Exhaust Gas Heat Exchanger Research Articles

Superstructure optimization of absorption chillers integrated with a large internal combustion engine for waste heat recovery and repowering applications: Thermodynamic and economic assessments

Internal combustion engines can suffer derating due the knocking phenomenon, which is caused by harsh climate conditions. In addition, large internal combustion engines release considerable heat to the environment through the cooling water and exhaust gas systems. This work is part of an R&D project, sponsored by a Brazilian thermal power plant, in which waste heat recovery and intake air conditioning are explored. The major contribution is the development of a superstructure modelling based on absorption systems integrated with one engine, permitting to determine the best chiller that should be installed at the power plant. Genetic algorithm is used to optimize the complex system, presenting as an optimal result a single-effect chiller powered by the engine’s cooling water, which is preheated at an exhaust gas heat exchanger. The benefits are demonstrated in terms of additional electric power output (1.47 MW ≈17.2%) and reduction of brake specific fuel consumption (2.4 g kWh−1≈1.44%) over the engine’s performance on site (8.54 MW and 167.06 g kWh−1). Moreover, 37.35% of electrical energy savings are achieved at the radiator after the optimization. The optimal profit is 30.7 US$ h−1 with a Levelized Cost of Energy of 19.2 US$ MWh−1. The investment risk requires a payback under three years. The exergy analysis revealed that the absorption chiller is recovering 391.55 kW of wasted exergy, which is 1.67% of the total amount of chemical exergy from the fuel and 11.33% of the total amount of available exergy in the waste streams (cooling water and exhaust gases).

Use of diesel engine exhaust gas heat for heating passenger cars

Introduction. The tasks of increasing energy saving in heating systems for passenger cars of diesel trains are currently relevant. As an alternative source of energy for these systems, the possibility of using the waste heat of the diesel locomotive engine is analysed.Materials and methods. The article provides an analysis of the engine waste heat sources, cooling water and exhaust gases. A schematic diagram of exhaust gas heat exchanger for its use in the heating system of passenger cars has been deve loped. As a possible heat-exchange surface of the waste heat exchanger, plate-ribbed, coiled and tube surfaces with longitudinal boundary layer turbulators are proposed. The required area of this surface for the maximum power of the heating system for a passenger train is determined.Results. The article shows the possibility of using engine exhaust heat in the heating system of a 15-car passenger train without involving third-party energy sources.Discussion and conclusion. The obtained results demonstrate a sufficient potential for increasing the efficiency of using the diesel engine fuel energy when utilising its waste heat for the heating system of passenger cars. The selection of a waste heat exchanger is justified based on a performance of 50 % of the peak load on the heating system at the middle position of the controller.

Analysis of printed circuit heat exchanger (PCHE) potential in exhaust waste heat recovery

Exhaust waste heat recovery technology based on power cycles requires high efficiency, low flow resistance, and a compact structure for exhaust gas heat exchangers. It is a huge challenge for traditional heat exchangers, such as double tube or shell and tube heat exchangers. A printed circuit heat exchanger (PCHE), which is a compact heat exchanger, has not been used in the heat exchange process between the exhaust gas and supercritical CO2. Focusing on this application, a novel design concept of PCHE based on a comprehensive performance index is proposed, which fully considers the differences in physical properties and working conditions between the exhaust gas side and the CO2 side. A series of experiments were carried out in a CO2-based transcritical power cycle system. The experimental test results show that the PCHE with a novel structure is stable and feasible. To further optimise the PCHE, a numerical analysis of different structures was conducted. The calculation results show that the comprehensive performance of the PCHE with an optimised structure was improved by 11.92%. This research shows that PCHE has great potential for achieving a compact design with excellent performance, especially for use in engine waste heat recovery.

