Darbeli (Titreşimli) yanmanın teorik ve deneysel incelenmesi
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Fen Bilimleri Enstitüsü
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Bu çalışmada darbeli yanma ve uygulamaları araştırıldı. Darbeli yanmanın kütle transferini, momentumu ve ısı transferini artırdığı gözlemlendi. Daha sonrada çalışma karakteristikleri, teorik hesaplan, darbeli yanmanın avantajları ve dezavan tajları görüşüldü. Avantajları basit dizayn, kendi kendine aspirasyon ve düşük CO ve kurum emisyonudur. Ayrıca NOx emisyonuda büyük oranda azalmıştır. Prob lem olarak gürültü kalır, fakat akustik susturucu ve ses izolasyonu kullanarak ka- uledilebilir seviyelere indirilebilir. Darbeli yanma kütle transferini, momentum ve ısı transferini artırdığından da ha fazla yakıt tasarufiı sağlar ve verimliliği artırır. Darbeli yanma, su buharlaştırma da, kireç taşı ocaklarında, metal eritmede, çimento ve kağıt üretiminde ve yanma nın olduğu bütün işlerde kullanılabilir. Teorik kısımda süreklilik, momentum ve enerji denklemleri incelendi. Bu denklemlerde belirli sınır şartları ve ilk şartlar altinda denklemlerin çözümü yapıldı. Sistemin boyutsuz ısı ilaveli basmç, hız ve sıcaklık ifadeleri bulundu. Deney kısmında yanmadaki C02,CO,02,X,NO^, S02 ve sıcaklıklar ölçüldü. Bunların zamanla değişimleri grafik halinde verildi. Ayrıca sistemin ses kayıtlarından frekansı ölçüldü. Ayrıca termo eleman ve osiloskopla sıcaklık titreşimleri ölçüldü.
The state of the art of pulse combustion and its applications are investigated in this study. Evidence showing that pulsations generally increase the rates of mass, momentum and heat transfer and destabilize flows at certain unstable frequncies is presented. Next, the operational characteristics, advantages and disavantages of pulse combustors are discussed. Advantages include simple desing, compactness, self aspiration, and low emissions of CO and soot. Results showing that NOx emissions from pulse combustors can be significantly reduced using fuel staging, air staging and exhaust flow recirculation are presented. Noise remains a problem, but it can be damped to acceptable levels using acoustics decouplers and sound insula tions. These pulsations increase the rates of mass, momentum and heat transfer within the process, which generally results in significant fuel savings and product ivity increases. Evidence showing the benefits of resonant driving in water evapo ration, limestone calcining and metal heating is presented. Finally, data obtained in recent tests in an Rijke combustor showing mat resonant driving significantly re duced soot emissions during the incineration of solid and hazardous wastes are pre sented. Theory Altough chemically reacting flow involves many different and separately complex fields such as turbulance, chemical kinetics, thermodynamics etc.. The model is derived in a concise manner following the basic principles of mixture theory within continuum mechanics. The intention is that with on model, it should be possible to describe different objects by changing geometry, boundary VI conditions and constitutive relations. However, since the time scales in the chemical reactions in combustion are much smaller than the time scale in the flow, special care has to betaken when the reaction rates should be calculated. In many combustion applications we are interested in studying the growth of instabilities. Under these circumstances we can usually linearize the equations of motion by assuming that initially the deviations from some known background state are very small. One