Transient natural ventilation of a room with a distributed heat source

2007 ◽  
Vol 591 ◽  
pp. 21-42 ◽  
Author(s):  
SHAUN D. FITZGERALD ◽  
ANDREW W. WOODS
Keyword(s):  
Heat Source ◽  
Thermal Stratification ◽  
Room Temperature ◽  
Natural Ventilation ◽  
Initial Temperature ◽  
Lower Layer ◽  
Ambient Air ◽  
Equilibrium Temperature ◽  
Transient Flows ◽  
Hot Air

We report on an experimental and theoretical study of the transient flows which develop as a naturally ventilated room adjusts from one temperature to another. We focus on a room heated from below by a uniform heat source, with both high- and low-level ventilation openings. Depending on the initial temperature of the room relative to (i) the final equilibrium temperature and (ii) the exterior temperature, three different modes of ventilation may develop. First, if the room temperature lies between the exterior and the equilibrium temperature, the interior remains well-mixed and gradually heats up to the equilibrium temperature. Secondly, if the room is initially warmer than the equilibrium temperature, then a thermal stratification develops in which the upper layer of originally hot air is displaced upwards by a lower layer of relatively cool inflowing air. At the interface, some mixing occurs owing to the effects of penetrative convection. Thirdly, if the room is initially cooler than the exterior, then on opening the vents, the original air is displaced downwards and a layer of ambient air deepens from above. As this lower layer drains, it is eventually heated to the ambient temperature, and is then able to mix into the overlying layer of external air, and the room becomes well-mixed. For each case, we present new laboratory experiments and compare these with some new quantitative models of the transient flows. We conclude by considering the implications of our work for natural ventilation of large auditoria.

Modeling of Buoyancy-Driven Natural Ventilation in Workshop: Optimization of Distance between Heat Source and Ground

2012 ◽  
Vol 170-173 ◽  
pp. 2579-2582 ◽  
Author(s):  
Ya Xin Su ◽  
A Long Su ◽  
Xin Wan
Keyword(s):  
Heat Source ◽  
Indoor Air ◽  
Energy Cost ◽  
Lower Energy ◽  
Natural Ventilation ◽  
Waste Heat ◽  
Heat Sources ◽  
Hot Air ◽  
Computational Fluid Dynamics Cfd ◽  
Cfd Method

Natural ventilation is suitable for application to workshops with heat sources to keep good indoor air quality at lower energy cost. In this paper, the authors numerically investigated the buoyancy-driven natural ventilation in a workshop with heat source based on computational fluid dynamics (CFD) method. The effect of the distance between heat source and ground on the air flow and temperature distribution was examined. Results showed that the average air temperature at operation zone could be effectively reduced when the distance between heat source and ground increased. The temperature field in the upper zone of the workshop was improved by diminishing the hot air zone near the ceiling and the waste heat directly going into the operation zone decreased when the distance between heat source and ground increased.

On the effect of distributed cooling in natural ventilation

2008 ◽  
Vol 600 ◽  
pp. 1-17 ◽  
Author(s):  
S. R. LIVERMORE ◽  
A. W. WOODS
Keyword(s):  
Heat Source ◽  
Laboratory Experiments ◽  
Natural Ventilation ◽  
Lower Layer ◽  
Heated Plate ◽  
Distributed Source ◽  
Low Level ◽  
High Level ◽  
Enclosed Space

We examine the natural ventilation flows which develop when a low-level heat source interacts with a distributed zone of cooling at high level in an enclosed space. We develop some new analogue laboratory experiments in which we use a saline plume to model a localized heat source and a heated plate to model a distributed source of cooling. The experiments show that in a building with a low-level point source of heating, a two-layer steady stratification develops in which the depth of the lower layer decreases as the intensity of the cooling at the ceiling increases. We develop a theoretical model which accounts for the penetrative entrainment across the interface associated with the convection in the upper layer. We show that this becomes more dominant as the cooling increases and eventually the room becomes well-mixed. We discuss the role of such distributed cooling on the design of natural ventilation and its ability to provide sufficient flow and adequate temperature control.

