Question

(2 pts) Heat is transferred from a hot fluid (temperature T1 and heat transfer coefficient h2) through a plane wall of thickness 8, surface area A and the thermal conductivity k. The thermal resistance for the set up is + (a) AC ) (b) A (i + + ) (c) 2 (na + + n2) (d) A (na + b +h2) (2 pts) An increase in convective heat transfer coefficient over a fin will (a) increase effectiveness (b) decrease effectiveness (c) does not influence effectiveness (d) influence only the efficiency (2 pts) Lumped analysis method can be used when (a) the thickness is small (b) when the conductivity is high (c) when the convective heat transfer coefficient is low (d) when conditions (a), (b), and (c) are true (2 pts) In the lumped analysis method, the temperature variation is (a) linear with time (b) sinusoidal with time (c) exponential with time (d) cubic with time (2 pts) Heat transfer rate will be (a) will be higher in the turbulent flow (b) will be lower in turbulent flow (c) will depend only on the fluid (d) will depend only on viscosity (2 pts) Reynolds number is (a) ratio of conduction to convection resistance (b) ratio of buoyancy to inertia forces (c) ratio of inertia forces to viscous forces (d) ratio of heat conducted to the heat capacity (2 pts) in laminar flow over a flat plate (a) the thermal boundary layer and hydrodynamic boundary layers are of equal thickness (b) the thermal boundary layer is thicker if the Prandtl number is greater than one (c) the thermal boundary layer is thicker if the Prandtl number is less than one (d) the thermal boundary layer is always thinner in the laminar region (2 pts) In laminar flow over a flat plate the convection coefficient is proportional to (a) x-0.5 (b) x0.5 (c) x-0.2 (d) x

Answer 1

hot fluid lle Heat is transferred from (temperature Ti and heat transfer coretticiens ha) through a plane wall of thickness s, surface area A and the thermal conductivity k. The thermal resistance for the set up 18 Ang + ( h + s + the) An increase in convective heat transfer co-efficient over a tin will AW! b decrease effectiveness. @ wmped analysis method can be used when Aus! - a (9 In the lumped analysis method, the temperature variation is exponential with time. Heat transter rate will be. AW! @ will be higher in the turbulent flow. 6 Reynolds number is AUS! Aus! - c ratio of inertia forces to viscous forces

O In Laminar How over a flat plate. Д-g", - с the thermal boundary layer 18 thicker it the prandt number 18 less than one. In Laminar flow over a flat plate the convection coefficient 18 proportional to AUS! 2 10.5