Constant Internal Temperature Research Articles

Thermal performance analysis of hollow bricks integrated phase change materials for various climate zones

AbstractThis comprehensive research addresses the significant challenge of building‐related energy consumption in Morocco. Our innovative approach involves integrating phase change materials (PCMs) into hollow bricks, strategically addressing the diverse climate zones prevalent in the country. The primary focus is on enhancing energy efficiency within structures. Leveraging detailed simulations and employing the enthalpy‐porosity approach, our study models the impact of PCMs on internal temperatures. Optimal outcomes are achieved by partially filling brick holes with PCMs in specific configurations, demonstrating the materials' ability to adapt to varying conditions. A noteworthy finding is the 2–3‐h phase shift observed in cold zones, indicating the potential for PCMs to effectively regulate temperatures. Equally significant is their capability to maintain a constant internal temperature of 26°C in hot zones, even amidst extreme external conditions reaching up to 47°C. This resilience underscores the novel and tailored thermal regulation potential of PCMs. Beyond the technical insights, our research highlights the paramount importance of considering regional climates in PCM applications' implementation. This awareness is crucial for optimizing energy performance in buildings and ensuring sustainability. In essence, this study contributes valuable knowledge and practical implications for the strategic deployment of PCMs to enhance building energy efficiency, emphasizing the need for context‐specific solutions in diverse environmental conditions.

Sex differences in thermoregulation in mammals: Implications for energy homeostasis.

Thermal homeostasis is a fundamental process in mammals, which allows the maintenance of a constant internal body temperature to ensure an efficient function of cells despite changes in ambient temperature. Increasing evidence has revealed the great impact of thermoregulation on energy homeostasis. Homeothermy requires a fine regulation of food intake, heat production, conservation and dissipation and energy expenditure. A great interest on this field of research has re-emerged following the discovery of thermogenic brown adipose tissue and browning of white fat in adult humans, with a potential clinical relevance on obesity and metabolic comorbidities. However, most of our knowledge comes from male animal models or men, which introduces unwanted biases on the findings. In this review, we discuss how differences in sex-dependent characteristics (anthropometry, body composition, hormonal regulation, and other sexual factors) influence numerous aspects of thermal regulation, which impact on energy homeostasis. Individuals of both sexes should be used in the experimental paradigms, considering the ovarian cycles and sexual hormonal regulation as influential factors in these studies. Only by collecting data in both sexes on molecular, functional, and clinical aspects, we will be able to establish in a rigorous way the real impact of thermoregulation on energy homeostasis, opening new avenues in the understanding and treatment of obesity and metabolic associated diseases.

Numerical Investigation of a Novel Controlled-Temperature Double-Skin Façade (DSF) Building Element

This paper investigates a novel controlled-temperature double-skin façade (DSF) building element. A three-dimensional time-dependent numerical model was developed for six different geometries for the investigation of thermal performance under different orientations (azimuth 0°, 90°, 180° and 270°). The boundary conditions of the numerical model were determined with the PVGIS tool and adjusted with the sol-air temperature equation. The results of the numerical simulation were validated with the use of measurements from an experimental test cell. The numerical results indicated an improved thermal performance when temperature-controlled air and flow were supplied through the building envelope with annual total energy savings in kWh/m2 of 1.99, 1.38, 2.13 and 2.06 for azimuth 0°, 90°, 180° and 270°, respectively. In regard to the total energy savings in %, the maximum benefit was considered to be in the winter season, with values of 65, 29, 80 and 28 for azimuth 0°, 90°, 180° and 270°, respectively. The experimental measurements revealed the test cell’s ability to maintain a relatively constant internal surface temperature and to not be significantly affected by the orientation and diverse ambient conditions.

Some aspects of the influence of extreme climatic factors on the physical performance of athletes

