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Abstract

The thermal energy represents a significant portion of energy potential in municipal wastewater and may be recovered as electricity by a thermoelectric generator (TEG). Converting heat to all-purpose electricity by TEG has been demonstrated with large heat gradients, but its application in waste heat recovery from wastewater has not been well evaluated. Herein, a bench-scale Bi2Te3-based waste heat recovery system was employed to generate electricity from a low temperature gradient through a combination of experiments and mathematical modeling. With an external resistance of 7.8 Ω and a water (hot side) flow rate of 75 mL min−1, a maximum normalized energy recovery of 4.5 × 10−4 kWh m−3 was achieved under a 2.8 °C temperature gradient (ΔT). Model simulation indicated a boost in both power output and energy conversion efficiency from 0.76 mW and 0.13% at ΔT = 2.8 °C to 61.83 mW and 1.15% at ΔT = 25 °C. Based on the data of two-year water/air temperature obtained from the Christiansburg Wastewater Treatment Plant, an estimated energy generation of 1094 to 70,986 kWh could be expected annually with a saving of $163 to $6076. Those results have revealed a potential for TEG-centered direct electricity generation from low-grade heat towards enhanced resource recovery from wastewater and encouraged further exploration of this approach.

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... The latter is particularly appealing in the framework of water-energy sustainable urban development; in particular, the heat energy recovery potential from wastewater could possibly be even higher than its recoverable chemical energy potential [14,15], and it does not require biological treatment to be converted into a directly usable form. Waste heat from wastewater is reportedly able to generate electrical energy via a thermoelectric generator [16], but the implementation of this is difficult within an urban context. A more accessible technology is the energy recovery from wastewater using heat exchangers installed directly in the sewage collection system [17]. ...
... A heat exchanger is installed in direct contact with the wastewater that serves as a heat source or sink, and is later connected to a heat pump and then to the heating and cooling system of a building situated in close proximity. Temperatures of civil wastewater may be more than 25-27 • C in domestic outflows [18], representing a significant thermal energy source [16]; at the inlet of water treatment plants or water resource recovery facilities (WRRFs), the temperature is far lower (15-25 • C or lower, depending on the climate) [16,19,20], and thus, its use for heat recovery may be less practical. Also, heat recovery at this stage should be carefully considered, as it might interfere with treatment processes: biological processes, including denitrification, are sensitive to wastewater temperature, as biological reaction rates depend on Arrhenius' law, and excessive heat extraction from sewage could harm their efficiency [21]. ...
... A heat exchanger is installed in direct contact with the wastewater that serves as a heat source or sink, and is later connected to a heat pump and then to the heating and cooling system of a building situated in close proximity. Temperatures of civil wastewater may be more than 25-27 • C in domestic outflows [18], representing a significant thermal energy source [16]; at the inlet of water treatment plants or water resource recovery facilities (WRRFs), the temperature is far lower (15-25 • C or lower, depending on the climate) [16,19,20], and thus, its use for heat recovery may be less practical. Also, heat recovery at this stage should be carefully considered, as it might interfere with treatment processes: biological processes, including denitrification, are sensitive to wastewater temperature, as biological reaction rates depend on Arrhenius' law, and excessive heat extraction from sewage could harm their efficiency [21]. ...
Article
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To achieve technically-feasible and socially-desirable sustainable management of urban areas, new paradigms have been developed to enhance the sustainability of water and its resources in modern cities. Wastewater is no longer seen as a wasted resource, but rather, as a mining ground from which to obtain valuable chemicals and energy; for example, heat energy, which is often neglected, can be recovered from wastewater for different purposes. In this work, we analyze the design and application of energy recovery from wastewater for heating and cooling a building in Brno (Czech Republic) by means of heat exchangers and pumps. The temperature and the flow rate of the wastewater flowing in a sewer located in the proximity of the building were monitored for a one-year period, and the energy requirement for the building was calculated as 957 MWh per year. Two options were evaluated: heating and cooling using a conventional system (connected to the local grid), and heat recovery from wastewater using heat exchangers and coupled heat pumps. The analysis of the scenarios suggested that the solution based on heat recovery from wastewater was more feasible, showing a 59% decrease in energy consumption compared to the conventional solution (respectively, 259,151 kWh and 620,475 kWh per year). The impact of heat recovery from wastewater on the kinetics of the wastewater resource recovery facility was evaluated, showing a negligible impact in both summer (increase of 0.045 • C) and winter conditions (decrease of 0.056 • C).
... This work studies the effects of different fluid combinations on a low-temperature WHR thermoelectric system. The source of low-temperature waste heat can be air or water because most heat exchange systems are cooled by these two fluids [2,23]. Therefore, the working fluid used in the simulation includes air and water. ...
... The flow rate is set in the range of Reynolds numbers from 10 to 1,000. The working fluids are set to heated water and air from the industrial system [2,23]. The air and water are often used as cooling fluids to absorb hightemperature heat. ...
... Seeing that the installation of the fins makes the hot-side surfaces ascend drastically (Fig. 10c-e) and Eqs. (22) and (23) show that the heat flow rate is directly proportional to the temperature difference, the fins substantially push up the heat flow rate (Fig. 12a-c), thereby improving the total output power and the average conversion efficiency. For example, the total output power and mean conversion efficiency of the TEMs without fins at Re = 1,000 are 0.197 W and 0.664%, respectively. ...
Article
Low-temperature waste heat has great potential for renewable power because it accounts for around 60% of total industrial waste heat. This study develops a model of integrating thermoelectric generation, computational fluid dynamics, and plate fins to figure out a low-temperature waste heat recovery system for power generation. The effect of the number of partitions of a thermoelectric module on its performance is examined, and the results show that a single module without a partition can provide accurate predictions. Four different combinations between wastewater and air in the hot and cold channels under three different Reynolds numbers (i.e., Re = 10, 100, and 1,000) on thermoelectric modules’ performance suggest that only combining hot wastewater and cooling water can contribute electricity to a certain extent. By installing fins with a number range of 0–27, it indicates that fin installation can dramatically intensify heat transfer and thermoelectric modules’ performance. The optimal number of fins at Re = 10 and 100 is 21, whereas it is 27 at Re = 1,000. The maximum total output power and mean conversion efficiency are 0.411 W and 0.95%, respectively, with 27 fins at Re = 1,000. These values account for 105.5% and 43.94% improvements when compared to the TEMs without fins. Even though installing fins increases the pressure drop in the channel, its value is much smaller than the generated power (less than1%). The developed method in this study can be used to efficiently and accurately predict the performance of thermoelectric modules, and obtained results have provided practical insights into the design of low-temperature waste heat recovery systems for green power generation.
... This system simulation relied on a simplified 1D governing equation of the TEG. Furthermore, Zou et al. (2018) assessed this type of systems. They reached a conclusion that TEG modules may recover 1094 to 70,986 kW h/year for a temperature difference range of 2.5 • C-25 • C between the hot water and ambient air when the water average flow rate is 75 mL/min. ...
