Influence of rheology on laminar heat transfer to viscoelastic fluids in a rectangular channel

Experimental studies of the laminar pressure drop and heat-transfer behavior of two types of aqueous polymer solutions were carried out in a 2:1 rectangular channel. The fluids studied were 1000 wppm of neutralized Carbopol 934 in deionized water and 1000 wppm of Separan AP-273 in tap water. Three different thermal boundary conditions were studied. The experimental friction factors for the two polymer solutions agree with the value predicted for a purely viscous power law fluid. The measured Nusselt values for the two polymer solutions were considerably higher than the corresponding values for a power law fluid and higher than the experimental values for water. It is postulated that these high heat-transfer values are the result of secondary flows which arise from normal stress differences imposed on the boundaries of viscoelastic fluids in laminar flow through noncicular geometries. In addition, it is hypothesized that under laminar flow conditions the low frequency oscillatory behavior determines the relative elasticity, which in turn influences the heat-transfer performance of such fluids.