Maximizing Food Processing Production Efficiency

In many food processing applications, hydraulic spray nozzles apply vegetable oil to food products or pans to act as a release agent. More common is to apply these oil-based agents as product moves along a conveyor.  As such, in order to achieve a uniform spray coating, manufacturers must take into account product size and shape, conveyor speed, temperature, humidity and oil chemistry. Furthermore, to improve profitability, the cost per unit should be minimized, while maintaining or improving product quality. One method to improve profitability in these applications is to maximize transfer efficiency.

Transfer efficiency is the ratio of the sprayed material that ends up on the target to that which lands elsewhere (in the air, on the conveyor, etc.). Ideally, we aim to achieve a 100% transfer efficiency, meaning 100% of the spray ends up on the target and no amount of sprayed material is over-sprayed. This is incredibly difficult, if not impossible to accomplish, therefore, a transfer efficiency above 80% is acceptable. Maximizing transfer efficiency for our customers means less waste, more material and improved worker safety. So, our goal with this research study was to find the best methodology for maximizing the transfer efficiency of our hydraulic nozzles when spraying vegetable oil during food processing.

We initially employed an experimental design approach to measure and validate the critical parameters of a peanut oil spray system. A combination of Particle Image Velocimetry (PIV), Laser Induced Florescence (LIF), and Phase Doppler Interferometry (PDI) was performed under controlled laboratory conditions. Using this same peanut oil coating, we carried out these controlled tests with various hydraulic nozzles and under multiple operating conditions. Among these controlled tests, we also utilized a conveyor system to simulate a substrate moving below a stationary nozzle header.

Experimental results show that heated oil had better transfer quality. In terms of transfer efficiency, preliminary observations show that increases in pressure and temperature decrease the transfer efficiency due to an increase in material loss to free roaming small droplets. So, the higher the pressure and the higher the temperature, the lower the overall transfer efficiency of the spray system. For food processing applications, these initial results suggest that to maximize transfer efficiency, a lower pressure, controlled temperature would work best. However, further data and testing will be required in order to quantify the material loss of high pressure, high temperature scenarios and confirm our conclusions.

Furthermore, a CFD simulation was conducted to obtain the approximate liquid volume fractions and velocities of the hydraulic nozzles. It was loosely validated with high speed imaging, by comparing the developing spray. The computational model’s agreement and disagreement with the experimental results provides insight for the appropriate considerations when constructing simulations to evaluate coverage and transfer efficiency.

Our CFD model, for instance, underestimated the fan angle of the flat spray nozzles and showed hints of heavy edging not present in the experimental simulations. As such, we're working on refining the CFD models to accurately predict transfer efficiency in such applications using CFD alone. This would make future requests for testing the efficiency and production value of our food processing spray systems quicker and easier.