Geometry Of Legs Research Articles

Performance improvement and thermomechanical analysis of a novel asymmetrical annular thermoelectric generator

Enhancing thermoelectric performance hinges on optimizing the geometry of thermoelectric legs. In this study, we present a novel asymmetrical annular thermoelectric generator (ATEG) in which the proportions of P-type and N-type legs are meticulously balanced. We construct a one-dimensional analytical model tailored to this ATEG. Utilizing this model, we derive the relationship governing thermal-electrical impedance matching in an asymmetrical ATEG and formulate a general expression for optimizing the asymmetry coefficient. We explore the influence of various thermal boundary conditions on optimal impedance matching, ideal annular leg parameters, and the optimal asymmetry coefficient. Our findings reveal that thermal boundary conditions significantly affect the optimal load ratio. Furthermore, in comparison to traditional ATEGs, our proposed asymmetrical ATEG with the optimized structure exhibits a remarkable 16.2 % increase in output power while maintaining the same material volume. Additionally, we perform a three-dimensional numerical analysis of the asymmetrical ATEG using Comsol. Our research findings indicate that introducing the asymmetric structure leads to higher maximum thermal stress on the legs. Interestingly, the study of asymmetric thermal boundary conditions highlights that improving heat transfer between the ATEG and the cooler yields higher mechanical reliability compared to enhancing heat transfer between the ATEG and the heat source.

Thermal control of parallelly connected thermoelectric coolers in a uniform temperature field

The possibility of using a set of thermoelectric devices to control the thermal regime of a number of thermo-dependent and heat-loaded elements of radio-electronic equipment, which are subject to increased requirements for reliability indicators and dynamic characteristics, is considered. A mathematical model of a thermoelectric device has been developed for a uniform temperature field, a typical range of power dissipation of the products used, a range of standard values of the supply voltage, and a fixedgeometry of thermoelement legs. A relation is obtained for determining the relative operating current depending on the relative temperature difference at a given supply voltage, the geometry of the thermoelement branches, and the magnitude of the thermal load. The region of real values of the relative operating current in the zone of relative temperature differences is determined for a given geometry of branches and thermal load. An analysis is made of the relationship between the relative operating current of a single-stage thermoelectric cooler and the coefficient of performance, the amount of energy expended, the heat-removing capacity of the radiator, the time to reach a stationary mode, and the probability of failure-free operation. The dependence ofthe relative failure rate and the probability of failure-free operation, the amount of energy expended, the heat-removing capacity of the radiator, and the number of thermoelements on the supply voltage of the thermoelectric cooler has been studied. This made it possible to evaluate the control features and identify the effectiveness of the control actions when the coolers are connected in parallel in a uniform temperature field. The possibility of choosing the optimal supply voltage is shown, taking into account a number of restrictive factors in terms of weight, size, energy, dynamic and reliability characteristics of a complex of thermoelectric coolers as part of systems for ensuring thermal regimes of heat-loaded radio-electronic equipment.

Method for increasing the dynamic characteristics of thermoelectric coolers

The influence of the efficiency of the initial thermoelectric materials on the dynamics of the functioning of the thermoelectric cooling device for various characteristic current modes of operation in the range of operating temperature drops and heat load at a given geometry of thermoelement legs is considered. The parameters of thermoelectric materials of thermoelements are conventionally divided into three groups: used for batch production, laboratory research and maximum values.The criterion for choosing the operating mode of the thermoelectric cooler takes into account the mutual influence and weight of each of the limiting factors. Since the design conditions can be very diverse, simultaneously varying several limiting factors (constructive, energy and reliability), you can choose the most rational mode of operation.The analysis was carried out for typical current modes of operation of thermoelectric coolers: maximum cooling capacity, maximum cooling capacity at a given current, maximum coefficient of performance, minimum failure rate. It is shown that with an increase in the efficiency of the initial thermoelectric materials, the time for reaching the stationary operating mode of the thermoelectric cooler, the required number of thermoelements, and the maximum temperature difference increase.A method is proposed for reducing the time constant of thermoelectric coolers due to the revealed relationship between the efficiency of thermoelectric materials and the dynamic characteristics of thermoelements. It is shown that an increase in the dynamic characteristics of thermoelectric coolers is achieved without changing the design documentation, manufacturing technology and additional climatic and mechanical testing of products.

