Transient Thermal Environment Research Articles

Prediction on Chinese elderly's thermo-physiological and cardiovascular responses to non-uniform and transient thermal environment during getting-up process

Getting-up process after sleep would typically involve the non-uniform transition with temperature reduction, increased activity level, and change in clothing insulation, which is rarely explored in existing research. Due to the decline of physiological adaptability of the elderly, they may have sudden changes in physiology under transient environment. It is necessary to develop prediction models for the elderly to prevent or reduce health risks. The aim of this research is to predict the thermo-physiology and cardiovascular responses to non-uniform and transient thermal environments during getting-up process, a 4-node thermoregulatory-cardiovascular predicted model was established based on Gagge's thermoregulatory and heart rate model in International Organization for Standardization. Experimental data of twenty-six Chinese elderly subjects aged over 60 at a caring home in Chongqing both in winter and summer conditions was collected for validating. The results showed that the non-uniformity and dynamic states were 5.0–15.0 °C temperature differences between cover and bedroom. Core and overall skin temperatures decreased by 0.1–0.3 °C, while the heart rate increased by 5–10 %. Bare skin temperature decreased significantly by 0.2–1.0 °C. It implied that the process posed a potential risk to body cooling, local thermal discomfort, and cardiovascular health in the elderly, which was more severe in winter. The prediction result's error was below 6.0 %, which was more accurate by 6.0 %–18.0 % than that of typical models. This research can provide a reference for creating comfortable and healthy bedroom temperatures after sleeping for the elderly by intelligent air conditioning at residences and care homes.

Sex differences in body temperature and thermal perception under stable and transient thermal environments: A comparative study

Sex difference stands as a crucial factor necessitating consideration in personalized thermal environment control, with the mechanisms of its emergence potentially differing across different thermal environments. However, a comparative analysis of sex differences regarding body temperature (skin and core body temperature) and thermal perception across different environments is lacking. A stable environmental experiment (comprising three conditions: 16 °C, 20 °C, and 24 °C) and a transient environmental experiment (involving a whole-body step-change from 19 °C to 35 °C and back to 19 °C) were conducted, with participation from 20 young males and 20 young females. Skin temperature and core body temperature were continuously recorded during the experiments, and three types of thermal perceptions were regularly collected. The results showed that: (1) The impact of thermal environment on females' skin temperature surpassed that on males, in stable environment, with every 1 °C rise in ambient temperature, the mean skin temperature increased by 0.28 °C for males and 0.35 °C for females respectively; in transient environment, females' mean skin temperature raise and fell at a faster rate. (2) Males exhibited stronger thermal regulation abilities than females, particularly evident during sudden increase in ambient temperature (from 19 °C to 35 °C), where the reduction magnitude of males' core body temperature was notably larger. (3) Whether in stable or transient environments, significant sex differences often occurred in skin temperature and thermal sensation at distal parts, particularly at the hand. (4) Males typically fed back higher levels of thermal comfort and thermal acceptability than females, suggesting that in addition to physiological sex differences, psychological sex distinctions also play a role. In summary, personalized design for stable thermal environment can focus on sex differences in skin temperature, while transient thermal environment requires consideration of both skin temperature and core body temperature. A comprehensive consideration of physiological and psychological sex differences aids in creating personalized thermal environments with greater precision.

Intelligent Space Thermal Control Radiator Based on Phase Change Material with Partial Visible Transparency

Coating structures with dynamically adjustable infrared emissivity are crucial in spacecraft components to cope with the transient thermal environments of space. For a long time, thermochromic phase change materials have been widely used in applications requiring emissivity adjustment, and optimizing the range of adjustable infrared emissivity has always been at the forefront of research. However, reducing the absorption of solar radiation has significant implications for the practical application and thermal stability of spacecraft components in space environments. In this paper, we propose a multilayer film structure based on the phase change material VO2 combined with the materials ZnSe and ITO to achieve low solar radiation absorption and adjustable infrared emissivity for intelligent thermal radiators in space. Through finite element simulation analysis of the structure, we achieve a solar radiation absorption rate of 0.3 and an adjustable infrared emissivity of 0.49. According to Stefan–Boltzmann’s law, the structure exhibits strong radiative heat dissipation at high temperatures and weak energy dissipation at low temperatures to maintain the thermal stability of the device and ensure efficient operation. The intelligent thermal radiator operates based on the principles of Fabry–Perot resonance. Therefore, the multilayer structure based on the phase change material VO2 demonstrates excellent performance in both solar radiation absorption and adjustable infrared emissivity, showcasing its tremendous potential in the field of intelligent thermal control in aerospace.

