Why do we never get an answer
When we're knocking at the door?

("Question," by J. Hayward of the Moody Blues, 1970)

WRAPPING UP THE PTOA's
PV PRESSURE INTRODUCTION FOCUS STUDY

PTOA Readers and Students who are reading the PTOA Segments in the intended sequential order ...

are already aware that PTOA Segments #145, #146, and #147 included Do It Yourself (DIY) challenges that helped explain some of the PV Pressure fundamentals.

The answers to those challenges are included in this PTOA Segment #156.

However ...

PTOA Readers and Students who are reading the PTOA Segments in the intended sequential order probably noticed that the review of SI (metric) and English conversion units was skipped... so that subject will be covered first.

 

CONVERTING BETWEEN ENGLISH AND SI UNITS

PTOA Segment #148 formally introduced and compared the English, SI, and metric measuring units.

Why was the discussion on conversion factors delayed until the 148th PTOA Segment?

There was no need to bring up how to covert between the English and SI (metric) measuring units for the PV Temperature.

 

PTOA Readers and Students have grown up observing a variety of Temperature scales posted throughout society ... many that show the correspondence between the °F and ° C scales.

 

 

Thus, PTOA Readers and Students have grown up with a cognitive awareness about the differences between these two Temperature scales.

 

 

 

When it comes to the PV Pressure, converting between the English and SI (metric) measuring systems is not as straightforward.

By now PTOA Readers and Students can probably predict that some of the confusion equating the English to SI (metric) measuring systems is due to Sir Isaac Newton creating confusion between the meaning of a lb_f and a lb_m.

Until the difference between a lb_f is delineated from a lb_m, the person performing the conversion exercise may erroneously attempt to convert a lb_m (a unit of Mass) into a kPa (the SI/metric unit of Force).

And this happenstance conveniently segues into another conversion challenge:

The SI (metric) system avoided mistaking Mass for Force by using "derived definitions"...

for example "Newton" is the SI measuring unit for Force and ...

the SI measuring unit for Pressure is the "Pascal."

Hence ... unlike the PV Temperature ...

It is simply more challenging to acquire an intuitive understanding of the correspondence between the English and SI (metric) systems used to measure the PV Pressure!

A PI that indicates BOTH psi and kPa units for Gauge Pressure certainly helps to correlate the relative difference between the English and SI pressure-measuring units.

 

 

And of course, nowadays there "an app" for instant conversion between English and SI measuring units.

Still ...

PTOA Readers and Students are living in a globalized world and should devote some effort to gain a sense of the quantitative difference between the measuring systems.

After all ...

Even traveling "abroad" from the USA to processing plants located in Canada and Mexico requires a working knowledge of metric units applied in the processing industries.

 

Ergo,

PTOA Segment #48 included a handy dandy conversion chart that has served Your Mentor well throughout the years since the days of the dinosaur... when conversion calculations were done by hand and brain!

 

DIY ANSWERS FOR THE PTOA'S
PV PRESSURE INTRODUCTION FOCUS STUDY

DIY ANSWERS for PTOA Segment # 145:

Determine Fred's Specific Gravity and, based on the answer, state whether Fred will sink or float in water.

Fred's Mass = 175 lb_m (79 kg)

Note: Fred's mass was inferred from his weight!

Fred's Volume = 6.25 ft * 1.5 ft * 1 ft = 9.38 ft³  (0.26 m³)

Fred's Density = 175 / 9.38 = 18.69 lb_m/ft³  (304  kg/m³)

Fred's Specific Gravity = 18.7 lb_m/ft³ ÷ 62.4 lb_m/ft³ = 0.30

or in SI/Metric Units           304 kg/m³  ÷  1000 kg/m³   = 0.30

Fred's Specific Gravity is less than 1.0 so Fred will float in water!

NOTE: Specific Gravity is a dimensionless number ... but STILL very useful as it instantly reveals the relative density of the two liquids.

 

DIY ANSWERS PTOA Segment #146

#1. Determine the Pressure on the hull of the sunk U-96

     Pressure (psi)  = SG_seawater * 0.433 / l ft * h (in ft) =

The SG_seawater is the same for the Kursk:  SG =1.2

Pressure (psi) =1.2 * 0.433 * 919 = 477.5 psi  (3292 kPa)

NOTE: Even the Pressure exerted by the liquid in an extremely large container ... like the ocean ... is easy to calculate!

 

#2. What are the maximum pressures exerted by 3 feet and 9 feet of water ... the depth of the shallow and deep ends of a swimming pool?

Pressure (psi) = SG * 0.433 * h

Pressure at 3 feet = 1.0 * 0.433 * 3 = 1.3 psi

Pressure at 9 feet = 1.0 * 0.433 * 9 = 3.9 psi

NOTE: The volume of the contained water in the swimming pool does not impact the Pressure that the liquid exerts on the sides and bottom of the swimming pool.

 

DIY ANSWER PTOA Segment #147:

Why is the dam shown in the schematic wider at the base than at the top?

The Pressure Profile of the head pressure exerted on the reservoir-side wall of the dam would

• Indicate 0 psig (or 14.7 psia) at the surface of the water and
• A growing amount of pressure exerted on the dam up to
• The maximum head pressure which would be exerted on the reservoir-side wall of the dam at the bottom of the reservoir.

The trapezoid structure of the dam with the wide base at the bottom geometrically limits the length of the head ... and hence Pressure ... at each level of the dam.

NOTE: The outcome of the trapezoidal construction shape is a less severe Pressure Profile impacting the dam as compared to the pressure that would be exerted on the flat face of a square or rectangle dam structure.

 

TAKE HOME MESSAGES: PTOA Readers and Students have finished The PTOA PV Pressure Focus Study Area.

Onto the relationship between the PV Pressure with the PV Temperature, PV Flowrate, and PV Level!

©2017 PTOA Segment 0156
PTOA Process Variable Pressure Focus Study Area
PTOA Introduction to PV Pressure Focus Study

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