Emptying non-adiabatic filling boxes: the effects of heat transfers on the fluid dynamics of natural ventilation

2012 ◽  
Vol 701 ◽  
pp. 386-406 ◽  
Author(s):  
G. F. Lane-Serff ◽  
S. D. Sandbach
Keyword(s):  
Heat Transfer ◽  
Natural Ventilation ◽  
Lower Layer ◽  
Relative Size ◽  
Ambient Air ◽  
Conductive Heat Transfer ◽  
Radiant Heat Transfer ◽  
Conductive Heat ◽  
Heat Transfers ◽  
Radiant Transfer

AbstractA model for steady flow in a ventilated space containing a heat source is developed, taking account of the main heat transfers at the upper and lower boundaries. The space has an opening at low level, allowing cool ambient air to enter the space, and an opening near the ceiling, allowing warm air to leave the space. The flow is driven by the temperature contrast between the air inside and outside the space (natural ventilation). Conductive heat transfer through the ceiling and radiant heat transfer from the ceiling to the floor are incorporated into the model, to investigate how these heat transports affect the flow and temperature distribution within the space. In the steady state, a layer of warm air occupies the upper part of the space, with the lower part of the space filled with cooler air (although this is warmer than the ambient air when the radiant transfer from ceiling to floor is included). Suitable scales are derived for the heat transfers, so that their relative importance can be characterized. Explicit relationships are found between the height of the interface, the opening area and the relative size of the heat transfers. Increasing heat conduction leads to a lowering of the interface height, while the inclusion of the radiant transfer tends to increase the interface height. Both of these effects are relatively small, but the effect on the temperatures of the layers is significant. Conductive heat transfer through the upper boundary leads to a significant lowering of the temperature in the space as a proportion of the injected heat flux is taken out of the space by conduction rather than advection. Radiative transfer from the ceiling to floor results in the lower layer becoming warmer than the ambient air. The results of the model are compared with full-scale laboratory results and a more complex unsteady model, and are shown to give results that are much more accurate than models which ignore the heat transfers.

Investigation of Plasma Treatment Conditions for Wafer-Scale Room-Temperature Bonding Using Ultrathin Au Films in Ambient Air

2019 ◽  
Vol 139 (7) ◽  
pp. 217-218
Author(s):  
Michitaka Yamamoto ◽  
Takashi Matsumae ◽  
Yuichi Kurashima ◽  
Hideki Takagi ◽  
Tadatomo Suga ◽  
...  
Keyword(s):  
Plasma Treatment ◽  
Room Temperature ◽  
Ambient Air ◽  
Wafer Scale ◽  
Treatment Conditions

The ecological state of the Elefsis Bay prior to the operation of the athens sea outfall

1994 ◽  
Vol 30 (10) ◽  
pp. 161-171 ◽  
Author(s):  
A. J. Theodorou
Keyword(s):  
River Discharge ◽  
Thermal Stratification ◽  
Lower Layer ◽  
Ecological State ◽  
Annual Cycles ◽  
Untreated Wastewater ◽  
Resistant Species ◽  
Acartia Clausi ◽  
Gyrodinium Aureolum ◽  
Agricultural Areas

Nutrient pollution in Elefsis Bay arises mainly from the disposal of Athens untreated wastewater at the eastern entrance of the Bay. The absence of river discharge, lack of cultivated agricultural areas providing runoff and the Bay's limited circulation provide the conditions for the Bay's eutrophication by the discharge of untreated wastewater. In the spring of 1993 this discharge was replaced by a new deep outfall system. To monitor any future changes an assessment of the present ecological state of the Bay is required. Analysis of appropriate data showed that Elefsis Bay accumulates nutrients. In summer a strong thermal stratification causes anoxic conditions to occur in the lower layer. The ecosystem exhibits reduced species diversity and strong oscillations of plankton annual cycles. Flagellates (Cryptomonas sp.) dominate the phytoplankton, followed by dinoflagellates (Gyrodinium aureolum, Prorocentum dentatum) and only in the spring diatoms (Nitzschia) predominate. The zooplankton was dominated by copepods (Acartia clausi) and cladoceran (Podon polyphemoides). Macrobenthos consists of a small number of pollution-resistant species of Polychaeta (Capitela capitata), whilst in summer only one species of Molluscs (Corbula gibba) survives.

