Experimental study of the interaction between thermal plumes and human breathing in an undisturbed indoor environment (original) (raw)
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Analysis of thermal plumes generated by a seated person, a thermal manikin and a dummy
In this work, the main features of the mean velocity and temperature fields developed above different kinds of stationary heat sources, in quiet and isothermal surroundings, are presented and discussed. The major objective of the present contribution concerns the analysis of the modeling capabilities of thermal manikins and heated dummies, as compared to the case of real occupants, engaged on sedentary activities, typical of office work. As it might be expected, the buoyancy driven flow promoted by a thermal manikin (nude or dressed) provides a more sound reproduction of what may be generated by a human being, here restricted to the case of a seated person, normally dressed with common winter clothing. Consideration of the axial decay of mean velocities and temperatures clearly suggest that the development of an axisymmetric turbulent plume originating at a point source is not fully attained. Instead, the flow field seems to be better described by a shear free heated wake, a situation that calls for further analysis.
Air temperature investigation in microenvironment around a human body
Building and Environment, 2015
ABSTRACT The aim of this study is to investigate the temperature boundary layer around a human body in a quiescent indoor environment. The air temperature, mean in time and standard deviation of the temperature fluctuations around a breathing thermal manikin are examined in relation to the room temperature, body posture and human respiratory flow. To determine to what extent the experiments represent the realistic scenario, the additional experiments were performed with a real human subject. The results show that at a lower room air temperature (20 °C), the fluctuations of air temperature increased close to the surface of the body. The large standard deviation of air temperature fluctuations, up to 1.2 °C, was recorded in the region of the chest, and up to 2.9 °C when the exhalation was applied. The manikin leaned backwards increased the air temperature in the breathing zone, which was opposite from the forward body inclination. Exhalation through the mouth created a steady air temperature drop with increased distance from the mouth without disturbing the region of the chest. Exhalation through the nose did not affect the air temperature in front of the chest due to physics of the jets flow from the nose. The additional carbon dioxide (CO2) measurements showed that the exhaled air from the nose could penetrate the region below the chest. Small discrepancies between the results obtained with the breathing thermal manikin and a real human subject suggest that the manikin can be used for accurate measurements of occupant’s thermal microenvironment.
Experimental study about how the thermal plume affects the air quality a person breathes
2011
Work shop session 1 Modeling and visualization Natural, hybrid and mechanical ventilation Ventilation for low energy, passive houses/zero emissions buildings Ventilation of heavy industry Room R1 Room R2 Room R3 Room R10 Monday, June 20, 15:30 to 17:00 Work shop session 2 Technical session 8 Technical session 9 Technical session 10 Room R2 Room R3 Room R10 Ventilation in Zero Emission Buildings Evaluation, control or measurements of indoor air quality Evaluation, control or measurements of indoor thermal environment New technologies for heat recovery system Ventilation strategies for large rooms in historic build. New technologies for heating and cooling or ventilation/AC Codes and regulations Room R1 Room R2 Room R3 Room R10 Room R1
Heat and Mass Transfer, 2017
Exhalation flow and room temperature can have a considerable effect on the microenvironment in the vicinity of human body. In this study, impacts of exhalation flow and room temperature on the microenvironment around a human body were investigated using a numerical simulation. For this purpose, a computational fluid dynamic program was applied to study thermal plume around a sitting human body at different room temperatures of a calm indoor room by considering the exhalation flow. The simulation was supported by some experimental measurements. Six different room temperatures (18 to 28°C) with two nose exhalation modes (exhalation and non-exhalation) were investigated. Overhead and breathing zone velocities and temperatures were simulated in different scenarios. This study finds out that the exhalation through the nose has a significant impact on both quantitative and qualitative features of the human microenvironment in different room temperatures. At a given temperature, the exhalation through the nose can change the location and size of maximum velocity at the top of the head. In the breathing zone, the effect of exhalation through the nose on velocity and temperature distribution was pronounced for the point close to mouth. Also, the exhalation through the nose strongly influences the thermal boundary layer on the breathing zone while it only minimally influences the convective boundary layer on the breathing zone. Overall results demonstrate that it is important to take the exhalation flow into consideration in all areas, especially at a quiescent flow condition with low temperature. List of symbols AHU Air handling unit°C Degree of centigrade CBL Convective boundary layer CFD Computational fluid dynamic Clo A measure of clothes thermal insulation (1 Clo = 0.155 m 2 K/W) cm Centimeter GB Gigabyte sec Second RANS Reynolds-averaged Navier-Stokes RNG k-ε Renormalization-group K-epsilon turbulence model T amb Ambient temperature T surf Surface temperature TBL Thermal boundary layer Y + A non-dimensional distance * Noradin Gharari
Experimental Study about Human Local Thermal Sensation Using a Thermal-Manikin
In this work an experimental study about local thermal discomfort, due to the draught sensation, that an occupant is subjected in ventilated spaces, will be presented. In the study, done in a climatized full-scale compartment with controlled air temperature, will be used a thermal-manikin, to simulate the human body posture, and a local ventilator, to simulate the non-uniform airflow around an occupant. It will be measured and analysed the air velocity fluctuations around a thermal-manikin in 25 points. During the tests, with the air-forced ventilation system located 2 m in front the manikin, the air velocity values will be measured during 5 minutes with a rate of 50 samples per second. This experimental data will be used to evaluate the undesirables air velocity fluctuations, using the spectral analysis.
