Exhaust Heat Research Articles

Magnetically assembled flexible phase change composites with vertically aligned structures for thermal management and electromagnetic interference shielding

Phase change material (PCM) is promising in achieving zero-energy thermal management because of its prominent thermal storage capacity and steady phase-change temperature. However, low intrinsic thermal conductivity (TC), liquid leak, and solid rigidity are long-standing bottlenecks for heat-related applications. Here, we report an innovative dual-encapsulation strategy to develop multifunctional phase change composite (FMP) with vertically aligned NdFeB@Ag arrays and styrene-ethylene-propylene-styrene (SEPS) crosslinked network in paraffin (PA). The NdFeB@Ag arrays induced by magnetic-field driven procedure can offer the consecutive/oriented highways for efficient heat-transfer, and an electric/magnetic heterostructure for electromagnetic interference shielding efficiency (EMI SE). The flexible SEPS block copolymer not only ensures the high flexibility of PCM, but also combines with oriented NdFeB@Ag arrays for dual encapsulating PA. This multifunctional FMP can achieve high TC of 2.59 W m−1 K−1, attractive EMI SE of 35.42 dB, prominent enthalpy density of 120 J g−1, and impressive Joule heating performance, together with leakage-proof, dynamic assembly, and salient charging/discharging durability. Furthermore, the FMP-supported device is demonstrated for thermal energy harvesting and utilization. This dual-encapsulation design opens a new avenue for exploiting multifunctional PCMs for thermal management, anti-EM radiation, and low-grade exhaust heat utilization.

Broadening of the Divertor Heat Flux Profile in High Confinement Tokamak Fusion Plasmas with Edge Pedestals Limited by Turbulence in DIII-D.

Multimachine empirical scaling predicts an extremely narrow heat exhaust layer in future high magnetic field tokamaks, producing high power densities that require mitigation. In the experiments presented, the width of this exhaust layer is nearly doubled using actuators to increase turbulent transport in the plasma edge. This is achieved in low collisionality, high confinement edge pedestals with their gradients limited by turbulent transport instead of large-scale, coherent instabilities. The exhaust heat flux profile width and divertor leg diffusive spreading both double as a high frequency band of turbulent fluctuations propagating in the electron diamagnetic direction doubles in amplitude. The results are quantitatively reproduced in electromagnetic XGC particle-in-cell simulations which show the heat flux carried by electrons emerges to broaden the heat flux profile, directly supported by Langmuir probe measurements.

Techno-economic analysis of zero-carbon ammonia-hydrogen fuel blend production through a catalytic membrane reformer and packed bed reactor

Ammonia-hydrogen fuel blends are an attractive alternative for zero carbon combustion and power generation. Herein we present a comprehensive techno-economic analysis for distributed production of these fuel mixtures from liquid NH3 comparing catalytic membrane reformer (CMR) and packed bed reactor (PBR) processes. The technical and economic feasibility was evaluated as a function of product composition (10–50 % H2), and delivery pressure (1–50 bar), and process scale (0.1–10 MW). To facilitate comparisons with conventional power and common hydrocarbon fuels the results are presented as NH3 processing cost (¢/kWh), H2 production cost (USD/kg), and overall fuel cost (USD/thm). The results show that the CMR is superiorly positioned for the generation of ammonia/hydrogen fuel mixtures with 2.7–7.2 times lower NH3 processing cost and requiring <0.5 USD/kg H2 production costs with exhaust heat recuperation. CMR advantages stem from more efficient NH3 reforming and H2 separation processes, eliminating the need for capital and operating intensive compression. These benefits are amplified with increasing H2 composition and fuel delivery pressure. The processing cost for both reformer options drops by 30 % with a scale increase from 0.1 to 10 MW. CMR-generated ammonia/hydrogen fuel blends are cost-competitive with refined liquid hydrocarbon fuels such as gasoline, diesel, and jet A. Nevertheless, the NH3 cost would have to be reduced by more than half to become competitive with natural gas. These findings suggest that ammonia/hydrogen fuel blends are an attractive option for the decarbonization of heavy industry and commercial transport.

