The pro­duc­tion of modern mate­ri­als requi­res pre­cise tem­pe­ra­tu­re con­trol during heat tre­at­ment. The pro­ces­ses for trea­ting alu­mi­ni­um and cop­per mate­ri­als as well as some types of steel with a tre­at­ment tem­pe­ra­tu­re of up to 800 °C are often car­ri­ed out in high con­vec­tion fur­naces with forced cir­cu­la­ti­on. This requi­res a high degree of tem­pe­ra­tu­re uni­for­mi­ty in the fur­nace. Sin­ce heat is trans­fer­red by con­vec­tion, this results in the requi­re­ment for the lar­gest pos­si­ble and most uni­form volu­me flow. Fans of various types are used in high con­vec­tion sys­tems, main­ly axi­al and cen­tri­fu­gal fans; tan­gen­ti­al fans have been the excep­ti­on so far. The fol­lo­wing table lists the most important pro­per­ties (effi­ci­en­cy and maxi­mum ope­ra­ting tem­pe­ra­tu­re) as well as advan­ta­ges and dis­ad­van­ta­ges of the dif­fe­rent fan types.

Com­pa­ri­son of fan designs

As an alter­na­ti­ve to the fan types main­ly used up to now, tan­gen­ti­al fans are an opti­on. Tan­gen­ti­al fans are fans that suck in and blow out the pro­cess gas radi­al­ly. For the same volu­me flow, tan­gen­ti­al fans achie­ve a hig­her flow uni­for­mi­ty than a com­pa­ra­ble cen­tri­fu­gal fan. The flow velo­ci­ty is almost homo­ge­neous across the width. This is a decisi­ve advan­ta­ge for use in ther­mopro­ces­sing plants, sin­ce here a uni­form volu­me flow is requi­red over the enti­re fur­nace or zone width. In the pre­vious IGF pro­ject 18418 N, it was shown that tan­gen­ti­al fans ful­fil the flu­id dyna­mic requi­re­ments for use in typi­cal indus­tri­al fur­naces. The hot test rig set up in the pre­vious IGF pro­ject 18418 N at the Depart­ment of Indus­tri­al Fur­naces and Heat Engi­nee­ring is sui­ta­ble for inves­ti­ga­ting tan­gen­ti­al fans at a pro­cess tem­pe­ra­tu­re of up to 500 °C. The tan­gen­ti­al fan is flan­ged to a flow chan­nel so that the fan modu­le can be easi­ly repla­ced. The air is con­vey­ed in a clo­sed cir­cuit in the hot test stand. The sys­tem cha­rac­te­ristic cur­ve can be adjus­ted via a thrott­le device. Four co-rota­ting thrott­le val­ves are con­trol­led by a line­ar actua­tor. The ope­ra­ting point can be set repro­du­ci­b­ly by the posi­ti­on feed­back of the elec­tric cylin­der. The test rig is hea­ted via a 40 kW hea­ting regis­ter with asso­cia­ted con­trol. A ther­mo­cou­ple in the hea­ting regis­ter is used as the con­trol­led varia­ble. The­re are two mea­su­ring points for flow mea­su­re­ment, one in the lower hori­zon­tal duct seg­ment, at the out­let of the fan. Here, the out­flow pro­fi­le of the fan can be mea­su­red with local reso­lu­ti­on. In case the volu­me flow can­not be deter­mi­ned pre­cis­e­ly enough due to tran­si­ent effects, ano­ther mea­su­ring point is pro­vi­ded in the upper hori­zon­tal sec­tion. Here the flow is rec­ti­fied by two 90° baf­f­les and the throttling.

Tan­gen­ti­al fan hot test rig at IOB

The aim of this pro­ject is to design a ther­mo­me­cha­ni­cal­ly sta­ble tan­gen­ti­al fan for use in ther­mopro­ces­sing plants. For this pur­po­se, nume­ri­cal inves­ti­ga­ti­ons are car­ri­ed out to increase the ther­mo­me­cha­ni­cal sta­bi­li­ty using the fini­te ele­ment method and the influence on the flu­id mecha­ni­cal pro­per­ties using com­pu­ta­tio­nal flu­id dyna­mics. Based on the results of the­se inves­ti­ga­ti­ons, a pro­duc­tion sam­ple is desi­gned and manu­fac­tu­red. This func­tion­al sam­ple will then be instal­led in the hot test stand, which has been sup­ple­men­ted with detail­ed sen­sor tech­no­lo­gy, and its flow and vibra­ti­on beha­viour will be inves­ti­ga­ted.
Based on the results of this pro­ject, plant manu­fac­tu­r­ers and sup­pli­ers should be able to adapt the design recom­men­da­ti­ons in order to build ther­mo­me­cha­ni­cal­ly sta­ble tan­gen­ti­al fans. As a result, tan­gen­ti­al fans should find wider appli­ca­ti­on in con­vec­ti­ve heat tre­at­ment plants.