Fan Pressure Research Articles

Enhanced heat transfer in a refrigerated container using an airflow optimized refrigeration unit

The present study numerically investigates the airflow and heat transfer characteristics in a conventional refrigerated container (CRC), and an improved refrigerated container (IRC) loaded with cargoes by modeling the refrigeration unit and the cargoes in the container as porous media. The IRC design is based on a previous study by the current authors, where the airflow in the refrigerated container was enhanced by improving the refrigeration unit design. The airflow inside the refrigerated container is simulated by using the fan pressure jump boundary conditions at the location of the evaporator fans in the refrigeration unit. The CRC and IRC are simulated for three fan pressure jump conditions of 50, 100, and 150 Pa. Initially, the airflow and heat transfer results under 50 Pa fan pressure jump condition are compared for CRC and IRC to estimate the enhanced heat transfer in IRC. Then, the behavior of the heat transfer characteristics in CRC and IRC under increasing fan pressure jump conditions is studied by comparing the results of CRC and IRC under the three fan pressure jump conditions. Results show that the heat transfer and the temperature homogeneity of the cargoes in IRC are significantly improved due to the enhanced airflow by the improved design of the refrigeration unit in IRC.

Evaluating methods for estimating whole house air infiltration rates in summer: implications for overheating and indoor air quality

PurposeAccurate values for infiltration rate are important to reliably estimate heat losses from buildings. Infiltration rate is rarely measured directly, and instead is usually estimated using algorithms or data from fan pressurisation tests. However, there is growing evidence that the commonly used methods for estimating infiltration rate are inaccurate in UK dwellings. Furthermore, most prior research was conducted during the winter season or relies on single measurements in each dwelling. Infiltration rates also affect the likelihood and severity of summertime overheating. The purpose of this work is to measure infiltration rates in summer, to compare this to different infiltration estimation methods, and to quantify the differences.Design/methodology/approachFifteen whole house tracer gas tests were undertaken in the same test house during spring and summer to measure the whole building infiltration rate. Eleven infiltration estimation methods were used to predict infiltration rate, and these were compared to the measured values. Most, but not all, infiltration estimation methods relied on data from fan pressurisation (blower door) tests. A further four tracer gas tests were also done with trickle vents open to allow for comment on indoor air quality, but not compared to infiltration estimation methods.FindingsThe eleven estimation methods predicted infiltration rates between 64 and 208% higher than measured. The ASHRAE Enhanced derived infiltration rate (0.41 ach) was closest to the measured value of 0.25 ach, but still significantly different. The infiltration rate predicted by the “divide-by-20” rule of thumb, which is commonly used in the UK, was second furthest from the measured value at 0.73 ach. Indoor air quality is likely to be unsatisfactory in summer when windows are closed, even if trickle vents are open.Practical implicationsThe findings have implications for those using dynamic thermal modelling to predict summertime overheating who, in the absence of a directly measured value for infiltration rate (i.e. by tracer gas), currently commonly use infiltration estimation methods such as the “divide-by-20” rule. Therefore, infiltration may be overestimated resulting in overheating risk and indoor air quality being incorrectly predicted.Originality/valueDirect measurement of air infiltration rate is rare, especially multiple tests in a single home. Past measurements have invariably focused on the winter heating season. This work is original in that the tracer gas technique used to measure infiltration rate many times in a single dwelling during the summer. This work is also original in that it quantifies both the infiltration rate and its variability, and compares these to values produced by eleven infiltration estimation methods.

An inquiry into the use of indoor CO2 and humidity ratio trend data with inverse modelling to estimate air infiltration

Air infiltration has a significant impact on building energy performance and the indoor environment. An accurate estimate of air infiltration rate informs envelope retrofit decisions to improve airtightness. However, air mobility and other environmental factors, such as wind or indoor-outdoor temperature differences, often make the accurate measurement of air infiltration challenging. Further, conventional air infiltration testing approaches such as fan pressurization and tracer gas tests possess certain drawbacks limiting their applicability in commercial buildings. To address the limitations of air infiltration tests, this study proposes a low-cost inverse model-based approach for estimating air infiltration rates by extracting the naturally occurring indoor CO2 and relative humidity (RH) data from a building automation system (BAS). These data were used to develop a linear regression model, and a tracer gas experiment was also used to verify the applicability of the proposed approach. The results indicated that the proposed method could conveniently lend itself to estimate air infiltration rates at a reasonable accuracy using existing CO2 data; however, humidity ratio data (converted from RH and temperature sensor measurements) may only help to track building infiltration characteristics over time due to inaccuracies caused by adsorptive and desorptive properties of various building materials.