Performance improvement of the automotive thermoelectric generator by extending the hot side area of the heat exchanger through heat pipes

In pursuit of enhancing the utilization of exhaust heat in the automotive thermoelectric generator (ATEG), this study introduces a novel heat exchanger with integrated heat pipes to extend the effective hot-side surface area. Meanwhile, a numerical model containing multiphysical fields is developed, and the quantity and arrangement of heat pipes are optimized based on this model. Results suggest that (i) The incorporation of heat pipes markedly enhances the recovery of heat energy from the ATEG, leading to a substantial increase in its output power; (ii) With an increasing heat pipe quantity, the ATEG’s output power exhibits a continuous upward trend before eventually reaching stability; (iii) The arrangement of heat pipes also influences system performance, and through optimizations, the optimal quantity of heat pipes is determined to be N = 11 and toleration to be d = 1 mm. At an exhaust temperature of 550 K and a mass flow rate of 60 g/s, the ATEG achieves an output power of 213.19 W and a heat absorption of 4318.02 W, which increased by 42.95 % and 55.6 % respectively, compared with the traditional structure without heat pipes. This structural optimization concept for the heat exchanger provides a new approach to performance improvements of ATEGs. This study provides a design basis and guidance for optimizing the design of ATEG systems with integrated heat pipes.

The Performance Evaluation of a Hybrid System Combining an Alkaline Fuel Cell with an Inhomogeneous Thermoelectric Generator

To harness the full potential of the exhaust heat produced by an alkaline fuel cell (AFC), a novel coupling system that combines an AFC with an inhomogeneous thermoelectric generator (ITEG) is proposed. Detailed models of both the AFC and ITEG are developed, accounting for various irreversible losses. Following model validations, mathematical expressions for the power output density (POD) and energy efficiency (EE) of the hybrid system are derived. Though performance comparisons, the hybrid system’s effectiveness and competitiveness are demonstrated. Our calculation results reveal that the hybrid system achieves a 31.19% increase in its maximum POD and 54.61% improvement in its corresponding EE compared to that of the standalone AFC. Furthermore, numerous parametric studies are conducted. Some findings indicate that the POD of the hybrid system can be improved by elevating the operating temperature of the AFC and the environmental temperature, and that it can be optimized using the geometric characteristics of an ITEG. However, the EE of the hybrid system gains improvement via increasing the operating temperature of the AFC or decreasing both the environmental temperature and geometric characteristics of the ITEG. Additionally, the coefficient of the spatial inhomogeneity of the ITEG determines the optimal operating current density of the AFC. These insights offer valuable guidance for the integration and operation of practical hybrid systems.

Role of turbulent separatrix tangle in the improvement of the integrated pedestal and heat exhaust issue for stationary-operation tokamak fusion reactors

The magnetic separatrix surface is designed to provide the final and critical confinement to the hot stationary-operation core plasma in modern tokamak reactors in the absence of an external magnetic perturbation (MP) or transient magneto-hydrodynamic perturbation, while diverting the exhaust heat to divertor plates. All the stationary operational boundary plasma studies and reactor designs have been performed under this assumption. However, there has been a long-standing suspicion that a stationary-operation tokamak plasma even without external MPs or edge localized modes (ELMs) activities may not have a stable closed separatrix surface, especially near the magnetic X-point. Here, the first gyrokinetic numerical observation is reported that the divertor separatrix surface, due to homoclinic tangles caused by intrinsic electromagnetic turbulence, is not a stable closed surface in a stationary operation phase even without MPs or ELMs. Unlike the MP- or ELM-driven homoclinic tangles that could cause deleterious effects to core confinement or divertor plates, it is found that the micro-turbulence driven homoclinic tangles could connect the divertor plasma to the pedestal plasma in a constructive way by broadening the divertor heat-exhaust footprint and weakening the pedestal slope to the ELM-safe direction. Micro-turbulent homoclinic tangles can open a new research direction in understanding and controlling these two most troublesome and non-locally connected edge-plasma issues in a tokamak fusion reactor.

