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In this research, an elastic cylinder that utilized vortex-induced vibration (VIV) was applied to improve convective heat transfer rates by disrupting the thermal boundary layer. Rigid and elastic cylinders were placed across a fluid channel. Vortex shedding around the cylinder led to the periodic vibration of the cylinder. As a result, the flow-structure interaction (FSI) increased the disruption of the thermal boundary layer, and therefore, improved the mixing process at the boundary. This study aims to improve convective heat transfer rate by increasing the perturbation in the fluid flow. A three-dimensional numerical model was constructed to simulate the effects of different flow channel geometries, including a channel with a stationary rigid cylinder, a channel with a elastic cylinder, a channel with two elastic cylinders of the same diameter, and a channel with two elastic cylinders of different diameters. Through the numerical simulations, the channel maximum wall temperature was found to be reduced by approximately 10% with a stationary cylinder and by around 17% when introducing an elastic cylinder in the channel compared with the channel without the cylinder. Channels with two-cylinder conditions were also studied in the current research. The additional cylinder with the same diameter in the fluid channel only reduced the surface wall temperature by 3% compared to the channel without any cylinders because the volume of the second cylinder could occupy some space, and therefore, reduce the effect of the convective heat transfer. By reducing the diameter of the second cylinder by 25% increased the effect of the convection heat transfer and reduced the maximum wall temperature by around 15%. Compared to the channel with no cylinder, the introduction of cylinders into the channel flow was found to increase the average Nusselt number by 55% with the insertion of a stationary rigid cylinder, by 85% with the insertion of an elastic cylinder, by 58% with the insertion of two cylinders of the same diameter, and by approximately 70% with the insertion of two cylinders of different diameters (the second cylinder having the smaller diameter). Furthermore, it was also found that the maximum local Nusselt number could be enhanced by around 200%-400% at the entrance of the fluid channel by using the elastic cylinders compared to the channel without cylinders.

The insecticides permethrin, fenvalerate, methamidaphos and carbaryl were tested against diamondback moth, Plutella Xylostella (L.) under the laboratory conditions by caging the larvae on broccoli leaf discs sprayed under Potter's tower and by spraying the adults directly. The LC₅₀'s were determined at 48h. The toxicity of permethrin and fenvalerate to third instar larvae was approximately 10 and 160 times more than methamidaphos and carbaryl respectively. The adult susceptibility to permethrin and fenvalerate was two and 260 times greater than methamidaphos and carbaryl. The effect of post-treatment temperature of 15 and 25⁰C on the toxicity of the four insecticides to larvae was determined. A marked increase in toxicity of pyrethroids and decrease in toxicity of carbaryl was observed at 15⁰C. The effect of sublethal concentrations (LC₁ and LC₅₀) on diamondback moth development, female fecundity and insect behaviour was investigated. All the insecticides had deleterious effects on the number of larvae surviving to pupae duration of pupal period, number of pupae surviving to adulthood and cocoon formation in the pupae. Prolonged duration of larval-period from third instar to pupation and deformed pupae were also observed. Permethrin, fenvalerate and carbaryl caused latent toxicity and deformed wings of the adults. Pyrethroids and methamidaphos reduced the longevity of the adults where as carbaryl increased it. Except for permethrin all the other insecticides inhibited the female fecundity. At LC₁ and LC₅₀ concentrations pyrethroids showed repellent and antifeedant activity against larvae. The female moths did not prefer to oviposit onto leaf discs treated with LC₅₀ of pyrethroids. A field trial was laid down to study the period of crop protection given by single application of permethrin and fevalerate (50 and 150 g AI/ha), methamidaphos (900g AI/ha) and carbaryl (2000g AI/ha). The pyrethroids at a rate 50 and 150g AI/ha effectively controlled P. Xylostella population for 26 and 33 days respectively. The larval density in carbaryl and methamidaphos treated plots were significantly lower than the untreated control for 19 and 33 days respectively.