The Data Sentry Sharing Information Through Collaboration Sites By Phil Ledgerwood Sentries of all kinds are valuable to society as they keep vital locations and items protected and secure. While security is needed for data and documents, certain problems arise once an organization or a group within that organization has data that must be shared. For instance, it might be several days before Person A has time to send a document that Person B needs. Or perhaps Person A doesn t want to give access to their data store, so they must export data for whoever needs it, which may or may not be in a useful format for the receiver. Person A is part of a group known as data sentries. People who need their data must go through the sentries, any updates or changes must also go through them, and woe to you if you should try to go around them. Bad Security? There is a potential for collateral damage in an organization with data sentries. The obvious problem is the bottlenecks and slow turnaround times. With busy schedules, even the most wellintentioned data sentry can take some time to get you the data you need. There are a number of less obvious problems. You might need the data in a different format, so another file is created. What if one of the versions gets updated? Does everyone s copy need to be updated? What if there aren t two copies of this information, but five, or 50? Organizations end up with multiple versions and formats of the same data, bandwidth clogged with email attachments, and requests for information that sit on desks. Sharing the data freely, however, seems equally unattractive, as we envision people making modifications to centralized data with no way to reverse them or even find out who did what (Figure 1). Is there a viable solution that avoids both sets of pitfalls a light at the end of the tunnel? The Light at the End of the Tunnel In order to deal with these pervasive business pains, a few companies have developed products to try to alleviate at least portions of them, ranging from Framework Technologies Active Project to Microsoft SharePoint. Microsoft has perhaps made the largest recent effort with its Office 2003 suite and SharePoint services. Products such as these emphasize secure ways of communicating and collaborating sharing. Collaboration sites are shared workspaces accessible from the Web. They can store libraries of files. They can be used for group postings, appointments, task lists, live communication, content management, document versioning, and more. Users can often create their own subsites with their own users and permissions. Through the use of collaboration solutions, groups have a centralized repository for their data and documents (Figure 2). Security is maintained by assigning permissions to the various users. People only see what they need to see and can only change what they need to change. On the other hand, people also have immediate access to the most up-to-date version of the data whenever and wherever they need it. These solutions typically include features for version control, so it is easy to determine who TECHBriefs 2005 No. 1 4 Burns & McDonnell
Figure 1: Client machines receive, store, maintain, and update unconnected, individual copies of the same document. Figure 2: Client machines see and update the same document, not individual, personal copies. Phil Ledgerwood is a developer for the Business & Technology Services Group. He serves on the national board of the World Organization of Webmasters as a technical advisor and holds the Certified Professional Developer and Certified Internet Webmaster designations. He has a bachelor's degree from Covenant College. made what changes and restore to an earlier version if necessary. The TechSolutions Group at Burns & McDonnell has used this software to design collaboration solutions for clients with great effect. Collaboration sites have allowed clients to bring participants from all over the country to the same, virtual meeting table to share and collectively work on documents and tasks. One food processing client projects that the collaboration solution designed for them by TechSolutions will save them at least $100,000 per year, paying off the cost of their solution within the first year of operation. Conclusion Businesses need to realize that they may have a problem even if they ve had the same process for years. Their problem stems from having scattered copies of the same data in different formats, or multitudes of email attachments, or time lost due to requests for information. However, these problems can be solved with a collaborative solution that is right for each business. Productivity and profitability are on the line as companies are seeing great returns on investment from making their data more accessible and manageable to the people who need it. For more information on this subject please send an email to the following address: Phil Ledgerwood <techbriefs@burnsmcd.com> Burns & McDonnell 5 TECHBriefs 2005 No. 1
Estimating System Leak Rates Using Spreadsheet Models to Measure Pressure Loss By Don Meyer, P.E., and Geoff Stephenson, P.E. Introduction Environmental regulations state that if some materials leak from a system, it must be reported if the leak exceeds some threshold value. In a recent project, a refrigeration system began leaking ammonia. If the ammonia leak had exceeded 100 lb/day, the leak would have been reportable and there would have been a fine for noncompliance. This article presents a calculation procedure that was used to demonstrate that the leak was only 41 lb/day. It also demonstrates how parameters of a nonlinear equation can be determined using a least squares technique in a spreadsheet. The calculations were based on a leak test using nitrogen. The pressure loss in the system was modeled as though the leak were through an orifice. The leak data was fit to a pseudo orifice coefficient. This coefficient was then used to calculate the loss of ammonia. The first step in the test was to fill the system with nitrogen. The pressure in the system was recorded as a function of time. This loss in pressure