... During different studies on the waste heat recovery by TEG, different models were proposed to simulate the performance of the TEG. Several models relied on simplified 1D and 2D governing equations when calculating the thermoelectric performance Kim, 2018;Zhang, 2016;Zou et al., 2018). Other studies relied on even more simplified equations which compute output power according to the temperature difference, connected the electrical load and average thermo-electrical properties of the materials without considering their exact variation across the TEG (Dai et al., 2011;Lan et al., 2018;Lv et al., 2018). ...
Article
This paper presents three-dimensional study on the enhancement of waste heat recovery from vertical chimney via thermoelectric generators (TEG) by using heat spreader. The physical model composes of aligned TEGs mounted on the chimney wall where each TEG is cooled at its cold side by rectangular finned heat sink. The spreaders are installed on the generators’ cold sides between the generators and the heat sinks’ bases. The studied model represents three of the TEGs installed on the chimney wall. Three-dimensional model is presented for the physical model coupling the governing equations of thermal, fluid flow and electrical models and is solved by using ANSYS software. Results indicate that using spreader increases total output generators power by 17% and 42% at spreader length 40 and 140 mm, respectively and pitch 140 mm. The increase of the TEGs power is about 17% and 21% due to using spreader length of 40 and 80 mm, respectively at 80 mm pitch. Using heat spreader with maximum length of 140 mm, increases the conversion efficiency of the lower, middle generator and upper TEGs by 22.2%, 18.8%, and 19.7%, respectively, while the overall efficiency of the system rises by 20.4%. Using spreader with 140 mm reduces the used generators and heat sinks numbers to approximately the half.
... Different from previous cooling methods, Zhang cooled the heat sink fitted to the cold side of the TEG by burying a vertical hollow pipe in the soil and connecting the outlet of the pipe to the heat sink, which can be cooled by cool air from the pipe in this arrangement. Other researchers have generated thermoelectric power from the exhaust of car engines [9], waste heat in municipal wastewater [10], hot flue gases in chimneys [11] and even human body heat [12,13]. Stevens [14] used the energy in soil by transferring soil heat to the ground level through a heat exchanger; two TEGs were stacked as a pair: the hot side of the first TEG faced the ground-side heat exchanger, and the cold side of the second TEG faced the air-side heat exchanger. ...
... The conversion efficiency of the TEG can be obtained by dividing F into P max . In Harbin, the temperature [10], the energy conversion efficiency is much lower because the heat transfer capacity of soil is much lower than that of water, so the heat cannot be replenished in time. Thus far, the conversion efficiency of the thermoelectric power generation device is miniscule, and measures should be taken to enhance the thermal conductivity of soil and to improve the heat dissipation on the cold side of the TEG and the heat insulation between the upper part of the gravityassisted heat pipe and the surrounding environment [25,26]. ...
Article
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As a new strategy to power forest wireless sensors in remote areas, an environmental microenergy collection device has been improved, and field experiments were carried out under natural conditions for the first time. The thermoelectric power generation devices used a gravity-assisted heat pipe to transmit heat from shallow soil to ground level, and a thermoelectric generator (TEG) was employed to generate electric power from the temperature difference between soil and air. Over the 6-month experimental period at two natural sites, approximately 128.74 J of energy could be harvested in a single day, and 5 209.92 J of energy could be harvested in a generation cycle. The results showed the feasibility of using this green energy to power wireless sensors in remote forests or other environments, This work is relevant to the current acute energy shortages and environmental pollution problems.
... The efficiency is directly related to the temperature difference (DT) with higher conversion at a higher temperature difference. It was reported that a small wastewater treatment plant (WWTP) with a treatment capacity of 3 MGD could produce as much as 70,986 kWh energy per year by converting wastewater thermal energy to electric energy using TEG [29]. However, using mainstream wastewater as a heat source can be challenging given its large quantity (thus a high requirement for TEG size) and also depend on geographic location (temperature). ...
... The maximum power density at DT ¼ 18 C was 108 mW m À2 , much higher than 31 mW m À2 at DT ¼ 10 C. An evaluation of TEG based on mathematic modeling for conversion of wastewater heat to electricity found similar results that 10 C of temperature difference could create a fourfold increase in the power production [29]. The estimated internal resistance of a single TEG unit at DT ¼ 18 C was 12.9 U, smaller than 13.7 U at DT ¼ 10 C. To drive HER for hydrogen production in an MEC, a theoretical minimum of 0.14 V is required and in practice (based on published literature) the applied voltage is often greater than 0.4 V to overcome the overpotential [21]. ...
Article
Waste heat from anaerobic digesters can be converted to electricity by using thermoelectric generators (TEG). Herein, such energy was employed to power a microbial electrolysis cell (MEC) for producing hydrogen gas. Four TEG units could deliver a voltage of ~0.5 V, sufficient to drive the MEC that achieved a hydrogen production rate of 0.48 ± 0.13 m³ m⁻³ d⁻¹. This rate was further improved to 0.75 ± 0.05 m³ m⁻³ d⁻¹ when the temperature difference for TEG was increased from 18 to 28 °C. There was no significant difference between the TEG-powered MEC and power supply-supported MEC (at 0.6 V), in terms of current generation, hydrogen production, and organic removal. Ambient air was also studied as a cold-side source for TEG, although some challenges were encountered to maintain a large temperature difference. Those results will encourage further exploration of using TEG as a feasible power supply for sustainable MEC operation.
... Domestic, commercial, and industrial wastewater can have a temperature difference of several degrees compared to the sewer headspace or wall ( Figure 1). Heat recovery from wastewater is increasing in popularity [9], [10]; however, the potential varies depending on altitude, time of day, time of year, and catchment area of the drainage system [11]. Temperature measurements in the sewer over a period of 12 months in Eawag's urban water observatory (UWO) [12] show that seasonal variations affect both water and air temperatures similarly ( Figure 1). ...
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Underground infrastructure networks form the backbone of vital supply and disposal systems. However, they are under-monitored in comparison to their value. This is due, in large part, to the lack of energy supply for monitoring and data transmission. In this paper, we investigate a novel, energy harvesting system used to power underground sewer infrastructure monitoring networks. The system collects the required energy from ambient sources, such as temperature differences or residual light in sewer networks. A prototype was developed that could use either a thermoelectric generator (TEG) or a solar cell to capture the energy needed to acquire and transmit ultrasonic water level data via LoRaWAN. Real-world field trials were satisfactory and showed the potential power output, as well as, possibilities to improve the system. Using an extrapolation model, we proved that the developed solution could work reliably throughout the year.
... A review is proposed in [222] to clarify the perspectives in terms of heat recovery from waste in Europe. Among the works related to the use of various types of waste materials (municipal waste, wastewater, farming waste) for electricity production it is worth considering [230][231][232][233][234]. This resource is particularly suitable in DH, particularly in low-temperature DH, where also poor exergy heat can be significantly exploited. ...
