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Revision as of 23:48, 8 October 2009

Client Comments on Report 1

We received your report, and we have some comments and questions. It looks like there are quite a few possible directions for improvement, and you should have a great starting point for brainstorming solution concepts in phase 2. Please respond point by point to the items below. We are looking forward to seeing your ideas in Report 2.

• Executive Summary: Very thorough and clear. Would be even better if somewhat shorter (~50%) keeping major findings and compacting filler/transition/intro text.
• Stakeholder Needs: Good start, but aren't there other important potential stakeholders (e.g.: repair/maintenance, rental owner, etc.)? Please include major needs in a bullet list. There appear to be many important needs missing, such as low cost, safety, quiet operation, intuitive use, flexibility to dish shape and size, operation time, low energy consumption, ease of installation, ease of storage, etc. Please be more comprehensive.
• Use: Good documentation of basic use. Is there any chance of the user hooking up hoses backward? Is there any chance of a hose falling out of the sink due to fluid dynamic forces? Flexibility in attachment to faucets was mentioned in the presentation but not the report. We are surprised that you did not bring up issues such as cups flipping over in the dishwasher and filling with water. Hopefully you will address more of these in the phase 2 user study.
• Assembly: An assembly image with labeled components appears to be missing.
• Mechanical Function: Good general explanation, but what prevents the faucet from continuing to feed water into the unit even while the pump is not running? What is the valve mechanism that switches the inlet from the faucet to recycled water? An assembly image with components labeled would be a big help to understanding details.

A few additional pieces of information are provided after a request for more information. There is no possibility of the user hooking the inlet hose or outlet hose backwards. Both hoses are anchored to the unit, thus leaving only one end to be attached to a faucet or drain. The inlet hose comes with a special adapter capable of screwing on to a faucet with threads. The outlet hose has no threads and cannon be "attached" to anything. The outlet hose in this case was simply placed in a sink to drain. The chance of the drainage hose falling out of the sink due to dynamic fluid forces is very close to zero. The water drains with such a a slow velocity that even the small jerk associated with the pump's transient is negligible. We would say that it is safe to conclude that the hose would only fall from a very shallow or small sink or drain. There is no valve that explicitly switches the inlet from the faucet to recycled water. For the dishwasher, the fresh water from the inlet is controlled by the main solenoid inlet valve. As we understand it, this feed water is fed into the device using the natural pressure of the water line. Once water has entered the device, the main pump is used to recycle and move the water until it is time to be drained via the wast pump. Assembly images below have been labeled.

• Mechanical Analysis: Please include a complete free body diagram of each problem you are solving, and clearly define your notation, including subscripts, before or immediately after you use them. Please state the equations you are using and write them out before plugging in numbers.
  • For the numbers you have assumed (P2=65 psi, c =0.01 N-s) please explain why you chose those values and cite references where appropriate.
  • Point 2 is zero velocity and a desired pressure? The pressure build up is at the point of stagnation - why a pressure target instead of a velocity target?
  • Why is Aout 8 times the orifice?
  • What is beta and inv?
  • Are you assuming the 45degree orifice is the only orifice?
  • Why do you think approach 2 with 90 cycles is more reasonable than 200?
  • To determine the flow rate in the pump, can you tell how much of the running time is spent pulling in clean water from the sink at the beginning of the cycle, and how much water that is? Is there any other way to find the flow rate other than guessing what the scale is compared to the other dishwasher you found numbers for?
  • What design implications does your analysis have?
• Bill of Materials: Good list. Is the sprayer arm injection molded as a single piece? You should be clear in your text that there are significantly more than 64 unique parts, since you have many subassemblies listed with single part numbers. Given the complexity of the product, this is okay, but please be clear.
• DFMA: Good observations.
• FMEA: What happens if faucet not turned on? Is the wobbling of the spray arm intentional in order to add variability to the spray pattern?

FMEA Comments: If the faucet is not turned on, the solenoid valve will open, attempt to allow water in, and be unable to do so. The pump will run for a full cycle since there is no water to raise the float to trip the shutoff circuit. The dishes will not get cleaned and the user should be able to quickly diagnose the problem. No damage is done to the unit.
The spray arm wobbling may be intentional. However, it is most likely not necessary as the jets cover the entire area and the nature of fluid flows mean that even small variations cause large changes in fluid direction. The possible additional variability is not worth the possible failure of one of the most critical components.

• DFE: Since use phase seems to dominate, it looks like energy efficiency is the most critical factor - and possibly a good selling point. Please describe the assumptions made in this section and explain your conclusions.
• If any of your images, figures, or text were taken from another source, please be certain to provide proper attribution.

Revisions based on DFE feedback- The assumptions and conclusions have been more clearly defined. The frequency of use was every 3 days and the amount of detergent used was 2 ounces per use. Also the conclusions that were covered in the executive summary have been explained in the DFE analysis section.