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FPE Midterm
| The state of a system refers to the _____ ______ of the system. | equilibrium condition |
| Define extensive properties. | Depend on the size of the system. eg. mass, length, volume, energy |
| Define intensive properties. | Do not depend on the size of the system. eg. temperature, pressure, density |
| T or F: Solid density accounts for pore spaces in food. | False |
| T or F: Temperature is a measure of our response to perceived hotness or coldness. | False |
| T or F: A closed system can exchange work or hear with its surroundings. | True |
| Define an adiabatic system. | Does not permit the exchange of heat with surroundings. |
| Define an isolated system. | Does not exchange heat, mass, or work with surroundings. |
| Define latent heat. | Heat required to change the physical state of materials. |
| Define sensible heat. | Heat which when added or subtracted from food changes the food's temperature. |
| T or F: Gases are considered a fluid in fluid flow processing. | True |
| What are the basic components of liquid transport systems? | Tanks, pipelines, pumps, and fittings. |
| Why are most pipes in food processing plants made of steel? | Smooth, easy to clean, resistance to corrosion. |
| Define cleaning in place. | Cleaning the inside surfaces of pips without disassembling the unit. |
| What are the two types of pumps? | Centrifugal pumps, positive displacement pumps. |
| How do centrifugal pumps work? | Centrifugal force is used to increase liquid pressure. |
| What are centrifugal pumps ideal for? | Low viscosity fluids, high flow rates, moderate pressure requirements, liquids with solid particles. |
| How is the flow rate controlled in a centrifugal pump? | valves |
| How to positive displacement pumps work? | Direct force is applied to the liquid to increase pressure and more liquid from one place to another. |
| T or F: Centrifugal pumps provide more precise control than positive displacement pumps. | False |
| T or F: Positive displacement pumps can be used for highly viscous liquids. | True |
| T or F: Rotary pumps can reverse flow direction. | True |
| Describe reciprocating pumps. | Delivers a pulsating discharge flow via a piston. |
| Viscosity and density of liquids influence _____ requirements and ____ characteristics. | power, flow |
| Define normal stress. | If the force is acting perpendicular to the surface. |
| Define shear stress. | If the force is acting parallel to the surface. |
| Define viscosity. | Measure of resistance force of a material to shear induced flow. |
| Define Newtonian fluid. | Shear stress is proportional to shear rate. |
| ____ viscosity is used to express the viscosity of non-food materials. | Kinematic |
| Define Reynolds number. | A ratio of inertial forces to viscous forces; gives an indication of flow behavior. |
| T or F: The velocity of a liquid is maximum at the surface of the pipe. | False |
| Flow characteristics are normally similar throughout the pipe except at the _____ region. | entrance |
| T or F: In the entry region of pipe, velocity depends on both radial and axial distances. | True |
| T or F: In a fully developed region of pipe, velocity depends on axial distance only. | False |
| Major frictional energy loss is due to flow of viscous fluid in _____ portions of the pipe. | straight |
| Define head loss for pumps. | Used to describe the energy of the fluid. |
| T or F: The suction head of a pump is the summation of all the energy from everything after pump. | False |
| How can the efficiency of a pump be described? | Fluid power/break power |
| T or F: The design flow rate describes operation at peak efficiency. | True |
| Define cavitation. | The formation of gas bubbles due to vaporization in a flowing liquid. |
| T or F: Pressure is lowest in the system at the eye of the pump. | True |
| What is the purpose of a pump? | To increase the energy of the liquid so that it can be moved from one location to another. |
| The intersection of a system curve and a pump performance curve is called the ________. | operating point |
| What are the three pressure in a flow measurement system? | Static pressure, stagnation pressure, dynamic pressure |
| What are the two steam generation systems used in the food industry? | Fire-tube, water-tube |
| Describe fire-tube steam generators. | Hot gases within tubes are surrounded by water. |
| Describe water-tube steam generators. | Water within tubes are surrounded by hot gases; larger capacity and higher pressure; greater flexibility. |
| Describe steam quality. | Extent to which phase change has progressed; number represents percentage of steam to water. |
| Describe specific heat. | The amount of heat required per kg of water to increase the temperature by 1 degree C. |
| What is the direction of heat transfer energy flow? | From higher temperature to lower temperatures. |
| Define steady state heat transfer. | Temperature changes with respect to location only; q is constant. |
| Define unsteady state heat transfer | Temperature changes with respect to location and time. |
| Define thermal conductivity. | Amount of heat which will be conducted per unit time through a unit thickness of material if a temperature gradient exists. |
| T or F: Ice has a higher thermal conductivity than water. | True |
| What are the two mechanisms of conduction? | Lattice molecular vibration, molecular collision. |
| Describe molecule vibration. | Molecules with high energy transfer energy to molecules with low energy. |
| Describe molecular collision. | Free electrons in metals move around and conduction is due to collision/diffusion of molecules in random motion. |
| In fluids, _____ is the predominate mode of heat transfer. | convection |
| T or F: h, the convective heat transfer coefficient, is a property of the solid material. | False |
| T or F: Free convection has a larger h value than forced convection. | False |
| Describe radiation. | Heat transfer by emission and absorption of electromagnetic waves. |
| Most gases are _____ to radiation whereas solids are _____ to radiation. | transparent, opaque |
| Define the Nusselt number. | Enhancement of rate of heat transfer caused by convection over conduction mode. |
| Define the Prandtl number. | Describes the thickness of hydrodynamic boundary layer compared to the thermal boundary layer; ratio of molecular diffusivity of momemtum to heat. |
| Define the Grashof number. | Ratio between buoyancy forces and viscous forces; determines if laminar or turbulent. |
| The Reyleigh number is a product of the _____ number and ______ number. | Grashof, Prandtl |
| Define the surface heat transfer coefficient, h. | The resistance of a hypothetical surface film of the cooling medium. |
| T or F: Fouling increases the resistance to heat transfer. | True |
| Describe fouling. | When liquid food comes into contact with a heated surface. |
| Define natural convection. | Occurs when a fluid is in contact with a surface hotter or colder than itself; eg. food in a freezer. |
| Define forced convection. | Fluid is forced past a solid body and heat is transferred; fluid is constantly replaced; rate of heat transfer is higher. |
| T or F: Plate heat exchangers are useful for high viscosity foods. | False |
| Plate heat exchangers can be difficult due to _____. | fouling |
| T or F: The heat capacity of a heat exchanger can be increased by adding more plates. | True |
| Describe regeneration. | A heated fluid transfers part of its heat to incoming raw fluid; less energy needed. |
| A _____ heat exchanger is used in evaporation of liquid foods. | tubular |
| Define number of transfer units. | A measure of heat transfer surface area for a given heat transfer coefficient and minimum heat capacity. |
| _____ convection is used in a plate heat exchanger. | Forced |
| Define fluid power. | Power output from the pump. |
| Define break power. | Power required to drive the pump. |
| T or F: In fluids, convection is the predominate form of heat transfer. | True |
| T or F: All objects above absolute zero temperature emit thermal radiation. | True |
| A plate heat exchanger consists of a ______ section and a _____ section. | heating,regeneration |
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