Search results for: heat exchange

Authors: Kunya Bowornchockchai

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The objective of this research is to forecast the monthly exchange rate between Thai baht and the US dollar and to compare two forecasting methods. The methods are Box-Jenkins’ method and Holt’s method. Results show that the Box-Jenkins’ method is the most suitable method for the monthly Exchange Rate between Thai Baht and the US Dollar. The suitable forecasting model is ARIMA (1,1,0)  without constant and the forecasting equation is Y_t = Y_t-1 + 0.3691 (Y_t-1 - Y_t-2) When Y_t  is the time series data at time t, respectively.

Keywords: Box–Jenkins method, Holt’s method, mean absolute percentage error (MAPE), exchange rate

Procedia PDF Downloads 218

Authors: Imane Khalil, Quinn Pratt

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In a nuclear reactor, an array of fuel rods containing stacked uranium dioxide pellets clad with zircalloy is the heat source for a thermodynamic cycle of energy conversion from heat to electricity. After fuel is used in a nuclear reactor, the assemblies are stored underwater in a spent nuclear fuel pool at the nuclear power plant while heat generation and radioactive decay rates decrease before it is placed in packages for dry storage or transportation. A computational model of a Boiling Water Reactor spent fuel assembly is modeled using FLUENT, the computational fluid dynamics package. Heat transfer simulations were performed on the two-dimensional 9x9 spent fuel assembly to predict the maximum cladding temperature for different input to the FLUENT model. Uncertainty quantification is used to predict the heat transfer and the maximum temperature profile inside the assembly.

Keywords: spent nuclear fuel, conduction, heat transfer, uncertainty quantification

Procedia PDF Downloads 192

Authors: Wisam K. Hussam, Ali Alfeeli, Gergory J. Sheard

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Solar panels that use photovoltaic (PV) cells are popular for converting solar radiation into electricity. One of the major problems impacting the performance of PV panels is the overheating caused by excessive solar radiation and high ambient temperatures, which degrades the efficiency of the PV panels remarkably. To overcome this issue, an aluminum heat sink was used to dissipate unwanted heat from PV cells. The dimensions of the heat sink were determined considering the optimal fin spacing that fulfils hot climatic conditions. In this study, the effects of cooling on the efficiency and power output of a PV panel were studied experimentally. Two PV modules were used: one without and one with a heat sink. The experiments ran for 11 hours from 6:00 a.m. to 5:30 p.m. where temperature readings in the rear and front of both PV modules were recorded at an interval of 15 minutes using sensors and an Arduino microprocessor. Results are recorded for both panels simultaneously for analysis, temperate comparison, and for power and efficiency calculations. A maximum increase in the solar to electrical conversion efficiency of 35% and almost 55% in the power output were achieved with the use of a heat sink, while temperatures at the front and back of the panel were reduced by 9% and 11%, respectively.

Keywords: photovoltaic cell, natural convection, heat sink, efficiency

Procedia PDF Downloads 123

Authors: Mina Ganji Morad, Maziar Azadisoleimanieh, Sina Ganji Morad

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A green roof is formed by green plants alive and has many positive impacts in the regional climatic, as well as indoor. Green roof system to prevent solar radiation plays a role in the cooling space. The cooling is done by reducing thermal fluctuations on the exterior of the roof and by increasing the roof heat capacity which cause to keep the space under the roof cool in the summer and heating rate increases during the winter. A roof garden is one of the recommended ways to reduce energy consumption in large cities. Despite the scale of the city green roofs have effective functions, such as beautiful view of city and decontaminating the urban landscape and reduce mental stress, and in an exchange of energy and heat from outside to inside spaces. This article is based on a review of 20 articles and 10 books and valid survey results on the positive effects of green roofs to prevent energy waste in the building. According to these publications, three of the conventional roof, green roof typical and green roof with certain administrative details (layers of glass) and the use of resistant plants and shrubs have been analyzed and compared their heat transfer. The results of these studies showed that one of the best green roof systems for mountainous climate is tree and shrub system that in addition to being resistant to climate change in mountainous regions, will benefit from the other advantages of green roof. Due to the severity of climate change in mountainous areas it is essential to prevent the waste of buildings heating and cooling energy. Proper climate design can greatly help to reduce energy.

Keywords: green roof, heat transfer, reducing energy consumption, mountainous areas, sustainable architecture

Procedia PDF Downloads 372

Authors: Amit Arora, P. M. V. Subbarao, R. S. Agarwal

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This study attempts to find promising locations of upwash delta winglets for an inline finned tube heat exchanger. Later, location of winglets that delivers highest improvement in thermal performance is identified. Numerical results clearly showed that optimally located upwash delta winglets not only improved the thermal performance of fin area in tube wake and tubes, but also improved overall thermal performance of heat exchanger.

