Average Outlet Research Articles

Heat transfer analysis of an integrated double skin façade and phase change material blind system

In this study, the heat transfer in an integrated double skin facade (DSF) and phase change material (PCM) blind system has been theoretically analysed. Both heat transfer and airflow models with CFD methods have been developed for the integrated DSF and PCM blind system. Data from an existing typical DSF building have been obtained in order to define input parameters for the simulation exercise and validate the numerical models. The temperature and velocity fields in DSF with the PCM blind system has been predicted under overheating scenario using the ANSYS Workbench FLUENT software and been compared with case of conventional aluminium blind system. This study has shown that the integrated PCM blind system was able to reduce the average air temperature and outlet temperature of the DSF while improving the convective heat transfer between the cavity air and the blades. Compared with the aluminium blind, the PCM blind can absorb large amount of excessive heat in the cavity. Overall the integrated PCM blind system has the potential to be used as an effective thermal management device for minimising the overheating effect in DSFs.

CFD prediction of the flashing processes in a MSF desalination chamber

Vapourisation inside a desalination flashing chamber arises from the energetic evaporation with self-boiling of liquid brine flow due to a reduction of pressure, and is a complex, multiphase, thermo-fluid phenomenon. A computational field model for the flashing process inside a flashing chamber is developed around a two-phase VOF formulation. Two different phase-change mechanisms are allowed for, based on the saturation temperature and on the vapour pressure, respectively, that enable the model to compute the phase change regions, also the level and the shape of the free surface. The model is applied to solve for steady multiphase flow inside a flashing chamber without a baffle, and thus to predict the chamber flow details and behaviour. Thermo-fluid performance results are presented in terms of flow patterns and distributions of hydrostatic pressure, temperature, vapour volume fraction and mass transfer inside the flashing chamber. The average outlet temperature and average vapour temperature agree well with the values of a real MSF plant, as does the estimated vapour production rate. Two main mechanisms of phase change produced by the flashing process are captured in the simulation. Vapour bubbles are formed at the entrance to the flashing chamber, and bubble production reduces along its length. At the free surface of the liquid there is also a phase change and mass transfer. Computational field modelling is valuable for a better understanding of the combined heat transfer, mass transfer and the fluid dynamics during the flashing flow evaporation processes. Results can be used to estimate MSF design factors such as non-equilibrium temperature difference and flashing efficiency.

Numerical modelling of electrohydrodynamic airflow induced in a wire-to-grid channel

Electrohydrodynamic (EHD) airflows provide a means of generating air motion by a gas discharge across two electrodes without the need for moving parts. A two-dimensional numerical model for a wire-to-grid EHD air blower is developed, validated against previous data, and used to investigate the influence of key design parameters on blower efficiency, including the emitter wire diameter, the blower height, the locations of the collecting surfaces and grid wires, and the collecting grid density. The optimal locations of both collectors from the corona wire are determined based on blower efficiency at a fixed operating power, resulting in improvements in the average outlet velocity between 9% and 15%, depending on blower thickness. The presence of the grid has a strong influence on the electric field distribution and increases the blower performance, with higher flow, lower operating voltage and reduced blower size. An investigation into the effect of grid density reveals that using coarse collecting grids is generally beneficial, leading to higher efficiency with lower pressure losses.

A thermal neutronics coupling analysis method for lead based reactor core

In this research paper, a sub-channel thermal hydraulic analysis code is coupled with the point reactor neutron kinetics model with six group delayed neutron. The coupling code is mainly used to perform the transient calculation of ADS/lead based alloy cooled fast reactor. The thermal hydraulic model is used for calculating temperature distribution profile and the feedback temperature information, providing input parameters for point kinetic model. This sub-channel analysis model can provide a new approach to solve the problem of one-dimension thermal hydraulic model and simulate the temperature distribution accurately. Furthermore the accuracy and reliability of calculated results are tested by another coupled code named FLUENT/PK and good agreements are achieved. To improve computational speed, one equivalent assembly is used to replace the whole core and the study shows that using of equivalent assembly which has the same average outlet temperature with the core obtained more reasonable results. The effects of fuel rods pitch diameter P/D ratio on simulation results are discussed. The code is capable to the quick calculations and safety analysis for reactivity accidents.

