EGR2500 Lab2 W24 (1)

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Apr 3, 2024

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INTRODUCTION TO THERMAL ENGINEERING EGR 2500 Winter 2024 Laboratory Assignment #2 Measuring the Energy Content of Food The purpose of this laboratory exercise is to apply the First Law of Thermodynamics to determine the energy content (i.e. food calories) of some simple foods. Lab Procedure 1. Carefully read the operating instructions for the Parr Instruments® model 1341 Oxygen Bomb Calorimeter. Ensure that every group member has thoroughly read the instructions. Discuss the details of the experiment so that you are properly prepared before attempting to conduct the experiment, as you will be given only one food sample. Prepare a data sheet for recording the water-bath temperature rise, as discussed in the operating instructions. 2. Sign-out a food sample from the lab. You should do this just prior to conducting the experiment. Do not open your sample capsule. The capsule and contents have been weighed to the closest 0.1mg. Moisture will damage the gelatin capsule. 3. Prepare the oxygen bomb, using your food sample, and burn the sample within the bomb calorimeter. Record the water-bath temperature as detailed in the handout. If you have any questions about operating the calorimeter, please ask before you attempt the experiment. Report Analysis 1. Plot the water-bath temperature as a function of time, and determine the actual temperature rise. 2. Develop a First Law model of the system that is composed of the water-bath, bomb, fuse wire and food sample. Use your model and the measured temperature rise, to estimate the energy value, e fs , of your food sample 1 in cal/g and “food calories”/g. Note that one ‘food calorie’ is equal to one kilocalorie. 3. Perform an uncertainty analysis on your calculation of e fs , and specify the magnitude of the uncertainty for your experiment. You will need to research, list and reference the uncertainty of the digital thermometer used for temperature measurements. 4. Your sample consists of one of the following:  Domino Premium Sugar Cane Granulated  Honey Maid Graham Crackers  Kirkland organic whole cashews unsalted unroasted  Lay’s Baked Potato Chips Original 1 The derivation in the combustion bomb instruction sheet does not consider a gelatin capsule. You must modify the derivation to account for the capsule by decomposing the total “energy release” from the test sample into 2 terms: one accounting for the food sample itself and the other for the gelatin capsule. The heat of combustion of the gelatin capsule is E equiv/gc and is listed in the preliminary calculations section of the handout.

 Research the calorie information for these foods and tabulate in your report (include # food calories (kcal), serving size (g) and energy value per unit mass (kcal/g)). Clearly indicate and cite your sources of information and comment on the reliability of these sources . Which sample would you guess that you measured? Justify your answer. 5. Research and summarize other uses of a bomb calorimeter, as well as approved methods set by the Food and Drug Administration (FDA) of determining the caloric content listed in nutritional labels of packaged food items. Clearly indicate and cite your sources of information and comment on the reliability of these sources . This summary must be written in your own words and must cite the references according to the guidelines specified in the lab report guidelines document. Laboratory Report Contents: Your lab report should include the following:  Title page with abstract  Theory section which includes the derivation of the equation for the energy value e fs of the food sample (theory section from lab report modified to account for gelatin capsule), the derivation of the uncertainty equation for e fs , as well as any other relevant equations.  Results and Discussion section which should include:  Data table(s) that include your collected and calculated data (time, temperature, masses, fuse length, slopes in pre- and post-periods, temperature rise, etc.)  Graph of temperature versus time  Typed equations used to determine the energy value of your food sample and its uncertainty.  Data table listing caloric information for the possible food samples (make sure you cite sources of information).  Discussion of results: Make sure you discuss the results and indicate what food sample you tested based on your results.  Summary of findings from information search (uses of bomb calorimeters; approved ways set by the Food and Drug Administration (FDA) of determining the caloric content listed in nutritional labels of packaged food items; make sure you cite sources of information)  References (remember to cite these references in your report)  Appendix (Lab handout, original data sheet and sample calculations) pg. 2

