You are on page 1of 47 Search inside document Designation: C — 89 Reapproved e1 Standard Practice for Determination of Heat Gain or Loss and the Surface Temperatures of Insulated Pipe and Equipment Systems by the Use of a Computer Program1 This standard is issued under the fixed designation C ; the number immediately following the designation indicates the year of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript epsilon e indicates an editorial change since the last revision or reapproval. Scope Determine the Precision of a Test Method3 1. This procedure is based upon an assumption of a X3.
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More C This data is presented for typical insulation thicknesses, operating temperatures, surface orientations facing up, down, horizontal, vertical , and in the case of pipes, different pipe sizes. The exterior surface temperature of the insulation is often shown to provide information on personnel protection or surface condensation.
However, additional information on effects of wind velocity, jacket emittance, ambient conditions and other influential parameters may also be required to properly select an insulation system. Due to the large number of combinations of size, temperature, humidity, thickness, jacket properties, surface emittance, orientation, and ambient conditions, it is not practical to publish data for each possible case, Refs 7,8.
This cost can be substantially reduced by the use of accurate engineering data tables, or available computer analysis tools, or both. The use of this practice by both manufacturers and users of thermal insulation will provide standardized engineering data of sufficient accuracy for predicting thermal insulation system performance. However, it is important to note that the accuracy of results is extremely dependent on the accuracy of the input data.
Certain applications may need specific data to produce meaningful results. In the rectangular coordinate system, Practice C can be applied to heat flows normal to flat, horizontal or vertical surfaces for all types of enclosures, such as boilers, furnaces, refrigerated chambers and building envelopes. In the cylindrical coordinate system, Practice C can be applied to radial heat flows for all types of piping circuits. In the spherical coordinate system, Practice C can be applied to radial heat flows to or from stored fluids such as liquefied natural gas LNG.
Infrared inspection, in-situ heat flux measurements, or both are often used in conjunction with Practice C to evaluate insulation system performance and durability of operating systems. This type of analysis is often made prior to system upgrades or replacements. The change in thermal conductivity with temperature is different for different materials, and for operation at a relatively small temperature difference, an average thermal conductivity may suffice. With the existence of radiation and convection modes of heat transfer, the measured value should be called apparent thermal conductivity as described in Terminology C The main reason for this is that the premise for pure heat conduction is no longer valid, because the other modes of heat transfer obey different laws.
Also, phase change of a gas, liquid, or solid within a solid matrix or phase change by other mechanisms will provide abrupt changes in the temperature dependence of thermal conductivity. For example, the condensation of the gaseous portions of thermal insulation in extremely cold conditions will have an extremely influential effect on the apparent thermal conductivity of the insulation.
With all of this considered, the use of a single value of thermal conductivity at an arithmetic mean temperature will provide less accurate predictions, especially when bridging temperature regions where strong temperature dependence occurs.
Computers are readily available to most producers and consumers of thermal insulation to permit the use of this practice. The range of application of these programs and the reliability of the output is a primary function of the range and quality of the input data.
Under this system, intermediate output guides the user to make programming adjustments to the input parameters as necessary. The computer controls the terminal interactively with program-generated instructions and questions, which prompts user response.
This facilitates problem solution and increases the probability of successful computer runs. Also, additional calculations may be desired to include other data such as system costs or economic thickness. No conflict exists with such modifications as long as the user verifies the modifications using a series of test cases that cover the range for which the new method is to be used. For each test case, the results for heat flow and surface temperature must be identical within resolution of the method to those obtained using the practice described herein.
To date, there is no accepted system of metric dimensions for pipe and insulation systems for cylindrical shapes. The dimensions used in Europe are the SI equivalents of American sizes based on Practice C , and each has a different designation in each country. Therefore, no SI version of the practice has been prepared, because a standard SI equivalent of this practice would be complex.
When an international standard for piping and insulation sizing occurs, this practice can be rewritten to meet those needs. In addition, it has been demonstrated that this practice can be used to calculate heat transfer for circumstances other than insulated systems; however, these calculations are beyond the scope of this practice.
Scope 1. The range and quality of the physical and thermal property data of the materials comprising the thermal insulation system limit the calculation accuracy.
Persons using this practice must have a knowledge of the practical application of heat transfer theory relating to thermal insulation materials and systems.
The computer program is intended for flat slab, pipe and hollow sphere insulation systems. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
The wind part is what I want to confirm. Is that what the standard really says? Also, if you examine the equation, it appears that the higher the average air film temp, the lower the Hcv becomes, approaching 0. The same holds for increasing pipe OD.