Experimental and simulation studies of parabolic trough collector design for obtaining solar energy

Abstract Concentrated solar power has great potential for large scale renewable energy sources, and is currently an eye catching one for its utilization with wide area of improvement. Especially, parabolic trough solar collectors (PTSCs) are gaining popularity due to their increased efficiency as compared to photovoltaics. In this work, an effort has been made to evaluate the performance of a designed 5-m length PTSC model. Heat collecting element was made of stainless steel with water as working fluid. The authentication of the proposed model is justified based on the results obtained on a yearly scale with respect to average inlet and outlet temperatures, surface temperatures and thermal efficiency for the climatic conditions of Ramanagaram. It was observed that March to May yielded better outlet temperatures ranging from 93 °C to 103 °C. Experiments were carried out at different flow rates of 0.4 LPM, 0.8 LPM and 1.2 LPM and corresponding Reynolds number was calculated. It was seen that February to May gave good surface and outlet temperatures as compared with other months while the liquid flow is laminar. Simulation studies were carried out using ANSYS software on receiver tube to ensure the robustness and design effectiveness under static loading conditions.

Influence of pore density on thermal development in open-cell metal foam

Herein heat transfer measurements due to water flow in commercial open-cell aluminum foam confined by a cylindrical shell, which was heated by a constant heat flux, are described. Two kinds of commercial foam were tested: 10 and 40 pores per inch (ppi). Measurements included wall temperature along flow direction as well as average inlet and outlet temperatures of water. Flow rates ranged from Darcy to Forchheimer regimes. The wall temperature along the foam, as well as the local Nusselt number lucidly displayed thermal entry effects leading to thermal fully-developed conditions. The thermal entry length was about 2.9 pipe diameters (150mm) for 10-ppi and 2.4 pipe diameters (122mm) for 40-ppi foam; these were same for Darcy and Forchheimer flow regimes. It can be stated that the thermal entry length in open-cell metal foam was found to be significant and different from its porous-media analytically-predicted values and behavior. Moreover, the thermal entry length in metal foam was found to inversely proportional to the pores density but in a weak manner.

Comparative numerical analysis and optimization in downhole combustion chamber of thermal spallation drilling

Thermal spallation drilling is a non-contact and efficient technology, which is suitable for hard rock formations. It uses downhole combustion to generate high temperature media to heat the bottom rock, which leads to the spallation of the rock. However, no investigation has been carried out in combustion of thermal spallation drilling. In this paper, three combustion models (eddy dissipation model, eddy dissipation concept model and non-premixed model) are applied and compared to simulate the reaction in the combustion chamber. Through modifying Magnussen constants, the eddy dissipation model is optimized and validated. Results show that under high velocity conditions, combustion models based on infinite fast reaction mechanism may not be accurate. An additional reaction step in eddy dissipation model may significantly improve the accuracy. Besides, there is a linear relationship between the average outlet temperature and Magnussen constant in eddy dissipation model. Moreover, through modifying the Magnussen constants, the accuracy of the results can be significantly improved. The optimized eddy dissipation model with two reaction steps not only has the advantages of small computational cost, but also may reflect the actual situation of the combustion reaction. Results in this paper could provide guidance in the design of combustion chamber in thermal spallation drilling.

Thermal Performance Analyses of Multiborehole Ground Heat Exchangers

Geothermal energy known as a clean, renewable energy resource is widely available and reliable. Ground heat exchangers (GHEs) can assist the development of geothermal energy by reducing the capital cost and greenhouse gas emission. In this paper, a novel semianalytical method was developed to study the thermal performance of multiborehole ground heat exchangers (GHEs) with arbitrary configurations. By assuming a uniform inlet fluid temperature (UIFT), instead of uniform heat flux (UHF), the effects of thermal interference and the thermal performance difference between different boreholes can be examined. Simulation results indicate that the monthly average outlet fluid temperatures of GHEs will increase gradually while the annual cooling load of the GHEs is greater than the annual heating load. Besides, two mechanisms, the thermal dissipation and the heat storage effect, will determine the heat transfer underground, which can be further divided into four stages. Moreover, some boreholes will be malfunctioned; that is, boreholes can absorb heat from ground when the GHEs are under the cooling mode. However, as indicated by further investigations, this malfunction can be avoided by increasing borehole spacing.

