Natural Draft Research Articles

Numerical Simulation Study on the Response of Ship Engine Room Structure Under Fire Based on Thermo-Mechanical Coupling Model

Ship structures may collapse or be severely deformed during a fire. To precisely assess the post-fire structural integrity of ships, in this study, a thermal–mechanical coupling data interface was created, employing a significant eddy simulation algorithm for fire dynamics and a technique to analyze the structural thermal–mechanical coupling reaction. PyroSim was utilized to build a fire scenario, exporting 3D data through the device’s own program, and then the ANSYS thermal–mechanical coupling model was employed to study the spatial temperature distribution under fire-induced conditions. Data from the three-dimensional spatial temperature field served as the boundary condition for the determination of the structural temperature burden. Building on this, an analysis was conducted on the structural response of the intricate two-story interior compartment under fire conditions. The results showed that the location of the fire source and the structural distribution of the mechanical equipment inside the cabin had a great influence on the temperature and combustion heat, followed by the ventilation conditions, while the temperature variations in the parallel dual fuel tanks were greatly influenced by the stack effect. By comparing the stress and strain of the two-layer cabin under normal and fire conditions, the damage and mechanisms associated with important positions in the cabin under fire conditions were revealed.

The Impact of an Office Fire Combined with the Stack Effect in a Multi-Story Building

The current study was based on two simulations conducted in FDS that examined the influences of an office fire on the ground floor of a 10-story building (with 9 above-ground floors) and its impact on air and smoke flow. After reviewing the literature, we observe a significant gap in current research addressing the dynamic interdependence between fire development and the stack effect in multi-story residential buildings. It was found that the fire significantly intensified the stack effect, increasing the temperature in the stairwell, particularly on the ground floor. Gas velocities within the building increased but do not endanger the lives of the occupants. Visibility remained sufficient for evacuation from the apartments, except in critical areas such as the fire-affected apartment and the stairwell. Lethal concentrations of CO and CO2 were rapidly reached, severely impairing evacuation capability within the fire-affected apartment and the stairwell. Natural ventilation proved insufficient for controlling smoke and toxic gasses, highlighting the need for additional sealing measures and forced ventilation.

Impact of chimney structure and ambient wind on heat pipe heat dissipation

ABSTRACT Spontaneous combustion of coal gangue piles poses a significant environmental threat, and gravity heat pipes are considered a simple and effective solution for managing this issue. This study presents a novel method to achieve efficient heat pipe cooling without relying on ambient wind, by utilizing the chimney effect to enhance the heat dissipation efficiency of the condenser section. Initially, chimney parameters were optimized. Subsequently, the optimal chimney parameters were further examined under conditions with ambient wind. The results indicate that in the absence of ambient wind, a chimney height-to-condenser length ratio of approximately 6:1, a chimney inner radius-to-heat pipe radius ratio of about 1.4:1, and a chimney inlet radius-to-inner radius ratio of around 1.5:1 can increase the airflow velocity over the gravity heat pipe surface by a factor of three. When the chimney is located in an area with ambient wind, setting the ratio of inlet radius to chimney inner radius to 1:1 effectively reduces the adverse impact of wind. The optimized chimney can harness the heat generated by spontaneous combustion of coal gangue piles to enhance heat dissipation at the heat pipe condenser, thereby shortening the remediation time of the gangue pile.

Study on synergistic efficiency of zonal water distribution and wind-conducting structure of high-level water-collecting natural draft wet cooling towers under crosswinds

The high-level water collection cooling tower has broad application prospects in the field of nuclear power, but the high crosswind environment will significantly reduce the flow and heat transfer performance of the high-level water collection natural ventilation wet cooling tower (HNDWCT). So a synergistic model of zoned water distribution and wind guiding structures is proposed in this paper. Numerical simulations were performed to compare and analyze the cooling tower’s flow and heat transfer characteristics in the synergistic and traditional models under a 0–10 m/s crosswind environment. The results show that the synergistic model increases the inlet air flow of the natural ventilation high-rise cooling tower by 7.8–46 %, reduces the standard deviation of the inlet air velocity by 0.22–0.81, and reduces the outlet water temperature by 0.32–3.51 K, which improves the cooling performance of the cooling tower.

