Week 13
After learning about Digital Fabrication 💻📐 i.e. learning about the design and production process of creating a product specifically - where digital data 💹📉📊 directly drives manufacturing equipment to create various parts of the product 📦, this week we ventured into learning more about the operating principles and mechanism designs - more so about how the product will work 💫 (principles) and the mechanisms 🔩🔧that allows it to do so (physically).
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📌What does 'Operating Principle' mean?
For example: Distillation, a separation process. How does it happen i.e. how are the liquids separated? We have to look at its Operating Principle -> Differences in relative volatilities.
Basically, all devices/apparatus/equipment/products are designed based on operating principle/working principle which can be mechanical, electrical, chemical or magnetism.
For example: In terms of devices e.g LINK TO PRACTICAL 2...
Air-lift Pump 💨 -> inside a coffee maker. How does it drive the rising hot vapour+liquid mixture up the tubing where it will eventually condense and contact the dry coffee beans? We have to look at its operating principle -> BUOYANCY.
What about the Coffee Maker ? Its a device too! How does it brew coffee? Operating principle -> LEACHING [of coffee solubles] ☕.
📌Our Chemical product .
📌Operating principle for selected Idea
- Heat transfer
Modes: conduction and convection
Exothermic reaction to produce heat via MRE
and water.
(Exothermic Chemical reaction): Mg + 2H2O → Mg(OH)2 + H2 [+
heat (q)]
The heat produced by the exothermic
reaction is transferred via conduction and convection to heat up the food in
the portable food heater.
Elaboration: The heat generated by the exothermic reaction taking place below the metal container with the food (refer to sketch) will be transferred by the rising hot gases via convection to the metal plate – stainless steel. This plate acts as a barrier to prevent the harmful gases released as a result of the reaction from contacting the food in the detachable container which rests on the metal plate and acts as a solid medium which would in turn transfer heat to the base of the container via conduction. From the base of the container, heat would then be transferred to the food via conduction placed in the container thus heating up the food. As for the hot harmful gases produced (Mg(OH)2 + H2) as a result of the reaction, they would rise upwards due to them being hot and less dense and would eventually escape via the top opening, preventing any danger of contamination or posing a risk to the safety of consuming the food. As they rise upwards, being less dense, some of the hot gases would contact the metal plate to transfer heat via convection [start of heat transfer process] and some would rise upwards towards the opening to escape.
📌Research
- Source of heat: MRE pack, activated by water
- · How does it work? (Exothermic Chemical reaction) Mg + 2H2O → Mg(OH)2 + H2 [+ heat (q)]
The
idea behind a MRE heater is to use an electron-transfer process: oxidation of a
metal to generate heat. Magnesium metal is a better choice than iron in terms
of the component of the MRE heater because iron rusts much more quickly. The process is like iron being rusted by
oxygen and proceeds at about the same slow rate, which is too slow to generate
usable heat. To accelerate the reaction, iron metal particles and salt (NaCl)
are mixed with the magnesium particles. Iron and magnesium, when suspended in
an electrolyte, form a galvanic
cell
(Electrochemical cells in which oxidation-reduction reactions produce
electrical energy) that can generate electricity. When water is added to the MRE
heater, it dissolves the salt to form a salt-water electrolyte, which turns
each particle of magnesium and iron into a tiny battery. As the magnesium and
iron particles are in contact, they become thousands of tiny, short-circuited
batteries quickly burning out thereby producing heat. This heat generated is
transferred via modes: conduction and convection to heat up the food. (HowStuffWorks, Science, Military and Soldiers,
2021)
Reference:
HowStuffWorks,
Science, Military and Soldiers, 2021. How MREs Work. [online] HowStuffWorks. Available at:
<https://science.howstuffworks.com/mre4.htm> [Accessed 18 July 2021].
- · Amount of heat supplied in one use? How much water is needed to activate it? How much heat energy can it release? How long does it last?
Typically, a self-heating MRE heater uses 7.5 grams of a
powdered magnesium-iron alloy, consisting of 95 % magnesium and 5 % iron by
weight, 0.5 grams of salt, in addition to an inner filler and anti-foaming
agent. Upon adding 1 US fluid ounce (30 ml) of water, the heat generated by the
chemical reaction can heat an 8-ounce (230 g) meal packet by 100 °F (38 °C) in
about 10 minutes, releasing approximately 50 kilojoules (47 BTU) of heat energy
at about 80 watts. (How Does it Work? -
HeaterMeals, 2021)
Reference:
HeaterMeals. 2021. How Does it Work? - HeaterMeals. [online] Available at: <https://heatermeals.com/how-does-it-work/> [Accessed 18 July 2021].