Effect of thermal environmental factors on female students during summer and spring season: promoting a sustainable campus initiative

PurposeThe present study was conducted at the female campus of the United Arab Emirates University (UAEU), with a specific emphasis on the outside environment. This study aims to explore the influence of external conditions, including AC (AC), Time of Day (TD) variations, and Landscape Sites (LS) differences, on changes in physiological temperatures. Specifically, the focus is on understanding the dynamics of skin and abaya temperature (AT) when exposed to transient thermal environments, considering factors such as AC, LS, and different TD. By investigating these parameters, the research aims to gain insights into the thermal dynamics experienced by female students at the UAEU campus which can further lead to evaluate the thermal comfort (TC).Design/methodology/approachThe study involved three college-aged female participants simulating a daily walk to class on a arid tropical university campus. Real-time thermal measures were captured at 10-min intervals using the FLIR Thermal Camera. Statistical analyses, including the Kruskal–Wallis test and Don Bonferroni pairwise comparisons, were employed to assess significant differences in thermal conditions based on AC, TD, and LS. These tests rigorously analyzed the data to identify statistically significant variations in thermal conditions among the specified factors. Additionally, temperature data from the ECMWF ERA5 dataset, covering global climate from January 1940 to the present, was utilized. The GRADS application on a Linux-based system was used for data visualization and map chart creation.FindingsThe study reveals a slight influence of AC on both Abaya temperatures (AT) and Skin temperatures (ST) during the summer, with more pronounced diurnal changes in the afternoon significantly affecting both metrics. Site characteristics minimally impact AT, but they have a noteworthy effect on ST. In the spring season, AT and ST remain unaffected by AC, while temporal fluctuations, particularly in the afternoon, exert a significant influence. LS variations show statistically insignificant impacts on both AT and ST. Additionally, temperature maps for specific 2023 dates provide distinctive trends in the UAE, offering insights into dynamic climatic conditions varying by season and TD.Originality/valueThe study aims to address a knowledge gap by investigating the influence of AC, TD, and LS variations on physiological temperature change, specifically focusing on skin and AT. This investigation is conducted in the context of individuals exposed to thermal environmental factors within a arid tropical university campus setting.Practical implicationsThis research contributes to the existing knowledge by providing specific data on thermal conditions within the campus, enabling informed decision-making for creating a more comfortable and conducive environment for the students, thereby contributing to the goal of a sustainable campus.

Transient simulation and experimental analysis for the response of dual-cycle air-carrying energy radiant diffuse terminal

A novel air-carrying energy radiant diffuse terminal is proposed, and the response of the terminal is investigated by field experiment and numerical simulation. This paper explores the dynamic operation characteristics of the new system to guide the optimal operation of the system. A transient simulation method of three factors (conduction, convection, and radiation) with dual-circulation (air-carrying energy zone and occupied zone) is put forward for the radiant diffuse terminal with a fresh air system. This transient simulation sets up the porous baffle model coupling radiation model concurrently, revealing the dynamic thermal performance for the system's response accurately, quickly, and comprehensively. This method avoids the limits for the complexity of mini porous (Pore size of 1 mm–3mm) geometric models and the transient uncertainty in multiple combination models. The results show that the average error between the convective-conductive model and the convective-conductive-radiative model is about 8% at five different heights. This system has high response performance, which can quickly heat the room while maintaining the comfort requirements of vertical temperature. The radiated heat transfer between the radiant diffuse terminal and the occupied zone is greater than the convective heat transfer (Radiation accounts for 74%). This system has a short response time, high energy efficiency, uniform airflow, and eliminates draught rating. Moreover, the indoor non-uniform transient thermal and humid environments, the thermal comfort, and air quality for the response of the terminal with fresh air system under four different diffuser placements are compared using computational fluid dynamic simulation. The results indicate that introducing heating strategies featuring higher-positioned fresh air inlet and lower-positioned recirculation return air outlet for this system leads to a temperature efficiency increase by 5%, velocity uniformity by 8%, and age of air reduction by 16–50% in human-breathed zone and the response time by 25%, which shows substantial potential for energy savings. The transient simulation and experiments in the paper are beneficial to optimize design parameters and carry out energy-saving applications of operation energy consumption for the response of this terminal with a fresh air system in the future.

