Acta Polytechnica. 2019, vol. 59, no.3http://hdl.handle.net/10467/856392024-03-29T14:03:52Z2024-03-29T14:03:52ZFABRICATION OF Mg-Zn-Al HYDROTALCITE AND ITS APPLICATION FOR Pb<sup>2+</sup> REMOVALHeraldy , EddyRahmawati , FitriaArdiyanti , DwiNurmawanti , Ikahttp://hdl.handle.net/10467/856512022-05-03T11:34:07Z2019-01-01T00:00:00ZFABRICATION OF Mg-Zn-Al HYDROTALCITE AND ITS APPLICATION FOR Pb<sup>2+</sup> REMOVAL
Heraldy , Eddy; Rahmawati , Fitria; Ardiyanti , Dwi; Nurmawanti , Ika
The fabrication of Mg-Zn-Al Hydrotalcite (HT) was carried out by the co-precipitation method at various molar ratios. The Mg-Zn-Al HT compound at the optimum molar ratio was then calcined to determine the effect of calcination on the Pb2+ adsorption. The kinetics of the adsorption type was determined by applying pseudo first order and pseudo second order kinetics models. Meanwhile, to investigate the adsorption process, the Freundlich and Langmuir equations were applied to determine the adsorption isotherm. The results showed that the optimum Mg-Zn-Al HT was at a molar ratio of 3 : 1 : 1 with an adsorption efficiency of 73.16 %, while Mg-Zn-Al HT oxide increased the adsorption efficiency to 98.12 %. The optimum condition of Pb2+ removal using Mg-Zn-Al HT oxide was reached at pH 5 and a contact time of 30 minutes. The adsorption kinetics follows the pseudo second order kinetics model with a rate constant of 0.544 g/mg·min. The isotherm adsorption follows the Langmuir isotherm model with a maximum capacity of 3.916 mg/g and adsorption energy of 28.756 kJ/mol.
2019-01-01T00:00:00ZGENERAL MODEL OF RADIATIVE AND CONVECTIVE HEAT TRANSFER IN BUILDINGS: PART II: CONVECTIVE AND RADIATIVE HEAT LOSSESFicker , Tomášhttp://hdl.handle.net/10467/856502019-11-12T14:39:43Z2019-01-01T00:00:00ZGENERAL MODEL OF RADIATIVE AND CONVECTIVE HEAT TRANSFER IN BUILDINGS: PART II: CONVECTIVE AND RADIATIVE HEAT LOSSES
Ficker , Tomáš
The present paper represents the second part of the serial publication, which deals with convective and radiative heat transfers in buildings. The algebraic computational method for combined convective-radiative heat transport in buildings has been proposed. The convective transport of heat has been formulated by means of the correlation functions of the Nusselt number. The radiative heat transfer has been specified by using the radiosity method explained in the first part of the serial publication. The system of transcendent equations has been formed to couple the convective and radiative heat transports. The transcendent system has been solved iteratively, which has facilitated to obtain the optimized surface temperatures as well as the optimized values of the coefficients of heat transfer. On the basis of these optimized values, a more precise overall heat loss has been computed and compared with the results obtained from the thermal standard. The strong and weak points of the both used numerical methods have been discussed.
2019-01-01T00:00:00ZGENERAL MODEL OF RADIATIVE AND CONVECTIVE HEAT TRANSFER IN BUILDINGS: PART I: ALGEBRAIC MODEL OF RADIATIVE HEAT TRANSFERFicker , Tomášhttp://hdl.handle.net/10467/856492019-11-12T14:39:41Z2019-01-01T00:00:00ZGENERAL MODEL OF RADIATIVE AND CONVECTIVE HEAT TRANSFER IN BUILDINGS: PART I: ALGEBRAIC MODEL OF RADIATIVE HEAT TRANSFER
Ficker , Tomáš
Radiative heat transfer is the most effective mechanism of energy transport inside buildings. One of the methods capable of computing the radiative heat transport is based on the system of algebraic equations. The algebraic method has been initially developed by mechanical engineers for wide range of thermal engineering problems. The first part of the present serial paper describes the basic features of the algebraic model and illustrates its applicability in the field of building physics. The computations of radiative heat transfer both in building enclosures and also in open building envelopes are discussed and their differences explained. The present paper serves as a preparation stage for the development of a more general model evaluating heat losses of buildings. The general model comprises both the radiative and convective heat transfers and is presented in the second part of this serial contribution.
2019-01-01T00:00:00ZCYLINDRICAL ROLLER BEARING LUBRICATION REGIMES ANALYSIS AT LOW SPEED AND PURE RADIAL LOADChmelař , JakubPetr , KarelMikeš , PetrDynybyl , Vojtěchhttp://hdl.handle.net/10467/856482019-11-12T14:39:39Z2019-01-01T00:00:00ZCYLINDRICAL ROLLER BEARING LUBRICATION REGIMES ANALYSIS AT LOW SPEED AND PURE RADIAL LOAD
Chmelař , Jakub; Petr , Karel; Mikeš , Petr; Dynybyl , Vojtěch
In this article, we describe a method of the roller bearing lubrication regime prediction. It uses a mathematical model of the bearing based on the standard ISO/TS 16281 to obtain the external load distribution over the rolling elements. We consider the effects of press fit and thermal gradient etween bearing rings on the internal clearance. The model is limited to an input of an uni-axial radial load and it neglects the centrifugal forces and gyroscopic moments due to its application for the region of low speeds. The lubrication film thickness is evaluated for the most loaded rolling element by a numerical solution of Reynolds’ equation for the line contact. The assessment of the lubrication regime takes into the account the surface roughness by employing the lubrication coefficient as an output parameter. Presented outcomes of the study, based on the measured geometry of the bearing, show the importance of an appropriate lubricant selection for the application.
2019-01-01T00:00:00Z