Progress Towards an Optimization Methodology for Combustion-Driven Portable Thermoelectric Power Generation Systems

A vapor compression cycle (VCC) with integrated thermoelectric (TE) modules to boost the heating capacity of the system in an energy-efficient way, especially for cold climate operation, is suggested in this paper. While a baseline heat pump (HP) cycle absorbs heat from a source through an evaporator, the proposed system utilizes TE modules as an intermediate (or third) stage of an otherwise two-stage vapor compression system with a vapor injection compressor. This increases the overall system efficiency and augments the system capacity through the high coefficient of performance (COP) of the TE for small temperature lift conditions. To demonstrate the concept, a prototype refrigerant-to-solid (TE) heat exchanger, consisting of TE modules and microchannel flat tubes, was designed and fabricated so that the whole system could realize an additional 1 kW of heating capacity compared with the baseline system. The TE heat exchanger was integrated into a residential HP unit that uses R-410A as a refrigerant, and the system was tested in a laboratory under the severe condition of −17.8°C, in order to investigate the capacity improvement and the overall COP. Finally, an application of this technique in an automotive heating, ventilating, and air-conditioning system with HFC134a working fluid has been studied for the purpose of providing supplemental heating for electric vehicles and hybrid electric vehicles by establishing a detailed simulation model of a HP system with the TE heat exchanger. Both the laboratory test and the calculation study show that a VCC with integrated TE modules has both reasonable efficiency and increased heating capacity.

An experimental investigation on the application of thermoelectric modules for cooling and heating supply air of the conventional fan system is performed. The thermoelectric cooling module is comprised of six thermoelectric plates, two cold water boxes and a hot water box. While the thermoelectric heating module is comprised of three thermoelectric plate, a cold and hot water boxes. The obtained results from the heating capacity of the sensible air cool-warm fan system are presented and compared with those from the conventional fan system (without thermoelectric module). It can be found that the minimum and maximum water temperature obtained from the thermoelectric module are 12 °C and 70 °C, respectively. For on-off modes every 5 min, average cool air obtained from the fan system with thermoelectric module is 2.0 °C lower than that without thermoelectric module while average warm air temperature is 2.5 °C higher than that without thermoelectric module. The obtained results are also expected to guideline that will allow designing and developing the sensible air cool-warm fan system with thermoelectric module system to higher thermal performance.

The research conducted and described in this paper focuses on the design of a cooling system using thermoelectric or peltier module (TEM) and heatsinks with considerations for temperate climatic conditions. A case study of Nigeria has been chosen. Nigeria as a tropical region experiences high temperature difference between the year (18 - 40 with sunhours ranging between (100 – 210 hrs) monthly, such that the desire for chilled beverages almost throughout the day becomes paramount neccesitating the need for a peltier mobile cooler in tropical regions especially with inadequate electricity supply. A 9-litre rectangular shaped cooler was chosen with an area of 1.155m 2 , a dimension of 0.65 estimated to contain 120 beverages with an estimated heat load of 483W. It is estimated to use five thermoelectric modules, a temperature sensor, tec controller, DC powered battery and ten heat sinks. Comparatively, the design criterias of these peltier cooler were compared with the performance evaluation of existng similar designs and found to be within optimum performance levels. At 10 , the thermoelectric modules are powered to start cooling until the beverages are at 0 estimated to be a period of fifteen minutes), afterwhich the tec controller turns off power and the system is temporarily off until a temperature of 10 is detected by the temperature sensor and a re-cooling is initiated. With these the frozen beverage products received in the morning can be re-cooled as many times as possible.

This paper presents simulation results of a new hybrid thermoelectric power generator combining solar energy and biomass energy. The system considered is composed of a domestic cook-stove that uses charcoal or wood as fuel, thermoelectric (TE) modules, a photovoltaic panel and control devices. Simulations were performed using TRNSYS with Ilsibat program with a new component we developed for thermoelectric modules. Different TE input data could be used corresponding to different manufacturers (China, USA). Temperature profile of cook-stove was extracted from the experiment and the minimum of average 5 years (1998-2002, Bangkok) hourly solar radiation and ambient temperature were used. The operating conditions of the system are as follows: hot side temperature of thermoelectric modules of about 250/spl deg/C and power output of 100 W that represents a minimum domestic requirement of a small family. By considering equal power generated by the TE modules and the PV panel, the maximum power output that could be produced by this hybrid TE-PV cook-stove, on the worst-month (September) is 55.38 W. The TRNSYS software and the developed thermoelectric component is therefore an extremely useful tool for the design of solar-biomass thermoelectric power generation of whatever size.

