Heat Transfer Assignment - Advanced heat transfer

Learning objectives:

• To understand how real-life problems are simplified for solution.
• To understand the limitations of real life modelling.
• To understand how the heat transfer properties of materials selected will affect the thermal performance of a system.

The assignment will assess:

• Your understanding of transient heat transfer theory.
• Your understanding of the thermal resistance network.
• Your understanding of convective heat transfer.
• Your understanding of numerical methods in heat transfer.
• Your presentation skills.
• Your ability to find the correct information from references and reference them properly.

Pizza delivery problem -

Pizza is cooked at oven to about 570 K (about 300C), some of the heat is converted into bond energy as water evaporates and chemical reactions occur. However, most of the heat energy causes a rise in temperature in the cheese, toppings, sauce and pie. The total structure of pizza can be considered in thermal equilibrium with the oven when it leaves it.

Delivery of pizza is usually done by using boxes placed inside well-insulated bags, usually one bag can consist more than one pizza.

In this assignment we are going to assume we have one pizza box inside the bag, the bag is travelled to a customer for half an hour using a motorbike travelling at an average velocity of 50km/hr in still air, the pizza is required to reach the customer at a temperature above 65C.

Assumptions in the model:

• Loss of heat from side of the box is negligible.
• Ambient air is at 30 C.
• Flow of heat is 1 dimensional.
• Each Pizza element ( e.g. cheese, source etc) can be treated as a lumped capacitance.
• Use the standard properties of materials used for bag and pizza.

1) Write down the suitable correlation for Nusselt number based on wind speed and pizza bag dimensions.

2) Write the overall heat transfer relations for the pizza in 1 dimensional transient format.

3) State all assumptions used and explain why they are used.

4) Plot clear thermal resistance network of the system.

5) What is the minimum temperature of the Pizza at 30 minutes on the way to customer?

6) Modify the structure of the insulating materials of the bag and number of layers to make the temperature 65 C at 30 minutes of travel.

7) What is the expected cost increase to improve the bag?

8) Use Excel spread sheet or MATLAB to model the system.

9) Discuss how your modifications has improved the performance.

10) Make at least one suggestion for an alternative way to get good thermal performance at a reasonable cost, discuss in details.

Attachment:- Assignment File.rar