SummaryStudents learn the importance of heat transfer and heat conductance. Using hot plates, student groups measure the temperature change of a liquid over a set time period and use the gathered data to calculate the heat transfer that occurs. Then, as if they were engineers, students pool their results to discuss and determine the best fluid to use in a car radiator.
Heat is a concept that is used throughout most all engineering fields. It is particularly important for civil, mechanical and chemical engineers, for which heat transfer plays an important role in material selection, machinery efficiency and reaction kinetics, respectively. In this activity, students play the role of engineers by measuring and determining the best fluid for cooling a car's engine.
Students should be familiar with the concept of energy and the law of conservation of energy. Students should know how to use a thermometer.
After this activity, students should be able to:
- Explain the process of conduction as it relates to heating a liquid.
- Use their experimental findings to perform calculations.
- Explain why certain specific heat capacities are desirable in fluids used as heat exchangers.
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All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN),
a project of D2L (www.achievementstandards.org).
In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics;
within type by subtype, then by grade, etc.
Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.
All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).
In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.
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Each group needs:
- hot plate
- beaker (600–750 ml)
- (non-mercury) thermometer
- stopwatch or wrist watch
- Measuring Heat Transfer Worksheet, one per student
To share with the entire class: (liquid amounts depend on how many groups)
- 2 liters tap water
- 35 g (1 oz) sea salt
- 1 liter vegetable oil
- 1 liter corn syrup
- 1 liter maple syrup
- hot mitt or towel to handle hot glassware
Heat transfer is an important concept in both science and engineering. Who can describe for me a situation in which you felt extremely hot, maybe on a summer day or when playing sports? (Allow a few students to respond; avoid storytelling and sidetracking conversations.) During those times what were some ways that you cooled yourself? (Expected answers: Jumped in a swimming pool, drank a cold drink.) Good, so you already know the basics of heat transfer! For example, when you are hot, jumping in a pool cools your body because the water is cooler (less hot) than your body, and thus thermal energy moves from your body to the water.
In order to better understand heat transfer let's look at a way that we can calculate it mathematically. For conduction specifically, the equation for heat transfer is,
Q = m*C*ΔT,
where Q is heat, m is the mass of material, C is the specific heat capacity of the material, and ΔT is the change in temperature of the material (write the equation on the board).
Before we move any further, let's talk a little bit about specific heat capacity. We know that conductance is a material's ability to transfer heat throughout its body. For example, a good conductor transfers heat quickly throughout its body and a poor conductor transfers heat slowly throughout its body. Specific heat capacity is a measurement used to quantify how good a conductor a material is. Precisely, specific heat capacity is the amount of heat required to raise one unit mass of material one degree. For example, the specific heat capacity of fresh water is 4.19 kJ/kg-K, which means that it takes 4.19 kJ of heat to raise 1 kg of water 1 K.
It is important that engineers understand the specific heat capacity of the materials that they work with, especially if they are using them for applications in which heat is involved. Today we are going to look at five different fluids, all with different heat capacities, and calculate how much heat is added to the liquids over a 10-minute period. Once we generate the results, each one of you is going to be the engineer that chooses which fluid would work best in a car's radiator.
conduction: The transfer of heat by atomic movement due to direct contact from systems of high temperature to systems of low temperature.
heat : The transfer of thermal energy across systems or within a single system.
specific heat capacity: The amount of heat required to raise one unit mass of material one degree.
Determining the amount of heat transferred in each of the liquids helps students see that some liquids resist the transfer of heat more than others. This helps explain the concept of specific heat capacity and provide some experience for students to base their discussion on choosing which fluid to use in a car radiator.
- Determine the necessary number of stations to accommodate two to four students at each. Depending on the availability of hot plates and space, adjust how many students at each station.
- Gather materials and make copies of the Measuring Heat Transfer Worksheet, one per student.
Right Before the Activity
- At each station, place a hot plate, thermometer and beaker.
- Turn on the hot plates. The temperature of each hot plate should be between 150 ⁰C to 200 ⁰C. It is important that all the hot plates are close to the same temperature, because otherwise the resulting calculations are not comparable.
- (optional) Place a sign in front of each hot plate with the warning, "Hot!"
- Make the salt water by adding 35 g (1 oz) of sea salt to a liter of water.
- At each station, put 500 ml of one of the five liquids into a beaker. It is okay to have multiple stations with the same liquid. Indicate at the station which liquid is in the beaker (A, B, C, D or E).
- Make sure all liquids are at room temperature or cooler. If the activity is started with liquids that are already heated, the liquid may reach its boiling point, which is undesirable
- Draw a two-column table on the board with the headers, "Liquid" and "Heat Transferred (kJ)."
With the Students
- Hand out the worksheets and direct students to answer the first question pertaining to their thoughts about what type of fluid would work the best to be used in a radiator to cool a car's engine.
- Review and clarify all the activity procedures and safety instructions.
- Divide the class into groups of two to four students each.
- Direct the groups to take initial temperature readings, start their stopwatches, and place their beakers of liquid on the hot plate (as illustrated in Figure 1).
- Instruct student groups to stir the liquid gently every minute with the thermometer for 10 seconds and then take and record a temperature reading.
- For each temperature reading, have students rotate who takes the temperature measurement.
- After 10 minutes, have all groups take their final measurement and turn off the hot plate.
- Direct student groups to leave the beaker on the hot plate and go back to their seats to fill out the worksheet. The worksheet requires students to graph temperature vs. time, calculate the heat transferred into the liquid, and answer some questions about the activity. Note: The quantity of heat transfer over time should remain constant; therefore, the graphs of temperature vs. time should be close to linear for all the liquids. If students' graphs are not linear, potential causes are: not enough mixing, the hot plate temperature was changing, or the liquid reached its boiling point, which suggests the liquid may have been warmer than room temperature when the experiment began.
