is developed to provide a systematic analysis of buoyant convective particle-laden air flow and heat losses from a solar cavity receiver with free-falling particles. The fundamental mechanisms of heat loss from a solar cavity particle receiver are poorly understood and difficult, if not impossible, to obtain experimentally. Studies on particle-laden air flow and heat transfer mechanisms in a solar cavity free-falling particle receiver are extremely limited. As such, this study is the first attempt to unravel the convective heat transfer mechanisms of a solar cavity particle receiver while considering the influence of the entrained air, air recirculation patterns, and solid–gas thermal dynamics. Furthermore, the receiver efficiency due to air recirculation and particle transport in addition to the relative losses due to heat exiting the receiver aperture and outlet ports is investigated. It is found that the particle mass flow rates have profound implications on the air recirculation patterns, entrained air, and heat fluxes of the solar receiver. The heat losses at the particle outlet greatly increase with increasing particle mass flow rate due to the higher thermal mass of the entrained air. An increase in the particle injection rate from 100,000 pps to 3,000,000 pps leads to an increase in the net heat by 48.6% although the aperture heat loss decreases by 24.4%. This is linked to the high entrained air velocities which recirculates much of the heated air in the cavity thereby reducing the aperture heat loss. This also infers a linear increase in the thermal efficiency and exponential decrease in exit loss ratios of the solar cavity receiver. It is also found that a competition exists between the various flow intensities of the particle curtain, the ambient air, and the entrained air velocities, which is quantified by the dimensionless thermal energy. Scientists and engineers can further optimize the geometric morphologies of solar cavity receivers after gaining a solid comprehension of the flow structures and thermal efficiencies of the solar receiver. To this end, a modified receiver geometry is proposed to mitigate convective heat losses. The modified receiver is about 26% efficient than the original receiver, which is linked to the 45° plate which impedes the velocity of the particle curtain at the outlet and reduces the entrained air velocity and heat losses from the cavity. Furthermore, a high particle initialization velocity greatly amplifies the heat losses at the particle outlet port. This high thermal mass at the outlet port amplifies the entrained air velocity regardless of the geometric morphology of the solar receiver. The results from the validated numerical model can be used by engineers and scientists to better optimize geometric morphologies of solar particle receivers.

Modeling heat losses in microfluidic devices: The case of static chamber devices for DNA amplification

Most of the functions integrated in lab-on-a-chip (LoC) systems require the heating and cooling of samples in order to activate specific reactions. A common example in LoC systems for molecular diagnostics of pathogens is DNA amplification by the polymerase chain reaction (PCR). The practical use of such LoC systems is strictly related to the speed of the operations and the power and energy consumption, especially in case of point-of-care (PoC) applications, the latter influenced by the heat losses to the ambient. This study investigates the effect of the heat loss mechanisms and parameters on the heating and cooling rates, and the power and energy requirements through a systematic computational analysis. The case study is a static chamber microfluidic device for DNA amplification based on PCR and the means is a detailed 3d computational framework taking into account the air flow around the microfluidic device. An evaluation of existing simplified models for heat losses is performed, in terms of the accuracy provided and the computational cost. Furthermore, a new effective model for the convective heat losses is proposed: Beyond the constant values of the heat transfer coefficient (h) used in the literature and overcoming the applicability problems of empirical equations for h to the small-sized microfluidic devices, a function of h versus the surface temperature is derived from a parametric study in a 2d axisymmetric geometry resembling the real geometry of the microfluidic device. The results of the new model not only compare satisfactorily with those of the detailed 3d framework, but also entail a 10-fold lower computational cost. Measurements of the temperature profile in a thermal cycle are also performed and are in good agreement with the computational results.

Effects of a Heated Anesthesia Breathing Circuit on Body Temperature in Anesthetized Rhesus Macaques (Macaca mulatta).

This study evaluated the effects of using a heated anesthesia breathing circuit in addition to forced-air warming on body temperature in anesthetized rhesus macaques as compared with forced-air warming alone. Hypothermia is a common perianesthetic and intraoperative complication that can increase the risk of negative outcomes. Body heat is lost through 4 mechanisms during anesthesia: radiation, conduction, convection, and evaporation. Typical warming methods such as forced-air warming devices, conductive heating pads, and heated surgical tables only influence radiative and conductive mechanisms of heat loss. A commercially available heated breathing circuit that delivers gas warmed to 104 °F can easily be integrated into an anesthesia machine. We hypothesized that heating the inspired anesthetic gas to address the evaporative mechanism of heat loss would result in higher body temperature during anesthesia in rhesus macaques. Body temperatures were measured at 5-min intervals in a group of 10 adult male rhesus macaques during 2 anesthetic events: one with a heated anesthesia breathing circuit in addition to forced-air warming, and one with forced-air warming alone. The addition of a heated breathing circuit had a significant positive effect on perianesthetic body temperature, with a faster return to baseline temperature, earlier nadir of initial drop in body temperature, and higher body temperatures during a 2-h anesthetic procedure. Use of a heated anesthesia breathing circuit should be considered as a significant refinement to thermal support during macaque anesthesia, especially for procedures lasting longer than one hour.