Numerical investigation of heat transfer intensification in shell and helically coiled finned tube heat exchangers and d
Published by (Chemical Engineering and Processing: Process Intensification 121, 125-143/Elsevier)
Authors: Ashkan Alimoradi, Mohammad Olfati, Meysam Maghareh. Published November 01, 2017
In this work, the heat transfer intensification in shell and helically coiled tube heat exchangers via installing annular fins on the outer surface of the helical coil, has been numerically investigated. Thirteen heat exchangers were designed for this purpose. All geometrical parameters of the heat exchangers are same except, fin's number or height. All of the heat exchangers have been studied at three different shell side Reynolds number (Resh = 7500, 15,000 and 30,000). In order to validation of the numerical model two method has been used. In the first method, the calculated heat transfer has been compared with the approximate method which is based on the experimental correlations for both coil and shell side Nusselt numbers and consideration of the E-NTU relations of these types of heat exchangers. In the second method, the heat transfer coefficient of the shell side has been compared with the experimental heat transfer coefficients of the previous works. An acceptable agreement has been observed in these comparisons. Furthermore, the optimum cases and some correlations have been obtained for prediction of the heat transfer coefficient of the shell side. Results indicate that, in the range of 7500 ≤ Resh ≤ 30,000, the heat transfer rate can increase up to 44.11%.
A comprehensive analysis of energy and exergy characteristics for a natural gas city gate station considering seasonal v
Published by (Energy/Elsevier)
Authors: Mohammad Olfati, Mehdi Bahiraei, Setareh Heidari, Farzad Veysi. Published July 15, 2018
Comprehensive energy and exergy analyses are conducted on a City Gate Station (CGS) having nominal capacity of 20,000 SCMH. For this purpose, thermodynamic properties of Natural Gas (NG) fed into the CGS are firstly determined using American Gas Association Equation of State (AGA-8 EOS). Then, a quantitative analysis is carried out to explore magnitude and exact locations of energy/exergy losses as well as exergy destructions. To this end, four different seasonal strategies are regarded. In all strategies, the largest losses occur within the stack. Although from energy viewpoint, the regulator is a high-efficiency equipment, it is found to be the most exergy destructive component in the CGS. Moreover, maximum and minimum exergy losses occur in the winter (15.33 kW) and summer (1.60 kW), respectively. The best performance based on the second law of thermodynamics for the CGS occurs in the winter with exergy efficiency of 77%, whereas the lowest one happens in the summer with exergy efficiency of 69%. The exergy destruction due to pressure drop in filter and pipes are insignificant. The results obtained from this study can be employed as a guide to reduce exergy destruction in the whole CGS with recognition of the main sources of irreversibility.
A novel modification on preheating process of natural gas in pressure reduction stations to improve energy consumption,
Published by (Energy/Elsevier)
Authors: Mohammad Olfati, Mehdi Bahiraei, Farzad Veysi. Published April 15, 2019
One of the tools for optimizing energy systems is the design of the system output based on real (desired) demand. Thermodynamic performance of natural gas pressure reduction stations are functions of inlet conditions. In order to investigate the impacts of changes in inlet pressure and temperature on performance of a natural gas pressure reduction station, energy consumption and exergy destruction of a natural gas pressure reduction station of 10,000 SCMH are evaluated for different inlet conditions. In order to improve the station performance, a novel modification is proposed in the present research based on the real demand of preheating, wherein thermodynamic operation of the regulator is modeled and minimum pre-heating temperature of natural gas is calculated based on desirable temperature at the regulator outlet (natural gas hydrate formation temperature). Indeed, once the temperature at the heater outlet reaches the calculated minimum temperature, the heater is turned off. Compared to conventional stations, the modified station exhibits at least 33% and 15% reductions in energy consumption and exergy destruction, respectively. The results of investigating the performance of two sample stations also show that by implementing the proposed modification, CO2 emission can be reduced by up to 80% or even higher.
A novel technique based on artificial intelligence for modeling the required temperature of a solar bread cooker equippe
Published by (Food and Bioproducts Processing/Elsevier)
Authors: Saeed Nazari, Alimohammad Karami, Mehdi Bahiraei, Mohammad Olfati, Marjan Goodarzi, Hossein Khorasan. Published September 01, 2020
In the present study, a combination of the modified sine and cosine algorithm (MSCA) and teaching–learning-based optimization (TLBO) algorithm is integrated with the neuro-fuzzy system to obtain three hybrid models. The proposed model predicts the effects of design parameters including the bottom galvanized protective edge of the cooking plate, top insulator cap of the cooking plate, position of the cooking plate, time duration of bread cooking and weather conditions on the dependent parameter which is the required temperature of a solar bread cooker equipped with a concentrator. For this purpose, the networks are trained on the basis of the experimentally measured data. The goal is to assess the ability of the hybrid networks for modeling cooking plate required based on the input variables. The quality of the bread produced by the solar cooker is evaluated by proper selection of the design parameters. The results show twelve breads per hour each with 200 g weight of dough can be produced by the cooker for at least six hours in every sunny day in eight months of the year, and also, the best hybrid network predicts the results with a low error which guarantees the performance of the applied hybrid model.
A comprehensive assessment of low-temperature preheating process in natural gas pressure reduction stations to better be
Published by (Energy/Elsevier)
Authors: Mohammad Olfati, Mehdi Bahiraei, Saeed Nazari, Farzad Veysi. Published July 25, 2020
In this study, a thermodynamic model is developed for a natural gas pressure reduction station, which uses solar energy as an auxiliary energy source for preheating the natural gas. To increase the duration of solar energy usage per day and the consequent decrease in the fuel consumption of the heater, a novel design is presented in which preheating the gas to lower temperatures becomes possible through the use of multi-stage preheating and pressure reduction. Through this novel design, it becomes possible to utilize a single heater to preheat all stages, which reduces the costs dramatically. To investigate the effectiveness of the proposed design in different climate conditions, a comprehensive economic analysis is conducted based on fuel saving and carbon dioxide emission reduction. The results show that the return of capital is within 1–10 years considering different parameters, including: 1- daily time duration of solar energy usage by the station before implementation of the new design, 2- additional daily time duration of solar energy usage after implementation of the new design, and 3- number of preheating and pressure reduction stages. Finally, the effects of different parameters on the return of capital are discussed.
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