Keywords: apparent friction factor, delta winglet, fin and tube heat exchanger, longitudinal vortices

Procedia PDF Downloads 279

Authors: R. Whalley

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The heat transfer modelling for a diffusion process will be considered. Difficulties in computing the time-distance dynamics of the representation will be addressed. Incomplete and irrational Laplace function will be identified as the computational issue. Alternative approaches to the response evaluation process will be provided. An illustration application problem will be presented. Graphical results confirming the theoretical procedures employed will be provided.

Keywords: heat, transfer, diffusion, modelling, computation

Procedia PDF Downloads 522

Authors: Esther T. Akinlabi, Stephen A. Akinlabi

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This paper reports on the effects of heat treatment on 3CR12 and AISI 316 stainless steel grades. Heat treatment was conducted on the steel grades and cooled using two different media; air and water in order to study the effect of each medium on the evolving properties of the samples. The heat treated samples were characterized through the evolving microstructure and hardness. It was found that there was a significant grain size reduction in both the heat treated stainless steel specimens compared to the parent materials. The finer grain sizes were achieved as a result of impediment to growth of one phase by the other. The Vickers micro-hardness values of the heat treated samples were higher compared to the parent materials due to the fact that each of the steel grades had a proportion of martensitic structures in their microstructures.

Keywords: austenite, ferrite, grain size, hardness, martensite, microstructure and stainless steel

Procedia PDF Downloads 249

Authors: Abdul Rauf, Xiaoxing Liu, Waqas Amin

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Stock markets are fascinating more and more conductive to each other due to liberalization and globalization trends in recent years. China Pakistan Economic Corridor (CPEC) has dragged Pakistan stock exchange to the new heights and global investors are making investments to reap its benefits. So, in investors and government perspective, the study focuses co-integration of Pakistan stock exchange with world’s five big economies i-e US, China, England, Japan, and France. The time period of study is seven years i-e 2010 to 2016 and daily values of major indices of corresponding stock exchanges collected. All variables of that particular study are stationary at first difference confirmed by unit root test. The study Johansen system co integration test for analysis of data along with Granger causality test is performed for result purpose. Co integration test asserted that Pakistan stock exchange integrated with Shanghai stock exchange (SSE) and NIKKEI stock exchange in short run. Granger causality test also proclaimed these results. But NASDAQ, FTSE, DAX not co integrated and Granger cause at a short run but long run these markets are bonded with Pakistan stock exchange (KSE). VECM also confirmed this liaison in short and long run. Investors, therefore, need to be updated regarding co-integration of world’s stock exchanges to ensure well diversified and risk adjusted high returns. Equally, governments also need updated status so that they could reduce co-integration through multiple steps and hence drag investors for diversified investment.

Keywords: CPEC, DAX, FTSE, liberalization, NASDAQ, NIKKEI, SSE, stock markets

Procedia PDF Downloads 274

Authors: J. Y Jang, C. Y. Tseng

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A three-dimensional numerical model of thermoelectric generator (TEG) modules attached to a large chimney plate is proposed and solved numerically using a control volume based finite difference formulation. The TEG module consists of a thermoelectric generator, an elliptical pin-fin heat sink, and a cold plate for water cooling. In the chimney, the temperature of flue gases is 450-650K. Therefore, the effects of convection and radiation heat transfer are considered. Although the TEG hot-side temperature and thus the electric power output can be increased by inserting an elliptical pin-fin heat sink into the chimney tunnel to increase the heat transfer area, the pin fin heat sink would cause extra pumping power at the same time. The main purpose of this study is to analyze the effects of geometrical parameters on the electric power output and chimney pressure drop characteristics. In addition, the effects of different operating conditions, including various inlet velocities (Vin = 1, 3, 5 m/s) and inlet temperatures (Tgas = 450, 550, 650K) are discussed in detail. The predicted numerical data for the power vs. current (P-I) curve are in good agreement (within 11%) with the experimental data.

Keywords: thermoelectric generator, waste heat recovery, pin-fin heat sink, experimental and numerical analysis

Procedia PDF Downloads 350

Authors: Gurmeet Singh Cheema, Navjotinder Singh, Gurjinder Singh, Amardeep Singh

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Aluminium and its alloys play have excellent corrosion resistant properties, ease of fabrication and high specific strength to weight ratio. In this investigation an attempt has been made to study the effect of different post weld heat treatment methods on the mechanical and metallurgical properties of TIG welded joints of the commercial aluminium alloy. Three different methods of post weld heat treatments are, solution heat treatment, artificial aged and combination of solution heat treatment and artificial aging are given to TIG welded aluminium joints. Mechanical and metallurgical properties of as welded and post weld treated joints of the aluminium alloys was examined.

