Chocolate Melter
group 1 Nathanael Tan . Tan Boon Yu . Eiros Tan
Content:
1. Introduction 2. Designs and concepts of existing melters 3. Parameters of given task 4. Previous designs 5. Final design 6. Data/analysis
1| Introduction The importance of liquid chocolate in the confectionary, bakery or normal kitchen scene of today cannot be understated. Be it delicious home-made chocolate ice cream, chocolate brownies or chocolate fondue for the Christmas party, melting chocolate is without a doubt an important part of home kitchens.
With raring taste buds, the team sat down with the following workplan to accomplish this term’s PBL of creating a solar chocolate melter:
No. item 1 B/G of chocolate melters 2 Define the parameters conventional melters work within 3 Define our own set of parameters we have to comply by 4 Identify the most prominent source of heat transfer from our parameters 5 Design the concept for the melter 6 BUILD!
We wanted to start by going through various conventional melters and melting techniques, as well as the differences in products by each melting method (some creates a sloshy chocolate texture where others melt it down to the liquidy state. This is no doubt most affected by the type of chocolate used, but the method of melting also affects this). After seeking out the pros and cons of each melting method, we then propose defining the parameters these systems work within (mainly them having electricity and “space-age” materials). With this parameters, we would then aim to either replicate this with our solar mechanisms. If the replication process becomes impossible we will then try to redefine our parameters and figure out a separate system. Brainstorming on these ideas will naturally be followed by trouble predictions and solutions.
2| design analysis of existing melters This section will cover 2 main areas: chocolate melting METHODS and purchasable chocolate melters. It is important to note here that different types of chocolates require different set temperatures to melt to the state that we want (as liquid as possible). Certain types of chocolates burning at overly high temperatures, causing them to solidify thus disallowing the toothpick on top of the chocolate chip to fall. An example of this follows:
If you heat chocolate at too high a temperature, it "seizes," separating into liquid cocoa butter and clumps of cocoa powder, or it can even burn.
To add to the challenge, bittersweet and semisweet chocolate -- which you'll find in baking chips and fine chocolate bars -- can be heated to a slightly higher temperature than milk chocolate or white chocolate. When professional bakers melt chocolate, they may use a candy thermometer to keep dark chocolate between 100°F to just under 120°F and white or milk chocolate at no more than 115°F.
In this case chocolate can actually change state or burn at high temperatures. Conventional melting methods can regulate the temperature by varying the microwave intensity or the size of the flame used. Electrical melters can also vary in heat production by reducing or increasing the amount of electricity reaches the heating elements. However the team has decided that since Ms Tan mentioned that her first attempt to melt the chocolate took 1 hour 15 minutes and our first try with no device (just placing the chip in the sun) took about 30 minutes, we will just go all out into transferring as much heat to the chocolate chip as possible. Also, we are not able to control the temperature in the first place (not easy, given the varying amount of sun, angles and convection of air around).
METHODS
There are 3 known methods for melting chocolate without a professional chocolate melting machine/chocolate melter.
Water bath: Fill a large skillet with water, and heat to just below simmering. Place the chocolate in a heatproof bowl, such as stainless steel, and place the bowl in the water. Gently and constantly stir the chocolate while keeping the water below simmering.
Double boiler: Fill the bottom half of a double boiler with water, making certain the bottom of the top half doesn't touch the water. Bring the water to a simmer. Place the chocolate in the top half, and place over the simmering water. Be careful that the water doesn't boil or
splash into the chocolate, because any moisture will cause it to seize.� Microwave oven: Place room temperature chocolate in a microwave-safe bowl. Microwave at medium power. The chocolate won't completely melt, but it will turn glossy and soft to the touch. Remove from the microwave and stir to finish melting. Microwave 1 ounce of chocolate for about 90 seconds; 6 ounces for about 31/2 minutes, stopping halfway through to stir the chocolate. Since times are approximate, always start with the suggested melting time and repeat in 30-second intervals.
Observations/explanations:
observation method explanation Water is heated and placed below the chocolate container
Hot water bath and double boiler
Ms Tan mentioned this in the notes on thermal cooking. If the heating is not evenly done, the chocolate will turn out to be lumpy and thus not consistent in texture. However the general applicable idea we can obtain from this method is chocolate in contact with a metal piece can be melted well as long as a heat source is provided below. However the chocolate chip will be on a toothpick thus this is not applicable CONDUCTION
Microwave the chocolate Microwave oven
The microwave option seems the most probable for a design. Heat is radiated to the chocolate with specific timings in this case. Radiated heat can be easily obtained on a hot sunny day by reflecting sunlight. RADIATION
Existing melters
All existing chocolate melters involve the chocolate being heated by conduction. This happens when the chocolate is placed in a ceramic or metal bowl which is then placed in a machine with either induction cooker magnets or heating coils that heat up when electricity is run through them. AGAIN this cannot be applied in our current PBL as the chocolate chip cannot be in contact with anything. Therefore the following pictures will only cause us to think further and deeper into the problem of melting:
http://recipes.howstuffworks.com/tools-and-techniques/questions-about-cooking-with-chocolate2.htm
Parameters available to the conventional chocolate melter:
• Electricity heats via heating coils or induction we are not allowed to use electricity.
• Chocolate is in direct contact with a surface for conduction again not allowed to have direct contact.
• Conventional melters and methods have to create a consistent melt consistent melt not needed, only requirement is to drop the toothpick and become semi-slushy.
