Sustainable earth walls to meet the building regulations

The thermal conductivity and diffusivity of un-fired clay bricks, a straw clay mixture and straw bales have been measured using a thermal probe technique, with an iterative method for data analysis. The steady-state air-to-air thermal transmittance, or U-value, and the time-dependent thermal properties of some proposed sustainable earth wall constructions are presented. Sustainable cavity walls of un-fired clay bricks with paper, straw or wool cavity insulation have thermal transmittances less than 0.35 W/m2 K, and therefore meet the current United Kingdom Building Regulations. A review of possible methods for thermally up-grading existing earth walls, by adding an internal insulated timber frame construction, again demonstrates possible compliance with the current UK thermal regulations

Developing Computational Fluid Dynamics (CFD) Models to Evaluate Available Energy in Exhaust Systems of Diesel Light-Duty Vehicles

[EN] Around a third of the energy input in an automotive engine is wasted through the exhaust system. Since numerous technologies to harvest energy from exhaust gases are accessible, it is of great interest to find time- and cost-efficient methods to evaluate available thermal energy under different engine conditions. Computational fluid dynamics (CFD) is becoming a very valuable tool for numerical predictions of exhaust flows. In this work, a methodology to build a simple three-dimensional (3D) model of the exhaust system of automotive internal combustion engines (ICE) was developed. Experimental data of exhaust gas in the most used part of the engine map in passenger diesel vehicles were employed as input for calculations. Sensitivity analyses of different numeric schemes have been conducted in order to attain accurate results. The model built allows for obtaining details on temperature and pressure fields along the exhaust system, and for complementing the experimental results for a better understanding of the flow phenomena and heat transfer through the system for further energy recovery devices.Authors wish to thank the financial support provided by the Spanish Ministry of Economy and Competitiveness to the project POWER Ref. ENE2014-57043-R and Universidad de Castilla-la Mancha for the pre-doctoral funding [2015/4062].Fernández-Yáñez, P.; Armas Vergel, O.; Gómez, A.; Gil, A. (2017). Developing Computational Fluid Dynamics (CFD) Models to Evaluate Available Energy in Exhaust Systems of Diesel Light-Duty Vehicles. Applied Sciences. 7(6):1-20. https://doi.org/10.3390/app7060590S12076Hossain, S. N., & Bari, S. (2014). Waste Heat Recovery from Exhaust of a Diesel Generator Set Using Organic Fluids. Procedia Engineering, 90, 439-444. doi:10.1016/j.proeng.2014.11.753Galindo, J., Dolz, V., Royo-Pascual, L., Haller, R., & Melis, J. (2016). Modeling and Experimental Validation of a Volumetric Expander Suitable for Waste Heat Recovery from an Automotive Internal Combustion Engine Using an Organic Rankine Cycle with Ethanol. Energies, 9(4), 279. doi:10.3390/en9040279Zhang, X., & Romzek, M. (2008). Computational Fluid Dynamics (CFD) Applications in Vehicle Exhaust System. SAE Technical Paper Series. doi:10.4271/2008-01-0612Konstantinidis, P. A., Koltsakis, G. C., & Stamatelos, A. M. (1997). Transient heat transfer modelling in automotive exhaust systems. Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, 211(1), 1-15. doi:10.1243/0954406971521610Kandylas, I. P., & Stamatelos, A. M. (1999). Engine exhaust system design based on heat transfer computation. Energy Conversion and Management, 40(10), 1057-1072. doi:10.1016/s0196-8904(99)00008-4Guardiola, C., Dolz, V., Pla, B., & Mora, J. (2016). Fast estimation of diesel oxidation catalysts inlet gas temperature. Control Engineering Practice, 56, 148-156. doi:10.1016/j.conengprac.2016.08.020Shayler, P. J., Hayden, D. J., & Ma, T. (1999). Exhaust System Heat Transfer and Catalytic Converter Performance. SAE Technical Paper Series. doi:10.4271/1999-01-0453Kapparos, D. J., Foster, D. E., & Rutland, C. J. (2004). Sensitivity Analysis of a Diesel Exhaust System Thermal Model. SAE Technical Paper Series. doi:10.4271/2004-01-1131Fu, H., Chen, X., Shilling, I., & Richardson, S. (2005). A One-Dimensional Model for Heat Transfer in Engine Exhaust Systems. SAE Technical Paper Series. doi:10.4271/2005-01-0696Fortunato, F., Caprio, M., Oliva, P., D’Aniello, G., Pantaleone, P., Andreozzi, A., & Manca, O. (2007). Numerical and Experimental Investigation of the