Water-urea mixtures are used in diesel vehicles for exhaust aftertreatment. The liquid mixture, stored in a tank, is susceptible to freezing in cold weather. Depending on weather conditions, the tank size and the liquid fill level, the freezing of the entire liquid may span over a day. Mitigation strategies require understanding of the freezing history. Traditional computational fluid dynamics and heat transfer (CFD/CHT) methodologies are impractical for modeling such freezing processes because of restrictions in the time-step size — typically milliseconds — posed by numerical stability and physical time-scale considerations. The primary constraint for using small time-step sizes is the fine-scale motion generated by natural convection in both the liquid and the gas (unoccupied space). A new model is proposed and demonstrated for efficient prediction of the propagation of the solidification front. In this model, heat transfer due to natural convection is modeled as a diffusive process analogous to how turbulent transport is modeled using an eddy diffusivity and a gradient diffusion model. The model enables use of large time-steps since the fine-scale motions due to natural convection are no longer resolved. The model was validated against experimental data, which were also collected as part of the study. Each experiment collected data at intervals of 6 seconds for a total duration of about 24 hours. Several different tank fill levels were considered, and good agreement with experimental data was noted, especially for shallow fill levels. Large-scale parallel three-dimensional calculations were conducted in a few days of computational time using the proposed model as opposed to a year (projected) of computational time using traditional CFD/CHT models and the same computational resources.

In the aluminum production industry, metal furnaces are operated by diffusion flame over the metal surface to maintain the aluminum metal at the set point temperature for alloying and casting. Heat is transferred from the flame and its exhaust gases to the metal surface via radiation and convection. The exhaust gases leaves through the furnace’s chimney carrying a significant amount of waste heat to the atmosphere. Furnace efficiency could be improved by enhancing the heat transfer inside the furnace. In this study, a validated full-scale 3-D CFD model of a natural gas fired aluminum furnace is developed to investigate the effect of flue gas ventilation configurations and burner operating conditions on the heat transfer inside the furnace. Onsite measurements are carried out for the fuel and airflow rates as well as flue gas temperature. Four flue ventilation configurations are considered with eight furnace’s operation modes. The flue-gas’s waste-heat varies from 49–58%, with the highest value occurring at the high-fire operating mode. This indicates a significant room for improvement in the furnace performance. Results suggest that a symmetrical positioning of the exhaust duct favors effective exhaust gas circulation within the furnace and hence, increases hot-gases’ heat-transfer effectiveness inside the furnace. These results provide some guidelines for optimal aluminum reverberatory furnace designs and operation.

The capabilities of a pilot-scale reciprocating biomass conversion reactor (RBCR) and its sensitivity to changes in various input parameters are examined. The RBCR is a 4-stroke diesel engine repurposed as a novel reactor to produce bio-oil by fast-pyrolysis of biomass. An external source powers the RBCR through the intake, compression/heating, expansion and exhaust strokes. Biomass is carried to the RBCR by an inert gas and is converted during compression as part of the compression work provides the heat of pyrolysis. A control-volume energy balance is coupled with a biomass decomposition mechanism from literature to predict the evolution of bio-products during compression and expansion strokes. The RBCR calculations are compared to experimental results from the state of the art considered to be a lab-scale fluidized-bed reactor (FBR). Calculations predict that the RBCR will increase the biomass throughput, and decrease the energy requirement for biomass conversion with a 6.8 times return on energy investment. The sensitivity analysis indicates the need for finely pulverized biomass for significant conversion, and highlights the versatility of the RBCR since operation parameters can be adjusted to achieve near complete conversion to bio-gas or to yield bio-oil up to 70% of biomass weight.

Cargo compartment fire has become the major security threat for cruising aircraft, the depressurization measurement could effectively suppress the cargo compartment fire through the reduction of the air pressure and oxygen concentration. The objective of this work is to study fire behavior characteristics in half confined chamber and high altitude laboratory at identical low atmospheric pressure, and explore the controlling effects of air exhaust condition, oxygen concentration. N-heptane pool fire experiments were conducted separately in Langfang low pressure chamber (altitude 50m) and Kangding airport laboratory (altitude 4290m) at 60 kPa air pressure, both assembled ISO-9705, but their gas supplying condition is different. Mass burning rate, gas composition, flame temperature, and radiant heat flux had been measured as the principal characteristic parameters for analysis. This paper reveals the variation characteristics of the fire behavior under different oxygen concentration but identical low atmospheric pressure. The gas composition of the chamber is controlled by the liquid fire and air intake quantity, the oxygen concentration of the chamber decreases with decreasing gas intake quantity. The mass burning rate increases and the mass burning time decreases with the increase of the oxygen concentration. The higher air intake quantity or the higher oxygen concentration could increase cargo compartment fire radiation intensity, and exacerbate the fire further propagation. However, under the low oxygen concentration condition, the liquid fire still have a higher flame temperature above a certain height. The depressurization measurement could increase the flame height and flame temperature may be caused the cabin fire-resistant liners layer is easier to burn through. The more reasonable adjustment of the cargo compartment air exhaust quantity and air pressure is very meaningful for the comprehensive fire suppression of cruising commercial airplanes.

