effective mixture temperature of the blowdown section, whilst downstream, both gas and metal temperatures are assumed to be at 5˚C due to heat-tracing. Downstream of the orifice, there is a 5.9m long 3-inch diameter pipe modelled as a vessel with the equivalent volume. Figure 3-1 shows the variation of inner wall metal temperature and gas temperature upstream of the blowdown valve as depressurisation commences when the blowdown valve fails open. The inner wall temperature downstream of the blowdown orifice falls to a minimum of -20˚C during blowdown although the gas temperature falls down to as low as -87˚C at the start of depressurisation. The maximum Mach number observed during the depressuring scenario is 0.36 at the start of depressurisation. Note that this maximum Mach number is based on the 2-inch diameter of the 3”x2” reducer downstream of the 3-inch pipe.

Что в данном контексте означает Downstrean и upstream?

Спасибо за ответ!