was converted to a pseudo orifice coefficient using the following model. FO w=lb/hr Vent Rate V=System Volume ft3 W= Weight of Gas in System lb Figure 1: Fixed Volume Vessel The system can be viewed as a fixed volume vessel with an opening at the top as shown in Figure 1. The system is filled to an initial pressure, P 0, with nitrogen. Using the initial pressure, system temperature, the gas molecular weight and the system volume, the initial weight of the gas in the system is given by: V * P 0 * MW W = V* v = 10.73 * Z * (T + 460) Where: W = weight of gas in the system, pounds V = volume of the system, cubic feet v = vapor density, lb/cf P 0 = the initial system pressure, psia MW = molecular weight of the gas Z = gas compressibility T = system temperature, ºF For these calculations, the system was assumed to be ideal. Therefore, Z is equal to 1. The system was also assumed to be isothermal so that T is constant. The model assumes that at time equals 0, material begins to leak out of a flow orifice, which represents the leak from the system. This leak rate is w. By material balance, the rate of change of the system contents (W in lbs) is given by: dw dt = w(t) Where t is time in hours and w is flow in lb/hr. TECHBriefs 2005 No. 1 6 Burns & McDonnell
140 Nitrogen Venting Data Compared to Model 120 Pressure psia 100 80 60 Data Source 40 20 0 0 2 4 6 8 10 12 14 16 Day Figure 2: Test Data The t in parenthesis after the w indicates that the flow is a function of time. Substituting in the above definition of weight in the system yields: P is the pressure in the system after time 0. becomes sonic when the pressure drop is more than 50% of the upstream pressure. At this point, the flow rate is proportional to the square root of the product of the density times the upstream pressure. This can be expressed as: K is the pseudo orifice coefficient. This equation relates the rate of change of the pressure in the system to the vent rate. The flow through a control device such as a flow orifice or control valve for compressible flow is given by the following equation: Where: w = Cv * N6 * Y * X * P 1 * 1 Cv = flow device sizing coefficient N6 = constant depending on the units system used Y = expansion factor X = ratio of absolute pressure drop to upstream pressure P 1 = upstream pressure 1 = upstream density w = the rate of flow through the orifice In general, the flow through a control device Since at any given time w(t) = dw/dt, the above two equations can be combined and integrated to yield the following expression relating system pressure to time: -Ln P = P 0 K * t V 10.73 * (T+460) MW Figure 2 shows the data taken during the test. The equation above relates the pressure in the system versus time. The pressure curve is a function of the initial pressure, P 0 and K. The objective is to find the values of P 0 and K, which minimize the error between the calculated and the predicted values. This is fairly easy when the equations are linear. However, in this case the equations are nonlinear and the math required to complete the least squares calculations is difficult. Burns & McDonnell 7 TECHBriefs 2005 No. 1
However, Excel has a tool for solving these types of problems. It does require some trial and error work. The first step is to set up a column in the data spreadsheet that calculates the pressure at each point in the data set using assumed values for P 0 and K. The errors are calculated as the square of the difference between the calculated value using the assumed constants and the measured values. These errors are summed together to get the error for that set of constants. In Excel there is a tool called Solver (most spreadsheet programs have something similar). This tool allows the spreadsheet to change one cell to match a value in another cell. This tool will also search for maximums and minimums. In the above case, the Solver tool is used to adjust the K parameter to minimize the sum of the squares of the errors. The next step is to change the value of P 0 and repeat the minimization to see if the result is a lower error level. Since P 0 should be close to the initial point in the data set, it should be easy to get a first approximation. Using this procedure, the least error level occurred at P 0 = 98 psig and K = 0.2748. The curve in Figure 2 represents the above equation using these constants. In the nitrogen test, the leak rate is the highest at the initial pressure. The maximum leak rate can be calculated from K and the system volume. For nitrogen, the initial leakage rate is 2.17 lb/ hr, the pressure is 112.7 psia and the density is 0.555 lb/cf. When the system is full of ammonia, there is both liquid and vapor present. At 60º F, the pressure in the system is approximately 90 psig. As some of the ammonia vapor leaks out, ammonia liquid vaporizes to take its place. Therefore, the ammonia system would have maintained a constant pressure until all of the liquid had evaporated and then the pressure would have fallen as in the nitrogen test. At 90 psig, the density of ammonia vapor is 0.38 lb/cf. The leakage rate of ammonia is given by the following equation: (104.7 * 0.38) 2.17 0.5 = 1.73lb/hr (112.7 * 0.555) 0.5 Conclusion Based on the nitrogen data and this calculation procedure, it was demonstrated that the ammonia leak was less than the reportable 100 pounds per day. For more information on this subject please send an email to the following addresses: Geoff Stephenson <techbriefs@burnsmcd.com> or Don Meyer <techbriefs@burnsmcd.com Don Meyer is a principal chemical engineer in the Burns & McDonnell Process & Industrial Group. He has a master's in chemical engineering from Purdue University, and has been involved in designing chemical separation and heat transfer systems for more than 30 years. Geoff Stephenson is the process technology manager for the Burns & McDonnell Process & Industrial Group. He has a bachelor's in chemical engineering from the University of California, Santa Barbara and has been involved in the design of chemical and refining facilities for over 15 years. TECHBriefs 2005 No. 1 8 Burns & McDonnell