Waterjetting 1d - Not quite that simple!

When I first began the research on the applications of high-pressure water that was be one of the major parts of my professional life I must confess to a certain naïve innocence in regard to other folk’s work. One assumed that other folk had made similar mistakes to mine, and then corrected them, so that when different systems were compared that the early, obvious, mistakes had not been made.

One of the first times I found that this wasn’t the case was when we were asked to go and demonstrate that high-pressure waterjets could economically cut granite, in quarries located in the heart of the Granite industry, in Elberton, Georgia. We were working with Georgia Institute of Technology (Georgia Tech) at the time and were asked if we could, at very short notice, go down to a couple of quarries and run a demonstration.

Back during my graduate studies I had found that Russian claims were true that said that it was possible, with a 10,000 psi jet pressure to cut through a rock with a compressive strength of 30,000 psi. (I'll tell you how later)

Figure 1. 9-inch thick block of granite drilled through by a 10,000 psi waterjet at Leeds University. It took over 30 minutes. (Summers, D.A., Disintegration of Rock by High Pressure Jets, Ph.D. Thesis, Mining Engineering, University of Leeds, U.K., 1968.)

Knowing this, and having a suitable pump at Rolla, our group ran some tests at the RMERC to get the angles right between the two jets that we were to use, and then, about a week later, we went down to Elberton and set up a system in the quarry.

Figure 2. Starting to cut a 1-inch wide slot in granite, pressure 14,000 psi, 90 rpm, linear cutting speed around 9 ft/min, areal cutting rate around 20 sq. ft./hour.( Raether, R.J., Robison, R.G., Summers, D.A., "Use of High Pressure Water Jets for Cutting Granite," 2nd US Water Jet Conference, Rolla, MO., April, 1983, pp. 203 - 209.)

The trials demonstrated that high-pressure water could cut granite at commercial rates, we cut a slot some 11 ft long and about 2-ft deep, and, after a couple of days of work, we went home. Georgia Tech then went to one of our competitors who set up to run a similar test. We had been done in 2 days, it took them two weeks to cut a slot about 2 ft long and 6-ft deep. They were running a jet system at 45,000 psi, roughly 3 times the pressure of our system. Why did they do so badly?

Well it turned out that they connected their pumps to the nozzle through a very narrow length of high-pressure tubing, and we calculated (as later did they) that of the 45,000 psi being supplied at the pump, some 35,000 psi had been lost in overcoming friction between the pump and the nozzle, As a result they were trying to cut the granite with jets at a pressure of 10,000 psi effective pressure, and it was much slower than our system which retained most of the 14,000 psi from the pump to the nozzle. (Hilaris, J.A., Bortz, S.A., "Quarrying Granite and Marble using High Pressure Water Jet," paper D3, 5th International Symposium on Jet Cutting Technology, Hanover, FRG, June, 1980, pp. 229 - 236.)

Now you may note that I said something about mistakes – it turns out that we had made an identical mistake a few years earlier and had added a second 10-ft length of narrow diameter tubing to the nozzle, and suddenly a system that had cut adequately with 10-ft of tubing did not work with 20-ft. The reason was the pressure loss in the tubing was too great at the longer length, and the pressure fell below that required to cut into the rock. (But at the shorter length we were drilling the hard sandstone at 12-ft/minute).

It is a very simple mistake, and many folk have made it over the years. The system has to be designed from one end to the other to ensure that all the parts are properly sized for the systems that are to be used. (And I will refer to other cases such as that above as we go through this series.)

It is not just the diameter of the feed lines that is important. In 1972 it took, on average, 150 man-hours and about $2,000 for the U.S. Navy to clean a single ship boiler using chemicals and mechanical scrubbing and cleaning. An enterprising company showed the Navy that it was possible to use waterjet lances to clean the tubes. In the demonstration they cleaned a boiler in 10 hours, and it cost around $700. This being Government work, the Navy then arranged a competition to find the most effective contractor. Based on the performance of the system that had been used in the first demonstration they asked 5 companies to compete in cleaning boilers. The operating equipment was designated as having to operate at 20 gpm, at a pressure of 10,000 psi. The results were not even close, even with systems nominally the same.

Figure 3. Relative cleaning efficiency in areal percentage cleaned, of five competing systems in cleaning heat exchanger tubes in Navy boilers. (Tursi, T.P. Jr., & Deleece, R.J. Jr, (1975) Development of Very High Pressure Waterjet for Cleaning Naval Boiler Tubes, Naval Ship Engineering Center, Philadelphia Division, Philadelphia, PA., 1975, pp. 18.)

One of the differences between the competing systems, you won’t be surprised to hear, was that some had smaller feed hoses than others.

There are many different reasons that the various systems performed as they did. One of the aims of this series is to ensure that, should you be asked to engage in such a competition, you will know enough to follow the path of company A, rather than company E.

