Showing papers in "Applied Thermal Engineering in 2006"
TL;DR: In this paper, the properties of the graphite matrix and paraffin phase change material (PCM) composites were measured for graphite matrices with bulk densities ranging from 50g/L to 350 g/L.
Abstract: The thermal conductivity of paraffin wax was increased by two orders of magnitude by impregnating porous graphite matrices with the paraffin. The graphite matrices were fabricated by compacting flake graphite that had been soaked in a bath of sulfuric and nitric acid then heat-treated at 900 °C. The properties of the graphite matrix and paraffin phase change material (PCM) composites were measured for graphite matrix bulk densities ranging from 50 g/L to 350 g/L. The properties studied include the thermal conductivity in directions parallel and perpendicular to the direction of compaction, paraffin mass fraction, and the latent heat of fusion of the composite samples. The latent heat of fusion and phase change characteristics of the graphite/paraffin composites were studied using differential scanning calorimetry (DSC). Scanning electron microscope (SEM) pictures are included to visualize the morphology of the graphite during each stage of the composite fabrication process. The performance of the PCM-composite was demonstrated by using the PCM-composite as a passive thermal management system for a lithium ion battery pack discharged at high rates.
560 citations
TL;DR: In this article, the cooling performance of a microchannel heat sink with nanoparticle-fluid suspensions (nanofluids) is numerically investigated by using a theoretical model of thermal conductivity of nanofluid that accounts for the fundamental role of Brownian motion.
Abstract: In this paper, the cooling performance of a microchannel heat sink with nanoparticle–fluid suspensions (“nanofluids”) is numerically investigated. By using a theoretical model of thermal conductivity of nanofluids that accounts for the fundamental role of Brownian motion, we investigate the temperature contours and thermal resistance of a microchannel heat sink with nanofluids such as 6 nm copper-in-water and 2 nm diamond-in-water. The results show that the cooling performance of a microchannel heat sink with water-based nanofluids containing diamond (1 vol.%, 2 nm) at the fixed pumping power of 2.25 W is enhanced by about 10% compared with that of a microchannel heat sink with water. Nanofluids reduce both the thermal resistance and the temperature difference between the heated microchannel wall and the coolant. Finally, the potential of deploying a combined microchannel heat sink with nanofluids as the next generation cooling devices for removing ultra-high heat flux is shown.
431 citations
TL;DR: The organic rankine cycle (ORC) was defined as a bottoming cycle in this article, which refers to the power cycle that uses waste industrial heat for power generation by supplementing heat from any f...
Abstract: The organic rankine cycle (ORC) as a bottoming cycle1The expression "bottoming cycle" refers to the power cycle that uses waste industrial heat for power generation by supplementing heat from any f ...
359 citations
TL;DR: In this paper, the nano-fluid was employed as the working medium for a conventional 211-μm-wide and 217-mm-deep grooved circular heat pipe and the experiment was performed to measure the temperature distribution and to compare the heat pipe thermal resistance using nanofluid and DI-water.
Abstract: Nano-fluid is employed as the working medium for a conventional 211 μm wide × 217 μm deep grooved circular heat pipe. The nano-fluid used in this study is an aqueous solution of 35 nm diameter silver nano-particles. The experiment was performed to measure the temperature distribution and to compare the heat pipe thermal resistance using nano-fluid and DI-water. The tested nano-particle concentrations ranged from 1 mg/l to 100 mg/l. The condenser section of the heat pipe was attached to a heat sink that was cooled by water supplied from a constant-temperature bath maintained at 40 °C. At a same charge volume, the measured nano-fluid filled heat pipe temperature distribution demonstrated that the thermal resistance decreased 10–80% compared to DI-water at an input power of 30–60 W. The measured results also show that the thermal resistances of the heat pipe decrease as the silver nano-particle size and concentration increase.
