Abstract:
A test apparatus and method of its use for evaluating various performance aspects of a piping segment locates a piping segment between two cold boxes. A first cold box conditions test fluid before providing the fluid into the piping segment. The first and second cold boxes both significantly reduce, if not eliminate, any heat transfer from the ends of the piping so that accurate measurements of heat leak rates from the sides of the piping segment may be determined.

Description:
ORIGIN OF THE INVENTION 
     This invention was made in the performance of work under a NASA contract and by an employee of the United States Government and is subject to the provisions of Public Law 96-517 (35 U.S.C. §202) and may be manufactured and used by or for the Government for governmental purposes without the payment of any royalties thereon or thereof In accordance with 35 U.S.C. §202, the contractor elected not to retain title. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a mobile test apparatus and a method of making precise thermal performance measurements of process piping and systems, and more specifically to a testing method and apparatus for evaluating thermal insulation systems of pipelines of various media at various temperatures. 
     2. Prior Art 
     U.S. Pat. No. 4,978,229 is directed to a method and apparatus for testing thermal conductivity of insulation placed over a test apparatus. While this device is an improvement over the prior art in recognizing that the shape of the insulation contributes to the conductivity of the insulation, this device is not designed, or even capable, of measuring the conductivity of a piping system which is transporting fluid during the test. 
     U.S. Pat. No. 4,396,300 is directed to a test apparatus for testing the heat transfer and friction characteristics of a tube. It appears that the disclosed apparatus is designed to test an uninsulated tube which would be evaluated for possible use as a heat exchanger tube. There is no provision for eliminating end effects discussed in this reference since the piping segment is a continuous loop. Furthermore, there is no provision for a static boil off test for cryogenic fluids, only a flow through test. 
     Precise measurement of thermal performance of piping systems is advantageous in certain applications. As technology advances, the use of cryogenics will be more and more commonplace. As an example, hydrogen may provide a more common fuel source. Liquification of hydrogen would then be appropriate for storage in many applications. When handling liquefied gas, i.e., which is typically done at very cold temperatures, there is often a need for cryogenic piping systems. 
     In the past, data has been obtained from tests of specific segments of a system such as a segment of insulation for a pipe as described in U.S. Pat. No. 4,978,229. The data was then extrapolated as segments were conceptually combined together to approximate the thermal performance of piping systems. Tables provided by certain manufacturers including Chart-CVI of Columbus, Ohio, Chart-MVE, and PHPK include an estimated heat leak rate of some components utilized in the cryogenic piping systems. However, as components are combined together, different components are utilized together, and an approximation, or extrapolation, has been employed to provide an expected thermal performance criteria for the system. However, in field installations, the actual performance values for the insulation system can be as much as 10 to 100 times worse than the ideal laboratory values. Accordingly, a need exists to more definitively predict the thermal performance of actual pipelines and piping systems. 
     Heat leak measurements for higher performance insulation systems are by nature difficult since small heat leak errors can be very large with respect to the desired measurement. Variables such as external ambient conditions like wind, temperature, humidity, solar radiation, etc. could contribute large errors. Accordingly, a need exists to evaluate a piping configuration with test equipment which can be easily reproduced and provide a standard. 
     SUMMARY OF THE INVENTION 
     Consequently, it is a primary object of the present invention to provide a method and apparatus for obtaining data to measure the heat leak rate of cryogenic pipelines. 
     It is a further object of the present invention to provide a method and apparatus for comparing the thermal performance of piping systems. 
     Another object of the present invention is to provide a method and apparatus which is easily employed to provide the thermal performance of actual full-scale pipelines and piping systems. 
     Accordingly, the present invention provides a test apparatus and method to measure the heat leak rate of piping systems. Cold boxes are connected to each end of the piping systems. The test apparatus may be employed in one of two ways: a boil-off method for pipelines carrying cryogenic fluid, or a flow-through evaluation. For the boil off method, the flow rate of boil off is determined for the system, and the heat leak rate may be calculated as the boil-off flow rate times the latent heat of vaporization. For the flow through method, heat leak rate is equal to the liquid mass flow rate times the specific heat and the change in temperature across the system. 
