Experimental Study on Heat Transfer Coefficients in Double Pipe Heat Exchanger | Study notes Law

Double Pipe Heat Exchanger

CE 328

Spring 2003

Objective:

To study and evaluate the effects of flow conditions and flow configurations on the rate of heat

transfer through thin walled tubes. To determine the overall heat transfer coefficient for the

double pipe heat exchanger for countercurrent flow and parallel (or co-current) flow.

System:

The heat exchanger consists of two thin wall copper tubes mounted concentrically on a panel.

The flow of water through the center tube can be reversed for either countercurrent or parallel

flow. The hot water flows through the center tube, and cold water flows in the annular region.

• Valves are used to set up desired flow conditions (rate and direction). Set the hot water

valve in the correct position to achieve either countercurrent or parallel flow. (Valves are

red for hot water and blue for cold water.)

• Thermometers and thermocouples are placed near the entrance, midpoint and exit of each

pipe. The thermometer should give coarse readings compared to the thermocouple. The

thermocouples are connected to a selector switch on the front of the panel.

• The flow meter has a direct read scale in ft3/min. It is adjustable for the purpose of

zeroing the reference mark on the tube. The flow meter can read either the cold or hot

water flow rate by turning the appropriate valves.

• A synopsis of operation is as follows: Determine the direction of flow to study and the

rates of flow that you wish to study. Open or close the appropriate valves. (All globe

valves should be totally opened or totally closed.) The metering valves at the outlets

should be used to control flow rates. Allow the system to reach steady state before taking

measurements. Take at least three readings for each rate, and at least five rates for each

flow configuration. The two heat exchanger groups must work together once the flow

has been initiated because the adjustment of flow in one group will affect the other

team’s flows. You must communicate when you are ready to change flow rates. (Do not

use the same actual flow rates, just change them at the same time.) Once you have taken

readings for all five rates of flow, repeat the experiment for the opposite direction of

flow.

• Fix the flow for one of the fluids and vary the other. (Should you and the group next to

you keep the same fluid at a fixed rate?)

3/5/2003 1

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Double Pipe Heat Exchanger

CE 328 Spring 2003

Objective: To study and evaluate the effects of flow conditions and flow configurations on the rate of heat transfer through thin walled tubes. To determine the overall heat transfer coefficient for the double pipe heat exchanger for countercurrent flow and parallel (or co-current) flow.

System: The heat exchanger consists of two thin wall copper tubes mounted concentrically on a panel. The flow of water through the center tube can be reversed for either countercurrent or parallel flow. The hot water flows through the center tube, and cold water flows in the annular region.

Valves are used to set up desired flow conditions (rate and direction). Set the hot water valve in the correct position to achieve either countercurrent or parallel flow. (Valves are red for hot water and blue for cold water.)
Thermometers and thermocouples are placed near the entrance, midpoint and exit of each pipe. The thermometer should give coarse readings compared to the thermocouple. The thermocouples are connected to a selector switch on the front of the panel.
The flow meter has a direct read scale in ft^3 /min. It is adjustable for the purpose of zeroing the reference mark on the tube. The flow meter can read either the cold or hot water flow rate by turning the appropriate valves.
A synopsis of operation is as follows: Determine the direction of flow to study and the rates of flow that you wish to study. Open or close the appropriate valves. (All globe valves should be totally opened or totally closed.) The metering valves at the outlets should be used to control flow rates. Allow the system to reach steady state before taking measurements. Take at least three readings for each rate, and at least five rates for each flow configuration. The two heat exchanger groups must work together once the flow has been initiated because the adjustment of flow in one group will affect the other team’s flows. You must communicate when you are ready to change flow rates. (Do not use the same actual flow rates, just change them at the same time.) Once you have taken readings for all five rates of flow, repeat the experiment for the opposite direction of flow.
Fix the flow for one of the fluids and vary the other. (Should you and the group next to you keep the same fluid at a fixed rate?)

Background and Theory: A single-pass heat exchanger is one through which each fluid runs through the exchanger only once. An additional descriptive term identifies the relative directions of the two streams. Parallel (or co-current) flow is the term for fluids that flow in the same direction. Countercurrent flow describes fluids that flow in opposite directions.

A simple, first law of thermodynamics for each stream gives:

q = m & (^) c cpc ( T (^) co − Tci ) (1)

for the cold fluid, and

q = m &^ h cph ( T (^) hi − Tho ) (2)

for the hot fluid, where q = heat, J m & = mass flow rate, kg/s T = temperature, K cp = heat capacity, J/kg-K Subscripts c and h denote cold and hot fluids, respectively Subscripts i and o denote fluid inlet and outlet, respectively

The following definitions are given for parallel flow:

ho co

hi ci T T T

T T T

1 ∆

For countercurrent flow:

hi co

ho ci T T T

T T T

1 ∆

The energy transfer between the two fluids is given by:

2 1 ln T T

T T

q UA ∆

where U = overall heat transfer coefficient, W/m^2 -K A = heat exchange area, m^2

Experimental Study on Heat Transfer Coefficients in Double Pipe Heat Exchanger, Study notes of Law

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