The Importance of In Situ Characterisation for the Mitigation of Poor Indoor Environmental Conditions in Social Housing

The energy efficiency improvements in existing buildings have become priority concerns of the European Union to encourage energy efficiency amongst residents and buildings as well as facility managers. The characterisation of the building stock plays an important role in the definition of energy renovation strategies. In Portugal, there are over 120,000 social housing flats. This paper focused on the holistic characterisation of a social housing neighbourhood concerning the “in situ” assessment of the indoor environmental conditions and thermal comfort over one year as well as air permeability tests of the flats and evaluation of the energy consumption. The hygrothermal monitoring campaign was carried out using thermo-hygrometer sensors to record the indoor air temperature and relative humidity of a large number of flats over a 12-month period. The airtightness of these flats was determined resourcing fan pressurisation test (blower door test). A relationship between the users’ modifications in the flats and their consequence over the air permeability was pursued and the importance of balconies and exhaust fans for the flats’ air permeability was discussed. The hygrothermal monitoring campaign of the case study was carried out, in order to assess the indoor thermal comfort according the ASHRAE 55 standard. The results show a significant discomfort rate, suggesting that the users are living in unhealthy environmental conditions and the issues that most contribute to the poor indoor environmental conditions that characterise this building stock. In addition, the energy, gas, and water consumption of the flats were collected, and a statistical analysis was performed. Correlations between the variables were observed and two clusters were identified. Cluster 1 includes the lower energy consumption flats, but no real impact on the thermal comfort was found as the entire dataset presented low indoor air temperatures.

High fidelity modeling tools for engine liner design and screening of advanced concepts

With aircraft engines trending toward ultra-high bypass ratios, resulting in lower fan pressure ratios, lower fan RPM, and therefore lower blade pass frequency, the aircraft engine liner design space has been dramatically altered. This result is also due to the associated reduction in both the available acoustic treatment area (axial extent) as well as thickness (liner depth). As a consequence, there is current need for novel acoustic liner technologies that are able to meet multiple physical constraints and simultaneously provide enhanced noise attenuation capabilities. In addition, recent advances in additive manufacturing have enabled the consideration of complex liner backing structures that would traditionally be limited to honeycomb cores. This paper provides an overview of engine liner modeling and a description of the key physical mechanisms, with some emphasis on the use of low to high-fidelity tools such as empirical models and commercially available software such as COMSOL, Actran, and PowerFLOW. It is shown that the higher fidelity tools are a critical enabler for the evaluation and construction of future complex liner structures. A systematic study is conducted to predict the acoustic performance of traditional single degree of freedom liners and comparisons are made to experimental data. The effects of grazing flow and bias flow are briefly addressed. Finally, a more advanced structure, a metamaterial, is modeled and the acoustic performance is discussed.

Quantification of air leakage paths: a comparison of airflow and acoustic measurements

Today, the fan pressurization method is the most frequently used method to evaluate a building's airtightness. However, the localization and quantification of leaks remain difficult. In this paper, an acoustic method is introduced to estimate the leakage size of single leaks. Acoustic and airflow measurements were conducted and compared in laboratory tests within the same boundary conditions. This work aims to investigate if various leak sizes can be predicted using acoustic measurement methods. The test apparatus consists of two chambers, separated by a test wall. This wall represents a single characteristic air leakage path. Various types of wall structures with different slit geometries, wall thicknesses, and insulation materials were investigated. The acoustic measurements were performed with a sound source placed in one chamber and ultrasonic microphones located in both chambers. These results were compared to measured airflows through the test wall to provide estimates of uncertainty in the acoustic approach, which indicate a linear trend. Finally, these laboratory measurements were compared to the same measurements at a real office building. Although the acoustic measurement uncertainty is still significant (greater than +/- 50%), the acoustic method has the potential to give an order of magnitude of single leak sizes.