Article
Integration of different energy infrastructures (heat, electricity and gas vectors) offers great potential for better managing energy sources, reducing consumption and waste as well as enabling a higher share of renewables, lower environmental impact and lower costs. This paper aims at reviewing the state-of-the-art energy system infrastructures in order to provide a comprehensive overview of technologies, operational strategies, modelling aspects and the trends towards integration of heat, electricity and gas infrastructures. Various technological domains are taken into account, ranging from energy distribution networks (thermal, electric and gas), components for the energy vector conversion (e.g. combined heat and power, power to heat, power to gas, etc.) and energy storage. Furthermore, the aspects related to smart management in energy systems are investigated, such as integration of renewable energy sources and energy recovery systems.
... In both cases the resource, if not used, is dissipated in the environment. Concerning the use of wastes for heat in DH [68,69] various types of waste materials can be used (municipal waste, wastewater, farming waste) [70][71][72][73][74]. Solid waste for heat production are usually burned in cogeneration plants, therefore use of TES in this case is similar to the one discussed in 2.2.1, except for the operating schedules. ...
Article
Full-text available
Thermal storage facilities ensure a heat reservoir for optimally tackling dynamic characteristics of district heating systems: heat and electricity demand evolution, changes of energy prices, intermittent nature of renewable sources, extreme wheatear conditions, malfunctions in the systems. The present review paper explores the implementation of thermal energy storage in district heating and cooling systems. Both short-term and long-term storages are considered highlighting their potential in combination with district heating. Connections of sensible, latent (phase change material) and chemical heat storage are analyzed taking into account the research maturity of each type technology. The transition of current energy systems towards next generation district heating, and sustainable multi energy networks is considered. Performance assessment by using proper thermodynamic indicators and costs are investigated. Further addressed topics include the use of heat capacity of the network and the buildings connected to the system to store energy. The main issues currently limiting the diffusion of daily and seasonal thermal storage and the main research paths are discussed.
... A low ΔT of 4°C could reach an open circuit voltage of 1.4 V from the TEG and a model predicted that with a temperature difference of 50°C, the TEG system will produce 31 V as open circuit voltage [18]. A theoretical analysis reported that using TEG to harvest energy from warmer wastewater could deliver 1094 to 70,986 kW h to a small-scale wastewater treatment plant with an annual saving of $163 to $6076 [19]. ...
Article
Using alternative power sources to drive hydrogen production in microbial electrolysis cells (MECs) is important to implementation of MEC technology. Herein, thermoelectric generators (TEG) were to power MECs using simulated waste heat. With the MEC anolyte as a cold source for TEG, current generation of the MEC increased to 2.46 ± 0.06 mA and hydrogen production reached 0.14 m³ m⁻³ d⁻¹, compared to the TEG-MEC system without hydraulic connection (1.16 ± 0.07 mA and 0.07 ± 0.01 m³ m⁻³ d⁻¹). A high recirculation rate of 30 mL min⁻¹ doubled both current generation and hydrogen production with 10 mL min⁻¹, benefited from a stronger cooling effect that increased the TEG voltage output. However, the optimal recirculation rate was determined as 20 mL min⁻¹ because of comparable performance but potentially less energy requirement. Reducing anolyte hydraulic retention time to 4 h has increased hydrogen production to 0.25 ± 0.05 m³ m⁻³ d⁻¹ but decreased organic removal efficiency to 69 ± 2%. Adding three more TEG units that captured more heat energy further enhanced hydrogen production to 0.36 m³ m⁻³ d⁻¹. Those results have demonstrated a successful integration of TEG with MEC through both electrical and hydraulic connections for simultaneous wastewater treatment and energy recovery.
... Hence, there is a need for technical and economic studies that will develop the feasibility of large-scale applications that, in the medium and long term, would make this a competitive source of clean energy [178]. Zou et al. [179] demonstrated that municipal wastewater can be used to produce electricity using a thermoelectric generator (TEG). Their theoretical study, performed for the Christiansburg Wastewater Treatment Plant, estimated energy generation of 1094 to 70,986 kWh per year, with a saving of USD 163 to USD 6076. ...
Article
Full-text available
A thermoelectric effect is a physical phenomenon consisting of the direct conversion of heat into electrical energy (Seebeck effect) or inversely from electrical current into heat (Peltier effect) without moving mechanical parts. The low efficiency of thermoelectric devices has limited their applications to certain areas, such as refrigeration, heat recovery, power generation and renewable energy. However, for specific applications like space probes, laboratory equipment and medical applications, where cost and efficiency are not as important as availability, reliability and predictability, thermoelectricity offers noteworthy potential. The challenge of making thermoelectricity a future leader in waste heat recovery and renewable energy is intensified by the integration of nanotechnology. In this review, state-of-the-art thermoelectric generators, applications and recent progress are reported. Fundamental knowledge of the thermoelectric effect, basic laws, and parameters affecting the efficiency of conventional and new thermoelectric materials are discussed. The applications of thermoelectricity are grouped into three main domains. The first group deals with the use of heat emitted from a radioisotope to supply electricity to various devices. In this group, space exploration was the only application for which thermoelectricity was successful. In the second group, a natural heat source could prove useful for producing electricity, but as thermoelectricity is still at an initial phase because of low conversion efficiency, applications are still at laboratory level. The third group is progressing at a high speed, mainly because the investigations are funded by governments and/or car manufacturers, with the final aim of reducing vehicle fuel consumption and ultimately mitigating the effect of greenhouse gas emissions.
... Hence, there is a need for technical and economic studies that will develop the feasibility of large-scale applications that, in the medium and long term, would make this a competitive source of clean energy [178]. Zou et al. [179] demonstrated that municipal wastewater can be used to produce electricity using a thermoelectric generator (TEG). Their theoretical study, performed for the Christiansburg Wastewater Treatment Plant, estimated energy generation of 1094 to 70,986 kWh per year, with a saving of USD 163 to USD 6076. ...
Article
Full-text available
A thermoelectric effect is a physical phenomenon consisting of the direct conversion of heat into electrical energy (Seebeck effect) or inversely from electrical current into heat (Peltier effect) without moving mechanical parts. The low efficiency of thermoelectric devices has limited their applications to certain areas, such as refrigeration, heat recovery, power generation and renewable energy. However, for specific applications like space probes, laboratory equipment and medical applications, where cost and efficiency are not as important as availability, reliability and predictability, thermoelectricity offers noteworthy potential. The challenge of making thermoelectricity a future leader in waste heat recovery and renewable energy is intensified by the integration of nanotechnology. In this review, state-of-the-art thermoelectric generators, applications and recent progress are reported. Fundamental knowledge of the thermoelectric effect, basic laws, and parameters affecting the efficiency of conventional and new thermoelectric materials are discussed. The applications of thermoelectricity are grouped into three main domains. The first group deals with the use of heat emitted from a radioisotope to supply electricity to various devices. In this group, space exploration was the only application for which thermoelectricity was successful. In the second group, a natural heat source could prove useful for producing electricity, but as thermoelectricity is still at an initial phase because of low conversion efficiency, applications are still at laboratory level. The third group is progressing at a high speed, mainly because the investigations are funded by governments and/or car manufacturers, with the final aim of reducing vehicle fuel consumption and ultimately mitigating the effect of greenhouse gas emissions.