280 citations
TL;DR: In this article, the effect of compression ratio on engine performance and exhaust emissions was examined at stoichiometric air/fuel ratio, full load and minimum advanced timing for the best torque MBT in a single cylinder, four stroke, with variable compression ratio and spark ignition engine.
Abstract: Renewable energy sources for the gasoline engines alcohols gain importance recently. These renewable energy sources have attracted the attention of researchers as alternative fuel due to their high octane number. In addition, these are also clean energy sources and can be obtained from the biomass alcohols with low carbon like ethanol. In this study, the effect of compression ratio on engine performance and exhaust emissions was examined at stoichiometric air/fuel ratio, full load and minimum advanced timing for the best torque MBT in a single cylinder, four stroke, with variable compression ratio and spark ignition engine.
265 citations
TL;DR: In this paper, the authors used the heating degree-days concept to obtain the annual heating requirements of buildings in different climates zones of Turkey and calculated the optimum insulation thicknesses, energy savings, and payback periods.
Abstract: In Turkey, heat loss from buildings is one of the primary sources of energy waste since no or little insulation is used in existing and new buildings. Therefore, considerable energy savings can be obtained by using proper thickness of insulation in buildings. Given the significant climatic variations that exist in different parts of Turkey, 16 cities from four climate zones of Turkey are selected for analysis and optimum insulation thicknesses, energy savings, and payback periods are calculated. The annual heating requirements of buildings in different climates zones were obtained by means of the heating degree-days concept. The optimization is based on life-cycle cost analysis. Five different fuels; coal, natural gas, fuel oil, liquefied petroleum gas (LPG), and electricity, and as an insulation material polystyrene are considered. The results show that optimum insulation thicknesses vary between 2 and 17 cm, energy savings between 22% and 79%, and payback periods between 1.3 and 4.5 years depending on the city and the type of fuel.
261 citations
TL;DR: In this paper, the performance and gaseous emission characteristics of a diesel engine when fuelled with vegetable oil and its blends of 25, 50, and 75% of vegetable oil with ordinary diesel fuel separately were evaluated.
Abstract: Experimental tests have been carried out to evaluate the performance and gaseous emission characteristics of a diesel engine when fuelled with vegetable oil and its blends of 25%, 50%, and 75% of vegetable oil with ordinary diesel fuel separately. Tests on ordinary diesel fuel have also been carried out for comparison purposes. A series of tests are conducted and repeated six times for each of the test fuels. The engine works at a fixed speed of 1500 rpm, but at different loads respectively, i.e. 0%, 25%, 50%, 75% and 100% of engine full loads. The performance and the emission characteristics of exhaust gases of the engine are analyzed and compared. The experimental results show that the basic engine performance – power output and fuel consumption are comparable to diesel when fueled with vegetable oil and its blends. The emission of nitrogen oxides (NO x ) from vegetable oil and its blends are lower than that of pure diesel fuel. This emission character found in the tests to some extent is of significance for the practical application of vegetable oil to replace ordinary diesel fuel. The results for the other emissions are also shown in the figures and tables.
252 citations
TL;DR: In this paper, a solar energy powered Rankine cycle using supercritical CO2 for combined production of electricity and thermal energy is proposed, which utilizes evacuated solar collectors to convert CO2 into high-temperature supercritical state, used to drive a turbine and thereby produce mechanical energy and hence electricity.
Abstract: A solar energy powered Rankine cycle using supercritical CO2 for combined production of electricity and thermal energy is proposed. The proposed system consists of evacuated solar collectors, power generating turbine, high-temperature heat recovery system, low-temperature heat recovery system, and feed pump. The system utilizes evacuated solar collectors to convert CO2 into high-temperature supercritical state, used to drive a turbine and thereby produce mechanical energy and hence electricity. The system also recovers heat (high-temperature heat and low-temperature heat), which could be used for refrigeration, air conditioning, hot water supply, etc. in domestic or commercial buildings. An experimental prototype has been designed and constructed. The prototype system has been tested under typical summer conditions in Kyoto, Japan; It was found that CO2 is efficiently converted into high-temperature supercritical state, of while electricity and hot water can be generated. The experimental results show that the solar energy powered Rankine cycle using CO2 works stably in a trans-critical region. The estimated power generation efficiency is 0.25 and heat recovery efficiency is 0.65. This study shows the potential of the application of the solar-powered Rankine cycle using supercritical CO2.
