This study is focused on determining the convenience of the use of displacement ventilation strategy in airborne infection isolation rooms (AIIRs). Thermal comfort of the occupants of the chamber, ...ventilation and contaminant performance indices and the exposure of the health worker (HW) to the contaminants exhaled by the confined patient (P) are considered in a typical AIIR set up with two thermal breathing manikins and a radiant wall simulating an external wall. Three air renewal rates are tested to determine their influence in the studied variables. Results show that ventilation performance, contaminants and general comfort indices for both manikins perform well in the cases studied. Lockup phenomenon associated with displacement ventilation occurs above P but it has a low influence on contaminant exposure of HW because of the influence of the convective boundary layer of HW. The influence of the radiant wall could lock the air path near the exhaust grille.
•BOS can visualize very little density gradients with only a small number of tools.•Large scale air flows can be visualized without spatial restrictions using BOS.•BOS as an optical technique nearly ...does not hamper weak indoor air flows.•BOS is a promising tool to extensively investigate indoor air flows.
This article focuses on further developments of the background-oriented schlieren (BOS) technique to visualize convective indoor air flow, which is usually defined by very small density gradients. Since the light rays deflect when passing through fluids with different densities, BOS can detect the resulting refractive index gradients as integration along a line of sight. In this paper, the BOS technique is used to yield a two-dimensional visualization of small density gradients. The novelty of the described method is the implementation of a highly sensitive BOS setup to visualize the ascending thermal plume from a heated thermal manikin with temperature differences of minimum 1 K. To guarantee steady boundary conditions, the thermal manikin was seated in a climate laboratory. For the experimental investigations, a high-resolution DLSR camera was used capturing a large field of view with sufficient detail accuracy. Several parameters such as various backgrounds, focal lengths, room air temperatures, and distances between the object of investigation, camera, and structured background were tested to find the most suitable parameters to visualize convective indoor air flow. Besides these measurements, this paper presents the analyzing method using cross-correlation algorithms and finally the results of visualizing the convective indoor air flow with BOS. The highly sensitive BOS setup presented in this article complements the commonly used invasive methods that highly influence weak air flows.
This paper investigates experimentally the flame height and temperature profile of window ejected thermal plume from compartment fire without facade wall. The previous works and correlations on these ...characteristics of such thermal plume mainly concern the condition with a facade wall, where the air entrainment of the thermal plume from the side of the facade wall is restricted. However, such entrainment constraint effect does not exist when the fire occurs at the top floor of the building noting that there is no facade above the top floor, for which scenario the flame height and temperature profile of the thermal plume characteristics have not been quantified in the literature. In this work, comprehensive experiments were carried out by employing a reduced-scale model (1:8), consisting of a 0.4 m cubic fire compartment with six different window openings corresponding to various ventilation factors (AH). A propane square porous burner was set as fire source with various fuel mass flow meters and hence heat release rate. All the tests were designed as un-ventilated condition that stable flame was observed outside the window. The flame height outside the window was recorded through a CCD camera from the side view. The temperature profiles of the ejected fire plume outside the window were measured by the thermocouple arrays (7 rows, 7 columns) located above the top of the compartment. These measured quantities without the facade wall were compared from those with a facade wall. Results showed that the flame height can be still well correlated non-dimensionally by the excess fuel heat release rate and the characteristic length scale (ℓ1=(AH)2/5) of the window. However, the flame height with a facade wall was higher, being 1.31 times of those without a facade wall. This difference was physically quantified by the air entrainment change due to constraint effect from the facade wall. The radial temperature profile in the ejected thermal fire plume at various height can be globally represented by the Gaussian function (Tz,x−T∞Tz,max−T∞=e−β(x−xmFWHM)2) with and without facade wall, where the value of β was found to be 2ln2. These quantifications and correlations on window-ejected thermal plume characteristics without a facade wall, providing a significant supplementary over previous works focusing on condition with the facade wall, will be an important addition for the estimation of such thermal plume characteristics and its thermal impacts. This work, providing experimental data and correlations on window ejected thermal plume characteristics from compartment fire at the top level of the building without the effect of facade wall, will be an important supplementary over previous knowledge focusing on the scenario with the effect of facade wall.
