Engineering White Paper
Coldwave Performance Verification Using Rapid Prototype Rev-2
David M. Dussault August 1, 2012
IceColdNow Inc. Confidential & Proprietary Information
Table of Contents 1 Introduction........................................................................................................................................ 2 2 Test Setup and Procedure.................................................................................................................2 3 Results............................................................................................................................................... 3 4 Discussion......................................................................................................................................... 4 5 Conclusion......................................................................................................................................... 4 6 References........................................................................................................................................ 5 7 Appendix............................................................................................................................................ 6 7.1 CAD Renderings........................................................................................................................ 6 7.2 Supplemental Plots.................................................................................................................... 6
1 Introduction A rapid prototype of the Coldwave was tested in study [1]. Since that time, a number of refinements have been made to the design, including centering, standoff, and alignment features as well as an overall taller aspect ratio. A new rapid prototype was built. The objective of this study is to test the new rapid prototype.
2 Test Setup and Procedure Figure 1 shows the major test components, including the rapid prototype, a measuring cup, a stop watch, and a thermometer. The Coldwave shown has the natural rapid prototype color and a nondesign wooden knob for the purposes of prototype assembly. A CAD rendering is provided in the Appendix, showing the design knob and color scheme. Water was used as the test beverage. A number of test runs were made, varying the cooling time from 1 to 2 minutes, with a constant starting temperature of 200 F. Although the time for a full recharge is 4-6 hours, the Coldwave was stored in the freezer for 24 hours between test runs as a matter of working convenience and as a factor of safety.
Figure 1. Test components.
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The test procedure was as follows: – – – – – – –
boil water measure 11 oz of hot water ensure starting temperature is 200 F pour hot water into Coldwave wait for specified test duration (1.0, 1.5, or 2.0 minutes) pour cold water out of Coldwave measure final temperature and volume of water
The starting volume was conservatively set to 11 oz rather than the spec value of 12 oz as a factor of safety considering the possibility of an incomplete manual ice-water fill, as learned in study [1]. The tests were repeated to quantify variability.
3 Results Figure 2 shows the final beverage temperature as a function of cooling time for three cases: the simulation using the prototype material (PP), the simulation using the production material (HDPE), and the test data (supplemental plot included in the Appendix for reference including data from study [1]). The simulation was used from study [2]. The final temperature of the prototype simulation is higher than the production simulation because the thermal conductivity of HDPE is greater than that of PP by a factor of 2.
Figure 2. Performance results. The final temperature falls asymptotically with cooling time, approaching 32 F as time approaches infinity. For reference, the working production performance spec is 200 F to 38 F in 1.5 minutes. Considering the production simulation calculates roughly 34 F at 1.5 minutes, the spec includes a factor of safety. The prototype verifies the performance spec, even with the material difference.
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4 Discussion The final temperature measurements were less than the simulated prototype calculations. There are three likely factors. First, the simulation was formulated to be conservative. See [2] for a detailed description. Briefly in words, the thermal resistance changes during the cooling process, and the maximum value was used as a constant for the whole cooling process. Second, the pour-in and pourout processes have a heat transfer enhancement due to convection, while the simulation is based on pure conduction. Third, the cooling time was started after the pour-in was complete. A number of pour tests were performed. The pour-in time varied from 5 sec for a very fast pour to 15 sec for a very slow pour, giving an average of 10 sec. Pour-in times less than 5 seconds risked overflowing the Coldwave. The pour-out process was similar, 10-15 seconds. For the first 10 seconds the pour-out is roughly fast, while the last 5 seconds reduces from a stream to the final drops. The before and after volume data showed typically half an oz of fluid remaining on the heat exchanger walls. As shown in study [1], this consistent with a thin film of beverage remaining on the heat exchanger surface area (1 mil over 4 ft2). Test runs were also performed for a “very long� cooling time, 10 min, representing the scenario of a user forgetting to pour after 1-2 minutes or even just personal preference. The beverage did not freeze up. The final temperature was roughly 33 F. Repeated runs were also performed where the Coldwave was not recharged between runs. The final temperature of the second run varied from 40-50 F and depended on a number of factors including the final temperature of the first run, the starting temperature of the second run, and the cooling time of the second run. An extra 30-60 seconds were required for the second run, or else final temperatures above 50 F were measured. The current maximum thermal capacity of the Coldwave is sized to cool two beverages from 200 to 40 F. Note that 200 F is conservative for brewed coffee, which according to in-house experiments vary anywhere from 160-190 F. Next steps in testing will be to experiment with other beverages including soda, beer, wine, and vodka. The cooling is expected to be shorter, roughly 30 seconds, and the number of runs per Coldwave charge is expected to be larger, roughly 6 servings. The effect on carbonation is a concern. The production-style seals were not used for the rapid prototype assembly; rather an adhesive was used for the joints. A test plan is in place to make another rapid prototype revision with all production style features including the seals, knob, scored aluminum corrugation (for refreeze), and the latch for pouring.
5 Conclusion The rev-2 rapid prototype was tested, and the performance spec of 200 to 38 F in 1.5 minutes was verified. The results are conservative with respect to the production unit, which has a higher thermal conductivity material. The next phase of performance testing will focus on room temperature beverages: carbonated and non-carbonated, alcoholic and non-alcoholic. Life testing will follow, incorporating the design-style seals.
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6 References 1. Coldwave Test Verification – Using Rapid Prototype Rev-1, IceColdNow report, David Dussault, 8/1/12. 2. Coldwave Performance Calculations - Updated for Sensible Heating and Repeated Runs, IceColdNow report, David Dussault, 2/21/11.
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7 Appendix 7.1 CAD Renderings
Figure A-1. CAD rendering (with beverage for scale).
7.2 Supplemental Plots
Figure A-2. Performance results – including prototype rev-1 data.
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