Professional athletes often have to participate in competitions in climatic conditions that differ from the optimal or habitual ones for their place of residence. In this regard, it seems relevant to the question of how borderline and extreme external conditions (low and high ambient temperatures, changes in atmospheric pressure, altitude) affect sports performance and endurance. The review presents the biochemical mechanisms underlying the adaptation of athletes to environmental conditions. The human body maintains a fairly constant internal temperature (in some articles — the core) of the body at a level of 37 ± 10C throughout its life, despite a wide range of environmental parameters. The intensity of the processes providing for the release of heat is reflexively regulated. The neurons responsible for heat exchange are located in the center of thermoregulation of the hypothalamus. In the course of evolution, mammals have developed a variety of mechanisms for regulating body temperature, including nervous and humoral, that affect energy metabolism and behavioral responses. There are two ways of heat generation: contractile thermogenesis, due to contractions of skeletal muscles (a special case — cold muscle tremors), and non-contractile — when the processes of cellular metabolism are activated: lipolysis (in particular, brown adipose tissue) and glycolysis. When exposed to extreme ambient temperatures, the thermoregulatory system adjusts to maintain a stable core body temperature by preventing heat loss and increasing heat production in cold conditions, or increasing heat dissipation if the ambient temperature rises. The ambient temperature corresponding to 20–25 ºС on land and 30–35 ºС in water is considered thermoneutral for humans in a state of relative rest. However, any deviations from these conditions, especially against the background of intense physical exercise, can lead to functional overstrain, decreased endurance and sports performance.

Low-Level Radiofrequency Exposure Induces Vasoconstriction in Rats.

Recent studies have revealed that rodents' physiological responses to low-intensity radiofrequency (RF) electromagnetic fieldswere similar to thermoregulatory responses to cold conditions. The primary autonomic response to cold exposure is peripheral vasoconstriction that allows rodents to reduce heat loss and maintain a relatively constant internal body temperature. In the present study, we investigated the effects of 900 MHz RF at a low level (SAR of 0.35 W/kg) on tail skin temperature (Ttail ) in rats. We showed that rats exposed to RF had lower Ttail than control rats at ambient temperatures between 27 and 28 °C, suggesting that RF could induce a noticeable degree of vasoconstriction under mild-warm ambient temperatures. This difference in Ttail was suppressed after the intraperitoneal injection of a vasodilator, an α-adrenergic antagonist, confirming the hypothesis of the vasoconstriction in exposed rats. Moreover, like a response to cold stimuli, RF exposure led to increased plasma concentrations of important factors: noradrenaline (a neurotransmitter responsible for vasoconstriction and thermogenesis)and fatty acids (markers of activated thermogenesis). Taken together, these findings indicate that low-intensity RF levels triggered some key physiological events usually associated with responses to cold in rats. © 2021 Bioelectromagnetics Society.

Creep of a heterogeneous polymer cylindrical shell

The article deals with the problem of calculating an heterogeneous cylindrical shell made of a filled polymer, which is in the process of creep under the action of constant internal pressure and temperature. The calculation is based on the Maxwell -Gurevich equation, which has been repeatedly tested in the calculations of structural elements made of polymer and composite materials. The dependence of the physical and mechanical characteristics of the material on temperature is taken into account.

ОЦЕНКА ДЛИТЕЛЬНОЙ ПРОЧНОСТИ ЭЛЕМЕНТОВ КОНСТРУКЦИЙ ПРИ ТЕРМОМЕХАНИЧЕСКОМ НАГРУЖЕНИИ

The paper discusses the issue of evaluating strength and service life of critical engineering facilities, the exploitation properties of which are characterized by multi-parametric nonstationary thermal-mechanical effects. The main degradation mechanisms of structural materials (metals and their alloys), characteristic for such facilities, are examined. Basic requirements to mathematical models of such processes are formulated.In the framework of mechanics of damaged media, a mathematical model is developed, which describes processes of inelastic deformation and damage accumulation due to creep. The model consists of three interconnected parts: relations defining inelastic behavior of the material, accounting for its dependence on the failure process; equations describing damage accumulation kinetics; a strength criterion of the damaged material.The results of numerically simulating the carrying capacity of a reactor vessel of a NPP in the event of a hypothetical accident are presented. The accident conditions were modeled by applying pressure modeling the effect of meltdown, constant internal pressure and temperature varying within the part of the vessel in question. The analysis of the obtained numerical results made it possible to note a number of characteristic features accompanying the process of deformation and failure of such facilities, connected with the time and place of the forming macrocracks, the stressed strained state history and the damage degree in the failure zone, etc.In general, the results of comparing the numerical and experimental data make it possible to conclude that the proposed defining relations adequately describe degradation of initial strength properties of the material for the long-term strength mechanism and can be effectively used in evaluating long-term strength of structural elements under thermal-mechanical loading.

