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  1. #1
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    Question how to calculate the suction,discharge,and liquid line capacities



    Hi, all
    I am new and reading some books by myself, but something is difficult to understand, casually, I found this forum and people here are very kind.
    截图00.jpg截图01.jpg
    About the ASHRAE 2010(SI), chaper1 (halocarbon refrigeration systems), it gives some tables, but I donít understand how the data calculated out:
    1. Tables 3 and Table 4 both list suction line capacities under -40 and -30 SST, but why the corresponding Δp are different(marked in red), for example 196 in Table3 while 121 in Table 4 at SST=-40 ℃?
    The pressure loss Δt=0.04k/m, I calculate the correspondingΔp, for example, =saturated pressure(@-40℃)- saturated pressure(@-40.04℃), right?

    2. In the Table3, the discharge lines Δt=0.02k/m, but where does Δp=74.90 come from? And also liquid linesΔp=749?

    3. How to calculate the capacities for suction, discharge, and liquid lines?

    Best regards and thanks



  2. #2
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    Re: how to calculate the suction,discharge,and liquid line capacities

    3. How to calculate the capacities for suction, discharge, and liquid lines?
    About the suction line capacity, I think the calculation procedure maybe:

    the capacity Q=cross section area of the pipe x velocity x density x unit capacity( enthalpy difference)

    according the SST and refrigeration properties, we can get the density and the unit capacity.

    About the velocity, because we know the corresponding pressure drop( Δt=0.04k/m), use the Darcy-Weisbach equation and Moody diagram to calculate out.

    But the result I calculate is far away the table data.

    So I reverse the calculation, use the capacity listed by the Table3 to get the velocity, and then use the Darcy-Weisbach equation to get the Reynolds number, friction factor.

    But according to the MOODY diagram, the three parameters( Reynolds number, friction factor and relative roughness) donít match to each other.

    I donít know whatís wrong with my calculation or maybe wrong from beginning?

    I attach the calculating excel file.

    Iím not native English speaker, excuse me my expression is not quite concise.

    Any comments would be appreciate.
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