Performance assessment and gained operational experiences of a residential scale solar thermal driven adsorption cooling system installed in hot arid area

In this study, performance assessment of a residential scale size solar thermal driven adsorption cooling system installed in hot arid and dusty area at Upper Egypt, and, in operation since summer 2012 until now is carried out experimentally for four years in operation, moreover, the gained operational experiences are presented. The system performance is expressed in term of the solar collectors' field thermal efficiency, actual chiller chilling capacity, the temperature of cold-water outlet from the chiller, chiller coefficient of performance (COP) and cooling-water temperature outlet from the cooling tower. The system performance results show that the daily solar collector efficiency during the reported period was ranged from about 50% to 78%. While, the average chiller COP was varied from 0.4 to 0.64 in combination with average chilling power ranged from 3.6 to 6.42kW and average chiller outlet cold water temperature ranged from 19°C to 12.12°C correspondence to cooling tower outlet cooling water temperature ranged from 31.4°C to 23.4°C, respectively. In the cooling session of 2014, a 50kW cooling capacity wet cooling tower is integrated into the system, and the measurements show that the outlet water temperature from the cooling tower is about 23.4°C at ambient air dry bulb temperature of 35.7°C and wet bulb temperature of about 19°C. Consequently, under this new heat rejection condition, the chiller average cooling capacity and COP reaches were 6.42kW and 0.64 with a chilled water temperature of 15°C. Clearly from the system operation period, the heat rejection through the re-cooling sub-system has the main significant impact on the system performance in the hot arid areas. Therefore, it should be based on alternative heat sink recourses with appropriate cost performance techniques.

Thermal performance assessment of a novel liquid desiccant-based evaporative cooling system: An experimental investigation

Energy consumption in buildings due to heating, cooling and air conditioning (HVAC) systems has a steadily growing trend as a consequence of enhanced indoor thermal comfort conditions. The role of cooling in HVAC oriented energy consumption is remarkable especially in regions with extreme climatic conditions such as Africa and Middle East. In hot and arid climates, cooling demand is usually met by cost-effective evaporative cooling solutions. However, in hot and humid climates, evaporative cooling systems are not capable of providing cooling as the outdoor air is already almost saturated in most cases. Therefore in this research, a novel desiccant-based evaporative cooling system is presented. For different values of inlet supply air temperature and relative humidity provided by a standard environmental chamber, temperature and relative humidity values are measured experimentally at the inlet and outlet of dehumidification and humidification unit, respectively. Since the main purpose of the system developed is to provide cost-effective thermal comfort conditions especially in humid climates, dehumidification effectiveness is calculated for each case tested. The results indicate that the system provides attractive findings for temperate and humid climatic conditions, where stand-alone evaporative cooling systems are inconclusive. For a case of average inlet relative humidity of 94.7% and average inlet air temperature of 38.6°C, the average outlet relative humidity and air temperature are determined to be 65.5% and 33.3°C, respectively. An average of 5.3°C reduction is achieved in supply air temperature as well as an average of 63.7% dehumidification effectiveness which is attractive and promising.

