Progress 08/15/16 to 04/14/18
Outputs
Target Audience:The target audience includes anyone interested in the final status of the hay dryer research. Changes/Problems:The biggest problem encountered during the execution of this project was the slow transfer of heat from the heating probes to the specimen. This resulted in slowing the vaporization process to a rate that makes the system infeasible for actual field use. A larger surface area on the probes could help, but we are also limited by the size of the hay bale and the number of probes that can be inserted. Solutions to this problem remain elusive. A microwave heater would certainly solve the problem, but it creates another one by losing the ability to capture the energy released when the water vapor is re-condensed. What opportunities for training and professional development has the project provided?This project provided an exciting opportunity to test and develop an idea for drying hay quickly. Although the project seems to be a dead end, it did provide a much deeper understanding of the drying process and the heat transfer characteristics involved. In addition, the work provided an opportunity to learn the intricacies of pumping high vacuum levels, especially in the presence of water vapor. Drying foodstuffs will always be an important area of research in order to prevent valuable farming outputs from being wasted due to spoilage. There are many other potential applications to such drying technologies, such as drying corn, wheat, or soybeans. The ability to capture the energy released when the water vapor is re-condensed would significantly reduce the costs of drying grains. However, being placed in a vacuum would most likely cause the kernels to crack, causing damage that would offset the advantages of the fast and efficient drying. How have the results been disseminated to communities of interest?
Nothing Reported
What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
During the previous reporting period, the vacuum chamber was instrumented with temperature sensors, as well as heating probes and a cold water condenser. A major setback was the inability to pump down to the required vacuum levels to reduce the boiling point of water to the targeted 40 degrees Fahrenheit. It is known that vacuum pumps exist and are relatively affordable (less than $2k) that are capable of pumping the required vacuum levels. In the short amount of time remaining on the contract, however, it was not feasible to acquire a unit for testing. It was determined, however, that the feasibility of the vacuum dryer concept could still be tested with the 28" Hg vacuum levels that could be obtained with the current system. At 28" Hg, the boiling point of water is about 95 degrees F, compared with the target of 40 degrees F. The target system specified heating the hay bale with 120 degree F probes (hotter probes would damage the hay by breaking down the proteins), representing an 80 degree differential. Thus, for the sake of understanding the maximum rate of vaporization, it was decided to re-run the experiments, but using 170 degree F heating water rather than 120 F. This represents the same differential between the heating probes and the boiling point of water that were expected in the original design, equating the speed of heat transfer from the probes to the liquid water. Once again, rather than inserting the heating probes into a wet bale of hay, they were placed into a bucket of water, which represents a much simpler test case than a hay bale. In order to ensure that enough heat was available, a large bath of hot water (> 100 gallons) was heated to 170 degrees F using two military surplus M67 immersion heaters (this heating process took several hours to complete). At the same time, another large water tank was cooled with 80 lbs of ice. Note that the hot water is used to vaporize the water by passing it through the heating probes, while the cold water is used to re-condense the water vapor by passing it through a heat exchanger mounted inside the vacuum chamber. Once everything was ready and placed in the chamber, the lid was attached and the chamber was pumped down to vacuum levels approaching 28" Hg and the hot and cold water circulation pumps were started. Temperature sensors located in the water bucket inside the chamber showed that the boiling point was approximately 95 degrees F. The monitoring system also recorded the input and exit temperatures of both the hot and cold water, along with the flow rates. Using these measurements, the total amount of water vaporized and condensed could be calculated - assuming minimal extraneous heat losses. Real time data showed that the estimated amount of water vaporized and condensed were in close agreement. After approximately 30 minutes, the system was shut down. The calculations based on the temperature measurements showed that almost 3 quarts of water had been vaporized. After opening the chamber, the water level in the bucket was measured, and showed that almost exactly 3 quarts of water had been boiled away, a perfect agreement with the calculations. When the test results are expanded, to reflect the additional heating probes that will be placed in the hay bale (15x as many), it shows that the maximum rate that the system could vaporize water is approximately 3 quarts every 2 minutes. This is a significant amount of water being removed in 2 minutes. However, the threshold for the project was to dry a hay bale from 30% moisture to 15% moisture in 2 minutes. That would require boiling off 8.5 lbs of water (slightly over 1 gallon). Thus, our prototype system would only have been able to dry a hay bale from about 26% moisture down to 15% in 2 minutes. Although our experiments were able to come close to the targeted amount of moisture removal, they were unable to meet the requirements. Further, the final experiment was a much simpler test, where the heating probes were placed directly into liquid water rather than a hay bale. The true system would have to contend with heat transfer through the hay bale, which would undoubtedly slow the system to rates that make it nearly unusable to a farmer. Although the results of this research are discouraging, there is still some hope that alternative heating methods could be used to heat the bale, such as microwave heating. This type of heating would not be limited to the heat conduction rates through the hay bale, or even the heating probes. Rather, a microwave heating source would target any moisture in the hay bale. However, there is a huge drawback for microwave heating in that it is difficult or impossible to use the heat released by the water vapor when it is re-condensed. Even if a Rankine cycle heat engine were used to harvest the energy from the condensing water vapor, they are at most 40% efficient. In this case, huge amounts of power would still need to be generated to provide the additional electricity to the microwave.