Enhanced Heat Transfer in Thermoelectric Generator Heat Exchanger for Sustainable Cold Chain Logistics: Entropy and Exergy Analysis

This study investigates the application of thermoelectric power generation devices in conjunction with cold chain logistics transport vehicles, focusing on their efficiency and performance. Our experimental results highlight the impact of thermoelectric module characteristics, such as thermal conductivity and the filling thickness of copper foam, on the energy utilization efficiency of the system. The specific experimental setup involved a simulated logistics cold chain transport vehicle exhaust waste heat recovery thermoelectric power generation system, consisting of a high-temperature exhaust heat exchanger channel and two side cooling water tanks. Thermoelectric modules (TEMs) were installed between the heat exchanger and the water tanks to use the temperature difference and convert heat energy into electrical energy. The analysis demonstrates that using high-performance thermoelectric modules with a lower thermal conductivity results in better utilization of the temperature difference for power generation. Additionally, the insertion of porous metal copper foam within the heat exchanger channel enhances convective heat transfer, leading to an improved performance. Furthermore, the study examines the concepts of exergy and entropy generation, providing insights into the system energy conversion processes and efficiency. Overall, this research offers valuable insights for optimizing the design and operation of thermoelectric generators in cold chain logistics transport vehicles to enhance energy utilization and sustainability.

Conceptual design and multi-objective optimization of a hybrid system based on direct ammonia protonic ceramic fuel cell and alkali metal thermal electric converter

As a power generation device, direct ammonia protonic ceramic fuel cells (NH3–PCFCs) also produce a significant amount waste heat, which not only results in energy wastage but also abnormal operation if the waste heat is not removed. To address these concerns and enhance generation electricity capacity, a novel waste heat recovery system based upon NH3-PCFC and alkali metal thermal electric converter (AMTEC) is first proposed, wherein the AMTEC converts the high-grade exhaust heat produced by the NH3-PCFC to extra electricity. Considering ammonia decomposition sluggish kinetics, various irreversible overpotential losses of NH3-PCFC as well as thermodynamic losses within the integrated system, the energetic/exergetic performance parameters evaluating the NH3-PCFC, AMTEC and the hybrid system are formulated. The general performance characteristics of the proposed system are revealed, along with a sensitive analysis conducted under specific operational conditions or structural parameters. Numerical calculation exhibited that the maximum attainable power density of the hybrid system has been promoted 20.5 % than that of stand-alone NH3-PCFC system. The multi-objective genetic algorithm is utilized to optimize the hybrid system performance for trade-off the power output and efficiency. Optimized results show the power density and corresponding efficiency of proposed system can respectively reach 6762.3 W m−2 and 49.8 % in the corresponding optimization conditions.

Investigation on the natural smoke exhaust performance by vertical shaft in tunnel fires under different ambient pressures

In high-altitude tunnels, due to the ambient pressure and density of air being different from those under normal pressure, the convection and heat radiation in tunnels are also different when fires occur. As a result, the smoke exhaust capacity varies under different pressures. This work aimed to numerically explore the impact of ambient pressure on the smoke exhaust efficiency at high-altitude shallow tunnels with natural ventilation by shaft. The numerical results demonstrated that the smoke exhaust capacity is enhanced with increasing ambient pressure. This is because of the increase in the air entrainment coefficient and air density, and it causes plug-holing more easily to occur under higher ambient pressures. Once the plug-holing has taken place, the fresh air can be directly exhausted through the shaft, which results in a poor smoke exhaust capacity. By accounting for the factors of the smoke layer thickness, ambient pressure, the exhausted smoke temperature and heat release rate, the Richardson number was introduced as the criterion for determining whether plug-holing occurs. As ambient pressure was increased, the critical Richardson number for plug-holing was observed to decrease, a finding supported by existing research.

