Experimental research of pressure drop in packed beds of monosized spheres a novel correlation for pressure drop calculation

Flow through packed beds of spheres is a complex phenomenon and it has been extensively studied. Although, there is many different correlations there is still no reliable universal equation for prediction of pressure drop. The paper presents the results of experimental research of pressure drop in packed bed of monosized spheres of three different diameters, 8, 11, and 13 mm set within cylindrical vessel of diameter d(k) = 74 mm, and two different heights of packed bed, h(s) = 300 and 400 mm. It has been proposed modification of widely used Ergun's equation in the form of f(p) = [150 + 1.3(Re-p/(1 - epsilon))](1 - epsilon)(2)/(epsilon Re-3(p)) and new correlation f(p) = 1/[(27.4 - 25700d(h))/Re-p + 0.545 + 6.85d(h)] for pressure drop calculation in simple and convenient form for hand and computer calculations. For total number of 362 experimental runs the correlation ratio of the modified Ergun's relation was CR = 99.3%, and standard deviation SD = 12.2%, while novel relation has CR = 93.7% and SD = 5.4%

Experimental research of pressure drop in packed beds of monosized spheres a novel correlation for pressure drop calculation

Flow through packed beds of spheres is a complex phenomenon and it has been extensively studied. Although, there is many different correlations there is still no reliable universal equation for prediction of pressure drop. The paper presents the results of experimental research of pressure drop in packed bed of monosized spheres of three different diameters, 8, 11, and 13 mm set within cylindrical vessel of diameter d(k) = 74 mm, and two different heights of packed bed, h(s) = 300 and 400 mm. It has been proposed modification of widely used Ergun's equation in the form of f(p) = [150 + 1.3(Re-p/(1 - epsilon))](1 - epsilon)(2)/(epsilon Re-3(p)) and new correlation f(p) = 1/[(27.4 - 25700d(h))/Re-p + 0.545 + 6.85d(h)] for pressure drop calculation in simple and convenient form for hand and computer calculations. For total number of 362 experimental runs the correlation ratio of the modified Ergun's relation was CR = 99.3%, and standard deviation SD = 12.2%, while novel relation has CR = 93.7% and SD = 5.4%

ENERGY EFFICIENCY AS A KEY DRIVER FOR SUSTAINABLE GROWTH IN SMEs IN INDUSTRIAL SECTOR IN SERBIA

In light of the post-Covid pandemic and the Ukraine crisis, electricity and natural gas have become goods in high demand and prices. As a result, electricity and natural gas prices reached their highest level, and trends show there is still uncertainty in price forecasting, which leads us to conclude that the value of energy saved by applying energy efficiency measures becomes much higher than the value of primary energy sources themselves. Therefore, the concept of energy efficiency becomes a keyword in every speech to the public. Since the first energy crisis back in the 1970’s energy efficiency has been introduced as a critical term in solving the problem of limitations of fossil fuel sources. The second energy crisis accelerated the introduction of new, more energy-efficient technologies and renewable energy sources. Today, we have new challenges – an unfinished energy transition and an artificially induced lack of energy sources like natural gas. The Republic of Serbia is among the European countries with the highest energy intensity and is significantly dependent on fossil fuels, especially coal. The energy intensity of Serbia (ratio between primary energy consumption and the GDP) has been consistently higher than the EU member states and other non-EU countries of Europe (2 to 3 times higher than in the neighboring EU countries and up to 4 times higher than EU-15). In 2013 Serbia introduced an energy management system (EnMenS). Through this system, significant final energy consumers are recognized and obliged by Energy Efficiency Law to implement energy efficiency measures to reduce energy consumption by at least 1% per annum. However, EnMenS do not recognize “small” energy consumers, where small to medium size enterprises (SMEs) are categorized. The SMEs sector in the Republic of Serbia accounted for 27.3 % of total active enterprises, employing 46.2 % of employees in the non-financial sector and participating with 43.2 % in the GDP of the non-financial sector. However, the distribution of the number of companies, employees, and their economic activity is highly uneven, where the Belgrade region “carries” 45.8 % of activities in the SME sector, Vojvodina 25.9 %, Šumadija and Western Serbia 18.4 % and Southern and Eastern Serbia 9.8 %. SMEs are primarily concentrated in labor-intensive and service activities - manufacturing, wholesale and retail trade, construction, and transport. The manufacturing industry dominates within the tradable sector - 17.1 % of companies, 28 % of employees, 21.1 % of turnover, and 24.7 % of GDP. It is dominated by sectors of lower complexity and lower productivity (labor and resource-intensive activities). During 2021 energy audits in ten selected SMEs of the production sector were performed. The primary purpose was to support SMEs in improving the efficient use of energy and reducing costs and emissions, directly contributing to the competitiveness of the Serbian industrial sector and awareness raising in the energy efficiency field. However, although there is a high potential for energy savings in Serbian SMEs, there are several barriers: - SMEs are not aware of energy-saving opportunities; - SMEs do not have the human and financial resources to analyze and explore energy-saving opportunities; - SMEs recognize the direct cost benefits, but energy-saving measures categorize as high-cost and high-risk activities. This paper presents the result of performed energy audits showing that in current conditions, energy efficiency is a crucial driver for the sustainable growth of SMEs in Serbia’s industrial sector

