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- ItemExperimentally Verified Flow Distribution Model for a Composite Modelling System(MDPI, 2021-03-23) Babička Fialová, Dominika; Jegla, ZdeněkA composite modelling system is currently being developed for accurate design of such complex heat transfer equipment. The modeling approach requires a flow distribution model enabling to yield accurate-enough predictions in reasonable time frames. The paper presents the results of complex experimental and modeling investigation of fluid flow distribution in dividing headers of tubular-type equipment. Different modeling approaches were examined on a set of header geometries. Predictions obtained via analytical and numerical models were validated using data from the experiments conducted on additively manufactured header samples. Two case studies employing parallel flow systems (mini-scale systems and a conventional-size heat exchanger) demonstrated the applicability of the distribution model and the accuracy of the composite modelling system.
- ItemTransient Thermal Stress Calculation of a Shell and Tube Condenser with Fixed Tubesheet(Wiley-VCH, 2021-10-12) Pernica, Marek; Létal, Tomáš; Lošák, Pavel; Naď, Martin; Reppich, Marcus; Jegla, ZdeněkThe present article deals with transient thermal stress calculation on a safety horizontal shell and tube condenser. This condenser is used in a power plant for cooling of hot steam diverted from the turbine in the case of its emergency shutdown. The standard stress calculation was provided according to the EN 13445 standard in steady regime. As consistent with this calculation, an expansion joint must be used on the shell. The main aim of this article is to describe a detailed calculation of the transient temperature field on the shell and tubes, using finite element method analysis, and longitudinal thermal stresses on the shell and tubes during the start-up process. Transient analyses are useable for more accurate EN 13445 calculation and, furthermore, for fatigue calculation.
- ItemComputation of temperature field by cell method and comparing with commercial software(IOP Publishing, 2020-04-01) Pernica, Marek; Létal, Tomáš; Lošák, Pavel; Naď, MartinThis paper deals with the temperature field of the shell and tube heat exchanger with segmental baffles. Two different types of shell and tube heat exchangers were analysed by a numerical model for thermal-hydraulic rating called the cell method. The cell method is a numerical computational model for calculating of temperature field of a shell and tube heat exchanger with segmental baffles. A huge benefit of the cell method is especially its simplicity. The computation of temperature field by the cell method is very fast and without the necessity of powerful hardware accessories. For analyses, two different types of shell and tube heat exchangers with segmental baffles were used. First, a co-current flow heat exchanger with a floating head and second a counter-current flow heat exchanger with a fixed tubesheet. Both analysed heat exchangers are horizontal, have one tube and one shell pass and segmental baffles. The results from cell method were compared with results from the HTRI, which is one of the most widely used commercial software for solving thermal-hydraulic rating of heat exchangers. The scope of this paper is to assess how exact the cell method is and if its results are useful for a mechanical design of shell and tube heat exchanger with segmental baffles.
- ItemTechnology for Hot Spring Cooling and Geothermal Heat Utilization: A Case Study for Balneology Facility(MDPI, 2023-03-23) Vondra, Marek; Buzík, Jiří; Horňák, David; Procházková, Michaela; Miklas, Václav; Touš, Michal; Jegla, Zdeněk; Máša, VítězslavReducing energy costs in Europe is more challenging than before due to extreme price increases. The use of local renewable energy sources is one way to contribute to this effort. In the case of spa resorts, the use of heat from hot springs for therapeutic baths is an option. It is necessary to cool down this thermal mineral water to a temperature acceptable to the human body. However, due to the high mineral content of this water, heavy fouling can be a problem for conventional heat exchangers. The purpose of this study is to identify the suitable cooling technology in terms of required cooling capacity and waste heat recovery capability. The cooling technology was selected on the basis of a literature search. A pilot cooling unit consisting of vacuum cooler and plate heat exchanger was designed and tested in a real spa resort for six months. Both selected technologies have demonstrated the ability to cool thermal mineral water in long-term operation, as well as the possibility to utilize waste heat for domestic hot water heating. However, fouling problems occur in the plate heat exchanger. The vacuum cooler demonstrated greater operational robustness and resistance to encrustation.
- ItemEffects of Oxygen-Enhanced Combustion Methods on Combustion Characteristics of Non-Premixed Swirling Flames(MDPI, 2022-03-21) Skryja, Pavel; Hudák, Igor; Bojanovský, Jiří; Jegla, Zdeněk; Korček, LubomírThe objective of the present study was to experimentally investigate and compare the characteristics of three oxygen-enhanced combustion (OEC) methods; premix enrichment (PE), air-oxy/fuel combustion (AO), and additionally also oxygen lancing (OL) method. The overall oxygen concentration varied from 21% to 38%. Combustion tests were carried out using the gas burner with the thermal input of 750 kW fired by natural gas. The characteristics of OEC methods, such as the concentration of nitrogen oxides and carbon monoxide in flue gas, in-flame temperatures distribution in the horizontal symmetry plane of the combustion chamber, heat flux to the combustion chamber wall, flue gas temperature, and the stability of flame were investigated. NOx emissions increased by more than 40 times and by 20 times for the PE method. The tests using the AO and OL methods with NOx emissions below 150 mg/Nm3 at all oxygen concentrations showed significantly better results. For all OEC methods, radiative heat transfer increased with increasing oxygen concentration. The available heat was 20% higher at 38% O2 than at 21% O2. The flue gas temperature decreased with increasing oxygen concentration, which was affected by a decrease in N2 concentration in the oxidizer and a simultaneous increase in radiant heat flux