High efficiency Thermo-Electric power generator

The subcooling technique is a well-known method that improves the energy performance of CO2 transcritical refrigeration cycles, being the suction-to-liquid heat exchanger a widely used example of this technique. Among all methods which provide subcooling, thermoelectric subcooling has been highlighted as one of the most incipient methods for standalone systems due to its robustness, compacity, durability and low-cost implementation. Taking into account the promising results from a previous computational analysis, the aim of this work is to experimentally analyse the results of including a thermoelectric subcooler in a small-capacity CO2 refrigerating plant. Tests were conducted at two ambient temperatures of 25 and 30oC, maintaining a constant evaporating temperature of -10oC. Varying the voltage supply to the thermoelectric modules and the heat rejection pressure, the experimental results provided a maximum increment of COP and cooling capacity of 9.9% and 16.0%, respectively, at the optimum voltage supply of 2 VDC.

We compare the thermoelectric (TE) performances between two types of unit cell arrangements of planar unileg TE generators of silicon-nanowire (Si-NW). The planar TE generators are driven by the temperature gradient along the Si-NW. The TE performance highly depends on how the hot and cold sides of the unit cell is oriented with respect to the neighboring cells. If the hot sides of neighboring cells are placed next to each other, TE power is improved compared to the case where the hot and cold side of TE generator is arranged alternately. Optimal conditions of Si-NW length and metal wiring structure are also discussed.

The U.S. military uses large amounts of fuel during deployments and battlefield operations. Consequently, the U.S. military has a strong need to develop technologies that increase fuel efficiency and minimize fuel requirements all along the logistics trail and in all battlefield operations. There are additional requirements to reduce and minimize the environmental footprint of various military equipment and operations and reduce the need for batteries (non-rechargeable) in battlefield operations. The tri-agency SERDP (Strategic Environmental Research and Development Program) office is sponsoring a challenging, high-payoff project to develop a lightweight, small form-factor, soldier-portable advanced thermoelectric generator (TEG) system prototype to recover and convert waste heat from a variety of deployed equipment with the ultimate purpose of obtaining additional power for soldier battery charging, advanced capacitor charging, and other battlefield power applications. The project seeks to achieve power conversion efficiencies of 10% (double current commercial TE conversion efficiencies) in a system with ˜1.6-kW power output for a spectrum of battlefield power applications. In order to meet this objective, the project is taking on the multi-faceted challenges of tailoring LAST/LASTT-based thermoelectric (TE) materials for the proper temperature ranges (300 K – 700 K), fabricating these materials with cost-effective hot-pressed and sintered processes while maintaining their TE properties, measuring and characterizing their thermal fatigue and structural properties, developing the proper manufacturing processes for the TE materials and modules, designing and fabricating the necessary microtechnology heat exchangers, and fabricating and testing the final TEG system. The ultimate goal is to provide an opportunity to deploy these TEG systems in a wide variety of current military equipment. This would help the Army in achieving one of the Office of Secretary of Defense’s major strategic objectives to maintain and enhance operational effectiveness while reducing total force energy demands. The presentation will review the progress made on 1) the performance of LAST / LASTT TE materials and tailoring their temperature dependency; 2) evaluating the structural (Elastic modulus, Poisson’s ratio and mechanical strength) properties of these materials, 3) development of the necessary LAST/LASTT-based TE modules, 4) development of the required hot- and cold-side microtechnology heat exchangers, and 5) the overall system designs for 30 kW and 60 kW TQG applications and potential performance pathways/differences for these two TQG cases. This work leverages critical fundamental research performed by the Office of Naval Research in developing LAST/LASTT materials.

Mg2Si thermoelectric (TE) elements and modules were fabricated using a commercial polycrystalline Mg2Si source. A monobloc plasma-activated sintering technique was used to fabricate the TE elements and Ni electrodes. The TE modules were composed of n-type Mg2Si, using pin–fin structure elements, in order to achieve simple assembly and to realize stable operation at a temperature of ~800 K. The dimensions of each pin–fin element were 4.2 mm × 4.2 mm × 9.8 mm, and the TE module comprised nine pin–fin elements connected in series. The output characteristics of the pin–fin elements and the TE module were evaluated at temperature differences, ΔT, ranging from 100 K to 500 K. The observed values of open-circuit voltage (V OC) and output power (P) of a single pin–fin element were 98.7 mV and 50.9 mW, respectively, at the maximum ΔT of 500 K. The maximum V OC and P values for the TE module were 588 mV and 174.3 mW, respectively, at ΔT = 500 K.