Hyperbolic Conduction–Radiation in Participating and Inhomogeneous Slab With Double Spherical Harmonics and Lattice Boltzmann Methods

This work deals with the combined mode of non-Fourier conduction and radiation transfer in isotropically/anisotropically scattering, homogeneous, and inhomogeneous planar media with reflective boundaries subjected to the constant internal temperature of the medium and the externally isotropic diffuse incidence at one boundary. An analytical double spherical harmonics method (DPN) is proposed to solve the radiative problem. The non-Fourier conduction is described with the Cattaneo–Vernotte model, and the governing hyperbolic energy equation is solved using the lattice Boltzmann method (LBM). For radiative problems through the layer/layered media, the radiative heat fluxes, hemispherical radiative intensities, transmissivity, and reflectivity are found, while for coupled conduction and radiation, the temperature distributions are found for various optical thicknesses, space-dependent scattering albedo, conduction–radiation parameters, and boundary reflectivities. Results of the present work are in excellent agreement with those available in the literature. Moreover, these results demonstrate that the proposed analytical double spherical method is an efficient, robust, and accurate method for radiative transfer through inhomogeneous layer/layered planar media analysis. Furthermore, it is observed that space-dependent scattering albedo and boundary reflectivities have a very significant effect in the hyperbolic sharp wave front of non-Fourier conduction.

Analysis of Heat Transfer through PVC Window Profile Reinforced with Ti6Al4V Alloy

This requires the use of additional reinforcement in order to prevent excessive or permanent deformation of PVC windows. In the paper particular attention was devoted to space located in a corrosive environment exposed to chemical agents. For this purpose, proposed to change the previously used steel profiles reinforcements made of Ti6Al4V titanium alloy corrosion-resistant in the air, at sea and many types of industrial atmosphere. Analysis of the thermal insulation properties of PVC windows with additional reinforcement of profile Ti6Al4V titanium alloy was performed. PVC window set in a layer of thermal insulation was analyzed. Research was conducted using Finite Element Analysis. Numerical models and thermal calculations were made in the program ADINA, assuming appropriate material parameters. The constant internal temperature of 20 ̊ and an outer-20 ̊ was assumed. The course of temperature distribution in baffle in time 24 hours and graphs of characteristic points was obtained. The time of in which followed the steady flow of heat, as well as the course of isotherm of characteristic temperature in the baffle was determined. On the basis of numerical analysis obtained vector distribution of heat flux q [W/m2] and was determined heat transfer coefficients U [W/m2K] for the whole window with titanium reinforcement . All results were compared with the model of PVC windows reinforced with steel profile.

POWER CONSUMPTION COMPARISON OF FIVE BUILDING ENVELOPES IN THE NORTHERN PRAIRIE CLIMATE OF MANITOBA

The energy efficiency of a building depends on building envelope performance. The results presented in this paper are the first of a long-term building envelope research project at the Alternative Village at the University of Manitoba in Winnipeg, Manitoba, Canada. Five test buildings were constructed using the following systems: two wood frames with fiberglass batt insulation and dense pack cellulose, one polyurethane structural insulated panels (PUR SIP), and two with the Stay in place PVC concrete form building system using 102mm and 204mm of concrete externally insulated with 102mm of expanded polystyrene foam. All of the buildings had a common foundation and roof system with a footprint of 23.8 m2. Blower door tests were conducted to determine air tightness. Each structure was heated with an electrical resistance heater and maintained at a constant internal temperature. The thermal gradient through the wall and power consumption were monitored. The study period discussed in this report represents the main heating season from October 2011 to April 2012 consisting of 209 days. Based on the power consumption, the PUR SIP consumed the least at 2498 kWh, while the 204 mm Stay in place PVC concrete form building used the most at 2898 kWh for the same time period. The thermal gradient through the cross section of the wood frame structures was compared through the cavity insulation and at the stud. It was found that the cellulose building provided better thermal resistance along the stud when compared to the fiberglass batt insulation.

Temperature monitoring: the consequences and prevention of mild perioperative hypothermia

Homeothermic species require a nearly constant internal body temperature. Significant deviations from “normal” internal temperature cause the metabolic function to deteriorate. Usually, the human thermoregulatory system maintains a core body temperature within 0.2°C of normal, near 37°C. Hypothermia results from exposure to cold, or exposure combined with drugs or illness that decrease thermoregulatory efficacy. Exposure to a cold operating room environment during anaesthesia and surgery commonly combines with anaesthetic-induced inhibition of thermoregulation to produce hypothermia. The prevention and management of temperature-related complications is expedited by an understanding of both normal and druginfluenced thermoregulation. Keywords : mild perioperative hypothermia; consequences; prevention

