T. Kumpeerapun

Performance of Low-Cost Thermoelectric Modules Fabricated from Hot Pressing and Cold Pressing Materials

The present work is focus on thermoelectric materials synthesized by economical technique and less production time for low-cost thermoelectric module fabrication. BixSb2-xTe3 polycrystalline with x = 1.6 for n-type and x = 0.45 for p-type thermoelectric materials were synthesized using two different methods, hot pressing and cold pressing process. The thermoelectric properties were measured at room temperature. The obtained ingots were cut into pellets of 3.5 x 3.5 mm 2 in cross-section and 3.8 mm in height. Two kinds of thermoelectric modules consist of seven pairs of n-p pellets from each process were constructed on aluminum substrates with polymer layer and copper layer on the top. The performances of the two modules were evaluated with temperature difference between hot side and cold side up to 100 degC. The internal resistance of hot pressing material modules is 152 mOmega, the open circuit generated voltage is 152 mVK-1 . For cold pressing materials module, the internal resistance is 175 mOmega, the opened circuit voltage generated is 1.75 mVK-1 .The maximum output power of 70.1 mW and 71.1 mW at 100 degC in temperature difference were obtained from the hot pressing material module and the cold pressing materials module respectively

Preparation of nanostructures thermoelectric materials using PLA technique

We present experimental investigation of synthesis nanostructures of p-type Bi0.6Sb1.4Te3 thermoelectric materials. These semiconductor materials are the best convention thermoelectric materials for use near room temperature. A new synthesis method of nanopowder using the laser ablation on high speed moving target and long laser pulse has been used and carried out in an argon atmospheric pressure. The comparison between nanoparticles obtained from hot pressing process targets and low cost cold pressing process targets have been studied. The nanostructures have been characterized by x-ray diffraction, scanning electron microscope and transmission electron microscope.

Thermoelectric Properties of BixSbyTezSew Nanocomposite Materials

Nanopowders of n-type (Bi0.95Sb0.05)2(Te0.95Se0.05)3 and p-type (Bi0.2Sb0.8)2Te3 have been synthesized by laser fracture of micron-sized powders in water. These alloys are the best conventional thermoelectric materials for use in room temperature applications. The nanopowders have been characterized by x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The nanopowders have been mechanically mixed in different ratios with the micron sized powders. These mixtures have then been cold pressed in order to perform thermoelectric characterization and to see the influence of nano-particle inclusions on the transport properties.

Fabrication of p-n junctions of Bi-Sb-Te thermoelectric materials

The aim of the investigation is to attempt to build-up a p-n junction by means of utilizing conventional thermoelectric materials, i.e. bulk polycrystalline p-type Bi_0.45Sb_1.55Te₃ and n-type Bi_1.6Sb_0.4Te₃. The fabrication used a rapid and ordinary sintering procedure. The current-voltage (I-V) characteristic curves are measured for several heating times and temperatures. The results show the feasibility of obtaining a diode-like behavior with a low leakage current at ambient temperature.

Low-Cost Thermoelectric Module Attic Ventilation

Abstract This paper investigates the performance of a new attic ventilation concept using low-cost thermoelectric (TE) modules. Incident solar radiation heats up roof tiles thus creating a temperature difference between tiles and attic. By making use of this temperature difference, laboratory made low-cost thermoelectric modules, assimilated as roof tiles, could produce an electric current to drive a fan for attic ventilation. First, a low-cost TE module consisting of 7 couples of N and P type Bi-Sb-Te materials was fabricated on a 2×2 cm2 aluminium substrate. Electrical performance was measured in the laboratory for various temperature differences of roof tiles obtained from field measurement. Then a TE tile of 0.1656 m2 surface area was designed based on the laboratory made TE module. In total 414 modules were used. Two TE tiles were considered sufficient to generate a 5 V electrical current to drive two small DC fans. Heat gain reduction due to the induced TE attic ventilation was estimated using the TRNSYS program for a regular house in Thailand. It was found that the TE tiles could induce an air ventilation rate of about 100–250 m3/h. The average daily percentage of total rate of heat gain reduction through the ceiling during 9 – 17 h was about 14–18%. The proposed concept, using low-cost TE modules, offers a new interesting alternative as it uses the heat accumulated in roof tiles to generate electricity for ventilation.

Reducing Thermal Effect on Thermoelectric Thin Films Fabrication Using Mechanical Chopper Coupling with CO2 Laser Ablation

The aim of this experiment was to use mechanical chopper coupling with CO2 laser ablation to reduce thermal effect on thermoelectric thin film fabrication. The average power at 10 W of sealed tube CO2 laser together with the mechanical chopper was used for the thermoelectric (TE) thin film fabrication on silicon substrate in vacuum system. The 1.02 ms of pulse duration with 600 Hz of repetition rate were generated by the optimized speed of chopper at 4500 rpm with 8 channels of circular apertures which were used for the reduction of thermal effect on the bismuth antimony telluride (Bi-Sb-Te) target. The experiment results illustrated the thickness and the thin films fabricated by using 10 seconds of exposure time with the chopper, illustrated the smaller grain size than without the chopper while the thickness increased as the exposure time increased at constant speed of chopper. The output efficiency referred to the ratio of the thickness per target lost in unit time which increased from 19.6 to 181.8 μm/g per hour, due to the increase of the exposure time with the chopper while without the chopper resulted in 55.0 μm/g per hour caused by the higher temperature raise on the thermoelectric target which affected to the as-deposited thin films and the re-evaporation occurred. In this experiment, the chopper speed was measured by the digital tachometer, the target loss was analyzed by the digital analytical balance and the morphology of the 600 tilted surface of thin film was characterized by scanning electron microscope (SEM).

Preparation and Characterization of Tellurium Nano-Particles by Long Pulsed Laser Ablation

A long pulsed laser ablation with a moving target at high speed technique was applied to prepare tellurium nanoparticles from a tellurium target under argon gas at atmospheric pressure. The prepared nanoparticles were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDX), and X-ray diffraction (XRD). The influence of the moving speed of the target on the size, morphology and crystallographic structure of the nanoparticles was investigeated. The results show that for the target moving at high speed without burning of the target the production of isolated nanoparticles is obtained. The diameter of the nanoparticles is ranging from 30 to 200 nm.

Simple Thermoelectric Module

The short-time-consumption melting and hot pressing processes were used to synthesize n-type and p-type Bi-Sb-Te thermoelectric materials. The synthesis materials were characterized and used for the module fabrication. The aluminium substrate was used instead of alumina substrate because it is easy to cut and to avoid fragility of the module. The performance of 20 x 20 mm2 prototype thermoelectric module consists of 7 pairs of n-type and p-type Bi-Sb-Te thermoelectric materials was investigated and then compared its performance to 40 mm x 40 mm commercial module. The output power densities as a function of temperature difference across the devices and open circuit voltages from the module are reported.