Flow-pressure analysis of loop gas networks

This paper proposes a mathematical model underlying a computer program for flow-pressure analysis of loop gas pipe networks. The method is used on a test case with four nodes. The HAPN application for flow-pressure analyses of low pressure gas pipe networks is completely designed in object-oriented programming technology. The equations, which describe the physical flow-pressure conditions through every cross point are assumed to be continuous and the energy of every closed loop of analyzed network conserved. The system of non-linear equations was linearized by LTM (Linear Theory Method). The algorithm for numerical module LTM and the method for solution of sparse matrix are developed at the Faculty of Chemistry and Chemical Engineering, University of Maribor, Slovenia

Comparison of the performances of absorption refrigeration cycles

This paper compares the performance of absorption refrigeration cycles that are used for refrigeration temperatures below 0°C. Since the most common vapor absorption refrigeration systems use ammonia-water solution with ammonia as the refrigerant and water as the absorbent, research has been devoted to improvement of the performance of ammonia-water absorption refrigeration systems in recent years. In this paper the performances of the ammonia-water and possible alternative cycles as ammonia-lithium nitrate, ammonia-sodium thiocyanate, monomethylamine-water, R22-DMEU, R32-DMEU, R124-DMEU, R152a-DMEU,R125-DMEU, R134a-DMEU, trifluoroethanol (TFE)-tetraethylenglycol dimethylether (TEGDME), methanol-TEGDME and R134a-DMAC are compared in respect of the coefficient of performance (COP) and circulation ratio (f). The highest COP and the lowest f, were found as a function of the generator, condenser, absorber and evaporating temperature

Verification of the mathematical model of pulverized coal combustion in swirl burners

Prikazan je matematički model sagorevanja ugljenog praha u ložištu sa vrtložnim gorionicima. Model se zasniva na dvojednačinskom k-ε simulacionom modelu jednofaznog turbulentnog strujanja, a koji uzima u obzir prisustvo čvrste faze putem PSI-Cell metode. Disperzna faza se tretira Lagranževskim stohastičko - determinističkim modelom. Prenos toplote zračenjem se tretira pomoću metode Šest flukseva. Devolatilizacija uglja, kao i homogene i heterogene reakcije su modelirane skupa koristeći model globalnog sagorevanja uz upotrebu sopstvenih podataka o kinetici reakcije. Model se verifikuje poređenjem računskih i eksperimentalnih rezultata pri sagorevanju polidisperznog ugljenog praha u dva eksperimentalna ložišta. Zaključeno je da se ovaj model može sa uspehom iskoristiti za predviđanje, optimizaciju i projektovanje vrtložnih gorionika za različite geometrijske, strujne i temperaturske granične uslove kao i ugljeve različitog kvaliteta.Mathematical model of pulverized coal combustion in furnaces with swirl burners is presented. The model is based on two equation k-ε single phase turbulent flow simulation model, considering presence of the solid phase via PSI-Cell method. Disperse phase is treated by Lagrangian Stochaistic Deterministic model. The radiation heat transfer is treated via Six-Flux method. Coal devolatilization, homogeneous and heterogeneous reactions are modeled together via global combustion model using own reaction kinetics data. Model was verified comparing computational and experimental results for combustion of polydisperse pulverized coal in two experimental furnaces. It is concluded that the model can be successfully used for prediction optimization of parameters and design of swirl burners, for different burner geometries, flow and temperature boundary conditions and coals of different rank

Exploitation of Excess Low-Temperature Heat Sources from Cogeneration Gas Engines

The chapter presents an innovative technical solution for the use of low-temperature excess heat from the combined heat and power (CHP) of gas engines using gas or liquid fuel for district heating, building heating or industry. The primary fuel efficiency of CHP gas engines for heat production can be significantly increased by using the low-temperature excess heat of the exhaust gasses and the cooling system of the CHP gas engine, which are released into the environment thereby also reducing CO2 emissions. District heating hot water systems generally work with higher temperatures of the heating water, which is transported to the heat consumer via the supply line, and the cooled heating water is returned to the CHP gas engine via the return line. In order to make use of the excess low-temperature heat of the exhaust gasses and the cooling system of the CHP gas engine, a condenser must be installed in the exhaust pipe in which the water vapor contained in the exhaust gasses condenses and a mixture of water and glycol is heated, which later leads to the evaporator of the high-temperature heat pump (HTHP). The cooled heating water is returned from the heat consumer via the district heating return pipe to a condenser of one or more HTHPs connected in series, where it is reheated and then sent to a CHP gas engine, where it is reheated to the final temperature. The Aspen plus software package is used to run a computer simulation of one or more HTHPs connected in series and parallel to the district heating system and to demonstrate the economics of using the excess heat from the exhaust gasses and the cooling system of the CHP gas engine

