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Monday, 06 March 2017 11:00

Технически Университет – София

Машинно-технологичен факултет

Научно-изследователската лаборатория

“CAD/CAM/CAE в индустрията“

 

Coupled field analyses for extremely high loaded thermal sensor

characterization at design development stage

 

Technical University – Sofia, Faculty of Industrial Engineering, Laboratory “CAD/CAM/CAE in Industry”

 

1    Introduction

 
 


The focus of this study is set on an extremely loaded temperature sensor. One area where temperature sensors find particular usefulness is in the area of exhaust gas environments. Various applications require measurement of temperature of gas or mixture of gases at elevated temperatures. One such application involves automotive or combustion applications in which a need exists for measuring the exhaust gas temperature for emission control using Selective catalytic reduction (SCR) and Exhaust Gas Recirculation (EGR) based emission after treatment systems. The sensor should function in a harsh and corrosive automotive exhaust gas environment containing, for example, soot particles, SOx, moisture, diesel, NH3, NOx, HC, CO, CO2 etc. [2, 3] Examined sensor is generally suitable for monitoring of moderately supercharged petrol engines, designed for applications that almost never exceed 850°C.

Fig. 1
Examined temperature sensor and used approach

 

 

 
   

Design development requires information concerning sensor behaviour under thermal loads, especially in two directions – response time and structural stresses that are results of thermal expansion of the structure. This is achievable through virtual prototyping, using numerical techniques. [1,3]

2    Problematics and approach. Experimental data

Two major problems are examined through this research:

  • How protective cap design influences sensor response dynamics?
    • Thermofluid problem (coupled field analysis)
  • How heating characteristics influences structural behavior of sensor components?
    • Structural problem (structural analysis, using data from thermo-CFD analysis)

Problematics require coupled field analysis approach, as for accurate results, it is needed to examine fluid flow, thermal parameters and force-deflection behaviour. Thermo-fluid simulation is needed to be performed to evaluate influence of protective cover over sensor reponse. The results are also to be used for more precise loads definition for structural analysis. All simulations are to be compared to measured by certain experiments data.

General schematics of used approach is shown on figure 1 above. Experimental measurements for fluid flow parameters and sensor response temperatures will be used as reference to adjust built thermo-CFD analysis. This coupled field simulation will be performed over design variants with protective cover and without. Transient analyses results are to be compared and detailed fluid flow and thermal parameters are to be examined to find relations between protective cover design and sensor response time.

Two sets of experiments are performed – with and without protective cover. Representatives of the performed measurements are shown on figure 2 below.

 

Fig. 2

Experimental data

3    Thermo-CFD simulations

Transient thermo-CFD analyses are performed as to obtain sensor behaviour when is subjected to heated fluid flow. Results for variant with protective cover are compared to these without protective cover – as fluid flow parameters and as temperature response over time (figure 3). Temperature distribution by zones are determined to be used as input data for subsequent structural analysis (figure 3 c)).

 

Fig. 3

Coupled thermo-CFD analyses results

 

4    Structural analysis

Last step is to performed structural (steady state) analyses under thermal loads - determined layered temperature fields. Major searched results are sensor deflections (character of loading is explored mainly) and equivalent stresses (strength check against materials limits). This allows to evaluate mechanical behaviour of examined variants in detail as well and to obtain a complex general view of problematics. Critical zones are marked for further research and optimisation. Sample results – as overall deformation field and stresses – are shown on figure 4.

Fig. 4

Structural analyses results

 

5    Conclusions

Turbulent hot air flow is modeled in detail as to track design changes impact over sensor response times, caused by protective cover design. Performed simulations are verified over physical prototypes of the examined design variants. Obtained temperature distribution field and computed convection parameters are used for subsequent structural analysis to evaluate design force-deflection behavior. Demonstrated engineering analyses process is a good base for future practice of design evaluation at earliest possible design stage using virtual prototypes.