Total System Heat Loss Measurements

    Published: Jan 1983

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    Excessive heat losses from insulated systems in service raise critical design questions when compared with performance data obtained from individual insulation specimens tested in the laboratory. In many cases, excessive heat loss is caused by the incorrect design assumption that total system heat loss is equal only to that through individual insulation sections. However, additional heat losses result from the following sources: (1) free convective flows through the insulation system, (2) uninsulated surface, (3) insulation joints, (4) conduction paths that pass through the insulation, such as support fect, and (5) fluid leaks from the insulated system, such as those through valves and pump packing.

    The object of the present work was to verify analytical methods for predicting total system heat loss. These methods predicted that some of the heat loss components listed above—in particular, free convective air flows—can be significant. Verification was accomplished by quantifying the major heat loss components from a relatively large system: a 6.55-m (21.5-ft)-high steam-water pressurizer operating at 280°C (540°F) and insulated with all-metallic reflective insulation.

    Experimentally verified analytical models were used to predict heat losses throug the insulation and its joints, and the convective air flow. The other heat loss components were calculated from measured cold surface heat fluxes, hot surface and air temperatures, and changes in water level in the pressurizer. The expected total system heat loss was compared with the total system heat input by measuring the steady-state power input.

    Significant results from the analysis and experiment included: (1) the insulation heat loss was only 39 percent of the total system loss, (2) the convective air flow was a major heat loss at 33 percent of the total, as previous analyses had indicated, and (3) the heat balance agreed to within 11 percent of the measured power input.

    Since the additional heat loss components exist to some extent for all insulated systems, regardless of the type of insulation, they must all be considered in the design stage if the desired system heat loss is to be achieved.


    insulation, thermal insulation, reflective insulation, insulation system, heat loss, system heat loss

    Author Information:

    Allmon, BA
    Research Engineer and Manager, Experimental Apparatus Section, Research and Development Division, Babcock & Wilcox Company, AllianceOhio,

    Rausch, DA
    Marketing Manager, Diamond Power Specialty Company, Mirror Insulation Unit, Lancaster, Ohio

    Wahle, HW
    Research Engineer and Manager, Experimental Apparatus Section, Research and Development Division, Babcock & Wilcox Company, AllianceOhio,

    Committee/Subcommittee: C16.30

    DOI: 10.1520/STP29491S

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