Second and higher-order perturbations of a spherical spacetime

The Gerlach and Sengupta (GS) formalism of coordinate-invariant, first-order, spherical and nonspherical perturbations around an arbitrary spherical spacetime is generalized to higher orders, focusing on second-order perturbation theory. The GS harmonics are generalized to an arbitrary number of indices on the unit sphere and a formula is given for their products. The formalism is optimized for its implementation in a computer algebra system, something that becomes essential in practice given the size and complexity of the equations. All evolution equations for the second-order perturbations, as well as the conservation equations for the energy-momentum tensor at this perturbation order, are given in covariant form, in Regge-Wheeler gauge.Comment: Accepted for publication in Physical Review

Numerical Optimization of an Ejector for Waste Heat Recovery Used to Cool Down the Intake Air in an Internal Combustion Engine

[EN] In the present paper, a numerical investigation of a jet-ejector is carried out using a real gas model of R1234yf. The prototype under investigation works with specific operating conditions of a jet-ejector refrigeration system intended for waste heat recovery in an internal combustion engine (ICE). In the first instance, the geometry optimization involving nozzle exit diameter, mixing chamber diameter, and nozzle exit position (NXP) is performed. Once the optimum geometry has been obtained, the jet-ejector prototype is tested with different operating pressure ratios to determine its off-design performance. The flow structure in relevant cases has been examined with an emphasis on critical and subcritical modes. The flow phenomena occurring during expansion, entrainment, and mixing processes are discussed so performance degradation can be directly related to physical processes. The analysis has been completed fitting simulated points to critical and subcritical planar surfaces. The results in terms of goodness of fit are satisfactory so the jet-ejector performance in off-design operating conditions can be reflected through simple mathematic models. When the overall cycle is assessed by using previous computational fluid dynamics (CFD) maps, it is observed that the achievable cooling drops significantly when an ambient temperature of 31 degrees C is exceeded.The authors want to acknowledge the institution "Conselleria d'Educacio, Investigacio, Cultura i Esport de la Generalitat Valenciana" and its grant program "Subvenciones para la contratacion de personal investigador de caracter predoctoral" for doctoral studies (ACIF/2018/124).Galindo, J.; Gil, A.; Dolz, V.; Ponce-Mora, A. (2020). Numerical Optimization of an Ejector for Waste Heat Recovery Used to Cool Down the Intake Air in an Internal Combustion Engine. Journal of Thermal Science and Engineering Applications. 12(5):1-13. https://doi.org/10.1115/1.4046906S113125Varga, S., Oliveira, A. C., & Diaconu, B. (2009). Influence of geometrical factors on steam ejector performance – A numerical assessment. International Journal of Refrigeration, 32(7), 1694-1701. doi:10.1016/j.ijrefrig.2009.05.009Yan, J., Cai, W., & Li, Y. (2012). Geometry parameters effect for air-cooled ejector cooling systems with R134a refrigerant. Renewable Energy, 46, 155-163. doi:10.1016/j.renene.2012.03.031He, S., Li, Y., & Wang, R. Z. (2009). Progress of mathematical modeling on ejectors. Renewable and Sustainable Energy Reviews, 13(8), 1760-1780. doi:10.1016/j.rser.2008.09.032Zhu, Y., Cai, W., Wen, C., & Li, Y. (2009). Numerical investigation of geometry parameters for design of high performance ejectors. Applied Thermal Engineering, 29(5-6), 898-905. doi:10.1016/j.applthermaleng.2008.04.025Jia, Y., & Wenjian, C. (2012). Area ratio effects to the performance of air-cooled ejector refrigeration cycle with R134a refrigerant. Energy Conversion and Management, 53(1), 240-246. doi:10.1016/j.enconman.2011.09.002Wang, L., Yan, J., Wang, C., & Li, X. (2017). Numerical study on optimization of ejector primary nozzle geometries. International Journal of Refrigeration, 76, 219-229. doi:10.1016/j.ijrefrig.2017.02.010Ruangtrakoon, N., Thongtip, T., Aphornratana, S., & Sriveerakul, T. (2013). CFD simulation on the effect of primary nozzle geometries for a steam ejector in refrigeration cycle. International Journal of Thermal Sciences, 63, 133-145. doi:10.1016/j.ijthermalsci.2012.07.009Dong, J., Kang, C. L., Wang, H. M., & Ma, H. B. (2016). Experimental Investigation of Steam Ejector System With an Extra Low Generating Temperature. Journal of Thermal Science and Engineering Applications, 8(2). doi:10.1115/1.4032483Soroureddin, A., Mehr, A. S., Mahmoudi, S., & Yari, M. (2013). An experimental and theoretical study of a jet-pump refrigeration system designed using a new two-dimensional model for the entrainment region of the ejector. Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy, 227(4), 486-497. doi:10.1177/0957650913477092Zhu, Y., & Jiang, P. (2014). Experimental and analytical studies on the shock wave length in convergent and convergent–divergent nozzle ejectors. Energy Conversion and Management, 88, 907-914. doi:10.1016/j.enconman.2014.09.023Zhu, Y., & Jiang, P. (2014). Experimental and numerical investigation of the effect of shock wave characteristics on the ejector performance. International Journal of Refrigeration, 40, 31-42. doi:10.1016/j.ijrefrig.2013.11.008Sargolzaei, J., Pirzadi Jahromi, M. R., & Saljoughi, E. (2010). Triple-Choking Model for Ejector. Journal of Thermal Science and Engineering Applications, 2(2). doi:10.1115/1.4002752Armstead, J. R., & Miers, S. A. (2013). Review of Waste Heat Recovery Mechanisms for Internal Combustion Engines. Journal of Thermal Science and Engineering Applications, 6(1). doi:10.1115/1.4024882Luján, J. M., Climent, H., Dolz, V., Moratal, A., Borges-Alejo, J., & Soukeur, Z. (2016). Potential of exhaust heat recovery for intake charge heating in a diesel engine transient operation at cold conditions. Applied Thermal Engineering, 105, 501-508. doi:10.1016/j.applthermaleng.2016.03.028Aghaali, H., & Ångström, H.-E. (2015). A review of turbocompounding as a waste heat recovery system for internal combustion engines. Renewable and Sustainable Energy Reviews, 49, 813-824. doi:10.1016/j.rser.2015.04.144Hsiao, Y. Y., Chang, W. C., & Chen, S. L. (2010). A mathematic model of thermoelectric module with applications on waste heat recovery from automobile engine. Energy, 35(3), 1447-1454. doi:10.1016/j.energy.2009.11.030In, B. D., & Lee, K. H. (2015). A study of a thermoelectric generator applied to a diesel engine. Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering, 230(1), 133-143. doi:10.1177/0954407015576440Dolz, V., Novella, R., García, A., & Sánchez, J. (2012). HD Diesel engine equipped with a bottoming Rankine cycle as a waste heat recovery system. Part 1: Study and analysis of the waste heat energy. Applied Thermal Engineering, 36, 269-278. doi:10.1016/j.applthermaleng.2011.10.025Aly, S. E. (1988). Diesel engine waste-heat power cycle. Applied Energy, 29(3), 179-189. doi:10.1016/0306-2619(88)90027-xGalindo, J., Ruiz, S., Dolz, V., Royo-Pascual, L., Haller, R., Nicolas, B., & Glavatskaya, Y. (2015). Experimental and thermodynamic analysis of a bottoming Organic Rankine Cycle (ORC) of gasoline engine using swash-plate expander. Energy Conversion and Management, 103, 519-532. doi:10.1016/j.enconman.2015.06.085Glover, S., Douglas, R., Glover, L., & McCullough, G. (2014). Preliminary analysis of organic Rankine cycles to improve vehicle efficiency. Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering, 228(10), 1142-1153. doi:10.1177/0954407014528904Zegenhagen, M. T., & Ziegler, F. (2015). Feasibility analysis of an exhaust gas waste heat driven jet-ejector cooling system for charge air cooling of turbocharged gasoline engines. Applied Energy, 160, 221-230. doi:10.1016/j.apenergy.2015.09.057Novella, R., Dolz, V., Martín, J., & Royo-Pascual, L. (2017). Thermodynamic analysis of an absorption refrigeration system used to cool down the intake air in an Internal Combustion Engine. Applied Thermal Engineering, 111, 257-270. doi:10.1016/j.applthermaleng.2016.09.084Galindo, J., Dolz, V., Tiseira, A., & Ponce-Mora, A. (2019). Thermodynamic analysis and optimization of a jet ejector refrigeration cycle used to cool down the intake air in an IC engine. International Journal of Refrigeration, 103, 253-263. doi:10.1016/j.ijrefrig.2019.04.019Galindo, J., Serrano, J., Dolz, V., & Kleut, P. (2015). Brayton cycle for internal combustion engine exhaust gas waste heat recovery. Advances in Mechanical Engineering, 7(6), 168781401559031. doi:10.1177/1687814015590314Zegenhagen, M. T., & Ziegler, F. (2015). Experimental investigation of the characteristics of a jet-ejector and a jet-ejector cooling system operating with R134a as a refrigerant. International Journal of Refrigeration, 56, 