Combined Supercritical CO2 Brayton Cycle and Organic Rankine Cycle for Exhaust Heat Recovery

Abstract In order to reduce energy consumption and related CO2 emissions, waste heat recovery is considered a viable opportunity in several economic sectors, with a focus on industry and transportation. Among different proposed technologies, thermodynamic cycles using suitable organic working fluids seem to be promising options, and the possibility of combining two different cycles improves the final recovered energy. In this paper, a combination of Brayton and Rankine cycles is proposed: the upper cycle has supercritical carbon dioxide (sCO2) as its working fluid, while the bottomed Rankine section is realized by an organic fluid (organic Rankine cycle (ORC)). This combined unit is applied to recover the exhaust energy from the flue gases of an internal combustion engine (ICE) for the transportation sector. The sCO2 Brayton cycle is directly facing the exhaust gases, and it should dispose of a certain amount of energy at lower pressure, which can be further recovered by the ORC unit. A specific mathematical model has been developed, which uses experimental engine data to estimate a realistic final recoverable energy. The model is able to evaluate the performance of each recovery subsection, highlighting interactions and possible trade-offs between them. Hence, the combined system can be optimized from a global point of view, identifying the most influential operating parameters and also considering a regeneration stage in the ORC unit.

Simultaneous production of electricity and potable water underwater by integrating concentrating photovoltaic with air gap membrane distillation

This paper combines underwater concentrating photovoltaic and air gap membrane distillation, enabling the simultaneous production of electricity and potable water in underwater environments. Given its submerged nature and absence of land occupation, it proves particularly advantageous for land-deficient regions with limited access to electricity and potable water, such as islands and Coastal cities. It primarily comprises innovatively designed underwater solar concentrators featuring extensive light interception angles, photovoltaic modules, and membrane distillation units. It utilizes exhausted heat from photovoltaic modules to separate clean water from seawater via membrane distillation process. Furthermore, it is engineered to prevent any contact between metal materials and seawater, thereby mitigating the risk of corrosion. An experimental setup with photovoltaic cells’ areas of 0.006 m2 is developed and tested in the laboratory and under real weather conditions to assess its performance. The steady-state experimental findings indicate that as solar irradiation increases from 500 W/m2 to 900 W/m2, its electricity generation efficiency ranges from 9.0% to 9.7%, while the water yield efficiency ranges from 32.8% to 35.1%. Besides, outdoor experiments demonstrate that its power output during normal incidence ranges from 38.89 W/m2-85.56 W/m2, with an average electrical efficiency of 10.5%. Its average potable water yield reaches 0.537 kg/m2/h and average water production efficiency reaches 48.3%.

DESIGN OF RICE HUSK ROTARY DRYER USING WASTE HEAT ELECTROSTATIC PRECIPITATOR OF THE CEMENT INDUSTRY

ESP or electrostatic precipitator is a device used to capture particulate matter, such as dust, in exhaust gases using electrostatic principles. In the cement industry, ESP is commonly placed after the clinker cooler to clean the exhaust air from the cooling process, ensuring it is free from clinker dust. The clinker cooler is a device that cools down the clinker using air, reducing its temperature from an initial temperature of around 1450°C to approximately 100°C - 120°C. The exhaust air from the clinker cooler is then passed through the ESP at temperatures ranging from around 237°C to 311°C. Based on the temperature data, the exhaust air from the ESP has the potential for heat reuse for other processes, including as a heat source for drying rice husk, which is a common alternative fuel used in the cement industry and typically has a moisture content of around 25%-37%. The results of this design indicate that the exhaust heat from the ESP, with an input temperature of 275°C, is capable of drying rice straw pellets from a moisture content of 25% to 14.73% using a designed rotary dryer with a capacity of 21.6 t/h, a length of 41.58 m, and a diameter of 2.92 m. It is constructed using ASTM 283 C material with a thickness of 8.76 mm and is insulated with a 15.6 mm thick layer of aluminum foil.