244 citations
TL;DR: In this paper, the laminar forced convection flow of these nanofluids between two coaxial and parallel disks with central axial injection has been considered using temperature-dependent nano-fluid properties.
Abstract: Heat transfer enhancement capabilities of coolants with suspended metallic nanoparticles inside typical radial flow cooling systems are numerically investigated in this paper. The laminar forced convection flow of these nanofluids between two coaxial and parallel disks with central axial injection has been considered using temperature dependent nanofluid properties. Results clearly indicate that considerable heat transfer benefits are possible with the use of these fluid/solid particle mixtures. For example, a Water/Al2O3 nanofluid with a volume fraction of nanoparticles as low as 4% can produce a 25% increase in the average wall heat transfer coefficient when compared to the base fluid alone (i.e., water). Furthermore, results show that considerable differences are found when using constant property nanofluids (temperature independent) versus nanofluids with temperature dependent properties. The use of temperature-dependent properties make for greater heat transfer predictions with corresponding decreases in wall shear stresses when compared to predictions using constant properties. With an increase in wall heat flux, it was found that the average heat transfer coefficient increases whilst the wall shear stress decreases for cases using temperature-dependent nanofluid properties.
234 citations
TL;DR: In this article, the authors report on the measuring technique and values of the measured thermal properties of some commonly used insulation materials produced by local manufacturers in Saudi Arabia, and they show that the thermal conductivity increases with increasing temperature and decreases with increasing density over the temperature and density ranges considered in the present investigation.
Abstract: The paper reports on the measuring technique and values of the measured thermal properties of some commonly used insulation materials produced by local manufacturers in Saudi Arabia. Among the thermal properties of insulation materials, the thermal conductivity ( k ) is regarded to be the most important since it affects directly the resistance to transmission of heat ( R -value) that the insulation material must offer. Other thermal properties, like the specific heat capacity ( c ) and density ( ρ ), are also important only under transient conditions. A well-suited and accurate method for measuring the thermal conductivity and diffusivity of materials is the transient plane source (TPS) technique, which is also called the hot disk (HD). This new technique is used in the present study to measure the thermal conductivity of some insulation materials at room temperature as well as at different elevated temperature levels expected to be reached in practice when these insulations are used in air-conditioned buildings in hot climates. Besides, thermal conductivity values of the same type of insulation material are measured for samples with different densities; generally, higher density insulations are used in building roofs than in walls. The results show that the thermal conductivity increases with increasing temperature and decreases with increasing density over the temperature and density ranges considered in the present investigation.
224 citations
TL;DR: In this article, the ability of an artificial neural network model, using a back propagation learning algorithm, to predict specific fuel consumption and exhaust temperature of a Diesel engine for various injection timings is studied.
Abstract: The ability of an artificial neural network model, using a back propagation learning algorithm, to predict specific fuel consumption and exhaust temperature of a Diesel engine for various injection timings is studied. The proposed new model is compared with experimental results. The comparison showed that the consistence between experimental and the network results are achieved by a mean absolute relative error less than 2%. It is considered that a well-trained neural network model provides fast and consistent results, making it an easy-to-use tool in preliminary studies for such thermal engineering problems.
TL;DR: In this paper, the authors compared three alternative technologies of sludge management where sludge is used to produce energy, i.e., anaerobic digestion of mixed raw sludge with subsequent cogeneration of obtained biogas.
