Abbreviations
and Definitions:
Let's start
with some abbreviations we use in our formulas:
AC = Air Changes ( Usually expressed in changes per hour or per minute. Air change
is the number of times the air within a structure is exhausted and replaced during a specified period such as hour or minute).
Absolute Pressure - This term
refers to th pressure measured on the scale that has it's zero point at approximately 14.7 psi (at sea level) below atmospheric
pressure. it is a true measurement of all the pressure, rather than just the pressure above atmospheric.
Absolute Temperature -
Similar to absolute pressure, absolute temperature has its zero point where no heat exists. This is approximately 460°f
below 0°f. An absolute degree is the same size as a Fahrenheit degree. The freezing point of water (32°f) is about
492°f above absolute zero, or 492° absolute.
Air/Fuel
Ratio (AFR) - AFR is the ratio of the weight of air to the
weight of fuel in a combustible mixture. AFR is critical in the proper functioning of an engine.
Ambient -
Ambient refers to the surrounding atmospheric pressure and temperature.
Atmospheric - This word has recently taken on the
connotation of an engine operating without any form of super-charger. My lawn mower has an atmospheric engine.
Boost - Boost is the pressure
above atmospheric, measured in the intake manifold.
Boost Threshold - Same as Boost Point. This is the lowest engine
RPM at which the turbo-charger will increase power over the engines atmospheric equivalent. More simply put, the lowest RPM
at which noticeable boost can be achieved.
Bypass Valve - The bypass valve permits a bleed of flow around the
turbo-charger when the engine is under boost.
BTUH =
British Thermal Units per Hour. A measure of heat or the
absence of heat ("cold" can be defined as the absence of heat) in a volume of air or space. BTUH is not commonly
used in evaporative cooling terminology but necessary to calculate heating and mechanical refrigeration. (It is most often
used as "heat of vaporization = 1043 BTU/lb in the formula for calculating evaporation rate and standard CFM).
Clearance Volume - Combustion
chamber volume above the piston at top dead center is called clearance volume.
(S)CFM = (Standard) Cubic Feet
per Minute. Usually referred to as simply CFM. This is a necessary ingredient in any formula involving evaporative cooling.
It is a measure of air volume movement in one minute.
Compression Ratio - This is the displacement volume plus clearance
volume divided by the clearance volume.
Compressor - For this writing, the compressor is the air pump itself.
The front half of the turbo-charger, through which the intake air passes. it is also frequently refereed to as the "
Cold side" of the turbo-charger.
Compressor Efficiency (Ec) -
Efficiency is the ratio of what really happens to what should happen. In the case of the compressor, measurement of the temperature
gain caused by compressing the air exceeds what thermodynamic says it should be. Compressor efficiency converts calculated
temperature gains to real temperature gains.
Compressor Surge - Compressor surge occurs when the throttle is slammed
shut and air is caught between a pumping turbo and the throttle plate. This air blasts its way backward out the front of the
turbo-charger. When this happens, there is a suddenly room for more air in the manifold, and air is pumped back in my a still
pumping turbo-charger. The throttle is still closed, so the air again blast back out through the front of the turbo. This
continues until the turbo losses enough speed for leak back around the compressor to dampen the air oscillations. Compressor
surge can als occur under boost, if too much boost pressure is present with low airflow through the system. The chirping sound
heard from the turbo when lifting off the throttle while operating under boost results from the oscillating air volume. This
noise is suppressed by the bypass valve.
Crossover point - This is the point at which manifold boost pressure
equals turbine inlet pressure.
Detonation - Detonation is spontaneous combustion of the air/fuel mixture ahead of the flame front. When pressure
and temperature exceeds that required for controlled combustion, the mixture auto-ignites. The metallic pinging sound is the
resulting explosion's shock wave colliding with the cylinder walls.