- Go around to all of the stations and use a hot mitt to remove beakers from the hot plates.
- Have a student from each group write its results in the table on the classroom board so the class can see all results.
- Lead a class discussion to share group results and conclusions, as described in the Assessment section. Which fluid is best for use in a radiator to cool a car engine? Reveal the identities of the five "unknown" liquids.
- Caution students to be careful not to spill or touch the beakers or liquids.
- The hot plates get very hot so warn students to be careful when working near them.
- Depending on school or classroom policy, have students wear safety goggles.
In case any group spills a beaker, have some extra of all of the liquids so that students can quickly restart the activity.
Have cleaning materials ready in case of any spills. Some of the oils and syrups are difficult to clean up without soap.
Hot plates pull a large amount of watts, so be careful not to overload your classroom circuits by putting too many hot plates on one circuit. A classroom designed for lab work should not have a problem with this, but be aware of this possibility.
Use the following question to lead into the lab and start the process of thinking about what type of liquid would work best in a radiator. What is the radiator on a car? And what is its purpose? (Answer: A car's radiator is located near the front of the engine compartment [hood] and is used along with a water pump to move coolant liquid through the engine block in order to cool the engine. As the engine heats up due to fuel combustion, heat is transferred through conduction to the coolant, which is circulated back to the radiator where it is cooled before being circulated back to the engine.)
Prediction: On the Measuring Heat Transfer Worksheet, have students answer the first question pertaining to their thoughts about what type of fluid would work best in a radiator to cool a car engine.
Activity Embedded Assessment
Group Check: Move about the room to each group and ask what types of heat transfer students think are taking place during this activity. (Answer: Mainly conduction, but some convection as well, as the fluid at the bottom on the beaker rises to the top. Some students may say radiation because of the lights in the room, but explain that while that is true, the amount of radiation energy compared to conduction and convection is negligible.)
Worksheet: Have students complete the Measuring Heat Transfer Activity Worksheet. If students are not able to complete all of the worksheet questions, assign the remainder as homework. Review their data, graphs and answers to gauge their comprehension of the material
Concluding Discussion: Upon completion of the experiment and worksheet, lead a class discussion to share results and conclusions.
- Which fluid do you consider to be the best for use in a radiator to cool a car engine? (After students share their conclusions and choices, reveal the identities of the five different "unknown" liquids.)
- Why does fresh water work the best of these five options? (Water works great in a radiator because of its high specific heat capacity, which means it has a high potential to adsorb heat from the engine.)
- Is the specific heat capacity of a fluid the only consideration? What other considerations might go into an engineer's decision on the best fluid to use? (While the specific heat capacity of a fluid is an important component in choosing a heat exchange fluid, it is not the only factor. Other requirements and/or factors must be taken into consideration, such as how well the liquid would flow in the engine, if the liquid would leave any residues, if we want the liquid to help prevent rust, or if freezing in cold weather would be an issue. For example, in cold climates the water in a radiator can freeze and ruin the radiator when the engine is not running. That is why a certain ratio of antifreeze is added even though it decreases the specific heat capacity of water.)
Explain to students that using water to cool a radiator is an example of the second law of thermodynamics. This law tells us that when two components of a system (water and the radiator) at different temperatures are combined, the result is a uniform energy distribution in the system. This energy can be measured as temperature. Ask students to brainstorm and design an experiment that uses the same materials as those in this activity to test this law. Allow students to work in their groups. After providing students time to develop a plan, allow each group to share ideas. One option is to heat the same volume of two different liquids on separate hot plates as they did in the previous experiment. After a few minutes, students should turn off the hot plates, remove each beaker of liquid from the hot plate and measure the temperature of each liquid. From the previous experiment, students should recognize these temperatures should not be equal. Then students carefully pour one liquid into the beaker with the other liquid, gently stir them together and take the temperature of the combined liquids. The resulting temperature should be between the temperature of the two liquids before mixed, and therefore represent the uniform distribution of energy in the system.
Have students actually conduct this second experiment. If any group has a different, yet safe and feasible, plan for an experiment, allow them to try their experiment. Make sure that all students are exercising caution while working with hot surfaces and/or liquids, and require that students write out all procedural steps for this new experiment and have the steps approved before conducting their experiment. If you use the recommended experiment option, you may choose to combine groups, so that there are a sufficient amount of materials, specifically hot plates and beakers.
For lower grades, have students measure the temperature in larger intervals and remove the graphing portion. Also simplify the worksheet questions.
Liquids and Fluids – Specific Heat. The Engineering ToolBox. Accessed December 7, 2012. (Source for specific heat capacities of the fluids.) http://www.engineeringtoolbox.com/specific-heat-fluids-d_151.html
Sonntag, Richard. E., Claus Borgnakke, and Gordan J. Van Wylen. Fundamentals of Thermodynamics. 7th edition. Hoboken, NJ: John Wiley & Sons, Inc., 2008.
ContributorsBradley Beless; Jeremy Ardner
Copyright© 2013 by Regents of the University of Colorado; original © 2012 University of Houston
Supporting ProgramNational Science Foundation GK-12 and Research Experience for Teachers (RET) Programs, University of Houston
This digital library content was developed by the University of Houston's College of Engineering under National Science Foundation GK-12 grant number DGE 0840889. However, these contents do not necessarily represent the policies of the NSF and you should not assume endorsement by the federal government.
Last modified: May 10, 2017