... Hence, there is a need for technical and economic studies that will develop the feasibility of large-scale applications that, in the medium and long term, would make this a competitive source of clean energy [178]. Zou et al. [179] demonstrated that municipal wastewater can be used to produce electricity using a thermoelectric generator (TEG). Their theoretical study, performed for the Christiansburg Wastewater Treatment Plant, estimated energy generation of 1094 to 70,986 kWh per year, with a saving of USD 163 to USD 6076. ...
... Wastewater treatment plants are considered as units aiming the effective removal of nutrients and organic matter from contaminated wastewaters to avoid the accumulation of these pollutants in the environment. Although these benefits, WWTPs have been found to consume a great portion of energy, resulting in increasing of greenhouse gases emissions and other impacts on the environment (Yoshida et al., 2014;Zou et al., 2018). More than 50% of the energy consumption in WWTPs is caused by mechanical aeration (Au et al., 2013;. ...
Article
Most of wastewater treatment plants (WWTPs) in developing countries comprised primary and secondary treatment without including any tertiary treatment or sludge processing. Decision makers think that additional treatment is costly and the gained environmental benefits are limited. This study aims to investigate the environmental and economic benefits of improving current conventional WWTPs in developing countries by adding tertiary treatment and/or anaerobic digestion of sludge. For this purpose, life cycle assessment (LCA) for four different scenarios was studied for a wastewater plant located in Gamasa, Egypt. The 1st scenario is the plant in its current state. The 2nd scenario is the addition of anaerobic digestion of sludge. The 3rd scenario is the addition of a tertiary treatment stage. The 4th scenario is the addition of anaerobic digestion of sludge and tertiary treatment stage. CML 2000 method was used for assessing the environmental impacts of the four scenarios. The 4th scenario attained maximum environmental benefits for all categories due to the energy saving and the prospect of water reuse. The application of the 4th scenario achieved environmental benefits in some important categories such as ozone layer depletion. According to the economic evaluation, the addition of tertiary treatment leads to gain financial profits due to the value of the reusable produced water. This study underlines the importance of considering LCA in development of WWTPs in developing countries.
Article
If made in porous foam, thermoelectric ceramics for power generation can enhance the power output by directly extracting thermal energy from heat sources. This paper discusses the time-dependent power output and elastic/plastic fracture of the porous thermoelectric generator (TEG) with a small oblique-through crack. Analytical solutions of temperature and thermal stress of the TEG are derived based on an effective model of porous foam. The finite element numerical model is created to validate the analytical solutions and to explore more thermomechanical properties and constitutive behaviors of the porous materials. Comparing to the traditional bulk TEG, porous TEG can greatly improve the power output however the thermal stress is enhanced therefore the strength is substantially reduced. The power output gradually increases to a peak value and then decreases with the length of the TEG. Based on the criterion of fracture mechanics, a simplified and useful expression of the critical heat flux for crack propagation is identified. The critical heat flux for crack growth is inversely proportional to the porosity and the crack length. A more rigid contact between the TEG and the elastic boundary results in a larger thermal stress and a smaller critical heat flux. The velocity of crack propagation is mostly determined by the porosity and the ratio of the initial crack length to the arbitrary crack length. Also observed is that the length of plastic zone at the crack tips increases with the increasing porosity.
Article
Theoretical model of thermoelectric generator (TEG) cooled by direct evaporative cooling technology is developed. In the theoretical model, thermoelectric material properties depending on temperature change and effects of heat loss by radiation, conduction, and Thomson phenomenon are considered. To investigate the effect of evaporative cooling to the efficiency of TEG, the simulation conditions are set as hot-side temperature of 40–120 °C and 1 mm thickness of thin water film covering for cold-side. The ambient temperature is 25 °C and the relative humidity of the air is set from 25% to 75%. Based on the developed theoretical model, the output power of TEG is increased as increasing hot side temperature under fixed relative humidity or as decreasing relative humidity under fixed hot-side temperature. Consequently, the maximum output power of 130.69 W m⁻² and an efficiency of 1.63% are obtained with 25% relative humidity and 120 °C for the hot-side temperature condition. The results show that the output power and efficiency are increased 100.53 and 10.53 times higher than without evaporative cooling (natural convection case, output power of 1.30 W m⁻² and efficiency of 0.1548%), respectively.
Article
The present work concerns parametric analysis and case study of the performance of a newly suggested Multi Drain Heat Recovery System (MDHRS) that uses the relatively hot water of different drain sources such as the shower, the dish washer, the washing machine, and the sink simultaneously to heat/preheat residential cold water. To proceed, an appropriate thermal modeling along with its associated in-house code are developed. The heat rate error between numerical and experimental results is always below 14.2% for different inlet cold water temperatures and for different cold and hot water flow rates. The parametric analysis performed treated the effect of the hot and cold water inlet temperatures and flow rates on the performance of the system and allowed to raise practical recommendations in terms of application of the suggested concept. In the case study presented, the monthly amount of energy reduced, the monthly amount of money saved and the monthly amount of CO2 emissions reduction are considered. It was shown that when the heat exchanger length increases from 0.2 m to 1 m, the monthly amount of reduced energy increases from 102.2 kWh to 410.9 kWh, the monthly amount of money saved increases from 13.3 $ to 53.4 $ and the monthly amount of emissions reduction increases from 72.5 kg to 291.7 kg for a drain water temperature of 25 °C for the case of Lebanon.
Article
Efficiency and cost-effectiveness play dominant roles in the commercialization of thermoelectric generator (TEG) technology. In this paper, the exergy analysis of a TEG module with 199 TE couples was considered. Two objective functions, the exergy efficiency and levelized cost of energy (LCOE), were established for exergoeconomic analysis. The geometric structure and working conditions involving TE couple length, base area ratio, working temperature, and load resistance were varied. The particle swarm optimization (PSO) method has excellent convergence and few parameters need to be adjusted. Mutation can increase randomization for the PSO method, making it possible to improve its search direction. Therefore, the mutation-PSO (M-PSO) algorithm was used to optimize the exergy efficiency and LCOE for the TEG. Through the M-PSO algorithm, the optimum corresponds to an exergy efficiency of 29% and LCOE of 1.93 $US/kWh·m² under a maximum temperature difference of 40 K. In order to achieve a balance between the two exergoeconomic indices, the ξ-constraint combined with the M-PSO method was used to obtain alternatives, named Pareto solutions. Then, these alternatives were ranked to acquire an ideal solution based on a technique for order preference by similarity ideal solution (TOPSIS) method. The TOPSIS ideal solution corresponds to an exergy efficiency of 22.2% and LCOE of 3.02 $US/kWh·m².
