Lab: Cool Science: Building and Testing a Model Radiator FOR THE TEACHER 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 High and middle school Submitted by Steve Sogo Laguna Beach High School Laguna Beach, CA Thanks to: 2016 AACT-Ford Content Writing Team NGSS 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. 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 American Association of Chemistry Teachers 1-262 1
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 6 inch Flexible plastic tubing (e.g. Tygon), ¼inch ID 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 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. American Association of Chemistry Teachers 1-262 2
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. o Video 1: shows an overview of the radiator set-up, with discussion of experimental variables. o 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. Intestine Design Helix Design 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. American Association of Chemistry Teachers 1-262 3
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 anticorrosion 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 on the next page. 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) Intestine (flattened) Yes 250 ml 5+ min 68.0 C 35.8 C -32.2 C 69% 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 American Association of Chemistry Teachers 1-262 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% American Association of Chemistry Teachers 1-262 5
FOR THE STUDENT Lesson Cool Science: Building and Testing a Model Radiator Background The combustion of gasoline creates a tremendous amount of heat in a car s engine. To prevent the engine from overheating, a coolant system circulates fluid that extracts heat from the engine. After absorbing heat from the engine, the hot fluid is passed through a radiator. Air flows over the radiator, cooling the fluid by transferring its heat to the atmosphere. The cooled fluid is then recirculated to extract more heat from the engine. In this project, you will construct a device that will model the working of a car s radiator. You will heat a reservoir of liquid using a microwave oven and then run the hot liquid through your model radiator. The effectiveness of your radiator will be determined by measuring the temperature (in C) and the heat content (in calories or joules) of the fluid as it enters and exits your radiator. Success will be calculated as the percent efficiency of your radiator, as shown below: CCCCCCCCCCCCCCCC/JJJJJJJJJJJJ oooo heeeeee rrrrrroooooooo ffffffff tthee ffffffffff PPPPPPPPPPPPPP eeeeeeeeeeeeeeeeeeee = 100 CCCCCCCCCCCCCCCC/JJJJJJJJJJJJ oooo heeeeee oooooooooooooooooooo aaaaaaaaaa tttt tthee ffffffffff Objective In this lab activity, you will experiment with a variety of radiator models to discover factors that are important in producing an effective heat-exchanging system. Materials 250 ml of fluid, which will either be tap water or a solution of 50% propylene glycol in water (dyed green). The density of the propylene glycol solution is 1.04 0.85 cccccccccccccccc 3.6 jjjjjjjjjjjj g/ml, and it has a specific heat capacity of OR gggggggg gggggggg Two 3-inch lengths of flexible plastic tubing (1/4-inch inner diameter) 5-feet of copper tubing (1/4-inch outer diameter) coiled into a particular shape (three or four different designs available) A 4-inch diameter funnel Wire twist ties A plastic pitcher in which the liquid will be heated in a microwave oven A plastic or glass container to capture the cooled liquid A ring stand with clamps to support the funnel and copper tubing A valve to control flow rate A fan Unlimited quantities of aluminum foil Scale Thermometer Safety Always wear safety goggles when handling chemicals in the lab. Wash your hands thoroughly before leaving the lab. Follow the teacher s instructions for cleanup of materials and disposal of chemicals. Propylene glycol solution should be recollected and stored for future use. American Association of Chemistry Teachers 1-262 6
Use care when pouring/transporting hot liquids. Liquids in this lab activity should not be heated above 75 C. Procedure: 1. Measure 250 ml of water into a beaker. Weigh the liquid if a scale is available. If no scale is available, calculate the mass of the water in your beaker using the density value of 1.00 grams per milliliter. 2. Measure the initial temperature of the water, record it below. 3. Microwave your beaker of water for 60-90 seconds to reach a final temperature of 65 to 75 C. 4. Remove the beaker from the microwave oven and stir to create a uniform temperature within the beaker. 5. Measure the temperature of the hot water after stirring. Record this temperature on the t = 0 line in the table below. 6. Allow the beaker to sit undisturbed while you take temperature measurements every 30 seconds. Record your temperature data in the table shown below: Data Time Temp Time Temp original 2 min 30 sec t = 0 3 min t = 30 sec 3 min 30 sec 1 min 4 min 1 min 30 sec 4 min 30 sec 2 min 5 min American Association of Chemistry Teachers 1-262 7