Hydrogeothermal cascade heat pump – Economic and ecologic appropriacy

The article considers economy of exploiting heat from low-temperature geothermal sources for high-temperature heating of buildings using a heat pump. For the exploitation of low-temperature geothermal sources, a two stage heat pump with a heat transmitter was planned. The pump consists of two single stage heat pumps which use different refrigerants at each stage. At stage one, the calculation of the heat pump is conducted with refrigerant R407c; at stage two of the heat pump, the refrigerant R600a is used. The main operational characteristics of a two stage heat pump are presented in the form of diagrams. For the exploitation of heat from geothermal water with a temperature of 45°C, a profitability evaluation of the investment in the heat pump was carried out, using the method of the net present value. In the research, also the coefficient of profitability and the period of time in which the investment is going to return itself were established

External atmospheric influences on the mechanical properties of resin-bonded grinding wheels with aluminium oxide and silicon carbide grains

Ageing effects on resin-bonded grinding wheel properties are presented, including aluminium oxide and silicon carbide influence. Furthermore, humidity is examined as the most likely cause of significant downgrade in mechanical properties. Toward this aim a new system of accelerated ageing of grinding wheels (additional humidification) is used under special atmospheric conditions. The mechanisms for microstructural changes during ageing are analysed, based on the microstructure exposure to thermo-mechanical impacts

External atmospheric influences on the mechanical properties of resin-bonded grinding wheels with aluminium oxide and silicon carbide grains

Ageing effects on resin-bonded grinding wheel properties are presented, including aluminium oxide and silicon carbide influence. Furthermore, humidity is examined as the most likely cause of significant downgrade in mechanical properties. Toward this aim a new system of accelerated ageing of grinding wheels (additional humidification) is used under special atmospheric conditions. The mechanisms for microstructural changes during ageing are analysed, based on the microstructure exposure to thermo-mechanical impacts

Каскадна геотермална топлотна пумпа - техно-економска анализа и еколошки утицај

Razmotrena je ekonomska i ekološka opravdanost iskorišćenja toplote niskotemperaturne geotermalne vode za potrebe centralnog grejanja stanova uz pomoć toplotne pumpe. Uređaj se sastoji iz dve jednostepene toplotne pumpe koje rade u kaskadnoj sprezi. Proračun prvog stepena toplotne pumpe je sproveden za rashladni fluid R407c; u drugom stepenu koristi se fluid R600a. Osnovne radne karakteristike toplotne pumpe date su u obliku dijagrama. Za eksploataciju toplote iz geotermalne vode temperature +45°C, izvršena je tehno‑ekonomska analiza investicionih troškova toplotne pumpe, korišćenjem metode neto prisutne vrednosti. U okviru istraživanja, određeni su koeficijent isplativosti i period vremena nakon kojega će investicija otplatiti samu sebe. U radu je razmotren i uticaj predloženog tehničkog rešenja na okolinu i konstatovana je opravdanost ovakve eksploatacije hidrogeotermalne energije. Economic and envirnnmental feasibility analysis was performed regarding the use of heat of the low‑temperature geothermal water for the residential central heating by using a heat pump. The unit consists of two single‑stage heat pumps operating in a cascade connection. The calculation of the heat pump‘s first degree was made for the refrigerant R470c; in the second stage, the R600a fluid was used. The basic operation characteristics of the heat pump were presented in the form of diagrams. As for exploitation of heat from geothermal water of 45°C, a technological and economical analysis was performed regarding the heat pump investment costs, by using the net present value. Within the research, the payback coefficient and investment payback time period were determined. The environmental impact of the proposed technical solution was discussed and the described use of hydro‑geothermal energy was found justifiable