[Heat and Mass Transfer] Speech

Hello, Everyone. My name is 변병근. from sixth team. Thank you for coming to today's presentation.
As you can see the screen, I'd like to talk to you "Heat transfer in refrigerator".
We, sixth team has found this journal from "International Communications in Heat and Mass Transfer", which name is "Experimental study of heat transfer characteristics for a refrigerator by using reverse heat loss method".

You might be curious about this term, Reverse heat loss method. This is the new concept, this author just came up with.
This main experiment in this journal is differently checking the heat transfer between freezer side and refrigerator side. By putting heaters into each section, they have found how and which paths the heat go forward to. This is the new concept differently checked from the original principle of refrigerator.
-----------------------------------------------------------------------------
We've divided our presentation into three parts.
First, I will explain you the reason why our team chose this journal and how important it is.
Then, we'd like to introduce you "The basic principle of fridge cooling down temperature"
Finally we will talk about the main purpose of the journal we've chosen.
So through the last part, you will know the point our team is going to discuss about at the final presentation.
Please Be ready to take a note and feel free to ask a question whenever you have.
-----------------------------------------------------------------------------
Here is a very interesting fact that a refrigerator inside a house runs for 24 / 7 and 365 days in a year until it is out of order. There is no home appliance other than a refrigerator which always runs in the world. So it is obvious that the electric power consumption by fridge
is considered as a huge cost. So for reducing electric power energy, we've chosen this journal, because it shows the experimental fact saving electric power energy in the aspect of heat transfer.
-----------------------------------------------------------------------------
Pay attention to here. This is the simplest figure which is showing the heat transfer in refrigerator. it is composed of four big parts in terms of heat transfer.

Compressor, Condenser, Expansion valve and Evaporator unit with Refrigerant.

The fluid flowing this system is Freon Gas (R12, R22 - Air condition). It is a noncorrosive fluid which means it has no a harmful function to break down the valve and pipes inside of fridge. and it is easily liquefied even at the low pressure to absorb ambient heat. So We can say that it is a qualified material as a refrigerant (fluid). I will just call it fluid to make it easy.
-----------------------------------------------------------------------------
The refrigeration process begins with the compressor. Freon Gas is compressed until it becomes very hot and high pressure.
This heated gas flows through the coils behind the fridge, which allow excess heat to be released into the surrounding air.
This is why people sometimes feel warm air circulating around the fridge.

Eventually the Freon Gas cools down to the point where it becomes a liquid at condenser.
This freon liquid is forced through an expansion valve.

Essentially, the expansion valve has such a small opening. That's why when the liquid Freon pass through this valve, it is turned into a very cold, fast-moving mist, evaporating.
This is explained by Bernoulli's theorem.

This low temperature freon liquid with low pressure is vaporized by absorbing more heat from inside of the insulation.
then its temperature rises.
this phenomenon cools down the temperature inside of fridge.

The freon gas is drawn back into the compressor, and then this circulation system begins again to continuously lower the temperature.
----------------------------------------------------------------------------
Finally, Here in the last part, We are going to give you an introduction for final presentation.

In this journal, they had tried finding these four facts based on reverse heat loss method.

First, They found How long the temperature distribution inside fridge takes to reach the steady state condition from the fridge has a electric power at the first stage.

Second, They checked the efficiency of role of circulating fans between freezer side and refrigerator side.

Third, They separated the fridge into three parts like this picture. And they utilized the concept, The overall heat transfer coefficients respectively.
So they shows the relationship between them by derivation using mathematical calculation based on zeroth and first law of thermodynamics.


Above all facts have proven the performance of circulating fan and insulation in the aspect of Heat transfer.

Basically, There are several ways to cut down the cost of electric power energy.
I will explain them at the final presentation with sub journals.

We will see you later. Thank you very much.

Does anyone have a question?