Compact Diesel Engine Waste-Heat-Driven Ammonia–Water Absorption Heat Pump Modeling and Performance Maximization Strategies

Abstract An investigation of the best ways to achieve optimal performance from a waste-heat-driven ammonia–water absorption heat pump over a wide range of operating conditions is presented. Waste heat from an 8-kWe diesel engine generator is recovered using an exhaust gas heat exchanger and delivered to the desorber by a heat transfer fluid loop. The absorber and condenser are hydronically coupled in parallel to an ambient heat exchanger for heat rejection. The evaporator provides chilled water for space-conditioning with a baseline cooling capacity of 2 kW. All heat and mass exchangers employ novel microscale geometries. A detailed thermodynamics model is developed to simulate performance and develop strategies to achieve the best performance in both cooling and heating modes over a range of operating conditions. These parametric studies show that improved coefficients of performance can be achieved by adjusting the coupling fluid temperatures in the evaporator and the condenser/absorber as the ambient temperature varies. With the varying return temperatures, the system is able to provide the 2-kW design cooling capacity for a wide range of ambient temperatures.

Heat Exchanger Assisted Exhaust Heat Recovery with Thermoelectric Generator in Heavy Vehicles

The automobile industry is in a constant pursuit to improve the fuel economy of vehicles. The internal combustion engine is inefficient due to its inherent irreversibility. Around 30% of the combustion energy is lost in the form of heat with the exhaust gasses. If this lost energy is recovered and utilized, then it will improve the overall fuel economy of the vehicle. Herein, a waste heat recovery concept is presented to recover heat from exhaust gasses in a heavy commercial vehicle. Two exhaust gas heat exchangers are conceptualized and their performances are compared. A novel idea of immersing thermoelectric modules in coolant is proposed instead of using a separate cooling block or channel. The thermal performance is evaluated considering transformer oil as coolant instead of commonly used engine coolant. The performance of two heat exchangers one having a parallel flat plate fin core and the other having a pin fin core configuration is investigated. The effect of coolant volume flow rate and exhaust gas mass flow rate also is analyzed.

Investigation of the heat transfer coefficient during the condensation of small quantities of water vapour from a mixture with a high proportion of non-condensable gas in a horizontal smooth tube

During heat recovery of exhaust gas energy in a shell and tube heat exchanger, the exhaust gas is cooled down and the water vapour content may condense when the corresponding temperature is reached. In this case, a condensation heat exchanger allows recovering the latent heat in addition to the sensible heat and is therefore beneficial for a preferably high heat recovery. The database and algorithms for the design of this kind of apparatus are still nowadays quite week because only little experimental work is realized with condensation of water vapour from a mixture with a very high proportion of non-condensable gas in horizontal tubes. The actual research work improves this database with a considerable amount of experimental data and proposes a correlation for the prediction of the heat transfer coefficient in an exhaust gas heat exchanger in which parts of the gas humidity condense. All experiments were carried out under conditions, which are typical for this kind of heat exchangers, hence the presented results can be used for the design of condensation heat exchangers in industrial heat transfer systems. A gas inlet temperature of 120 °C, a range of the air-steam mixture Reynolds number 11,000 ≦ Re ≦ 31,000, three tube lengths between 1.87 m and 3.04 m, water vapour volume fractions of 7 % to 14.5 % as well as tube diameters of 22 mm and 28 mm were selected to derive the correlation. Furthermore, additional tube lengths (0.574 m, 0.973 m, 1.373 m) were investigated to determine the parameters influencing the condensation rate and comprehensive location profiles over the tube length. A correlation for a correction factor fC is derived, which enables to calculate the increase of the heat transfer coefficient due to condensation from the dry heat transfer coefficient without condensation. This dry heat transfer coefficient is calculated by the measured values in the inlet and outlet for a purely dry air-steam mixture cooling without condensation. The correction factor fC depend on the water vapour volume fraction, the Reynolds number and the geometry ratio between the inner diameter and the tube length.