Abstract: This paper is focused on heat and economic aspects of selected sludge management options. Sewage sludge produced by waste water cleaning process is biodegradable material with growing production. This paper compares three alternative technologies of sludge management where sludge is used to produce energy. Alternative 1 considers anaerobic digestion of mixed raw sludge with subsequent cogeneration of obtained biogas. Alternative 2 covers incineration of mixed raw sludge utilizing energy contained in flue gases. Alternative 3 represents a combination of the above two alternatives – incineration of digested sludge utilizing energy contained in biogas and flue gas. Heat and economic balances were performed on the basis of the pilot tests of sludge dewatering at a big waste water treatment plant with the aim to use credible data for all the analyses. Therefore results provide information of practical value.
TL;DR: In this article, the combustion characteristics of a direct-injection natural gas engine under various fuel injection timings were investigated and the results showed that fuel injection timing had a large influence on the engine performance, combustion and emissions and these influences became largely in the case of late injection.
Abstract: The combustion characteristics of a direct-injection natural gas engine under various fuel injection timings were investigated. The results showed that fuel injection timing had a large influence on the engine performance, combustion and emissions and these influences became largely in the case of late injection. Over-late injection would supply insufficient time for the fuel–air mixing of the late part of the injected fuel, bringing poor quality of mixture formation and subsequently resulting in the slow combustion rate, the long combustion duration and high HC concentration. However, early injection gave a slight influence on both engine combustion and emissions. There existed an optimum fuel injection timing where the maximum cylinder pressure, the maximum rate of pressure rise and the maximum rate of heat release would get their highest values along with the shortest combustion durations, the shortest heat release duration and more concentrated heat release process closing to the top-dead-centre while maintaining the low level of HC and CO emissions.
TL;DR: The experimental data obtained are compared with those obtained from plain tube published data as mentioned in this paper, and the empirical correlations developed in terms of twist ratio and Reynolds number, are fitting the experimental data within plus or minus 15% and 13% for Nusselt number and friction factor, respectively.
Abstract: Experimental investigation of heat transfer and friction factor characteristics of circular tube fitted with full-length helical screw element of different twist ratio, and increasing and decreasing order of twist ratio set have been studied with uniform heat flux. The experimental data obtained are compared with those obtained from plain tube published data. The heat transfer coefficient increases with twist ratio. There is no much change in the magnitude of heat transfer coefficient enhancement with increasing twist ratio and with decreasing twist ratio set, as the magnitude of swirl generated at the inlet or at the outlet in the order of increasing twist ratio or decreasing twist ratio, is same in both the cases. The empirical correlations developed in terms of twist ratio and Reynolds number, are fitting the experimental data within plus or minus 15% and 13% for Nusselt number and friction factor, respectively.
TL;DR: In this article, a model for structural and operational optimisation of a distributed energy system (DES) is presented, where production and consumption of electrical power and heat, power transmissions, transport of fuels to the production plants, and transport of water in the district heating pipelines and storage of heat are taken into account.
Abstract: A distributed energy system (DES) is a system comprising a set of energy suppliers and consumers, district heating pipelines, heat storage facilities and power transmission lines in a region. Distributed energy production has got an increasingly important role in the energy market. In this paper, a model for structural and operational optimisation of DES is presented. In the model, production and consumption of electrical power and heat, power transmissions, transport of fuels to the production plants, transport of water in the district heating pipelines and storage of heat are taken into account. The problem is formulated as a mixed integer linear programming (MILP) problem where the objective is to minimise the overall cost of DES, i.e., the sum of the running costs for the included operations and the annualised investment costs of the included equipment. An illustrative example is presented for a complex DES situation. The solution gives the DES structure, i.e., which production units, heat transport lines and storages should be built as well as their locations be, together with design parameters for plants and pipelines. The model enables the involved parties—suppliers, consumers, designers and authorities—to form a joint view of different situations as a basis for the decision making. A tool based on the model is built, which can be used in design, in creating guidelines for regional energy policies and for versatile what-if analyses.