typical example of such linerazition is the classical field of acoustics. Here, for the simplest case the background 'flow' is assumed to be a quiescent gas with costant state properties in which all fluctuation quantities are small. If the flow is restricted to be one-dimensional nonsteady the basic equations that apply are optained by writing Eqs (1) and (2) do du dp du du 18P dt dx pdx Furthermore, using the heat-addition-working-fluid (constant gamma) model to determine the relationship between pressure and density are obtain dP dP, Jdq dq~\ within the framework of the acoustic approximation we assume that p=p0+8p P = P0+8P -r = Sp«l and - ' " 2 ° yP0 «o where - - = Sp« 1 and - - « 1 with a] = - - = const we note here that the acoustic condensation, s, is defined in terms of pressure rather than density because the pressure and flow velocity are the important balan ce parameters along a particle path in the flow. This yields the equations vu 5(5p) du %+±*&.o (5) at p0 ax ö(8p) 1 8(5P) p0 c^r & a02 a a02 v' "' dt zt(y-»-± <6> Cross-difFerantion of Eqs (4) and (5) and substitution of (6) then yields the acous tics equation in terms of the dimensionless pressure \dt2 * dxz dt2{Cp.TJ (7) This equation has a soluation of the form sp(x,t) = F(x).G(t) Let us now assume that q=0, that is, that the fluid is unreactive. With this assump tion we can also cross-differentiate Eqs (4) and (5) in the other direction to obtain d2» i ^u Under these conditions with both ends open, the soluation can be expressed in the following form vni = 5X sın- nm0t nice -sirt-r~ (9) u=Zc, mux J nice cos n t -cos- (10) The resonant frequencies are given by the expression / = -j- for a tube which both ends open Returning now to the case of heat addition we note that if we assume J cycle 8q_ dt dt = 0 (11) the background conditions become constant. Toong et all [4] has experimentally observed and analyzed the case when the gas is undergoing an exothermic reaction while acoustic waves are present. We now assume the simplest case relative to combustion driven instabi lity. Assume that homogeneously through the tube the rate of heat addition is proportional to the perturbation quantity s, that is, that CJo k.s (12) where k is a constant. With this assumption, Eq.(7) becomes ^-*£-~" at2 da. dt (13) We have a tube with both ends open, Eq (13) becomes fk.t^ sp (*.*)= exp - - - 2j race ^sin-- k 2 ;v L ^ rrna0 nita0 A"sm---t + Bncos--t L, Li J (14) IX Where the coefficients An and Bn are functions of the initial conditions. Now we can find heat equation C T % x - ? = -^^sin-^.e2.4(*.sinw"./-2wBcoswfl./) (15) n EXPERIMENTAL STUDY The test equipment consists of iron cylinder. The diameter of the cylinder is 100 mm and with height of 1,5 meters. Air is supplied from the bottom by means of a compressor. The test equipment is equipped with thermoelements and a gas sampling probe. The temparature is measured in the top of the cylinder. The com bustion products ( CO, C02, 02 S02 NOx ) are measured by gas analyzer. Besi des, sound and frequencies are measured. Coal is charged from the top of the cylinder and ignited from the bottom of the combustion chamber. The experiments is carried out for two kinds of coals with three different particle size ranges of 0-3 mm and 3-5 mm and 5-8 mm at dif ferent air fluxes. But, 3-5 particle size is the best combustible coal. Results of the experiments have been compared with each other. The frequency of sound records is measured. The frequency is approximately 156 Hz. At theory, frequency was 170 Hz. This difference is the reason of missing.