The study investigates the temperature gradients achieved across a thermoelectric generator by using the exhaust gases from a vehicle as a heat source and the radiator coolant as the cold sink. Various heat transfer enhancement features are employed in order to achieve as high a temperature gradient as possible. Effect of flow Reynolds numbers and inlet temperatures are examined to create a body of data predicting total power output from the TEG. Data is normalized against results from baseline heat exchanger designs investigated in the past. The experiments are carried out at 1/5th scale of the previously examined geometry. Impingement geometry is employed on the coolant side to enhance heat transfer. The experimental test sections are fabricated using metal 3D printing. Water is used instead of radiator coolant and heated air is used for exhaust gases. The results from the experiments provide valuable data which can be used for system level optimization.

This study investigates using numerical methods the performance of thermoelectric devices (TEDs) integrated with heat exchangers and applied to automotive exhaust gas waste-heat recovery. Air as an exhaust gas and water as a cooling fluid are used. The effects of temperature-dependent properties of materials (TE elements, ceramic plates, connectors, insulation materials and fluids) and interface electrical and thermal contact resistances on TED’s performance are included in the analysis. Additionally, the fluid heat exchangers and the insulation materials are modeled using a porous media approach. The response of hot and cold fluid inlet temperatures (T hi , T ci ) and flow rates, number of modules N, permeability of heat exchangers and TE materials type on TED’s hydro-thermoelectric characteristics is studied. An increase in either T hi or a decrease in T ci is resulted in an enhancement in TED’s performance. The addition of modules is shown a significant effect on heat input Q h and power output P 0 predictions; however, a minimal impact on efficiency η is displayed with N. For instance, at T hi = 873.15 K and T ci = 353.15 K with clathrate n-Ba 8 Ga 16 Ge 30 and p-PbTe material’s combination, compared to single module case, TED with four modules showed 3.77- and 3.7-fold increase in P 0 and Q h , respectively. In the studied 1–4 modules range, the cold fluid flow rate and the permeability of heat exchangers are exhibited a negligible effect on TED’s P 0 and η, whereas the hot fluid flow rate is shown an appreciable change in η values. Further, when T hi is less than 500 K, TED with bismuth-tellurides showed a higher performance when compared to the clathrates and lead-tellurides materials combination.

The Industrial Revolution in the nineteenth century has introduced chemical leavening agents such as baking soda. In today’s Biscuit and Cracker Industry, ammonia is one of the most common ingredients for the bakery product. According to the EPA, ammonia vapor constitutes about 99% of total emissions from a biscuit oven. Air control equipment, such as catalytic oxidizers, is often installed at bakeries to convert the NH 3 to nitrogen and NOx. It is a highly expensive and complicated method of controlling pollution. Integration of waste heat recovery and ammonia extraction processes gives us an effective, non-expensive and more natural solution to this problem. This method can be accomplished by using the solubility property of ammonia for the process of exhaust cooling and condensation with high moisture content.

About 60% of unrecovered waste heat in US is low temperature waste heat (<230°C). In case of exhaust flows that contain water vapor over 20% by mass (baking, drying, biofuel production) the latent heat of the “wet component” plays a key role in the process of energy recovery and makes such a recovery economically feasible. Low temperature sources of waste heat have a few specific features, so majority of available techniques developed for high temperature waste heat recovery cannot be successfully applied to justify the cost-effective benefits. The paper discusses the basic requirements for appropriate equipment development along with possible options for heat and water recovery.