- What material would be the most suited to conduct the heat transfer?
Metal plate to enhance heat transfer via conduction
Properties of the Metal Plate:
As Stainless Steel has the best chemical
compatibility with the reagents and products in the reaction between the MRE
heating pack and water thus in terms of the danger of toxicity it poses it is
eliminated and it will not threaten the safety of the consumption of food. In
terms of the thermal properties, for the metal plate in our food heater, we
want it to be able to transfer as much heat as possible and thus, Since Copper
has the highest thermal conductivity, the second lowest specific heat capacity
and a high melting point, it is the best option for the metal plate. This is
because it can transfer the highest amount of heat in a short period of time
since it requires a low amount of heat in comparison to the other metals to increase
its temperature by 1 unit of temperature. Thus, the heating efficiency of the
heater with copper as the metal plate material to in turn transfer heat to the
food will be high since a high amount of heat from the source (MRE pack
reaction) will be transferred to the food and it will get heated up in a short
amount of time and the user will not have to wait long for the food to get
heated. In terms of the chemical compatibility, copper has a good chemical
compatibility with the product gases of the reaction which will be in direct
contact with the metal plate and it has a poor chemical compatibility with
water. However as water is not going to be in direct contact with the metal
plate and the food is secured in a separate container sitting on the metal
plate, the risk posed to the contamination and safety of consumption to the
food is low. Thus Copper is chosen as the material for the metal plate.
References:
-
Emporium, S., 2021. carbon steel material
supplier, carbon steel price in india, low carbon steel price in india. [online] Steelemporium.co.in. Available at:
<https://www.steelemporium.co.in/carbon_steel.html> [Accessed 18 July
2021].
-
iscrapapp.com. 2021. [online] Available at:
<https://iscrapapp.com/prices/> [Accessed 18 July 2021].
-
Calpaclab.com. 2021. Carbon Steel Chemical
Compatibility Chart. [online] Available at:
<https://www.calpaclab.com/carbon-steel-chemical-compatibility-chart/>
[Accessed 18 July 2021].
-
Calpaclab.com. 2021. Stainless Steel Chemical
Compatibility Chart. [online] Available at: <https://www.calpaclab.com/stainless-steel-chemical-compatibility-chart/>
[Accessed 18 July 2021].
-
Matweb.com. 2021. Online Materials Information
Resource - MatWeb. [online] Available at: <http://www.matweb.com/index.aspx>
[Accessed 18 July 2021].
- · What is the quantity needed in the desired product?
1 pack of MRE heater and approximately1 oz
of water. (Eat, n.d.)
Reference
Eat, F., n.d. FAQ: MRE Meals Ready to Eat.
[online] Theepicenter.com. Available at: <https://theepicenter.com/faq-mres-ready-to-eat#:~:text=Follow%20instructions%20on%20the%20MRE,Heater%20into%20the%20cardboard%20box.>
[Accessed 17 July 2021].
- · What is the quantity of food it
can heat?
1 serving of food.
Reference
Eat, F., n.d. FAQ: MRE Meals Ready to Eat.
[online] Theepicenter.com. Available at: <https://theepicenter.com/faq-mres-ready-to-eat#:~:text=Follow%20instructions%20on%20the%20MRE,Heater%20into%20the%20cardboard%20box.>
[Accessed 17 July 2021].
- · Does it take place at room temperature?
The heating take place at room temperature
with 1oz of water added to heat up food. (Eat,
n.d.)
Reference
Eat, F., n.d. FAQ: MRE Meals Ready to Eat.
[online] Theepicenter.com. Available at: <https://theepicenter.com/faq-mres-ready-to-eat#:~:text=Follow%20instructions%20on%20the%20MRE,Heater%20into%20the%20cardboard%20box.>
[Accessed 17 July 2021].
- · How fast does it take to heat the food? 12 mins to raise temperature by 38 oC and 50 kilojoules of energy released from heating.
Reference Video: (Shows the chemical reaction and explains it)
- How is it related to OPERATING PRINCIPLES?
- HOw so?
- Difference between the term 'MECHANISMS' in CHEMISTRY🔬 and 🔨👷ENGINEERING...
- 6 Essential Mechanism in functional prototypes 💥
- Acutators
📃📌Mini Presentation to apply the 6 types of mechanisms
Boomerang of the Boat in Action:
Mechanism:
- - Bevel Gear (90 degrees gears which allow for the rotary motion of the propellers)
- - Actuator (When the user propels the boat’s propellers manually the actuator stores the elastic potential energy and upon the user releasing the elastic potential energy is converted to kinetic energy allowing the boat to move)
- - Ratchet (Prevents the boat from rowing backwards)
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