Numerical Study on Optimizing the Geometry of Segmented Asymmetrical Thermoelectric Generator

Quite large amount of heat generated in various industrial processes was wasted. Recovering the waste heat can save cost and benefit the environment protection. The device that convert heat energy to electricity is called thermoelectric generator (TEG), and therefore it can be used for waste heat recovery. Improving the efficiency is the main direction of present study. The configuration and geometry of the thermoelectric legs are proved can influence the thermoelectric performance of the thermoelectric generator. Compared with the conventional TEG which is assembled with symmetrical (rectangular) legs, asymmetrical thermoelectric generator (ATEG) has a greater temperature gradient in a leg due to the convergent geometry which can reduce overall thermal conduction of the device and Thomson effect is also harnessed. In this study, three-dimensional finite element analysis (COMSOL) is employed to investigate the numerical simulations of a segmented pyramidal thermoelectric generator (SPTEG) and a segmented cone thermoelectric generator (SCTEG) to optimize the leg length ratio of two materials, and it’s effect on the electrical and mechanical performances of SPTEG and SCTEG was also studied. Results obtained shows that the height ratio of SATEG can influence electrical and mechanical performances and the optimum height ratio provided a better electrical performance while thermal stress developed in leg was less. In addition, the open-circuit voltage of two types SATEG is similar because they have the same cross sectional area and the same volume, however, SCTEG has a dispersive thermal stress distribution while the thermal stress of SPTEG concentrates in four corners. Compared to the maximum von Mises stress in SPTEG, the maximum von Mises stress in SCTEG reduced about 10%. Results obtained from this study would provide references in producing and design of segmented asymmetrical thermoelectric generators.

Performance Evaluation of a Nanomaterial-Based Thermoelectric Generator with Tapered Legs

A thermoelectric generator (TEG) converts thermal energy to electricity using thermoelectric effects. The amount of electrical energy produced is dependent on the thermoelectric material properties. Researchers have applied nanomaterials to TEG systems to further improve the device’s efficiency. Furthermore, the geometry of the thermoelectric legs has been varied from rectangular to trapezoidal and even X-cross sections to improve TEG’s performance further. However, up to date, a nanomaterial TEG that uses tapered thermoelectric legs has not been developed before. The most efficient nanomaterial TEGs still make use of the conventional rectangular leg geometry. Hence, for the first time since the conception of nanostructured thermoelectrics, we introduce a trapezoidal shape configuration in the device design. The leg geometries were simulated using ANSYS software and the results were post-processed in the MATLAB environment. The results show that the power density of the nanoparticle X-leg TEG was 10 times greater than that of the traditional bulk material semiconductor X-leg TEG. In addition, the optimum leg geometry configuration in a nanomaterial-based TEG is dependent on the operating solar radiation intensity.

ANALYSIS OF DYNAMIC AND RELIABILITY INDICATORS OF ATHERMOELECTRIC COOLER AT MINIMIZATION OF A COMPLEX OFTHREE BASIC PARAMETERS

The inclusion of a thermoelectric cooler in the thermal mode control circuit of a heat-loaded element operating in a pulsed mode makes the requirements for dynamic characteristics and reliability indicators more stringent. The main parameters of thermoelectric devices that provide a given thermal mode of operation include: the number of thermoelements, the magnitude of the operating current and the heat dissipation capacity of the radiator. With the optimal design of a thermoelectric cooler, one should strive to reduce the number of thermoelements, the magnitude of the operating current and the heat sink surface of the radiator. With agiven geometry of thermoelement legs, a decrease in the number of thermoelements leads to a decrease in the specified cooling capacity or heat load. This can be compensated by an increase in the operating current, and, conversely, a decrease in the operating current leads to the need to increase the number of thermoelements, which affects the reliability indicators. The possibility of controlling the thermal regime of single-stage thermoelectric cooling devices while minimizing this complex is considered.The number of thermoelements, the magnitude of the operating current and the heat dissipation capacity of the radiator were investigated in the range of temperature drops from 10K to 60K at a thermal load of 0.5 W for different geometry of thermoelement legs. A relationship is obtained to determine the optimal relative operating current corresponding to the minimum of the complex of the number of thermoelements, the value of the operating current and the heat sink surface of the radiator.The analysis of the model revealed that with an increase in the relative operating current for different geometry of thermoelement legs,the required number of thermo-elements decreases, the time to reach a stationary mode, the relative value of the failure rate increases, and the probability of failure-free operation decreases. The functional dependence of the coefficient of performance has a maximum;the heat sink capacity of the radiator has a minimum, and does not depend on the geometry of thermoelements and the amount of energy expended.It is shown that the use of the current mode of operation at the minimum value of the complex provides optimal control of the thermal mode of the thermoelectric cooler with a minimum amount of consumed energy.