Thermo-economic optimization of a Rankine cycle used for waste-heat recovery in biogas cogeneration plants

In a typical biogas cogeneration plant, a part of the exhaust gas energy is used for heating buildings within the plant. However, a certain amount of this energy remains unused. This study examined the utilization of this waste-heat through the Rankine cycle and organic Rankine cycle. A multiobjective thermo-economic optimization procedure of a waste-heat recovery unit installed at the exit of an engine before the engine cooling fluid–exhaust gas heat exchanger is proposed herein. The optimization procedure includes sizing all heat exchangers in the waste-heat recovery unit based on the measured Colburn and friction factors. The thermo-economic optimization was performed to investigate the maximal power output and the minimal payback period while preserving the function of the heating system. The procedure was applied to a biogas power plant with two engines (mass flow rate of the exhaust gases from each engine was 1.77 kg/s at a temperature of 410 °C). The electrical efficiency of this system was 42.1% and the measured overall yearly energetic efficiency was 66.7%. Optimization shows that the waste-heat recovery unit based on Rankine cycle is more economical than the unit based on the organic Rankine cycle using toluene. The electrical efficiency of the entire power plant increased by 2.97% and the payback period of the investment was 6.8 years, while the Levelized Cost of Electricity was 0.0419 $/kWh. The proposed method could be used to analyze the investment profitability of waste-heat utilization in other cogeneration plants.

Exhaust Gas Heat Exchanger Design Based on the Engine Backpressure and Heat Rate Criteria

The use of shell and tube heat exchangers for waste heat recovery has shown excellent results in increasing engine performance, as well as offering a large surface area for small volumes, ease of cleaning, good mechanical layout, and well-known design procedure. This article presents the modeling of the coupling circuit and thermo-fluid design of the heat exchangers in the thermal oil circuit in order to maximize the heat transfer of this equipment at the lowest pressure drop and acquisition cost, which is obtained with a smaller heat transfer area. The research results show the existence of optimal values for the studied system parameters, type of organic working fluid, type of heat exchangers, besides the size of the other system components, which are particular for the studied application. However, these results cannot be compared with the real projects already implemented in the industry due to their absence. It has been verified that the fluids that have showed the best performance in terms of thermal efficiency have been acetone and benzene, with an overall thermal efficiency of 17% and 15%, respectively.

Effect of phase formation due to holding time of vacuum brazed AISI 304L/NiCrSiB joints on corrosion fatigue properties

Whether in turbine components or exhaust gas heat exchangers, vacuum-brazed nickel-based joints are subjected to varying cyclical loads during their applications, often in corrosive environments. The microstructure of the brazed seam, which is determined by the alloy composition and the brazing process parameters, is essential for the service life. In this experimental study a modified BNi-5a foil was produced and used to braze cylindrical AISI 304L butt joints with two different holding times. Using energy dispersive spectroscopy analyses, a direct correlation of the element distribution at the brazing seam with the holding time was detected as a result of diffusion processes. Individual phases were identified, and it could be shown that the longer holding time led to a reduction of borides and silicides as well as to a more even microhardness curve through the seam. The effect of the microstructure on the corrosion fatigue properties was evaluated using multiple amplitude tests by a stepwise increase of the maximum stress amplitude in synthetic exhaust gas condensate. Thereby, improved corrosion fatigue and cyclic deformation behaviors were achieved for the more homogeneous microstructure. Afterwards, topography analyses of the fracture surfaces and cross-sectional fracture investigations enabled an understanding of microstructure-dependent damage mechanisms including fatigue crack initiation and propagation.