TL;DR: In this article, numerical results of a supersonic ejector for refrigeration applications are presented, which is based on the NIST-this articlePROP database for refrigerants properties calculations.
Abstract: This paper represents numerical results of a supersonic ejector for refrigeration applications. The working fluid used for this study is R142b for which some 1-D simulation data is available in the literature for comparison purposes. One of the interesting features is that the current model is based on the NIST-REFPROP database for refrigerants properties calculations. To the authors'knowledge, it is the first paper dealing with local CFD modeling that takes into account shock–boundary layer interactions in a real refrigerant. The numerical results obtained, contribute to understanding the local structure of the flow and demonstrate the crucial role of the secondary nozzle for the mixing rate performance. In addition, these results point out to the need for an extensive validation of the turbulence model, especially in the modeling of the off-design mode.
TL;DR: In this paper, the authors presented a mathematical model regarding the conjugate problem of transient forced convection and solid-liquid phase change heat transfer based on the enthalpy formulation, which was validated with experimental data obtained by experimental investigations that have been performed on the test unit with technical grade paraffin as the phase change material and water as the heat transfer fluid (HTF).
Abstract: A transient heat transfer phenomenon during charging and discharging of the shell-and-tube latent thermal energy storage system has been analysed in this paper. The mathematical model, regarding the conjugate problem of transient forced convection and solid-liquid phase change heat transfer based on the enthalpy formulation, has been presented. A fully implicit two-dimensional control volume FORTRAN computer code has been developed for solving governing equations with initial and boundary conditions. The numerical model is validated with experimental data obtained by experimental investigations that have been performed on the test unit with technical grade paraffin as the phase change material (PCM) and water as the heat transfer fluid (HTF). Numerical predictions match the experimental results. This pointed out that the presented numerical procedure could be accurately used for transient heat transfer simulation. A series of numerical calculations have been done in order to analyse the influence of several HTF operating conditions and several geometric parameters on the heat transfer process inside the water-paraffin shell-and-tube latent thermal energy storage (LTES) unit. Numerical results, which could be used for operating conditions and geometry optimization, provide guidelines for the design of the latent thermal energy storage system.
TL;DR: In this paper, a novel design and performance prediction tool for the ground source heat pump (GSHP) system was introduced, which features, a user-friendly interface for data input and graphical output.
Abstract: This paper introduces a novel design and performance prediction tool for the ground source heat pump (GSHP) system. This tool features, a user-friendly interface for data input and graphical output. First, an outline of this tool was described. Next, the authors validated temperature variation calculated by theoretical method of the developed tool compared with one measured in the thermal response test. The thermal response test was carried out in a house garden in Sapporo. Giving the calculated conditions, the calculated temperature variation almost traced the measured value. The developed tool’s preciseness was proved with the results. In final, performance prediction and feasibility study of a residential GSHP system in Sapporo was performed with this tool as an example. Results of the calculations show that the life cycle CO 2 emission (LCCO 2 ) of the GSHP system is 2038 kg-CO 2 /year and it is less than half compared to conventional oil boiler systems. Also, the GSHP system can reduce life cycle cost (LCC) by 50,000–90,000 Japanese-yen/year. The payback time for increased investment cost of the GSHP system is about 9–14 years in comparison with other conventional systems.
TL;DR: In this article, the heat transfer and pressure drop characteristics of pin fin arrays were investigated in terms of appropriate dimensionless variables and the final judgment of the performance of the pin fin cross-section was performed based on the heat exchanger performance plot.