Structural Reliability Evaluation of Thermoelectric Generator Modules: Influence of End Conditions, Leg Geometry, Metallization, and Processing Temperatures

Structural reliability of thermoelectric generators (TEGs) in medium to high temperature applications still remains a challenge. Currently there are no established standards for evaluating the thermomechanical reliability of TEGs during new material and module development phases in the industry. In this work we implemented a procedure for evaluating the reliability of brittle TE materials based on the common practice in the ceramics industry. The probabilistic thermomechanical reliability of TEG couples and modules is evaluated using Weibull analysis. Finite element simulations were carried out to study the influence of TEG couple parameters such as leg geometry, dimensions, spacing, metallization thickness, and processing conditions on the stresses, and the structural reliability evaluations were conducted based on the TE material stresses. Results showed that the boundary conditions and processing temperatures have significant influence on the TE material and metallization stresses and overall device reliability. The external compressive load significantly enhanced structural reliability. Results also showed that among geometrical parameters the leg length has a dominating influence on the overall stresses compared to the leg cross-sectional shapes. The cross-section geometry of legs showed considerable effect at shorter lengths, and the influence diminished with increased lengths. The proposed approach for evaluating the structural reliability could be integrated with performance optimization techniques for developing optimal and reliable TEG devices.

Enhanced performance thermoelectric module having asymmetrical legs

Key concepts like waste heat recycling or waste heat recovery are the basic ideas in thermoelectricity so as to the design the newest solid state sources of energy for a stable supply of electricity and environmental protection. According to several theoretical predictions; at device level, the geometry and configuration of the thermoelectric legs are crucial in the thermoelectric performance of the thermoelectric modules. Unlike to conventional geometry thermoelectric legs, asymmetrical (pyramidal) legs could help by lowering the overall thermal conductance of the device so as to increase the temperature gradient in the legs, as well as by harnessing the Thomson effect, which is generally neglected in conventional symmetrical (rectangular) thermoelectric legs. Curiously, experimental studies confirming the previous predictions have not been carried out so far, perhaps because of the existing constraints to fabricate thermoelectric legs with complex geometrical shapes. In this work, based on the promising enhancement of the thermoelectric performance in thermoelectric modules via legs with non-constant cross sections, it has been developed a novel design of a thermoelectric module having asymmetrical legs with truncated square pyramid shape, and by first time it has been validated experimentally its thermoelectric performance by realizing a proof-of concept device which shows to have almost twofold the thermoelectric figure of merit as compared to conventional one with a constant square cross section. Besides, the variables required to engineer enhanced performance thermoelectric devices are properly identified for use as power sources especially in low consumption portable devices. Therefore, the present results prove that geometrical configuration of the device legs can improve significantly the thermoelectric performance of the device.

Design and Fabrication of 90 GHz TES Polarimeter Detectors for the South Pole Telescope

We present information about the design and fabrication of 90 GHz Transition Edge Sensor (TES) detectors deployed in the SPTpol camera for investigation of the cosmic microwave background (CMB) polarization signal. The 90 GHz portion of the camera consists of 180 individual feedhorn modules with dual polarization-sensitive detectors. We discuss microfabrication details and the characterization of detector elements. Each detector incorporates a dipole-like Pd-Au absorber and Mo/Au TES thermometer, suspended together on a rectangular silicon nitride (SiN) membrane via 6 long (640 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\mu\hbox{m}$</tex></formula> ) and narrow (10 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\mu\hbox{m}$</tex></formula> ) legs. The geometry of the SiN legs was optimized to provide the target thermal conductance of 200 pW/K in combination with mechanical robustness and reliability. The proximity effect in superconductor (Mo) and normal metal (Au) bilayers was utilized to obtain a TES operating temperature between 520 and 540 mK. Excellent superconducting properties (transition width <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$&lt;$</tex></formula> 1 mK) and <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$T_{\rm c}$ </tex></formula> uniformity ( <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$&lt;$</tex></formula> 3 mK) across 2 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{\prime\prime}$</tex></formula> wafers were achieved by sputtering in a confocal system under a single vacuum using an independent RF bias applied to the substrate. Superconducting Nb dots patterned on the TES surface provided controllable broadening of the transition width. We report the results of transition measurements, along with characterization of film morphology.

