Uncertainty analysis: Design of a fouling test device for the liquid-to-refrigerant heat exchangers

Fouling usually builds up on the waterside heat transfer surface of heat exchangers after long-term operation due to the impurity of the working water. Fouling research is important in the HVAC&R and chemical industries in order to develop fouling mitigation strategies and to direct manufacturers and designers for producing better heat exchangers. Fouling thermal resistance was studied using a heat exchanger installed in a testing system, which should have a high accuracy. Many operation parameters could affect the fouling test, thus a thorough design of the testing system is necessary to get reliable and robust data. This paper analyzes the effect of different operating parameters on the uncertainty of the fouling test results (fouling thermal resistance), including the length of the test tube, the surface heat transfer coefficient, the heat flux, the water velocity, and the fouling thermal resistance. Results show that the fouling test on tubes with higher surface heat transfer coefficient has a higher accuracy; Longer tube, higher heat flux, and lower water velocity can reduce the test uncertainty; When the fouling resistance is lower than 1E-5 m2K/W, the uncertainty is very high. The work in this paper is intended to help other fouling researchers to build a reliable test set-up so as to achieve accurate and comparable results.