Evaluation of a Regional Aircraft with Boundary Layer Ingestion and Electric-Fan Propulsor

This paper presents a conceptual study of a regional aircraft with a turboelectric propulsion system and boundary-layer ingestion. The aircraft has an additional electric propulsor installed at the aircraft tail cone, which is driven by generators installed on both underwing engines, aiming to ingest the fuselage boundary layer and improve the aircraft overall performance. The proposed configuration is an aircraft reengining of the reference aircraft platform, the Embraer 175-E1, targeting minimizing airframe modifications. Parametric variations of the thrust split ratio as well as the electric fan pressure ratio were performed in order to create a design space of possible solutions for the proposed concept and also to provide insights of the aircraft key variables trends. From that, a feasible and optimized configuration in terms of efficiency was selected and compared to the reference aircraft. As the main conclusion, it was determined that the studied propulsion system has the potential to provide specific air range benefits in the order of 4 to 7%, which may not be enough to justify a new development.

Influence of gas outburst dynamic flow on mine ventilation system

This study was conducted to analyze the influence of outburst power from coal and gas on mine ventilation systems in order to avoid damage from secondary disasters to mine ventilation systems. Through the outburst dynamic experiment of a simple ventilation network system, the unsteady movement characteristics of mine air flow under the combined action of gas outburst source flow and fan ventilation are studied. In this study, the “11.8” coal and gas outburst accident that occurred in the Qunli Coal Mine was simulated numerically. The TF1M simulation program was used to analyze the entire process of the diffuse flow of the countercurrent and outburst gas in the mine ventilation system as well as the dynamic change process of the natural wind pressure in each stage. The results indicate that the power of the outburst source causes the ventilation system to run against the current, the gas in the air intake system of the mine exceeds the limit, and the airflow disturbance of the mine ventilation system is influenced by natural gas pressure and fan pressure. The air pressure of the fan cannot change the rate of air flow but can reduce the time of air flow disorder and promote the gas discharge in the ventilation system. In a word, the research achievements do have important theoretical and practical significance for disaster prevention and aid in outburst mine as well as effectively preventing the occurrence of secondary disasters.

Interaction and influence of a flow field and particleboard particles in an airflow forming machine with a coupled Euler-DPM model.

Particleboards are widely used in the artificial board market, which can be constructed from a variety of raw materials and require small amounts of energy to be produced. In the particleboard production process, forming machines play an important role as the key equipment for achieving continuous production. In recent years, airflow forming machines have received increasing attention in particleboard production lines because of their strong separation ability and low price. However, the internal flow field is complex and difficult to control, which affects the surface quality and strength of the particleboard. The most pressing technical difficulty is controlling the flow field characteristics of the airflow paver. At present, the research on this subject is conducted primarily through repeated experiments, which entail long research periods and high processing costs. To reduce human and financial costs, in this study, Computational Fluid Dynamics (CFD) is employed to investigate the flow field and the gas-solid two-phase flow field coupled with particle movement of an airflow forming machine. The accuracy of the calculation model is verified by comparing characteristic point velocities obtained from experimental analysis and a simulation. The simulation results show that in practical production, the frequency of a negative pressure fan should be greater than 27 Hz. It is necessary to set the shoulder properly, and the slab smoothness can be improved by moving the shoulder back on the premise of meeting the strength requirements of the box. The distance between the shoulders of the box body should be less than 2570 mm, and particles with uniform diameter should be added to the paving box to reduce the turbulence effect, improve the quality of particle forming and provide actual particleboard production with a solid theoretical foundation.

DETERMINING THE AERODYNAMIC CHARACTERISTIC OF A MINE AXIAL FAN WHEN OPERATING IN REVERSIBLE MODE

This paper describes the procedure for determining the approximate aerodynamic characteristics of a fan operating in a reversible mode with the reverse direction of impeller rotation and deployed position of the straightener blades. To calculate the aerodynamic characteristic, the results of computational modeling of the flow around a flat cascade of airfoil blades were used. To check the adequacy of the applied design models, the comparison of flow deflection angles and total pressure losses when flowing around flat cascades composed of NACA65 airfoils in the direct mode and the known experimental data was made. Using the example of a OV-103 fan made according to the design of Central Institute of Aerohydrodynamics, with the known experimentally obtained aerodynamic characteristic of the reversible mode, the angles of reverse flow deflection in a cascade at the middle radius and total pressure loss in it were calculated. The obtained data were used to calculate the values of the coefficient of total fan pressure depending on the flow rate of air flowing through the fan. The obtained characteristics showed the value of maximum air flow rate higher than in the experimental characteristics. But in this case, it is closer to experimentally obtained data than the value calculated from the known theoretical characteristics of flat cascades.

