Modeling and optimization of flow pattern in tanks for seaweed culture

Integrated multitrophic aquaculture (IMTA), more precisely the seaweed (macroalgae) cultivation integrated with RAS -recirculating aquaculture systems, is currently one of the most promising lines of action to increase sustainability of fish farms . In our study we analyze the flow pattern in tanks for seaweed culture. Seaweeds are usually tumbled (mixed) by vigorous bottom aeration.MEYS of the Czech Republic - projects CENAKVA (No. CZ.1.05/2.1.00/01.0024), CENAKVA II (No. LO1205 under the NPU I program), by the long-term strategic development financing of the CTU,Spanish Ministerio de Economia y Competitividad (AGL2013-41868-R).Postprint (published version

Advanced Computational Fluid Dynamics Study of the Dissolved Oxygen Concentration within a Thin-Layer Cascade Reactor for Microalgae Cultivation

High concentration of dissolved oxygen within microalgae cultures reduces the performance of corresponding microalgae cultivation system (MCS). The main aim of this study is to provide a reliable computational fluid dynamics (CFD)-based methodology enabling to simulate two relevant phenomena governing the distribution of dissolved oxygen within MCS: (i) mass transfer through the liquid–air interface and (ii) oxygen evolution due to microalgae photosynthesis including the inhibition by the same dissolved oxygen. On an open thin-layer cascade (TLC) reactor, a benchmark numerical study to assess the oxygen distribution was conducted. While the mass transfer phenomenon is embedded within CFD code ANSYS Fluent, the oxygen evolution rate has to be implemented via user-defined function (UDF). To validate our methodology, experimental data for dissolved oxygen distribution within the 80 meter long open thin-layer cascade reactor are compared against numerical results. Moreover, the consistency of numerical results with theoretical expectations has been shown on the newly derived differential equation describing the balance of dissolved oxygen along the longitudinal direction of TLC. We argue that employing our methodology, the dissolved oxygen distribution within any MCS can be reliably determined in silico, and eventually optimized or/and controlled

Heat transfer in a confined impinging jet with swirling velocity component

Heat transfer measurements based on an infrared experimental method (TOIRT) are compared with CFD simulations of a confined impinging jet with tangential velocity component. The tangential velocity component added to a pure impinging jet introduces into the flow field and heat transfer some similarities with real industrial processes like agitated vessels with axial-flow impellers. The tangential velocity component significantly influences the velocity field and heat transfer intensity in the stagnant region when compared to the classic impinging jet characteristics. Several turbulence models were used in numerical simulations of an agitated vessel with axial-flow impeller in a draft tube. Heat transfer coefficients at the vessel bottom were evaluated using the TOIRT method and compared with numerical results. The lateral heat conduction in the impinged wall was analysed with the conclusion that it has relatively small impact on the measured heat transfer coefficients. Quite good agreement of experimental data and simulation results was achieved concerning the size and position of the heat transfer maximum at the vessel bottom

IMRT using simultaneous integrated boost (66 Gy in 6 weeks) with and without concurrent chemotherapy in head and neck cancer – toxicity evaluation

AimTo evaluate the toxicity of intensity-modulated radiotherapy with simultaneous integrated boost (SIB-IMRT) in head and neck cancer patients treated using a protocol comprising 66 Gy to the PTV1 (planning target volume; region of macroscopic tumour) and 60 Gy and 54 Gy to the regions with high risk (PTV2) and low risk (PTV3) of subclinical disease in 30 fractions in six weeks.Material and MethodsBetween December 2003 and February 2006, 48 patients (median age 55; range 25–83, performance status 0–1) with evaluable non-metastatic head and neck cancer of various localizations and stages (stages: I–1; II–8; III–12; IV–27 patients, resp.) were irradiated according to the protocol and followed (median follow-up 20 months; range 4–42). Ten patients underwent concurrent chemotherapy (CT) and in 15 patients the regimen was indicated postoperatively because of close or positive margins. In all cases the regimen was used as an alternative to conventional radiotherapy (70 Gy in 7 weeks). The acute and late toxicities were evaluated according to RTOG and RTOG/EORTC toxicity scales, respectively.ResultsAll patients finished the treatment without the need for interruption due to acute toxicity. No patient experienced grade 4 toxicity. More severe acute toxicity was observed in patients with CT, but the most severe toxicity was grade 3. Grade 3 toxicity was observed in the skin, mucous membrane, salivary glands, pharynx/oesophagus and larynx in 8.4%, 35.4%, 39.6% and 2.1%, in the CT subgroup in 10%, 100%, 90%, 10%, respectively. The trend of impairment of acute toxicity by concurrent chemotherapy was statistically confirmed by Fisher's exact test (for mucous membranes p=0.000002 and pharyngeal/oesophageal toxicity p=0.0004). The most severe late toxicity was grade 2 subcutaneous tissue (34.2%), mucous membrane (36.8%) and larynx (11.1%), grade 3 in salivary gland (2.6%) and grade 1 in skin (84.2%) and spinal cord (5.4%). The late toxicity was not increased by chemotherapy.ConclusionIn light of the toxicity profile we consider the presented regimen to be an alternative to conventional radiotherapy 70 Gy in 7 weeks. The addition of CT requires more intensive supportive care

Preoperative neoadjuvant chemoradiation for locally advanced gastric adenocarcinoma