173-185. doi:10.1016/j.ijrefrig.2015.01.001Chen, X., Worall, M., Omer, S., Su, Y., & Riffat, S. (2013). Theoretical studies of a hybrid ejector CO2 compression cooling system for vehicles and preliminary experimental investigations of an ejector cycle. Applied Energy, 102, 931-942. doi:10.1016/j.apenergy.2012.09.032Sriveerakul, T., Aphornratana, S., & Chunnanond, K. (2007). Performance prediction of steam ejector using computational fluid dynamics: Part 2. Flow structure of a steam ejector influenced by operating pressures and geometries. International Journal of Thermal Sciences, 46(8), 823-833. doi:10.1016/j.ijthermalsci.2006.10.012Bartosiewicz, Y., Aidoun, Z., Desevaux, P., & Mercadier, Y. (2005). Numerical and experimental investigations on supersonic ejectors. International Journal of Heat and Fluid Flow, 26(1), 56-70. doi:10.1016/j.ijheatfluidflow.2004.07.003Mazzelli, F., Little, A. B., Garimella, S., & Bartosiewicz, Y. (2015). Computational and experimental analysis of supersonic air ejector: Turbulence modeling and assessment of 3D effects. International Journal of Heat and Fluid Flow, 56, 305-316. doi:10.1016/j.ijheatfluidflow.2015.08.003Mazzelli, F., & Milazzo, A. (2015). Performance analysis of a supersonic ejector cycle working with R245fa. International Journal of Refrigeration, 49, 79-92. doi:10.1016/j.ijrefrig.2014.09.020Croquer, S., Poncet, S., & Aidoun, Z. (2016). Turbulence modeling of a single-phase R134a supersonic ejector. Part 1: Numerical benchmark. International Journal of Refrigeration, 61, 140-152. doi:10.1016/j.ijrefrig.2015.07.030Lee, Y., & Jung, D. (2012). A brief performance comparison of R1234yf and R134a in a bench tester for automobile applications. Applied Thermal Engineering, 35, 240-242. doi:10.1016/j.applthermaleng.2011.09.004Vaghela, J. K. (2017). Comparative Evaluation of an Automobile Air - Conditioning System Using R134a and Its Alternative Refrigerants. Energy Procedia, 109, 153-160. doi:10.1016/j.egypro.2017.03.083Wang, L., Liu, J., Zou, T., Du, J., & Jia, F. (2018). Auto-tuning ejector for refrigeration system. Energy, 161, 536-543. doi:10.1016/j.energy.2018.07.110Chen, S., Chen, G., & Fang, L. (2015). An experimental study and 1-D analysis of an ejector with a movable primary nozzle that operates with R236fa. International Journal of Refrigeration, 60, 19-25. doi:10.1016/j.ijrefrig.2015.08.011Zegenhagen, M. T., & Ziegler, F. (2015). A one-dimensional model of a jet-ejector in critical double choking operation with R134a as a refrigerant including real gas effects. International Journal of Refrigeration, 55, 72-84. doi:10.1016/j.ijrefrig.2015.03.013Besagni, G., Mereu, R., Chiesa, P., & Inzoli, F. (2015). An Integrated Lumped Parameter-CFD approach for off-design ejector performance evaluation. Energy Conversion and Management, 105, 697-715. doi:10.1016/j.enconman.2015.08.029Gagan, J., Smierciew, K., Butrymowicz, D., & Karwacki, J. (2014). Comparative study of turbulence models in application to gas ejectors. International Journal of Thermal Sciences, 78, 9-15. doi:10.1016/j.ijthermalsci.2013.11.009Hakkaki-Fard, A., Aidoun, Z., & Ouzzane, M. (2015). A computational methodology for ejector design and performance maximisation. Energy Conversion and Management, 105, 1291-1302. doi:10.1016/j.enconman.2015.08.070Besagni, G., & Inzoli, F. (2017). Computational fluid-dynamics modeling of supersonic ejectors: Screening of turbulence modeling approaches. Applied Thermal Engineering, 117, 122-144. doi:10.1016/j.applthermaleng.2017.02.011Pianthong, K., Seehanam, W., Behnia, M., Sriveerakul, T., & Aphornratana, S. (2007). Investigation and improvement of ejector refrigeration system using computational fluid dynamics technique. Energy Conversion and Management, 48(9), 2556-2564. doi:10.1016/j.enconman.2007.03.021Richter, M., McLinden, M. O., & Lemmon, E. W. (2011). Thermodynamic Properties of 2,3,3,3-Tetrafluoroprop-1-ene (R1234yf): Vapor Pressure and p–ρ–T Measurements and an Equation of State. Journal of Chemical & Engineering Data, 56(7), 3254-3264. doi:10.1021/je200369mGarcía del Valle, J., Saíz Jabardo, J. M., Castro Ruiz, F., & San José Alonso, J. F. (2014). An experimental investigation of a R-134a ejector refrigeration system. International Journal of Refrigeration, 46, 105-113. doi:10.1016/j.ijrefrig.2014.05.028Poles, S., Geremia, P., Campos, F., Weston, S., & Islam, M. (s. f.). MOGA-II for an Automotive Cooling Duct Optimization on Distributed Resources. Evolutionary Multi-Criterion Optimization, 633-644. doi:10.1007/978-3-540-70928-2_4

