Créer une présentation
Télécharger la présentation

Télécharger la présentation
## Melting Ice Cubes aka. Thermodynamics and Heat Transfer

- - - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - - -

**Melting Ice Cubesaka. Thermodynamics and Heat Transfer**HIGH ASPIRATIONS Created by: Dave Johnson Kathy Holliday-Darr**Miracle Thaw**• Is it really a miracle? • Let’s check it out…**Melting Ice Cubes: “Icebreaker” J**First experiment objective: Determine how fast each different test material melts an ice cube AND how the melting of the ice cube effects the test material’s temperature. • Establish teams and have them create a company name • Run first experiment**What is the room temperature?**• Measure and record the temperature of each material. • Measure the weight of the material being tested. • 5th grade: Convert the weight from pounds to kilograms • 6th grade: Calculate the mass of the material and compare it to the actual measurement. • High school: Compare methods for calculating mass and converting units. I.e., by hand, calculator, spreadsheet, draw 3-dimensionally on a CAD system and measure the properties, web (http://n93.cs.fiu.edu/measures/fulltable.asp), etc.**Calculate the area of the ice cube.**• Discuss: • What shape is the ice cube? • What is the formula for this shape? • What measurements will be needed? • How can the necessary measurements be found?**Calculate Area**• Trace ice cube • Measure chord length: c = • Measure height: h =**Calculate Area**• Discuss the best way to locate the following measurements: • Measure angle: α = • Measure the radius: r = • Calculate l**To Locate Center of Circle**• Rotate ice cube, overlapping the curved portion of the ice cube, and trace it again. • Fold the circle in quarters to locate center or use a compass.**Area answers.**• Give your results to your teacher. • Break into small groups and compare answers. • Come up with one answer per group. • Compare group answers. • Using the initial readings, calculate the average. • Compare the average to the group answers. • The teacher will use this answer to calculate the volume of the ice cube.**Place the ice cube, side down, on the material.**• Time from the placement to completely melted. • Students discuss: • Why is the ice cube melting? • What is happening? • How is it changing form? • Where does the heat come from?**Record:**• the finish time • temperature at the center of the puddle • outside edge of the plate • Share data with other groups.**Summary of First Experiment**• Where did the heat come from to melt each ice cube (from the test material or from the surrounding air) ? • What makes one test material faster at melting the ice cube than another ? • Why did the ice cubes move ? • Level of answers will depend on grade level.**Thermodynamics**• Greek words describe early forms of thermodynamics • Therme (heat) • Dynamics (power) • Today it covers a wider spectrum of energy and energy transformation • I.e., space shuttle to refrigeration**Thermodynamics**• Is the interaction between energy and matter and it is everywhere • Hair dryers and heat guns, irons, furnace, air conditioners, hot water tanks, etc. • Also must be considered when designing computers, automobile engines, VCRs, CD players, dimmer switches, etc. • What happens if • a hair dryer gets too hot? • a computer gets too hot?**5th Grade**• Calculate DT (Delta Time - change in temperature of the material being tested.) • (Tfinal - Tinitial) • Compare student DT results to calculated DT, supplied by the teacher, in a line graph on graph paper or using a spreadsheet. • Discuss the results**5th Grade con’t.**• Compare the amount of heat (Q) each material has available to the amount of heat required to melt the ice cube in a combination bar/line graph. (Data supplied by the teacher) • Which material(s) did not have enough heat available to melt the ice cube? • What can be done to increase the available heat? • Do you see any correlations between the two graphs?**Summary**• What test material was the best at melting ice cubes ? • Did the color seem to effect the performance ? • Why would an ice cube melt, even if the test material did not have enough energy to do it ?**Thermodynamics**• Therefore, different materials are used to the transfer heat • I.e., the material in the computer chip in the electric radio alarm clock is used to help keep the chip from overheating.