Association between thermal response and endogenous dopamine: Step-change environments in winter

Temperature step change is the typical transient thermal environment. The purpose of this study was to explore the association of subjective and objective parameters in a step-change environment, including thermal sensation vote (TSV), thermal comfort vote (TCV), mean skin temperature (MST) and endogenous dopamine (DA). Three temperature step changes defined as I3 (15 °C–18 °C to 15 °C), I9 (15 °C–24 °C to 15 °C) and I15 (15 °C–30 °C to 15 °C) were designed for this experiment. Eight male and eight female healthy subjects who participated in the experiment reported thermal perception (TSV and TCV). Skin temperatures of six body parts and DA were measured. Results show that the inverted U-shaped in TSV and TCV was deviated by seasonal factors of the experiment. The deviation direction of TSV in winter was to the warm sensation side, which was opposite to the inherent cold and hot impression of people in winter and summer. The association between dimensionless dopamine (DA*), TSV and MST were described as follows: DA* was the U-shaped change with exposure times when MST was not greater than 31 °C, and TSV was at −2 and −1, and DA* increased with exposure times when MST was greater than 31 °C, and TSV was at 0, 1 and 2. The changes in the body heat storage and autonomous thermal regulation under temperature step changes may potentially be related to the concentration of DA. The human state on thermal nonequilibrium and stronger thermal regulation would correspond to a higher concentration of DA. This work is conducive to exploring the human regulation mechanism in a transient environment.

Study on physiological response considering blood flow volume in transient and non-uniform bathing thermal environment using thermo-cardiovascular regulation model

In transient and non-uniform thermal environments, such as bathing, the human thermal physiological response changes dramatically and accidents often occur owing to cardiovascular system diseases. Blood flow volume is a crucial index of the cardiovascular system; thus, studying the human thermal physiological response considering blood flow volume in a bathing thermal environment is essential. In this paper, we proposed a novel integrated thermo-cardiovascular regulation model that merged a human thermoregulation model (HTM) and a cardiovascular regulation model (CRM), to predict the human physiological response in a transient and non-uniform bathing environment considering blood flow volume and the thermal environment, metabolic rate, and heart rate changes. First, based on the Stolwijk model, more nodes representing different human body parts have been added to the HTM, and it takes into consideration metabolic rate changes. Second, based on the Windkessel model, the circulatory system of the CRM is divided into four parts. Meanwhile, the changes in heart rate over time is used to adjust the cardiac output of the CRM's circulation in real time. To assess the accuracy of the prediction model, we conducted a bathing experiment with a 50-year-old man. The results revealed that the proposed model could accurately predict the participant's thermal physiological response, including skin temperature, core temperature, blood pressure, and blood flow volume during bathing.

Intrusive and non-intrusive early warning systems for thermal discomfort by analysis of body surface temperature

Buildings consume huge amounts of energy for the thermal comfort maintenance of the occupants. Real-time thermal comfort assessment is both important in the occupants’ thermal comfort optimization and energy conservation in the building sector. Existing thermal comfort studies mainly focus on the real-time assessment of the occupant’s current thermal comfort. Nonetheless, in the transient thermal environment, the occupant’s current thermal comfort is not steady and changes moment by moment. Hence, a prediction error will be elicited if we merely assess the occupant’s current thermal comfort. To address this problem, it is crucial to comprehend the occupant’s real-time thermal sensation trend in the transient thermal environment. A novel thermal sensation index that directly accounts for an occupant’s current thermal sensation trend is investigated in this study. By integrating the novel thermal sensation index into an ordinary thermal comfort model, a novel composite thermal comfort model is derived, which can simultaneously address the occupant’s current thermal comfort and current thermal sensation trend. Next, by utilizing machine learning classifications, we propose the intrusive and non-intrusive assessment methods of the composite thermal comfort model by analysis of the skin/clothing temperatures of ten local body parts measured by thermocouple thermometers and upper body thermal images measured by a low-cost portable infrared camera. The intrusive method reached a mean accuracy of 59.7% and 52.0% in Scenarios I and II, respectively; the non-intrusive method reached a mean accuracy of 45.3% and 42.7% in Scenarios I and II, respectively. The composite thermal comfort model provides a thermal discomfort early warning mechanism and contributes to energy conservation in the building sector.