The Impact оf Investments оn Enterprise Transformation аnd Business Activities

Predmet istraživanja u disertaciji je analiza uticaja investicija na transformaciju i poslovne aktivnosti preduzeća sa posebnim akcentom na istraživanje performansi primene modela investiranja, a u funkciji efektivnog i efikasnog procesa transformacije preduzeća. Opšti cilj je utvrđivanje performansi investicija, odnosno uticaja investicija na tok i efekte transformacije i poslovne aktivnosti preduzeća u Republici Srbiji. Rezultat istraživanja je da su strane direktne investicije u države regiona od zanemarljivog indirektnog značaja za berzu Republike Srbije, a samim tim i za ekonomski rast Republike Srbije.The subject of research in the dissertation is the analysis of the impact of investments on transformation and business activities of the company with special emphasis on the research of the performance of the application of the investment model, as a function of effective and efficient process of transformation of the company. The overall objective is to determine the performance of investments, that is, the impact of investments on the flow and effects of transformation and business activities of companies in the Republic of Serbia. The result of the research is that foreign direct investments in the countries of the region are of negligible indirect importance for the stock exchange of the Republic of Serbia, and therefore for the economic growth of the Republic of Serbia

The Impact оf Investments оn Enterprise Transformation аnd Business Activities

Predmet istraživanja u disertaciji je analiza uticaja investicija na transformaciju i poslovne aktivnosti preduzeća sa posebnim akcentom na istraživanje performansi primene modela investiranja, a u funkciji efektivnog i efikasnog procesa transformacije preduzeća. Opšti cilj je utvrđivanje performansi investicija, odnosno uticaja investicija na tok i efekte transformacije i poslovne aktivnosti preduzeća u Republici Srbiji. Rezultat istraživanja je da su strane direktne investicije u države regiona od zanemarljivog indirektnog značaja za berzu Republike Srbije, a samim tim i za ekonomski rast Republike Srbije.The subject of research in the dissertation is the analysis of the impact of investments on transformation and business activities of the company with special emphasis on the research of the performance of the application of the investment model, as a function of effective and efficient process of transformation of the company. The overall objective is to determine the performance of investments, that is, the impact of investments on the flow and effects of transformation and business activities of companies in the Republic of Serbia. The result of the research is that foreign direct investments in the countries of the region are of negligible indirect importance for the stock exchange of the Republic of Serbia, and therefore for the economic growth of the Republic of Serbia

Waste heat potentials in the drying section of the paper machine in Umka Cardboard Mill

This paper deals with methods for calculation of potentials of waste heat generated in paper/board production process. For that purpose, the material and heat balance of the cardboard machine at Umka Cardboard Mill has been determined. Field measurements were conducted in order to define the unknown values of process parameters used for calculation in the balance equations and modelling. The focus was given to the cardboard drying section, which consumes most of the energy supplied to the machine. Additional aim of the work presented in the paper was to evaluate the specific energy consumption and the thermal efficiency of all individual energy units within the machine's drying section. The results indicate two main sources of waste heat: waste heat released to the atmosphere with the discharge air from the present waste heat recovery system (14,380 kW), and waste heat released in the hall from the machine and extracted by the hall ventilation system (4,430 kW). Waste heat from both sources is characterized by fairly low temperatures 58-75°C and fairly high moisture content (30-40 g/kg). The specific heat consumption and specific steam consumption (consumption per tonne of produced cardboard) of the machine was 1,490 kWh/t and 1.4 t/t, respectively. The thermal efficiency of drying section and coating drying section was 55.6% and 33.6%, respectively. All these figures imply necessity for further waste heat utilization with the aim of improving the efficiency of energy use