Design - This term is used in many ways to define the parameters of an application or
specifications. Some common uses are as follows: IDb = Indoor Dry Bulb. ODb = Outdoor Dry Bulb. IWb = Indoor Wet Bulb. OWb
= Outdoor Wet Bulb. EDb = Entering Dry Bulb. LDb = Leaving Dry Bulb. EWb = Entering Wet Bulb. LWb = Leaving Wet Bulb. This
term is often used in conjunction with "conditions" such as "Climate Design Conditions". In evaporative
cooling, climate data is considered to be Dry Bulb and Wet Bulb levels. It would require a "Psychometric Chart"
to locate the juncture of the Dry Bulb and Wet Bulb lines to find the grains or pounds of moisture per pound of dry air or
relative humidity (RH). Refer to Table 1 for a psychometric chart digitalized for easy reading of relational elements of Db,
Wb and RH.
Displacement Volume - is defined in several ways: 1. The swept volume
of the cylinder; 2. The area of the bore times the length of the stroke; 3. Total engine displacement divided by the number
of cylinders.
Draw-Through - This indicates that the throttle is on the inlet side of the turbo compressor.
Dry Bulb temperature (Db or DB) - Measurement (usually in Fahrenheit)
of temperature taken by a standard thermometer or similar thermal indicator.
End Gas - The end gas is the last part of the air/fuel mixture to
burn. It's importance to a turbo-charged engine is paramount, because it is this end gas in which detonation usually occurs.
External Static Pressure - Expressed in inches, water column. The
pressure against which the air flow must move. The pressure external to the cooling unit opposing air flow (i.e. restrictive
ductwork, etc.)
Fahrenheit (f
or F) - Temperature conforming to a thermometric scale on which water boils at 212 degrees and freezes at 32 degrees.
Named after Gabriel D. Fahrenheit, 1736.
Fv (or) FV = Face Velocity - Face velocity or "air velocity" is the measure expressed in feet per
minute (FPM) the air is moving at the entry side (face) of the cooling media. This is another necessary ingredient in any
formula in evaporative cooling to determine efficiency.
FPM = Feet Per Minute - The measure of speed (velocity) of the air
.
Gallons
per Hour (GPH) - A measure of liquid (usually water) moving during one hour.
Gallons per Minute
(GPM) - A measure of liquid (usually water) moving in one minute.
IN. HG - This phrase reads " Inches of mercury" and is
the measure of pressure on yet a different scale. In this project, in-Hg will reefer to vacuum in the intake manifold, and
the scale works downward toward atmospheric pressure. For example, idle speed vacuum is usually about 18in.Hg, and as throttle
is applied, the vacuum goes toward 0 gauge, which is atmospheric pressure.
Inertia - The tendency of a body to resist
acceleration; the tendency of a body at rest to remain at rest or of a body in straight line motion to stay in motion in a
straight line unless acted on by an outside force. Resistance or disinclination to motion, action, or change.
Inter-cooler - An inter-cooler
is a heat exchanger placed between the turbo and the engine to remove heat from the air exiting the turbo-charger when operating
under boost. Inter-cooler are also called charge air coolers.
Inter-cooler Efficiency (EI) - An Inter-cooler's efficiency
is measured by how much heat it removes relative to the heat added by the compressor.
Inertial Load - Internal loads
are those created by weight and acceleration. A heavier piston creates a greater inertial load. likewise, an increase in RPM
means greater acceleration and, thus a greater inertial load.
Lag - Lag is the delay between a change in throttle and the production
of noticeable boost when engine RPM is in a range in which boost can be achieved.
Lean - lean means not enough
fuel to achieve the correct air/flue ratio for the existing conditions.
Non-sequential Fuel Injection - EFI that pulses independently of valve position is non sequential.OEM - Original Equipment manufacturer; the company the built it in
the first place.
Power - Strictly speaking,
power is the result of how fast a certain amount of work is done. In automotive context, power is the product of torque at
any specific RPM times that RPM.
Power Load - This is the load
induced into all engine components by pressure created by the burning gases.
Pre-Detonation - This is a meaningless phrase and should not be included here or anywhere else.
Pre-Ignition - Pre-ignition refers to spontaneous combustion of the
air/fuel mixture prior to the spark.
Pressure ratio - The ratio
of absolute boost pressure to atmospheric pressure.
Pulse Duration
- The amount of time, measured in thousandths of a second (msec), that an electronic fuel injector is held open on
any single pulse. Pulse duration is a relative measurement of the amount of fuel delivered to one cylinder per combustion
cycle.