OPERATING INSTRUCTIONS For the Parr 1341 Oxygen Bomb Calorimeter These instructions cover the steps to be taken in setting up and operating a Parr 1341 Plain Oxygen Bomb Calorimeter. They are extracted from the manufacturer’s complete manuals, which are available upon request. The user should study these instructions carefully before starting to use the calorimeter so that he/she will fully understand the capabilities of the equipment, and so that he/she will be well aware of the safety precautions to be observed in its operation. OPERATING THE CALORIMETER Place the jacket on a sturdy bench or table in a location that is reasonably free from drafts and is protected from sources of radiant heat, preferably in an air-conditioned room. Temperature changes in the room should be minimal. There should be convenient access to running water, to a drain and to an appropriate grounded electrical outlet. About 8 square feet of workspace will be required. The lab assistant will provide already-weighed test samples. A balance capable of weighing up to 2.0 kg with 0.1 g sensitivity, and a tank of oxygen are available in the lab. All operations required to test an unknown sample or to standardize the 1341 plain calorimeter should proceed step-wise in the following manner: 1. Prepare the sample and charge the oxygen bomb. Precautions. Combustion with oxygen in a sealed bomb is a very effective and reliable method for releasing all heat energy obtainable from a sample and for preparing hydrocarbon compounds and carbonaceous materials for analysis, but there are certain precautions, which must always be observed when using this equipment. In particular:  Do not overcharge the bomb with too much sample or with a sample, which might react with explosive violence.  Do not overcharge the bomb with too much oxygen. The initial charging pressure should not exceed 40 atm (590 psig). About 30 atm is recommended here.  Do not fire the bomb alone on an open bench without providing a protective cooling medium. Usually the bomb should be completely submerged in water during firing.  Do not fire the bomb if gas bubbles are released from any point on the bomb when it is submerged in water.  Do not ignite a volatile sample without using one of the sealed sample holders (which would be provided).  Stand away from the bomb during firing and do not handle the bomb for at least 1 minute after firing.  Keep the bomb in good condition at all times. Any parts that show signs of weakness or deterioration must be replaced promptly. Allowable Sample Size. To stay within safe limits, the bomb should never be charged with a sample, which will release more than 8000 calories when burned in oxygen, and the initial oxygen pressure should never exceed 40 atmospheres (590 psig.). To avoid damage to the bomb and possible injury to the operator, it should be a standing rule in each laboratory that the bomb must never be charged with more than 1 of the samples provided (approx 1 g) of material. Attaching the Fuse. Set the bomb head on the A38A support stand and fasten a 10 cm length of fuse wire between the two electrodes. Parr 45C10 nickel alloy wire, used for most tests, is furnished on cards from which uniform 10 cm lengths can be cut. To attach the fuse to quick-grip electrodes, insert the ends of the wire into the eyelet at the end of each stem and push the cap downward to pinch the wire into place. No further threading or twisting is required. Place the fuel capsule with its weighed sample in the electrode loop and bend the wire downward toward the surface of the charge. It is not necessary to submerge the wire in a powdered sample. In fact, better combustion will usually be obtained if the loop of the fuse is set slightly above the surface. When using pelleted samples, bend the wire so that the loop bears against the top of the pellet firmly enough to keep it from sliding against the side of the capsule. It is also good practice to tilt the capsule slightly to one side so that the flame emerging from it will not impinge directly on the tip of the straight electrode. pg. 3