Thermal Behavior of a Complete Exhaust System. SAE Technical Paper Series. doi:10.4271/2007-01-1094Liu, X., Deng, Y. D., Zhang, K., Xu, M., Xu, Y., & Su, C. Q. (2014). Experiments and simulations on heat exchangers in thermoelectric generator for automotive application. Applied Thermal Engineering, 71(1), 364-370. doi:10.1016/j.applthermaleng.2014.07.022Hamedi, M. R., Tsolakis, A., & Herreros, J. M. (2014). Thermal Performance of Diesel Aftertreatment: Material and Insulation CFD Analysis. SAE Technical Paper Series. doi:10.4271/2014-01-2818Voltz, S. E., Morgan, C. R., Liederman, D., & Jacob, S. M. (1973). Kinetic Study of Carbon Monoxide and Propylene Oxidation on Platinum Catalysts. Industrial & Engineering Chemistry Product Research and Development, 12(4), 294-301. doi:10.1021/i360048a006Oh, S. H., & Cavendish, J. C. (1982). Transients of monolithic catalytic converters. Response to step changes in feedstream temperature as related to controlling automobile emissions. Industrial & Engineering Chemistry Product Research and Development, 21(1), 29-37. doi:10.1021/i300005a006Dubien, C., Schweich, D., Mabilon, G., Martin, B., & Prigent, M. (1998). Three-way catalytic converter modelling: fast- and slow-oxidizing hydrocarbons, inhibiting species, and steam-reforming reaction. Chemical Engineering Science, 53(3), 471-481. doi:10.1016/s0009-2509(97)00313-8Koltsakis, G. C., Konstantinidis, P. A., & Stamatelos, A. M. (1997). Development and application range of mathematical models for 3-way catalytic converters. Applied Catalysis B: Environmental, 12(2-3), 161-191. doi:10.1016/s0926-3373(96)00073-2Wurzenberger, J. C., Wanker, R., & Schüßler, M. (2008). Simulation of Exhaust Gas Aftertreatment Systems - Thermal Behavior During Different Operating Conditions. SAE Technical Paper Series. doi:10.4271/2008-01-0865Guojiang, W., & Song, T. (2005). CFD simulation of the effect of upstream flow distribution on the light-off performance of a catalytic converter. Energy Conversion and Management, 46(13-14), 2010-2031. doi:10.1016/j.enconman.2004.11.001Hayes, R. E., Fadic, A., Mmbaga, J., & Najafi, A. (2012). CFD modelling of the automotive catalytic converter. Catalysis Today, 188(1), 94-105. doi:10.1016/j.cattod.2012.03.015Chatterjee, D., Deutschmann, O., & Warnatz, Jã¼. (2001). Detailed surface reaction mechanism in a three-way catalyst. Faraday Discussions, 119(1), 371-384. doi:10.1039/b101968fKumar, R., Sonthalia, A., & Goel, R. (2011). Experimental study on waste heat recovery from an IC engine using thermoelectric technology. Thermal Science, 15(4), 1011-1022. doi:10.2298/tsci100518053kPong, H., Wallace, J., & Sullivan, P. E. (2012). Modeling of Exhaust Gas Treatment for Stationary Applications. SAE Technical Paper Series. doi:10.4271/2012-01-1300Cárdenas, M. D., Armas, O., Mata, C., & Soto, F. (2016). Performance and pollutant emissions from transient operation of a common rail diesel engine fueled with different biodiesel fuels. Fuel, 185, 743-762. doi:10.1016/j.fuel.2016.08.002Andrade, J. S., Costa, U. M. S., Almeida, M. P., Makse, H. A., & Stanley, H. E. (1999). Inertial Effects on Fluid Flow through Disordered Porous Media. Physical Review Letters, 82(26), 5249-5252. doi:10.1103/physrevlett.82.5249Benjamin, S. F., Liu, Z., & Roberts, C. A. (2004). Automotive catalyst design for uniform conversion efficiency. Applied Mathematical Modelling, 28(6), 559-572. doi:10.1016/j.apm.2003.10.008Mladenov, N., Koop, J., Tischer, S., & Deutschmann, O. (2010). Modeling of transport and chemistry in channel flows of automotive catalytic converters. Chemical Engineering Science, 65(2), 812-826. doi:10.1016/j.ces.2009.09.034Patankar, S. ., & Spalding, D. . (1972). A calculation procedure for heat, mass and momentum transfer in three-dimensional parabolic flows. International Journal of Heat and Mass Transfer, 15(10), 1787-1806. doi:10.1016/0017-9310(72)90054-3Shih, T.-H., Liou, W. W., Shabbir, A., Yang, Z., & Zhu, J. (1995). A new k-ϵ eddy viscosity model for high reynolds number turbulent flows. Computers & Fluids, 24(3), 227-238. doi:10.1016/0045-7930(94)00032-tAgudelo, A. F., García-Contreras, R., Agudelo, J. R., & Armas, O. (2016). Potential for exhaust gas energy recovery in a diesel passenger car under European driving cycle. Applied Energy, 174, 201-212. doi:10.1016/j.apenergy.2016.04.092Launder, B. E., & Spalding, D. B. (1974). The numerical computation of turbulent flows. Computer Methods in Applied Mechanics and Engineering, 3(2), 269-289. doi:10.1016/0045-7825(74)90029-