Keywords: aluminium alloys, TIG welding, post weld heat treatment

Procedia PDF Downloads 535

Authors: Beom-Ryeol Choi, Won-Poong Lee, Jin-Young Choi, Young-Hak Shin, Dong-Jun Won

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A Microgrid (MG) has a major role in power system. There are numerous benefits, such as ability to reduce environmental impact and enhance the reliability of a power system. Hence, Multi-MG (MMG) consisted of multiple MGs is being studied intensively. This paper proposes the optimal power exchange of MMG with hierarchical coordination. The whole system architecture consists of two layers: 1) upper layer including MG of MG Center (MoMC) which is in charge of the overall management and coordination and 2) lower layer comprised of several Microgrid-Energy Management Systems (MG-EMSs) which make a decision for own schedule. In order to accomplish the optimal power exchange, the proposed coordination algorithm is applied to MMG system. The objective of this process is to achieve optimal operation for improving economics under the grid-connected operation. The simulation results show how the output of each MG can be changed through coordination algorithm.

Keywords: microgrids, multi-microgrids, power exchange, hierarchical coordination

Procedia PDF Downloads 349

Authors: Joon-Suk Kim, Hae-Woo Lee

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This study discusses the effect of welding heat input on intergranular corrosion of the weld metal of Inconel 625 alloy. A specimen of Inconel 625 with a weld metal that controlled welding heat input was manufactured, and aging heat treatment was conducted to investigate sensitization by chromium carbides. The electrochemical SL and DL EPR experiments, together with the chemical ferric sulfate-sulfuric acid and nitric acid tests, were conducted to determine intergranular corrosion susceptibility between the specimens. In the SL and DL EPR experiments, specimens were stabilized in the weld metal, and therefore intergranular corrosion susceptibility could not be determined. However, in the ferric sulfate-sulfuric acid and nitric acid tests, the corrosion speed increased as heat input increased. This was because the amount of diluted Fe increased as the welding heat input increased, leading to microsegregation between the dendrites, which had a negative effect on the corrosion resistance.

Keywords: Inconel 625, weling, overlay, heat input, intergranular corrosion

Procedia PDF Downloads 328

Authors: Kanit Aroonrat, Somchai Wongwises

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A heat exchanger is one of the vital parts in a wide variety of applications. The tube with surface modification is generally referred to as an enhanced tube. With this, the thermal performance of the heat exchanger is improved. A dimpled tube is one of many kinds of enhanced tube. The heat transfer and pressure drop of two-phase flow inside dimpled tubes have received little attention in the literature, despite of having an important role in the development of refrigeration and air conditioning systems. As a result, the main aim of this study is to investigate the condensation heat transfer and pressure drop of refrigerant-134a flowing inside dimpled tubes. The test section is a counter-flow double-tube heat exchanger, which the refrigerant flows in the inner tube and water flows in the annulus. The inner tubes are one smooth tube and three dimpled tubes with different helical pitches. All test tubes are made from copper with an inside diameter of 8.1 mm and length of 1500 mm. The experiments are conducted over mass fluxes ranging from 300 to 500 kg/m²s, heat flux ranging from 10 to 20 kW/m², and condensing temperature ranging from 40 to 50 ˚C. The results show that all dimpled tubes provide higher heat transfer coefficient and frictional pressure drop compared to the smooth tube. In addition, the heat transfer coefficient and frictional pressure drop increase with decreasing of helical pitch. It can be observed that the dimpled tube with lowest helical pitch yields the heat transfer enhancement in the range of 60-89% with the frictional pressure drop increase of 289-674% in comparison to the smooth tube.

Keywords: condensation, dimpled tube, heat transfer, pressure drop

Procedia PDF Downloads 187

Authors: Soheil Mohtaram, Wu Weidong, Yashar Aryanfar

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This research investigates the points with heat recovery potential in a triple-pressure cogeneration combined cycle power plant and determines the amount of waste heat that can be recovered. A modified cycle arrangement is then adopted for accessing thermal potentials. Modeling the energy system is followed by thermodynamic and energetic evaluation, and then the price of the manufactured products is also determined using the Total Revenue Requirement (TRR) method and term economic analysis. The results of optimization are then presented in a Pareto chart diagram by implementing a new model with dual objective functions, which include power cost and produce heat. This model can be utilized to identify the optimal operating point for such power plants based on electricity and heat prices in different regions.