Liquids in the Bomb. Most bomb combustion procedures call for a small amount of liquid to be placed in the bottom of the bomb as a sequestering agent and absorbent. If the amount and type of liquid are not otherwise specified, add 1.0 mL of distilled or deionized water from a pipet Closing the Bomb. Care must be taken not to disturb the sample when moving the bomb head from the support stand to the bomb cylinder. Check the sealing ring to be sure that it is in good condition and moisten it with a bit of water so that it will slide freely into the cylinder; then slide the head into the cylinder and push it down as far as it will go. For easy insertion, push the head straight down without twisting and leave the gas release valve open during this operation. Set the screw cap on the cylinder and turn it down firmly by hand to a solid stop. When properly closed, no threads on the cylinder should be exposed. If the screw cap tends to bind to the cylinder at this point, indicating that it might be difficult to open the bomb after it has been fired, turn the screw cap back slightly - but only a few degrees - enough to release the binding, since the bottom thread must remain fully engaged. It is not necessary to use a wrench or spanner on the screw cap. Hand tightening should be sufficient to secure a tight seal. Filling the Bomb. The pressure connection to the bomb is made with a slip connector on the oxygen hose, which slides over the gas inlet fitting on the bomb head. Slide the connector onto the inlet valve body and push it down as far as it will go. If it does not slide easily, a drop of water spread around the inlet valve will lubricate the sealing rings. Close the outlet valve on the bomb head; then open or "crack" the oxygen tank valve not more than one-quarter turn. Open the filling connection control valve slowly and watch the gage as the bomb pressure rises to the desired filling pressure (usually 27 atm., but never more than 40 atm.); then close the control valve. The bomb inlet check valve will close automatically when the oxygen supply is shut off, leaving the bomb filled to the highest pressure indicated on the 0-55 atm. gage. Release the residual pressure in the filling hose by pushing downward on the lever attached to the relief valve. The gage should now return to zero. If the pressure drops slowly and a large amount of gas escapes when the pressure relief valve is opened, the check valve in the bomb head is not operating properly. This trouble will have to be corrected before the bomb can be used. If too much oxygen should accidentally be introduced into the bomb, do not proceed with the combustion. Detach the filling connection; exhaust the bomb; remove the head and reweigh the sample before repeating the filling operation. 2. Fill the calorimeter bucket by first taring the dry bucket on a solution or trip balance; then add 2000 (+/-0.5) grams of water. The water temperature should be approximately 1.5° C below room temperature, but not less than about 19.2 °C. 3. Set the bucket in the calorimeter, noting the three dimples in the bottom of the bucket, which rest on supporting pins in the bottom of the jacket. The single dimple must always face forward when setting the bucket in the jacket. Attach the lifting handle to the two holes in the side of the screw cap and lower the bomb into the water with its feet spanning the circular boss in the bottom of the bucket . Handle the bomb carefully during this operation so that the sample will not be disturbed. Remove the handle and shake any drops of water back into the bucket; then push the two ignition lead wires into the terminal sockets on the bomb head, being careful not to remove any water from the bucket with the fingers. 4. Connect the ignition unit. The Parr 2901 Ignition Unit operates from any standard electrical outlet to provide the proper low voltage firing current, providing also a convenient push switch, indicating lamp and connecting terminals. Connect the two lead wires from the calorimeter jacket, one to the "l0 CM" terminal and the other to the “common” terminal on the ignition unit; then plug the power cord into any appropriate grounded electrical outlet. After the unit has been plugged into an outlet do not press the firing button unless the lead wires inside the jacket are connected to a bomb. If the bare terminals on these wires happen to be in contact with each other or with a metal object when the circuit is closed, the resulting short-circuit may cause serious damage to the ignition system. 5. Set the cover on the jacket with the thermometer facing toward the front. Turn the stirrer by hand to be sure that it runs freely; then slip the drive belt onto the pulleys and start the motor. 6. Let the stirrer run for 5 minutes to reach equilibrium before starting a measured run. At the end of this period record the time or start a timer and read the temperature. 7. Read and record temperatures at one-minute intervals for 6 minutes. Then, at the start of the 6th minute... 8. Stand back from the calorimeter and fire the bomb by pressing the ignition button and holding it down until the indicator light goes out. Normally the light will glow for only about 1/2 second but release the button within 5 seconds pg. 4

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