Energy cost analysis and optimization of thermoelectric (TE) power generators burning fossil fuel show a lower initial cost compared with commercialized micro gas turbines but higher operating cost per energy due to moderate efficiency. The quantitative benefit of the thermoelectric system on a price-per-energy ($/J) basis lies in its scalability, especially at a smaller scale (<10 kW), where mechanical thermodynamic systems are inefficient. This study is based on propane as a chemical energy source for combustion. The produced heat generates electric power. Unlike waste heat recovery systems, the maximum power output from the TE generator is not necessarily equal to the economic optimum (lowest $/kWh). The lowest cost is achieved when the TE module is optimized between the maximum power output and the maximum efficiency, dependent on the fuel price and operation time duration. The initial investment ($/W) for TE systems is much lower than for micro gas turbines when considering a low fractional area for the TE elements, e.g., 5% to 10% inside the module. Although the initial cost of the TE system is much less, the micro gas turbine has a lower energy price for longer-term operation due to its higher efficiency. For very long-term operation, operating cost dominates, thus efficiency and material ZT become the key cost factors.

Abstract

This work deals with the design and a prototype implementation of a maximum power point tracker (MPPT) for a thermoelectric (TE) module aiming to improve energy conversion efficiency in battery charging. This system uses TE devices that directly convert heat energy from a water gas heater to electricity to charge a battery. The TE module exhibits a non-linear I-V characteristic and its maximum power point varies with the change of its surfaces temperatures. A SEPIC (single-ended primary inductance converter) DC-DC converter is applied and controlled by a microcontroller and to achieve the maximum power point tracking it is used the perturbation and observation (P&O) algorithm. The microcontroller will also control the charging process of lead-acid battery making an autonomous system that is used to feed the necessary electronics that controls an autonomous gas water heater system. The objectives of this work are to study the principle of TE power generation and to design and develop a TE battery charger that uses heat of a water gas heater system making an autonomous electrical system. The two different charging stages of a lead-acid battery lead us to a good interface board. Finally, experimental results performance of the first stage of charge using P&O MPPT algorithm are presented and compared with the results achieved with the direct connection of the TE module to the battery.

The objective of this study is to produce the thermoelectric (TE) module called as a Peltier module or element using new and promising materials that work at high temperature for generation of electricity with thermoelectric energy conversion from waste heat at high temperatures. Peltier modules used commercially nowadays can work at relatively low temperatures and their efficiency increase in proportion to the temperature difference between the surfaces of the modules. They consist of a pair of p- and n-type semiconductor. In this study, calcium cobalt oxide was chosen as a p-type semiconductor whilst zinc oxide was chosen as n-type semiconductor. Pure and aluminum-doped zinc oxide and silver-doped calcium cobalt oxide powders were synthesized via sol–gel processing successfully. The obtained powders were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), fourier transform infrared (FTIR), differential thermal analysis-thermogravimetry (DTA-TG), and scanning electron microscopy (SEM). In addition, the particle size distribution of the powders obtained via sol–gel processing was determined using a particle size analyzer. One and two leg oxide thermo-electric modules consisting of one pair of p-type 0.03 percent silver doped calcium cobalt oxide and n-type 0.02 percent aluminum doped zinc oxide bulks of 25 square millimeter cross-section and 3 millimeter heights were constructed. The thermoelectric module constructed was tested at high temperatures, and compared to other similar oxide modules reported in literature. Ultimately, the thermal stress and alteration of thermal stress depending on the leg length and side length of semiconductors were calculated using the finite element analysis (FEA) model in ANSYS 15.0 software. According to the results of the analysis, TE module was optimized in terms of mechanical behavior.

Uncertainty and sensitivity of the maximum power in thermoelectric generation with temperature-dependent material properties: An analytic polynomial chaos approach

Traditional fossil fuel power generation process typically has low efficiency. Large amount of the energy loss in Rankine cycle steam turbines (ST) is due to the temperature difference between the combustion flame temperature ∼2250 K (adiabatic) and the high pressure steam temperature up to 900 K. However, some of this energy can be harvested using solid-state thermoelectric (TE) power generators which are placed into the gap between the flame temperature and the steam temperature that produce additional electrical power. This study investigates the potential placement of TE on water tube wall inside a boiler at a coal-fired power plant. Three-dimensional (3D) numerical model of a simplified TE module is developed, and hot gas temperature and steam temperature from the boiler are used as boundary conditions at the hot side and cold side of the TE. The numerical results are compared with analytical calculations. The 3D effects of the thermal spreading in the TE module are investigated. Parameters such as TE leg cross section area and TE fill factor are examined in order to maximize the electrical power production of the TE without sacrificing the boiler efficiency (i.e., reducing the steam temperature). The study also looks into the various locations inside the boiler that have good potential for TE installation.