Design Improvement, Thermal Efficiency Optimization and Comparative Study of a Natural Draft Chulha

ABSTRACT This work inscribes the rural-based biomass cookstove (chulha) fabrication with the aim of modification and enhancement of the existing natural draft low smoke heat-efficient stoves and also comparing its thermal efficiency output. This study is important from the perspective of a rural society who cooks their daily meals on biomass-based cookstoves/chulhas. Enhancing its thermal efficiency and reducing smoke emissions from biomass combustion in the cookstove are the primary focuses of this work. Principle used to design the improved chulha is double co-axial cylinder secondary combustion. Mild steel is used for fabricating maximum parts of the stove including the outer cylinder surface, and the inner cylinder surface is made of galvanized steel, and the insulation between both the surfaces of the cylinders is made of fiber glass wool. Addition of a novel insulating material in the chulha for thermal insulation, resizable air inlet, design and incorporation of smoke rings and pot seat in such a way that no smoke passes through the cooking utensil assisted in achieving better thermal efficiency of the cookstove. Pine wood, bamboo, sagun wood, sal wood and neem wood have been selected as per local availability as biomass feedstock for combustion. To calculate the thermal efficiency, a water boiling test (WBT) has been performed. Best thermal efficiency of 47.08% has been achieved for pine wood biomass feedstock and due to proper placements of the grate and the air inlets in the improved chulha design. Also, a very negligible or no smoke has been observed due to the introduction of the advanced design of the smoke ring and pot seat and the chimney for the outlet making a green energy-efficient biomass cookstove.

Monitoring of thermal conditions and snow dynamics at periglacial block accumulations in a low mountain range in central Germany

AbstractThe Rhoen Mountains, a relict periglacial landscape in central Germany, feature a wide range of openwork block accumulations. Although located in a temperate climate, those have characteristics comparable with cold regions of higher altitude or latitude such as arctic‐alpine species, longer lasting snow patches or the discussed existence of summer or even year‐round ice lenses in one of the largest of these landforms in the Central German Uplands. This study aims for a characterization of the microclimatic conditions of two neighbouring block accumulations. Therefore, temperatures were registered by data loggers along profiles, and snow dynamics were monitored using time‐lapse cameras and terrestrial laser scans. These observations are finally compared with geophysical measurements to address the question of potential isolated low‐altitude permafrost occurrences. Mean ground surface temperatures show an inverse thermal gradient along the Schafstein block accumulation. Furrows were identified as the cold spots in winter, whereas snow melt holes are signs of a chimney effect. In summer, cold air flows out at ventilation holes along the front causing temperatures of up to 25°C below air temperatures, although no clear signs of permafrost were detected. Temperature correlations reveal periods indicative of a recurring internal summer air circulation. Coarse blocky substrate also favours ground cooling of the smaller Mathesberg block accumulation compared with its surroundings. Winter temperatures are influenced by a persistent snowbank forming due to drifting and blowing snow at the leeward edge of a plateau as little amounts of snow are sufficient to be redistributed by westerlies. The prolonged melt of the snowbank might have had or still has a local hydrological and geomorphological impact. Uncertainties remain regarding the behaviour of the microclimate of block accumulations in a warming climate. Being ‘cold spots’ of high ecological value further investigations are suggested.

On the effect of a tangential intake on the performance of natural dry draft cooling towers in crosswind conditions

Crosswind has a negative effect on the performance of natural draft dry cooling towers, NDDCTs, serving thermal power plants. This, in turn, lowers the efficiency of the thermal power plant as less heat can be rejected to the ambient air through the tower. This occurs due to interaction of cross wind and cooling tower structure. This phenomenon leads to generation of primary and secondary vortices inside the tower which located in leeward side (downwind side) and windward side (upwind side) of the tower, respectively. In an innovative interpretation of the challenge, this paper aims at directing the crosswind flow through the tower shell above the heat exchangers to assist the buoyancy-induced plume. In particular, the intake of the crosswind through the tower is utilized as a tangentially-induced swirl source to help the upward draft, and its penetration in the ambient air, enhancing the tower performance which otherwise would have been significantly deteriorated. Two independent approaches are presented to assess the proposed design quantitatively. CFD simulation of a small scale tower model has revealed significant performance improvement (in terms of natural draft blockage and outlet flow velocity) when the crosswind is allowed to penetrate the tower shell, through an opening on the tower side-wall, above the heat exchangers. Results of the simulations have been validated against the experimental data collected using the tests ran on an identical model, with and without the side opening, in a wind tunnel.