New Hybrid CHP System Integrating Solar Energy and Exhaust Heat Thermochemical Synergistic Conversion with Dual-Source Energy Storage

New Hybrid CHP System Integrating Solar Energy and Exhaust Heat Thermochemical Synergistic Conversion with Dual-Source Energy Storage

Study on the Applicability of Green and Efficient Refrigeration and Air Conditioning Based on Exhaust Air Heat Recovery Technology

With the sustained and stable development of the national economy, China has stepped into a new stage of green emission reduction. Under the environment of comprehensively promoting the market share of green and efficient refrigeration products, the popularization and use of exhaust air heat recovery technology in different fields will further promote the green and efficient transformation of the refrigeration industry, improve the industry's independent innovation technology, and accelerate the construction of ecological civilization. This project firstly analyzes the research background, reviews domestic and international research, and clarifies the research background and current situation; secondly, it builds a comprehensive evaluation system for green refrigeration development based on three major energy-saving concepts, and measures the level of green refrigeration development in China's first-tier cities; secondly, it applies empirical evidence based on the data of three districts and cities, namely, Beijing, Shanghai, and Guangzhou, in the period of 2011-2021, to analyze the effect of the exhaust heat recovery technology on the development of high-efficiency green refrigeration. Then, based on the data of Beijing, Shanghai and Guangzhou from 2011 to 2021, we use the empirical analysis to analyze the effect of exhaust air heat recovery technology on the development of high-efficiency green refrigeration.

Application of exhaust heat dissipation in improving the performance of diesel generators via thermoelectric generator kit accompanied by Cu2O-water nanofluid

Application of exhaust heat dissipation in improving the performance of diesel generators via thermoelectric generator kit accompanied by Cu2O-water nanofluid

Theoretical studies of the expedient radius of thin pipe insulation

Decentralized ventilation systems with exhaust heat recovery are an energy-efficient solution for organizing and maintaining comfortable microclimate parameters in apartments and individual residential buildings. Such supply and exhaust systems do not require additional space for the distribution network of air ducts and significant intervention in the interior of the premises. One such device is the Vents TwinFresh regenerative installation. Twin Fresh install in the structure of the outer wall. The task of follow-up is to increase the efficiency of its work. Studies of heat exchange processes in the thin channels of the heat regenerator carried out. Channels with different thermophysical properties are studied. Experimental uncertainty decreases with better thermal insulation of the investigational stand. It is confirmed by the decrease in overheating and the heat transfer coefficient of the external surface thermal insulation when its thickness increases. Overcoming the critical diameter of the insulation of the experimental installation allows to minimize the measurement error, which takes into account the influence of heat exchange processes of the outer surface of the insulation with the environment. It is necessary to determine not the critical but the expedient diameter of the insulation. When using the appropriate thickness of thermal insulation, the temperatures on the inner and outer surfaces of the pipe have practically the same value. Thus, it is possible to take temperature readings of thin tubes from the outside, not from the inside, with the same accuracy. Accordingly, the design of the test stands for experimental research is simplified. The scope of application of the appropriate diameter of thermal insulation is not limited only to studies of heat transfer. This concept can used in any systems, equipment, and techniques that require insulating materials.

Effect of an Exhaust Heat Exchanger with Inserts on the Performance of Thermoelectric Generators