Abstract: Pin fin arrays are frequently used for cooling of high thermal loaded electronic components. Whereas the pin fin accomplishment regarding heat transfer is always higher than that of other fin configurations, the high pressure drop accompanying pins seriously reduces their overall performance. In order to check how the form of pin cross-section influences the pressure drop and heat transfer capabilities, six forms of pin cross-section were numerically investigated. By employing the conjugate heat transfer boundary conditions, numerical simulations close to realistic working conditions were performed. Two geometric comparison criteria were applied so that the conclusions derived from numerical computations were valid for various possible geometric parameters and working conditions. Both staggered and inline pin arrangements were investigated as these are common in practical applications. The heat transfer and pressure drop characteristics are presented in terms of appropriate dimensionless variables. The final judgment of the performance of the pin fin cross-section was performed based on the heat exchanger performance plot. Such a plot allows the assessment of the pin performance including their heat transfer and the pressure drop.
TL;DR: In this article, the authors present a clear description and understanding of the uses and limitations of many different project evaluation techniques and show when these methods are connected and are applicable to cogeneration plants.
Abstract: The combined production of mechanical or electrical and thermal energy using a simple energy source affords remarkable energy savings and in many cases makes it possible to operate with greater efficiency when compared to a system producing heat and power separately. The economic optimisation in the design and operation of a combined heat and power (CHP) unit is usually performed through an examination of the investment criteria. In spite of the numerous criteria available, virtually the only ones used to determine whether to reject or to accept a project have been the net present value (NPV), internal rate of return (IRR) and payback period (PP). The aim of this paper is to develop a clear description and understanding of the uses and limitations of many different project evaluation techniques and to show when these methods are connected and are applicable to cogeneration plants. With this end in mind the different techniques will be applied to the selection between two CHP units for a tyre factory in Spain.
TL;DR: In this paper, the results of a performance study on v-groove solar air collector for drying applications indicate better thermal efficiency for a v-corrugated collector compared to a flat plate collector effects of operating variables on the thermal performance have been investigated and the results show that the temperature of the fluid at the exit of the collector decreases with flow rate resulting in an increase of efficiency due to decreased thermal losses to the environment.
Abstract: This paper reports the results of a performance study on v-groove solar air collector for drying applications Experimental results indicate better thermal efficiency for a v-corrugated collector compared to a flat plate collector Effects of operating variables on the thermal performance have been investigated The results show that the temperature of the fluid at the exit of the collector decreases with flow rate resulting in an increase of efficiency due to decreased thermal losses to the environment After a certain flow rate, these changes become less significant Flow rate of 0035 kg/m2 s is recommended for most drying purposes in consideration of collector efficiency and outlet temperature
TL;DR: In this article, a hydrate-based refrigeration system based on a novel conceptual design is presented, which forms a closed cycle, which is more or less analogous to the conventional vapor-compression refrigeration cycle.
Abstract: This paper gives a preliminary overview of our attempt at developing a hydrate-based refrigeration system based on a novel conceptual design. The system forms a closed cycle, which is more or less analogous to the conventional vapor-compression refrigeration cycle. The cycle of present interest is performed by a multiphase refrigerant, which is typically a mixture of one or two hydrate-forming substances and water. The refrigerant is required to form a hydrate at a temperature as high as ∼30 °C or above, desirably under a modest pressure, such that the heat released by the exothermic hydrate formation can be efficiently removed by an environmental fluid such as the atmospheric air, groundwater or river water. The hydrate slurry thus formed is depressurized to dissociate at a lower temperature, typically 5–9 °C, thereby absorbing heat from a space to be refrigerated. To confirm the feasibility of the above conceptual design of the hydrate-based refrigeration system, a thermodynamic analysis of the system and a simulation of its operation have been performed. Also a laboratory-scale refrigerator based on the above design was constructed and tested. The paper summarizes the results of these efforts to show the potential advantages of the hydrate-based refrigeration system over conventional ones and to give the prospects of our refrigeration-system development.
TL;DR: In this article, two typical types of small-scale natural gas liquefaction process in skid-mounted package were designed and simulated and the key parameters of the two processes were compared, and the matching of the heating and cooling curves in heat exchangers was also analyzed.
