Summary

In this lab students construct a model of a car radiator to investigate parameters that lead to efficient cooling. Students investigate multiple variables as they experiment with various radiator designs. This lesson focuses on thermochemistry calculations and engineering practices.

Grade Level

Middle and high school

NGSS Alignment

This lab will help prepare your students to meet the performance expectations in the following standards:

• HS-PS3-1: Create a computational model to calculate the change in the energy of one component in a system when the change in energy of the other component(s) and energy flows in and out of the system are known.
• HS-PS3-4: Plan and conduct an investigation to provide evidence that the transfer of thermal energy when two components of different temperature are combined within a closed system results in a more uniform energy distribution among the components in the system (second law of thermodynamics).
• HS-PS3-2: Energy cannot be created or destroyed—only moves between one place and another place, between objects and/or fields, or between systems.
• HS-ETS1-2: Design a solution to a complex real-world problem by breaking it down into smaller, more manageable problems that can be solved through engineering.
• HS-ETS1-4: Systems and System Models:Models (e.g., physical, mathematical, computer models) can be used to simulate systems and interactions—including energy, matter, and information flows— within and between systems at different scales.
• Scientific and Engineering Practices:
  • Using Mathematics and Computational Thinking
  • Analyzing and Interpreting Data
  • Planning and Carrying Out Investigations
  • Constructing Explanations and Designing Solutions

AP Chemistry Curriculum Framework

This lab supports the following unit, topic, and learning objective:

• Unit 6: Thermochemistry
  • Topic 6.4: Heat Capacity and Calorimetry
    • 6.4.A: Calculate the heat q absorbed or released by a system undergoing heating/ cooling based on the amount of the substance, the heat capacity, and the change in temperature.

Objectives

By the end of this lab, students should be able to

• Calculate calories/joules of heat absorbed by/lost from a liquid of known specific heat.
• Delineate factors that improve the efficiency of a heat exchanging device.
• Create a graph of temperature vs. time (a cooling curve) and interpret its meaning.
• Design controlled experiments that accurately determine the effect of a particular variable.

Chemistry Topics

This lab supports students’ understanding of

• Thermodynamic calculations
• Specific heat values
• Engineering design
• Molecular kinetic energy

Time

Teacher Preparation
2 hours for initial preparation of materials. After the initial constructions/purchases have been made, 30-40 minutes of set-up time required.

Lesson

• Engage: 10 minutes
• Explore: 50 - 100 minutes
• Explain: 20 - 30 minutes
• Elaborate: 20 minutes
• Evaluate: 20 - 60 minutes

Materials

For each lab group

• 5-feet of ¼inch copper tubing (sold at hardware stores such as Home Depot)
• One plastic funnel: 4 inch diameter with ¼ inch diameter stem
• One clamp or stopcock valve
• One ring stand (at least 24 inch tall, 36 inch recommended)
• Wire for twist ties
• One plastic pitcher or beaker (500 or 1000 mL recommended)
• 250 mL of 50% Propylene glycol solution (or ethylene glycol solution) dyed green using food coloring
• A plastic or glass container to capture the cooled liquid
• A fan
• Unlimited quantities of aluminum foil
• Scale
• Thermometer

Safety

• Always wear safety goggles when handling chemicals in the lab.
• Students should wash their hands thoroughly before leaving the lab.
• When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals.
• Ethylene glycol can be highly toxic for sensitive individuals. Propylene glycol is a safer alternative.
• Students will heat water to scalding temperatures. Caution will be required when pouring and transporting hot liquids.