Reversion - Reversion occurs when some of the burned exhaust gases
are pushed back into the combustion chamber and intake system during valve overlap. This is caused by exhaust manifold pressure
exceeding intake pressure or by shock waves in the exhaust ports and manifold.
Relative Humidity (RH) - Expressed in percent. The percent of water vapor in the
air compared to the amount of water vapor the same air could contain. (i.e. 15% RH indicates the air is 15% saturated with
water vapor)
Rich - A condition that exist when
too much fuel is present to achieve a maximum -power air/fuel ratio.
Saturation Efficiency (SE) - This is the percent of the Wbd (Wet Bulb Depression)
achieved by the cooling process. I.E. At 100 degrees (f) Dry Bulb and 70 degrees (f) Wet Bulb, the Wbd would be 30 degrees
(f). If the actual temperature drop measured at the discharge side of the media was 73 degrees (f), the percent of saturation
efficiency would be 90%. This means that the air passing through the media has been saturated with water vapor (moisture)
to 90% of its maximum. "Cooling Efficiency" is the same as Saturation Efficiency and is most often used to define
the performance level of the media. Also called just "efficiency".
Sequential Fuel Injection - A fuel injection pulse timed to discharge fuel when the
intake valve is in the most advantageous position is called sequenced. It pulses the injectors in the same sequence as the
firing order.
OEM - Original Equipment manufacturer; the company the built it in
the first place.
Power - Strictly speaking,
power is the result of how fast a certain amount of work is done. In automotive context, power is the product of torque at
any specific RPM times that RPM.
Power Load - This is the load
induced into all engine components by pressure created by the burning gases.
Pre-Detonation - This is a meaningless phrase and should not be included here or anywhere else.
Pre-Ignition - Pre-ignition refers to spontaneous combustion of the
air/fuel mixture prior to the spark.
Pressure ratio - The ratio
of absolute boost pressure to atmospheric pressure.
Pulse Duration
- The amount of time, measured in thousandths of a second (msec), that an electronic fuel injector is held open on
any single pulse. Pulse duration is a relative measurement of the amount of fuel delivered to one cylinder per combustion
cycle.
Reversion - Reversion occurs when some of the burned exhaust gases
are pushed back into the combustion chamber and intake system during valve overlap. This is caused by exhaust manifold pressure
exceeding intake pressure or by shock waves in the exhaust ports and manifold.
Relative Humidity (RH) - Expressed in percent. The percent of water vapor in the
air compared to the amount of water vapor the same air could contain. (i.e. 15% RH indicates the air is 15% saturated with
water vapor)
Rich - A condition that exist when
too much fuel is present to achieve a maximum -power air/fuel ratio.
Saturation Efficiency (SE) - This is the percent of the Wbd (Wet Bulb Depression)
achieved by the cooling process. I.E. At 100 degrees (f) Dry Bulb and 70 degrees (f) Wet Bulb, the Wbd would be 30 degrees
(f). If the actual temperature drop measured at the discharge side of the media was 73 degrees (f), the percent of saturation
efficiency would be 90%. This means that the air passing through the media has been saturated with water vapor (moisture)
to 90% of its maximum. "Cooling Efficiency" is the same as Saturation Efficiency and is most often used to define
the performance level of the media. Also called just "efficiency".
Sequential Fuel Injection - A fuel injection pulse timed to discharge fuel when the
intake valve is in the most advantageous position is called sequenced. It pulses the injectors in the same sequence as the
firing order.
Static
Pressure Drop - Expressed in inches, water column. The amount of pressure required to push the air through the media
as measured with a magnehelic gage. The difference between the pressure of the air flow at the intake of the media and the
discharge side of the media. The measure of pressure for any component through which air flow is measured at the intake and
discharge. This is an important consideration in some evaporative cooling applications.
Supercharge - To force more
into an engine than the engine can breathe by itself is to supercharged it. A supercharger is a device that does this, it
may be driven by belts, gears or a turbine. When driven by a turbine, it's called turbocharging.