Abstract: Two typical types of small-scale natural gas liquefaction process in skid-mounted package were designed and simulated. The key parameters of the two processes were compared, and the matching of the heating and cooling curves in heat exchangers was also analyzed. The results show that the N2–CH4 expander cycle precedes the mixed-refrigerant cycle on the premise of lacking propane pre-cooling. Large temperature difference and heat exchange load are the primary reasons of exergy loss in heat exchangers. The power consumption of compressors is influential to power consumption per unit LNG, so compression with intercooling should be adopted.
TL;DR: In this article, an air-blast simulation is described using Eulerian multi-material formulation, and a comparison of two examples with experimental results is performed to validate the numerical approach and prove its ability for high pressure wave propagation.
Abstract: The accurate numerical simulation of air-blast is an industrial concern. Because the experimental investigation of these fast transient events is expensive and time-consuming, several numerical approaches of air explosion are carried out. In this paper, an air-blast simulation is described using Eulerian multi-material formulation. In order to validate the numerical approach and prove its ability for high pressure wave propagation, comparison of two examples with experimental results is performed. Both simulations lead to the same prediction for the pressure time history. Good agreement between the test results and the predicted pressure response is achieved.
TL;DR: In this paper, the influence of errors in measured variables and geometric and heat transmission parameters on the results of a diagnosis combustion model for direct injection diesel engines have been studied, and a simulated pressure cycle has been used along with known input parameters, so that any uncertainty in the inputs is avoided.
Abstract: Thermodynamic diagnosis models are valuable tools for the study of Diesel combustion. Inputs required by such models comprise measured mean and instantaneous variables, together with suitable values for adjustable parameters used in different submodels. In the case of measured variables, one may estimate the uncertainty associated with measurement errors; however, the influence of errors in model parameter estimation may not be so easily established on an experimental basis. In this paper, a simulated pressure cycle has been used along with known input parameters, so that any uncertainty in the inputs is avoided. Then, the influence of errors in measured variables and geometric and heat transmission parameters on the results of a diagnosis combustion model for direct injection diesel engines have been studied. This procedure allowed to establish the relative importance of these parameters and to set limits to the maximal errors of the model, accounting for both the maximal expected errors in the input parameters and the sensitivity of the model to those errors.
TL;DR: In this paper, the performance and NOx and hydrocarbon emissions of a diesel engine operating on a typical diesel oil emulsion and examine through the use of heat release analysis differences found during its combustion relative to standard diesel in the same engine.
Abstract: Emulsions of diesel and water are often promoted as being able to overcome the difficulty of simultaneously reducing emissions of both oxidises of nitrogen (NOx) and particulate matter from diesel engines. In this paper we present measurements of the performance and NOx and hydrocarbon emissions of a diesel engine operating on a typical diesel oil emulsion and examine through the use of heat release analysis differences found during its combustion relative to standard diesel in the same engine. While producing similar or greater thermal efficiency and improved NOx and hydrocarbon emission outcomes, use of the emulsion also results in an increase in brake specific fuel consumption. Use of the emulsion is also shown to result in a retarded fuel injection, but smaller ignition delay for the same engine timing. As a result of these changes, cylinder pressures and temperatures are lower.
TL;DR: In this paper, the authors investigated solutions that may improve cooling performance of cooling towers in windy days, with particular interest in wind-break methods in and around towers, and analyzed the relationship between the cooling efficiency recovery and the size of wind break walls, indicating an optimal scale of windbreak walls.
Abstract: Cross-wind can significantly reduce cooling efficiency of natural-draft dry-cooling towers. This paper investigates solutions that may improve cooling performance of cooling towers in windy days, with particular interest in wind-break methods in and around towers. The study explores a realistic scenario with two cooling towers in-tandem arranged under cross-wind conditions. Both experimental and numerical approaches were employed to optimize the wind-break measures. The results show that wind-break walls placed at the lateral sides of cooling towers perpendicular to the cross-wind is a straightforward and effective method, which can recover about 50% of the reduced cooling capacity. The study analyzes the relationship between the cooling efficiency recovery and the size of wind-break walls, indicating an optimal scale of wind-break walls.