     The piping system is preferably shrouded with a heater shroud to practically eliminate any environmental effects. Bellows at either end of the piping system allow for thermal expansion and contraction while being equipped to eliminate heat transfer from the pipe ends. Low conductivity pipe supports minimize thermal contact to reduce possible sources of errors. A plurality of temperature and pressure measurement sensors monitor temperatures and pressures at a number of locations to determine the pressures and temperatures at a number of locations along a piping system. Flow meters are also utilized at various locations to evaluate mass flow rates through the piping system. These temperatures, pressures and mass flow rates are utilized to provide the thermal performance characteristics of the piping system. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The particular features and advantages of the invention as well as other objects will become apparent from the following description taken in connection with the accompanying drawings in which: 
     FIG. 1 is a first schematic of a test apparatus illustrating a preferred embodiment of the present invention; 
     FIG. 2 is a second schematic of the test apparatus showing detail within the cold boxes shown in FIG. 1; and 
     FIG. 3 is a partial cutaway elevational view of one end of the test apparatus of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the FIG. 1, a test apparatus  10  is illustrated. The test apparatus  10  is provided to test the thermal performance of a piping segment  12  so that when the piping segment is utilized in a design, the designers and/or builders may accurately predict the heat losses from the piping segment  12 . 
     Piping segments  12  may include pipe sections, insulation, valves, and/or other components in a stretch of piping which are desired to be evaluated for their thermal performance characteristics such as the heat transfer rate (Q) from a piping segment  12 , the Heat Flux rate (q), the apparent thermal conductivity value (k), and the insulating effectiveness value (R). Although a linear piping segment  12  is illustrated, bends and irregularities could be handled as well. 
     In order to evaluate piping segments  12  under similar conditions so that one piping segment may be compared to another under similar conditions, a test apparatus  10  is useful. The preferred embodiment of the test apparatus  10  has an upstream cold box  14  and a downstream cold box  16 . The upstream cold box  14  is useful in conditioning a supply of fluid to be provided into the piping segment  12 . Both the upstream and downstream cold boxes  14 ,  16  are useful in obtaining stability of the piping system, and in eliminating end effects, i.e., errors caused by heat transfer from the pipe ends instead of radially (axially) outwardly from the piping segments  12 . 
     The piping segment  12  is preferably encased within a jacket  18  which is surrounded with a heater  20 , illustrated as a heater wire. The heater wire utilized in the preferred embodiment is a 150 W/ft, but other heater designs could be utilized. Within the jacket  18  may be insulation  22  such as Aerogel (TM), MLI, foam, etc. The jacket  18  and heater  20  arrangement has been found helpful in eliminating variable external ambient conditions like wind, temperature, humidity, solar radiation, etc. which could otherwise introduce large errors. In other embodiments, the piping system  12  may be located indoors in a controlled environment rather than outdoors where the preferred embodiment was constructed and has been successfully utilized. In a controlled environment, the heater  20  and jacket  18  could possibly be omitted. 
     At the ends of the piping segment  12  are inner flanges  24 , 26  which may be welded, or otherwise connected to the piping segment  12 . Outer flanges  28 , 30  are connected to bellows  32 , 34  which allow for thermal expansion and contraction of the piping segment  12 . Shrouds  36 , 38  are connected to cold boxes  14 , 16 . External to the shrouds  36 , 38  are purge cans  40 , 42  which are filled with insulation, such as aerogel beads or other suitable material. The purge cans  40 , 42  may be secured with hose clamps, or otherwise. The cans  40 , 42  have caps  44 , 46  which may assist in retaining the insulation or temperature boundary within the purge cans  40 , 42 . 
     The outer flanges  28 , 30  allow the piping segment  12  to pass through while providing a controlled environment external to the piping segment  12 . The controlled environment may be maintained essentially at least up to the inner flanges  28 , 30 , if not all of the way up to the caps  40 , 42 . At various locations along the piping segment, temperature sensors  48 , illustrated as thermocouples are placed. The thermocouples may be placed on external surfaces of the piping segment  12 , or if internal portions are accessible, such as between pipe portions and insulation, or even within the pipe itself, some sensors may be placed there as well. 
     Pressure sensors  50 , illustrated as pressure transducers, may be utilized if internal portions of the piping segment  12  are accessible to assist in measuring pressure drops of cold vacuum pressure of the piping segment  12 . Pressure sensors  50  may also be utilized to monitor pressures within the flow of liquid or for other purposes. A vacuum valve  52  may accompany the pressure sensors  50 . 
     FIG. 2 is helpful in understanding the construction of the cold boxes  14 , 16  and the piping which supports them when utilized for cryogenic testing. A liquid supply  54  provides liquid nitrogen (LN2), or other appropriate fluid, such as oxygen, or chilled water, etc . . . through cutoff valve  56  to both the cold boxes  14 , 16 . Just past the cutoff valve  56  is a relief valve  58  for safety. The relief valve  58  in the preferred embodiment is set at about forty-five psig. The cold box  14 , or upstream box is where the liquid begins and flows to the dowstream box, or cold box  16  through the piping segment  12 . In FIG. 2, there are three piping segments  12  illustrated which may be tested simultaneously to reduce costs of conducting the tests. 