Thermal Load - On this site, we will take the rather narrow definition
of heat added to the system by the turbo-charger. This comes from heat produced in the air that is compressed by the turbo
and the mixture heat increase due to reversion.
Throttle Response
- A change in the speed and torque of an engine brought about by change in the throttle position is called throttle
response.
Torque - The amount of twisting force
provided by a turning shaft is called torque. It is measured in foot-pounds, inch-pounds and even Newton-meters.
Turbine - The turbine is a fan driven by the engine's exhaust
gases. it is often called the "hot" side of the turbo-charger.
Turbo-Charger - A turbo-charger is a super charger driven by a turbine.
Under Boost - When a system has greater than atmospheric pressure in the intake manifold, it is operating
under boost.
Volumetric Efficiency (ev) - This is the ratio of the number of molecules of air that actually
get into a combustion chamber to the number of molecules in an equal volume at atmospheric pressure.
Waste-gate - The waste-gate is a boost-pressure
-activated valve that allows only enough exhaust gas into the turbine to achieve desired boost. The waste-gate routes the
remainder of the exhaust gas around the turbine and out the tailpipe.
Water gauge or Water Column in Inches ( WG or w.g. or WC or w.c.) This is a measure
of static pressure. A Pilot Tube is used to take this measurement. The Pitot Tube is a curved (U-shaped) glass tube with a
prescribed amount of water and a scale. The tube is hollow. When air is blown into one end the water column will be forced
up the other side to some level. The level to which the column of water rises is a measure, in inches, of the pressure of
the force required.
Wet Bulb Temperature (wb or WB) - The lowest temperature that can be reached by evaporatively
cooling the air. This measurement is usually taken with a "sling psychrometer". This device is a standard thermometer
with a "wet sock" over the sensor bulb. The psychrometer is slung in a circular motion rapidly enough to cause evaporation
to occur around the sensor bulb to drop the temperature to it's lowest point possible with the evaporation process.
Wet Bulb Depression (wbd or WBD) - The difference between the Dry Bulb and the Wet Bulb temperatures. This
temperature is the total amount of cooling available through the evaporative cooling process. At 100% cooling efficiency,
the temperature drop would be equal to the Wet Bulb Depression. Also known as Wet Bulb Differential.
Wet
Bulb Temperature (wb or WB) - The lowest temperature that can be reached by evaporatively cooling the air. This measurement
is usually taken with a "sling psychrometer". This device is a standard thermometer with a "wet sock"
over the sensor bulb. The psychrometer is slung in a circular motion rapidly enough to cause evaporation to occur around the
sensor bulb to drop the temperature to it's lowest point possible with the evaporation process.
Wet Bulb Depression (wbd or WBD) - The difference between the Dry Bulb and the Wet Bulb temperatures. This
temperature is the total amount of cooling available through the evaporative cooling process. At 100% cooling efficiency,
the temperature drop would be equal to the Wet Bulb Depression. Also known as Wet Bulb Differential.
Leaving Dry Bulb = [ODb - (SE x (Odb-OWb)]
Leaving Wet Bulb =
Normally considered same as entering Wb.
Wet Bulb Depression = ODb - OWb
Evaporation Rate =
[CFM x WBd x (SE / 8700)] ( this is simple method)
Bleed - Off Rate = Evaporation Rate x .20 (prox)
(Recirculation)
Water flow Rate = 3 times the evaporation rate (prox)
Standard CFM = Sensible BTU/hr / (1.08
x (IDb - Db) x Density Ratio
Where IDb = Indoor Design Dry Bulb (f)
CFM = Standard CFM / Density
Ratio
BTU = CFM X Delta T x 1.08
Density Ratio = 1.325 x Barometric Pressure / (Db(f)
Water
weight (US gallon) = 8.33 pounds per gallon (based on distilled water)
Water volume (US gallon)
= 7.481 gallons per cubic foot
Water weight (US gallon cubic foot) = 7.481 x 8.33 = weight of cubic
foot of water (62.288#)
Face Area = Width x Height of open face area through which air will flow (expressed
in square feet.)
Face Velocity = CFM / Face Area (Sq Ft) (expressed in Feet per minute
(FPM).