Performance assessment of a solid oxide fuel cell turbine-less jet hybrid engine integrated with a fan and afterburners

Reducing carbon emissions in the field of aviation is important with the rising prosperity of air transport. Electric aircraft play an essential role in the process. Hybrid engines, composed of a solid oxide fuel cell, a fan, a compressor, and an afterburner are proposed. Fuel cells provide energy to the compressor and the fan. Internal duct air and external duct air are mixed at the inlet of the nozzle. Propulsion power is output by the nozzle. In order to study the effects of operating parameters on the performance of the hybrid engine, thermodynamic performance models are built. The main conclusions are as follows: (1) The specific thrust and specific impulse of the engine are dramatically increased with increasing bypass ratios. Meanwhile, fuel cell power rises slowly, which indicates that the engine with fans has more advantages than the one without fans in the respect of thrust-weight ratios. (2) Fuel cell power first increases then decreases with increasing fan pressure ratio under the conditions of constant overall pressure ratios. (3) Increasing afterburner temperature is the most effective way to improve the thrust of the engine. When the temperature is 2217 K, the specific thrust is up to 3085 N/(kg⋅s−1). Meanwhile, the specific impulse and thermal efficiency are 2693 s and 60.5%, respectively.

Ventilation control of tunnel drilling dust based on numerical simulation

In order to control the dust pollution produced by air leg rock drill in the trolley area during the excavation of long-distance single ended tunnel, the full-scale physical model of working face was established by using FLUENT software, and the numerical simulation analysis of tunnel drilling ventilation and dust removal parameters was carried out. The results show that it is difficult to control the dust pollution of the face by conventional ventilation, and the drilling dust is distributed in the range of 10 m from the face; after the introduction of the long pressure and short suction ventilation scheme, when the ratio of compressed air volume to exhaust air volume is 0.72, the height of the pressure fan is 2.5 m, the distance between the pressure fan and the palm face is 20 m, and the exhaust fan is 12 m away from the palm, the dust concentration control efficiency of the working face is increased by about 60%. Therefore, in the similar long-distance single head tunnel construction, it is appropriate to adopt the dust removal method of long-distance short suction and exhaust fan to ensure the working environment.

Airtightness of buildings – Assessment of leakage-infiltration ratio and systematic measurement error due to steady wind and stack effect

The fan pressurization method that is widely used to measure the airtightness of buildings is known to have quite large measurement error. It is made up of random measurement error (precision) and systematic measurement error (bias).The first part of the present article explains, with analytical evidence, why steady wind and stack effect generate systematic measurement error and it assesses this error through Monte Carlo simulations. Tables with practical results are provided for common zero-flow pressure difference intervals. For example, they show that with a typical zero-flow pressure difference of 5 Pa, the systematic measurement error at a reference pressure difference of 4 Pa is in the order of −1,1% to −2,2%. Possible improvement of the test method is also suggested and assessed.The second part of this article calls on the Monte Carlo simulations to assess the variability of the leakage-infiltration ratio. A simplified analytical formula has been developed to allow comparison and it shows very good correlation. Tables with practical results are also provided. For example, they show that the well-known value of 20 can be associated with a natural pressure field of [−3 Pa; +3Pa].