Teacher Notes

• This resource could be used as a post-AP Chemistry exam activity.
• Engage: Use this video that investigates the cooling system of a car. It introduces the need for removal of engine heat and discusses mechanisms used in a car engine to exchange heat with the environment. Chemical components of automotive coolant solutions are also discussed.
• Explore: The heart of this activity is the experimentation that students do with various radiator designs. Students should perform at least three trials using variations in design/materials. Each trial will take about 15 minutes to perform, including set-up and collection of data. The teacher should encourage students to discuss which variables they would like to test and how the experiment can be designed to focus on a single variable in each trial. Variables include the use of water vs. a propylene glycol solution, the rate of fluid flow through the model radiator, the use of a fan, and a variety of copper tubing designs (helix vs. coil vs. boustrophedonic (intestine) designs).
• Explain: After performing several trials, students will calculate the efficiency of each design and develop scientific explanations for why some designs were more effective.
• Elaborate: Ideally, students will be able to generalize from their specific results to discover general truths. Students should be encouraged to look at radiators in real cars to see whether the general truths they propose are borne out in professional radiator designs.
• Evaluate: This activity is structured so that students will produce a written report of their findings, including graphs, calculations, and answers to analysis questions. It is possible that the teacher will want students to explain their findings to their classmates using posters or presentations.
• Preparation of materials: Two videos are available to help construct the model radiators used in this lab activity. A class set of copper tubing modules can be created in about 1-hour.
  • Video 1: shows an overview of the radiator set-up, with discussion of experimental variables.
  • Video 2: provides details for the instructor on how to bend the copper tubing and how to install a plastic syringe to allow easy connection of a stopcock valve.
• This project uses 5-foot lengths of copper tubing bent into various shapes as shown below. A 50-foot roll of ¼ inch copper tubing at Home Depot will cost around $40.

• The images above, from left to right, represent the intestine design, the helix design and the spiral design.
• The copper tubing acts as a heat exchanger. The conductivity of the copper helps to disperse the heat of the water into the atmosphere.

• At the top of the radiator module, the copper tubing is connected to a 4 inch funnel using a short segment of ¼ inch Tygon tubing. The copper-Tygon junction should be secured with a twist tie made of wire. A 4 inch funnel has a capacity of 250 ml.

• At the bottom of the copper tubing module, a 1-mL plastic syringe can be cut and inserted into a segment of Tygon to allow for easy connection of a stopcock. Alternatively, a Hoffman style clamp can be used to control the flow rate.

• A tall ring stand is used to support the design. The funnel should be supported using a 3” ring clamp. An additional clamp should be used to support most of the weight of the copper tubing.
• I recommend creating a solution of 50% propylene glycol using stock propylene glycol from Flinn Scientific. This solution can then be dyed green using normal food coloring. It is possible to use commercial antifreeze solutions in place of a home-made solution, but the commercial products will contain an anti-corrosion molecule (tolyltriazole) that has an unpleasant, fishy odor (when heated). Using pure propylene glycol (or ethylene glycol) allows for an odor-free experiment. If a commercially available antifreeze is chosen, Sierra brand is propylene glycol based. Other commercial antifreeze solutions are likely to utilize ethylene glycol.
• Sample data collected by the author using various designs is shown below.
• This video shows students collecting and analyzing data from their radiator trials.
  
  
• Teacher-collected data from radiator design tests:
  Feb 16 (Ambient temp = 23°C) and Feb 17, 2016 (Ambient temperature = 21°C)

Date	Module	Fan?	Volume of water	Flow through time	Initial temp	Final temp (after 5 min)	ΔT	% Cooling Efficiency
2/16	Helix	No	300 mL	3 min	68.6°C	53.0°C	-15.6°C	34%
	Helix	Yes	250 mL	4 min	68.0°C	41.4°C	-26.6°C	59%
	Spiral	Yes	250 mL	?	70.0°C	41.4°C	-28.6°C	61%
2/17	Intestine (flattened)	Yes	250 mL	5+ min	68.0°C	35.8°C	-32.2°C	69%
	Intestine (flattened)	Yes	250 mL	4:30	68.7°C	37.0°C	-31.7°C	66%

Passive Cooling of Water without use of a heat exchanger: Feb 16 data

Time	Temp °C	Notes
0	70.1
30 sec	69.4
60 sec	68.3	Stirred prior to temp reading
90 sec	67.7
120 sec	66.6	Stirred prior to temp reading
150 sec	66.0
180 sec	65.0	Stirred prior to temp reading
210 sec	64.4
240 sec	63.4	Stirred prior to temp reading
270 sec	63.0
300 sec	62.0	Stirred prior to temp reading
Passive Cooling Efficiency = 17%