Design and Performance Evaluation of a Hydronic Type Compost Heat Exchanger

Abstract

While much research has been published on the Compost Heat Recovery Systems (CHRs), little has been documented on the design and performance evaluation of the Hydronic compost heat exchangers using numerical and computational methods, occasionally resulting in compost process inhibition. A CHRs (0.036 m3/7.2 m2) Hydronic-type heat exchanger and 12.43 m2/2.83 m3, compost reactor (CR), was designed and developed with the main objective of evaluating the design and its performance. The numerical design and performance evaluation was achieved by using Kern’s and the effectiveness and Number of Transfer Units methods (ε-NTU), respectively. Empirically, data were captured by using the Polytetrafluoroethylene (PTFE) thermocouples connected to the TC-8 Picolog Data loggers. Data validation (empirical and mathematical), was achieved by modifying a free computer-based software developed by the Chemical Engineering Calculations (CHECAL), into a Hydronic Compost Heat Exchanger design and performance evaluation software (HYDROCOHE). Between the HYDROCOHE and numerical, and between empirical and HYDROCOHE, R2 values of 0.99938–0.9995, and R2 of 0.99269–0.9432 with the effectiveness of 0.4853–0.4848 were achieved with 0.99 kW-empirical and 2.10 kW-HYDROCOHE, respectively. The power disparity may be ascribed to the compost reactor’s insufficient thermal insulation. Counterflow arrangement was more effective (0.4766) than crossflow (0.4622) and parallelflow (0.4430) setups. Parallelflow heat exchanger system, therefore, has the potential to extract heat steadily, minimizing the composting cycle inhibition. Further work on the impact of various flowrates on the direction of flow and heat extraction is recommended.