Heat Transfer Principles Quiz

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Questions and Answers

What is the thermal conductivity of the metal plate mentioned?

1.5 W m-1 K-1

5 W m-1 K-1

17 W m-1 K-1 (correct)

0.05 W m-1 K-1

How much was the thickness of the metal plate increased?

30%

40%

20% (correct)

10%

What will be the effect of adding insulation to the pipe?

It will increase the heat loss.

It will reduce the heat loss. (correct)

It will have no effect on heat loss.

It will stop heat transfer completely.

What is the outer face temperature of the fluid into which heat is dissipated?

40°C Signup and view all the answers

What is the thickness of the frozen food mentioned in the content?

20 mm Signup and view all the answers

What is the correct statement regarding the outer radius of the pipe and critical radius?

The outer radius is less than the critical radius. Signup and view all the answers

Which of the following characteristics does the food material possess?

Density of 1080 kg/m3 Signup and view all the answers

What is the specific heat of the food material mentioned?

3550 J/kg.⁰C Signup and view all the answers

What is the heat transfer coefficient for the metallic ball cooling in air?

20.34 Signup and view all the answers

Which option represents the effective thermal conductivity of the composite made up of two plates with thermal conductivities K and 2K?

10 K/m Signup and view all the answers

How is the thermal conductivity of a common metal used in food processing equipment represented in SI units when given as 120 BTU ft-1 h-1 °F-1?

208 Signup and view all the answers

Given a cork slab of 100 mm thickness with one face at -12 °C and the other at 21 °C, how does the temperature gradient at surface Q relate to the rate of heat transfer?

The rate of heat transfer is directly proportional to the temperature gradient. Signup and view all the answers

What would be the expected heat transfer through one square meter of the cork wall based on its thermal conductivity and temperature gradient?

Directly related to the temperature difference and the thermal conductivity. Signup and view all the answers

In the cooling scenario of the metallic ball, what temperature change occurs per minute?

4 °C/min Signup and view all the answers

What is necessary to calculate the rate of heat transfer through the cork slab?

Both the thermal conductivity and temperature difference. Signup and view all the answers

When neglecting thermal gradients inside the metallic ball, what assumption is made about its internal temperature?

The internal temperature is uniform throughout. Signup and view all the answers

What is the temperature of the surroundings from which the steam pipe loses heat?

30 0C Signup and view all the answers

If the insulation thickness of the steam pipe is 2 cm, how does this impact the rate of heat loss compared to an un-insulated pipe?

It will be less than that of the un-insulated steam pipe Signup and view all the answers

What is the specific heat capacity of the liquid that must reach a desired temperature?

4 kJ/kg 0C Signup and view all the answers

What heat transfer coefficient is assumed for the heat transfer from the pipe surface to the surroundings?

8.0 W/m2 0C Signup and view all the answers

What is the required time taken for the liquid to reach the desired temperature assuming it has a specific heat of 4 kJ/kg 0C?

10 min Signup and view all the answers

In a composite wall of two plates, under steady state conditions, when is the temperature difference across plate A greater than that across plate B?

When CpA > CpB Signup and view all the answers

What is the conductivity of the insulation covering the steam pipe?

0.6 W/m 0C Signup and view all the answers

Which of the following describes the state conditions of plate B in comparison to plate A?

Plate B has twice the thickness of plate A Signup and view all the answers

What is the rate of change of energy storage in the wall?

120 kW Signup and view all the answers

During transient convective cooling, when the Biot number approaches 0, what condition does this indicate?

Uniform temperature throughout the object Signup and view all the answers

What is the heat flow across the thickness of a plastic slab with a temperature difference of 10 K?

19 W Signup and view all the answers

If the thickness of layer P in a composite wall is doubled, how is the rate of heat transfer affected?

Decreases by 40% Signup and view all the answers

What happens to the steady-state interface temperature as the thickness of layer P is doubled?

Decreases slightly Signup and view all the answers

In the case of transient convective cooling, what does a Biot number of 1 indicate?

Equal conduction and convection Signup and view all the answers

What thermal condition is expected in a solid object with negligible convection at its surface?

Uniform temperature Signup and view all the answers

What does a cooled fluid at 30ºC flowing over a heated flat plate at 100ºC imply about the boundary layer temperature distribution?

Non-linear temperature gradient at different points Signup and view all the answers

What type of heat loss occurs when hot metal at 1700 K is poured into a sand mould that is open at the top?

