Krzysztof Wojciechowski

Mechanism of thermal decomposition of cadmium nitrate Cd(NO3)2·4H2O

Abstract The thermal decomposition of Cd(NO 3 ) 2 ·4H 2 O was studied using DTA, TG, QMS and XRD techniques. It has been found that decomposition process of this compound proceeds through three stages. A possible mechanism for the investigated process has been proposed. The quasi-isothermal method was used to determine the activation energy E act values of thermal decomposition of Cd(NO 3 ) 2 .

Development of the method for the preparation of Mg2Si by SPS technique

The aim of the study was to develop a fast and simple method for preparation of polycrystalline Mg2Si. For this purpose a Spark Plasma Sintering (SPS) method was used and synthesis conditions were adjusted in such a manner that no excess Mg was required. Materials were synthesized by the direct reaction of Mg and Si raw powders. To determine the phase and chemical composition, the fabricated samples were studied by X–ray diffraction and SEM microscopy coupled with EDX chemical analysis. Thermoelectric properties of samples (thermal conductivity, electrical conductivity and Seebeck coefficient) were measured all over temperature range of 300–650 K. The analysis by the scanning thermoelectric microprobe (STM) shows that samples have uniform distribution of Seebeck coefficient with mean value of about −405 μVK−1 and standard deviation of 94 μVK−1. Prepared materials have intrinsic band gap of 0.45 eV and thermal conductivity λ = 7.5 Wm−1K−1 at room temperature.

Anisotropy analysis of thermoelectric properties of Bi2Te2.9Se0.1 prepared by SPS method

The n-type Bi2Te2.9Se0.1 materials were synthesized by the direct fusion technique. The polycrystalline samples were fabricated by the uniaxial pressing of powders in spark plasma sintering (SPS) apparatus. The materials were subjected to the heat treatment in H2-Ar atmosphere at 470 K for 24 h. The influence of preparation conditions on the anisotropy of electrical and thermal properties was thoroughly studied for the direction perpendicular and parallel to the pressing force. The microstructure and the chemical composition of both types of samples were examined using a scanning microscope (SEM) equipped with an X-ray energy dispersion detector (EDX). The XRD method was applied for the phase analysis of materials, as well as, for determination of preferred orientation of Bi2Te2.9Se0.1 grains. The Seebeck coefficient distribution was studied by the scanning thermoelectric microprobe (STM). Temperature dependences of thermoelectric properties (thermal and electrical conductivities, Seebeck coefficient) wer...

The Analysis of Exhaust Gas Thermal Energy Recovery Through a TEG Generator in City Traffic Conditions Reproduced on a Dynamic Engine Test Bed

We present an analysis of thermal energy recovery through a proprietary thermoelectric generator (TEG) in an actual vehicle driving cycle reproduced on a dynamic engine test bed. The tests were performed on a 1.3-L 66-kW diesel engine. The TEG was fitted in the vehicle exhaust system. In order to assess the thermal energy losses in the exhaust system, advanced portable emission measurement system research tools were used, such as Semtech DS by Sensors. Aside from the exhaust emissions, the said analyzer measures the exhaust mass flow and exhaust temperature, vehicle driving parameters and reads and records the engine parameters. The difficulty related to the energy recovery measurements under actual traffic conditions, particularly when passenger vehicles and TEGs are used, spurred the authors to develop a proprietary method of transposing the actual driving cycle as a function V = f(t) onto the engine test bed, opn which the driving profile, previously recorded in the city traffic, was reproduced. The length of the cycle was 12.6 km. Along with the motion parameters, the authors reproduced the parameters of the vehicle and its transmission. The adopted methodology enabled high repeatability of the research trials while still ensuring engine dynamic states occurring in the city traffic.

The Influence of a Dispersion Cone on the Temperature Distribution in the Heat Exchanger of a Thermoelectric Generator

This paper presents the results of a numerical simulation of heat distribution in the heat exchanger of a prototype thermoelectric generator constructed and examined in the Thermoelectric Research Laboratory in AGH University, Cracow, Poland. The area of interest was to prepare a numerical model and determine the influence of a dispersion cone on the temperature distribution along the heat exchanger. The role of a dispersion element is to mix the air stream to improve the flow between the internal heat exchanger’s fins in order to enhance heat exchange. The estimation of power output parameters and exchanger efficiency has been performed in order to assess the cone impact for three selected air inlet temperatures. The results show that the presence of the cone increases the efficiency of the thermoelectric generator by at least 25%.

Analysis of possibilities of waste heat recovery in off-road vehicles

The paper presents the preliminary results of the waste heat recovery investigations for an agricultural tractor engine (7.4 dm3) and excavator engine (7.2 dm3) in real operating conditions. The temperature of exhaust gases and exhaust mass flow rate has been measured by precise portable exhaust emissions analyzer SEMTECH DS (SENSORS Inc.). The analysis shows that engines of tested vehicles operate approximately at constant speed and load. The average temperature of exhaust gases is in the range from 300 to 400 °C for maximum gas mass flows of 1100 kg/h and 1400 kg/h for tractor and excavator engine respectively. Preliminary tests show that application of TEGs in tested off-road vehicles offers much more beneficial conditions for waste heat recovery than in case of automotive engines.

A new concept of reducing nitrogen oxides emissions in a combustion engine -- combination of ceramic oxygen conductors and thermoelectric materials

The subject of this work is to present a new concept of reducing NOx emissions in a combustion engine based on full elimination of nitrogen from a supply system. The use of the oxygen separator (oxygen pump), composed of the ceramic ionic conductor, together with an electrical supply system based on thermoelectric materials that utilizes exhaust heat is the main assumption of the proposed solution. The paper focuses on analyzing several possibilities for the practical application of the idea suggested