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In the past several years, metal sulfides have been the subject of extensive research as promising thermoelectric materials with high potential in future commercial applications due to their low cost, low toxicity, and abundance. This review summarizes recent developments and progress in the research of metal sulfides, particularly for binary metal sulfides such as Bi2S3, Cu2−xS, and PbS. Methods for improving the thermoelectric properties of these binary sulfides are emphasized, and promising strategies are suggested to further enhance the thermoelectric figure of merit of these materials.
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Solid-state thermoelectric devices are currently used in applications ranging from thermocouple sensors to power generators in space missions, to portable air-conditioners and refrigerators. With the ever-rising demand throughout the world for energy consumption and CO[subscript 2] reduction, thermoelectric energy conversion has been receiving intensified attention as a potential candidate for waste-heat harvesting as well as for power generation from renewable sources. Efficient thermoelectric energy conversion critically depends on the performance of thermoelectric materials and devices. In this review, we discuss heat transfer in thermoelectric materials and devices, especially phonon engineering to reduce the lattice thermal conductivity of thermoelectric materials, which requires a fundamental understanding of nanoscale heat conduction physics.
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Organic semiconductors are attracting increasing interest as flexible thermoelectric materials owing to material abundance, easy processing and low thermal conductivity. Although progress in p-type polymers and composites has been reported, their n-type counterpart has fallen behind owing to difficulties in n-type doping of organic semiconductors. Here, we present an approach to synthesize n-type flexible thermoelectric materials through a facile electrochemical intercalation method, fabricating a hybrid superlattice of alternating inorganic TiS2 monolayers and organic cations. Electrons were externally injected into the inorganic layers and then stabilized by organic cations, providing n-type carriers for current and energy transport. An electrical conductivity of 790 S cm−1 and a power factor of 0.45 mW m−1 K−2 were obtained for a hybrid superlattice of TiS2/[(hexylammonium)x(H2O)y(DMSO)z], with an in-plane lattice thermal conductivity of 0.12 ± 0.03 W m−1 K−1, which is two orders of magnitude smaller than the thermal conductivities of the single-layer and bulk TiS2. High power factor and low thermal conductivity contributed to a thermoelectric figure of merit, ZT, of 0.28 at 373 K, which might find application in wearable electronics.
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Based on Fourier’s law and the Seebeck effect, this paper presents a mathematical model of a Thermoelectric Generator (TEG) device using the exhaust gas of vehicles as heat source. The model simulates the impact of relevant factors, including vehicles exhaust mass flow rate, temperature and mass flow rate of different types of cooling fluid, convection heat transfer coefficient, height of PN couple, the ratio of external resistance to internal resistance of the circuit on the output power and efficiency. The results show that the output power and efficiency increase significantly by changing the convection heat transfer coefficient of the high-temperature-side than that of low-temperature-side. The results also show that with variation in the height of the PN couple, the output power occur a peak value, and the peak value decreases when decreasing the thermal conductivity of the PN couple, and increases when increasing the Seebeck coefficient and electric conductivity of the material. Meanwhile, a maximum output power and efficiency of a TEG appear when external resistance is greater than internal resistance. This is different from a common circuit, and with the increment of ZT, the maximum value moves toward the direction of an increasing ratio of external resistance to internal resistance. Finally, we propose a new idea to reform our experiment design to achieve better performance.
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Solid-state thermoelectric devices are currently used in applications ranging from thermocouple sensors to power generators in satellites, to portable air-conditioners and refrigerators. With the ever-rising demand throughout the world for energy consumption and CO2 reduction, thermoelectric energy conversion has been receiving intensified attention as a potential candidate for waste-heat harvesting as well as for power generation from renewable sources. Efficient thermoelectric energy conversion critically depends on the performance of thermoelectric materials and devices. In this review, we discuss heat transfer in thermoelectric materials and devices, especially phonon engineering to reduce the lattice thermal conductivity of thermoelectric materials, which requires a fundamental understanding of nanoscale heat conduction physics.
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The efficiency of thermoelectric energy converters is limited by the material thermoelectric figure of merit (zT). The recent advances in zT based on nanostructures limiting the phonon heat conduction is nearing a fundamental limit: The thermal conductivity cannot be reduced below the amorphous limit. We explored enhancing the Seebeck coefficient through a distortion of the electronic density of states and report a successful implementation through the use of the thallium impurity levels in lead telluride (PbTe). Such band structure engineering results in a doubling of zT in p-type PbTe to above 1.5 at 773 kelvin. Use of this new physical principle in conjunction with nanostructuring to lower the thermal conductivity could further enhance zT and enable more widespread use of thermoelectric systems.
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Thermoelectric (Peltier) heat pumps are capable of refrigerating solid or fluid objects, and unlike conventional vapor compressor systems, they can be miniaturized without loss of efficiency. More efficient thermoelectric materials need to be identified, especially for low-temperature applications in electronics and devices. The material CsBi(4)Te(6) has been synthesized and its properties have been studied. When doped appropriately, it exhibits a high thermoelectric figure of merit below room temperature (ZT(max) approximately 0.8 at 225 kelvin). At cryogenic temperatures, the thermoelectric properties of CsBi(4)Te(6) appear to match or exceed those of Bi(2-x)Sb(x)Te(3-y)Se(y) alloys.
Article
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The dimensionless thermoelectric figure of merit (ZT) in bismuth antimony telluride (BiSbTe) bulk alloys has remained around 1 for more than 50 years. We show that a peak ZT of 1.4 at 100°C can be achieved in a p-type nanocrystalline BiSbTe bulk alloy. These nanocrystalline bulk materials were made by hot pressing nanopowders that were ball-milled from crystalline ingots under inert conditions. Electrical transport measurements, coupled with microstructure studies and modeling, show that the ZT improvement is the result of low thermal conductivity caused by the increased phonon scattering by grain boundaries and defects. More importantly, ZT is about 1.2 at room temperature and 0.8 at 250°C, which makes these materials useful for cooling and power generation. Cooling devices that use these materials have produced high-temperature differences of 86°, 106°, and 119°C with hot-side temperatures set at 50°, 100°, and 150°C, respectively. This discovery sets the stage for use of a new nanocomposite approach in developing high-performance low-cost bulk thermoelectric materials.