The state of the art of pulse combustion and its applications are investigated in this study. Evidence showing that pulsations generally increase the rates of mass, momentum and heat transfer and destabilize flows at certain unstable frequncies is presented. Next, the operational characteristics, advantages and disavantages of pulse combustors are discussed. Advantages include simple desing, compactness, self aspiration, and low emissions of CO and soot. Results showing that NOx emissions from pulse combustors can be significantly reduced using fuel staging, air staging and exhaust flow recirculation are presented. Noise remains a problem, but it can be damped to acceptable levels using acoustics decouplers and sound insula tions. These pulsations increase the rates of mass, momentum and heat transfer within the process, which generally results in significant fuel savings and product ivity increases. Evidence showing the benefits of resonant driving in water evapo ration, limestone calcining and metal heating is presented. Finally, data obtained in recent tests in an Rijke combustor showing mat resonant driving significantly re duced soot emissions during the incineration of solid and hazardous wastes are pre sented. Theory Altough chemically reacting flow involves many different and separately complex fields such as turbulance, chemical kinetics, thermodynamics etc.. The model is derived in a concise manner following the basic principles of mixture theory within continuum mechanics. The intention is that with on model, it should be possible to describe different objects by changing geometry, boundary VI conditions and constitutive relations. However, since the time scales in the chemical reactions in combustion are much smaller than the time scale in the flow, special care has to betaken when the reaction rates should be calculated. In many combustion applications we are interested in studying the growth of instabilities. Under these circumstances we can usually linearize the equations of motion by assuming that initially the deviations from some known background state are very small. One typical example of such linerazition is the classical field of acoustics. Here, for the simplest case the background 'flow' is assumed to be a quiescent gas with costant state properties in which all fluctuation quantities are small. If the flow is restricted to be one-dimensional nonsteady the basic equations that apply are optained by writing Eqs (1) and (2) do du dp du du 18P dt dx pdx Furthermore, using the heat-addition-working-fluid (constant gamma) model to determine the relationship between pressure and density are obtain dP dP, Jdq dq~\ within the framework of the acoustic approximation we assume that p=p0+8p P = P0+8P -r = Sp«l and - ' " 2 ° yP0 «o where - - = Sp« 1 and - - « 1 with a] = - - = const we note here that the acoustic condensation, s, is defined in terms of pressure rather than density because the pressure and flow velocity are the important balan ce parameters along a particle path in the flow. This yields the equations vu 5(5p) du %+±*&.o (5) at p0 ax ö(8p) 1 8(5P) p0 c^r & a02 a a02 v' "' dt zt(y-»-± <6> Cross-difFerantion of Eqs (4) and (5) and substitution of (6) then yields the acous tics equation in terms of the dimensionless pressure \dt2 * dxz dt2{Cp.TJ (7) This equation has a soluation of the form sp(x,t) = F(x).G(t) Let us now assume that q=0, that is, that the fluid is unreactive. With this assump tion we can also cross-differentiate Eqs (4) and (5) in the other direction to obtain d2» i ^u Under these conditions with both ends open, the soluation can be expressed in the following form vni = 5X sın- nm0t nice -sirt-r~ (9) u=Zc, mux J nice cos n t -cos- (10) The resonant frequencies are given by the expression / = -j- for a tube which both ends open Returning now to the case of heat addition we note that if we assume J cycle 8q_ dt dt = 0 (11) the background conditions become constant. Toong et all [4] has experimentally observed and analyzed the case when the gas is undergoing an exothermic reaction while acoustic waves are present. We now assume the simplest case relative to combustion driven instabi lity. Assume that homogeneously through the tube the rate of heat addition is proportional to the perturbation quantity s, that is, that CJo k.s (12) where k is a constant. With this assumption, Eq.(7) becomes ^-*£-~" at2 da. dt (13) We have a tube with both ends open, Eq (13) becomes fk.t^ sp (*.*)= exp - - - 2j race ^sin-- k 2 ;v L ^ rrna0 nita0 A"sm---t + Bncos--t L, Li J (14) IX Where the coefficients An and Bn are functions of the initial conditions. Now we can find heat equation C T % x - ? = -^^sin-^.e2.4(*.sinw"./-2wBcoswfl./) (15) n EXPERIMENTAL STUDY The test equipment consists of iron cylinder. The diameter of the cylinder is 100 mm and with height of 1,5 meters. Air is supplied from the bottom by means of a compressor. The test equipment is equipped with thermoelements and a gas sampling probe. The temparature is measured in the top of the cylinder. The com bustion products ( CO, C02, 02 S02 NOx ) are measured by gas analyzer. Besi des, sound and frequencies are measured. Coal is charged from the top of the cylinder and ignited from the bottom of the combustion chamber. The experiments is carried out for two kinds of coals with three different particle size ranges of 0-3 mm and 3-5 mm and 5-8 mm at dif ferent air fluxes. But, 3-5 particle size is the best combustible coal. Results of the experiments have been compared with each other. The frequency of sound records is measured. The frequency is approximately 156 Hz. At theory, frequency was 170 Hz. This difference is the reason of missing.
Açıklama
Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 1994
Konusu
Darbeli yanma, Pulsed combustion