| Compost tea is an organic agriculture product that is used as a biofertilizer and bio-pesticide in modern agriculture.It is produced from agricultural waste recycling using various brewing machines.In the past decade,many researchers have focused on the importance of compost tea in organic farming,contributing to its widespread use.It has been accompanied by the emergence of equipment of various designs,sizes,and trade names,for the production of compost tea.However,there are almost no published studies on tea machines;most of the information available on these machines comes from commercial publications such as catalogs,brochures,information leaflets,and fact sheets issued by the companies producing them.There are also sensitive data held by companies that are not revealed to the public.Airlift pumps are used in tea machines for circulation,mixing,aeration,and extraction of a compost solution,which circulates and flows through a fermentation tank.The equipment may contain one or more airlift pumps.These can produce a relatively large number of beneficial microorganisms compared with other mechanical techniques used in compost tea production.To the best of my knowledge,this is the first study which experimentally investigations of agricultural machinery from an engineering perspective,and aiming to development its design and improve efficiency.The study has identified the design and operational parameters that achieved the highest machine efficiency and the best compost tea quality and presented a new design of airlift pump for working with different liquid levels.The engineering and operational parameters tested in this study were;(air pressure,submergence ratio,air injection system,riser tube length and compost solution level in fermentation tank)that affect airlift pump performance and the basic performance of tea machines.This study includes four experimental studies addition to study of numerical simulation of airlift pump in compost tea machines;Firstly,the effects of mixing efficiencies,circulation,aeration,pump efficiency,effectiveness and energy consumption on pump performance were investigated with six different designs of airlift pump air jacket structure.Designs with total hole areas of 0.09 cm~2 achieved the highest compost liquid mass flow rates,pump effectiveness,and volumetric transfer coefficients,as well as good mixing efficiencies,owing to ideal air mass flow rates.Furthermore,the designs of orifice diameters 1.2 mm is achieved higher volumetric mass transfer coefficients and required less time to reach dissolved oxygen saturation in tea compared with orifice designs diameters 2 mm.Overall this data showed that the best air jacket design in this study was A2,which contained eight holes with diameter 1.2 mm;and achieved the best result with respect to pump efficiency,liquid compost mass flow,mixing efficiency,volumetric mass transfer coefficient,and pump effectiveness.Secondly,the effects of the submergence ratios of the airlift pump and air injection pressures on compost tea machine performance were examined.In this study used five different submergence ratios(80%,90%,100%,110%,and 120%)and five different air injection pressures(9,10,12,14,and 16 k Pa).The system was assessed in terms of liquid circulation,pumping effectiveness,mixing efficiency,total aeration time,energy consumption,and the microbial properties of the compost tea.Increasing the submergence ratio from 80% to 120% at fixed air pressure,contributed to a decrease in the air flow rates and a corresponding increase in the compost solution flow rate,an improvement in pumping effectiveness and an increase in compost solution mixing efficiency,and helped to reduce the total aeration time and energy consumption.This led to an increase in bacteria population density,thus increasing the efficiency of the tea machine and enhancing the quality of the compost tea.Therefore the study recommended that the appropriate submergence rate can be 100% or more.It was further demonstrated that an increase in air pressure from 9 to 16 k Pa for all submergence ratios led to increased air flow rates,and a corresponding increase in the compost solution flow which contributed to improved mixing efficiency,a decreasing total Aeration time and an increasing bacteria population density;however,the increased pressure led to an increase in hydraulic energy consumption.Thirdly,the effects of the riser tube length of the airlift pump and air pressures on compost tea machine performance were examined.Comparative experiments of three different designs of airlift pump,which different in the length of riser tube(50,45,40 cm)were performed at five different air injection pressures(9,10,12,14,and 16 k Pa).All designs have a fixed submergence ratio of 100%.The performance of compost tea machine was assessed in terms of liquid circulation,pumping effectiveness,mixing efficiency,and energy consumption.The experimental investigations result showed that the energy consumption was increasing with