Experimental investigation and design of a shape-variable compressor cascade

The design of jet engine compressor blading always implies a compromise between design and off-design operation. The reason for this is a fixed blade geometry which has to be operated over a wide range of operating conditions. Consequently, maximum achievable efficiencies at design operation are limited by off-design requirements, e.g., a certain stall margin. This paper describes an approach using shape-variable blades equipped with integrated piezoceramic-based macro fiber composite (MFC) Actuators on the blade’s suction and pressure sides. By applying a voltage to these actuators, it is possible to increase and to decrease the blade stagger angle and therefore the blade turning. Compared to a conventional fixed blade profile, the actuated design is thus adaptable within a certain range regarding ambient conditions. The first part of the paper describes the geometry and structure of the shape-variable blades for use in a compressor cascade experiment. In the next part, the three-dimensional deformation behavior of all manufactured blades at different shape conditions is characterized with a photogrammetric measurement system called ATOS. The first results without aerodynamic loads show an average displacement at the trailing edge of approximately Δz ≈ 0.9 mm compared to the non-actuated condition. This corresponds to an average outlet angle variation of approximately ∆κ2 ≈ ± 1°. The third part of the paper presents the results of the low speed cascade experiment using a fully actuated cascade. On the one hand, the objective is to determine the influence of blade actuation on aerodynamic characteristics such as flow outlet angle, total pressure loss and pressure distributions. On the other hand, optical blade displacement measurements are used to investigate combined 2D- and 3D-deformation effects of blade actuation in conjunction with aerodynamic loads. For these measurements, the ATOS system is also used. The wake evaluations show that maximum blade actuation leads to flow outlet angle deviations up to ± 1° which can be described by an almost linear shift of the cascade performance without changing the loss distribution significantly. Furthermore, for the chosen profile this margin is approximately constant over the operating range.

Simplified model for coefficient of performance calculation of surface water source heat pump

A simple and accurate method to calculate the energy consumption of a water source heat pump system is important for analyzing its economic and social benefits. This paper presents a study on performance of a lake-water source heat pump unit, the calculation models of inlet water temperature on lake water side was obtained. Our results have shown that the hourly temperature of inlet water on lake water side and outlet water on user side would change a little within a day, and there was a linear relationship between daily average lake-water temperature and daily average air dry-bulb temperature. The measured daily average outlet water temperature on user side during a whole cooling/heating season changed in a little margin. Then a simplified model for coefficient of performance (COP) calculation of unit was proposed, the feasibility was validated through data analysis. A simplified method has therefore been developed to calculate and predict energy consumption of surface water source heat pump (SWHP) unit and will therefore enable energy efficient operation of water source heat pump for HVAC (heating, ventilating and air-conditioning) applications in buildings.

Influence of aspect ratio on the thermal performance of rectangular shaped micro channel heat sink using CFD code

A numerical study has been carried out to investigate the heat transfer enhancement and fluid flow characteristics for various aspect ratios of rectangular micro channel heat sinks (MCHS). The working fluid considered for the analysis is water. The fluid flow and heat transfer characteristics of a three-dimensional MCHS are obtained numerically by solving the appropriate governing equations. The flow domain is discretized as finite volume elements and solved using ANSYS CFX 14.5, commercially available CFD code. The numerically predicted results obtained through CFD code are validated with the experiments carried out and it is found that the maximum deviation between the two is less than 5%. Hence the CFD code is further extended to study the influence of geometrical parameters. The channel size optimization has been carried out numerically to obtain the effective heat removal from the MCHS. Average convective heat transfer coefficient, outlet temperature, friction and pressure drop, pumping power and thermal resistance have been plotted against Reynolds number. Non-dimensional parameter, Nusselt number has been plotted as a function of Reynolds number for three heat sinks with different aspect ratios. Friction factor and pressure drop across the channels are obtained and plotted across the channels.

A new solution for thermal interference of vertical U-tube ground heat exchanger for cold area in China

This paper presents a new solution to reduce the thermal interference of vertical U-tube ground heat exchanger (UGHE): pipe insulation installed on the upward branch pipe of the U-tube. 3-dimensional numerical models of the UGHE with and without pipe insulation were developed to simulate the heat transfer process around the UGHE. The models were verified with previously published data. The effects of pipe insulation on outlet temperature, soil temperature, heat exchange rate per unit length of borehole depth and soil temperature recovery ratio were investigated. The effects of inlet velocity of heat transfer fluid (HTF) and the thermal conductivity of backfill material were also studied to fully assess the effects of the insulation. The results indicate that the average outlet temperature of HTF, soil temperature near the upward branch pipe and soil temperature recovery ratio all increased and the thermal interference can be effectively weakened when pipe insulation was installed.