A method of predicting the dynamic thermal sensation under varying outdoor heat stress conditions in summer

Heat stress events in urban areas are increasing as a result of global warming and urban heat islands. In response to heat stress, outdoor activators naturally often move themselves to a less hot place. An understanding of human physiological responses in dynamic outdoor thermal environments is desired. This study aims to reveal the dynamic physiological adjustment and thermal perception response characteristics under varying outdoor heat stress conditions. A robust model for predicting dynamic thermal sensation outdoors has been developed. Experiments involving heat stress changes in a hot summer were conducted with 25 subjects. Three categories of data were collected including meteorological data, physiological parameters, and thermal perception. The results showed that lower-arm skin temperature ( T lowerarm ) is more sensitive to changes in the outdoor thermal environment, and correlates closely with the thermal sensation vote ( TSV) . For a better practical application, based on the strong linear relationship between T lowerarm and T ty , the new dynamic outdoor thermal sensation model has been developed involving two parameters: T lowerarm and Δ T lowerarm /Δt (the change rate of T lowerarm ) . The validity of the model in transient outdoor conditions was verified. The algorithm can be integrated into a wearable armband to predict practical thermal sensation responses. This contribution will advance technologies based on the scientific findings to provide alert services to support human health and wellbeing, consequently increasing urban resilience and sustainability. • Experimental studies on heat stress were carried out under transient outdoor thermal environments. • The relationship between dynamic thermal sensation and physiological responses was revealed and quantified. • A dynamic outdoor thermal sensation model was developed with steady-state and dynamic terms. • The model can provide early overheating risk prediction during outdoor thermal exposure.

Experimental evaluation of thermal comfort, SBS symptoms and physiological responses in a radiant ceiling cooling environment under temperature step-changes

People usually experience transient thermal environments when entering or leaving a conditioned indoor environment. This has been previously explored but there is little knowledge on the impact of temperature step-changes on thermal comfort in a radiantly cooled environment. We aim to investigate human comfort and underlying physiological mechanism in such conditions. We assessed thermal comfort, sick building syndromes (SBS) symptoms, and physiological responses. Twenty healthy participants were exposed to three temperature step-change conditions with three outdoor air temperatures (29 °C, 33 °C and 36 °C) and one indoor air temperature of 26 °C. Subjective evaluation was collected through a questionnaire. Blood oxygen saturation (SpO2), skin temperature, and electrocardiograph (ECG) were measured. As expected, the overall thermal sensation, comfort, acceptability, preference, and subjective air freshness changed significantly before and after temperature step-changes. Perceived sweat and chest tightness were also affected by the temperature step-changes. Skin temperature, heart rate, time-domain, and nonlinear heart rate variability were affected significantly under temperature step-changes. We observed the overshoot phenomenon with thermal sensation and subjective air freshness under temperature down-step. Thermal sensation had a faster stabilization time than the measured physiological parameters (i.e., skin temperature, heart rate and heart rate variability) under temperature step-changes. The stabilization time before starting a thermal comfort experiment should be at least 30 min. Thermal sensation and skin temperature had an asymmetry effect on temperature step-changes.

Understanding how variable thermal environments affect the molecular mechanisms underlying temperature-sensitive phenotypes: lessons from sex determination.

