Effect of Condenser Fouling on Performance of Vapor Compression Refrigeration System

Effect of condenser fouling is evaluated on the performance of a vapour compression system with refrigerants HFO1234yf and HFO1234ze as an alternative to HFC134a. The condenser coolant temperature has been varied between 35 and 40°C to evaluate the effect of fouling at different condenser temperatures. A simulation model is developed in EES for computing the results. The results have been computed by varying condenser conductance. The same has been validated with literature available before calculating the results. It is observed that the condenser fouling has larger effect on compressor power (Wcp%) as it increases up to 9.12 for R1234yf and 7.41 for R1234ze, whereas for R134a its value increases up to 7.38. The cooling capacity (Qevap%) decreases up to 13.25 for R1234yf and 8.62 for R1234ze, whereas for R134a its value decreases up to 8.76. The maximum percentage of decrease in value of COP is up to 19.29 for R1234yf and 14.47 for R1234ze, whereas for R134a its value decreases up to 14.49. The second-law efficiency is also observed to decrease with decrease in the condenser conductance. The performance of HFO1234ze is found to be better under fouled conditions in comparison to R134a and R1234yf.

Prognosis of Component Degradation Under Uncertainty: A Method for Early Stage Design of a Complex Engineering System

This paper proposes a method that dynamically improves a statistical model of system degradation by incorporating uncertainty. The method is illustrated by a case example of fouling, or degradation, in a heat exchanger in a cogeneration desalination plant. The goal of the proposed method is to select the best model from several representative condenser fouling models including linear, falling rate, and asymptotic fouling, and to validate and improve model parameters over the duration of operation. Maximum likelihood estimation (MLE) was applied to obtain a stochastic distribution of condenser fouling. Akaike’s Information Criterion (AIC) and the Bayesian Information Criterion (BIC) were then computed at time intervals to assess the accuracy of the MLE results. The degradation model was further evaluated by estimating future prognoses and then cross-validating with real world fouling data. The results show the accuracy of a prognosis can be improved substantially by continuously updating fouling model parameters. The proposed method is a step toward facilitating prognosis of engineering systems in the early design stages by improving the prediction of future component degradation.

Experimental Studies of Shell and Tube Condenser Fouling and Accelerated Particulate Fouling in Internal Helical-Rib Roughness Tubes

This paper addresses fouling in a family of seven 15.54 mm I.D. copper, helically ribbed tubes, which have different ridge heights, helix angles, and number of ridge starts. A series of semi-theoretical linear fouling correlations as a function of the product of area indexes and efficiency indexes for long term combined precipitation and particulate fouling (PPF) in cooling tower systems and a series of semi-theoretical linear fouling correlations as a function of the efficiency indexes for particulate fouling were developed. The correlations can be directly used to assess the fouling potential of enhanced tubes in actual cooling water situations.