Heat Transfer across a Tube

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Questions and Answers

What is the purpose of the adjustable flap at the fan discharge?

To control the heat input to the heater element
To measure the surface temperature of the heater
To control the air flow (correct)
To adjust the temperature profiles of the experiment

What is the purpose of the thermocouple in the apparatus?

To adjust the temperature profiles of the experiment
To control the heat input to the heater element
To measure the surface temperature of the heater (correct)
To monitor the air flow in the duct

What is the equation used to calculate the surface area of the tubes?

A = (Voo.a/2) / a
A = (a/2) + b^2
A = N.p.d.l (correct)
A = Vmax / (a/2)

What is the purpose of the controlling console in the apparatus?

To control the heat input to the heater element (D) Signup and view all the answers

What is the formula for Vmax?

Vmax = [Voo.a/2 a] (B) Signup and view all the answers

What is the purpose of the fan in the apparatus?

To control the air flow in the duct (C) Signup and view all the answers

What is the formula for the mean film temperature?

Tmean=(To+Ts)/2 (B) Signup and view all the answers

What is the range of Reynolds number for which C = 0.683 and n = 0.466?

400 to 4,000 (D) Signup and view all the answers

What is the effect of wakes from upstream tubes on heat transfer in a tube bundle?

It decreases heat transfer (B) Signup and view all the answers

What is the expression for the Reynolds number in a tube bundle?

Re max = V max pd/µ (A) Signup and view all the answers

What is the heat transfer equation for transverse flow across a tube?

hav.d/k = C*.Vn (D) Signup and view all the answers

What is the range of Reynolds number for which C = 0.989 and n = 0.33?

0.4 to 4 (B) Signup and view all the answers

What is the procedure to switch off the power to the heater element?

Turning the power control knob counter clockwise (D) Signup and view all the answers

What is the configuration of the tube bundle in Figure 2.1?

Staggered configuration (B) Signup and view all the answers

What is the formula for the heat transfer equation in a tube bundle?

hav.d/k = C1.(Re max)n (B) Signup and view all the answers

What is the objective of the cross-flow heat transfer experiment?

To investigate the effects of air velocity, surface temperature, and tube position on heat transfer coefficients (B) Signup and view all the answers

What is the procedure to install the single tube heat exchanger plate?

By installing it on to the duct through the appropriate opening (D) Signup and view all the answers

Why is it necessary to wait until the steady state condition is observed?

To ensure accurate measurement of heat transfer coefficients (C) Signup and view all the answers

What is the purpose of repeating the experiment at various iris settings?

To investigate the effects of air velocity on heat transfer coefficients (C) Signup and view all the answers

What is the heater tube position in the multiple tube heat transfer analysis?

2nd row (C) Signup and view all the answers

What is the temperature difference DT approximately set to in one of the experiments?

60°C (B) Signup and view all the answers

What is the procedure to shut down the equipment?

Switch off the heater and then remove the single heater tube heat exchanger (C) Signup and view all the answers

What is the primary function of the thermocouple in the experimental setup?

To measure the temperature of the heater element (B) Signup and view all the answers

What is the maximum temperature allowed for the heater element during the experiment?

100°C (D) Signup and view all the answers

What should be done before switching off the air fan?

Switch off the heater power (C) Signup and view all the answers

What is the purpose of the digital temperature controller in the experiment?

To control the temperature of the heater element (B) Signup and view all the answers

Why should the exhaust air be avoided?

Because of its high velocity (B) Signup and view all the answers

What is the importance of wearing protective equipment during the experiment?

To handle hot surfaces or components (A) Signup and view all the answers

What should be done with the heater tube after the experiment is completed?

Remove it and switch off the heater power (D) Signup and view all the answers

What is the purpose of grounding the equipment in the experiment?

To prevent electrical hazards (D) Signup and view all the answers

What is the primary condition to be observed before measuring the values of Ts, Tinlet, and the heater power reading Q?

Reaching the steady state condition at an interval of 5 minutes (A) Signup and view all the answers

At what position should the air flow control of the blower be set initially?

Iris control to position no. 1 (A) Signup and view all the answers

What is the purpose of increasing the power input to the heater slowly?

To achieve a DT of approximately 40 °C (A) Signup and view all the answers

What is the correct sequence of actions when shutting down the experiment?

Switch off the heater, then switch off the blower and remove the heat exchanger (A) Signup and view all the answers

What is the position of the finned heater tube when the experiment is repeated for DT of approximately 60 °C?

3rd and 4th row (A) Signup and view all the answers

What is the temperature difference (DT) to be achieved in the first part of the experiment?

DT of approximately 40 °C (B) Signup and view all the answers

What is the purpose of waiting for the steady state condition at an interval of 5 minutes?

To ensure the heater power reading Q is stable (C) Signup and view all the answers

At which row should the finned tube bundle heat exchanger be installed?

2nd row (A) Signup and view all the answers

Study Notes

Heat Transfer Analysis

The heat transfer equation is expressed as Ren or ho = C* Vn, where C* is a constant for a given fluid.
The parameters for the mean film temperature are evaluated as Tmean = (To + Ts) / 2.

Case of a Single Cylinder

The values of C and n for transverse flow across a tube are given in Table 2.1:
- Re range: 0.4 to 4, C: 0.989, n: 0.33
- Re range: 4 to 40, C: 0.911, n: 0.385
- Re range: 40 to 4,000, C: 0.683, n: 0.466
- Re range: 4,000 to 40,000, C: 0.193, n: 0.618
- Re range: 40,000 to 400,000, C: 0.0266, n: 0.805

Case of a Bundle of Cylinders

The heat transfer equation is expressed as hav.d/k = C1.(Re max)n, where Re max = V max rd/µ.
The maximum flow velocity V max depends on the geometry of the configuration.
The area per unit width of opening a is calculated as the lowest of [(a-d)/2] or [{(a/2)2 + b2}1/2-d].
The surface area A of tubes is calculated using the equation A = N.p.d.l.

Apparatus

The apparatus consists of a vertically mounted duct fitted with a fan at the bottom.
The duct allows heat exchanger plates of various configurations to be fitted on for experimental purposes.
A tube in the heat exchanger configuration is heated electrically.
A thermocouple measures the surface temperature of the heater.
The apparatus is equipped with a controlling console, digital temperature controllers, and safety features.

Procedure

The experiment involves investigating the effects of air velocity, surface temperature, and tube position on heat transfer coefficients in a cross-flow heat exchanger.
The procedure involves installing the heat exchanger plate, switching on the power to the air blower and heater, and recording the inlet air velocity, inlet air temperature, and heater power reading.
The experiment is repeated at various iris settings and with different tube positions.

Safety Precautions

Always follow the laboratory's safety guidelines, particularly when working with heated elements and electrical equipment.
Ensure all equipment is properly grounded to prevent electrical hazards.
Wear protective equipment, such as gloves and safety glasses, when handling hot surfaces or components.
Avoid facing the direct blow of exhaust air, as the velocity of air is quite high.
Care should be taken not to touch the heater element when it is hot.
Switch off the heater and blower before removing the heat exchanger plate.

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Description

This quiz covers the calculation of heat transfer across a tube, including the evaluation of parameters such as the mean film temperature and values of C and n for transverse flow.