Investigation of co2 diluted methane and propane swirling premixed flames using ch* chemiluminescence imaging

Utilization of hydrocarbon gaseous fuels, such as biogas, landfill gas and others, is a valuable contribution to sustainable energy production and climate changing control. The presence of CO2 in these gases decreases heat of combustion, flame temperature, flame speed and can induce flame blow-off and combustion instabilities. In order to better understand the problem, flame geometry and location was investigated using chemiluminescence (CH*) imaging technique. Combustion took place in a purposely built, lean, premixed, unconfined swirl burner, fueled by methane and propane diluted with CO2. The fuel type, air-to-fuel equivalence ratio and CO2 content were chosen as the independent variables. The CH* imaging by means of a commercial CCD camera, fitted with an optical filter, was used for flame investigation. The analysis of images showed that the CH* emission intensity, flame geometry and location were remarkably affected by the fuel type and the air-to-fuel equivalence ratio, while the CO2 dilution was of minor importance

Size distribution of agglomerates of milk powder in wet granulation process in a vibro-fluidized bed

Results of experiments on the influence of technological parameters (intensity of vibration, granulation of the liquid feed, temperature of fluidization agent) on the change of size distribution, as well as mass mean diameter of the milk powder particles subjected to the wet granulation process (agglomeration) in a vibro-fluidized bed granulator are shown in this paper. Using water as a granulation liquid and air as a fluidization agent, it was found that mass mean diameter increases with increase of water feed, intensity of vibration, and decrease of air temperature. Increasing the intensity of vibration and decreasing the air temperature, primarily induces the increase of the dimensions of the initial nuclei. This can be explained on the basis of different influences that these changes (velocity of particle motion, intensity of particle collision, drying rate) have on the coalescence of particles with smaller and/or bigger dimensions

Investigation of co2 diluted methane and propane swirling premixed flames using ch* chemiluminescence imaging

Utilization of hydrocarbon gaseous fuels, such as biogas, landfill gas and others, is a valuable contribution to sustainable energy production and climate changing control. The presence of CO2 in these gases decreases heat of combustion, flame temperature, flame speed and can induce flame blow-off and combustion instabilities. In order to better understand the problem, flame geometry and location was investigated using chemiluminescence (CH*) imaging technique. Combustion took place in a purposely built, lean, premixed, unconfined swirl burner, fueled by methane and propane diluted with CO2. The fuel type, air-to-fuel equivalence ratio and CO2 content were chosen as the independent variables. The CH* imaging by means of a commercial CCD camera, fitted with an optical filter, was used for flame investigation. The analysis of images showed that the CH* emission intensity, flame geometry and location were remarkably affected by the fuel type and the air-to-fuel equivalence ratio, while the CO2 dilution was of minor importance

OPERATIONAL CHARACTERISTICS OF THE CHP PLANT IN THE DISTRICT HEATING SYSTEM OF BELGRADE

Kombinovana proizvodnja električne i toplotne energije (CHP ili kogeneracija) je najefikasniji i najpogodniji pristup za smanjenje troškova za energente kod industrijskih energana i toplana za daljinsko grejanje koje kao gorivo koriste prirodni gas u cilju proizvodnje toplotne energije za različite potrebe. U radu su analizirane eksploatacione karakteristike postrojenja za kombinovanu proizvodnju električne i toplotne energije koje radi od 1. januara 2021. godine na Toplani Voždovac u okviru sistema daljinskog grejanja Beograda. Kombinovano postrojenje se sastoji od tri gasna motora nominalne električne snage 10 MW i toplotne snage 10,1 MW koji kao gorivo koriste prirodni gas, i koristi se za potrebe grejanja i pripremu potrošne tople dok se električna energija predaje u lokalnu elektro mrežu. Akcenat analize u ovom radu je na eksploatacionim karakteristikama postrojenja: broju radnih časova, ukupnoj potrošnji energenta i produkciji energije, stepenu korisnosti kao i na troškovima eksploatacije i održavanja. Posebno je analiziran uticaj drastičnog poremećaja cena prirodnog gasa, električne energije kao i troškova održavanja u poslednjih godinu dana na finansijsku isplativost kombinovanog postrojenja