     The upstream box  14  has a box fill valve  60  and a test article fill valve  62 . A low pressure relief valve  64  is illustrated downstream of the test article fill valve  62 . The fluid from the box fill valve  60  is directed to the box  14  which is utilized to maintain a bath of fluid therein. The bath is utilized as a heat exchanger to cool fluid entering the piping segments  12 . The box  14  is open to atmospheric pressure so that the surface temperature of the liquid will be at saturated conditions and thus at the lowest temperature. This colder temperature fluid is utilized to cool the fluid from the supply tank  54  entering the piping segments  12  through coil  68  which is immersed in the bath. A gaseous nitrogen valve  70  may be utilized to precondition the test article if necessary. 
     The heat exchanger  72  which cools the fluid entering the piping segments  12  is located within the cold box  14 . The fluid then passes through an appropriate inlet valve  74 , 76 , 78  and past a pressure sensor  80  and into the piping segment(s)  12 . The cold box  14  is vented to atmosphere at vent  82 . A liquid level control valve  84  allows for liquid to be drained from the box  14 . A bottom drain valve  86  is also preferably included on the box  14 . 
     While cryogenic fluid, such as a liquid nitrogen (LN2), is the fluid utilized in a preferred embodiment, chilled water, or other fluids may also be tested with embodiments of the apparatus described herein. A fluid with a normal boiling point below ambient temperature may be used with the apparatus  10 . 
     Before describing the methods of using the apparatus  10 , it is helpful to understand the operation of the north cold box  16 . Liquid is directed from the supply  54  through a north cold box fill valve  88  past a relief valve  90  and through a fill isolation valve  92  into the downstream box  16 . Once again, the fluid is contained in a reservoir  94  to provide a controlled environment to reduce, and hopefully eliminate heat transfer from the ends of the piping segment  12 . If the reservoir is overfilled, there is a drain valve  96  which may direct the fluid out of the box  16 . Vent  98  is open to atmospheric so that the fluid in the reservoir  94  is at atmospheric pressure. A bottom drain  100  is also preferably installed in the cold box  16 . 
     Inside the downstream cold box  16  are pressure sensors  102  and relief valves  104  for each of the piping segment(s)  12 . The low pressure relief valves  104  are set as needed to ensure system safety. Outlet valves  106 , 108 , 110  are present as well as conduits to vaporizer coils  112 , 114 , 116  located external to the box  16 . Downstream of the vaporizer coils  112 , 114 , 116  are three way valves  118 , 120 , 122  which may be off or direct fluid toward one of two respective flow meters  124 , 126 , 128 , 130 , 132 , 134 . The relief valves  104  are preferably set at about 50 psig. 
     Since the cold boxes  14 , 16  may be similarly constructed, the primary difference in the preferred embodiment being the location of the coils  112 , 114 , 116  external to the box  16  instead of within the box as is coil  68  in box  14  for the reasons explained above, only one of the boxes is shown in FIG.  3 . Specifically a portion of box  16  is illustrated. The sensors  48 , 50 , 80 , 102  are connected to processor  136  which receives the data and calculates thermal performance parameters of the piping section  12 . One or more of the cold boxes  14 , 16  may have casters  140  which may be constrained by rails  142  to assist in responding to thermal expansion and contraction of the piping section(s)  12 . A V-shaped fully adjustable pipe support  144  is illustrated in FIG. 3 supporting the piping system  12 . The support  144  has a low conductivity surface indirectly contacting the piping section  12  such as a Teflon (TM) surface. 
     The test apparatus  10  may be operated for at least two testing procedures. First, a static boil-off test may be performed. When conducting a cryogenic boil off test, the box  14  is filled with liquid at atmospheric pressure. For this example, liquid nitrogen will be the liquid utilized. Accordingly, the temperature of the liquid at atmospheric pressure will be around minus  321  degrees Fahrenheit. Since the pressure in the supply  54  must be somewhat greater than atmospheric pressure so that the fluid will flow. As pressure increases, so does temperature. Accordingly, the temperature in the supply could be as high as minus  302  degrees Fahrenheit, if the liquid were only under about 2 psig of pressure. 