Keywords: heat loss, recycling, unused energy, efficient production, optimization, triple-pressure cogeneration

Procedia PDF Downloads 50

Authors: Abdeljalil Métioui

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The purpose of this paper is to present the results of research on the conceptual representations of 128 Quebec (Canada) pre-service teachers enrolled in their third year of university in a program to train elementary teachers about heat and temperature. To identify their conceptual representations about heat and temperature, we constructed a multiple-choice questionnaire consisting of five questions. For each question, they had to explain their choice of an answer. At the methodological level, this step is essential to be able to identify the student conceptual representations. It should be noted that the selected questions were based: (1) on the works have done worldwide on primary and secondary students’ misconceptions about heat and temperature; (2) on the notions prescribed in the curriculum related to the physical world and (3) on student’s everyday contexts. As illustrations, the following are the erroneous conceptual representations identified in our analysis of the data collected: (1) The change of state of the matter does not require a constant temperature, (2) The temperature is a measure in degrees to indicate the level of heat of an object or person, (3) The mercury contained in a thermometer expands when it is heated so that the particles which constitute it expand and (4) The sensation of cold (or warm) is related to the difference in temperature. In conclusion, we will see that it is possible to develop situations of conflict, dealing specifically with the limits of the analogy between heat and temperature. These situations must consider the conceptual representations of the pre-service teachers, as well as the relevant scientific understanding of the concept of heat and temperature.

Keywords: conceptual representation, heat, temperature, pre-service teachers

Procedia PDF Downloads 105

Authors: Misagh Irandoost Shahrestani, Hossein Shokouhmand, Mohammad Kalteh, Behrang Hasanpour

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In this paper, nanofluid conjugate heat transfer through a microtube with viscous dissipation effect is investigated numerically. The fluid flow is considered as a laminar regime. A constant heat flux is applied on the microtube outer wall and the two ends of its wall are considered adiabatic. Conjugate heat transfer problem is solved and investigated for this geometry. It is shown that viscous dissipation effect which is induced by shear stresses can not be neglected in microtubes. Viscous heating behaves as an energy source in the fluid and affects the temperature distribution. The effect of Reynolds number, particle volume fraction and the nanoparticles diameter on the energy source are investigated and an attempt on establishing suitable equations for assessing the value of the energy source based on Re, Dp and Φ is performed and they are depicted as 3D diagrams. Finally, the significance of viscous dissipation and the influence of these parameters on convective heat transfer coefficient are studied.

Keywords: convective heat transfer coefficient, heat transfer, microtube, nanofluid, viscous dissipation

Procedia PDF Downloads 481

Authors: Rajan Goyal, S. Lamba, S. Annapoorni

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The indirect exchange coupled system consists of two ferromagnetic layers separated by non-magnetic spacer layer. The type of exchange coupling may be either ferro or anti-ferro depending on the thickness of the spacer layer. In the present work, the strength of exchange coupling in FePt/Al₂O₃/Fe₃Pt has been investigated by varying the thickness of the spacer layer Al₂O₃. The FePt/Al₂O₃/Fe₃Pt trilayer structure is fabricated on Si <100> single crystal substrate using sputtering technique. The thickness of FePt and Fe₃Pt is fixed at 60 nm and 2 nm respectively. The thickness of spacer layer Al₂O₃ was varied from 0 to 16 nm. The normalized hysteresis loops recorded at room temperature both in the in-plane and out of plane configuration reveals that the orientation of easy axis lies along the plane of the film. It is observed that the hysteresis loop for ts=0 nm does not exhibit any knee around H=0 indicating that the hard FePt layer and soft Fe₃Pt layer are strongly exchange coupled. However, the insertion of Al₂O₃ spacer layer of thickness ts = 0.7 nm results in appearance of a minor knee around H=0 suggesting the weakening of exchange coupling between FePt and Fe₃Pt. The disappearance of knee in hysteresis loop with further increase in thickness of the spacer layer up to 8 nm predicts the co-existence of ferromagnetic (FM) and antiferromagnetic (AFM) exchange interaction between FePt and Fe₃Pt. In addition to this, the out of plane hysteresis loop also shows an asymmetry around H=0. The exchange field Hex = (Hc↑-HC↓)/2, where Hc↑ and Hc↓ are the coercivity estimated from lower and upper branch of hysteresis loop, increases from ~ 150 Oe to ~ 700 Oe respectively. This behavior may be attributed to the uncompensated moments in the hard FePt layer and soft Fe₃Pt layer at the interface. A better insight into the variation in indirect exchange coupling has been investigated using recoil curves. It is observed that the almost closed recoil curves are obtained for ts= 0 nm up to a reverse field of ~ 5 kOe. On the other hand, the appearance of appreciable open recoil curves at lower reverse field ~ 4 kOe for ts = 0.7 nm indicates that uncoupled soft phase undergoes irreversible magnetization reversal at lower reverse field suggesting the weakening of exchange coupling. The openness of recoil curves decreases with increase in thickness of the spacer layer up to 8 nm. This behavior may be attributed to the competition between FM and AFM exchange interactions. The FM exchange coupling between FePt and Fe₃Pt due to porous nature of Al₂O₃ decreases much slower than the weak AFM coupling due to interaction between Fe ions of FePt and Fe₃Pt via O ions of Al₂O₃. The hysteresis loop has been simulated using Monte Carlo based on Metropolis algorithm to investigate the variation in strength of exchange coupling in FePt/Al₂O₃/Fe₃Pt trilayer system.