Thermal Comfort While Sitting on Office Chairs – Subjective Evaluations

Thermal comfort is related to human physiological reactions. In order to maintain a constant internal temperature, the human body must dissipate heat in a warm climate, and prevent heat losses in a cold climate. The overall sensation of comfort accompanies the warmest part of the body in a warm environment and the coldest one in a cold environment. Chair design and clothing may affect the difference in sensitivity between certain parts of the body, that is, they may affect thermal comfort. This research focused on subjective sensation of warmth and moisture while sitting on offi ce chairs. The subjective method of evaluating thermal discomfort is based on ISO7730:2005 standard, according to which a questionnaire was made for this research. Six subjects took part in the research. They were sitting on fi ve different offi ce chairs as they performed their usual jobs in controlled conditions. From the point of view of the evaluation of the sensation of warmth, all chairs were evaluated neutrally. The sensation under the buttocks and thighs was reported to be somewhat warmer, while the sensation on the back was reported to be somewhat colder, which was affected by the design of the back of the chair. No correlation has been proven between the actual temperature and moisture measurements and subjective evaluations of thermal comfort, in spite of a number of direct links. The use of the present method offers the possibility of further research into this subject, which would prove more thoroughly a correlation between design and construction solutions of office chairs and the comfort perceived by sitting persons.

Vertical-Cavity Surface-Emitting Laser Light–Current Characteristic at Constant Internal Temperature

Two continuous-wave measurement methods for the laser P-I-characteristic at a constant internal temperature are presented (constant average cavity and constant junction (active region) temperature). The methods are used to correctly quantify the temperature dependence of threshold current and differential quantum efficiency without need for pulsed measurements. It is found that the deviations between both temperatures can be as high as 5 K in a 1390-nm InP-based buried tunnel junction vertical-cavity surface-emitting laser (BTJ-VCSEL), which is the reason for the slight sublinearity of the characteristics at constant cavity temperature.

Influence of Polydimethylsiloxane on the Oxygen Concentration of Oils at Various Temperatures

AbstractThe effect of temperature on the oil oxygen concentration, tested in both soybean and olive oils with no added polydimethylsiloxane (PDMS), showed that the oxygen concentration increased with temperature to approximately 100 °C. Above 100 °C, the oxygen concentration abruptly decreased. This change was attributed to the balance between the rates of oxygen uptake and consumption by oil oxidation, which favored oxygen consumption over uptake at temperatures above 100 °C. The addition of 100 ppb PDMS to soybean oil, enough to form a continuous layer over the surface of the oil, reduced the oxygen concentration when compared to a soybean oil control containing no added PDMS at temperatures ranging from 93 to 180 °C; thus suggesting an oxygen barrier effect of PDMS. The accumulation of PDMS at the air–oil interface in soybean oil held at 180 °C was determined by comparing the oil's internal temperature and the apparent surface temperature. A decrease in the apparent surface temperature while the oil was held at a constant internal temperature was attributed to a change in the emissivity of the surface as a consequence of the accumulation of PDMS in the air–oil interface. The presence of PDMS at the air–oil interface was confirmed for 100 ppm of PDMS, a concentration greater than the concentration necessary to form a monolayer of PDMS on the oil surface.

Whatʼs Hot in Thermoregulation

Homeothermic species require a nearly constant internal body temperature. Significant deviations from internal temperature cause metabolic function to deteriorate. Usually, the human thermoregulatory system maintains core body temperature within 0.2°C of normal, near 37°C. Hypothermia results from exposure to cold, or exposure combined with drugs or illness that decrease thermoregulatory efficacy. During anesthesia and surgery, exposure to a cold operating room environment commonly combines with anesthetic-induced inhibition of thermoregulation to produce hypothermia. Prevention and management of temperature-related complications is expedited by an understanding of both normal and drug-influenced thermoregulation.

Disorders of sweating.

The clinical spectrum of sweating disorders includes sudomotor excess and deficiency. Hyperhidrosis is characterized by sweating beyond that required to maintain a constant internal body temperature. Hypohidrosis and anhidrosis are distinguished by a reduced or absent ability to generate sweat for the purpose of evaporative heat dissipation. Whereas hyperhidrosis is usually benign, anhidrosis may predispose to hyperthermia. Either hyperhidrosis or anhidrosis may accompany a more serious underlying disorder. Correct diagnosis depends on determining the anatomical pattern of sweating and localizing the lesion within the autonomic nervous system. Sudomotor deficits may involve the frontal operculum, hypothalamus, brain stem, spinal cord, sympathetic chain ganglia, peripheral nerve, or eccrine sweat glands. Treatments for hyperhidrosis include topical aluminum chloride, oral anticholinergic agents, intradermal botulinum toxin for some localized syndromes, and thoracic ganglionic sympathotomy or sympathectomy for refractory palmar hyperhidrosis.