Experimental study on heat transfer of supercritical carbon dioxide in a long silica-based porous-media tube

The heat transfer phenomena of supercritical carbon dioxide were experimentally investigated in a vertical tube containing silica-based porous media. The experiment was conducted at various levels of static pressure, flow rates, and initial wall temperatures as well as with silica sand of porous media in a long test section to study the heat transfer characteristics of supercritical carbon dioxide (CO2). The results indicated that the average heat transfer coefficient and outlet temperature at an initial wall temperature of 150 °C were higher and lower than that of 200 °C. The heat transfer performance was significantly influenced by flow rate of supercritical CO2. The porous media was provided large heat exchange surface between particles and CO2 to increase the heat transfer coefficient, especially when small diameter of particles. When the inlet temperature was higher than the pseudocritical temperature, the heat transfer coefficient sharply dropped when x/L ≥ 0.5, because of the development of a thermal boundary and the decrease of CO2 thermophysical properties of CO2 in a far pseudocritical temperature. When the pseudocritical temperature was higher than the inlet temperature of the fluid, the local heat transfer coefficient was affected by a thermal boundary and thermophysical properties of CO2 in pseudocritical point at a higher initial wall temperature or lower supercritical pressure when x/L ≤ 0.75; only the thermophysical properties of supercritical CO2 in pseudocritical point played a pivotal role when x/L > 0.75 at a lower initial wall temperature or higher supercritical pressure. In the present study, the supercritical pressure of 10.5 MPa constituted an optimal operating condition for supercritical CO2 a long silica-based porous-media tube because of the high heat transfer performance at 150 and 200 °C.

CFD study of CO2 separation in an HFMC: Under non-wetted and partially-wetted conditions

This paper applies computational fluid dynamics (CFD) to explore a numerical simulation of mass transfer in a hollow fiber membrane contactor (HFMC) for non-wetted and partially-wetted conditions. A comprehensive 2D mathematical model based on the finite element method (FEM) was developed for modeling a gas–solvent HFMC which was applied to CO2 removal from a CO2/N2 gas mixture. Aqueous mono-ethanol-amine (MEA) solution was used as the CO2 absorbent and flowed in the fiber bore and then the gas mixture was circulated counter-currently in the shell side of HFMC. The average outlet CO2 concentrations, the absorption flux, overall mass transfer coefficient and the CO2 removal efficiencies are parametrically simulated by using the operational parameters such as gas and solvent flow rates, operating temperature, the fiber porosity and other geometrical characteristics. As a novel work, the effect of opposite fluid direction, i.e. absorbent flow in the shell and gas mixture in the fibers, on the mass transfer coefficient and CO2 removal efficiency was also taken into account for further considerations. It was concluded that while gas flows in the fibers and solvent flows in the shell an HFMC with a smaller size can be used. Furthermore, the effect of aqueous solution types such as MEA, 2-amino-2-methyl-1-propanol (AMP) and NaOH on the overall mass transfer coefficient and on the percentage removal of CO2 was investigated numerically and interesting results were obtained. Generally, the results showed that a reasonable agreement exists between the experimental and CFD results.

Development of a continuous membrane reactor process for enzyme-catalyzed lactulose synthesis

The study addresses three main issues which are usually encountered in membrane-assisted enzymatic reactions, such as membrane–enzyme electrostatic interaction, optimum operating conditions (with industrially relevant parameters) and maintenance of catalytic activity for prolonged synthesis. Considering Aspergillus oryzae β-galactosidase charge distribution at pH 4.6 was largely positive, a negatively charged PES membrane was not suited for the synthesis. With this, a rapid increase in transmembrane pressure occurred during continuous lactulose synthesis. The UFX membrane MWCO 10kDa is permanently hydrophilic and exhibited repulsion to the enzyme molecules and in turn, had an insignificant transmembrane pressure increase. Thus, this membrane was selected for further investigations. The operating conditions were optimized successively and were found to be: enzyme concentration=10U/mL, molar ratio of lactose to fructose=1/4, hydraulic residence time=9h and incubation temperature=40°C. With an inaccuracy of enzyme dosing protocol less than 5%, a long-term synthesis of lactulose was performed for 28 days with an average lactulose outlet concentration of 8.67g/L. The enzyme activity was maintained by addition of fresh enzyme every 48h. This is the longest continuous lactulose synthesis ever reported in fully automated membrane reactor.

