Characterisation of liquid mixing processes in turbulent free jets

BACKGROUND

A considerable proportion of global greenhouse gas emissions are caused by the chemical industry, which is one of the world's largest energy consumers and processes raw materials into important products. The production of chemicals takes place along a value chain involving many work steps, each of which consumes and emits energy and substances. Avoiding the unnecessary consumption of resources in each of these steps is therefore a core element of the green transition in the chemical industry and its process technology. Strict application of the "Green Chemistry" principles minimises risks in educts, products and processes, enables the use of renewable raw materials and energy and reduces their overall consumption.

A key step in chemical processes is the mixing of substances. The mixing speed is an important factor here, on which the product yield and therefore also the amount of waste depends in many cases. The advantages of particularly fast micro-mixing are particularly important where the speed of the mixing process must be considerably higher than that of the chemical reaction. For this reason, various mixing methods are being developed which - compared to conventional mixing technology (e.g. agitator in a stirred tank) - are capable of mixing orders of magnitude faster. One of these micro-mixing techniques is micro-injection, in which liquids are injected into a mixing zone in a turbulent free jet under high hydraulic power input. The smaller the turbulent eddies in the flow, the higher the mixing speed.

In order to utilise mixing technology on an industrially relevant level, mixing units are often connected in parallel. In the case of microinjection, arrangements of several nozzles are therefore the subject of the research work presented here.

OBJECTIVE

The aim of this work is to investigate microinjectors with different nozzles and nozzle arrangements in detail with regard to their mode of operation, characteristics and performance. A deeper understanding of parametric dependencies between injector geometry, flow fields and mixing time should help to better optimise injectors for their specific application in the future. In the case of increasing the process throughput with multi-nozzle microinjectors, for example, interactions between neighbouring nozzle flows play an important role. The aim is to determine the potential contribution of microinjection as a mixing technology to improving fast, mixing-sensitive reactions in terms of the quantities of waste produced, product quality, raw material and energy efficiency.