OPTIMIZATION OF HEAT AND MASS TRANSFER PROCESS IN PRE-CONDITIONER CUM SINGLE SCREW FLOATING FISH FEED EXTRUDER

Abstract

An existing floating fish feed extruder was improved by the incorporation of a temperature sensor to monitor the product temperature. The research was aimed at improving the machine to achieve necessary extrusion condition and to evaluate the effect of product temperature on the evaluation parameters. Machine improvement and the evaluation process were carried out at the Agricultural and Environmental Engineering Department workshop of the Federal University of Technology, Akure. Product temperature is a very important system parameter as well as an indicator of extrusion process. In this study, the product temperature response of a pre-conditioner cum single screw floating fish feed extruder developed locally was optimized. The pre-conditioner parameters were varied such that each experiment was repeated for all variations of the experiment. The parameters were speed (162.5, 180.6, 235.3 rpm), feed moisture content (20, 30, and 40 % wet basis) and fill ratio (2.85, 3.09, and 3.78). The best speed for pre-conditioner was 180.6 rpm, moisture content of 30 % has the highest product temperature value of 34.5 ⁰ C, fill ratio 3.068 has the best product temperature value of 34.0 8⁰ C, and energy requirement ranges from 20.35 to 21.8 J. A factorial experiment in completely randomized design was employed to study the effect of extrusion variables: feed moisture content (20, 30, and 40 % wet basis), screw speed (158.5, 245, 334 rpm), die size (4, 6, 8, mm) while checking for their effect on Product temperature, energy requirement, fill ratio, of the feed produced. The extruder speeds were measured using a tachometer while product temperature was monitored using thermocouple sensor. Product temperature is strongly related to the extrusion process parameters under study. Product temperature decreased with increasing moisture content. Optimum condition was found at 74.11 ⁰C at the feed section, 80.83 ⁰C at compression section, and 85.15 ⁰C at metering section, screw speed at 330.5 rpm, feed rate at 0.6 kg/min, die size at 7.47 mm, moisture content at 39.87 %, particle size at 1.1., and the 𝑅2 coefficient for the final model is 0.93 which indicated that the model is good. The extruder was found to be cost efficient for floating fish feed production. Process Parameters were expected to have effects on the product temperature of the final extrudates. Thus, model-fitting using response surface methodology was performed to examine their effect on product temperature. Quadratic coefficients fit the extrusion data very well, better than linear models. The equations relating the various dependent and independent variables were established to predict the performance of the machine. It was concluded that the extrusion condition are interrelated and a feasible and accessible solution now exist for the local production of floating fish feed in Nigeria.