بررسی تاثیر فشار بخار محرک بر روی عملکرد و جریان‌های بازگشتی ترموکمپرسور کارخانه قند: اعتبارسنجی و مطالعه عددی

ترموکمپرسور یا اجکتور به‌منظور افزایش آنتالپی بخار در صنایع تبدیلی مورد استفاده قرار می‌گیرد. هزینه ساخت و تعمیر نگهداری پایین در کنار ساختار ساده آن باعث افزایش کاربرد این تجهیز در زمینه‌های مرتبط با صنعت و کشاورزی شده است. پارامترهای ورودی به ترموکمپرسور شامل مشخصات ترمودینامیکی بخار محرک و بخار مکشی مهم‌ترین عوامل تاثیرگذار بر روی عملکرد یک ترموکمپرسور می‌باشند. در این مطالعه 4 سطح فشار بخار محرک شامل بخار با فشار 3.7 بار، 5 بار، 10 بار و 15 بار به‌عنوان سطوح مختلف فشار ورودی بخار محرک مورد بررسی قرار گرفته است. از مدل آشفتگی kε تحقق‌پذیر برای شبیه‌سازی آشفتگی‌های داخل جریان استفاده شده است ویژگی‌های ترمودینامیکی جریان‌های ورودی و تغییرات آن‌ها در خروجی، مانند فشار، سرعت، عدد ماخ و نسبت‌های جرمی به‌ازای فشارهای مختلف بخار محرک استخراج شده و مورد بحث قرار گرفته‌اند. نتایج نشان داد که با در نظر گرفتن پارامترهای عملکردی، عدم وجود جریان‌های بازگشتی و همچنین میزان تقویت فشار و دما، فشار 15 بار بهترین عملکرد را در بین 4 سطح اولیه مورد بررسی به‌خود اختصاص داده است. در استفاده از فشار محرک 15 بار، فشار بخار مکشی 0.1 بار، در خروجی تقویت شد و به مقدار 3/0 بار افزایش پیدا کرد. همچنین دما افزایشی قابل‌توجهی نسبت به جریان مکشی داشت و به مقدار 135 درجه سلسیوس رسید. همچنین با اعمال فشار بخار محرک 15 بار، به‌ترتیب مقادیر 0.59 و 0.41 برای نسبت‌های جرمی محرک و مکشی خروجی دیفیوزر به‌دست آمد.

Investigation of the Motive Steam Pressure Effect on Performance and Reverse Flows in Sugar Factory Thermo-compressor: Validation and Numerical Study

IntroductionThermocompressors or ejectors are used to enhance the vapor enthalpy in the process industry. The low costs of construction and maintenance, and simple structure, have increased by using this equipment in relevant fields of industry and agriculture. The thermocompressor’s inlet parameters, including the thermodynamic properties of the motive steam and suction vapor, are the foremost affecting factor of a thermocompressor.The steam used in processing factories loses its capability after passing through evaporators due to the reduction of pressure and temperature, gets cooled again, and returns to the boiler despite having a moderate energy level. Therefore, the use of vaporrecovery equipment can increase the efficiency of energy systems. That will lead to a significant reduction in greenhouse gas emissions and harmful environmental effects, which increase the lifetime of energy resources.Materials and MethodsThe realizable kε turbulence model is used to simulate turbulence within the flow. The thermocompressor geometry has meshed in 2D and 3D modes to apply the conservation laws. For this purpose, quadratic (quad) and hexahedral (hex) types are used for two and threedimensional meshing, respectively. Structured meshes have a high ability to obtain numerical results due to creation of structural meshes in the flow direction.The axisymmetric structure of the thermocompressor leads to a half simulation of geometry. The thermodynamic properties of the input flows and their variations in the output, such as pressure, velocity, Mach number, and mass ratios for different motive steam pressure are extracted and discussed.Results and DiscussionDifferent levels of meshes are examined to investigate the meshindependence test. In axisymmetric twodimensional analysis, these levels include 33460, 51340, 78620, and 103590 cells, respectively. The relatively insignificant difference in motive flow for the third and fourth mesh levels (which proves less than 5%) clearly shows the independence of the results from the mesh size. Regarding the time considerations, the grid with 78,620 meshes was used in the simulations.The experimental data from the article by Sriveerakul et al. (2007) are used to validate the numerical results of the present work. Validation shows that the results obtained from the simulations are in good agreement with the experimental data. Since the final results of the twodimensional analysis are very close to the threedimensional one, the first one is selected due to the time considerations and higher computational costs of the threedimensional mesh analysis.Considering the problem conditions, pressures of 10 and 15 bars are appropriate for practical application. Since the 15 bar motive stem creates a longer development length in the diffuser section, it is a better choice. At this level (15 bar), the temperature field within the thermocompressor is well distributed in the presence of ideal temperature conditions. The ideal velocity distribution within the thermocompressor and the uniformity of the motive and suction flows indicate the high performance of the thermocompressor in these operating conditions. Applying the motive steam of 15 bars, the values of 0.59 and 0.41 for the motive and suction mass ratios of the diffuser output were achieved, respectively.ConclusionGeometrically, the study was examined in asymmetrical twodimension and threedimension. It was observed that there is a slight difference between the two analysis modes by comparing the velocities along the longitudinal line of the thermocompressor. Therefore, to save computational and time costs, results are presented for the axisymmetric twodimensional mode.The effect of 4 levels of motive steam pressure on the thermodynamic properties within the computational domain, including pressure, temperature, velocity, Mach number, mass ratios of both motive steam, and suction vapor are evaluated. Finally, the values of the performance curve for steam with motive pressures of 3.7, 5, 10, and 15 bars are presented.