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Progress 08/15/17 to 04/14/18
Outputs
Target Audience:The target audience is anyone interested in the progress of this Hay Dryer research. A commercialization plan was developed during the previous reporting period, part of which involved a consumer survey of general interest in the hay drying product. Targeted feedback was obtained from internet forums for hay farmers. Changes/Problems:A major problem encountered during the execution of this research project is the poor performance of the gravity based vacuum pump. Although the pump is capable of pumping high vacuum levels, it is far too slow for this project (i.e., it would take several days of operation to pump the large vacuum chamber down to high vacuum levels required). Alternative vacuum pumping techniques/products are being researched to mitigate the problem, and feasibility studies have continued (although at lower vacuum levels) despite this setback. What opportunities for training and professional development has the project provided?
Nothing Reported
How have the results been disseminated to communities of interest?
Nothing Reported
What do you plan to do during the next reporting period to accomplish the goals?During the next reporting period, we intend to investigate the reasons for the poor performance of the gravity vacuum pump. Higher vacuum levels are a necessary aspect of this project, making vacuum pump design a priority. Note that commercial vacuum pumps typically do not tolerate the presence of water, necessitating a custom solution. Assuming that a solution exists, new experiments will be performed to analyze the rate of water vaporization that is possible with the new design.
Impacts
What was accomplished under these goals?
During the previous reporting period, the vacuum chamber was completed and tested to ensure a proper seal. Instrumentation software and hardware was developed to interface with the temperature sensors and log them to a file on a PC, as well as to allow a visualization of the current measurements. Further testing with the gravity based vacuum pump showed that although a relatively high vacuum levels can be achieved, it is prohibitively slow when connected to the large vacuum chamber. Therefore, initial tests were performed using the PTO vacuum pump, where only 28 inHg vacuum levels could be achieved. Despite the lower vacuum levels (and correspondingly higher boiling points), the system was able to vaporize 0.42 gallons of liquid water over a one hour period. This level falls short of the projectthreshold of 0.5 gallons per minute (objective #1, requires removing approximately 1 gallon of water from the hay bale). When the data is corrected for the number of heating probes used, the extrapolated capabilities are approximately 0.1 gallons per minute. At higher vacuum levels, this number may be improved due to the lower boiling point and therefore larger temperature difference between the heating probes and wet specimen.
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Progress 08/15/16 to 08/14/17
Outputs
Target Audience:
Nothing Reported
Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?
Nothing Reported
How have the results been disseminated to communities of interest?The results of this work are proprietary at this time and have not been disseminated. What do you plan to do during the next reporting period to accomplish the goals?Future Work Plans for the upcomingreporting period include completing the temperature logging/processing software, as well as doing some final assembly to get the test fixture up and running. Tests will begin by placing the heating apparatus into a bucket of water to determine how much water can be vaporized in a given period of time. The test results will be correlated with the anticipated water vaporization rate calculated using the input and output temperatures and flow rate of the heating water. Further tests will utilize actual bales of hay that were either recently baled (wet) or dry hay that has had water added (for the sake of drying it out again).
