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07062013, 03:24 PM #1
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.
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About the ASHRAE 2010(SI), chaper1 (halocarbon refrigeration systems), it gives some tables, but I don’t 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

08062013, 03:58 AM #2
Re: how to calculate the suction,discharge,and liquid line capacities
3. How to calculate the capacities for suction, discharge, and liquid lines?
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 DarcyWeisbach 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 DarcyWeisbach equation to get the Reynolds number, friction factor.
But according to the MOODY diagram, the three parameters( Reynolds number, friction factor and relative roughness) don’t match to each other.
I don’t know what’s wrong with my calculation or maybe wrong from beginning?
I attach the calculating excel file.
I’m not native English speaker, excuse me my expression is not quite concise.
Any comments would be appreciate.