FaMa-OVM: a Tool for the Automated Analysis of Ovms

Orthogonal Variability Model (OVM) is a modelling language for representing variability in Software Product Line Engineering. The automated analysis of OVMs is defined as the computer-aided extraction of information from such models. in this paper, we present FaMa-OVM, which is a pioneer tool for the automated analysis of OVMs. FaMa-OVM is easy to extend or integrate in other tools. It has been developed as part of the FaMa ecosystem enabling the benefits coming from other tools of that ecosystem as FaMaFW and BeTTy

Tool Supported Error Detection and Explanations on Feature Models

Automated analysis of feature models (FM) is a field of interest in recent years. Many operations over FMs have been proposed and developed, and many researchers and industrial companies have adopted FMs as a way to express variability. This last makes more necessary having support to detect, explain and fix errors on FMs. The notation of FMs makes very easy to express variability, but makes hard detecting errors and find their cause manually. and these errors may cause the model does not express the variability what we want of it. Therefore, we need support to detect errors and find their causes. The contribution of this paper is a method to detect errors in FMs, based on the concept of observation. We also present implementations of this approach and of an approach to explain errors, in FaMa Framework [1] tool. To detect FM errors, firstly we have to identify the different error types and what it means each of them. Void FM error means that the FM does not represent any product, dead feature error means that a feature of the FM does not appear in any product, false optional error means that an optional feature appears in every product that its parent feature also appears, and wrong cardinality error means that one or more values of a set relationship cardinality are not reachable. We can check for these errors in a intuitive way. For instance, to detect if a FM has dead features, we can calculate every product and check if each feature appears in, at least, one product. But further, we propose a method based on observations, it means, FM configurations associated with a specific element (feature or cardinality). Each type of error has its type of observation associated too. With an algorithm, we calculate the set of observations of a FM. Then, for each observation, we check if FM has at least one product. If not, we have found an error. For instance, dead feature observation sets its feature as selected. If the FM with a dead feature observation is not valid, it means the feature we are checking is dead. When we have found the errors, explanations tell us what is the cause of each error. An explanation is a set of relationships that originates one or more errors. Changing or removing these relationships we can fix a error. However, explanations by themselves do not provide information about how to change the relationship. For instance, if an explanation about a dead feature is a mandatory relationship, we can turn it into a optional relationship, but the explanation does not tell us directly. We have implemented observations and explanations approaches in FaMa Framework, a tool for the automated analysis of FMs. The observations approach implemented is the previously mentioned, while the explanations approach implemented is the one described by Trinidad et al. [3] [4]. With these approaches, we have detected errors in SPLOT FM repository [2], and we have obtained explanations for them also

A Variability-Based Testing Approach for Synthesizing Video Sequences

A key problem when developing video processing software is the di culty to test di erent input combinations. In this paper, we present VANE, a variability-based testing approach to derive video sequence variants. The ideas of VANE are i) to encode in a variability model what can vary within a video sequence; ii) to exploit the variability model to generate testable con gurations; iii) to synthesize variants of video sequences corresponding to con gurations. VANE computes T-wise covering sets while optimizing a function over attributes. Also, we present a preliminary validation of the scalability and practicality of VANE in the context of an industrial project involving the test of video processing algorithms.Ministerio de Economía y Competitividad TIN2012-32273Junta de Andalucía TIC-5906Junta de Andalucía P12-TIC-186