Graph the tabulated data using the axes shown below. Provide a title for the graph and label each axis appropriately. Graph Title: Make at least one comment that describes the data plotted in this graph. In other words, what is the message of this graph? American Association of Chemistry Teachers 1-262 8
Calculations A) Use the equation shown below to calculate the heat (calories or joules) added to the water by the microwave oven: Where QQ aa = mm CC TT aa Q a = heat (in calories or joules) added to the solution m = mass of water in the beaker C = specific heat of water ( 1.00 cccccccccccccccc gggggggg OR 4.18 jjjjjjjjjjjj gggggggg ) ΔT a = the change in the water s temperature (hot temp minus original temp) Note: your calculated quantity for heat added should be thousands of calories or joules, which may be more conveniently expressed as kilocalories or kilojoules. B) Use the equation below to calculate the heat lost from the beaker as it cooled for the 5-minute interval for which you recorded data in your data table. QQ rr = mm CC TT rr Where Q r = heat (in calories or joules) removed from the beaker (transferred to the atmosphere) m = mass of water in the beaker C = specific heat of water ( 1.00 cccccccccccccccc gggggggg OR 4.18 jjjjjjjjjjjj gggggggg ) ΔT r = Change in temperature during the 5-minute run c) Calculate the percent heat lost from the beaker during the 5-minute interval: PPPPPPPPPPPPPP heeeeee llllllll = 100 QQ rr QQ aa American Association of Chemistry Teachers 1-262 9
Explore/Create: Design your own radiator! After performing the initial scripted experimental work, you should have an understanding of the methods used to calculate heat added to the original liquid and removed through passive cooling. Your challenge is now to develop a system that will enable you to more effectively cool a fluid. In a car engine, the heat produced by the car s engine must be transferred to the atmosphere so that the car s engine does not overheat. To accomplish this, most cars have a coolant system that includes a radiator. If the coolant in a car overheats, the radiator may boil over, creating a hazardous situation and imperiling the workings of the engine. General guidelines 1. Follow the guidelines in the instructional video to link together a funnel, copper tubing, and a flow-control valve. Video URL on Youtube = https://youtu.be/cnsna5rqbq0. Note: if video instruction is not accessible, a text-based step-by-step guide is available! 2. Experiment with your set up by pouring room temperature water through the system look for leaks and measure the flow rate of fluid through your system. 3. You will run multiple cooling trials, investigating variables such as: a) the design of the copper tubing b) the flow rate of fluid through the radiator c) the use of plain water vs. a 50% solution of propylene glycol (dyed green) d) the presence or absence of a fan 4. You are encouraged to do internet research to discover how car radiators are constructed. This may give you some ideas for ways to improve the efficiency of your home-made radiator. 5. If you wish to use materials not on your standard-issue list, please consult your instructor. Constraints A. The official time for each experimental run is 5-minutes B. The volume of fluid passed through the radiator should be 250 Ml C. The fluid that you pass through your radiator may be water, or an aqueous solution of propylene glycol (colored green). If you use the propylene glycol solution, this solution must be recycled and NOT poured down the drain! D. The initial temperature of the hot liquid must be between 60 and 75 C. Data collection for the unscripted experiments A. You will be expected to produce a data table that summarizes important temperature data for each experiment that you run. This data table should also include calculated values for heat added, heat removed, and percent efficiency (i.e. percent heat loss). If your data table is well designed, it should American Association of Chemistry Teachers 1-262 10
be easy for the reader to determine which methods/strategies were most effective in cooling the fluid. B. You will also be expected to create a graphical representation of the effectiveness of your various trials. Consider using color in your graph as a way of illustrating the different variables you investigated. C. You are encouraged to create both the data table and graph(s) using a computer rather than writing by hand. Analysis 1. Discuss the factors that you feel led to more efficient radiator design. Try to provide scientific reasons why certain designs were more effective. It is expected that you will be able to discuss at least two important factors. For example, if you found that a fast flow rate was more effective at cooling the liquid, provide a scientific explanation for why a faster flow rate resulted in more heat removed. American Association of Chemistry Teachers 1-262 11
2. Discuss reasons why cars use a 50% solution of propylene glycol (or ethylene glycol) instead of plain water as coolant. Note: this discussion may rely on results from your experiments as well as internet research. Conclusion Provide suggestions for an optimal radiator design one that can remove a large percentage of heat in a short period of time. Discuss how a real car s radiator addresses these factors. American Association of Chemistry Teachers 1-262 12