Analysis of the Interaction of Thermal Plumes Within Office Environment Using a Thermal Manikin
The present work focus on the study of the interaction of the thermal plume generated by one person, engaged on sedentary activities, with furniture and with other buoyancy driven flow generated by other heat source typical of an office environment. The measurements took place in a climate chamber, using a thermal manikin seated on an office desk with a common desktop PC. The velocity and temperature profiles were obtained with 15 omni direction probes, spanning two normal axes. To cover the volume above the manikin, the desk and the personal computer, the measurements were made by means of an automatic traversing mechanism.
Evaluation of the Effects of Airflow Patterns on Human Thermal Perception
Highlights in Science, Engineering and Technology
Recently, greenhouse gas emissions have led to irreversible climate change, and in order to mitigate the changes, more and more research is focusing on energy efficiency and environmental protection in the building sector. Improving indoor ventilation airflow as a feasible solution for energy conservation as well as improving human thermal comfort. This study aims to provide reference for optimizing the thermal perception of occupants in indoor ventilation design. This research evaluates the effect of heat perception on students in a stable indoor environment (28 ℃, RH 50%) under two airflow patterns (dynamic and constant). The use of airflow was found to have a positive impact on thermal sensation vote (TSV) and thermal pleasure vote (TPV). There was non-significant difference in the effects of heat perception between airflow modes. This finding is consistent with the findings of Parkinson and de Dear's study. It is worth noting that differences in experimental results may be d...
International Journal of Biometeorology, 2011
The present experimental work is dedicated to the analysis of the effect of walking on the thermal insulation of the air layer (I a ) and on the convective heat transfer coefficients (h conv ) of the human body. Beyond the standing static posture, three step rates were considered: 20, 30 and 45 steps/min. This corresponds to walking speeds of approximately 0.23, 0.34 and 0.51 m/s, respectively. The experiments took place in a climate chamber with an articulated thermal manikin with 16 independent parts. The indoor environment was controlled through the inner wall temperatures since the objective of the tests was restricted to the influence of the walking movements under calm conditions. Five set points were selected: 10, 15, 20, 25 and 30°C, and the operative temperature within the test chamber varied between 11.9 and 29.6°C. The highest and lowest I a values obtained were equal to 0.87 and 0.71 clo, respectively, and the reduction in insulation due to walking ranged between 9.8 and 11.5%. The convective coefficients (h conv ) for the whole body and for the different body segments were also determined for each step rate. In the case of the whole body, for the standing static reference posture, the mean value of h conv was equal to 3.3 W/m 2°C and a correlation [Nu = Nu(Gr)] for natural convection is also presented in good agreement with previous results. For the other postures, the values of h conv were equal to 3.7, 3.9 and 4.2 W/m 2°C , respectively for 20, 30 and 45 steps/min.
Influence of air flow on skin temperature
Journal of human ergology, 1993
The skin temperature is fundamental to heat exchange between the human body and the environment. The convective and evaporative heat exchanges depend on the temperature gradient and the extent of air flow over the skin surface. An attempt was made to study the topographical differences in skin temperature (Tsk) under varied levels of air flow and to examine the possible body temperature regulatory mechanism. Five volunteers were examined in a climatic chamber at 30 and 36 degrees C DB at 55-60% RH (ambient vapour pressure of 2.58 and 3.53 kPa and air flow of 0.6, 1.4, 1.9, 2.1 m/s). The deep body temperature (Tc) and local Tsk were recorded at 5-min intervals during 10 min pre-exposure, 30 min exposure to heat and 15 min recovery period after air flow was withdrawn. The time taken to attain at the lowest Tsk in different air speeds varied from 30 to 45 min. The highest drop in Tsk (2.4 degrees C) was recorded for forehead at 30 degrees C DB and significant skin cooling was achieved ...
Building and Environment, 2018
In warm and hot environments, the possibility of increasing air velocity reduces energy consumption without compromising occupants' thermal comfort; whereas the cooling efficiency pertains to the temperature limits. To address the coupling effect of air velocity and temperature on thermal comfort and evaluate the cooling efficiency objectively, 9 experimental conditions with side air supply (piston flow) were conducted in a well-controlled climate chamber, covering temperatures from warm (28 o C) to hot (34 o C). Both skin temperatures and questionnaires were measured on 20 subjects. The results showed the cooling efficiency by airflow was significantly affected by temperatures. Subjects' mean skin temperatures(MST) and thermal sensations (TSV) were improved by increasing air velocities when temperature was lower than or equal to 32 o C, but no significant differences were found between different air velocities at each temperature level (except for MST at 28 o C). The air velocity failed to modify subjects' thermal responses but caused negative thermal and pressure due to higher air temperature and airflow at 34 o C. Thanks to the uniform air movement, subjects' total heat loss from skin surface(Q skin) was quantified that significantly reduced from 46.98W/m 2 at 28 o C/0m/s, to 31.45W/m 2 at 34 o C/1.4m/s, indicating the poor cooling efficiency of air velocity in hot environments. The relation between air velocity and temperature with a prerequisite of neutral thermal sensation was obtained based on Q skin , which can reserve as a reference for air velocity design in warm and hot environments considering thermal comfort, cooling efficiency and energy savings.