decrease the length of riser tube from 50 to40 cm and at the same time the compost solution mass flow rate,pumping effectiveness,and mixing efficiency were decreased.Also,this study compares the effects of the submergence ratio and the riser tube length on the performance of airlift pump,at changing liquid level in the fermentation tank.The results showed a significant improvement in the performance of compost tea machine with changing riser tube length compared with using a fixed length of riser tube.The liquid circulation,pumping effectiveness,mixing efficiency,and addition to the energy consumption efficiency of airlift pump in the compost tea machine have been improved.Fourthly,this study was undertaken to develop the multi-phase flow model by use of the standard model of RANS turbulence model to predict the performance of airlift pumps in compost tea machine.The computational geometry model of fermentation tank is established,and the multi-phase flow VOF model and SIMPLE algorithm in ANSYS Fluent was used to simulate the internal flow field of fermentation tank of compost tea machine.Also,two software programs have been written in C++ language for solution the set of the equations of the Reinemann model and the Stenning and Martin model to predict the performance of airlift pumps in compost tea machine.The results from both analytical models are compared with the present numerical simulation results and the experimental data of airlift pumps of the chapters three and four.The simulations considered the influence of the liquid level in the tank of compost tea machine on the performance of airlift pump.In the first case is discussed used the same design of airlift pump with change liquid level in the tank to predicting the performance of airlift pump with change of the submergence ratio from 100% to 80%.In the second case are discussed used two designs of airlift pump that different in riser tube length from 50 to 40 cm at the fixed submergence ratio of 100%.RANS models present have provided results goodly of predicting the airlift pump performance.In the riser tube length of 50 cm,the maximum relative errors in the RANS computation of liquid mass flow rate across the airlift pump of operational range were 4% and 3% corresponding to submergence ratio of100% and 80% respectively.While,in the riser tube length of 40 cm,the maximum relative errors in the RANS computation of the tea mass flow rate across the airlift pump operational range was 3%.The gas-liquid two-phase flow has been lifted in a riser tube of tea machine in a spiral move,and it moves from the side wall to the other side wall,and increased in the process of moving to in the sides of the wall.The spiral move of the gasliquid in riser tube and the moves to in the sides of the wall were increased with increasing submergence ratio.These moves with the submergence ratio of 100% were clearer than 80% submergence ratio.This spiral motion improves the mechanical mixing.So,with a submergence ratio of 100%,the bottom fluid was continuously circulated and mixed with the top fluid,whereas for a submergence ratio of 80%,the internal fluid of the tea machine was intermittently mixed,that is,the bottom fluid and the top fluid were not continuously mixed,owing to the reduced liquid mass flow rate at the lower submergence ratio.Fifthly,the farming processes and variable practices prompted to need a variable amounts from compost tea.So,there was need to development a new design of compost tea machine which is being capable to produce these amounts.This study involved the development of a new design of airlift pump,that is capable of working with different levels of liquid in the tank of the compost tea machine without changing the submergence ratio and capable to produce a different amounts from compost tea.A new design airlift pump(smart pump)in the present study could change its design automatically under microcomputer control by adjusting the length of a riser pipe to maintain a constant submergence ratio.The results of experimental investigations indicates,that the low water level in the reservoir led to significant decreases in water flow,pumping effectiveness,and volumetric mass transfer coefficient in the conventional design(with these becoming zero at the lowest water level)and to an increase in power consumption because it led to a decrease in the submergence ratio of the riser pipe and thus to decreased liquid pumping.While,the new design of airlift pump exhibited significantly improved performance,with increased water flow,pumping effectiveness,and volumetric mass transfer coefficient,and decreased power consumption.This work represents the first engineering study to address this type of agriculture machinery,and will provide insight into relatively unknown aspects of agricultural machinery.I hope this work will serve as a foundation for more future studies and as a reference for both academic and industrial research perspective. |
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