# Heat Transfer Test 2 Heat Transfer Test 2 Notes and Quiz

Question Answer
____: resistance to heat transfer inside the object is negligible compared to resistance between the object and its surroundings. Therefore, the temperature is assumed to be spatially uniform in the object but still a function of time. Lumped Capacitance
___: a measure of how fast a system responds to changes in its surroundings. Time Constant (Tau)
The larger the time constant the more ____ an object responds to changes in its thermal environment. Slowly
___: is used to check the validity of the lumped capacitance method. Can be interpreted as a ratio of thermal resistances. Biot Number
A biot number less than .1 can occur for objects with (3): 1. a good conducting material. 2. small dimensions. 3. slow heating process.
Lumped capacitance is based on two major aspects: 1. assumption that temperature is uniform in the object under consideration. 2. application of the control volume energy balance to the object.
___: heat transfer into a solid which extends infinitely in all but one direction. This ideal case is approximated when the heat transfer domain is much larger than the region of interest. Semi-Infinite Solid
4 things that influence heat transfer: 1. geometry 2. fluid properties 3. flow speed and direction 4. surface roughness
___: region of fluid in which the temperature is influenced by the surface temperature with thickness delta t. Thermal Boundary Layer
___: at the surface the velocity is zero (no slip condition) and far away from the surface, freestream velocity is Uinfinity. The region of the flow affected by the surface is the _____ with thickness delta. Velocity Boundary Layer
___: relatively low shear stress and convection heat transfer. Characterized by a steady and ordered velocity field. Laminar
____; relatively high shear stress and convection heat transfer. Characterized by violent, apparently random, fluctuations. Turbulent
A developing boundary layer is always initially ____. The boundary layer will transition to ____ when the Reynold's number reaches a critical value. Laminar, Turbulent
___: internal heat generation due to fluid friction. Viscous Dissapation
The ___ number is a condition of flow details but the ___ number is a thermo physical property of the fluid. Reynolds, Prandtl
___: represents the enhancement of heat transfer through a fluid layer as a result of convection relative to conduction. Nusselt Number
____: represents heat transfer as a result of convection relative to advection. Stanton Number
___: expresses the idea that conditions producing high shear stress also produce high heat flux and vice versa. Reynold's Analogy
___: occurs when heat transfer from/to a surface at temp, Ts, to/from a fluid with a far away temp, Tinfinity, that remains unaffected by the surface. Velocity and thermal boundary layers can develop freely. External Convection
___: characterized by developing boundary layers with clearly identified free stream conditions (Tinfinity and Uinfinity) i.e. regions of flow unaffected by the surface. External Flow
___: for expressions for flow over a flat plate the fluid properties are typically evaluated at this temperature. Film Temperature
For a lumped capacitance analysis, the temperature is assumed to be ____ in the object, but it is still a function of time. Spatially Uniform
____ is used to check the validity of using lumped capacitance analysis. Biot Number
When approximating circumstances in which the heat transfer domain is much larger than the region of interest, the _____ model is employed. Semi-Infinite Solid
Name three surface boundary condition that are typically considered for the Semi-Infinite Solid model: constant surface temp, constant heat flux, and convection.
The region in which a fluid is affected by a nearby surface is called a/an ____. Boundary Layer
The dimensionless parameter that expresses the ratio of inertial forces to viscous forces is the ____. Reynold's Number
The enhancement of heat transfer through a fluid layer as a result of convection relative to conduction is represented by the dimensionless parameter called _____> Nusselt Number
The dimensionless quantity that describes the relative thickness of velocity and thermal boundary layers is ____. Prandtl Number
For turbulent flow, expressions for shear stress and heat transfer were found from ____. Experimental Data
The two contributors to drag force are: friction and pressure differential
For laminar flow over a flat plate, expressions for shear stress and heat transfer were found from ____. Exact (analytical) Solutions