Guidelines for Predicting Airtightness in Residential Buildings under Climatic Pressure Conditions

This paper presents a generalized approach for predicting building airtightness based on pressure difference measurements. Furthermore, it provides practical guidelines for applying this method. Studies have proposed a method for predicting the airtightness of high-rise residential buildings in winter using the pressure difference caused by the stack effect. This method was validated using tests under various temperature differentials and building heights. However, practical guidelines for its implementation are lacking. To generalize the airtightness prediction method, a 95% confidence interval for the results was calculated using the blower door test. The applicable pressure difference was calculated based on the calculated results. For each building, the minimum differential pressure within a 95% confidence interval was at least 20 Pa. To provide guidelines for utilizing the proposed airtightness prediction method, acceptable conditions characterized by ΔH × ΔT ≥ 750 m∙°C were calculated. An acceptable condition, characterized by ΔH × ΔT ≥ 750 m∙°C, showed the highest agreement between predicted and measured values across all buildings. This study outlines practical guidelines for using the proposed methodology under these conditions. Overall, we present a straightforward method that relies solely on measuring pressure difference, thereby eliminating the need for a complex and challenging blower door test, typically used in real-world scenarios. By applying this method to predict airtightness in building conditions, the accuracy of predictions for energy use intensity and indoor air quality can be significantly improved.

Freeze protection performance of natural draft wet cooling tower with different partition water distributions

Freeze protection performance of natural draft wet cooling tower with different partition water distributions

Assessing the Need for Additional Evacuation Measures in Deep Underground Stations

Underground railroad stations face evacuation challenges owing to the rapid spread of smoke and extended escape routes during fires. Evacuation in deeply underground domestic railroad stations relies solely on stairways, with no legal standards for additional evacuation methods. In contrast, international standards such as NFPA 130 and Japan’s Fire Protection Engineering Association (JAFPE) recommend using evacuation elevators as a supplementary means of evacuation. This study analyzed smoke behavior in deep underground railroad stations through fire simulations at the Soongsil University and Guryong station. It also examined additional evacuation measures to enhance evacuation safety through evacuation simulations. The results show that during a fire, smoke spread follows the same path as the passenger evacuation routes because of the chimney effect. Even with smoke control and ventilation systems in operation, smoke follows the same evacuation routes, such as stairways or escalators. Therefore, the study concluded that evacuation elevators should be installed as an additional means to improve evacuation efficiency, and placed in smoke-protected evacuation routes. The study also found that combining evacuation stairways and elevators significantly enhances the evacuation efficiency.

Radon Concentration Assessment in Urban Romanian Buildings: A Multistory Analysis

Radon (Rn 222) is a significant contributor to natural radiation exposure in residential environments such as single-family houses and multistory buildings. This study monitored radon activity concentration (RAC) in 455 apartments in 30 multistory buildings in Buzău, Romania. Integrated measurements of the RAC using CR-39 nuclear track detectors were conducted for a period of 3 to 4 months. The results revealed that the RAC varies between buildings, with an annual average between 33 and 77 Bq/m3. This variation may be attributed to poor ventilation and the chimney effect in common ventilation ducts, which may facilitate radon displacement vertically. Also, apartments with low occupancy or inadequate ventilation showed higher radon levels of up to 285 Bq/m3. The study highlights the potential risk of increased radon exposure in energy-efficient buildings due to poor ventilation, emphasizing the need for special attention to radon mitigation measures in building design. The results emphasize that the RAC is influenced by building characteristics, room use, and ventilation, with significant implications for health risks in urban residential environments.

