• Energy Research

{"references": ["Richard Stobart and Rohitha Weerasinghe, \"Heat Recovery and\nBottoming Cycles for SI and CI Engines - A Perspective\", 2006-01-0662,\n2006", "T. Endo, S. Kawajiri, Y. Kojima, K. Takahashi, T.Bada, S. Ibaraki,\nT.Takahashi, M. Shinohara,\"Study on Maximizing Exergy in Automotive\nEngines\", SAE 2007-01-0257, 2007.", "Ho Teng, Gerhard Regner, Chris Cowland, \"Waste Heat Recovery of\nHeavy-Duty Diesel Engines by Organic Rankine Cycle Part I: Hybrid\nEnergy System of Diesel and Rakine Engines\", SAE 2007-01-0537, 2007.", "Ho Teng, Gerhard Regner, Chris Cowland, \"Waste Heat Recovery of\nHeavy-Duty Diesel Engines by Organic Rankine Cycle Part II: Working\nFluids for WHR-ORC\", SAE2007-01-0543, 2007.", "Sukjung Bae, Hyungseok Heo, Heonkyun Lee, Youngdae Choung,\nJaesoon Hwang\u00d4\u00c7\u00f1 Chunbeom Lee \"An Investigation on Working Fluids\nfor an Exhaust Waste Heat Recovery System of a Gasoline Engine\",\nKSAE 09-A0027, 2009.", "J. Ringler, M. Seifert, V. Guyotot, W. H\u251c\u255dbner, \"Rankine Cycle for Waste\nHeat Recovery of IC Engines\", SAE 2009-01-0174, 2009."]} A co-generation system in automobile can improve thermal efficiency of vehicle in some degree. The waste heat from the engine exhaust and coolant is still attractive energy source that reaches around 60% of the total energy converted from fuel. To maximize the effectiveness of heat exchangers for recovering the waste heat, it is vital to select the most suitable working fluid for the system, not to mention that it is important to find the optimum design for the heat exchangers. The design of heat exchanger is out of scoop of this study; rather, the main focus has been on the right selection of working fluid for the co-generation system. Simulation study was carried out to find the most suitable working fluid that can allow the system to achieve the optimum efficiency in terms of the heat recovery rate and thermal efficiency.

Bu çalışmada, rotorlu ısı geri kazanımlı mekanik havalandırma cihazlarında verimlilik araştırılmıştır. Havalandırma cihazlarının iki ayrı hava hattı (taze hava ve egzoz hattı) arasındaki ısı transferi rotorlu tip ısı değiştirisi ile yapılmıştır. Rotorlu ısı değiştiricisinin hızının, rotorun sıcaklık verimine ve kendi basınç düşümüne etkisi deneysel olarak araştırılmıştır. Deneyler ısı geri kazanımlı havalandırma cihazı üretimi yapan bir firmanın cihazlarının termodinamik testlerinin gerçekleştirildiği laboratuvarda yapılmıştır. Rotor tek başına test edilmemiş olup, ticari tip bir havalandırma cihazının içerisinde gerçeğe en yakın haliyle test edilmiştir.Yapılan deneyler sonucunda elde edilen test sonuçları aynı zamanda literatür araştırmalarından elde edilen sayısal hesaplarla da kontrol edilmiş ve kıyaslanmıştır. NTU metodu kullanılmış ve daha önce yapılan çalışmalarda önerilen farklı algoritmalar kullanılmıştır. Bahsedilen farklı algoritmalar MATLAB kullanılarak çözümlenmiş ve hesaplanmıştır. Bu zamana kadar önerilen verim hesaplamalarının sonuçları ile test sonuçları karşılaştırılmış ve sonrasında bu tez için en yakın sonuçları veren yöntem belirlenmiştir. In this study, the thermal efficiency and pressure drop of the rotary (regenerative) heat exchanger has been investigated in heat recovery mechanical ventilation devices. The heat transfer between the two separate air streams (fresh air and exhaust stream) of the ventilation devices was performed by a rotary heat exchanger. The effect of the rotational speed of the rotary heat exchanger on the thermal efficiency and pressure drop of the ventilation unit have been investigated experimentally. Experiments have been carried out in a laboratory where a company, which manufactures heat recovery ventilation units, performs thermodynamic tests of its products. The rotor has been tested within a commercial ventilation device rather than being tested alone in order to realize the actual conditions.Test results have been also checked and compared with analytical results calculated with respect to the procedures according to the literature research. NTU (number of transfer units) method has been used to calculate the efficiency by using the various relevant algorithms which had been previously proposed by various researchers. MATLAB has been used to calculate those various algorithms. The most appropriate method has been determined by evaluating this comparison as a conclusion. 97