Aims and BackgroundTo evaluate toxicity and the radical resection rate in gastric adenocarcinoma treated with preoperative neoadjuvant chemoradiation.Materials & Methods32 patients, 22 males and 10 females with gastric adenocarcinoma, were treated with chemoradiation and hyperthermia.ResultsThe neoadjuvant regimen was completed as planned in 19/32 (59 %) patients; in the remaining patients the intensity of chemotherapy had to be reduced because of haematological and gastrointestinal toxicity. Surgical stage was as follows: 2 patients pathologically complete response, 3 patients AJCC stage I.A, 5 patients stage I.B, 7 patients stage II, 7 patients stage III.A, 1 patient stage III.B, 7 patients stage IV. R0 resection was achieved in 19/32 (59%) patients, R1 in 2/32 (6%) patients and R2 in 11 (34%) patients. Downstaging after neoadjuvant chemoradiotherapy was achieved in 17/32 (53%) patients. At the date of evaluation (31 March 2009), 4 patients were still alive 58, 81, 86 and 98 months from the date of diagnosis. Median survival was 18 months (95% confidence interval: 13–38 months). One-year survival was 69% (95% confidence interval: 53%–85%). Four-year survival was 19% (95% C.I.: 5%–34%).ConclusionsPreoperative neoadjuvant chemoradiotherapy has acceptable toxicity, and can lead to a high rate of R0 resections

Turbulent heat transport and its anisotropy in an impinging jet

The turbulent heat transport is anisotropic in many cases as reported by several researchers. RANS-based turbulence models use the turbulent viscosity when expressing the turbulent heat flux in the energy balance (analogy of the Reynolds stresses in the momentum balance). The turbulent (eddy) viscosity calculation comes from the Boussinesq analogy mainly and it represents just a scalar value, hence a possible anisotropy in the turbulent flow field cannot be simply transferred to the temperature field. The computational cost of a LES-based approach can be too prohibitive in complex cases, therefore simpler explicit algebraic heat flux models describing the turbulent heat flux in the time-averaged energy equation could be used to get more accurate CFD results. This paper compares several turbulence models for the case of a turbulent impinging jet and deals with a methodology of implementing a user-defined function describing the anisotropic turbulent heat flux in a CFD code

Heat transfer in a confined impinging jet with swirling velocity component

Heat transfer measurements based on an infrared experimental method (TOIRT) are compared with CFD simulations of a confined impinging jet with tangential velocity component. The tangential velocity component added to a pure impinging jet introduces into the flow field and heat transfer some similarities with real industrial processes like agitated vessels with axial-flow impellers. The tangential velocity component significantly influences the velocity field and heat transfer intensity in the stagnant region when compared to the classic impinging jet characteristics. Several turbulence models were used in numerical simulations of an agitated vessel with axial-flow impeller in a draft tube. Heat transfer coefficients at the vessel bottom were evaluated using the TOIRT method and compared with numerical results. The lateral heat conduction in the impinged wall was analysed with the conclusion that it has relatively small impact on the measured heat transfer coefficients. Quite good agreement of experimental data and simulation results was achieved concerning the size and position of the heat transfer maximum at the vessel bottom

Heat transfer measurements and CFD simulations of an impinging jet

Heat transport in impinging jets makes a part of many experimental and numerical studies because some similarities can be identified between a pure impingement jet and industrial processes like, for example, the heat transfer at the bottom of an agitated vessel. In this paper, experimental results based on measuring the response to heat flux oscillations applied to the heat transfer surface are compared with CFD simulations. The computational cost of a LES-based approach is usually too high therefore a comparison with less computationally expensive RANS-based turbulence models is made in this paper and a possible improvement of implementing an anisotropic explicit algebraic model for the turbulent heat flux model is evaluated

Heat transfer measurements and CFD simulations of an impinging jet

Heat transport in impinging jets makes a part of many experimental and numerical studies because some similarities can be identified between a pure impingement jet and industrial processes like, for example, the heat transfer at the bottom of an agitated vessel. In this paper, experimental results based on measuring the response to heat flux oscillations applied to the heat transfer surface are compared with CFD simulations. The computational cost of a LES-based approach is usually too high therefore a comparison with less computationally expensive RANS-based turbulence models is made in this paper and a possible improvement of implementing an anisotropic explicit algebraic model for the turbulent heat flux model is evaluated

Gnielinski’s correlation and a modern temperature-oscillation method for measuring heat transfer coefficients

The heat transfer coeffcient is one of the most important parameters in the design of apparatuses in which convective heat transport takes place. Classical direct methods based on determining basic thermal quantities can be used for measuring heat transfer coeffcients. Another option is to measure concentrations, electric current or other quantities that can be transformed to thermal quantities using the analogy between heat and mass transport. The temperature-oscillation method is less frequently used, although the theoretical basis of the method dates back to 1997, and although the method has the major advantage that the heat transfer coeffcients can be measured without making any contact with the heat transfer surface. In the temperatureoscillation method, the heat transfer surface is exposed to an oscillating heat flux, and the temperature response on this surface can be measured by a contactless method (e.g. infra-red thermography). The heat transfercoeffcients can be determined on the basis of mathematical relations between the oscillating heat flux and the temperature response. However, the method depends on an appropriate method for processing the measured data when it is necessary to correct some conditions that are not included in the mathematical model. This paper evaluates the impact of processing the experimental data on the resulting heat transfer coeffcients in one of the basic geometrical configurations – the flow of a liquid in a pipe with a circular cross section. In this paper, we present the results of a comparison of real experiments based on the temperature oscillation method and numerical modeling of the heat transfer in this geometry, using the ANSYS CFD commercial system