# Rate in the Thermal System. 1.What is the prime mover in the thermal system? - temperature difference 2. What does rate measure in the thermal system?

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Rate in the Thermal System

1.What is the prime mover in the thermal system? - temperature difference 2. What does rate measure in the thermal system? - heat flow 3. How does heat flow? - from areas of high temp to low temp

Rate in the Thermal System 4. Why does heat flow? - molecules with high temperature vibrates faster than molecules at lower temperature – more energy - when the molecules bump into one another, energy is transferred from the high energy molecule to the low energy molecule - this continues until all the molecules have equal energy levels

Rate in the Thermal System 5. How do we calculate heat flow? Heat Flow = Heat energy transferred Elapsed Time Q H = H t

Rate in the Thermal System 6. What are the units for heat flow? - there are not good, clear cut units for heat flow - any unit of heat / any unit of time - common units – J/s; cal/s; Btu/hr 7. What is a calorie? - amount of heat required to raise the temperature of one gram of water one degree Celsius; kilocalorie = 1000 cal

Rate in the Thermal System 8. What is a Btu? - British thermal unit - amount of heat required to raise the temperature of one pound of water one degree Fahrenheit

Rate in the Thermal System 9. What is specific heat? - every substance has a specific heat – it is a fixed amount - amount of heat required to raise one gram of a specific substance by one degree Celsius - used to determine the amount of heat required in changing the temperature of a substance

Rate in the Thermal System 10. What is the equation for calculating heat during a temperature change? H = (m)(c)(  T) H = amount of heat m = mass of sample c = specific heat of substance  T = Final temp – initial temp

Rate in the Thermal System 11. What is the specific heat of water? - 1 cal/gm-C o or 1 Btu/lb- o F 12. Example – How much heat is required to heat 417 pounds of water from 70 o F to 130 o F? - H = (m)(c)(  T) - H = (417 lbs)(1 Btu/lb- o F)(130-70) - H = (417)(1)(60) - H = 25,020 Btu

Rate in the Thermal System 13. Suppose you heat a piece of metal and place it in a cup of cold water. How does the heat flow? - heat will flow from the ball to the water - the amount of heat loss by the metal is equal to the amount of heat gained by the water

Rate in the Thermal System 14. An air conditioner is rated at 10,000 Btu. What does this mean? - it can remove heat at a rate of 10,000 Btu per hour

Rate in the Thermal System 15. Example – A 5000 Btu heater runs for 5 hours and 30 minutes. How much heat is moved? - Q H = H t - 5000 Btu/hr = H 5.5 hours - H = 27,500 Btu

Rate in the Thermal System 16. What is a change of state? - changing a substance from a solid to a liquid or a gas 17. What is sensible heat? - heat that is applied that changes the temperature of a substance

Rate in the Thermal System 18. What is latent heat? - heat that does not raise the temperature of a substance - the heat causes the substance to change state (from a solid to liquid)

Rate in the Thermal System 19. Example – A sample of ice at -10 o C is heated until it becomes steam at 110 o C. Classify the heat changes as latent or sensible. -10 o C ice to 0 o C ice  sensible 0 o C ice to 0 o C water  latent 0 o C water to 100 o C water  sensible 100 o C water to 100 o C steam  latent 100 o C steam to 110 o C steam  sensible

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