Keywords: indirect exchange coupling, MH loop, Monte Carlo simulation, recoil curve

Procedia PDF Downloads 165

Authors: Jie Liu, Wei Wei, Chun-Ping Chang

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Using a sample of 110 countries over the period 1984-2013, this paper examines the impacts of country risks on choosing a specific exchange rate regime (first by utilizing the Levy-Yeyati and Sturzenegger de facto classification and then robusting it by the IMF de jure measurement) relative to other regimes via the panel multinomial logit approach. Empirical findings are as follows. First, in the full samples case we provide evidence that government is more likely to implement a flexible regime, but less likely to adopt a fixed regime, under a low level of composite and financial risk. Second, we find that Eurozone countries are more likely to choose a fixed exchange rate regime with a decrease in the level of country risk and favor a flexible regime in response to a shock from an increase of risk, which is opposite to non-Eurozone countries. Third, we note that high-risk countries are more likely to choose a fixed regime with a low level of composite and political risk in the government, but do not adjust the exchange rate regime as a shock absorber when facing economic and financial risks. It is interesting to see that those countries with relatively low risk display almost opposite results versus high-risk economies. Overall, we believe that it is critically important to account for political economy variables in a government’s exchange rate policy decisions, especially for country risks. All results are robust to the panel ordered probit model.

Keywords: country risk, political economy, exchange rate regimes, shock absorber

Procedia PDF Downloads 275

Authors: Igor Medved, Anton Trnik, Libor Vozar

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Phase-change materials (PCMs) are of great interest in the applications where a temperature level needs to be maintained and/or where there is demand for thermal energy storage. Examples are storage of solar energy, cold, and space heating/cooling of buildings. During a phase change, the enthalpy vs. temperature plot of PCMs shows a jump and there is a distinct peak in the heat capacity plot. We present a theoretical description from which these jumps and peaks can be obtained. We apply our theoretical results to fit experimental data with very good accuracy for selected materials and changes between two phases. The development is based on the observation that PCMs are polycrystalline; i.e., composed of many single-crystalline grains. The enthalpy and heat capacity are thus interpreted as averages of the contributions from the individual grains. We also show how to determine the baseline and excess part of the heat capacity and thus the latent heat corresponding to the phase change.

Keywords: averaging, enthalpy jump, heat capacity peak, phase change

Procedia PDF Downloads 433

Authors: Zohreh Soleimani, Sally Salome Shahzad, Stamatis Zoras

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As a result of current energy and environmental issues, the human body is known as one of the promising candidate for converting wasted heat to electricity (Seebeck effect). Thermoelectric generator (TEG) is one of the most prevalent means of harvesting body heat and converting that to eco-friendly electrical power. However, the uneven distribution of the body heat and its curvature geometry restrict harvesting adequate amount of energy. To perfectly transform the heat radiated by the body into power, the most direct solution is conforming the thermoelectric generators (TEG) with the arbitrary surface of the body and increase the temperature difference across the thermoelectric legs. Due to this, a computational survey through COMSOL Multiphysics is presented in this paper with the main focus on the impact of integrating a flexible wearable TEG with a corrugated shaped heat sink on the module power output. To eliminate external parameters (temperature, air flow, humidity), the simulations are conducted within indoor thermal level and when the wearer is stationary. The full thermoelectric characterization of the proposed TEG fabricated by a wavy shape heat sink has been computed leading to a maximum power output of 25µW/cm2 at a temperature gradient nearly 13°C. It is noteworthy that for the flexibility of the proposed TEG and heat sink, the applicability and efficiency of the module stay high even on the curved surfaces of the body. As a consequence, the results demonstrate the superiority of such a TEG to the most state of the art counterparts fabricated with no heat sink and offer a new train of thought for the development of self-sustained and unobtrusive wearable power suppliers which generate energy from low grade dissipated heat from the body.

