PE 4B 129 Coil Types

Coils with a flat finned surface (usually) have an __________

'In line' tube pattern

Because of the movement and the changes in temp ______ must be installed in the top of the coil. Why?

*Air vents*- to remove entrained *air bubbles* that are entrained and entrapped.

Which of the following statements about coil surfaces is *false?* A) Air flows across the fins B) Finned coils are more compact than smooth tube coils of the same capacity C) Fins increase the contact surface area between the airstream and the tubes D) All fins must be crimped E) Finned coils are less expensive than smooth coils of the same capacity

*D) All fins must be crimped* (There's other ways of creating a good bond. Smoothness and compactness apparently not an issue for same sized capacities.)

*Half* Serpentine Coil Circuits feed every tube in the ______ of the header. This type of circuit is known as ______. When would it be used?

*Every other* tube in the first row; Half circuiting; High heat transfer with a *limited water capacity* systems.

*Single* Serpentine Coil Circuits feed every tube in the ______ of the header. This type of circuit is known as ______.

*First* Row; Full Circuiting

What is an older for term for *steam distributing coils* ? Why is it no longer used?

*Non-freeze coils* is a term no longer used because the coils are not immune freeze up problems if they are incorrectly selected or applied.

Name the 3 types of Coil circuiting to keep the water flow velocities in range:

*Single* Serpentine, *Double* Serpentine, *Half* Serpentine

With counter-flow arrangement of air & water: A) wtr supply on same side as entering air B) it decreases the heat transfer efficiency C) wtr supply on same side as leaving air D) wtr return is on same side as leaving air E) heat transfer efficiency is same as parallel arrangement of air & wtr

*Water Supply* is on the same side as *Leaving Air*

What is another way to say the tubes have fins?

*extended surface* coil types

List 3 methods to ensure uniform seam distribution in a steam heating coil.

- *Individual orifices* at supply of each tube - *Distributing Plates* inside steam header - *tube within a tube* construction

Name the 4 factors taken into consideration for water coils.

- Counter-flow arrangement - Tube circuiting (water flow vs. pressure drop) - Air venting from system - Air velocity over finned surface

For Water Coil Circuiting the acceptable velocity range is _____.

.3 m/s to 2.4 m/s (1 -8 ft/sec)

What's the normal Face Velocity range?

2.5 m/s to 5.6 m/s

Typical fin spacing for *Chilled Water & AC Direct Expansion Cooling Coils* is:

3.175 to 1.814 mm (8-14 fins per inch)

Typical fin spacing for *steam & hot water* is:

6.35 to 1.814 mm (4-14 fins per inch)

Typical fin spacing for * Direct Expansion Cooling coils for Low temp applications* is:

8.458 to 3.175 mm (3-8 fins per inch)

[T/F] A counter flow coil is less efficient than a parallel flow coil

A *Parallel flow coil* is *less efficient* than a *counter flow coil*

To ensure effective heat transfer which of the following is the most vital element? A) The fin must be crimped B) Highly conductive material is used in fins C) A good bond between the tube & fin D) Wide fin spacing E) Narrow fin spacing

A good bond must exist between the tube and fin

Two types of modern coils used for heating and cooling services in air handling systems are: A) continuous-plate finned surface & spiral-finned surface B) bare tube & spiral-finned surface C) continuous-plate finned surface & bare tube D) bare tube & insulated tube E) none of the above

A) continuous-plate finned surface & spiral-finned surface

Spiral Finned Tube coils have a ribbon of _______ tightly would across each copper tube.

Aluminum or Copper

Fin spacing of 6.35 - 1.814 mm is most normally used in which cases? A) Direct expansion coils for low temp applications B) Steam & hot water heating coils C) Chilled water cooling coils D) Cooling refrigerant coils E) Refrigerant condenser coils

B) Steam & hot water heating coils

How can the bond between the fins and tube in a heating coil be improved? A) installing a plastic insulator B) solder coating tubes & fins C) shrinking fins onto tubes D) pressure welding fins to tubes E) using thinner tubes

B) solder coating tubes & fins

Double serpentine water coil circuiting is used: A) where wtr velocity in tubes is less than 0.3 m/s B) where wtr velocity in tubes is more than 2.4 m/s C) for any tube wtr velocity D) where wtr velocity in tubes is 0.3 - 2.4 m/s E) where low wtr velocities & low wtr press drops are req.

B) where wtr velocity in tubes is more than 2.4 m/s

Rippled-finned surface type coils: A) used for low temp applications where ice may form B) decrease ht xsfer eff C) increase heat xsfer eff by creating more turbulence at fin surfaces D) have no effect on heat xsfer eff E) not used in air handling systems

C) increase heat transfer efficiency *by creating more turbulence* at fin surfaces

What is a benefit of plumbing the supply & return connections of a steam coil on the same side? A) reduces space requirements B) reduces resistance to flow C) requires less piping which leads to a cost savings D) condensate is heated by the steam E) steam is pre-cooled prior to giving up its heat

Condensate is heated by the Steam.

Where would the use of steam distributing coils be recommended? Its where: 1. Different temps across the coil are desirable 2. Freezing temperatures are encountered 3. Steam must be throttled for better control 4. Uniform temperatures over the entire length of the tube is needed A) 1,2 B) 3,4 C) 1,2 & 3 D) 2,3 & 4 E) 1, 2, 3, 4

D) 2,3 & 4 *It is never desirable for different temperatures across the coil*

Which of the following statements about water coils is *false?* A) Hooked up in a counter-flow arrangement. B) Need to be able to vent air. C) Adequate air velocity over finned surface must be maintained. D) Circuiting should minimize the performance of the water flow vs the pressure drop through the coil. E) The bottom connection should always be the water inlet.