**Miracle Thaw**• Is it really a miracle?**Suggestions for Higher Grades**• Complete 5th grade level mathematics, graphs, etc., only have the students calculate: • The volume and mass of the ice cube. • The amount of heat generated by each material. • How long a specific material will take to melt an ice cube. • Calculate the volume and mass of the material being tested, and compared to actual measured weight. • Discuss heat transfer in more depth.**Suggestions for Higher Gradescon’t.**• Create an interactive animated computer program that demonstrates the experiment. • Example: • http://socrates.berkeley.edu:7009/simple_machines/**Additional Exercises**• Compare the same material with different masses. • Compare different materials with the same mass. • Conduct a web search of items that use heat sinks. • Examples: • Library of Thermodynamics Arizona State Univ. • http://www.asu.edu/lib/noble/physics/thermo.htm • Heating system (heat pipe sinks) and fans • http://www.kita.or.kr/catalog/cheil/index.html • Laptops • http://www.indek.com/heatpipe/hp_app.htm • Computers • http://www.thermalloy.com/catalog/htm/dhs57.htm • http://www.web_tronics.com/webtronics/heatredmouns.html • http://www.heatsink.com/ • http://www.execpc.com/industrialelectronics/wakefld/wakepg19.html • http://www.marlow.com/d_heat.htm • Dimmer • http://home.swbell.net/evansjim/MyHomeRepair/DimmerSwitch.htm • http://www.thermalloy.com/catalog/htm/eprof41b.htm**THERMODYNAMICS**• The science of energy (or its ability to cause changes), and • The relationships among the properties of matter. • HEAT, Q, is the form of energy which melted our ice cubes. • In the SI system, we measure Q in Joules.**THERMODYNAMICS**Some important material properties: • m is the mass of the material (kg) • V is the volume (m3) • r is the density (kg/m3) • C is the specific heat (J/kg-oC)**THERMODYNAMICS**• For a solid, Q = m C DT • This is the amount of heat corresponding to a change in temperature • If you don’t know the mass, calculate it from: m = r V • DT is the change in temperature, (Tfinal - Tinitial)**How much heat does it take to melt one of our ice cubes ?**• If the ice cube is at 0oC, • “Latent Heat of Fusion” (amount of energy needed to go from solid to liquid states. • For water, that is 333,700 Joules/kg. • If our ice cube is 0.01 kg, the heat required is 3,337 Joules.**Do we have enough energy in our test materials to do that ?**Example: • A 0.5 kg. chunk of steel, starting at 22oC, releases 3255 Joules of heat when it is cooled to 7oC. • Q = m C DT = (0.5 kg)(434 Joules/kg-oC)(22-7 oC) = 3255 Joules • 3337 Joules is needed, therefore, there isn’t enough heat to melt the ice cube**Conservation of Energy**Better yet, we can solve for the final temperature of the steel to melt the ice:**Conservation of Energy**• A 0.5 kg block of steel • Cools from room temperature (22oC) to 6.62oC • Gives up enough heat to melt a 0.01 kg ice cube.**Heat Transfer**• is the flow of energy which happens when a difference in temperature exists. • can happen between two bodies or even within a single body. • What was the difference in temperature between our ice cubes and our test materials ?**CONDUCTION**• Heat flows through a material from molecule-to-molecule. • Fourier’s Law:**Fourier’s Law**• Q is the heat transfer rate • k is a material property, thermal conductivity • A is the area which heat flows through • DT is the temperature difference • Dx is the distance the heat must travel**Fourier’s Law**How do you make the ice cubes melt faster ? What do the terms in Fourier’s Law show us ? Which variables can you control ?**Fourier’s Law**• Fourier’s Law tells us how fast heat will flow. • Do we know if there is enough energy available in our test materials to melt our ice cube ?**Fourier’s Law**The rate of heat flow is: • The steel block cools from 22oC to 6.62oC in melting the ice which is 0oC. • As that happens, the value of DT decreases. • Therefore, the rate of heat transfer to the ice decreases. • How can we increase the rate for a given material ?**GO TO WORK !!!**• Determine: if your test materials have enough heat to melt an ice cube. • Measure the rate (time) of heat transfer. • Tabulate your experiment data.