An overview of srlife

srlife is a package for estimating the life of high temperature solar receivers. The package currently focuses on tubular, panel receivers though the package includes data for evaluating arbitrary high temperature components if the user provides the corresponding analysis results.

srlife provides life estimation approaches for both metallic and ceramic materials. These approaches differ, as described elsewhere in the documentation.

The package provides a complete assessment of a receiver design starting from the thermal and mechanical boundary conditions applied to the individual tubes in the receiver. This means that the package requires input from additional simulations in order to generate the boundary conditions. Specifically, srlife would usually sit on top of a simulation of the heliostat to calculate the indicant solar flux and simulations or measurements of the effective absorption of the receiver tube. The package, however, provides a simple thermohydraulic system solver for tubular receivers which can find the fluid and tube temperatures along each flow path if provided with the flow path inlet temperatures and flow rates.

Given this information, presented as time-dependent boundary conditions representing representative conditions on one or more thermal days, the package estimates the structural life of the receiver, providing this estimate as a number of repetitions of the user-provided daily cycle(s). For metallic materials the package provides a best-estimate life prediction using average material properties. For ceramic receivers the analysis is currently time independent and reports simply the reliability of the system under the provided thermomechanical conditions, i.e. the probability the design will not fail. Future versions of the software will extend the ceramic failure models to account for time dependent subcritical crack growth. When these improvements are completed the ceramic models will report the reliability as a function of time or, alternatively, the time until the receiver reliability falls below some reliability metric.

The package includes material information for a variety of receiver structural materials and working fluids. The user can add additional material models by manipulating a fixed XML file format – they do not need to alter the package source code to add new materials or provide variant material models for the materials already included in the base release.

srlife provides modules to:

  1. Define the receiver geometry and topology – how panels are connected to each other and how tubes are connected within a panel.

  2. Provide thermomechanical boundary conditions on the receiver, specifically options for:

    1. Outer diameter incident heat flux on each tube

    2. Inner pressure in each tube

    3. Collections of panels/tubes arranged in flow paths, giving: i. The inlet temperature of each flow path as a function of time ii. The flow path flow rate, again as a function of time

  3. A coupled finite difference, transient solid heat transfer code linked to a simple 1D thermohydraulic model for heat transfer through the receiver. The output of these solvers is both the fluid temperature as a function of position along each flow path and time and the solid temperatures in each tube given as a function of position and time.

  4. A full-scale finite element solver to take the tube temperatures and mechanical boundary conditions to the tube stress/strain/displacement fields.

  5. Connections to a extensive nonlinear material model library neml to provide accurate inelastic constitutive models.

  6. A receiver system solver that can account for connections between tubes in a panel and panels in a receiver, to accurately model the effect of structural connections with an abstract, numerically inexpensive representation.

  7. Damage solvers to estimate the level of creep-fatigue damage in a tube given the structural and thermal results for metallic materials and ceramic reliability calculations that link the applied stresses and temperatures to an expected reliability.

  8. An extensive material property library covering common high temperature metallic and ceramic receiver materials.

Conventions

With user-defined material models the end-user can apply any unit system they want. However, the built-in material library uses the following unit conventions:

Quantity

Unit

length

mm

angle

radians

stress

MPa

time

hr

strain

mm/mm

temperature

K

flux

W/mm2

conductivity

W/mm-K

diffusivity

mm2/hr

film coefficient

W/mm2-K

Warning

The built-in material model library aims for average life estimation, approximating the average time to failure for a particular component. This type of estimation is not suitable for a full design calculation, where lower-bound properties with adequate design margin must be used.