A design of a compact, integrated combustor and heat exchanger for low temperature applications is presented in this paper. The design involves use of several repeating unit cells that each performs three unit operations — combustion, recuperation, and heat exchange. Heat from combustion is transferred to a cold gas stream entering the device at 200K. Heterogeneous catalytic combustion occurs on the walls of microchannels in the presence of a platinum catalyst. Two levels of numerical simulations are performed to realize the design. The first level represents a single unit cell consisting of a combustor, exhaust gas, and heat exchange fluid channels. At the unit cell level, a two-dimensional numerical model with detailed surface chemistry is used to provide high unit cell thermal efficiency. It is shown that with the help of a novel distributed catalyst arrangement, extinction of the reaction due to the cold gas stream is prevented and a high hydrogen conversion (greater than 95 percent) is achieved for a range of operating conditions. The second level of simulations is at the device scale, consisting of multiple unit cells connected together with appropriate fluidic headers. At this device level, three dimensional simulations of fluid flow were performed to ensure uniformity in flow distribution while maintaining low pressure drop through the device. Fabrication constraints were also incorporated into the device level design and simulations.

Nowadays the Baking industry faces two main economic problems: low efficiency (significant waste heat losses) and negative environmental impact (air pollutions). Indeed, hot (about 400° F) stack gas flow, with content of vapor, carries about 2/3 of fuel that consumed by bakery oven to the ambient. Moreover, stack gas contains of the ethanol vapor (produced by yeast in oven bakery process). Amount of ethanol in stack gas is equivalent up to 8% of the fuel consumed by bakery oven at nominal operation. In addition, U.S. EPA regulates the bakery exhaust, so that plants are forced to install expensive oxidizing equipment to combust the dangerous pollutant (including ethanol) emissions prior to releasing the stack gas into atmosphere. It results in additional fuel consumption and extra heat losses generated at the bakery site. Ethanol is easy solvable in water so the traditional methods of its extraction are associated with condensing/evaporating processes. However, at the low concentration (in the oven stack it is about 0.5%) the ethanol starts condensing at 10.6 ° F. The optimal conditions for ethanol diffusion into water droplets, which forms clouds in the cooled to ambient temperature oven stack, were found.

Thermoelectric Generators (TEG) can be used on automobiles to harvest energy from exhaust waste heat. Besides the improvement on material side, the optimization of geometry of the module is also important to maximize the output power density and will be addressed in this paper. A thermal resistance network is established based on heat conduction and radiation from heat source to heat sink. Although the heat transfer model is based on cylindrical exhaust pipe geometry, the thermo-element is approximated as plane geometry because the ceramic layer and thermoelectric layer are much smaller compared with the exhaust pipe diameter. The TE material we proposed to recover waste heat energy is magnesium silicide (Mg 2 Si), which has a reasonable figure of merit in the automobile exhaust temperature range, and the process is thermal spray compatible, which is a mass productive method currently under investigation. Another material that used for comparison is titanium oxide. Based on the Seebeck coefficient, thermal and electrical conductivity of our thermal sprayed samples, the thermoelectric leg length and the area ratio between thermoelectric element and total module area are optimized for maximum power density output. The optimal leg length is around 0.85mm, and the air gap is as small as possible. A parameter sensitivity analysis is conducted to investigate the influence of ceramic layer thickness, exhaust pipe radius, electrical contact resistance, hot and cold side temperature, Seebeck and electrical conductivity on the optimal leg length.

Exhaust manifolds are used in many areas, such as turbocharged diesel engines. The purpose of an exhaust manifold is to direct the hot gases from the combustion chamber to the turbocharger or an acceptable exhaust outlet. The high gas temperatures in the exhaust manifolds lead to very high thermal stresses. This research focuses on the integration of computational fluid dynamics (CFD), Finite Element Analysis (FEA), and virtual reality visualization to analyze and visualize thermal stresses of manifolds for better understanding and better decision-making for design, troubleshooting, and optimization of manifolds. CFD is used to obtain the temperature distribution in the exhaust manifold. Using the temperature data FEA is then performed to determine the thermal stresses in the exhaust manifold. Using the results of the FEA analysis a 3-d virtual model is built to visualize the thermal stresses in the exhaust manifold. Methodologies have been developed for such integration and applied to industrial manifolds. Results will be presented in detail in the paper.

In this present work, we attempt to maximize the electrical power generation by optimizing Thermoelectric Generator (TEG) geometry for a prescribed TEG volume. A plate-fin heat exchanger topology is assumed and consideration is given to additional pressure drops associated with the fins placed in the exhaust flow path; and the cross-sectional changes across TEG inlet-exit ports. The thermal profile in the TEG is computed such that different thermoelectric modules may be placed where they provide the maximum Seebeck coefficient and hence provide the maximum power output. Multiple filled skutterudites are employed in the higher temperature regions and Bismuth Telluride modules are used at lower temperature regions of the TEG. Separate calculations are performed for cases where the available maximum number of TEMs is limited for cost optimization.