Assessment and optimization of exhaust gas heat exchanger with porous baffles and porous fins

The shell and tube heat exchanger with segmental baffles is widely applied in industry owing to its low cost and easy maintenance. However, when adopted it as the exhaust heat exchanger in engine waste heat recovery system, the large pressure drops on shell side and low thermal efficiency greatly affect the efficiency of the whole system. To overcome the aforementioned shortcomings, a structure of shell and tube heat exchanger with porous baffles and porous fins is put forward and numerically analyzed in this study. Comparisons on the pressure drop, heat transfer and comprehensive performance are firstly conducted between the proposed heat exchanger and other five heat exchangers with different structures. The results show that adding porous baffles and porous fins can increase heat transfer by 92.14%, decrease pressure drop by 64.70%, and reduce weight by 11.35% under the mass flow rate is 0.1280 kg/s, hence the proposed heat exchanger owns the best overall performance among six heat exchangers. Subsequently, the effects of key design parameters (fins number per meter, inner tube pitch and porosity) on the performance of the proposed heat exchanger are analyzed and optimized by artificial neural network and genetic algorithm to achieve the best for comprehensive performance. The results are as follows: when the above three parameters are 94 m−1, 58.6 mm and 0.702 respectively, the performance achieved the best.

Numerical analysis of flow characteristics and heat transfer of high-temperature exhaust gas through porous fins

Engine waste heat recovery technology based on thermodynamic cycles calls for highly compact and effective exhaust-gas heat exchangers, especially in the space-constrained applications. A porous fins heat exchanger was proposed and compared with the traditional solid fins heat exchanger in order to effectively enhance the heat transfer and realize the lightweight design. A three-dimensional model of the porous fins exhaust gas heat exchanger under forced convection has been developed and numerically investigated based on the Darcy-Forchheimer-Brinkman momentum equation and local thermal non-equilibrium energy equation. Computational studies are carried out to compare the hydraulic and thermal performance between the porous fins and solid fins of equal size at Reynolds number ranging from 5000 to 50,000. Results show that the porous fins heat exchanger greatly improves by 73.2–77.1% while brings an increase of 15.1–18.5% in the pressure drop. In terms of overall performance, the weight of porous fins heat exchanger is reduced by 90%, and the comprehensive performance factor measuring heat transfer and pressure drop is increased by 41% compared with solid fins heat exchanger. Subsequently, the effects of porous fins height, porous fins density, the porosity and pore density on the heat exchanger performances are also discussed. It is found that there is an optimal fin height to achieve the best comprehensive performance of porous fins heat exchanger.

Frequency‐dependent fatigue and corrosion fatigue assessment of brazed AISI 304L/BNi‐2 joints in air and synthetic exhaust gas condensate

AbstractSince brazed components are often cyclically loaded in corrosive environments, the corrosion fatigue behaviour of the joints has to be investigated. Fatigue tests of brazed AISI 304L/BNi‐2 joints, relevant for exhaust gas heat exchangers, were performed with specimens in the as‐received condition and after pre‐corrosion according to VDA 230‐214. Additionally, the superimposed corrosion fatigue loading in an exhaust gas condensate was realised using a corrosion cell. Corrosion‐induced and deformation‐induced microstructural changes were metallographically evaluated. The influence of the test frequency from 1 to 150 Hz on the cyclic deformation and damage behaviour was characterised. In a statistical analysis, the fatigue strength of 210 MPa at 2·107 cycles was determined for the as‐received condition with a 50% failure probability. The pre‐corrosion as well as the superimposed loading lead to a reduction of the fatigue strength down to 22%. A novel test strategy is suitable for precise fatigue and corrosion fatigue assessments.

The design of portable automobile refrigerator powered by exhaust heat using thermoelectric