Gimbals in the insect leg

We studied the common kinematic features of the coxa and trochanter in cursorial and raptorial legs, which are the short size of the podomers, predominantly monoaxial joints, and the approximate orthogonality of adjacent joint axes. The chain coxa-trochanter with its short elements and serial orthogonality of joint axes resembles the gimbals which combine versatility and tolerance to external perturbations. The geometry of legs was studied in 23 insect species of 12 orders. Insects with monoaxial joints were selected. The joint between the trochanter and the femur (TFJ) is defined either by two vestigial condyles or by a straight anterior hinge. Direction of the joint axes in the two basal podomers was assessed by 3D measurements or by goniometry in two planes. Length of the coxa is <15% (mostly <8%) of the total length of the cursorial leg, that of the trochanter <10%. Angles between the proximal and distal joint axes in the middle coxa range from 124 to 84° (mean 97 ± 14°), in the trochanter (in all legs studied) from 125 to 72° (mean 90 ± 13°). Vectors of the distal axis in the coxa are concentrated about the normal to the plane defined by the proximal axis and the midpoint between the distal condyles. These vectors in the trochanter lie at various angles to the normal; angles are correlated with the direction of the TFJ relative to the femur. Range of reduction about the TFJ is over 60° in the foreleg of Ranatra linearis, Mantispa lobata and the hind leg in Carabus coriaceus (confirming observations of previous authors), 40–60° in the foreleg of Vespa crabro and in the middle one in Ammophila campestris, 10–30° in other studied specimens. The special role of the trochanter in autotomy and in active propulsion in some insect groups is discussed. The majority of insects possess small trochanters and slightly movable TFJs with the joint axis laying in the femur-tibia plane. We pose the hypothesis that the TFJ damps external forces, the vectors of which lie off the femur-tibia plane, the reductor muscle acting as a spring. Thus the TFJ contributes to dynamic stability of legged locomotion.

Chicky Chicky Chook Chook (review)

Reviewed by: Chicky Chicky Chook Chook Hope Morrison MacLennan, Cathy Chicky Chicky Chook Chook; written and illus. by Cathy MacLennan. Boxer, 200728p ISBN 1-905417-40-3$12.95 Ad 2-4 yrs MacLennan's debut picture book features extensive onomatopoeia in a lighthearted tale of changing weather. The featured cast (chicks, bees, and kitties) starts the day warm in the yellow sunshine but soon raindrops begin to fall, quickly intensifying into an eye-boggling thunderstorm. A gentle breeze and more sunshine follow, and the rain-drenched creatures dry out. The plotline is slim and the character development even slimmer, and the tongue-twisting phrases ("Fizzy, fizzy, buzz buzz,/ fizz, fizz buzz./ Fizzy, fizzy, buzz buzz,/ busy . . . busy . . . buzzzzzz") get a little wearing on reader-aloud if not listener after awhile. Nonetheless, the energetic, sound-based language makes for a playful, quick readaloud. Employing a palette of mostly yellow, blue, green, and white and painted on brown corrugated cardboard, the animated paintings feature chicks, bees, and kitties in motion, busily pecking, buzzing, and scattering through the sunny parts of the day and growing visibly perturbed as the thunder begins to crash. Thickly applied brushstrokes suggest feathers and fur, punctuated with the crisp geometry of beaks, legs, and other details. The large-scale images will register well across a crowded storytime carpet, and young listeners just may have a go at imitating the range of sounds and noises resonating through the story's pages. Copyright © 2007 The Board of Trustees of the University of Illinois

Perceiving Whether or Not the World Affords Stepping Onto and Over: A Developmental Study

Abstract Children's perception of the critical (upper) limit of their stepping affordances, was tested at 6, 8, and 10 years of age for stepping onto (SONmax in Experiment I) and over (SOVmax in Experiment II) obstacles. Warren's (1984) proposition (similarity hypothesis) that adults perceive SONmax to be .88 of leg length (L) because the geometry of adults' legs is invariant over varying height was extended to varying height due to growth. Because the geometry of children's legs is both invariant over growth between 6 and 10 years and identical to adults, we predicted that children should both accurately perceive their critical limit and perceive it to be .88L. Experiment I confirmed these predictions and Experiment II demonstrated that children differentiate between the two stepping affordances. The similarity hypothesis is further supported by the fact that age does not interact with either observers' mean accuracy over conditions or variability within observers. This stable performance is interpreted ...