The thermal environment that organisms experience can affect many aspects of their phenotype. As global temperatures become more unpredictable, it is imperative that we understand the molecular mechanisms by which organisms respond to variable, and often transient, thermal environments. Beyond deciphering the mechanisms through which organisms respond to temperature, we must also appreciate the underlying variation in temperature-dependent processes, as this variation is essential for understanding the potential to adapt to changing climates. In this Commentary, we use temperature-dependent sex determination as an example to explore the mechanistic processes underlying the development of temperature-sensitive phenotypes. We synthesize the current literature on how variable thermal conditions affect these processes and address factors that may limit or allow organisms to respond to variable environments. From these examples, we posit a framework for how the field might move forward in a more systematic way to address three key questions: (1) which genes directly respond to temperature-sensitive changes in protein function and which genes are downstream, indirect responders?; (2) how long does it take different proteins and genes to respond to temperature?; and (3) are the experimental temperature manipulations relevant to the climate the organism experiences or to predicted climate change scenarios? This approach combines mechanistic questions (questions 1 and 2) with ecologically relevant conditions (question 3), allowing us to explore how organisms respond to transient thermal environments and, thus, cope with climate change.

Thermal comfort of Frail People under dynamic and non-uniform thermal environments using a thermal manikin with thermoregulatory control: An experimental study

The thermal comfort of frail people has to be considered carefully, mainly because of the high thermal sensitivity of this population and the negative influences that unsatisfactory thermal conditions have on their health. Most existing thermal comfort works have been conducted under steady-state, uniform thermal environments, with far fewer being performed in dynamic and non-uniform thermal environments, and even less for frail people. This study aimed at assessing the thermal responses of frail people under transient and non-uniform thermal environments, using a thermal manikin and a climatic test cell. Thermal responses were investigated and discussed in both genders. The analysis of variance showed a significant difference in thermal comfort and thermal sensation between females and males over time, under hot exposure. Under cold exposure, results showed a significant difference in thermal sensation between females and males over time, but no significant difference was observed in term of thermal comfort. Analysis revealed also significant differences in the dynamic thermal sensation between the sexes under cold exposure, while results confirmed that there is no significant difference in the dynamic thermal sensation between sexes under hot exposure.

Unsteady characteristics of sleeping thermal comfort during defrosting of a T-ASHP system

Defrosting is necessary for the normal operation of air source heat pump (ASHP) units to solve the frosting in the winter, which deteriorates the performance of ASHP. During this defrosting period, the ASHP cannot provide heat to the indoor space, leading to adverse thermal comfort, which may reduce the sleep quality. Hence, a task/ambient ASHP (T-ASHP) system was designed in this study, and the transient thermal environment was investigated through a computational fluid dynamic (CFD) method. The duration of t oz (average air temperature in the occupied zone) increase period was 4.33 times as long as t oz decrease period, although the duration of the phase 1 heating period was 1.9 times as that of defrosting period. During the defrosting procedure, the PMV value decreased to the lowest value of −0.83, and the period of feeling cool and slightly cool lasted for 45.4 min. The hand, foot and leg parts were much cooler than the whole body, and the non-uniformity of the PMV value on body parts was obviously enlarged during the defrosting period. Higher draught risk around 22% near the head and trunk regions was found during the defrosting period and was significantly reduced in the follow-up heating period. Practical application: The results from this study emphasize the sleeping thermal comfort during defrosting of air source heat pumps. The present study gave a map of transient thermal comfortable levels influenced by the operating of defrosting and re-heating. These results should serve as a recommendation to air source heat pump designers to determine suitable defrosting technology to maintain normal indoor thermal comfort.

Thermoregulatory and cardiovascular responses to up-step change transient thermal environments: A risk factor in individuals with prosthetic heart valves

Exposure to step-change thermal environments can trigger the human body's thermoregulatory processes. The reactivation of thermoregulatory mechanisms is usually accompanied by the excitation of cardiovascular responses. This paper presents a combined thermoregulatory-cardiovascular model for predicting the effect of transient thermal environments on heart rate and cardiovascular responses. The proposed model was validated against multiple sets of experimental data reported in the literature. The validation results showed that the proposed model, which considers the thermoregulatory effects, could predict heart rate more accurately compared to the Givoni and Goldman practical model. The impacts of different up-step temperature changes on cardiovascular responses were investigated using the proposed model. The results showed that exposure to a relatively small (10°C), medium (20°C), and large (30°C) up-step temperature changes increased the heart rate by about 7%, 20%, and 35%, respectively. It was also found that ambient relative humidity did not have remarkable effects on cardiovascular responses. The results of our analysis performed in the temperature range of 20°C to 50°C showed that the heart rate could reflect the reactivation of the body's thermoregulatory mechanisms. The findings indicated that in people with artificial heart valves, sudden exposure to temperature step-changes of 10°C to 30°C could increase the heart valve pressure drop by about 14%–85%, greatly increasing the risk of blood damage. Furthermore, it is concluded that the proposed model can pave the path for utilizing integrated wearable devices for predicting individualized thermal comfort and managing cardiovascular health risks associated with ambient heat stresses.