Investigation on a Temperature Control System Modeled after the Function of the Skin

The contraction and relaxation of muscles located below the skin play an important role to maintain a constant internal body temperature. In this paper, we propose a new temperature control system modeled after the functions of the muscles located below the skin. The most important feature of this system is that the precise control of internal temperature is achieved by the operation of flow rate allotment. Moreover, we used digital adaptive control to improve the performance and flexibility of this system. To verify the validity of this system, the experiments were carried out and it was shown that this system can control the internal temperature within the range of ±0.02°C.

Free [ADP] and Aerobic Muscle Work Follow at Least Second Order Kinetics in Rat Gastrocnemius in Vivo

The relationship between free cytosolic [ADP] (and [P(i)]) and steady-state aerobic muscle work in rat gastrocnemius muscle in vivo using (31)P NMR was investigated. Anesthetized rats were ventilated and placed in a custom-built cradle fitted with a force transducer that could be placed into a 7-tesla NMR magnet. Muscle work was induced by supramaximal sciatic nerve stimulation that activated all fibers. Muscles were stimulated at 0.1, 0.2, 0.3, 0.4, 0.5, 0.8, 1.0, and 2.0 Hz until twitch force, phosphocreatine, and P(i) were unchanged between two consecutive spectra acquired in 4-min blocks (8-12 min). Parallel bench experiments were performed to measure total tissue glycogen, lactate, total creatine, and pyruvate in freeze-clamped muscles after 10 min of stimulation at each frequency. Up to 0.5 Hz, there was no significant change in muscle glycogen, lactate, and the lactate/pyruvate ratios between 8-12 min. At 0.8 Hz, there was a 17% fall in glycogen and a 65% rise in the muscle lactate with a concomitant fall in pH. Above this frequency, glycogen fell rapidly, lactate continued to rise, and ATP and pH declined. On the basis of these force and metabolic measurements, we estimated the maximal mitochondrial capacity (V(max)) to be 0.8 Hz. Free [ADP] was then calculated at each submaximal workload from measuring all the reactants of the creatine kinase equilibrium after adjusting the K'(CK) to the muscle temp (30 degrees C), pH, and pMg. We show that ADP (and P(i)) and tension-time integral follow a Hill relationship with at least a second order function. The K(0.5) values for free [ADP] and [P(i)] were 48 microM and 9 mM, respectively. Our data did not fit any form of the Michaelis-Menten equation. We therefore conclude that free cytosolic [ADP] and [P(i)] could potentially control steady-state oxidative phosphorylation in skeletal muscle in vivo.

Thermal regulation and mild intraoperative hypothermia

Homeothermic species such as birds and mammals require an almost constant internal body temperature to preserve normal physiological and metabolic function. When the internal temperature deviates significantly from normal, metabolic function deteriorates and death may result. The efficiency of the thermoregulatory system is highly affected by the administration of medication and by illnesses. Hypothermia may result, especially when these conditions are associated with exposure to a cold environment. Because such conditions exist during anaesthesia and surgery, the understanding of the physiology of the thermoregulatory system and the associated perianaesthetic thermal disturbances is essential to a proper intraoperative management. The purpose of this review is to provide clinicians with a better understanding of these principles, and also to elaborate on the most recent advances in this field, which should help to improve intraoperative anaesthetic temperature management.

Chapter 3—Principles of thermal comfort

The human body, considered as a thermodynamic system, produces mechanical work and low temperature heat, using food (fuel) and oxygen as input. This system requires, in healthy conditions, to maintain a constant internal temperature around 37±0.5°C, otherwise the functionality of important organs like liver, spleen, etc, may be severely damaged. fn2 fn2 During heavy work it rises by a few tenths of degree; under extreme activity it may rise as high as 39.5°C for short durations; temperatures above 40°C maintained for many hours lead to a breakdown of the thermoregulatory system, causing death. Chilling of internal organs to 36°C is possible without damage; below this, muscular weakness, exposure and then death results. In carefully controlled situations, as in surgical hypothermia, 30°C can be reached. In order to achieve this goal, the rate of heat generation of the body must be equal to the rate of heat loss from it. The job of our thermoregulatory system is to maintain the heat balance, that is a fundamental condition for survival and necessary (but not sufficient) for comfort. Skin temperature, otherwise, is not constant, and it varies according to the part of the body and the air temperature; the absolute maximum and the minimum values, however, are 45 and 4°C (pain thresholds).