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Heat Transfer Test 1
Heat Transfer Test 1 Notes and Quiz
| Question | Answer |
|---|---|
| _____ : thermal energy in transit due to a spatial temperature difference. | Heat Transfer |
| ____: quantity of matter to be studied | System |
| ____: certain amount of matter is the area of interest, energy is transferred across the control surface by work and heat at the system boundary. | Closed System (Control Mass) |
| ____: certain volume is the area of interest, energy is transferred across the control surface by work, heat, and mass crossing control surface. | Open System (Control Volume) |
| _____: thermal energy that is converted from another form of energy not included in the analysis. Rate at which energy is generated per unit volume. | Heat Generation (qdot) |
| ___: has no volume or mass. Properties of the mass entering the ___ are identical to the properties of the mass exiting ___. Energy cannot be stored or generated in the ___. | Control Surface |
| ___: heat transfer rate per unit area. The area in _____ _____ is the area that is perpendicular to the direction that heat transfer is occurring. | Heat Flux (q") |
| ____: heat transfer due to molecular motion, energy is transferred from more energetic particles to adjacent less energetic particles. Occurs in solids and fluids. Transfer of energy in a medium do to a temperature gradient. | Conduction |
| ____: heat transfer due to a combination of conduction and advection (heat transfer due to bulk fluid motion). Heat transfer occurs between a solid surface and a moving fluid. | Convection |
| ____: heat transfer emitted by matter in the form of electromagnetic waves (or photons). Does not require a medium to transfer heat (can occur in a vacuum). | Radiation |
| Fourier's Law was developed from experiments and defines ____ _____. | Thermal Conductivity |
| ____: material property that indicates the rate at which energy is transferred by diffusion or a measure of the material's ability to conduct heat. | Thermal Conductivity (k) |
| ____: measures the ability of a material to store thermal energy. | Heat Capacity (Rho*Cp) |
| ____: ratio of thermal conductivity to heat capacity. Measures the material's ability to conduct heat to its ability to store heat. Used in transient (unsteady) analysis. | Thermal Diffusivity (alpha) |
| The purpose of the heat conduction equation is to determine the ___ _____ in a medium. | Temperature Distribution |
| _____; refers to temperature only varying in one spatial direction and heat is transferred in that direction. | 1-D |
| ____: temperature remains constant in time at every location. | Steady State |
| ___: heat transfer area (area normal to heat transfer) remains constant in the direction of heat transfer. | Planar |
| Temperature varies _____ with x when 1-D, steady state, conduction in a plane wall with no heat generation and constant properties. | Linearly |
| high thermal conductivity (k) = ___ conductor low thermal conductivity (k) = _____ conductor | Good Poor |
| Small thermal diffusivity (alpha) means that heat is mostly ____ by the material. | Absorbed |
| _____: defined as the ratio of driving potential to corresponding transfer rate. The analogy to circuits can only be used for 1-D heat transfer with no internal heat generation and constant properties. | Thermal Resistance (R) |
| Each distinct thermal pathway may be represented as thermal resistances in _____. | Parallel |
| Resistances in ____ represent the different layers through which heat passes within a given pathway. | Series |
| Conduction Resistance is only for cases that are: ___ ___ and ____. | 1-D, Steady State,and Constant Properties. |
| _____: we conceptualize a "convective layer" that is included as an extra resistance on either side of the wall. This accounts for the heat transfer to/from a solid surface from/to the fluid. | Convective Resistance |
| ____: two solid conduction layers do not make perfect contact due to surface roughness which acts as an additional resistance to heat transfer. | Contact Resistance (Rtc) |
| Surface roughness creates a temperature ____ at interface. | Drop |
| To decrease contact resistance, the aim is to decrease gaps or gap sizes by (5 methods): | 1. use a soft metallic insert. 2. decrease surface roughness of material. 3. increase interface pressure. 4. use thermal grease. 5. replace air between surface with a more conductive gas. |
| ____: when heat transfer occurs by conduction in one (primary) direction and simultaneously by convection in a perpendicular direction. | Extended Surface |
| ___: when an extended surface is attached to a solid body in order to enhance heat transfer between the solid body and the surrounding fluid. Increases heat transfer by increasing surface area. | Fin |
| Heat transfer rate by convection can be increased in 3 ways: | 1. increase h by increasing the fluid velocity. 2. decreasing the fluid temperature, Tinfinity. 3. increasing the surface area, As, where convection occurs. (fins use this method) |
| ____: the ratio of fin heat transfer rate to the heat transfer rate that would exist without the fin. | Fin Effectiveness (epsilon) |
| ____: the ratio of fin heat transfer rate to the heat transfer rate that would exist if the fin surface temperature was Tb over the entire surface. | Fin Efficiency (eta) |
| The heat transfer from the non-finned portion of the surface must also be considered as an additional resistance in ____, where the area is reduced by the total base area of the fins. | Parallel |
| Conduction is governed by ____ . | Fourier's Law |
| Convection is governed by ____ . | Newton's Law of Cooling |
| Radiation is governed by ____. | Stefan-Boltzman Law of Radiation |
| Explain why using the thermal resistance analogy cannot be used when there is internal (volumetric) heat generation. | Heat transfer rate is not constant. |
| ___ conduction occurs when area is a function of position. | Non-Planar |
Created by:
jrr409