A cool box for passenger car refers to a kind of box which is designed and fabricated using well insulating materials in order to ensure the coolness inside the cool box is always stable. Convectional refrigeration systems use ChloroFluoro Carbons (CFCs) and Hydro-Chlorofluorocarbons (HCFCs) as heat carrier fluids. The use of such fluids has over the years raised some very serious environmental concerns which has resulted in extensive research into development of novel refrigeration technologies. Thermoelectric Refrigeration (TER) has emerged as a promising refrigeration technology as it comes with far more distinctive advantages over conventional refrigeration systems. The research and development work carried out by different researchers on TER is thoroughly reviewed in this research. Having looked on these refrigeration systems Thermoelectric Cooler (TEC) refrigeration was used in the design of a 20 litre portable automobile refrigerator. In this design a Thermoelectric Generator (TEG) waste heat recovery system was designed to meet all the TEC refrigerator power requirements. Thus an internal combustion engine TEG system designed includes a stainless steel exhaust gas heat exchanger having an interior portion defined by a stainless steel wall and an exterior surface of the stainless steel wall distal to the interior portion. The exhaust gas heat exchanger receives a pressurized exhaust gas stream from the internal combustion engine and extracts thermal energy from the exhaust gas stream. The TEG modules converts thermal energy directly into electrical energy for TEC refrigerator consumption as well as storage for later use. Thus in this design a percentage of exhaust heat that could have otherwise be rejected into the environment is used in the generation of DC power to meet the TEC electrical power requirements making this system an independent system altogether thereby reducing the number of mechanical loads on the vehicle itself.

排熱回収熱交換器の性能解析と最適設計

Enhancement in performance of heat transfer is one of the most significant issues for a heat exchanger in waste heat recovery systems. In design of the heat exchanger, increases of the heat transfer area and the heat transfer coefficient have been generally considered until now. On the other hand, a practically-designed heat exchanger has not often provided enough performance in terms of the heat transfer due to restrictions of installation space of the system and pressure drop of working fluid. Especially, in the waste heat recovery system for internal combustion engines, it is necessary to pay attention for a design of exhaust system because high-pressure drop of exhaust gas has considerable effect on combustion in the engine. In this study, the mathematical models which can estimate heat transfer rate of the heat exchanger and the pressure drop of exhaust gas has been defined. The mathematical model has roughly validated by comparison with CFD. And then, the optimum design of the heat exchanger has been considered for the solution of a trade-off problem between the heat transfer rate and the pressure drop of exhaust gas based on a genetic algorithm coupled with the mathematical model. Moreover, the benchmark experiment has been carried out with some prototypes of heat exchanger based on the optimum calculations, and the validation study of the mathematical model has presented by the comparison with the experiments. The methodology of the optimum design for the exhaust gas heat exchanger has been mentioned from these results.

Experimental investigation of heat transfer and friction characteristic of fully developed gas flow in single-start and three-start corrugated tubes

18 helically corrugated tubes with different geometrical configurations for exhaust gas heat exchangers are investigated in this study. Experiments are carried out with air flow on the tube side, cooled by a secondary water flow. The dimensionless corrugation pitch p/di varies from 0.27 to 1.53, the dimensionless corrugation height e/di from 0.02 to 0.056, and the corrugation angle φ from 9.2° to 37.0°. To match the typical range of exhaust gas heat exchangers, the examined Reynolds number range is 5000<Re<23,000. Nusselt number and friction factor are correlated with a power law of the corrugation dimensions. Furthermore, the thermal performance of the tubes is examined. It is shown that the highest thermal performance is achieved by a single-start corrugated tube with p/di=0.517 and e/di=0.040. Finally, suggestions are made, how to handle different manufacturing constraints for additional optimization purposes.

Exergy and exergoeconomic assessments of an electricity production system in a running wastewater treatment plant

This study aims at presenting a detailed exergy and exergoeconomic analyses of a biogas engine powered electricity production system in a wastewater treatment plant located in Adana, Turkey. The overall system consists of a compressor, a turbine, a pump, four heat exchangers and a gas engine. The effect of the each system component on the exergy efficiency and exergoeconomic parameters is analyzed separately. The analysis indicates that major exergy destruction happens in the gas engine as 4055.31 kW, followed by the exhaust gas heat exchanger (EGHE) and lubrication oil heat exchanger (LOHE) as 99.86 kW and 92.64 kW, respectively. The second law efficiency of the compressor, turbine, pump, BGHE, LOHE, WHE, EGHE and gas engine are found as 76.50%, 78.43%, 6.49%, 13.40%, 11.56%, 60.44%, 67.36%, and 50.79%, respectively. The operating and maintenance costs, capital investment cost and total cost of the system are reckoned as 14.74 US$/h, 13.90 US$/h, and 28.64 US$/h, respectively to point out the exergoeconomic performance. The unit exergy cost and exergy cost of the fuel, which feeds the compressor, are reckoned as 4.88 US$/GJ and 141.12 US$/h. The exergy cost and electricity production unit exergy cost in the turbine are found as 4.87 US$/h and 11.32 US$/GJ.