Keywords: device simulation, flexible thermoelectric module, heat sink, human body heat

Procedia PDF Downloads 131

Authors: U. Schmidt, D. Dannehl, I. Schuch, J. Suhl, T. Rocksch, R. Salazar-Moreno, E. Fitz-Rodrigues, A. Rojano Aquilar, I. Lopez Cruz, G. Navas Gomez, R. A. Abraham, L. C. Irineo, N. G. Gilberto

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The integration of agricultural production systems into urban areas is a challenge for the coming decades. Because of increasing greenhouse gas emission and rising resource consumption as well as costs in animal husbandry, the dietary habits of people in the 21st century have to focus on herbal foods. Intensive plant cultivation systems in large cities and megacities require a smart coupling of information, material and energy flow with the urban infrastructure in terms of Horticulture 4.0. In recent years, many puzzle pieces have been developed for these closed processes at the Humboldt University. To compile these for an urban plant production, it has to be optimized and networked with urban infrastructure systems. In the field of heat energy production, it was shown that with closed greenhouse technology and patented heat exchange and storage technology energy can be provided for heating and domestic hot water supply in the city. Closed water circuits can be drastically reducing the water requirements of plant production in urban areas. Ion sensitive sensors and new disinfection methods can help keep circulating nutrient solutions in the system for a longer time in urban plant production greenhouses.

Keywords: semi closed, greenhouses, urban farming, solar heat collector, closed water cycles, aquaponics

Procedia PDF Downloads 299

Authors: M. Tarawneh

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This work is an experimental study on the heat transfer characteristics and pressure drop of different refrigerants during the condensation and evaporation processes in porous media. Four different refrigerants (R134a, R407C, 600a, R290), with different porosities were used to reach a real understanding of the actual heat transfer characteristics and pressure drop when using porous material inside the condenser and evaporator. Steel balls were used as porous media with different porosities (38%, 43%, 48%). The main goal of this project is to enhance the heat transfer coefficient during the condensation and evaporation processes when using different refrigerants and different porosities. Different correlations for the heat transfer coefficient and the pressure drop of the different refrigerants were developed. Also a generalized empirical correlation was developed for the different refrigerants. The experimental and predicted heat transfer coefficients and pressure drops were compared. It was found that, the Absolute standard deviation for the heat transfer coefficient and the pressure drop not exceeded values of 15% and 20%, respectively.

Keywords: condensation, evaporation, porous media, horizontal tubes, heat transfer coefficient, propane, butane

Procedia PDF Downloads 504

Authors: Badache Messaoud

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Geothermal thermosyphons (GTs) are increasingly used in many heating and cooling geothermal applications owing to their high heat transfer performance. This paper proposes a response surface methodology (RSM) to investigate and optimize the performance of a CO2 geothermal thermosyphon. The filling ratio (FR), temperature, and flow rate of the heat transfer fluid are selected as the designing parameters, and heat transfer rate and effectiveness are adopted as response parameters (objective functions). First, a dedicated experimental GT test bench filled with CO2 was built and subjected to different test conditions. An RSM was used to establish corresponding models between the input parameters and responses. Various diagnostic tests were used to assess evaluate the quality and validity of the best-fit models, which explain respectively 98.9% and 99.2% of the output result’s variability. Overall, it is concluded from the RSM analysis that the heat transfer fluid inlet temperatures and the flow rate are the factors that have the greatest impact on heat transfer (Q) rate and effectiveness (εff), while the FR has only a slight effect on Q and no effect on εff. The maximal heat transfer rate and effectiveness achieved are 1.86 kW and 47.81%, respectively. Moreover, these optimal values are associated with different flow rate levels (mc level = 1 for Q and -1 for εff), indicating distinct operating regions for maximizing Q and εff within the GT system. Therefore, a multilevel optimization approach is necessary to optimize both the heat transfer rate and effectiveness simultaneously.