As systems have become more sophisticated the different factors that control the performance of the jets have increased in number. As a simple example, when abrasive particles are mixed with high-pressure water in streams of abrasive-laden waterjets at pressures that can run up to 90,000 psi in pressure, for high precision cutting of material, the factors controlling performance now include not only the delivery system for the water, but also that for the abrasive, the type of abrasive and the configuration of the nozzle through which that final cutting jet is created.

Again, when we were asked to compare the performance of these different systems we set up nominally identical test conditions under which to determine which nozzle system would perform better. If I were honest I would tell you that before the tests began I expected that the variation in performance of the systems would vary by perhaps 10% between the best and the worst. We were quite surprised by the result.

Figure 4. Comparative performance between 12 nominally similar abrasive waterjet cutting nozzles in cutting through steel at a standard speed, pump pressure, and abrasive concentration.

I use these last two figures to show that all the details of a high-pressure waterjet system are important, when it comes to optimizing performance. One of the reasons to write this series is to ensure that folk that use these systems in the future do not make the mistakes that we made, as we learned how to tune the systems from getting poor performance to the commercially viable rates that are achieved today.

Unfortunately much of the early research and tests that are the basis for this knowledge were performed before the Internet existed. As a result I will have to use references to books and papers (as above) rather than using the electronic references that are the more common habit now.

This concludes the basic introduction to the series, which will now focus on more specific subjects.

Dr. Judith Curry on the IPCC

A fairly long time ago Jimmy Carter was elected President of the United States, and the Federal Agencies scrambled to find projects in Georgia that they might propose. The National Science Foundation looked to improve the quarrying of granite, one of the centers for which was in Elberton, GA, and some of the technology at the time was relatively unhealthy. Georgia Institute of Technology (GIT) was prime on the contract, and I was initially a member of the Advisory Panel, but eventually took a crew down to Georgia and, working with the Georgia Tech folk and the Elberton Granite Association, went to a quarry and cut a slot some 11 ft long, and about 2 ft deep to demonstrate that high pressure waterjets were a practical tool for use in the quarries. The technology has since transitioned into use around the world, and we carved the MS&T Stonehenge out of Elberton Granite (with water). It left me with a pleasant memory of the folks that deal with Earth Science down at GIT.

This week James Stafford, who runs the Oilprice.com web site contacted me to ask if I wanted to run an interview that they had conducted with Dr. Judith Curry, who is now the Chair of the School of Earth and Atmospheric Sciences at Georgia Tech. Dr. Curry writes the discussions on climate change at her Website Climate, Etc. The original interview can be found at Oilprice.com. I am glad to reproduce it here.

. . . . . . . . .
OilPrice.com: What are your personal beliefs on climate change? The causes and how serious a threat climate change is to the continued existence of society as we know it.

Dr. Curry: The climate is always changing. Climate is currently changing because of a combination of natural and human induced effects. The natural effects include variations of the sun, volcanic eruptions, and oscillations of the ocean. The human induced effects include the greenhouse gases such as carbon dioxide, pollution aerosols, and land use changes. The key scientific issue is determining how much of the climate change is associated with humans. This is not a simple thing to determine. The most recent IPCC assessment report states: "Most [50%] of the warming in the latter half of the 20th century is very likely [>90%] due to the observed increase in greenhouse gas concentrations." There is certainly some contribution from the greenhouse gases, but whether it is currently a dominant factor or will be a dominant factor in the next century, is a topic under active debate, and I don't think the high confidence level [>90%] is warranted given the uncertainties.

As I stated in my testimony last year: "Based upon the background knowledge that we have, the threat does not seem to be an existential one on the time scale of the 21st century, even in its most alarming incarnation."

OilPrice.com: You have said in the past that you were troubled by the lack of cooperation between organizations studying climate change, and that you want to see more transparency with the data collected. How do you suggest we encourage/force transparency and collaboration?

Judith Curry: We are seeing some positive steps in this regard. Government agencies that fund climate research are working to develop better databases. Perhaps of greatest interest is the effort being undertaken by the Berkeley Earth Surface Temperature project, which is a (mostly) privately funded effort to compile and document a new data base on surface temperatures, in a completely open and transparent way.

OilPrice.com: Do you feel climatologists should be putting more effort into determining the effect of the sun on our climate? As the IPCC primarily focuses on CO2 as the cause of climate change – Is the importance of CO2 overestimated and the importance of the sun is underestimated?

Judith Curry: I absolutely think that more effort is needed in determining the effect of the sun on our climate. The sun is receiving increased attention (and funding), and there is a lively debate underway on interpreting the recent satellite data record, reconstructing past solar variability, and predicting the solar variability over the 21st century. Nearly all of the solar scientists are predicting some solar cooling in the next century, but the magnitude of the possible or likely cooling is hotly debated and highly uncertain.

OilPrice.com: You are well known in climate and energy circles for breaking from the ranks of the IPCC and questioning the current information out there. What do you see as the reasons for the increase in skepticism towards global warming over the last few years.