Comparative analysis of different lamella geometries used in exhaust gas heat exchangers

In this study, the effect of lamella surface patterns on thermal performance of the finned tube heat exchangers used for exhaust gas and liquid, fluid pair and applied in motor vehicles was examined iteratively using finite volume and computational fluid dynamics programs. Furthermore, a new lamella has been designed using the biomimetic method and has been compared with existing lamella patterns. Expanding the actual heat transfer surface area and increasing the heat transfer, with minimal loss of pressure and consequently reducing the heat exchanger size, is aimed in this study. As a result, models with patterned heat transfer surfaces are more efficient than flat surfaces, thanks to the turbulence effect. The models used in this study, which are called lamella with angled fins structure, have been identified as the most suitable model in terms of selection criteria.

Feasibility analysis of an exhaust gas waste heat driven jet-ejector cooling system for charge air cooling of turbocharged gasoline engines

The present paper analyzes the feasibility of an exhaust gas driven jet-ejector cooling system for charge air cooling of turbocharged gasoline engines in addition to the conventional charge air cooler to increase the engine efficiency. Thereto, steady-state experiments of a jet-ejector cooling system and an exhaust gas heat exchanger prototype working with the refrigerant R134a are used to analyze the operation and control of the compound system and determine feasible cooling capacities, charge air temperatures, thermal COPth and hydraulic COPh. Moreover, the cooling system is rated regarding its power densities and engine backpressure. The exhaust gas waste heat recovery, system power densities, and engine backpressure are acceptable. However, the hydraulic COPh and the amount of reject heat need to be improved, necessitating for instance a multi-staging of the jet-ejection.

Simple models for the heat exchange from exhaust gas to super- and sub-critical refrigerant R134a at high temperature differences

The present paper aims at the simple modeling of the heat exchange of the exhaust gas to a super- and sub-critical fluid for heat recovery applications at high temperature differences and the analysis of their influence on the transferred heat flow. Thereto, a simple shell and tube exhaust gas heat exchanger prototype generating super-critical or saturated sub-critical refrigerant R134a was experimentally investigated. Simulation models based on heat transfer correlations from literature are compared to experiments, heat transfer coefficients quantified and some design improvements discussed. The experimental heat flows are reproduced quite well despite the models’ simplicity. The influence of the fluid property changes transverse to the flow on the calculated heat flows is significant, while the influence of the sub-critical changes in flow boiling mechanisms is negligible.

Economic comparison of ORC (Organic Rankine cycle) processes at different scales

The utilization of low temperature heat sources, e.g. waste heat, for power generation in Organic Rankine Cycles has become more and more important in recent decades. In this work, exhaust gas as the heat transfer medium is considered. Five organic working fluids in three cycle designs at three different scales are investigated in Aspen Plus V7.3. Additionally, two different constraints have been applied to the exhaust gas temperature: A minimum of 180 °C in order to avoid the acid dew point and a minimal temperature approach, where the pinch point in the exhaust gas heat exchanger is fixed at 10 K. The investigated turbine-bleeding process with regenerative pre-heating benefits higher exhaust gas outlet temperatures for further combined heat and power applications in conjunction with enhanced system performances. Also noteworthy is the lower total heat exchanger area of the process compared to the reference designs. Economic analyses are carried out in order to outline the economic merits of the turbine-bleeding cycle.