Testing the thermal performance of water cooling towers

Abstract The essential service water system (ESWS) in nuclear power plants circulates the water that cools fan coolers, cooling water heat exchangers, and condensers and other components before dissipating the heat into the environment. Because this includes cooling the systems that remove decay heat from both the primary system and the spent fuel rod cooling ponds, the ESWS is a safety-critical system. In locations without a large body of water in which to dissipate the heat, water is recirculated via a cooling tower. Cooling towers fall into two main categories: Natural draft and Mechanical draft. Since, the mechanical draft cooling towers are much more widely used; the focus is on them in this work to measure its performance. Therefore; the present work addresses the thermal acceptance test for mechanical draft water cooling tower in order to determine its thermal capability in accordance with the cooling technology institute (CTI) code recommendations. Both the Characteristic Curve and the Performance Curve Methods are used. A detailed description of the test procedure according to the CTI ATC-105 test code is presented, and the test code is applied on the Egypt second research reactor (ETRR-2) cooling tower as a case study. All the instruments used in the reactor plant are calibrated prior the test and the measured data is collected at regular intervals according to the code recommendations. The test result shows a tower capability of about 105 % and so the tower is thermally accepted.

A transient network model for cross-regional layered fire smoke diffusion in high-rise buildings

At present, research on smoke diffusion in high-rise building fires mainly focuses on the single smoke layer propagation within a limited area, with less attention paid to the smoke propagation under the joint action of the fire floor and the vertical shaft area. Moreover, research on fire spread often focuses on the composition of combustible materials and building structures, neglecting natural ventilation. To address the above issues, we propose a transient network model for layered smoke diffusion (CLDTN) based on multi-region integration and complex control parameters. This model considers the smoke stratification mode of the fire floor affected by the fire source and ventilation, as well as the vertical stratification mode of the shaft affected by the stack effect, achieving cross-regional smoke stratification and diffusion modeling through smoke coupling. Then, a time-dependent transient network model is used to analyze furniture materials and open ventilation conditions of doors and windows, and a differential equation for energy conservation in multiple scene layers is constructed to analyze the dynamic behavior of smoke propagation.The comparative experiment of smoke propagation between CLDTN and the Fire Dynamics Simulator (FDS) shows that CLDTN is more efficient in computation time and the model is more accurate.

Experimental studies on the influence of smoke acceleration effect feedback to the flame behavior in the U shaped shaft of a high-rise building

This paper presents an experimental investigation of the feedback effect with smoke acceleration on flame behaviors in the U shaped shaft of a high-rise building. Heat release rate of the fire, depths and widths of the U shaped shaft are changed. The flame height, vertical maximum temperature in the open shaft and the heat flux distribution on the façade are studied. Results show that the flame height is elongated by the smoke acceleration effect in the U shaped shaft and larger than that in the open space. Correlations for the flame height are established by taking into account the geometries of the U shaped shaft. The vertical maximum temperature in the U shaped shaft first decreases rapidly then keeps room temperature, which are compared with that under stack effect in the staircase. The exponential decay law between the vertical maximum temperature and height is modified. The total heat flux is mainly affected by the width and heat release rate. Radiation heat transfer fraction is larger than 80 % in the continuous and intermittent flame regions, of which the flame emissivity is about 0.53.

Air infiltration characteristics in oxygen-enhanced and heated chambers on the Qinghai-Xizang Plateau

