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MIT 2 810 - Water Jet

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Thor Eusner 2.810 Environmental Officer Report Nov. 3, 2006 Water Jet Summary The water jet uses 9,200 Watts of power when machining and 0 Watts when idle. During operation, the water jet consumes a significant amount of garnet and raw material due to the curf. Therefore, we need to take these two things into account. The water jet computer will output the length of machining time, the amount of garnet used, and the length of the cut. Using the above information and the energy cost of the raw material and garnet, the total energy consumed and total CO2 emissions can be calculated. See the Procedure section at the end of this handout for the formulas. Specifications, Measurements, Assumptions The manufacturer of the LMP water jet is OMAX. According to OMAX’s specifications, the water jet’s electrical requirements are 15,000 Watts of power provided via a 3-phase 440-500 V source. In reality, the LMP water jet gets its power from a 3-phase 480 V source which is consistent with the specifications. Joe and I measured the current to be 18.8A. Therefore, we measured that the water jet uses 9,000 Watts of power when the pump is on. The pump is what is responsible for the actual cutting of the water jet and is therefore only turned on when the water jet is machining. This value of 9,000 Watts is less than the specification of the manufacturer. This is probably because the manufacturer built in a safety factor. We measured the power consumed by the computer console and servos to be 177 Watts (1.61 A at 110 V). Therefore, when the water jet is actually machining, it consumes approximately 9,200 Watts of power and when it is idling, it consumes approximately 200 Watts of power. Therefore, for our calculations, we will assume that when the water jet is not machining (idling) it is not consuming energy. And, when the water jet is machining, it is consuming 9,200 Watts of power. Analysis/Model of Water Jet The main inputs into the water jet are: electricity to power it, garnet (which is the abrasive used to do the cutting), water (which is the delivery device for the abrasive), compressed air (which acts as a triggering mechanism to start the pump), and the raw material that gets machined. The main outputs are the garnet (which is in a non-recyclable form), the waste raw material (from the curf), the water, the air, the final product, and emissions that came from the fact that electricity was used to power the water jet.Additional Elements The water jet uses water to deliver the abrasive garnet particles at high pressure. This water, however, constantly gets drained and therefore, reenters the water supply. It is assumed that the water is a negligible part of the environmental accounting because water is simply cycling through the machine in a benign way. There are not any toxic materials or any significant heat energy that gets added to the water. The water jet also consumes a very small amount of compressed air. The air is used to trigger the pump to start. This compressed air comes from a line that continually supplies compressed air to building 35. Once again, this is a negligible part of the environmental accounting because the compressed air is not being contaminated with anything dangerous, it is simply being expanded. Another consumable of the water jet is part of its hardware, specifically its tip and nozzle. Each year, the water jet requires approximately $4,000 of replacement tips and nozzles. Since 2.810 will be using the water jet heavily for about a month and the class has 7 groups, the approximate cost of each group is approximately: ($4,000/(12*7)) = $50. In addition, each year, the used garnet particles need to be vacuumed out of the water jet tank. This costs $5,000 a year. Therefore, the approximate cost of each 2.810 group is approximately ($5,000/(12*7)) = $60. Garnet We need to know the energy cost of garnet because during the water jet process, a substantial amount of abrasive (garnet) is used. I could not find any explicit numbers for the energy content of garnet, but I found two very helpful graphs. Below, I have attached two graphs form the University of Cambridge in England. The one of the left shows the energy cost of certain materials verse monetary cost. Porous ceramics, like concrete are in the bottom left. I assume that garnet would fall in this category because it is a mineral and there are lots of minerals in cement (limestone) and other porous ceramics. Therefore, I approximate the energy cost to be approximately 5MJ/kg. The graph on the right shows the recycle fraction of materials. And the ceramic and porous ceramics have a very low recycle fraction. Therefore, I will assume that none of our garnet will be recycled. As a side note, the garnet costs $.50 per pound to buy.Procedure When a program is first uploaded to the water jet, the water jet software provide three important details: 1) the length of time that the water jet will cut 2) the length of the cut (inches) and 3) the pounds of garnet used. This is all of the information we need to know. We start first with electricity. Electricity: The electric energy used during the process = (9,200 Watts) x Seconds that the water jet was cutting (get from computer). Garnet: The energy used to make the garnet = (5,000 J/kg) x kg of garnet used (get from computer). Raw Material lost to curf: The energy used to make the material lost to curf = thickness of material x length of cut (from computer) x curf width (this is assumed to be 0.030”) x density x energy cost of that material. Total energy used in water jet process: Total energy = electricity energy + garnet energy + raw material energy lost to curf. Total CO2 emissions: It is assumed that the raw material was made primarily from electricity. Therefore total carbon dioxide emissions = (0.062 kg/MJ) x (Total energy used in water jet


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MIT 2 810 - Water Jet

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