Quires

Ram

Hello

I have following simple quires which i suppose the experts in here can answer

1. Flow Work is defined as: work done by each unit mass of flowing fluid on the Control Volume, or by control volume, as it flows across the control surface. In general, the flow work done by a unit mass is equal to the product of normal fluid stress and fluid specific volume, both evaluated at the control surface. If velocity gradients are NOT LARGE, the normal stress is essentially the simple thermodynamic pressure. QUESTION IS: how large is NOT LARGE above? Can one quantify it? What is the limit of velocity gradients where we can take normal stress to be equal to thermodynamic pressure? 2. We know heat flux equals product of heat transfer coefficient and temperature potential difference. It is well known that temperature potential difference is a thermodynamic property and heat transfer coefficient is a fluid – mechanic property. QUESTION IS: to what property can we assign heat flux? Is it a property at all? (After all we are multiplying two properties!!!) By the way, can we multiply two unrelated properties as above ( I mean Thermodynamic and fluid mechanic )

Thank you in advance

Ram