D) Circuiting should *minimize* the performance of the water flow versus the pressure drop through the coil. Should be *maximize* the performance

Which of the following is a limiting factor for the number of fins that can be used? A) Temp of steam in coils B) Temp of chilled wtr in coils C) Fin material D) Resistance to airflow E) Face velocity

D) Resistance to airflow

Single serpentine water coil circuiting is used where water velocity in the tubes is: A) less than 0.3 m/s B) more than 2.4 m/s C) any tube water velocity D) between 0.3-2.4 m/s E) in applications req hi wtr velocities & low wtr press drops

D) Water velocities between 0.3-2.4 m/s

When talking about heating or cooling coils, face velocity is the velocity of the A) supply water to coil B) air before it enters the coil C) air after it leaves the coil D) average velocity of the air flowing over face area of the fin surface E) return water from coil

D) average velocity of the air flowing over face area of the fin surface

To prevent moisture carry over in *higher Face Velocities* what has to be done?

Dry cooling or installing an *eliminator section* on the air leaving side.

Half serpentine water coil circuiting is used where the water velocity in tubes is: A) in applications requiring high wtr velocities & low wtr press drops B) more than 2.4 m/s C) between 0.3 - 2.4 m/s D) for any tube water velocity E) is less than 0.3 m/s

E) is less than 0.3 m/s

A characteristic of a double serpentine water coil is: A) low flow quantities B) high water pressure drop C) low face velocities D) low water velocities E) low water pressure drop

E) low water pressure drop

How do you calculate face velocity? What units are you left with?

FV is average velocity in cubic metres/second of air hitting the area of the cooler. FV= air velocity (m^3/s) / front area of coil (m^2) Final units are in meters/second

*Double* Serpentine Coil Circuits feed every tube in the ______ of the header. This type of circuit is known as ______. When would it be used?

First *& Second row*; Double Circuiting ; For High water quantities with low pressure drop.

Which type of coil circuiting is designed to produce a high heat capacity with a limited water quantity? A) Single serpentine B) Double serpentine C) Half serpentine D) Face velocity E) Steam coil

Half Serpentine.

Where are Flat Finned Surface Coils or Bare tubes used mainly? Why?

For low temperature applications like Freezers or cold storage rooms. The flat fins or bare tube allow any ice build up to be cleared easily in the defrost cycle.

Continuous Plate Finned Surface Coils have _________

Integral Spacing Collars

Flow of material in tube should be *counter flow* to the air. Air should be leaving with the return water side. If its in parallel how much could cooling capacity drop?

Loss of 10-15 % of cooling capacity

What is the issue if Face Velocities exceed 3.0 m/s?

Moisture will carry over into duct work.

Coil capacity increases with _________

Number of fins per unit length of tube.

_______________ can be a factor for how many fins are used

Resistance to airflow.

The fin surface area of a heating or cooling coil is called the _______ surface area A) primary B) secondary C) tube D) heater E) none of the above

Secondary Surface Area *(the fins)*

A finned tube coil may have a heat transfer rate of _________ more than bare tubes of the same capacity.

Ten to Thirty times greater.

For Water Coil Circuiting if velocity is below .3 m/s (1 ft/sec) it is ________

Sluggish

Name 2 types of finned tubes:

Spiral Finned Tube coil & Continuous Plate Finned Surface Coil

Coils with *Undulated* or *Ripple* Fins are of a _________ design

Staggered Tube design

What will determine the size of the fan motor - (in cases where the coils are already supplied) ?

The air pressure drop across the coil.

Face Velocity is the velocity of: a) supply water to coil b) air before it enters coil c) air after it leaves coil d) return water from coil e) average of air flowing over face area of fin surface

The average of the air flowing over face area of fin surface.

What is critical in the construction of finned tube coils? What could be the cost?

The bond created by fin and tube. Coil capacity could be reduced by 25-35%

A factor limiting the number of fins that can be used on coils is: a) diameter of the tube b) temp of fluid in tube c) material of the tube d) resistance to airflow e) direction fluid is flowing in tube

The direction fluid is flowing in tube.

With steam heating coils what must be designed in to ensure efficient heat transfer?

They must constantly eliminate condensate, air & non-condensable gases in individual tubes.

Which of the following statements about steam distributing coils is *true?*Steam distributing coils: A) never freeze B) distribute steam evenly over entire coil C) Used when steam cannot be throttled D) Cannot be used where freezing air temps over coils are encountered E) Can only have same end connections

They must distribute Steam evenly over entire coil.

What's the purpose of Undulated and Rippled fins? What's the benefit?

To create more turbulence in airflow. Increases heat transfer efficiency by 15-20%

What was the goal of fins on tubes?

To increase the contact surface of a bare tube - hence increasing heat transfer efficiency.

For Water Coil circuiting if velocity is above 2.4 m/s (8 ft/sec) there will be ________.

Unacceptably high pressure drops.

Coils lacking steam distributing features cause what problem and specifically *when does it appear?*

Uneven flow of condensate leading to uneven air temp across face of coil *presents itself as quite a problem at low load conditions.*