Obtaining of repair lime renders with microencapsulated phase change materials: optimization of the composition, application, mechanical and microstructural studies

Different batches of repair lime rendering mortars were designed by mixing microencapsulated Phase Change Materials (PCMs) and other additives. The final aim of these renders is to improve the thermal efficiency of the envelope of the Built Heritage, while allowing the practitioners to apply a render with positive final performance. The combinations of the PCMs in different weight percentages, a superplasticiser (to increase the fluidity of the render keeping constant the mixing water), an adhesion improver and a pozzolanic additive were studied. The adhesion of these renders onto bricks and limestone specimens and the shrinkage and cracking of the mortars were studied in detail. X-ray diffraction technique was used to study the composition and evolution of the carbonation process. Compressive strength measurements were studied in hardened specimens. In addition, the porous structure of the rendering mortars was studied by mercury intrusion porosimetry to assess the effect of the PCMs' addition. Samples underwent accelerated climatic ageing to study their durability and the preservation of the thermal efficiency. Results have shown that these thermally enhanced mortars are feasible materia Is for real-life application in the context of architectural heritage restoration and conservation

Enhancement of latent heat storage capacity of lime rendering mortars

Microencapsulated Phase Change Materials (PCMs) were included in air lime rendering mortars in order to improve the thermal comfort of the inhabitants and the energy efficiency of buildings of the Architectural Heritage under the premises of mínimum intervention and maximum compatibility. Three different PCMs were tested and directly added during the mixing process to fresh air lime mortars in three different percentages: 5, 10 and 20 wt. %. Some chemical additives were also incorporated to improve the final performance of the renders: a starch derivative as an adhesion booster; metakaolin as pozzolanic addition to shorten the setting time and to increase the final strength; anda polycarboxylated ether as a superplasticizer to adjust the fluidity of the fresh renders avoiding an excess of mixing water. The specific heat Cp, the enthalpy ti.H ascribed to the phase change and the melting temperature of the PCMs were determined by Differential Scanning Calorimetry (DSC). The capacity of the renders to store/release heat was demonstrated at a laboratory scale. The favourable results proved the effect of these PCMs with respect to the thermal performance of these rendering mortars, offering a promising way of enhancement of the thermal efficiency of building materia Is of the Cultural Heritage

Dynamic tests and adaptive control of a bottoming organic Rankine cycle of IC engine using swash-plate expander

This paper deals with the experimental testing of a bottoming Organic Rankine Cycle (ORC) integrate in a 2 l turbocharged gasoline engine using ethanol as working fluid. The main components of the cycle are a boiler, a condenser, a pump and a swash-plate expander. Both steady and transient tests were performed in three engine operating points to understand the behavior and inertia of the system. Pressure-Volume diagram during these transients were presented and analyzed. Operating parameters of the expander, such as expander speed and boiler power, were shifted. The objective of these tests is to understand the inertia of the system and to have a robust control in all the possible transient tests. New European Driving Cycle was tested with and without the expander because it is supposed to represent the typical usage of a car in Europe. It was used to validate the control of the ORC in realistic dynamic conditions of the engine. The importance of each parameter was analyzed by fixing all the parameters, changing each time one specific value. The main result of this paper is that using a slightly simple and robust control based on adaptive PIDs, the two dynamic effects of an ORC could be taken into account, i.e. high inertia effects (boiler and condenser) and low inertia effects (pump and volumetric expander).This work is part of a research project called "Evaluation of bottoming cycles in IC engines to recover waste heat energies" funded by a National Project of the Spanish Government with reference TRA2013-46408-R. The authors thank also to Raul Lujan and Rafael Carrascosa for their contribution in the testing process. Authors want to acknowledge the "Apoyo para la investigacion y Desarrollo (PAID)" grant for doctoral studies (FPI S2 2015 1067).Torregrosa, AJ.; Galindo, J.; Dolz Ruiz, V.; Royo-Pascual, L.; Haller, R.; Melis, J. (2016). Dynamic tests and adaptive control of a bottoming organic Rankine cycle of IC engine using swash-plate expander. Energy Conversion and Management. 126:168-176. https://doi.org/10.1016/j.enconman.2016.07.078S16817612