The solar splitting of H2O and CO2 via a thermochemical redox cycle offers a viable pathway for producing sustainable drop-in fuels for the transportation sectors. The key performance metric is its solar-to-fuel energy efficiency, which is strongly dependent on the ability to recover heat during the temperature swing between the reduction and oxidation steps. Here we report on the experimental investigation of a novel heat recovery method based on coupling the solar reactor with two thermocline energy storage units made of a packed-bed of alumina spheres. Using N2 as an inert heat transfer fluid, the heat rejected during cooling from the reduction to the oxidation temperature is stored and, following the oxidation step, delivered back to preheat the solar reactor towards the reduction temperature, thus reducing the required solar input and consequently increasing the efficiency. With a first experimental prototype, a heat extraction effectiveness of up to 70% from a 4 kW solar reactor is obtained with measured N2 outlet temperatures exceeding 1250°C. Energy flow modeling of a 50 kW solar reactor predicts a theoretical upper limit value of the energy efficiency of 42% for perfect heat recovery without transient losses, and 14.7% with such losses included. Several improvements and insights into high-temperature heat recovery are detailed. Applied Energy, 329 ISSN:1872-9118 ISSN:0306-2619

Heat produced by the engines is mostly wasted in absence of any system to recover it. This heat can be utilised for few applications with the system to effectively recover it. Heat pipes are useful to carry out the heat produced by the engines and machines. Heat absorption capacity of heat pipes makes them effective for designing the applications for heat recovery. Better control is provided by the heat pipes by controlling the temperature. The heat generated in most of the machines is not utilised anywhere and it is wasted in absence of a system to utilise it. Heat pipes are capable of heat transfer which can be useful to design the effective thermal based systems. The pipe based solar collectors are proven effective in heat exchange and transfer process. Authors have presented the recovery system for heat in order to utilise the waste heat.

International Transaction Journal of Engineering, Management, & Applied Sciences & Technologies, 11, 13, 11A13E: 1-6

The use of a binary mixture as a working fluid in bottoming cycles has in recent years been recognized as a means of improving combined cycle efficiency. There is, however, quite a number of studies dealing with components of plants that employ fluids other than water, and particularly binary mixtures. Due to different specific volume, viscosity, thermal conductivity, and Prandtl number, heat recovery boilers designed to work with water require certain modifications before they can be used with binary mixtures. Since a binary mixture is able to recover more heat from the exhaust fumes than water, the temperature difference between the hot and the cold fluids is generally lower over the whole recovery boiler; this necessitates greater care in sizing the tube bundles in order to avoid an excessive heat transfer surface per unit of thermal power exchanged. The aim of this paper is to provide some general criteria for the design of a heat recovery boiler for a binary mixture, by showing the influence of various dimensional parameters on the heat surface and pressure drop both in the cold and the hot side. Heat transfer coefficients and pressure drops in the hot side were computed by means of correlations found in the literature. A particular application was studied for an ammonia-water mixture, used in the Kalina cycles, which represents one of the most interesting binary cycles proposed so far.

Abstract In this work, two different options of waste heat recovery from internal combustion engines have been proposed and compared to each other. Both consider two thermodynamic cycles in order to maximize the energy recoverable. The first considers a Brayton-Joule cycle as top cycle, which is immediately interfaced with the exhaust gases and has a supercritical CO2 as working fluid; while an ORC is bottomed to this, using R1233zdE as the organic working fluid. In this way, the supercritical CO2 can have better efficiency and the bottomed ORC can further recover the low temperature energy discharged by the Brayton-Joule cycle. The second option considers an Inverted Brayton Cycle as top thermodynamic cycle, which uses the same exhaust gases as working fluid and, so, has a lower complexity. The thermal power discharged at low temperature by the inverted Brayton Cycle is further recovered by the ORC bottom unit. The two options will be studied using a mathematical model developed and tailored to a 3L turbocharged diesel engine, whose experimental data are available measuring the most relevant quantities (exhaust temperature and pressure, fuel consumption, brake efficiency, etc.) in typical operating points of a heavy duty vehicle. A comparison of the two combined systems assesses the most effective recovery option.

Abstract Waste heat recovery is a broadly considered opportunity for efficiency improvement in several energy consumption sectors, intending to reduce energy consumption and related carbon dioxide emissions to the atmosphere. The attention of research activities is focused on transportation and residential sectors, where the possible recovery is characterized by low enthalpy, but with a wider potential market. Therefore, the maximization of recovery is one of the principal aims of this option, and different kinds of technologies have been proposed in this regard. Thermodynamic cycles, which exploit the waste heat considering it as the upper thermal source, seem to be a promising option, and the possibility to combine two different cycles can increase the thermal power harvested. In this paper, a combination of a supercritical CO2 Brayton cycle with an ORC-based unit has been proposed to recover waste heat from the exhaust gases of an internal combustion engine for the transportation sector. Using CO2 as working fluid is under investigation in literature, for its low Global Warming Potential and its suitable thermodynamic characteristics in dense phase (just above the critical point). An Organic Rankine Cycle (ORC), then, has been bottomed to the CO2 section, to further recover thermal energy and convert it into mechanical useful work. Indeed, the CO2 cycle must have a lower temperature cold sink, where thermal power can be furtherly recovered. The introduction of this second stage of recovery interacts with the upper one, modifying the overall optimization parameters. Hence, this work aims to find the maximization of the recovery from a global point-of-view, identifying possible trade-offs happenings between the two recovery sections. Minimum sCO2 pressure, stack exhaust temperature, and the possibility to have a regeneration stage have been considered as optimizing parameters. Finally, the optimized system has been applied to a specific mission profile of a commercial vehicle, in order to evaluate the recovery potential during a realistic engine working points sequence. A recovery higher than 4% in every mission considered has been achieved, with values up to 7% in motorway and long-hauling conditions.