Experimental and numerical investigation of an air-to-water heat pipe-based heat exchanger

An experimental and analytical investigation was conducted on an air-to-water heat exchanger equipped with six wickless heat pipes (thermosyphons) charged with water as the working fluid. The flow pattern consisted of a double pass on the evaporator and condenser sections. The six thermosyphons were all made from carbon steel, measured 2m in length and were installed in a staggered arrangement. The objectives of the reported experimental investigation were to analyse the effect of multiple air passes at different air inlet temperatures (100 to 250°C) and air mass flow rates (0.05 to 0.14kg/s) on the thermal performance of the heat exchanger unit including the heat pipes. The results were compared with a CFD model that assumed the heat pipes were solid rods with a constant conductivity. The conductivity of the pipes was extracted from modifications of correlations available in the literature based around the theory of Thermal Resistance. The results proved to be very accurate within 10% of the experimental values

Impact of current speed on mass flux to a model flexible seagrass blade

National Science Foundation (U.S.) (Grant EAR 1140970

Thermal Dissipation and Variability in Electrical Breakdown of Carbon Nanotube Devices

We study high-field electrical breakdown and heat dissipation from carbon nanotube (CNT) devices on SiO2 substrates. The thermal "footprint" of a CNT caused by van der Waals interactions with the substrate is revealed through molecular dynamics (MD) simulations. Experiments and modeling find the CNT-substrate thermal coupling scales proportionally to CNT diameter and inversely with SiO2 surface roughness (~d/{\Delta}). Comparison of diffuse mismatch modeling (DMM) and data reveals the upper limit of thermal coupling ~0.4 W/K/m per unit length at room temperature, and ~0.7 W/K/m at 600 C for the largest diameter (3-4 nm) CNTs. We also find semiconducting CNTs can break down prematurely, and display more breakdown variability due to dynamic shifts in threshold voltage, which metallic CNTs are immune to; this poses a fundamental challenge for selective electrical breakdowns in CNT electronics

Miniature fiber‐optic refractometer for measurement of salinity in double‐diffusive thermohaline systems