Keywords: geothermal thermosiphon, co2, Response surface methodology, heat transfer performance

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Authors: Nila Febri Wilujeng, Helda Risman

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Enjoying stable security within its region for the last 50 years, ASEAN nowadays contends with the global context emerging dynamically, which brings about multidimensional challenges and threats such as terrorism, radicalism, armed rebellion, hijacking, and other non-traditional threats. Dealing with these circumstances, ASEAN member states tighten its capacity by enhancing regional cooperation and strategic information exchange among ASEAN member states so-called ASEAN Our Eyes. This initiative adopted for the sake of forestalling any possible threat posed by violent extremism, radicalization, and terrorism through timely strategic information exchange among ASEAN member states. By using qualitative method, this paper will utilize regional security complex and international cooperation theories in analyzing the process to examine ASEAN Our Eyes based on its terms of reference. As a result, it portrays that ASEAN Our Eyes is able to undermine the gaps in the realm of strategic information exchange in monitoring the movement of violent extremism, radicalism, foreign terrorist fighters, and crime-terror nexus. However, it remains premature as a strategic measure to encounter those threats in the years to come.

Keywords: regional cooperation, counter-terrorism, ASEAN our eyes, strategic information exchange

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Authors: A. Baloglu, A. Çınar

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Different tools and technologies were implemented for Crisis Response and Management (CRM) which is generally using available network infrastructure for information exchange. Depending on type of disaster or crisis, network infrastructure could be affected and it could not be able to provide reliable connectivity. Thus any tool or technology that depends on the connectivity could not be able to fulfill its functionalities. As a solution, a new message exchange framework has been developed. Framework provides offline/online information exchange platform for CRM Information Systems (CRMIS) and it uses XML compression and packet prioritization algorithms and is based on open source web technologies. By introducing offline capabilities to the web technologies, framework will be able to perform message exchange on unreliable networks. The experiments done on the simulation environment provide promising results on low bandwidth networks (56kbps and 28.8 kbps) with up to 50% packet loss and the solution is to successfully transfer all the information on these low quality networks where the traditional 2 and 3 tier applications failed.

Keywords: crisis response and management, XML messaging, web services, XML compression, mining

Procedia PDF Downloads 316

Authors: Kira Toxopeus, Kamran Siddiqui

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Channel flows are common in a wide range of engineering applications. In some types of channel flows, particularly the ones involving chemical or biological processes, the control of the flow temperature is crucial to maintain the optimal conditions for the chemical reaction or to control the growth of biological species. This often becomes an issue when the flow experiences temperature fluctuations due to external conditions. While active heating and cooling could regulate the channel temperature, it may not be feasible logistically or economically and is also regarded as a non-sustainable option. Thermal energy storage utilizing phase change material (PCM) could provide the required thermal regulation sustainably by storing the excess heat from the channel and releasing it back as required, thus regulating the channel temperature within a range in the proximity of the PCM melting temperature. However, in designing such systems, the configuration of the PCM storage within the channel is critical as it could influence the channel flow dynamics, which would, in turn, affect the heat exchange between the channel fluid and the PCM. The present research is focused on the investigation of the flow dynamical behavior in the channel during heat transfer from the channel flow to the PCM thermal energy storage. Offset vertical columns in a narrow channel were used that contained the PCM. Two different column shapes, square and circular, were considered. Water was used as the channel fluid that entered the channel at a temperature higher than that of the PCM melting temperature. Hence, as the water was passing through the channel, the heat was being transferred from the water to the PCM, causing the PCM to store the heat through a phase transition from solid to liquid. Particle image velocimetry (PIV) was used to measure the two-dimensional velocity field of the channel flow as it flows between the PCM columns. Thermocouples were also attached to the PCM columns to measure the PCM temperature at three different heights. Three different water flow rates (0.5, 0.75 and 1.2 liters/min) were considered. At each flow rate, experiments were conducted at three different inlet water temperatures (28ᵒC, 33ᵒC and 38ᵒC). The results show that the flow rate and the inlet temperature influenced the flow behavior inside the channel.

Keywords: channel flow, phase change material, thermal energy storage, thermal regulation

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Authors: Jinyoung Kim, Jinuk Kwon, Haksoo Han

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Polyimide is widely used in electronic industries, and heat dissipation of polyimide film is important for its application in electric devices for high-temperature resistance heat dissipation film. In this study, we demonstrated a new way to increase heat dissipating rate by adding carbon black as filler. This type of polyimide composite film was produced by pyromellitic dianhydride (PMDA) and 4,4’-oxydianiline (ODA). Carbon black (CB) is added in different loading, shows increasing heat dissipation rate for increase of Carbon black. The polyimide-carbon black composite film is synthesized with high dissipation rate to ~8W∙m−1K−1. Its high thermal decomposition temperature and glass transition temperature were maintained with carbon filler verified by thermogravimetric analysis (TGA) and differential scanning calorimetric (DSC), the polyimidization reaction of polyi(amide-mide) was confirmed by Fourier transform infrared spectroscopy (FT-IR). The polyimide composite film with carbon black with high heat dissipating rate could be used in various applications such as computers, mobile phone industries, integrated circuits, coating materials, semiconductor etc.