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Modeling thermoelectric generator (TEG) performances plays an important role in guiding the design of TEGs to achieve better efficiency. However, a rigorous 1-D TEG modeling performance has not yet been conducted, which prevents reliable prediction of TEG performance. In this work, a detailed 1-D model has been developed to take into account temperature-dependent thermoelectric material properties, heat loss due to radiation and conduction, and Thomson effect. A Lead Telluride (PbTe) TEG was chosen as a sample module and the modeling results agree very well with the experimental results, which proves how powerful the presented detailed 1-D model can be used to predict and validate TEG experimental results. TEG power and efficiency were found to have a respective decrease of 10% and 31% from the simplified model at a temperature gradient of 570 K. While heat loss attributable to conduction and radiation were found to be small, the Thomson effect, which is often neglected, was found to significantly reduce TEG performances. The deep analysis enabled by the new model provides useful guidelines to improve the performance of TEGs.
Article
In this work, a comparison between the performance of two- and three-stage cascaded thermoelectric generator (TEG) devices is analyzed based on a prescribed maximum hot side temperature of 973 K, an imposed maximum heat input of 505 W, and a fixed cold side temperature of 473 K. Half-Heusler is used as a thermoelectric (TE) material in the top higher temperature stage and skutterudite as a TE in the bottom lower temperature stage for the two-stage structure. Lead telluride is added in the middle stage to form the three-stage structure. Based on the prescribed constraints, the two-stage cascaded TEG is found to produce a power output of 42 W with an efficiency of 8.3%. The three-stage cascaded TEG produces a power output of 51 W with an efficiency of 10.2%. The three-stage cascaded TEG produces 21% more power than the two-stage does; however, if the system complexity, mechanical robustness, manufacturability, and/or cost of three-stage cascaded TEG outweigh the 21% percent power production increase, the two-stage TEG could be preferable.
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Microbial electrolysis cell (MEC) is a kind of environmental methods to produce H2. However, extra voltages are always supplied to overcome the energy barrier. In this study, the thermoelectric microconverter-MEC coupled system for H2 production from acetate was first investigated. The results showed that the thermoelectric microconverter could directly convert waste heat energy to electricity, even at relative low temperature difference as 5 °C. In the elevated hot side temperatures, the hydrogen yield and coulombic efficiency were gradually increased from 1.05 to 2.7 mol/mol acetate and from 27 to 83%, respectively. Meanwhile, the hydrogen production rate and current density were also increased with hot side of the thermoelectric microconverter ranging from 35 to 55 °C. A relatively high cathodic hydrogen recovery (81–95%) was obtained during the whole experimental period. The community analysis revealed that Geobacter accounted for over 29% of total genus in the anode biofilm, which matched the MEC performance well. Therefore, waste heat is a great potential power source and it could effectively help MEC produce hydrogen via using the thermoelectric microconverter.
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While the field of thermoelectricity continues developing, the academic world is still debating its applicability for wide-scale implementation. The main concerns revolve around its low energy conversion efficiency (5-10%), compared to photovoltaics (upto 46%), and the environmental impact of commonly used materials (e.g. Bi2Te3, PbTe). Although less scrutinized, other fields such as photoelectrochemistry and catalysis have suffered from similar drawbacks. In light of the recent developments, the question arises, if the introduction of hybrid devices combining those renewable energy sources is preferable to the current divided efforts. Several new papers bring arguments in favor of this combined approach, with an efficiency of 16% reported for a triboelectric-thermoelectric-photovoltaic water splitting cell.
Article
An attempt to dissolve thermoelectric materials such as Bi2Te3 and Sb2Te3 has been made with acidic solutions in order to separate tellurium from those materials. The chemical reagents of Bi2Te3 and Sb2Te3 were used for the dissolution tests. As a result, it could be found that percent extraction of Te was increased considerably with the concentration of nitric acid in the presence of hydrogen peroxide when Bi2Te3 was dissolved with nitric acid. It was found that the addition of oxidizing agent such as hydrogen peroxide may be essential for dissolution of Bi2Te3 with acidic solutions. It was also remarkable that percent extraction of Sb was extremely lower than that of Te when Sb2Te3 was dissolved by nitric acid. As far as the effect of temperature on dissolution of Sb2Te3 was concerned, extraction of Te was considerably increased with increase in temperature.
Article
Bismuth telluride based thermoelectric materials have been commercialized for a wide range of applications in power generation and refrigeration. However, the poor machinability and susceptibility to brittle fracturing of commercial ingots often impose significant limitations on the manufacturing process and durability of thermoelectric devices. In this study, melt spinning combined with a plasma-activated sintering (MS-PAS) method is employed for commercial p-type zone-melted (ZM) ingots of Bi0.5Sb1.5Te3. This fast synthesis approach achieves hierarchical structures and in-situ nanoscale precipitates, resulting in the simultaneous improvement of the thermoelectric performance and the mechanical properties. Benefitting from a strong suppression of the lattice thermal conductivity, a peak ZT of 1.22 is achieved at 340 K in MS-PAS synthesized structures, representing about a 40% enhancement over that of ZM ingots. Moreover, MS-PAS specimens with hierarchical structures exhibit superior machinability and mechanical properties with an almost 30% enhancement in their fracture toughness, combined with an eightfold and a factor of six increase in the compressive and flexural strength, respectively. Accompanied by an excellent thermal stability up to 200 °C for the MS-PAS synthesized samples, the MS-PAS technique demonstrates great potential for mass production and large-scale applications of Bi2Te3 related thermoelectrics.
Article
In this paper, after a short review of waste heat recovery technologies from diesel engines, the heat exchangers (HEXs) used in exhaust of engines is introduced as the most common way. So, a short review of the technologies that increase the heat transfer in HEXs is introduced and the availability of using them in the exhaust of engines is evaluated and finally a complete review of different HEXs which previously were designed for increasing the exhaust waste heat recovery is presented. Also, future view points for next HEXs designs are proposed to increase heat recovery from the exhaust of diesel engines.
Article
Copper sulfides and copper selenides have recently been reported as new and promising low-cost and environmentally friendly thermoelectric materials. Here, it is shown that these materials have actually been studied for more than 190 years and the absence of commercial thermoelectric modules based on them stems from some major intrinsic issues related to these chalcogenides. Further development of these semiconductors will require addressing and solving these problems before large scale utilization can be considered.
Article
The current economic downturn has put public budgets under pressure, reducing investments and revenues for local stakeholders to cope, among other things, with contemporary demands of environmental protection. Local-based partnerships may provide an efficient tool by adopting, integrating and implementing actions based on awareness and participation of a set of different players. This need is even more evident in rural areas in which a proposed decentralized bio-energy production model established in Agro-energy districtscan provide incentive and create a comfortable ground for the development of an energy production plant based on a mixed public-private partnership. Drawing on the implementation of a European co-funded research project the paper presents the efforts being made to build a partnership at a local level in order to cover the lack of an institutional plan and public investment for handling biomass production. Our aim is not primarily to present the best technical solution to bio-energy production but rather to illustrate the networking between different players, the public consultation, and the agreements being made under the form of Public Private Partnerships, as well as the levels of commitment and the risks taken. The gist of this study is that despite the civic engagements the inconsistent administrative environment, the dominance of the public sector and the State intervention through legislation and different political decisions, makes it still difficult for local partnerships to exercise their power and turn from government to governance in order to cope with the environmental challenges and tackle inequalities faced in rural areas.