This is the published version. Copyright © 1985 American Institute of PhysicsInformation on salinity and temperature distributions is important in the study of thermohaline systems. In order to overcome difficulties associated with existing measurement methods, a miniature fiber‐optic probe has been developed. The probe, which is capable of local quasisteady and fluctuating salinity and temperature measurements, is easily constructed, calibrated, and utilized. Probe measurements compare favorably with results obtained using a slant‐wire shadowgraph technique and clearly show local phenomena in double‐diffusive thermohaline systems

Thermal characteristics of a classical solar telescope primary mirror

We present a detailed thermal and structural analysis of a 2m class solar telescope mirror which is subjected to a varying heat load at an observatory site. A 3-dimensional heat transfer model of the mirror takes into account the heating caused by a smooth and gradual increase of the solar flux during the day-time observations and cooling resulting from the exponentially decaying ambient temperature at night. The thermal and structural response of two competing materials for optical telescopes, namely Silicon Carbide -best known for excellent heat conductivity and Zerodur -preferred for its extremely low coefficient of thermal expansion, is investigated in detail. The insight gained from these simulations will provide a valuable input for devising an efficient and stable thermal control system for the primary mirror.Comment: 14 pages, 8 figures, Accepted for publication in New Astronom

Reducing thermal transport in electrically conducting polymers: Effects of ordered mixing of polymer chains

Reducing the phonon thermal conductivity of electrically conducting polymers can facilitate their use as potential thermoelectric materials. Thus, the influence of the coupling between the longitudinal and transverse phonon modes on overall thermal conductivity is explored for binary mixtures of polyaniline (PANI) and polyacetylene (PA) chains by considering various geometricpolymer mixture configurations. The molecular simulations reveal that an increase in the interfacial area available for transverse interactions between dissimilar chains enhances atomic interactions that are orthogonal to the heat transfer direction. As transverse collisions between PA and PANI chains are enhanced, the motion of longitudinal phonons is disrupted, impeding thermal transport. This enhances phonon scattering and reduces longitudinal thermal transport. While there is a nonlinear decrease in the phonon thermal conductivity with increasing interfacial contact area, there is a corresponding linear growth in the nonbonded interaction energies between the different polymers

Unique Thermal Properties of Clothing Materials.

Cloth wearing seems so natural that everyone is self-deemed knowledgeable and has some expert opinions about it. However, to clearly explain the physics involved, and hence to make predictions for clothing design or selection, it turns out to be quite challenging even for experts. Cloth is a multiphased, porous, and anisotropic material system and usually in multilayers. The human body acts as an internal heat source in a clothing situation, thus forming a temperature gradient between body and ambient. But unlike ordinary engineering heat transfer problems, the sign of this gradient often changes as the ambient temperature varies. The human body also perspires and the sweat evaporates, an effective body cooling process via phase change. To bring all the variables into analysis quickly escalates into a formidable task. This work attempts to unravel the problem from a physics perspective, focusing on a few rarely noticed yet critically important mechanisms involved so as to offer a clearer and more accurate depiction of the principles in clothing thermal comfort

Simulation of multi-deck medium temperature display cabinets with the integration of CFD and cooling coil models

This is the post-print version of the final paper published in Applied Energy. The published article is available from the link below. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. Copyright @ 2010 Elsevier B.V.In this paper, the model for the multi-deck medium temperature display cabinets is developed with the integration of CFD and cooling coil sub-models. The distributed method is used to develop the cooling coil model with the airside inputs from the outputs of the CFD model. Inversely, the airside outputs from the cooling coil model are used to update the boundary conditions of the CFD model. To validate this cabinet model, a multi-deck medium temperature display cabinet refrigerated with a secondary refrigerant cooling coil was selected as a prototype and mounted in an air conditioned chamber. Extensive tests were conducted at constant space air temperature and varied relative humilities. The cabinet model has been validated by comparing with the test results for the parameters of air at different locations of the flow path, and temperatures of refrigerant and food product, etc. The validated model is therefore used to explore and analyse the cabinet performance and control strategies at various operating and design conditions.DEFR