A winter case study on synergy effect of temporal and spatial alliesthesia in temporarily occupied spaces

Temporarily occupied space (TOS) is defined as a conditioned space in which most of occupants stay for less than a certain period (e.g., 40 min). Base on the concept of TOS, specific application scenarios for transient and non-uniform thermal environments were explored by chamber tests. In the study, human subjective assessments were obtained from 16 subjects (8 males and 8 females). The synergy effect of temporal and spatial alliesthesia in TOS was quantitatively analyzed, which could achieve energy efficient thermal comfort. The synergy effect extended human thermal comfort under lower neutral temperature.

Psychophysical Adaptations to Pre-cooling in Transient Thermal Environments

The application of the thermal alliesthesial concept through pre-cooling strategies in tropical buildings has attracted customers by purging surplus body heat, particularly at the entry point of their transitional space. However, there is little empirical evidence on the impact of thermal alliesthesia on the human subject’s perception of sensation and pleasantness. This study aims to investigate this relationship in the thermoneutral zone and various affective responses based on simulated transient thermal environments. Twenty nine healthy college-aged participants are recruited for a series of thermal alliesthesia climate chamber experiments. The predominant ET* setting refers to the participant’s preferred temperature, that is, 25.1 °C (±1.0). Three experiment stages with a total of nine hours, namely, Stage A (predominant ET*: 22 °C), Stage B (predominant ET*: 24 °C), and Stage C (predominant ET*: 26 °C) are devised to simulate the working commute of office workers in and out of an air-conditioning building during warm weather conditions. The results show that a high proportion of participants are indifferent up to 11 °C of down-step despite encountering corrective transitions within the thermoneutral zone. Pre-cooling strategies are not successful in eliciting thermal pleasure responses in any of the three stages. These findings suggest that a preconditioned indoor environment of 24 to 26 °C ET* is thermally sufficient when designing for transient thermal environments, thereby, eliminating the need for over-cooling.

Metabolic response of Chlorella vulgaris to a transient thermal environment for supporting simultaneous air revitalization and thermal control in a crewed habitat

Implementing multifunctional bioregenerative technologies may provide mission carbon loop closure while simultaneously addressing multiple environmental control and life support system requirements. This paper proposes using water-based algal medium for thermal control of the spacecraft cabin, while taking advantage of the algae's photosynthetic activity for air revitalization. Consequently, this could expose the algal culture to transient thermal environments fluctuating between +4 °C and +30 °C, in the span of minutes, reflecting the operation of the International Space Station (ISS) internal thermal control and cabin system. This paper presents an initial investigation of the metabolic response of Chlorella vulgaris to transient environmental temperatures, reflecting temperature ranges and cycling frequency of the ISS cooling loop (+9 °C to +27 °C, 30 min). The constant 19 °C control represented the time-averaged temperature of the cycled condition. Growth and acclimation were observed in both tested conditions through pH, dissolved oxygen, optical density, and photosynthetic quantum yield measurements. However, there was significant reduction in the oxygen production rate, measured pH, and optical density for the cycled temperature condition when compared to the control (cycled temperature = 0.95 gO2 L−1 d−1, pH = 6.75, OD = 0.05; control = 1.17 gO2 L−1 d−1, pH = 8.20, OD = 0.08). No significant reduction in growth rate or photosynthetic quantum yield were recorded between the two tested conditions. Growth rate of the cycled temperature condition reflected those of psychrotolerant algae, suggesting some amount of culture acclimation to the rapidly dynamic environment. Results suggest that while C. vulgaris was viable within the tested temperature environment reflecting the ISS thermal control loop and cabin, there was a measurable reduction in the oxygen production rate.