The Qinghai-Xizang Plateau is characterized by a low-pressure and oxygen-deficient environment due to its high altitude, causing discomfort and major safety problems for the inhabitants. To address this, oxygen-enriched chambers can be used to alleviate the plateau reaction. However, little consideration has been given to air infiltration in these chambers, with a lack of information on the corresponding infiltration heat loss phenomenon. This paper addresses this by investigating the phenomenon of air flow in an oxygen-enriched chamber using experiments and simulations. The results highlight that when there is a difference in oxygen concentration between the interior and exterior of the chamber, mass transfer occurs due to both the molecular diffusion in addition to a flow due to the air density difference caused by the variation in concentration. Also, the simultaneous stack effect is roughly equivalent to 10 times the oxygen pressure, and the two pressure effects act in opposite directions. It is also noted that both the oxygen pressure and the stack effect decrease as the atmospheric pressure decreases. Overall, the oxygen-enriched chambers exhibit less infiltration in plateau areas with a low atmospheric pressure compared to plains areas with a relatively high atmospheric pressure. Finally, this study establishes formulas that can be used to calculate air infiltration rates in oxygen-enriched chambers. This study fills a gap in the existing literature regarding the air infiltration mechanism in oxygen-enriched chambers at high altitudes and low pressures, providing a theoretical foundation for improving indoor environments in the Qinghai-Xizang Plateau and other high-altitude regions.

Performance analysis of natural draft power plant cooling tower: Mathematical modeling of cross-flow type, application in capital cities of Iranian provinces

Cooling towers are heat exchangers that reduce the hot water temperature produced by process equipment through heat and mass transfer between water and air stream. This study investigates the performance of cross-flow cooling towers under various geometrical, physical, and environmental conditions. For this purpose, thermodynamic modeling of the cross-flow cooling tower was conducted, and the governing equations were numerically solved using the finite difference method. Unlike previous studies, the effects of water droplet deformation into an elliptical shape during its fall along the cooling tower were also considered. This deformation, which influences the drag coefficient, Reynolds number of the water droplets, droplet surface area, and its cross-section area, along with the incorporation of buoyancy force in the droplet momentum equation, led to an improvement in the results. Consequently, the maximum computational error in this case was reduced to 1.97 %, compared to the scenario where droplet deformation and buoyancy force were neglected. The change in geometrical parameters of the tower in Tehran and Rasht was investigated, revealing that increasing the outlet radius of the tower from 20 m to 22.5 m decreased the outlet water temperature by 1.21 °C and 0.67 °C and increased the thermal efficiency of the tower by 4.94 % and 2.88 % respectively, while increasing the tower height from 100 m to 120 m, only decreased the outlet water temperature by 0.47 °C and 0.26 °C, and increased the thermal efficiency of the tower by 1.89 % and 1.09 % respectively. Additionally, the cooling tower performance was assessed in the centers of different provinces .of Iran. Results showed that with an initial droplet radius of 1 mm and an inlet water temperature of 50 °C, the maximum and minimum temperature reductions occurred in Shahrekord by 20.16 °C and Bandarabbas by 12.37 °C, respectively.

Novel energy efficient integration of chimney ventilation, liquid desiccant dehumidification, and evaporative cooling for humid climates

The chimney effect for driving passively building ventilation is effective in dry and moderate climates to introduce cool fresh air into the space. However, its application in hot humid climates is limited due to the high energy demands associated with dehumidifying and cooling outdoor air. Thus, a novel energy-efficient assistive system is proposed integrating a chimney-driven ventilation with liquid desiccant dehumidification membrane loop and indirect evaporative cooling. This system leverages natural buoyancy to supply ventilation airflow and uses potassium formate loops through semi-permeable membranes for effective dehumidification. The objective is to dehumidify and cool the induced outdoor air to the room conditions of 24°C and relative humidity between 40% and 60% at minimal energy consumption. Mathematical models were developed to simulate the heat and mass transfer processes in the air and liquid desiccant flows within the system components. The system was sized, and its operation was optimized using an advanced machine learning-genetic algorithm model for a typical office space in Beirut. During the summer, the chimney air flowrate ranged from 45L/s to 48L/s, and it was delivered at the target room conditions. The system saved around 350kWh of electrical energy during the summer months due to elimination of the need to treat ventilation air by room cooling system. This was equivalent to the total energy required to handle the ventilation load during the summer season and resulted in a saving of $50/month in the case study.