Further improving energy efficiency in internal combustion (IC) engines is the research-topic for a large number of investigators. This project covers the integration of an IC-based cogeneration with a vapor-absorption chiller. Heat from the cogen is fed to the generator of the absorption chiller. It is to improve performance and efficiency of internal combustion engines for use in motor vehicles. Less than one third of the total energy in a given amount of fuel is transferred into the rotational motion that drives vehicles forward. The remainder is either used to overcome friction and drive mechanical devices such as the alternator and water pump or is rejected as heat through engine cooling and exhausted gas. The heat rejection from the exhaust is due to the Carnot law and it is low grade heat that cannot be efficiently converted to work in the engine and thus, requires a second system for energy recovery. The two forms of rejected heat each account for approximately a third of the available energy. Traditional methods of improving performance such as increasing capacity and air intake through forced induction also results in more fuel being consumed. Improving fuel efficiency meanwhile has resulted from running the engines leaner and downsizing engines. However the current methods have not taken advantage of the energy supply available in the exhaust stream. Harnessing the thermal waste energy in the exhaust can be achieved through integration of a heat exchanger in order to power a vapor absorption cycle for the purpose of cooling intake air. This cooler, denser charge improves both volumetric and mechanical efficiency of engines with the outcome being improved performance, better fuel economy and lower emissions. Recommendations for future work and other applications will be provided based on the analyzed results contained in the body of this paper.

The successful development of thermoelectric generators (TEGs) for automotive applications requires advances on several fronts: (1) abundant, low cost, and efficient thermoelectric (TE) materials, (2) industry-scalable material synthesis and device fabrication process, and (3) cost-efficient and reliable integration into existing vehicle systems. Most vehicle TEG approaches to date use flat, prefabricated modules that are placed in contact with a custom-built exhaust component/heat exchanger to capture waste heat. We are developing a single-step, integrated approach involving non-equilibrium synthesis, 3D conformal deposition and rapid formation of patterned structures, which is well-suited for large-scale waste-heat TEG applications.

Energy recovery from vehicle engine exhaust has attracted considerable interest recently. Key parameters associated with the engine exhaust, including temperature, mass flow rate, maximum extractable energy, and optimum location for energy extraction all factor strongly into the materials research and device design for waste heat recovery. This review paper compiles available data in literature on the vehicle engine exhaust resources for several different vehicles, and under various operational conditions. Three vehicles types, namely, mid-size sedans, light duty trucks, and heavy duty trucks, have been considered, and the driving cycles including Federal Test Procedure (FTP) series, Highway Fuel Economy Test (HFET) and New European Driving cycle (NEDC) are considered in this review. The results show the average temperatures at highway driving cycle and city driving cycle remain in the ∼500–650°C and ∼200–400 °C range, respectively. The mass flow rate varies significantly with vehicle size. The available thermal power calculated based on the collected data is 3–10 kW.

The purpose of this paper is to investigate the thermal flows and heat transfer phenomena occurring in the cooling circuit of a high specific power engine and to suggest a valid method to evaluate its effectiveness in keeping the temperature below a safety limit even in the highest thermal power points. This is a first work showing the analysis of the cooling circuit of a small single-cylinder, four-stroke, high power density gasoline engine carried out with a numerical three-dimensional CFD analysis by means of a CFD conjugate simulation, whose boundary conditions have been taken from a validated one-dimensional fluid dynamic engine model. Once its validity has been assessed by the comparison between the simulation results and data collected by literature and experiments, the interest for this procedure relies on the fact that heat fluxes are directly calculated by the CFD code through the knowledge of gas temperatures and convective heat transfer coefficients. Hence an arbitrary, a priori subdivision of the total heat flux released by fuel combustion into heat converted into mechanical work, heat released to the cooling system, heat rejected to the exhaust, etc. can be avoided; at the same time, the model provides the proper distribution of the heat rejected to the various surfaces constituting the water jackets. The evaluation of the effectiveness of the cooling system is then directly performed in terms of temperature distribution. By this way, once the engine has been designed from a fluid dynamic and mechanical point of view, the effectiveness of the cooling system can be immediately verified through the application of the described procedure. This study takes into consideration the evaluation of average and instantaneous heat transfer coefficient and in-cylinder gas temperature through the use of a validated 1D CFD model, the analysis of the temperature field by means of a conjugate heat transfer simulation of the whole head and cylinder group and an example of the application of this procedure for the evaluation of a simple modification of the cooling system.

