Sensitivity Analysis and Parameter Optimization of a Heat Loss Model for a Composting System

Abstract

A combined multi-parameter sensitivity analysis/frequency array analysis technique was employed to assess the impact of design conditions and matrix-specific properties on the rate of heat loss from a self-heating composting process. This method was specifically used to identify the range of parameters over which a model predicting the overall heat-transfer coefficients (U-values) for the heat loss process are particularly sensitive. The model was found to be most sensitive for the following range of input parameters: the internal diameter of reactor varying from 0.8m to 1.2m, the combined reactor wall and insulation thickness ranging from 4cm to 6cm, the free airspace of the matrix varying from 50% to 60%, the reactor length varying from 1.0m to 1.5m, the thermal conductivity of the organic substrates ranging from 0.1W/m.K to 0.2W/m.K and the preferred thermal conductivity of the insulation material being less than 0.2W/m.K. A second sensitivity analysis was performed to identify which input parameters actually influenced the model’s response the most. This analysis compared the acceptable and unacceptable frequency distributions of each input parameter, with model outputs below a U-value of 4.5W/m2.K being an acceptable composting performance from a thermodynamics consideration. This analysis disclosed the matrix free airspace, the internal diameter of the reactor and the combined thickness of reactor wall and insulation as the most important parameters which should be given high priority when designing invessel compost reactors.

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