A thermoelectric generator is used as a waste heat recovery system for generating electric power. The thermoelectric generator system consists of an exhaust heat exchanger, a thermoelectric module, and a water heat exchanger. The aim of the current work is to explore different types of inserts used in the test section of the exhaust heat exchanger and power generation of thermoelectric generators at different operating conditions. An experimental setup has been developed for conducting experimental investigation on thermoelectric generators to find the effect of the exhaust heat exchanger (EHE) with inserts on the performance of thermoelectric generators. The cone (G-type test section) and cone-cylinder (H-type test section) type inserts were introduced to enhance the performance of the thermoelectric generator. Compared with an insert-free (empty, F-type) thermoelectric generator with cone and cone-cylinder type inserts in terms of the output power, the average heat transfer rate and convection heat transfer coefficient of F-type, G-type, and H-type test sections of the EHE are 358, 468, and 459 W and 76, 100, and 97 W/m2K, respectively. It shows that the G-type test section of EHE exchanges more heat from engine exhaust to the hot surface of the thermoelectric module through the wall of the EHE. The G-type test section created more temperature difference; obviously, it generated more power output. It was observed that the G-type and H-type test sections of exhaust heat exchangers improved average maximum output power by 29.49% and 26.11% than that by the F-type test section of heat exchanger, respectively. The F-type, G-type, and H-type test sections of exhaust heat exchangers showed a maximum average efficiency of 0.80, 0.78, and 0.70%, respectively.

Modeling, thermodynamic performance analysis, and parameter optimization of a hybrid power generation system coupling thermogalvanic cells with alkaline fuel cells

During the operation of alkaline fuel cells (AFCs), a significant amount of waste heat is generated, which has negative impacts on energy utilization and the environment. To improve energy efficiency, cost savings, environmental sustainability, and industrial practices, an effective approach is proposed to employ thermogalvanic cells (TGCs) for electric power generation by harvesting low-grade exhaust heat produced in AFCs. A mathematical model of the AFC-TGC hybrid system is established, taking into account the three overpotential losses in AFCs and the irreversible heat losses in TGCs. Based on this thermal-electric coupled model, we investigate the hybrid system’s output performance characteristics and optimal parameter design. The calculated results indicate that the hybrid system achieves a considerable increase of 19.72% in maximum power density from 247.07 W m−2 to 295.80 W m−2 and 5.71% in conversion efficiency from 10.16% to 10.74% compared to a single AFC, respectively. In addition, the output performance of the hybrid system can be further improved by adjusting system parameters such as the AFC’s operating temperature, the length of each TGC cell, the heat sink temperature, and the thermal convection coefficient. More importantly, a comparative study of the maximum power density of AFC-based cogeneration systems reveals that the TGC demonstrates a remarkable ability to economically recover waste heat from the AFC, surpassing previously reported thermal energy utilization devices. This study provides important theoretical guidance for the optimal design and parametric analysis of AFC-TGC hybrid systems, thereby facilitating the development of high-performance energy cascade utilization systems based on AFC devices.

On the Possibility of Using CHP From a 1.4MW Direct Fuel Cell at Kettering University Engineering Building – A Demonstration Study

The concept of using a distributed power generation and a combined heat and power principle – CHP in public buildings, commercial facilities is widely gaining public acceptance as a result of reduced energy cost, reliable power supply and environmental and health issues. By using the exhaust heat from a high temperature fuel cell at 400 oC for cogeneration, space heating, to provide warm water for facility use - (swimming pool and sporting locker room) and cooling in chillers at no additional cost, we reduce energy cost and preserve the environment. By bottoming cycle, the efficiency of the entire system is increased. A study is conducted to compare the economic impact of using the CHP system against the conventional heating system using furnaces.

Biophotonic Combined Energy System (BCES)

A comprehensive outline of a new approach in closed loop processing for energy utilisation and biomass genera tion using micro algae for electricity, heat and chemicals is presented - the Biophotonic Combined Energy System (BCES). The basic idea proposes that life-cycle management is an es sential strategy in research and business. In terms of the BCES a carbon cycle driven by solar radiation via the photosystems of the Chlorophyceae species Scenedesmus rubescens serves as the core process from which valuable materials are extracted. The resi dues serve as the substrate for biogas generation which is used to run a Combined Heat and Power Plant (CHP) equipped with a gas motor and an exhaust gas carbon dioxide and heat recovery system. The electricity generated is fed into the public grid and the thermal energy is used to make the right temperature for the micro algae suspension. The carbon dioxide from biogas combus tion is injected into the algae suspension thereby closing the elementary loop within the system.