Performance analysis of a turbofan engine integrated with solid oxide fuel cells based on Al-H2O hydrogen production for more electric long-endurance UAVs

This work investigates a turbofan engine (a type of gas turbine, GT) integrated solid oxide fuel cells (SOFCs) based on Al-H2O hydrogen production to reduce the specific fuel consumption (SFC) and meet the increasing power demand in unmanned aerial vehicles (UAVs). The new engine uses an Al-H2O reactor to produce hydrogen for the SOFCs. To analyze the performance of the engine, the thermodynamic models of the turbofan engine, the Al-H2O reactor, and the SOFC are established and the key models are verified. The performance comparisons between the SOFC-GT engine and the turbofan engine under different electric power fractions are carried out. It is found that the SFC of the SOFC-GT engine can be reduced by 10.30%, 14.41%, 18.98%, and 24.08% compared with the turbofan engine when the electric power fractions are 15%, 20%, 25%, and 30% respectively. The effects of engine parameters such as bypass ratio, fan pressure ratio, compressor pressure ratio and turbine inlet temperature, reactor parameters such as H2O-to-Al-weight ratio, and aircraft flight parameters such as flight altitude and Mach number on the performance of the new engine are studied. The preliminary results are as follows: (1) Under the design conditions, the SFC, the specific thrust, the thermal efficiency, the propulsion efficiency, and the overall efficiency of the SOFC-GT engine could reach 16.71 g/(kN·s), 222.47 N·s/kg, 57.62%, 42.63%, 28.91%. (2) Bypass ratio and fan pressure ratio have a great influence on the performance. By adjusting these two parameters, the SFC can be reduced by more than half. (3) Compared with thermal efficiency, propulsion efficiency has a greater impact on the performance of the engine. (4) The increase of the H2O-to-Al-weight ratio is unfavorable to the performance of the engine. The optimal interval can be preliminarily determined between 3 and 4. (5) To achieve low SFC, high economy, and long endurance, while maintaining high efficiency and high specific thrust, the aircraft needs to be designed with high flight altitude and low Mach number.

Research on the Design Scheme of Explosive Dust Removal System and Piping

In the workplace where the material dust concentration is high and electric sparks are easy to generate, the dust is easy to explode. At this time, the design of the dust removal system and the piping layout plan are particularly important. This paper takes the design of dust removal system in a tobacco factory as an example. According to the working characteristics of the shredding and stem cutting equipment in the silk workshop, the corresponding wet dust removal device is designed in this kind of work environment. The structure of the dust removal system, process flow and piping design are given, Pressure loss calculation and fan selection, provide a reference for the design of dust removal systems in places that are prone to dust explosions.

Evaluation of the indoor pressure distribution during building airtightness tests using the pulse and blower door methods

Building airtightness is a critical aspect for energy-efficient buildings as the energy performance of a building can be significantly reduced by poor airtightness. The Pulse technique has been regarded as a promising technology, measuring building airtightness at a low pressure of 4 Pa. However, due to the rapid dynamic nature of the test, a frequently raised question concerns the uniformity of the pressure distribution across the internal space of the test building during the air pulse release. In order to investigate this point, experimental work was conducted in a five-bedroom dwelling. All the tests were conducted at wind speeds less than 0.45 m/s to minimise the wind impact on the indoor pressure. The results show a pressure difference within the building during the Pulse test does exist, but considering the accuracy of differential pressure transducers, the deviation is not significant. In addition, a subtle variation is noted when the Pulse test was conducted at different locations on the ground floor, which may also be caused by variations in the environmental conditions. In terms of the airtightness measurement, a good overall agreement was found between the Pulse technique and the conventional blower door fan pressurisation method, which indirectly verified the uniformity of the indoor pressure distribution during both tests. Moreover, the error analysis demonstrated the validity of the measurement results for the two test methods in this study.

Performance characteristics of a heat pump using renewable transcritical CO2 refrigerant for heating water

ABSTRACT Among non-toxic and inflammable working fluids, carbon dioxide (CO2) proving a possible choice of refrigerant is gaining full status because of its reducing capacity of global warming and ozone depletion. Heat pump (HP) equipment uses energy more rationally to heat water by reducing emissions and global warming caused by conventional refrigerants. HP capability demands an environmentally friendly refrigerant for their full utilization and high energy saving as well to attaining higher coefficient of performance (COP) without much design corrections. CO2 is checked for sustainability to eliminate the standardized refrigerants such as chlorofluorocarbons (CFC) and hydro-CFC. In this work, the performance of CO2 as an alternate refrigerant in HP for heating water at different pressure, flow rates, evaporator fan speed and preheating have been investigated. HP is accommodated with two condensers. The results showed that the increased mass flow rate had increased COP, overall heat transfer (HT) coefficient (U) and HT. However, logarithmic mean temperature difference was decreased for increasing evaporator’s fan speed and pressure. The outlet water temperature (TWO) of second condenser increased with decreasing water flow rate. Improved COP, HT and TWO of HP are observed from the experimental evaluation in case of preheating of water.

