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Sensitivity analysis of the effect of airflow velocity on the thermal comfort in underground mines

Roghanchi P., Kocsis K., Sunkpal M.

Journal of Sustainable Mining

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2016

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Vol. 15, iss. 4

175--180

EN

Displeasure in respect to air volumes and associated airflow velocities are well-documented complaints in underground mines. The complaints often differ in the form that there is too little airflow velocity or too much. In hot and humid climates such as those prevailing in many underground mines, convection heat transfer is the major mode of heat rejection from the human body, through the process of sweat evaporation. Consequently, the motion of the mine air plays a pivotal role in aiding this process. In this paper, a method was developed and adopted in the form of a “comfort model” to predict the optimum airflow velocity required to maintain heat comfort for the underground workforce at different activity levels (e.g. metabolic rates). Simulation analysis predicted comfort limits in the form of required sweat rate and maximum skin wetness. Tolerable worker heat exposure times were also predicted in order to minimize thermal strain due to dehydration. The results indicate that an airflow velocity in the range of 1 e2 m/s is the ideal velocity in order to provide a stress/strain free climate and also guarantee thermal comfort for the workers. Therefore, an optimal airflow velocity of 1.5 m/s for the miners' thermal comfort is suggested.

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Praktyczna realizacja oraz badania eksperymentalne pojemnościowego detektora wilgotności skóry

Gawędzki W., Marszałek Z.

Pomiary Automatyka Kontrola

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2013

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R. 59, nr 3

247--249

PL

W artykule przedstawiono praktyczną realizację prototypu oraz wyniki badań eksperymentalnych zaproponowanego przez autorów pojemnościowego detektora wilgotności skóry. Omówiono budowę detektora, przyjęty model skóry oraz przedstawiono sposób realizacji detektora i badań laboratoryjnych jego właściwości metrologicznych. Przedstawiono wyniki pomiarów pokazujące zależność pojemności detektora od wilgotności względnej materiału higroskopijnego. Proponowany detektor wilgotności może znaleźć zastosowanie podczas tzw. treningu biofeedback, do obserwacji reakcji wilgotności skóry na zmiany chorobowe organizmu, do sprawdzania działania środków kosmetycznych, leków itp.

EN

The paper presents practical implementation and experimental results of a prototype of the capacitive skin humidity detector. The detector construction, the adopted model of the skin, implementation of the detector and laboratory tests of its metrological properties are presented. The detector is made of a capacitor, constructed with comb braided isolated electrodes placed on the base surface (Figs. 3 and 4). A simplified model of the skin layer, as shown in Fig. 1, is presented in [3]. The skin, which the detector is applied to, constitutes the dielectric whose electric permittivity is dependent on its humidity. The detector therefore responds through a capacity change depending on the skin humidity. The aim of this experi-mental study was to determine static characteristics of the capacitive skin humidity detector, defining the relationship of the detector capacitance versus the skin relative humidity. For this purpose, in the laboratory tests the skin was replaced by a layer of the sample with high hygroscopic properties. The relative humidity of the sample was defined as the ratio of the mass of water contained in the sample to the dry sample weight. To determine the relative humidity, the termogravimetric method was used. It consists in determining the loss of mass during drying. The results of the measurements showing the dependence of the detector capacitance as a function of the relative humidity of the hygroscopic material are presented. Basing on the characteristics, it can be concluded that the electric capacitance of the detector is a nonlinear function of the relative humidity of the sample used, and a large value of the sensitivity occurs for the boundary humidity values in the considered range. The experimental research of the prototype of the capacitive humidity detector confirmed the correctness of the proposed design.

3

Badania symulacyjne pojemnościowego detektora wilgotności skóry

Gawędzki W., Marszałek Z.

Pomiary Automatyka Kontrola

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2012

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R. 58, nr 4

358-360

PL

W artykule przedstawiono wyniki badań symulacyjnych zaproponowanego przez autorów pojemnościowego detektora wilgotności skóry. Omówiono budowę detektora, przyjęty model skóry oraz przedstawiono sposób modelowania ich właściwości dla potrzeb obliczeń numerycznych metodą elementów skończonych. Przedstawiono wyniki symulacji pokazujące zależność pojemności detektora od przenikalności elektrycznej skóry. Proponowany detektor wilgotności może znaleźć zastosowanie podczas tzw. treningu biofeedback, do obserwacji reakcji wilgotności skóry na zmiany chorobowe organizmu, do sprawdzania działania środków kosmetycznych, leków itp.

EN

The results of simulation studies of a capacitive detector, which was proposed by the authors, allowing non-invasive definition of skin humidity are presented in this paper. The detector is a capacitor, constructed with comb braided isolated electrodes on the base (Figs. 1 and 2). A simplified model of the skin layer, as shown in Fig. 3, is presented [3]. The skin, which the detector is applied to, constitutes the dielectric of electric permittivity dependent on its humidity. The detector therefore responds through capacity change depending on the skin humidity. In each of the methods for determining skin humidity by measuring the skin conductivity, bioimpedance, or as in the proposed solution, the detector capacity, it is necessary to determine properly the conductivity equation, impedance or electric permittivity as a function of the skin humidity. Determination of this function is not necessary if the aim is to identify changes in skin humidity, which are a reaction to a stimulus interacts. Simulation studies of the proposed capacitive detector were carried out by using the finite element method in ANSYS Maxwell 3D application. Simulations were performed to determine the characteristics of the detector capacity versus the skin relative permittivity. Based on these char-acteristics (Figs. 5 and 6) it can be concluded that the capacity is a nonlinear function of the skin relative permittivity, and the greatest sensitivity of processing occurs for lower values of the relative permittivity. With the increase in the skin relative permittivity there is increase in the capacity, while the sensitivity of processing decreases. The modelling of the capacitive humidity detector con-firmed correctness of the proposed structure.