Impacts
What was accomplished under these goals?
During the previous reporting period, work began by constructing a vacuum pump suitable for the hay drying project, acquiring a vacuum chamber large enough to contain the hay bales for experiments, constructing a small prototype of the heating apparatus used to transfer heat into the hay bale, and developing the digital interface to temperature sensors. Vacuum Pump The vacuum pump used in this research needs to be: tolerant of water, able to draw a high vacuum (up to 29.75" Hg), and have a high pumping rate. This was achieved by designing, procuring necessary parts, and building a gravity based vacuum pump. Unfortunately, there are very few such pumps in existence, and none that can be obtained for a reasonable price. Therefore, a gravity based vacuum pump was designed and constructed during the previous reporting period. The design works on the principle that a vacuum can be obtained using a vertical column of water. Our gravity based vacuum pump has a water reservoir and a submersible water pump connected to a large section of pipe going up a steep hill. When the pump is cycled on, it fills the pipe with water, and when it is turned off, the water drains back into the reservoir at the bottom, causing a vacuum at the top of the pipe. Solenoid valves at the top of the pipe are synchronized to open/close with the water pump to allow for exhaust air to escape and direct the vacuum into the drying chamber. The system was developed and tested to achieve the required 29.75" Hg vacuum levels required for the hay dryer. The maximum vacuum obtained is limited by the temperature of the water in the water column. Unfortunately, however, the pump takes a long time to achieve such a high vacuum level. In order to speed the pump down, a V255 vacuum pump, made by Ingersoll Rand was obtained. This pump can achieve vacuum levels down to 28" Hg very quickly and will be used in tandem with the gravity based vacuum pump. Unfortunately, the V255 vacuum pump originally required a 3 phase electric motor to power the pump. Since 3 phase electric is not generally available, the pump was modified to draw power from a tractor Power Take Off (PTO). This allows the pump to be used in remote areas during testing. Using this configuration, the V255 will quickly draw the chamber down to 28" Hg, and the gravity pump will achieve the higher vacuum levels after that. Thus, the system is able to achieve the high vacuum levels required at a high pumping rate. Vacuum Chamber Initially, the project team was planning to build a custom vacuum chamber for use in this project. However, after the start of the project, a vacuum chamber was discovered for sale that suited the project's needs perfectly. Therefore, in order to reduce project risk, the vacuum chamber was obtained and modified for use in the hay drying research. Modifications included welding pipe bungs into the tank to allow for heating/cooling liquids and sensor signals (via wire feedthroughs) to be passed in and out of the chamber without leaking the vacuum. In addition, mounting bars were welded inside the chamber to mount hay bale and other equipment. Heating Apparatus Another complex aspect of the hay drying research is the design and construction of the heating apparatus. The heating apparatus is used to transfer heat into the hay bale to assist with the drying action. Our heating apparatus design consists of a series of probes inserted into the hay bale. Each probe is a tube inside of another tube with hot water circulating through it. A small heating manifold was constructed using 1/8 pipe nipples with 3/16 steel tubing inside and a point fabricated onto the ends. The small manifold has two probes spaced by approximately 4 inches. Temperature Logging Finally, in order to collect data during forthcoming drying trials, a temperature logging system was developed. The system uses DS1820b temperature probes to measure the temperature of the heat transfer liquids entering and exiting the chamber, as well as to monitor the temperature of the hay bale at varying distances from the heating probes. A circuit board was developed using the Microchip dsPIC30F3012 microcontroller to interface with the sensors (the sensors use a Dallas semiconductor proprietary 1-wire protocol), convert the data to temperatures in Fahrenheit, and transmit them through the RS232 port. The unique protocol allows many sensors to communicate over a single wire (which is beneficial due to the limited number of feedthroughs available to get information in and out of the chamber). It is anticipated that during the next reporting period, a PC program will be developed to receive the temperature values from the RS232 port and either log them or process them for real time data analysis.
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