     Once the bath is established, test fluid is directed through the coil  68  in the heat exchanger  72  which sub-cools the liquid, to near atmospheric saturated temperature. A control flow of liquid as required for a specific test article of steady state condition is obtained through the piping segment  12 . The heater  20  establishes a controlled exterior environment to the piping segment  12 . The cold boxes  14 , 16  provide a controlled environment to eliminate any heat transfer into the piping segment  12  at the ends of the piping segment  12 . 
     As the fluid exits the piping system into the downstream cold box  16 , it is retained in reservoir  94  which cools the systems within the cold box  16  in a similar manner as the systems in the cold box  14  are cooled with the tank  66 . 
     After achieving steady state, a static boil off test may be performed. To perform the boil off test, the inlet test valve  76  and outlet test valve  108 , assuming a single piping segment  12  as shown in FIG. 3 are shut. The flow selector valve  120  is then set to direct gas to one of the two flow meters  128 , 130 . As the pipe warms up, gas separates from the liquid. The piping segment  12  is preferably angled slightly in a cryogenic boil off test, such as at about 2 degrees or greater, so that the gas is directed into the downstream cold box  16  and through the flow meters  128  or  130  to eliminate the formation of a gas pocket in the test article. 
     The flow meters provide a flow rate (m) to the processor  136 . The processor can utilize this data, along with such data as the heat of vaporization at saturation pressure (h), 198.6 J/g to determine the Heat leak rate (Q) since Q=h×m×(delta T). Heat flux rate may be calculated from the heat leak rate (Q) divided by the Mean Heat Transfer Area which is the outside area of the piping system (the insulation outside area, Ao) less the inside area (the sleeve outside area, Ai) divided by the natural log of Ao/Ai. Also, the flow rate (m) is useful in determining the apparent thermal conductivity (k). k=h×m×LN(Do/Di)/2×3.1416×L×(WBT—CBT) where LN is the natural log, Do is the liquid pipe diameter, Di is the Insulation pipe diameter, L is the cold mass length, WBT is the warm boundary temperature and CBT is the cold boundary temperature. Once the apparent thermal conductivity is calculated, the insulation effectiveness (R) may be determined as it is one divided by the apparent thermal conductivity. 
     In running tests, the R value changes as the temperatures within the pipe change and with time. Graphs of the k or R values and other effectiveness values, such as temperatures, pressures, heat transfer, etc. may be produced. The test apparatus  10  provides a convenient way to standardized the evaluation of piping segments  12 . In actual tests, the predicted values of R were attained. 
     While the boil off method is particularly attractive for determining R values for piping segments  12  utilized in cryogenic systems, a dynamic flow through test may also be performed for cryogenic as well as other liquids, such as chilled water, oil, food product, liquid solid, etc. To perform a dynamic flow through test, inlet test valve  76  and outlet test valve  108  are maintained open after reaching steady state. The temperature at the inlet and the outlet is measured. The difference in temperature is multiplied by the mass flow rate of the liquid flowing the piping and the specific heat value (h) to provide the heat leak rate (Q). The heat flux, apparent thermal conductivity and R value may be calculated as described above. 
     While the preferred embodiment relates to use with cryogenic fluids, other fluids, including chilled water, and even high temperature fluids, may also utilize a similar test apparatus  10 . When evaluating cryogenic pipelines and piping systems, they are typically insulated with high performance materials and have an insulating effectiveness in the range of R-50 to R-2000. When evaluating the cryogenic temperature range, around minus 321 degrees Fahrenheit to the ambient temperature range, around positive 100 degrees Fahrenheit, having a good estimate for the insulation value may be of critical importance. In the past, critical performance of insulation can be 10 to 100 times worse than for the insulation under ideal conditions. 
     The preferred test apparatus  10  can test three pipelines  12  at a single time, such as with a standard reference pipe in the middle of two proposed designs. Other embodiments can be constructed which can test any number of pipelines  12 . The data from the sensors may be compared to determine the performance of the three systems on a relative as well as a quantitative level. With the sensors shown, the apparatus  10  may also be utilized to perform flow analysis experiments, heat leak, pressure drop, multi-phase flow studies, fluid handling component leak measurement, thermal relief characterization, and bleves testing. 
     Numerous alternations of the structure herein disclosed will suggest themselves to those skilled in the art. However, it is to be understood that the present disclosure relates to the perferred embodiment of the invention which is for purposes of illustration only and not to be construed as a limitation of the invention. All such modifications which do not depart from the spirit of the invention are intended to be included within the scope of the appended claims.