Numerical analysis of natural gas pressure during coal and gas outbursts

AbstractAny disturbance in the ventilation system of a mine during a coal and gas outburst can lead to secondary disasters. This is because, on the one hand, the expansion power of the outburst source makes the airflow in the ventilation system countercurrent, causing the gas in this system to exceed the allowable limit. On the other hand, the airflow density changes because of the outburst and the consequent airflow mixing in the mine roadway, thereby changing the natural wind pressure. From this, the concept of natural gas wind pressure is proposed, and a calculation method for this pressure in a 3D model mine ventilation system is derived. For the “11.10” major coal and gas outburst that occurred in Shizhuang Coal Mine in Qujing, Yunnan Province, the entire process of the counter flow and gas dispersion flow in the main and auxiliary shafts is analyzed using the TF1M 3D simulation program, including the dynamic change in the natural wind pressure in the mine in each stage. The simulation shows that during the gas outburst period, the natural gas pressure of the countercurrent circuit is greater than that of the main fan. Between 140 s and 225 s following the outburst, the natural wind pressure once overcomes the fan pressure and reverses the airflow in the 1824 transport roadway, and the gas is withdrawn from the 1727 service point. Evidently, the natural pressure of the gas produced by the outburst affects the mine ventilation system. In the event of a coal and gas outburst in a private village coal mine, if the natural gas wind pressure can be reasonably utilized and the main fan stopped or the entire mine reversed in time, casualties may be minimized. Scholars studying coal and gas outburst mines should pay attention to mine airflow disorder due to the varying natural gas wind pressure when an outburst occurs and perform simulation drills of the outburst beforehand. Thus, a scientific emergency management plan for mine disaster prevention and reduction can be formulated.

Loop Heat Pipe for Thermal Management of Aircraft Engine Equipment

According to recent aircraft engine development trends, the performance enhancement of the propulsion plants is accompanied by both an increase of the overall pressure ratio and a decrease of the fan pressure ratio. Projections for the next decade show that equipment within the engine compartments can exceed their temperature thresholds, penalizing aircraft safety. Loop heat pipes (LHP) represent a highly appealing solution that could be employed as part of future passive cooling architectures, either replacing or enhancing the heat transfer capabilities of currently adopted monophase solutions. To meet the compatibility, safety, and environmental constraints, a titanium–water LHP was designed, manufactured, and tested for the thermal management of aircraft engine equipment. The results encouraged the use of this technology, providing clues for the development of other prototypes. The sintered titanium wick showed an excellent mechanical resistance to repeated cycles of water freeze/thaw, providing that the LHP could be potentially exposed to a cold environment with limited risk to undergo structural failures. Experimental data suggest that a passivation process occurred in the first hours of operation, modifying wick wettability and improving LHP performance. This was accompanied by the generation of noncondensable gas. The impact on LHP behavior was carefully analyzed, together with the influence of heat transfer on the liquid line and the cold source temperature variations.

Thermodynamic Concepts on Efficiency of Aircraft Engines

Along with the development of engine technology to be able to produce maximum efficiency in aircraft jet engines, various modifications were made to the machine tools. Modifications are made by taking into account four main factors, namely: maximum power output, reduced engine weight, low fuel consumption and maximum aircraft payload. This research uses a meta-analysis method, namely the analysis of several research results in line with what has been done previously regarding the efficiency of aircraft jet engines. The thermodynamic concept related to the heat engine which implements the brayton cycle that maximum efficiency can be done by reducing wasted heat energy and maximizing the work produced. From this concept, several attempts to maximize aircraft efficiency, such as modification of design that have a significant impact on weight reduction, fuel barrier design with low fan pressure, high bypass design ratio are also carried out in an effort to reduce aircraft noise levels. Aircraft noise levels can also be minimized by modifying the nozzle and ejector on the engine.