| In the biogas project,the spiral coil is widely used in the anaerobic fermentation system because of its simple structure,convenient production and large heat transfer coefficient.The use of the spiral coil is mainly the inner coil and the outer coil.The two kinds of coils have their own advantages and disadvantages due to different installation positions,and also cause differences in heat transfer process,which in turn affects the heat transfer coefficient and heating effect.At present,the main research object of heating coils at home and abroad is the wet anaerobic fermentation with low TS value of water and fermentation raw materials.The inner coil heating system mainly studies the arrangement of coils,the simulation of temperature field and the flow in coils.In terms of characteristics,the research on external coil heating anaerobic fermentation system is relatively rare,and most of them are research and design calculation of overall heat transfer performance,but there are few researches on the heating process of dry fermentation system.In this thesis,the heating process and constant temperature operation process of the inner and outer coils to the fermentation system were studied under the conditions of 10°C and-10°C ambient temperatures with the TS values of 0%,8%and 20%,respectively.Comparing and analyzing the total heat transfer coefficient of the inner and outer coils,the heating time,the temperature field distribution in the tank,the Dean number D_e and the field synergy F_c,etc.,the heat transfer coefficient is obtained for the heating time,the heating rate and the temperature.The effect of uniformity,at the same time the internal and external coils in the process of warming,the heating rate,temperature uniformity,heat transfer coefficient and the synergy between the velocity field and temperature field in the tube,as well as the long-term heating and warming In the case,the effect of fouling on the outside of the coil on the heat transfer coefficient of the coil.The effects of heat transfer coefficient on the running time of the internal and external coil circulating water pump and the economical efficiency of the temperature control during the constant temperature operation of the fermenter were compared and analyzed.The difference between the internal and external coils in maintaining the stability of the fermentation system was obtained.The main conclusions of this paper are as follows:(1)When water is used as heating raw material,the ambient temperature,heat supply and hot water inlet and outlet position are the three key factors affecting the heating rate and the uneven temperature field in the tank,and the influence of the external coil heating process is more obvious.The heat supply is the most influential factor to the heating process of the inner and outer coils.The heat supply is increased from 11.2 kJ to 35.1 kJ,and the heat transfer coefficient of the inner and outer coils is 70 W/(m~2·K)and 9 W/(m~2·K)increased to105 W/(m~2·K)and 12 W/(m~2·K),and the heating rate was increased from 0.2°C/min and0.03°C/min to 0.5°C/min and 0.05°C/min,respectively.By comparing and analyzing the heating time,heating effect and anti-environmental interference ability of the inner and outer coils,the inner coil heating method is better than the outer coil method.(2)When the cow dung of different TS concentration is used as the heating raw material,The value of the heating raw material TS is the main factor affecting the heat transfer coefficient of the inner and outer coils,the heating rate and the temperature field unevenness in the tank.As the TS value of the raw material increases from 8%to 20%,the heating time of the inner and outer coils and the temperature field inhomogeneity increase are 4.2,1.7,0.25,and 0.14,respectively,and the heat transfer coefficient and heating rate are reduced to the original ones.23%,54%and 7%,40%.Compared with the raw material TS value,the ambient temperature has less influence on the heating process of the inner and outer coils,but the degree of unevenness of the temperature field in the tank is reduced,and the temperature field unevenness of the outer coil heating is always lower than the inner coil.Therefore,the temperature uniformity of the outer coil heating tank is better than the inner coil.(3)As the Dean number in the coil increases,the synergy between the temperature field and the velocity field in the coil becomes better,the convective heat transfer coefficient in the tube also increases,and because the curvature of the outer coil is smaller than the inner coil,When the heating raw material is water,the field synergy of the outer coil is always greater than the field synergy of the inner coil,and the convective heat transfer coefficient in the outer coil is always greater than the inner coil.Under the same Dean number,with the increase of TS value,the internal coordination number of the inner coil tube gradually decreases,the convective heat transfer coefficient in the tube gradually decreases,and the internal field synergy of the outer coil tube gradually increases,and the convection heat transfer in the tube The coefficient gradually increases.(4)The thermal resistance of the dirt outside the inner coil is not gradually generated,but is present after the fermentation raw material is added to the fermenter,and then the thermal resistance of the dirt gradually increases with time.During the whole experiment,the thermal resistance of the outer side of the inner coil increased from 0.0062(m~2·K)/W to 0.0085(m~2·K)/W,and the outer convective heat transfer coefficient decreased from 1640 W/(m~2·K)to 1520 W/(m~2·K),and as the TS value of the heating material increases,the thermal resistance of the dirt outside the coil increases,and the increase in the thermal resistance of the dirt increases.(5)Through the analysis of the running time and temperature control economy of the circulating water pump inside and outside the fermenter at different ambient temperatures,the running time and temperature control cost of the circulating water pump of the inner and outer coils are all decreased with the ambient temperature and the TS value of the heating raw material.Increase and increase,wherein the outer coil is always larger than the inner coil,and the increment is much larger than the inner coil.It can be obtained that for the normal operation of the high TS constant temperature fermenter,the energy consumption and temperature control economy of the inner coil heating mode are superior than the outer coil. |
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