Radiation, conduction and convection Signup and view all the answers

Given the temperature field T = 400 - 50z exp(-t - x² - y²), how does the temperature gradient (dT/dx) behave as x increases?

Decrease Signup and view all the answers

In one-dimensional steady state heat conduction along the x-axis with boundary surfaces at 0°C and 100°C, what is the expected direction of heat transfer?

From the surface at 100°C to the surface at 0°C Signup and view all the answers

If the heat conductivity of a wall is given by k = k0 + bT, what happens to the conductivity as temperature (T) increases?

It increases linearly with temperature Signup and view all the answers

Which of the following best describes the heat conduction process in a plane wall under steady-state conditions?

Heat conduction is influenced by internal heat generation Signup and view all the answers

What is a key characteristic of one-dimensional steady-state heat conduction?

The temperature gradient remains constant at any cross-section Signup and view all the answers

What effect does uniformly generated heat have on the temperature profile of a plane wall during steady-state conduction?

It results in a parabolic temperature profile Signup and view all the answers

When analyzing one-dimensional steady state heat conduction, what is assumed about the heat transfer rate at all sections of the wall?

It is constant across all sections of the wall Signup and view all the answers

Study Notes

Heat Transfer

A metal plate with thermal conductivity of 17 W m-1 K-1 and thickness of 10 mm has its faces maintained at 80⁰C and 100⁰C. Increasing the thickness by 20% will increase the thermal resistance, thus decreasing the heat transfer rate.
A steam pipe with 25 mm outer diameter is insulated to reduce heat loss. The critical radius of insulation is the radius at which the heat loss is minimized.
A food material with thickness of 10 mm and thermal conductivity of 1.5 W m-1 ⁰C-1 is subjected to a constant heat flux of 500 W m-2. The heat transfer coefficient between the food material and the surrounding fluid is 100 W m-2 ⁰C. The temperature of the surface where the heat flux is supplied is calculated based on these parameters.
A frozen food plate with thickness of 20 mm, thermal conductivity of 2.58 W m-1 ⁰C-1, and initial temperature of -20⁰C is undergoing a thawing process in a liquid. The time required to reach a desired temperature is dependent on the heat transfer rate (which is determined by various factors).
A steam pipe with 10 cm diameter and insulation thickness of 2 cm is losing heat to the surroundings at 30⁰C. The rate of heat loss from the insulated pipe is compared to the rate of heat loss from the un-insulated pipe.
A metallic ball with diameter 7.5 cm and specific heat capacity of 0.9 kJ/kg⁰C is cooling down in air at 25⁰C. The heat transfer coefficient is calculated based on the cooling rate.
Two plates with equal thickness and thermal conductivities of K and 2K are joined together to form a composite. The effective thermal conductivity of the composite is calculated based on the individual conductivities and the arrangement of the plates.
The thermal conductivity of a metal used in food processing equipment is 120 BTU ft-1 h-1 °F-1. This value can be converted to J m-1 s-1 K-¹.
A cork slab with thickness of 100 mm has faces maintained at -12 °C and 21 °C. The rate of heat transfer through the slab per unit area is calculated based on the thermal conductivity and the temperature difference.
When a solid object is undergoing transient convective cooling, the Biot number is a measure of the ratio of internal thermal resistance to external convective resistance. Biot number approaching zero indicates uniform temperature throughout the object.
For a composite wall consisting of layers P and Q, the steady state interface temperature is affected by the individual layer thicknesses and thermal properties. Doubling the thickness of layer P will alter the heat transfer rate.
A heated flat plate at a constant temperature of 100ºC is being cooled by a coolant fluid at 30ºC. The boundary layer temperature distribution at a given location is dependent on various factors.
During steady state heat conduction through a plane wall with uniform heat generation, the direction of heat transfer is determined by the temperature difference between the boundaries.
The temperature field of a slab is given by a mathematical expression. The temperature gradient in a specific direction can be calculated using partial derivatives.
For steady state heat conduction through a plane wall with uniform heat generation, the temperature gradient will vary along the x-axis based on the heat generation rate and the boundary conditions.
Hot metal at 1700 K is poured into a sand mould open at the top. Heat loss from the liquid metal occurs through radiation, conduction, and convection.

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Description

Test your understanding of heat transfer concepts, including thermal conductivity, insulation, and heat flux calculations. This quiz covers practical examples related to metal plates, steam pipes, and food materials during various thermal processes.