•Characteristics of window-ejected thermal plumes with no facade quantified.•Flame height and temperature profile compared with those with facade.•Their difference quantified and global correlations proposed.
Thermal water discharge within the gravity-driven groundwater flow system in the Alps and other similar areas around the world may be hidden in Quaternary deposits which, in these regions, often ...cover the regional aquifer. When thermal water drains into Quaternary deposits, the mixing of the deep thermal component and the cold shallow groundwater forms a thermal plume that extends parallel to the main groundwater flow in shallow system. In the Bled case study in Slovenia, the thermal water discharges from carbonate rocks into Quaternary glaciofluvial sediments, and as the Toplice spring at a rate of 5 l/s at an average temperature of 21.5 °C. Knowing the spatial extent and intensity of thermal outflow is essential to decision making related to the development and protection of this renewable resource. By approximating the thermal water outflow from a discharge zone as a planar source, a planar advective heat transport model can be used to evaluate its geometry and quantify rates. An analytical procedure follows rough assumptions leading to conservative results. Moreover, a numerical model using the FEFLOW code was applied for comparison with the simulations of the analytical model. The heat transport model was based on measured hydraulic parameters (e.g. groundwater levels) and borehole temperatures as well as on-site and international literature (e.g. dispersivity, thermal conductivity). Nine scenarios were applied accounting for different dimensions of the heat source and compared to the results of numerical simulations. Each scenario was verified by calculating the relative error between the analytical models and the measured borehole temperatures. The results confirm that the main outflow of thermal water can be determined using planar geometry, and is 200–300 m wide. The height of the thermal outflow zone is approximately 25 m, corresponding to the expected thickness of the direct contact between the fractured dolomite and the shallower Quaternary aquifer. Using the proposed widths and depths, the hidden natural thermal outflow rates are estimated at 57–86 l/s.
•Analytical model accounting for the planar heat transport and numerical model were applied to evaluate the heat plume dimensions caused by thermal water.•Modelling results were compared with measured temperatures in boreholes.•The thermal water outflow is predominantly bound to a continuous surface, and secondary thermal outflows may occur in some cases.
•The underground around a BHE may freeze and thaw due to intensive heat extraction.•Freeze-thaw cycles affect mechanical, thermal and hydraulic properties of sediments.•The thermal plume propagates ...significantly faster when phase change occurs.•The paper combines experimental input data with benchmarked freeze-thaw simulation.
In closed-loop geothermal systems the underground may freeze and thaw due to intensive heat extraction. Phase change alters the sediments’ mechanical and hydraulic properties and their thermal behaviour, thus affecting the thermal plume propagation and the area of potential changes. By means of a finite element model, this paper evaluates the thermal plume in a particular case study in several conditions, comparing the results obtained when considering or disregarding the freeze-thaw processes by applying a benchmarked plug-in. The model is based on experimental input data. The results show that the frost front propagates significantly faster when phase change occurs.
Buildings consume more than 40% of global energy use and ventilation is one of the largest source of energy consumption. Sustainable design requires choosing energy efficient ventilation strategies. ...Diffuse ceiling ventilation (DCV) has a great energy saving potential due to the low pressure drop (∼2 Pa) through the ceiling panel. A DCV system has three components: plenum, suspended ceiling and ventilated room. Conditioned air is supplied to plenum, then diffuses into the ventilated room through the suspended ceiling made of porous materials. The system can be designed to handle high cooling loads without inducing thermal discomfort. This review references research articles on DCV published from 2008 to 2018 to highlight the research outcomes and to identify the research gaps. One major objective of this review paper is to document simplified theoretical modelling methods for proposing quick DCV system design tool. The flow in the plenum can be described as impingement jet over porous materials. A design procedure is proposed to determine the size and number of nozzles. The heat transfer in the porous ceiling is treated as two-phase energy transport. Buoyancy force generated by the heat sources in the room has been identified to drive the airflow circulation, which motivates the thoughtful review of fundamental theories of thermal plumes in a stratified environment. The major task on thermal plumes is to calculate the height and induced volume flow rate, which are summarized according to the type of heat sources, e.g., point or area sources. The principle behind heating efficiency of DCV might be explained by theories of turbulent fountains. The rising height of warm air coming out of diffuse ceiling is determined by the source Froude number. The popular research methods to study DCV system are full-scale experiments and CFD modelling. Full-scale experiments are often used to evaluate the performance of the DCV system based on thermal comfort, indoor air quality and energy efficiency. On the other hand, CFD modelling is used for parametric analysis to improve the design of the DCV system. Finally, future research on DCV is discussed.
