The 0.75 lb smooth can is guided along

As a rule of thumb, the chart below can offer some guidance for determining the system effect for this situation. Remember the coefficients in the chart are only an estimate.

System Effect Table. Distance between Riser and Elbow. System Effect Coefficient K. The diagrams below show system effect factors for straight through elements and turning elements. The following formula should be used to calculate the pressure caused by system effect:. Straight Through Flow Turning Elements. The following diagrams show proper and improper methods of constructing ductwork:.

A fan performance spec is given as a Fan Total Pressure or a Fan Static Pressure which can handle a certain flow rate. Most manufacturers' performance charts are based on Fan Static Pressure. Fan total Pressure is the pressure differential between the inlet and the outlet of the fan. It can be expressed in these terms:. For Exhaust Systems with resistance only on the inlet side, the fan static pressure is:. For Supply Systems with resistance on the outlet side, the fan static pressure is:.

P v system outlet can be assumed to be 0. The diagram below illustrates the difference between exhaust and supply systems. Break the system into sections. A new section occurs at:. Calculate losses for each section. Begin at the section farthest from the fan and work towards the fan. For each section:. Write down or calculate all known variables. Air Flow Rate. Duct Cross-Sectional Area of the section. Center-Line Length of the section. Air Velocity through the section.

Velocity Pressure. Write down or calculate all pressure losses in the section. Incurred by hoods, ESPs, filters, dampers, etc.. Occur through elbows, transitions, tees, or any other type of fitting. Be sure to factor in System Effect! Sum up the Component, Dynamic, and Frictional Pressure for the section. Sum up the pressure losses for all of the sections. Standard Air Density,. Frictional losses based on galvanized metal duct with 40 joints per ft. Correction for "Non-Standard" Duct Material.

If material other than galvanized metal is used in parts of the system, you will have to adjust for the difference in the material's roughness factor. This means the Friction Chart typically used to determine frictional losses cannot be used and you must use a variation of the Darcy-Weisbach Equation.

See the section titled Equations for more information on this equation. Correction for Density. Correction for Moisture. The first step is to break the system into sections. Section 3 runs from the Bullhead Tee to the Exhaust Fan. Now calculate the pressure losses for each section. Section 1. Loss Calculations. Component Losses. Hood Loss. Look up from manufacturer hood static pressure curves. Here is a link to the Hood Static Pressure Calculator.

Frictional Losses. Use the Friction Chart to look up the pressure loss per ft of duct. Dynamic Losses. Mitered Elbow. Bullhead Tee. Look up coefficient from Appendix 3 - Bullhead Tee Curves. Some general rules for bullhead tees:.

For simplicity and ease of graphing, we round. The important thing is to know how to use the curves and get a reasonable value for K U. Now we can calculate the pressure drop contributed by the bullhead tee for Section The total pressure loss for Section 1 is:. Section 2. The total pressure loss for Section 2 is:.

Balance by Design. Note that the pressure loss of Section 2 is greater than the loss of Section 1. To balance the system by design increase the air flow rate in Section 1 to bring it up to the higher pressure loss of Section 2. To correct the air flow rate for Section 1 use the Fan Laws :.

Section 3. Total pressure loss for Section 3 is:. Total Pressure Loss of System. Since the pressure loss of Section 2 is greater than that of Section 1, it is used to calculate the pressure loss of the entire system as shown below:.

We will illustrate how once you know one CFM, S. There is no change. Total Section Loss:. Using the Fan Laws to calculate the new total pressure loss for Section Note that the pressure loss of Section 1 is now greater than the loss of Section 2. To balance the system by design we must increase the air flow rate in Section 2 to bring it up to the higher pressure loss of Section 1.

To correct the air flow rate for Section 2 use the Fan Laws:. Total System Loss. Calculated with the Fan Laws. Problem 3 - A Supply System. The first part of the problem will show the pressure gains obtained from measuring the total pressure at 3 points shown in the diagram above. It will provide some rules of thumb for estimating pressure for elbow and at the supply collar.

The second part of the problem will calculate the pressure gain of the system and compare it to the measured pressure gain. The entire system satisfies the definition of a section since there are no junctions or duct size changes. The transitions off the supply collars can be included in the section. Supply System - Measured Pressure. The pressure was measured for two different flow rates.

The results are show in the table below. Measurements Taken at 3 points of the Supply System. Point 1. Point 2. Point 3. The table shows:. Using the pressure gains for cfm flowing through the system, we see that the pressure gain for the first elbow is: 0. This reflects the system effect of having an elbow close to the supply opening of a hood. The pressure gain for the second elbow is: 0.

This reflects the system effect of having two elbows within close proximity to one another and being close to the hood. The table below provides some rules of thumb when estimating pressure gain at the supply collar:.

Hood Length L. Pressure Loss Estimate. To find the dynamic coefficient we calculate:. Two 90 o Radius Elbows. Assume a 3 piece elbow. We must figure in the system effect incurred by having an elbow close to the supply collar. Use the table in the System Effect section of this paper to estimate the system effect.

Now we must factor in the system effect for the 2 elbows in succession. The measured value of 0. Now we can determine the size fan we need. To calculate the Fan Static Pressure:.

Use the blower manufacturer product literature to get the dimensions for the blower outlet so the velocity pressure at the fan discharge can be calculated:. Appendix 1 - Equations. Total Pressure P T. Fan Static Pressure P s fan. Velocity Pressure P v. Friction Losses P fr. Surface Roughness Correlation Constants. Aluminum, Black Iron, Stainless Steel. Flexible Duct. Fitting Designing Air Flow Systems A theoretical and practical guide to the basics of designing air flow systems.

Air Flow 1. Types of Flow 1. Types of Pressure Losses or Resistance to Flow 1. Air Systems 2. Fan Laws 2. Air Density 2. System Constant 3. Pressure Losses of an Air System 3.

Sections in Series 3. Sections in Parallel 3. System Effect 4. Fan Performance Specification 4. Fan Total Pressure 4. Fan Static Pressure 5. Pressure Calculations 5. Methodology 5. Assumptions and Corrections 6. Problem 1 — An Exhaust System 7. Problem 3 — A Supply System 9. Appendix 1 — Equations Appendix 3 — Bullhead Tee Curves 1.

Air Flow Flow of air or any other fluid is caused by a pressure differential between two points. Types of Flow Laminar Flow Flow parallel to a boundary layer. Types of Pressure Losses or Resistance to Flow Pressure loss is the loss of total pressure in a duct or fitting. Component Pressure Due to physical items with known pressure drops, such as hoods, filters, louvers or dampers.

Dynamic Pressure Dynamic losses are the result of changes in direction and velocity of air flow. Total Pressure, Velocity Pressure, and Static Pressure It is convenient to calculate pressures in ducts using as a base an atmospheric pressure of zero. Total Pressure Consists of the pressure the air exerts in the direction of flow Velocity Pressure plus the pressure air exerts perpendicular to the plenum or container through which the air moves.

Air Systems For kitchen ventilation applications an air system consists of hood s , duct work, and fan s. Fan Laws Use the Fan Laws along a system curve. Calculate th A: As per the Bartleby guidelines, only three parts of a question can be answered at a time. Q: Q6 Determine the natural frequency for the system shown in Figure 2. Slender rod of mass m 2m. A: Given: The spring mass system is shown below:. Q: the gage pressure of an automobile tire is measured to be a kPa before a trip and kPa after a Determine:a the bendin Q: Water is pumped at 1.

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