Experimental

Figure 3a: Bare Tracer

Figure 3b: Cemented Tracer

The main deliverable was to obtain the minimum temperature at which the process fluid had to enter the pipeline, but other information such as the wall temperature and steam consumption were also important.

The interface designed for the simulation is shown in Fig. 3c and was written in Microsoft Excel:

Figure 3c: Interface

The detailed design and calculations can be found in Appendix 1. The design was done following an unconventional approach, in an attempt to make as few assumptions as possible.

Most of the equations were fundamentally derived, but some equations were employed from other sources. (See References)

All the necessary equations were developed and simplified to eliminate ambiguity. The equations were then solved simultaneously and by making use of iterations.

The inputs to the simulation were highlighted in yellow, on the left side of the page, and the outputs were highlighted blue, on the right hand side, to eliminate ambiguity in deciding which were inputs and which were outputs.

The inputs section mostly made use of drop-down menus to facilitate data input, and mostly made use of referencing techniques to look up the necessary values used in the calculations. For example, the user was only required to choose the NPS of the process fluid pipe, and the schedule number, and the program automatically looked up the outer diameter, inside diameter and wall thicknesses from a table containing accurate standard values for pipe sizes.

Also, the user was only required to specify the insulation material type, steam pressure, and ambient temperature, which the program used to calculate an average insulation temperature, and interpolate between different k-values, to obtain the specific thermal conductivity at that specific temperature, since thermal conductivity is temperature dependent. The program also used the lagging emissivity, together with the ambient temperature, surface temperature and wind velocity, to calculate an exact value for the surface film coefficient on the outside, which needed to be very accurate.

The program was also able to calculate a maximum surface temperature, to ensure safety protection for personnel, as the surface temperature, by standard, is not allowed to exceed 60 ºC. Temperatures higher than this would result in injury caused by touching the outside surface.

The steam consumption was also calculated by determining the heat loss from the system for a certain length of pipe. The steam is invariably subject to heat loss, and thus condensation, when sufficient heat has been lost. This corresponds to the maximum length of a tracer. Fresh, saturated steam then needs to be re-introduced into the system, to ensure efficient operation, and a steam trap needs to be installed at the end of the maximum length, to collect all the condensate which has formed. The condensate may be recycled to create new steam.

The simulation made use of macros, in the sense that the program automatically performs the calculations necessary to converge the answers to a final answer, by simply requiring the user to press a shortcut key.