Jinwei Heater analyzes stress concentration in tubular heater U-bends

Shengzhou Jinwei Electric Heating Appliance Co., Ltd. has developed an advanced finite element analysis (FEA) framework aimed at refining the design of tubular heaters. The company states this method helps predict surface load distribution and, crucially, stress concentrations in U-bends, which are identified as the dominant failure location.

A key finding from the analysis is that the bend radius-to-outer-diameter ratio (R/D) is the most significant variable influencing failure rates in the bends. Jinwei indicates that industry practice and its own FEA datasets support an R/D ratio of at least 2.5-3.0 for Incoloy and stainless-steel sheaths.

The study emphasizes that a sequentially coupled thermal-stress FEA approach is necessary because the temperature field drives thermal strain, which in turn drives bend stress. A purely mechanical FEA significantly under-predicts bend stress. Surface load, defined as watt density, is the design variable that drives temperature, not stress directly.

The company reports typical surface load ranges of 2-6 W/cm² for liquid immersion, 4-10 W/cm² for forced air, and 1-3 W/cm² for still air. However, these limits depend on the sheath material and the installation's cooling conditions. Comparing FEA results to the allowable stress for the chosen sheath material at the maximum operating temperature is essential for ensuring reliability.