Judith Curry: Because of the IPCC and its consensus seeking process, the rewards for scientists have been mostly in embellishing the consensus, and this includes government funding. Because of recent criticisms of the IPCC and a growing understanding that the climate system is not easily understood, an increasing number of scientists are becoming emboldened to challenge some of the basic conclusions of the IPCC, and I think this is a healthy thing for the science.

OilPrice.com: What are your views on the idea that CO2 may not be a significant contributor to climate change? How do you think such a revelation, if true, will affect the world economy, and possibly shatter public confidence in scientific institutions that have said we must reduce CO2 emissions in order to save the planet?

Judith Curry: Personally, I think we put the CO2 stabilization policy ‘cart' way before the scientific horse. The UN treaty on dangerous climate change in 1992 was formulated and signed before we even had ‘discernible' evidence of warming induced by CO2, as reported in 1995 by the IPCC second assessment report. As a result of this, we have only been considering one policy option (CO2 stabilization), which in my opinion is not a robust policy option given the uncertainties in how much climate is changing in response to CO2.

OilPrice.com: There has been quite a bit of talk recently on geo-engineering with entrepreneurs such as Bill Gates and Richard Branson pushing for a "plan B" which utilizes geo-engineering to manipulate the environment in order to cool the atmosphere. Geo-engineering could be much cheaper than reducing emissions, and also much quicker to produce results and scientists are lobbying governments and international organizations for funds to experiment with various approaches, such as fertilizing the oceans or spraying reflective particles and chemicals into the upper atmosphere in order to reflect sunlight and heat back into space. What are your thoughts on geo-engineering? Is it a realistic solution to solving climate change or is it a possible red herring?

Judith Curry: With regards to geo-engineering, there are two major concerns. The first is whether the technologies will actually work, in terms of having the anticipated impact on the climate. The second is the possibility of unintended consequences of the geoengineering.

OilPrice.com: You have been noted to criticize the IPCC quite openly in the past on several topics. Even going so far as to say: "It is my sad conclusion that opening your mind on this subject (climate change controversy) sends you down the slippery slope of challenging many aspects of the IPCC consensus."
Do you believe that the organization as a whole needs to be assessed in order to better serve progress on climate change? What suggestions do you have on how the organization should function?

Judith Curry: The IPCC might have outlived its usefulness. Lets see what the next assessment report comes up with. But we are getting diminishing returns from these assessments, and they take up an enormous amount of scientists' time.

OilPrice.com: Would renewable energy technologies have received the massive amounts of funding we have seen over the last few years without global warming concerns?

Judith Curry: I think there are other issues that are driving the interest and funding in renewables, including clean air and energy security issues and economics, but I agree that global warming concerns have probably provided a big boost.

OilPrice.com: What do you believe are the best solutions to overcoming/reversing climate change; is a common consensus needed in order to effectively combat climate change?

Judith Curry: The UN approach of seeking a global consensus on the science to support an international treaty on CO2 stabilization simply hasn't worked, for a variety of reasons. There are a range of possible policy options, and we need to have a real discussion that looks at the costs, benefits and unintended consequences of each. Successful solutions are more likely to be regional in nature than global.

OilPrice.com: I saw an interesting comment on another site regarding climate science that I thought I'd get your opinion on as it raises some very interesting arguments: Climate science has claimed for 30 years that it affects the safety of hundreds of millions of people, or perhaps the whole planet. If it gets it wrong, equally, millions may suffer from high energy costs, hunger due to biofuels, and lost opportunity from misdirected funds, notwithstanding the projected benefits from as yet impractical renewable energy. Yet, we have allowed it to dictate global policy and form a trillion dollar green industrial complex - all without applying a single quality system, without a single performance standard for climate models, without a single test laboratory result and without a single national independent auditor or regulator. It all lives only in the well known inbred, fad-driven world of peer review.

Judith Curry: I agree that there is lack of accountability in the whole climate enterprise, and it does not meet the standards that you would find in engineering or regulatory science. I have argued that this needs to change, by implementing data quality and model verification and validation standards.

OilPrice.com: Do you believe that the language used in papers and at conferences is a problem? The public just wants straight answers to questions: Is the climate warming, By how much, and what will the effects be? Scientists need to step out from behind the curtain and engage the public with straight answers and in their own words. Is this achievable, or is climate science too complex to be explained in laymen's terms? Or is it because even climate scientists can't agree on the exact answers?

Judith Curry: I think the biggest failure in communicating climate science to the public has been the reliance on argument from consensus. We haven't done a good job of explaining all this, particularly in the context of the scientific disagreement

OilPrice.com: What resources would you recommend to people who wish to get a balanced and objective view on climate science and climate change.

Judith Curry: There is no simple way to get a balanced and objective view, since there are so many different perspectives. I think my blog Climate Etc. at judithcurry.com is a good forum for getting a sense of these different perspectives.

Interview by. James Stafford, Editor Oilprice.com
Note that both sites appear on this site's blog roll.