Optimum end milling tool path and machining parameters for micro Laval nozzle manufacturing

Cutting tool path has significant effects on the performance of micro nozzles manufactured by micro machining. Different tool paths induced different directions of surface roughness. As for it, the manufacturers need to obtain optimal cutting tool path and cutting parameters. In this article, optimum machining parameters for the fabrication of micro Laval nozzle with two different end milling tool paths are presented. First, surface roughness models for different types of cutting tool paths are proposed. A case of machined nozzle surface is then given to verify the applicability of the developed roughness model. Second, theoretical profile geometries for the Laval nozzle to be manufactured are designed. Third, the influences of surface roughness on the nozzle performance parameters including total pressure, average outlet velocity and thrust are investigated through computational fluid dynamic analysis. Simulated performance parameters are contrasted with their theoretical values. It is found that for different tool paths, the nozzle of axial tool path has larger total pressure and average outlet velocity than that of circular tool path. Moreover, with surface roughness increasing, thrust decreases obviously when surface roughness Rz is larger than 4.8 μm. Micro end milling experiments based on axial tool path are then performed, and the optimum cutting parameters are obtained. Finally, a nozzle was manufactured with the axial tool path as well as the optimized cutting parameters.

Fabrication and properties of in-situ mullite-bonded Si3N4/SiC composites for solar heat absorber

Mullite-bonded Si3N4/SiC composite ceramics were fabricated via different pressureless sintering methods (in air and in graphite powders) using Si3N4, SiC, andalusite, α-Al2O3 and calcined bauxite as starting materials. Phase composition, mechanical properties, microstructure, thermal shock resistance, thermophysical properties and oxidation resistance were investigated. Results show that buried sintering method is more feasible which can protect Si3N4 and SiC free from oxidation effectively. After sintered at 1460°C in graphite powders, B3 sample exhibits the best mechanical properties, which also has high thermal conductivity of 8.84W/(mK). The sample has no damage after 30 thermal shock cycles (wind cooling from 1100°C to 25°C), and the bending strength remains 87.86MPa with a growth rate of 65.15%. Simulation results indicate that the average outlet air temperature of the volumetric absorber reaches 850°C with the efficiency above 65%. It is believed that mullite-bonded Si3N4/SiC composite ceramic is suitable for the use as heat absorbing material in concentrating solar power generation.

Exergetic and enviroeconomic analysis of semitransparent PVT array based on optimum air flow configuration and its comparative study

This paper carries out the exergetic and enviroeconomic analysis of semi-transparent photovoltaic thermal (PVT) array (size 10.08m×2.16m). Its exergetic and enviroeconomic performance has been compared with glass to tedlar i.e. opaque PVT array termed as case-A which has two integrated columns each having 18 PVT modules in series are connected in parallel and solar cell tile (SCT) based PVT array termed as case-B which has two integrated columns of 18 modules each having 36 PVT tiles (each solar cell having area 0.12m×0.12m) in the module is connected in series. The semi-transparent photovoltaic thermal (PVT) array considered as case-C which also has two integrated columns each having 18 semi-transparent PVT modules in series are connected in parallel. The size of all above array (10.08m×2.16m) is considered same. Four different climatic conditions of India (Delhi, Bangalore, Jodhpur and Srinagar) have been considered and the performances of the all above three cases have been compared on the basis of annual overall thermal energy and exergy gain. The comparative analysis shows that case-C has 28.8% and 12.1% lower cell temperature which yields 9.9% and 3.1% higher electrical efficiency than case-A and B respectively. Also the average outlet air temperature for case-C is higher by 40.6% and 19.1% than case-A and B respectively. The CO2 mitigation and enviroeconomic parameter for Bangalore in terms of overall thermal energy gain for case-C is 104.80tCO2/annum and 1519.56$/annum respectively, while in terms overall exergy gain is 48.76tCO2/annum and 707.09$/annum respectively. The CO2 mitigation potential of case-C is higher by 5.0% and 7.3% than case-B in terms of overall thermal energy and exergy gain respectively which indicates that case-C is a better performer than the other two cases.