PROCESS INDUSTRY JARGON RECAP 3-2
I never really believed in
Somethin' said with a word
At least I never trusted what I was told or ever heard ...
But you rocked that all the way
You rocked what words can't say ...
You rocked it all away.
("Rock It All Away," by Dwight Yoakum, 2012)
PTOA Segment 63: A-OK!
Thermal Conductivity: The thermal conductivity of a material is the ability of a material to conduct heat through it.
Thermal conductivity is represented by the letter "k" in the mathematical expression that defines conduction heat transfer.
At the atomic level, a material whose atoms quickly get excited when exposed to heat will be described as a material that has a high thermal conductivity.
Materials that conduct heat fast are "good conductors." Copper is a good conductor.
At the atomic level, a material whose atoms take a long time to get excited when exposed to heat will be described as a material with a low thermal conductivity.
Materials that conduct heat slowly are "good insulators." Wool and atmospheric air are good insulators.
Thermal Conductivity Table: A look up table that alphabetically lists materials and their corresponding Thermal Conductivity Factors (aka "k" in the expression that defines Conduction Heat Transfer).
Access the Engineeringtoolbox conductivity table here.
The Thermal Conductivity Factors that are listed in the table have been determined by heat transfer scientists who dedicated their lives to modelling how conduction heat transfer works in the Universe.
The SI units of k are [Watt / (meters-deg K)]; the British unit equivalent is 0.5779 [BTU / (foot-hr- deg F)].
PTOA Segment 64: Like A Heat Wave .... Yeah Yeah Yeah Yeah
Convection: Flowing movement of fluids due to changes in temperature.
The change in temperature changes the density of the fluid.
Heavier, higher density fluid flows downward.
Lighter, less dense fluid flows upward.
Convection Heat Transfer=Heat Transfer via Convection: The Heat of Convection contained in a fluid is a product of the Heat Capacity of the fluid (aka Specific Heat of the fluid), the fluid's mass, and the Delta T between the hot fluid and the colder surroundings as shown in the below mathematical expression:
q (in Joules) = Cp * m * (Delta T)
Cp = "The Heat Capacity of one kilogram of the flowing fluid" (at constant pressure) aka The Specific Heat of the fluid.
Otherwise stated, the amount of heat absorbed by one kilogram of the fluid while its temperature increases, measured in Joules/kilogram-deg C.
A fluid with a high Cp absorbs a lot of heat per each degree increase in temperature.
One kilogram of pure water at 20 deg C will absorb 4182 Joules for each deg C temperature increase. That's a lot!
A fluid with a low Cp does not absorb as many Joules of heat while its temperature increases one degree C.
Access Table of Specific Heats (Cp) from Engineering Toolbox here.
m= the symbol that represents the mass in kilograms of the fluid experiencing convection heat transfer.
q = the symbol that represents the amount of heat transfer via convection, expressed in the SI units of Joules which can then be converted to English units of BTUs.
PTOA Segment 65: Go With The Flow
The previous PTOA Segment 64 was focussed on fluids that lose their heat via convection into heat sinks. These fluids are held captive in containers and have a defined mass.
The following definitions were generated in PTOA Segment 65 after tweaking the Convection Heat Transfer definition into a form that is useful for fluids that flow through pipes and are therefore not openly exposed to heat sinks.
Convection Heat Transfer Rate = Rate of Conduction Heat Transfer: The amount of heat transferred via convection into or out of a flowing fluid over a specific time interval, usually an hour.
The definition and mathematical expression for Convection Heat Transfer Rate is:
q/t (BTU/hr) = Cp * m/t * (Delta T)
In a shell and tube heat exchanger, a hot flowing fluid transfers heat into a colder flowing fluid; each fluid flows at their own mass flow rate and each fluid has their own unique specific heat capacity, Cp .
The Delta T is adjusted as necessary depending upon if the convection heat transfer rate applies to the flowing fluid that is being heated up or cooled down.
The units of Convection Heat Transfer Rate (q/t) are Joules/hr or BTU/hr.
m/t: Mass flow rate of a flowing fluid measured in kilograms or pounds per hour.
q/t: See Convection Heat Transfer Rate defined above.
PTOA Segment 66: The Mother of All Heat Transfer
Heat Transfer via Radiation = Radiation Heat Transfer: Heat that is conveyed via electro magnetic beams that emanate from a point source that appears to be emitting light in all directions.
Radiation is easy to distinguish from convection because the electromagnetic beams (not waves) travel in straight lines in all directions from the emitting source.
Radiation heat transfer occurs when an exposed surface area lies in the pathway of the beams.
Rate of Radiated Energy: The amount of radiated heat over a specified interval of time. The Rate of Radiated Energy depends upon:
- how hot the emitting source is in the first place, measured in absolute temperature scale Rankin (which means it is ouch-chee-wa-wa way hot).
- how much of the emitter's surface area is actively radiating energy in the direction of the obstacle.
The definition and mathematical expression for Radiated Heat Energy (q with a dot over it) is below:
PTOA Readers and Students DO NOT NEED TO KNOW the definition. Fully understanding how radiation heat transfer works is beyond the scope of knowledge any Process Operator needs to have.
The point of focussing on the definition of Radiation Heat Energy is to note that it also includes at Hot Temperature for a driving force and has a surface area component as the other modes of heat transfer have.
The combined effect of the strange Greek letters "ε" and "α" in the definition characterize the material of the surface area that enters the pathway of the radiated beams. Ergo, the Greek letters have an analogous role to "k" in conduction heat transfer and "Cp" in convection heat transfer.
Man! That was a lot of Jabberwocky!
©2015 PTOA Segment 00090
PTOA Process Industry Jargon Recap 3-2
You need to login or register to bookmark/favorite this content.