•Diffuse ceiling ventilation features with low building energy use.•Thermal plumes drive the air motion in rooms with diffuse ceiling ventilation.•Turbulence fountain theory explains heating ability of diffuse ceiling ventilation.•Research methods for diffuse ceiling ventilation are CFD and full-scale experiment.•Future research themes for diffuse ceiling ventilation are proposed.
The lavatory is a fertile area for the transmission of infectious disease through bioaerosols between its users. In this study, we built a generic compact lavatory model with a vacuum toilet, and ...computational fluid dynamics (CFD) is used to evaluate the effects of ventilation and user behaviors on the airflow patterns, and the resulting fates of bioaerosols. Fecal aerosols are readily released into the lavatory during toilet flush. Their concentration rapidly decays in the first 20 s after flushing by deposition or dilution. It takes about 315 s to 348 s for fine bioaerosols (<10 µm in diameter) to decrease to 5% of the initial concentration, while it takes 50 and 100 µm bioaerosols approximately 11 and <1 s, respectively, to completely deposit. The most contaminated surfaces by aerosol deposition include the toilet seat, the bowl, and the nearby walls. The 10 µm aerosols tend to deposit on horizontal surfaces, while the 50 and 100 µm bioaerosols almost always deposit on the bowl. In the presence of a standing thermal manikin, the rising thermal plume alters the flow field and more bioaerosols are carried out from the toilet; a large fraction of aerosols deposit on the manikin’s legs. The respiratory droplets generated by a seated coughing manikin tend to deposit on the floor, legs, and feet of the manikin. In summary, this study reveals the bioaerosol dilution time and the easily contaminated surfaces in a compact lavatory, which will aid the development of control measures against infectious diseases.
•The simplification methods largely affect the thermal flow and contaminant fields.•The mesh decimating algorithm is promising to reduce cost but remain accuracy.•The recommended method is efficient ...for multi-occupant environment simulations.
While simplified computational thermal manikins (CTMs) are widely employed in CFD models of occupied indoor spaces in order to save the computational cost, a criterion of simplification is still absent and the effects of CTM simplification are yet not clear. In this study, six CTMs including a 3D scanned CTM and five simplified CTMs generated from various simplification approaches were employed to analyse the impact of CTM simplification on the prediction of airflow field and contaminant transport. Comparison of the predicted airflow field against the published data in the literature demonstrated that CTM simplification has a strong effect on the thermal airflow field prediction in the vicinity of manikin surfaces. For densely occupied indoor spaces such as a train cabin, the error induced by CTM simplification could be enlarged and further cause significant global error to the prediction of contaminant transport. This is especially true when contaminants are released from the CTMs. This study demonstrated that the mesh decimating algorithm is promising to simply CTMs that is not only able to reduce considerable computational cost but capable of maintaining an acceptable predictive error.
The purpose of this study is to investigate the influence of the heat dissipation of thermal manikins on the flow field in a seven-row cabin mockup that was fully occupied by thermal manikins. ...Temperature data from the cabin mockup, as measured by thermocouples, were analyzed using statistical methods for elucidation of the turbulence characteristics of the thermal plumes of manikins. The characteristics of the thermal plumes are illustrated by the skewness factors of the temperature signal. The results indicate the characteristics of the thermal plume from the torso differ from those from the thigh. A thin layer (approximately 5 mm) of the thermal plume was observed around the human torso. Further, thermal plumes were more fully developed at the thigh than the torso. The results contribute to the understanding of airflow patterns influenced by thermal plumes near the head, chest, abdomen and thigh.
•Through using the dynamic thermal turbulence measurements investigate the thermal plume of passenger in cabin.•A thin layer of torso thermal plume was observed around the human body in cabin.•The thermal plumes have influence on the flow field and enhanced turbulent fluctuation at abdomen region.
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