The use of Jojoba Methyl Ester as a pilot fuel was investigated for almost the first time as a way to improve the performance of dual fuel engine running on natural gas or LPG at part load. The dual fuel engine used was Ricardo E6 variable compression diesel engine and it used either compressed natural gas (CNG) or liquefied petroleum gas (LPG) as the main fuel and Jojoba Methyl Ester as a pilot fuel. Diesel fuel was used as a reference fuel for the dual fuel engine results. During the experimental tests, the following have been measured: engine efficiency in terms of specific fuel consumption, brake power output, combustion noise in terms of maximum pressure rise rate and maximum pressure, exhaust emissions in terms of carbon monoxide and hydrocarbons, knocking limits in terms of maximum torque at onset of knocking, and cyclic data of 100 engine cycle in terms of maximum pressure and its pressure rise rate. The tests examined the following engine parameters: gaseous fuel type, engine speed and load, pilot fuel injection timing, pilot fuel mass and compression ratio. Results showed that using the Jojoba fuel with its improved properties has improved the dual fuel engine performance, reduced the combustion noise, extended knocking limits and reduced the cyclic variability of the combustion.

The most part of energy losses in power system such as fuel cells is due to the heat released by the exhaust gas to atmosphere. The exhaust gas consists of non-condensable gas and steam with sensible and latent heat. As a lot of latent heat is included in the exhaust gas, its recovery is very important to improve the power system efficiency. Based on the previous basic studies, a thermal hydraulic prediction method for latent heat recovery exchangers was proposed. For the condensation of steam on heat transfer tubes, the modified Sherwood number taking account of the mass absorption effect on the wall was used. Two kinds of compact heat exchanger with staggered banks of bare tubes of 10.5 or 4mm in outer diameter was designed with the prediction method. The more compactness was obtained with the smaller tubes at a designed heat recovery. The thermal hydraulic behavior in the compact heat exchangers was experimentally studied with air-steam mixture gas. In the parametric experiments varying the steam mass concentration, the temperature distributions of cooling water and mixture gas were measured. The experimental results agreed well with the prediction proposed in this study and the more compactness with the smaller tubes was proved.

Rich-lean flame burners are widely used for supplying domestic hot water and heating in Japan. These burners exhaust low NOx and CO emissions, and conventionally consist of a layered structure of lean flame with two sides of rich flame. Top-runner regulation applied for the domestic hot water generator of fuel gas, is to run to achieve the CO 2 reduction two years later in Japan. Not only low NOx and CO emissions, but also higher efficiency, are required for the next generation of domestic hot water generators. Kurachi et al. confirmed experimentally that a new concept, a unique burner with air supplied from the boundary zone between the rich and lean premixed gas nozzles, produces lower NOx and CO emissions (1, 2, 3). Numerous experimental and numerical simulation studies of conventional rich-lean flame burners have been reported, and the mechanism of the complex field mixed with the rich and lean premixed gas has been clarified (4). But the characteristics of the new concept burner have only been investigated experimentally. In this study, a two-dimensional numerical simulation of the new burner was executed to clarify the mechanism of the lower NOx and CO emissions compared to the conventional burner (mesh; 25,000, chemical reaction; GRI-mech II, laminar flow). Heat input was 6.5kW (half of a full load). A conventional burner, without an air supply from the boundary zone, was also calculated to compare with the new concept burner. In a conventional burner, the reaction ratio R178 (N+NO = N 2 +O), which is a part of the Zeldovich mechanism, is dominant at the area downstream of the rich flame. This area is almost same as the maximum temperature area of the burned gas. The maximum temperature of the new concept burner (1,923K) is approximately 50K lower than that of the conventional burner, successfully maintaining stable combustion. Because of its lower maximum temperature, the amount of NOx emission from the new concept burner is approximately 40% of that from the conventional burner. With the air supply from the boundary zone, the concentration of CO in the flue gas also is decreased by approximately 1/3. In particular, the formation of thermal NOx in the lean flame zone is suppressed by lowering the flame temperature. The amount of CO emission from the rich flame zone is also decreased due to the promotion of complete combustion with the air supply from the boundary zone. As a result, these characteristics are in relatively good agreement with the experimental results, and the dominancy of the new concept burner is also clarified.