Hampton Cross Flow Forced Convection Lab Report

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ME 325 Heat Transfer

School of Engineering and Applied Sciences Fall 2018

Western Kentucky University

Forced Convection Heat Transfer Lab

Single Heated Circular Cylinder Element with Transverse Airflow

Laboratory Objectives:

The objective of this laboratory is to:

• To determine the overall steady state heat transfer correlations for a single heated cylinder in a transversely flowing air stream.

Background:

Flow across and heat transfer from a single heated circular cylinder is frequently encountered in

many engineering applications. The examples of such applications incorporates transmission lines

for electricity, heat exchangers and nuclear fuel elements. However, the corresponding flow field

is extremely complicated and the drag and heat transfer coefficients vary in an extremely complex

manner around the cylinder. In this experiment, we shall determine overall heat transfer

coefficients, which are of most practical interest in engineering calculations.

Refer to Cengel & Ghajar, Heat and Mass Transfer Fundamentals and applications, 8th

Edition, Chapter 7, pp. 425 – 452 for more background information.

Equipment Used:

Hampden MODEL H-6856 Cross Flow Heat Exchanger Unit, shown in Figure 1 below

Hampden MODEL H-6856A Single Tube Plate

Figure 1: Hampden MODEL H-6856 Cross Flow Heat Exchanger Unit

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Experimental Setup and Procedure:

Step 1. Make sure that the fan speed control and heater controls are fully counter clockwise (off).

Step 2. To measure the above thermocouple temperature, select ELEMENT SURFACE

TEMPERATURE with the thermocouple selector switch.

Step 3. Verify that the connections of the manometer tubing to the Pitot tube are as shown in

Figure 2.

Figure 2: Pitot Tube to Manometer Connections

Step 4. Turn ON the MAIN AC circuit breaker. The light above the breaker will illuminate.

Step 5. Rotate FAN SPEED control knob to obtain the desired airflow – start at 100%. The actual

air velocity will then be determined from the Pitot tube and manometer reading.

Step 6. Rotate HEATER SUPPLY clockwise to ~75% and set output to desired wattage on the

wattmeter.

NOTE: Do not allow the ELEMENT SURFACE TEMPERATURE to exceed 300°F (150°C). Use Table 1 as a guide to limit a HEATER SUPPLY maximum dial setting for a

FAN SPEED minimum dial setting to avoid overheating and possibly damaging the heater

element.

Table 1 - Minimum Fan Dial Position for Specific Heater Dial Positions

MINIMUM DIAL POSITION FOR FAN MAXIMUM DIAL POSITION FOR HEATER

33% 20 W

50% 30 W

100% 40 W

Step 7. To measure the air temperature, select AIR DUCT TEMPERATURE with the selector

switch. Normally keep the selector switch on the ELEMENT TEMPERATURE.

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Step 8. Set the heater to 75% power and allow the heater temperature to stabilize, which will

require approximately 10 minutes, then read and record data in Table 2. The purpose of

this first run is to create a constant wall temperature boundary condition (i.e., constant

ELEMENT SURFACE TEMPERATURE).

Step 9. Repeat at least 6 different airflow velocities while assuring that a constant ELEMENT

SURFACE TEMPERATURE is reached. Select velocities that are ~evenly spaced.

Step 10. When all runs have been completed, turn heater control to 0% (off position). Once the

temperature of the element drops below 150°F (65°C), the fan can then be turned down

and the MAIN AC circuit breaker SHUT OFF.

Table 2 – Data Collection for Forced Convection Heat Transfer Lab

CONSTANT ELEMENT SURFACE TEMPERATURE

SINGLE CYLINDER PLATE

DIAL

POSITION

FOR FAN

DIAL

POSITION

FOR HEATER

T-SURF

(°°°°F)

T-AIR

DUCT

(°°°°F)

∆∆∆∆P MANOMETER

(inches of Water) HEATER

POWER

(W)

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Post-Lab Work:

The following items should definitely be addressed in the report.

1. Calculate the average convective heat transfer coefficient vs. the airflow velocity.

2. Plot your average convective heat transfer coefficient (on y-axis) versus airflow velocity (on x-axis) and see if the relationship trend is as you would expected. (this will be in the

lab report)

3. Calculate the dimensionless parameters: fk

Lh Nu = ,

µ

ρVL =Re , and

f

p

k

Cµ

α

ν ==Pr for

today’s experiment and use Table 7-1 to determine the theoretical h value.

Project Requirements:

A well-written group lab report should have an appropriate professional title page, followed by a

report written as a thorough but brief executive summary (See “Report Writing Guidelines” for more

details). You should provide necessary calculations documented in an appendix with the memo. Your

lab report should address the following (perhaps detailed slightly more in the appendix):

Executive Summary: The lab’s purpose, what you are determining and how you did so.

Theory/Background: Briefly describe the experimental setup and the theory to calculate

the convection heat transfer co-efficient (h). Clearly define all dimensionless parameters

(Re, Pr, Nu) used in the experiment. Explain your experimental procedures (number of

data sets and why) and which experimental parameters you varied and which you held

constant (and why). Note: You can just state that thermocouples were used to measure

temperatures, and cylinder dimensions and electrical power input were measured, but

properly explain the theory and calculation of air velocity used in this lab.

Results and Discussion: From the data you collect, determine and then plot Nusselt number

versus Reynolds number. Develop your own experimental correlation for Nusselt number

as a function of the Reynolds and Prandtl numbers that is of the same form as the published

correlation. Compare your correlation to the published correlation (Cengel, Table 7-1),

and include both correlations on your experimental plot.

Uncertainty Analysis: I am not expecting an explicit numerical assessment of uncertainty

for this lab using Kline McClintock method; discuss it in qualitative terms (i.e., % error).

Conclusions: Characterize how well (or poorly) the experimental correlation for a

cylinder in cross flow compares to the published correlation in a quantitative way.

Explain any apparent deviations from the expected correlations and offer an evaluation of

how errors in the experiment might cause experimental uncertainty. What might be done

to improve the ability of the lab setup to replicate the published correlation more

accurately?

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Project Points and Teams:

This lab report is worth 6 points. Form three-person teams (you may prefer to work in pairs or

individual) to do the calculations and write a team lab report. This team report is due Friday

November 2. Submit to Blackboard (one submittal per team).

If you need assistance in any aspect of this report, see the instructor. Likewise, if you want a

draft review stop by and seek it out.