Keywords: polyimide, heat dissipation, electric device, filler

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Authors: Nguyen Thi Thanh Truc, Chi-Hyeon Lee, Srinivasa Reddy Mallampati, Byeong-Kyu Lee

Abstract:

This study evaluated to facilitate separation of ABS plastics from other waste plastics by froth flotation after surface hydrophilization of ABS with heat treatment. The mild heat treatment at 100oC for 60s could selectively increase the hydrophilicity of the ABS plastics surface (i.e., ABS contact angle decreased from 79o to 65.8o) among other plastics mixture. The SEM and XPS results of plastic samples sufficiently supported the increase in hydrophilic functional groups and decrease contact angle on ABS surface, after heat treatment. As a result of the froth flotation (at mixing speed 150 rpm and airflow rate 0.3 L/min) after heat treatment, about 85% of ABS was selectively separated from other heavy plastics with 100% of purity. The effect of optimum treatment condition and detailed mechanism onto separation efficiency in the froth floatation was also investigated. This research is successful in giving a simple, effective, and inexpensive method for ABS separation from waste plastics.

Keywords: ABS, hydrophilic, heat treatment, froth flotation, contact angle

Procedia PDF Downloads 323

Authors: Feyza Şahi̇n, Harun Deni̇zli̇, Mustafa Zabun, Hüseyi̇n OnbaşIoğli

Abstract:

Heat exchangers are devices that are widely used to transfer heat between fluids due to their temperature differences. As a type of heat exchanger, air coolers are heat exchangers that cool the air as it passes through the fins of the heat exchanger by transferring heat to the refrigerant in the coil tubes of the heat exchanger. An assembled fin and tube heat exchanger consists of a coil block and a casing with a fan mounted on it. The term “Fan hood” is used to define the distance between the fan and the coil block. Air coolers play a crucial role in cooling systems, and their heat transfer performance can vary depending on design parameters. These parameters can be related to the air side or the internal fluid side. For airside efficiency, the distance between the fan and the coil block affects the performance by creating dead zones at the corners of the casing and maldistribution of airflow. Therefore, a detailed study of the effect of the fan hood on the evaporator and the optimum fan hood distance is necessary for an efficient air cooler design. This study aims to investigate the value of the fan hood in a fin and tube-type air cooler heat exchanger through computational fluid dynamics (CFD) simulations and experimental investigations. CFD simulations will be used to study the airflow within the fan hood. These simulations will provide valuable insights to optimize the design of the fan hood. In addition, experimental tests will be carried out to validate the CFD results and to measure the performance of the fan hood under real conditions. The results will help us to understand the effect of fan hood design on evaporator efficiency and contribute to the development of more efficient cooling systems. This study will provide essential information for evaporator design and improving the energy efficiency of cooling systems.

Keywords: heat exchanger, fan hood, heat exchanger performance, air flow performance

Procedia PDF Downloads 38

Authors: Seon Tae Kim, Robert Hegner, Goksel Ozuylasi, Panagiotis Stathopoulos, Eberhard Nicke

Abstract:

High-temperature heat pumps (HTHP) that can supply heat at temperatures above 200°C can enhance the energy efficiency of industrial processes and reduce the CO₂ emissions connected with the heat supply of these processes. In the current work, the thermodynamic performance of 3 different vapor compression cycles, which use R-718 (water) as a working medium, have been evaluated by using a commercial process simulation tool (EBSILON Professional). All considered cycles use two-stage vapor compression with intercooling between stages. The main aim of the study is to compare different intercooling strategies and study possible heat recovery scenarios within the intercooling process. This comparison has been carried out by computing the coefficient of performance (COP), the heat supply temperature level, and the respective mass flow rate of water for all cycle architectures. With increasing temperature difference between the heat source and heat sink, ∆T, the COP values decreased as expected, and the highest COP value was found for the cycle configurations where both compressors have the same pressure ratio (PR). The investigation on the HTHP capacities with optimized PR and exergy analysis has also been carried out. The internal heat exchanger cycle with the inward direction of secondary flow (IHX-in) showed a higher temperature level and exergy efficiency compared to other cycles. Moreover, the available operating range was estimated by considering mechanical limitations.

Keywords: high temperature heat pump, industrial process, vapor compression cycle, R-718 (water), thermodynamic analysis

Procedia PDF Downloads 120