TL;DR: In this paper, the authors considered the thermodynamic, economic and emission criteria regarding both CO 2 and NO x emissions of a distributed combined heating, cooling and power generation (tri-generation) system in an urban residential area in Beijing.
Abstract: A simultaneous consideration of the thermodynamic, economic and emission criteria regarding both CO 2 and NO x emissions of a distributed combined heating, cooling and power generation (tri-generation) system in an urban residential area in Beijing has been realized through thermo-economic optimization. Technologies such as gas turbine, internal combustion engine, absorption chiller and gas boiler are considered as options of the plant optimum configuration. System Net Present Value (NPV) is taken as the objective to be maximized. The presented mixed integer and non-linear programming (MINLP) problem is solved by a Genetic Algorithms (GAs) optimizer. The optimal plant configurations are found with the consideration of system configuration, design and operation under different economic and environmental legislation contexts.
TL;DR: In this article, a simulation study on the operating performance of a new type of solar-air source heat pump water heater (SAS-HPWH) has been presented, which used a specially designed flat-plate heat collector/evaporator with spiral-finned tubes to obtain energy from both solar irradiation and ambient air for hot water heating.
Abstract: A simulation study on the operating performance of a new type of solar–air source heat pump water heater (SAS-HPWH) has been presented. The SAS-HPWH used a specially designed flat-plate heat collector/evaporator with spiral-finned tubes to obtain energy from both solar irradiation and ambient air for hot water heating. Using the meteorological data in Nanjing, China, the simulation results based on 150 L water heating capacity showed that such a SAS-HPWH can heat water up to 55 °C efficiently under various weather conditions all year around. In this simulation study, the influences of solar radiation, ambient temperature and compressor capacity on the performance of the SAS-HPWH were analyzed. In order to improve the overall operating performance, the use of a variable-capacity compressor has been proposed.
TL;DR: In this article, two different types of hydrophobic coatings have been analyzed experimentally for their ability to promote dropwise condensation (DWC) for more than 2600 h of experimentation and it showed good dropwise phenomena.
Abstract: Two different types of hydrophobic coatings have been analyzed experimentally for their ability to promote dropwise condensation (DWC). For any technique used for promoting dropwise condensation, the longevity of the coating is critical if it is to be used in any further applications. Previous studies using self-assembled monolayers of n-octadecyl mercaptan have not reported any information on the ability for promoting DWC beyond 500 h of experimentation. In the current research experiments were carried out using self-assembled monolayers for more than 2600 h of experimentation and it showed good dropwise phenomena. Stearic acid solution (SAM-1) and n-octadecyl mercaptan solution (SAM-2) were used to form an ultra-thin organic hydrophobic film on the surface. An oxide layer was initially formed on the substrate surface before coating the surface with monolayers. The oxide layer formed on the substrate surface tends to improve the bonding between the substrate and the monolayers which eventually improves the longevity of the coating. In general, a SAM system with a long-chain, hydrophobic group is nano-resistant, meaning that such a system forms a protective hydrophobic layer with negligible heat transfer resistance but a much stronger bond. When compared to complete filmwise condensation, the SAM-2 (n-octadecyl mercaptan) coating increased the condensation heat transfer coefficient by a factor of approximately 3 after 100 h of experimentation and by a factor of approximately 1.8 after 2600 h of experimentation for copper alloy surfaces, under vacuum condition (33.86 kPa). Lifetime of maintaining dropwise condensation is greatly dependent on the bonding of SAM coating to the condensing surface, form the experimental investigation it was evident that n-octadecyl mercaptan showed good DWC due to its covalent bonding with the substrate surface when compared to that of stearic acid which is bonded to the substrate surface by hydrogen bonding. Contact angles were measured for all the SAM coated surfaces before and after experimentation, respectively.