Visible-light-initiated Catalyst-free Oxidative Cleavage of Triaryl-Substituted Alkenes C=C Bonds under Ambient Conditions

2021 ◽  
Author(s):  
Wenjing Li ◽  
Shun Li ◽  
Lihua Luo ◽  
Yichen Ge ◽  
Jiaqi Xu ◽  
...  
Keyword(s):  
Visible Light ◽  
Room Temperature ◽  
Ambient Air ◽  
Oxidative Cleavage ◽  
Ambient Conditions ◽  
Blue Led ◽  
Catalyst Free

The catalyst-free oxidative cleavage of (Z)-triaryl-substituted alkenes bearing pyridyl motif with ambient air under irradiation of blue LED at room temperature has been developed. The reaction was facile and scalable,...

scholarly journals Room-Temperature Solution-Processed 0D/1D Bilayer Electrodes for Translucent CsPbBr3 Perovskite Photovoltaics

Nanomaterials ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 1489
Author(s):  
Bhaskar Parida ◽  
Saemon Yoon ◽  
Dong-Won Kang
Keyword(s):  
Solar Cells ◽  
Indium Tin Oxide ◽  
High Performance ◽  
Room Temperature ◽  
Low Cost ◽  
Perovskite Solar Cells ◽  
Ambient Air ◽  
Plasma Damage ◽  
Temperature Solution ◽  
Ito Nanoparticles

Materials and processing of transparent electrodes (TEs) are key factors to creating high-performance translucent perovskite solar cells. To date, sputtered indium tin oxide (ITO) has been a general option for a rear TE of translucent solar cells. However, it requires a rather high cost due to vacuum process and also typically causes plasma damage to the underlying layer. Therefore, we introduced TE based on ITO nanoparticles (ITO-NPs) by solution processing in ambient air without any heat treatment. As it reveals insufficient conductivity, Ag nanowires (Ag-NWs) are additionally coated. The ITO-NPs/Ag-NW (0D/1D) bilayer TE exhibits a better figure of merit than sputtered ITO. After constructing CsPbBr3 perovskite solar cells, the device with 0D/1D TE offers similar average visible transmission with the cells with sputtered ITO. More interestingly, the power conversion efficiency of 0D/1D TE device was 5.64%, which outperforms the cell (4.14%) made with sputtered-ITO. These impressive findings could open up a new pathway for the development of low-cost, translucent solar cells with quick processing under ambient air at room temperature.

scholarly journals Analysis and Comparison of Some Low-Temperature Heat Sources for Heat Pumps

Energies ◽  
2019 ◽  
Vol 12 (10) ◽  
pp. 1853 ◽  
Author(s):  
Pavel Neuberger ◽  
Radomír Adamovský
Keyword(s):  
Heat Transfer ◽  
Low Temperature ◽  
Heat Source ◽  
Heat Pump ◽  
Heat Exchangers ◽  
Ambient Air ◽  
Heat Transfer Fluid ◽  
Heat Sources ◽  
Ground Heat Exchangers ◽  
Temperature Heat

The efficiency of a heat pump energy system is significantly influenced by its low-temperature heat source. This paper presents the results of operational monitoring, analysis and comparison of heat transfer fluid temperatures, outputs and extracted energies at the most widely used low temperature heat sources within 218 days of a heating period. The monitoring involved horizontal ground heat exchangers (HGHEs) of linear and Slinky type, vertical ground heat exchangers (VGHEs) with single and double U-tube exchanger as well as the ambient air. The results of the verification indicated that it was not possible to specify clearly the most advantageous low-temperature heat source that meets the requirements of the efficiency of the heat pump operation. The highest average heat transfer fluid temperatures were achieved at linear HGHE (8.13 ± 4.50 °C) and double U-tube VGHE (8.13 ± 3.12 °C). The highest average specific heat output 59.97 ± 41.80 W/m2 and specific energy extracted from the ground mass 2723.40 ± 1785.58 kJ/m2·day were recorded at single U-tube VGHE. The lowest thermal resistance value of 0.07 K·m2/W, specifying the efficiency of the heat transfer process between the ground mass and the heat transfer fluid, was monitored at linear HGHE. The use of ambient air as a low-temperature heat pump source was considered to be the least advantageous in terms of its temperature parameters.

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