Surface conductivity effects during shock wave reflection off curved surfaces

Previous work has shown that heat transfer into a plane conducting surface affects shock wave reflection properties. In the more complex reflection case of a curved surface the situation would be different because of the increased number of reflection patterns, with a rapid change in reflection geometry as the wave propagates up the surface. Test pieces of different thermal conductivities (0.19 W/mK and 401 W/mK) and hydraulically smooth surfaces are used on both convex and concave cylindrical surfaces. The test pieces are placed in identical positions on either side of a plane of symmetry and at the same incident angles in a shock tube. Tests are performed at incident shock Mach numbers of 1.22< M <1.5 and imaged using high-speed shadowgraph photography. The images are analyzed both quantitatively through reflection angle measurements and qualitatively by searching for asymmetry. Both the qualitative and quantitative measurements clearly indicate that the thermal conductivity of the surface affects the reflection patterns due to the complex transient thermal environment. Asymmetry in the reflection patterns is found at all Mach numbers. In contrast to the plane wall case the lack of theory limits comparison, where in that case it was shown that the lower the thermal conductivity the closer the experimental results approached the ideal adiabatic case. Similar comparisons in the relationship of reflection types between different materials are found in the current case. The findings could be refined by using higher imaging frame rates and spatial resolution, and sophisticated numerical modeling.

Investigation on the thermal insulation regulating performance of a newly developed air inflatable garment

It is important to keep body thermal comfort experiencing transient thermal environments, and adjusting clothing thermal insulation is expected to be a feasible strategy. In this study, to realize the thermal insulation regulating performance, a novel air inflatable garment (AirIG) using natural air as the thermal insulator was developed, and the thickness of the air layer entrapped in AirIG was determined through computer simulation. The thermal insulation regulating performance of AirIG was investigated using ‘Newton’ thermal manikin. Thermal insulation values of the AirIG were measured under four air inflation volumes [i.e., CON (no air inflation), 1/3FULL, 2/3FULL and FULL (the maximum air inflation)]. Besides, the effects of garment pattern and air velocity (i.e., 0.15 m/s, 1.55 m/s and 3.04 m/s) on the thermal insulation regulating performance of the AirIG were also studied. Results showed that with the increasing air inflation volumes, thermal insulation in the upper of the AirIG firstly significantly increased and then remained stable (i.e., CON<1/3FULL<2/3FULL, FULL, p < 0.01). Adding sleeves remarkably increased the thermal insulation when the air inflation volume increased from CON to FULL (p = 0.056). Increasing air velocity significantly decreased the thermal insulation in the upper and local body regions of the AirIG. The thermal insulation regulating performance of the AirIG disappeared when the air velocity increased to 1.55 m/s, evidenced by the insignificant thermal insulation difference among the four air inflation volumes (p > 0.1). Therefore, the AirIG can be recommended as an effective thermal insulation regulating strategy for human body in low air velocities.

Proposal of Relative Thermal Sensation: Another Dimension of Thermal Comfort and Its Investigation

Real-time thermal comfort evaluation is not only essential in constructing the control module of Heating, Ventilation and Air Conditioning (HVAC) systems in residential buildings but also rather critical in energy conservation. In the transient thermal environment, current thermal comfort is not stable and varies from time to time. Therefore, if we only evaluate the current thermal sensation that will cause prediction error. Existing thermal comfort models mainly focus on the evaluation of current thermal comfort. However, research on the evaluation of thermal sensation variation trend is vacant. Furthermore, since individual differences play an important role in thermal comfort evaluation, physiological indices should be considered. To solve this problem, in this paper, the authors exclusively propose the concept of relative thermal sensation which accounts for the thermal sensation variation trend and give its real-time evaluation method by analysis of skin/clothes temperatures of ten local body segments using machine learning algorithms. By incorporating the relative thermal sensation model with an ordinary thermal comfort model, a novel complex thermal comfort model is derived, which has the ability to predict the current thermal comfort and the thermal sensation variation trend simultaneously and provides an early warning mechanism for thermal discomfort.