Article
The low crustal abundance of materials such as tellurium (Te) (0.001 ppm by weight), antimony (Sb) (0.2 ppm), and germanium (Ge) (1.4 ppm) contributes to their price volatility as applications (competing with thermoelectrics) continue to grow, for example, cadmium telluride photovoltaics, antimony-lead alloy for batteries, and Ge for fiber optics and infrared optical technologies. Previous consideration of material scarcity has focused on Te-based thermoelectrics. Here, we broaden the analysis to include recent high-figure-of-merit (ZT) materials such as skutterudites, Zintl phase compounds, and clathrates that employ Sb, ytterbium (2.8 ppm), and Ge. The maximum demonstrated ZT for each particular alloy exhibits an empirical dependence on the crustal abundance, A, such that ZT = A −b , where b is in the range from 0.05 to 0.10. This analysis shows that no material with crustal abundance of 30 ppm (~4 × 1018 metric tons) has ZT greater than 0.8.
Article
Thermoelectric materials have garnered considerable attention due to their unique ability to directly convert heat to electricity and vice versa. Polymers carry many intrinsic advantages such as low thermal conductivity, solution processability, and roll-to-roll production for fabricating high-performance, light-weight, and flexible thermoelectric modules. In this review, we highlight recent advances in the preparation, modification and optimization of polymer thermoelectric materials, focusing especially on the current state-of-the-art strategies to minimize the thermal conductivity and maximize the power factor, and finally provide an outlook on the future development of this field.
Article
We investigated WS2–multiwalled carbon nanotube composites prepared by powder metallurgy. The inclusion of a small amount of nanotubes (0.75 wt%) dramatically increased electrical conductivity (by 12300%) with a moderate decrease in the Seebeck coefficient (by 22%) and thermal conductivity (by 43%) enhancing both power factor and thermoelectric figure of merit at 300 K.
Article
There is a large potential in the heat losses from the wastewater leaving a building. We present a novel concept for recovering this heat. Instead of recovering it in a mixed state, the recovery immediately after use is evaluated. This allows the exploitation of the higher temperatures found at the points of warm water usage. By integrating a heat pump to utilize this heat, we can produce a higher temperature heat supply while maintaining a low temperature-lift requirement. This leads to the possibility of directly regenerating the hot water supply through wastewater heat recovery. The concept is a result of research into low exergy building systems, and is part of the IEA ECBCS Annex 49. We have modeled the annual performance of two different system scenarios, which result in a potential average annual coefficient of performance (COP) of over 6. The first scenario supplies up to 4400kWh of heat for all hot water events with only 790kWh of electricity, while the second scenario regenerated directly the hot water supply just for bathroom fixtures at 2400kWh with just 410kWh of energy. This is a significant reduction in the demand for hot water supply of a building compared to most modern installations.
Article
Taking into account inner and external multi-irreversibilities, a complete numerical model of commercial thermoelectric generator with finned heat exchangers is established by combining thermodynamics with heat transfer theory. A significant novelty is that physical properties, geometric dimensions, temperature parameters and flow parameters are all considered in the model. The inner effects include Seebeck effect, Fourier effect, Joule effect and Thomson effect. The irreversibilities include the heat transfer through the air gap (proposed and evaluated first time), the thermal and electrical resistance of the conducting strips, and the multiform external thermal resistances. Based on the numerical model, the performances of a typical commercial thermoelectric generator are simulated. Hot water at 60–100 °C and cold water at 27 °C are employed as heat source and sink of the generator module which consists of 127 thermoelectric elements. The results show that the maximum power output of 0.13 W and the maximum efficiency of 0.87% are available from the generator. The open circuit voltage is 1.80 V and the short circuit current is 0.28 A, respectively. The effects of external irreversibilities on the performance of the thermoelectric generator are analyzed by comparing this irreversible model with the exo-reversible model. The numerical model and calculation method can be applied to the performance prediction and optimization of thermoelectric generators with finned heat exchangers. The simulation results can be used as feasibility and effectiveness reference by employing low-grade energy or waste heat for power generation.
Article
Previous efforts to enhance thermoelectric performance have primarily focused on reduction in lattice thermal conductivity caused by broad-based phonon scattering across multiple length scales. Herein, we demonstrate a design strategy which provides for simultaneous improvement of electrical and thermal properties of p-type PbSe and leads to ZT ∼ 1.6 at 923 K, the highest ever reported for a tellurium-free chalcogenide. Our strategy goes beyond the recent ideas of reducing thermal conductivity by adding two key new theory-guided concepts in engineering, both electronic structure and band alignment across nanostructure-matrix interface. Utilizing density functional theory for calculations of valence band energy levels of nanoscale precipitates of CdS, CdSe, ZnS, and ZnSe, we infer favorable valence band alignments between PbSe and compositionally alloyed nanostructures of CdS1-xSex/ZnS1-xSex. Then by alloying Cd on the cation sublattice of PbSe, we tailor the electronic structure of its two valence bands (light hole L and heavy hole Σ) to move closer in energy, thereby enabling the enhancement of the Seebeck coefficients and the power factor.
Book
The purpose of this book is to examine the role of energy in wastewater treatment and to consolidate the information into a single document to provide a framework for future investigations in this area. Part I identifies the key factors that influence energy consumption in wastewater treatment and characterizes the relationship of energy use in wastewater processing to consumption in other sectors of the economy. In addition, specific terminology concerning energy in wastewater treatment is introduced in Chapter 2 to facilitate subsequent energy analysis and discussion. Chapters 5 through 8 present a broad overview of energy use by specific wastewater treatment processes. Part I is aimed primarily at administrators, utility managers, engineers, and regulatory officials who are interested in obtaining an overall perspective of energy in wastewater treatment. Part II concentrates on energy-efficient treatment technology, primarily in the areas of major energy use, the stabilization of organics and water conveyance. Energy-efficient aerobic and anaerobic treatment are discussed in detail in Chapters 9 and 10, and subsequent chapters examine pumping systems and energy recovery, among other significant topics. Part II is directed principally at engineers, plant operators, and public works officials who are interested in the technical aspects of energy-efficient treatment technology.
Chapter
The Long-Term Energy Picture Known Options Methanogenic Systems Microbial Fuel Cells Extensive Systems Carbon Capture Conventional and Nutrient Removal Oxidation and Disinfection How to Move Forward References
Article
Thermoelectric generation technology, due to its several kinds of merits, especially its promising applications to waste heat recovery, is becoming a noticeable research direction. Based on basic principles of thermoelectric generation technology and finite time thermodynamics, thermoelectric generator system model has been established. In order to investigate viability and further performance of the thermoelectric generator for waste heat recovery in industry area, a low-temperature waste heat thermoelectric generator setup has been constructed. Through the comparison of results between theoretic analysis and experiment, reasonability of this system model has been verified. Testing results and discussion show the promising potential of using thermoelectric generator for low-temperature waste heat recovery, especially in industrial fields. Several suggestions for system performance improvement have been proposed through the analysis on this system model, which guide optimization and modification of this experimental setup. By integrating theoretic analysis and experiment, it is found that besides increasing waste heat temperature and TE modules in series, expanding heat sink surface area in a proper range and enhancing cold-side heat transfer capacity in a proper range can also be employed to enhance performance of this setup.