Improving used Lubricant Oil Burner Performance: Effect of Swirled Flow of Internally Distributor Type on the Combustion and Flue Gas Temperature and Emission

This study aimed to experimentally investigate the combustion characteristics of used lubricant oil (ULO). A simple cylindrical burner of the natural draft vaporizing type, equipped with an internal air distributor, was designed and fabricated to achieve this objective. The burner’s efficiency was evaluated based on combustion temperature, flue gas temperature, and concentration levels. The key feature of this burner lies in the swirled flow of air combustion and ULO vapor within the combustion chamber, facilitated by the swirled flow air distributor type. Various air-fuel ratios (ϕ), ranging from 0.5 to 4, were considered in characterizing the burner’s performance. The results revealed increased combustion and flue gas temperatures in the radial airflow types. The highest temperatures achieved using the radial flow type are 930 oC and 410 oC for combustion and exhaust gas temperature, respectively. In contrast, the combustion chamber and exhaust gas temperatures are 980 oC and 465 oC for the swirled flow type, respectively. It was found that there is a decrease in the emission of CO and CO2 by volume under optimum conditions. This decrement was attributed to the swirled flow effects, which promoted a better mixture of air combustion and ULO vapor during combustion.

An Indoor Air Quality Analysis in Newly Constructed Apartments

This study analyzes the indoor air quality inspections of newly constructed apartments by the Busan Institute of Health and Environment for the last three years (2021-2023). Of the 41 inspections, 33 exceeded the recommended standard, and the average excess rate was 80.5%. When classified by measuring households, 148 out of 332 exceeded the standards, whereas, the average excess rate by household was 44.6%. Benzene was exceeded in two out of the 332 households; therefore, the excess rate was only 0.6%. However, the relative standard deviation was the largest, showing as the highest item in the scattergram. The average concentration of toluene was 1,006.0 µg/m3, which was 100.6% of the recommended standard and was exceeded by 138 households; hence, the excess rate was 41.6%. All six items(Formaldehyde, Benzene, Toluene, Ethylbenzene, Xylene, Styrene) reached the highest concentration in spring or summer when the indoor temperature increased. The average concentration of toluene in July was 1,922 µg/m3, close to 1.9 times the recommended standard; toluene is considered an item of particular concern in summer. In the correlation analysis with indoor temperature, the formaldehyde coefficient of determination was 0.4855, regarded as somewhat significant; it was difficult to confirm the correlation with temperature for the other five items, including benzene. In correlation with relative humidity, formaldehyde showed the same tendency as indoor temperature, with a coefficient of determination of 0.4404, which is believed to be due to its small molecular weight and high solubility. Due to the chimney effect, high concentrations of volatile organic compounds could be confirmed at low atmospheric pressure in the upper floors, and this trend was most evident for formaldehyde. For most items(Formaldehyde, Benzene, Toluene, Ethylbenzene, Styrene), a negative correlation was confirmed in which the emission amount decreased as the number of households increased. For large apartment houses, it is believed that it is due to sufficient bake-out and flush-out according to the adequate construction period and the use of eco-friendly and high-end building materials. Small apartments are classified together with many small houses. The emission concentration of small houses is relatively high because the proportion of the surface area where pollutants are released is high.

Numerical study on smoke temperature distribution in naturally ventilated inclined tunnels: Effects of tunnel width and tunnel slope

Inclined tunnel fires exhibit unique characteristics compared to horizontal tunnel fires as a result of the stack effect. Nevertheless, there is still a lack of consensus among previous scholars regarding the smoke temperature distribution in inclined tunnel fires. This work conducts a numerical investigation on the smoke back-layering length upstream of the fire source and the temperature decay downstream of the fire source in naturally ventilated inclined tunnels with varying widths and slopes. Results indicate that as the tunnel slope increases from 0° to 8°, the smoke back-layering length first decreases and then continues at a constant value of 1.47H4/3/W1/3, while the effect of tunnel width is negligible. The decay factor in the one-dimensional flow stage (x/H≥4) exhibits two distinct patterns related to tunnel width: it initially remains constant and then drops when the tunnel is wide, whereas it monotonically drops when the tunnel is narrow. Two empirical models are developed to identify the segmented characteristics and verified through the relevant data from existing literature with similar fire scenarios. This work offers a method for estimating the smoke temperature distribution in inclined tunnels, providing crucial insights for fire prevention, smoke detection, and safety strategies in tunnel engineering.