Article
In order to further studies on thermoelectric generation, an experimental thermoelectric generator unit incorporating the commercially available thermoelectric modules with the parallel-plate heat exchanger has been constructed. The experiments are carried out to examine the influences of the main operating conditions, the hot and cold fluid inlet temperatures, flow rates and the load resistance, on the power output and conversion efficiency. The two operation parameters such as the hot fluid inlet temperature and flow rate are found to significantly affect the maximum power output and conversion efficiency. A comparison of the experimental results with those from the previously published numerical model is also presented. The meaningful results obtained here may serve as a good guide for further improving the numerical model and conducting a system level optimization study in the next step. Also, the present study shows the promising potential of using this kind of thermoelectric generator for low-temperature waste heat recovery.
Article
In this study, the compression heat pump system using wastewater, as a heat source, from hotel with sauna was designed and analyzed. This study was performed to investigate the feasibility of the wastewater use for heat pump as a heat source and to obtain engineering data for system design. This heat pump system uses off-peak electricity that is a cheap energy compared to fossil fuel in Korea. For this, the charging process of heat into the hot water storage tank is achieved only at night time (22:00–08:00). TRNSYS was used for the system simulation with some new components like the heat pump, which we create ourselves.As a result, it was forecasted that the yearly mean COP of heat pump is about 4.8 and heat pump can supply 100% of hot water load except weekend of winter season. The important thing that should be considered for the system design is to decrease the temperature difference between condenser and evaporator working fluids during the heat charging process by the heat pump. This heat pump system using wastewater from sauna, public bath, building, etc. can therefore be effectively applied not only for water heating but also space heating and cooling in regions like as Korea.
Article
In this case study, a system to recover waste heat comprised 24 thermoelectric generators (TEG) to convert heat from the exhaust pipe of an automobile to electrical energy has been constructed. Simulations and experiments for the thermoelectric module in this system are undertaken to assess the feasibility of these applications. A slopping block is designed on the basis of simulation results to uniform the interior thermal field that improves the performance of TEG modules. Besides simulations, the system is designed and assembled. Measurements followed the connection of the system to the middle of an exhaust pipe. Open circuit voltage and maximum power output of the system are characterized as a function of temperature difference. Through these simulations and experiments, the power generated with a commercial TEG module is presented. Overview this case study and our previous work, the results establish the fundamental development of low-temperature waste heat thermoelectric generator system that enhances the TEG efficiency for vehicles.
Article
In seeking greater sustainability in water resources management, wastewater is now being considered more as a resource than as a waste-a resource for water, for plant nutrients, and for energy. Energy, the primary focus of this article, can be obtained from wastewater's organic as well as from its thermal content. Also, using wastewater's nitrogen and P nutrients for plant fertilization, rather than wasting them, helps offset the high energy cost of producing synthetic fertilizers. Microbial fuel cells offer potential for direct biological conversion of wastewater's organic materials into electricity, although significant improvements are needed for this process to be competitive with anaerobic biological conversion of wastewater organics into biogas, a renewable fuel used in electricity generation. Newer membrane processes coupled with complete anaerobic treatment of wastewater offer the potential for wastewater treatment to become a net generator of energy, rather than the large energy consumer that it is today.
Article
In a typical thermoelectric device, a junction is formed from two different conducting materials, one containing positive charge carriers (holes) and the other negative charge carriers (electrons). When an electric current is passed in the appropriate direction through the junction, both types of charge carriers move away from the junction and convey heat away, thus cooling the junction. Similarly, a heat source at the junction causes carriers to flow away from the junction, making an electrical generator. Such devices have the advantage of containing no moving parts, but low efficiencies have limited their use to specialty applications, such as cooling laser diodes. The principles of thermoelectric devices are reviewed and strategies for increasing the efficiency of novel materials are explored. Improved materials would not only help to cool advanced electronics but could also provide energy benefits in refrigeration and when using waste heat to generate electrical power.
Article
Thermoelectric materials are of interest for applications as heat pumps and power generators. The performance of thermoelectric devices is quantified by a figure of merit, ZT, where Z is a measure of a material's thermoelectric properties and T is the absolute temperature. A material with a figure of merit of around unity was first reported over four decades ago, but since then-despite investigation of various approaches-there has been only modest progress in finding materials with enhanced ZT values at room temperature. Here we report thin-film thermoelectric materials that demonstrate a significant enhancement in ZT at 300 K, compared to state-of-the-art bulk Bi2Te3 alloys. This amounts to a maximum observed factor of approximately 2.4 for our p-type Bi2Te3/Sb2Te3 superlattice devices. The enhancement is achieved by controlling the transport of phonons and electrons in the superlattices. Preliminary devices exhibit significant cooling (32 K at around room temperature) and the potential to pump a heat flux of up to 700 W cm-2; the localized cooling and heating occurs some 23,000 times faster than in bulk devices. We anticipate that the combination of performance, power density and speed achieved in these materials will lead to diverse technological applications: for example, in thermochemistry-on-a-chip, DNA microarrays, fibre-optic switches and microelectrothermal systems.
Conference Paper
Energy related carbon dioxide emissions are the largest contributors to greenhouse gasses [1]. Thermoelectric power generation that exploits natural temperature differences between the air and earth can be a zero-emission replacement to small stand-alone power sources. Maximizing the temperature drop across the module is crucial to achieving optimal output power. An equation relating output power to thermoelectric module parameters is derived. In addition, several configurations are investigated experimentally. Output power shows a significant dependence on module surface area. In the setups tested, one side of the thermoelectric module was thermally coupled to the earth, while the other side was left exposed to air. This paper evaluates three 110-hour experiments. The surface area of the exposed side was varied by a factor of about 15 without changing the area covered by thermoelectric elements. The output power shows a direct dependence on exposed surface area and changes by about a factor of 25.
Wastewater Management Fact Sheet, Energy Conservation, EPA 832-F-06-024
  • F J Disalvo
DiSalvo, F.J., 1999. Thermoelectric cooling and power generation. Science 285, 703-706. EPA Office of Water, 2006. Wastewater Management Fact Sheet, Energy Conservation, EPA 832-F-06-024. U.S. Environmental Protection Agency.
CRC Handbook of Thermoelectrics
  • D M Rowe
Rowe, D.M., 1995. CRC Handbook of Thermoelectrics. CRC press.