3| Parameters of given task There are 2 ways to approach elaborating on the parameters given by the task. The first consists of looking at limitations and possibilities of the 3 methods of heat transfer. The second involves considering the possible uses of various materials/equipment and deciding which will work better in the given external environment.
External factors:
Factor Effect remarks Extreme sunlight Extreme sunlight serves
as a positive thing in this situation because it provides the MAIN SOURCE of heat via radiation
Since the chocolate chip cannot be in direct contact with any surface, the main use of this radiant energy should be applied directly on to the chocolate chip. This energy can be used to heat air. When the heating of air is combined with a possible green-house effect, convection currents of air can be created which will provide mild heating to the chocolate chip1
Heat radiated off the surface of the roof
The ground on the roof is black. Since the Sun provides heat energy via radiation, black surfaces absorb and re-emit this energy very well (it’s emissitivity is probably close to 1)
The black roof will absorb radiant energy from the Sun (sunlight) and get hot very quickly. Though the ideal would be to place the chocolate chip on this surface to let it burn, it’s against the rules. However the heated black ground can re-emit this heat energy via radiation to the chocolate chip.
Angle of the sunlight This is an important factor because it will greatly reduce the efficiency of
If the system is to be sealed for a green house effect, how can we angle it
the system if shiny surfaces are not able to reflect this sunlight (radiant energy) onto the chocolate chip effectively.
to face the sun. also, if there is only one huge silver component, will we maximize the use of sunlight on the chocolate chip?
Wind on the roof Because we’re carrying out the experiment in the open (the roof) there will be quite abit of wind. This wind will be able to help cool down the chocolate chip with moving air blowing away the heated air (convection).
The dilemma lies in if we do try to prevent the effects of convection cooling the chocolate chip, will we end up reducing our ability to make full use of the sunlight or the black surface of the roof?
1: remember we mentioned in the previous section that excessively quick heating of the chocolate will cause it to char and harden. Raising the ambient temperature around the chocolate chip will reduce the probability of the charring because the temperature difference between the focal spot of heating and the rest of the chocolate chip won’t be so great.
3 methods of heat transfer: possible implementations
method Possible source apparatus Conduction Air in a green house-like
chamber Some way to contain air around the chocolate chip. Therefore, again: -black container (gets heated up be absorbing radiant heat from the sun. conducts heat to the air inside and around the chocolate chip)
Convection Heat rising from the ground
-black container with a lid -cling wrap to seal and make the internals air tight
Radiation The sun’s light -lens
-mirrors -black container (conduction, convection)
With these information, we set out on the task of building prototypes for our chocolate melter.
4 | previous designs As mentioned in the previous sections, our chain of thoughts included 2 main ideas.
The first consists of using a “gas chamber” and the properties of black objects with relation to radiant energy. This involves creating some type of black, air-tight container around the chocolate chip. This will absorb heat via radiation and conduct it to the air inside the chamber. Because the chamber will be sealed on the top, hot heat will not be able to escape the chamber via the top. This green house effect will create a slower, more gradual, and more consistent (around the surface of the chocolate) way of heating. It will not run the risk burning the chocolate chip and making it hard instead of sloshy. However air is a bad conductor of heat thus this method of heating probably will have to be secondary as it will not melt the chocolate quickly.
The Second involves directing and concentrating the sun’s radiant energy onto the spot which the toothpick is attached to the chocolate. By utilizing as many angles as possible, a combination of mirrors and lenses could be used to direct sunlight onto a specific point on the chocolate chip to drop the toothpick as quickly as possible. The radiant energy that follows the sun’s light, if concentrated on a single spot will not have to be dependant on any medium or convection currents (unlike the first method) and thus might prove to be more robust and reliable
Both methods of melting the chocolate chip should be combined if possible however since the first method would only be effective if there is a large surface area of the container being blacked, which effectively means it reduces the number of angles from which sunlight can be directed to the chocolate chip. Conversely, the great number of mirrors and lenses around the chocolate chip will required a large area around the chocolate chip to be unobstructed. Therefore by an large, both methods can only be in a “either or” basis.
First prototype
Our initial concept was an attempt to combine both methods of using a magnifying glass to concentrate the sun’s energy onto the chocolate chip as well as contain the chocolate chip within a black air tight container that was to be as small as possible.
The setup has 2 components:
The first is a handyhand. This device, more commonly used for soldering consists of a high intensity magnifying glass on a stand. This stand allows the magnifying glass to be angled apositioned in a multitude of ways, ultimately allowing us to modify the angles of the magnifying glass to be perpendicular to the sun’s rays. This will maximize the amount of sunlight captured by the magnifying glass and thus deliver the most amount of energy straight onto the chocolate chip.
nd
The second involves a completely bla
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ecidin
cked out toilet roll (a lot like the picture to theleft just without the paper). This is the “black chamber” we have been referring to. Reasons for choosing the toilet roll include the size (it’s just nice for 2 toothpick and a chocolate chip) and its recyclability. The toilet roll would bspray-painted matt black and cling wrapped tthe ground to create an air-tight seal with theground which is radiating heat itself. This foa green house with the chocolate chip in it.
The following are the formulae involved in d g if this method is good:
)( 42
41 TTAe
tQ
−=ΔΔ σ
The equation above is used the calculate heat transfer via radiation. This affects the amount of heat energy the black toilet roll is able to absorb per unit time. Variables we have control over is the surface area (A) and the emissivity (e). we found that a long and slender toilet roll gave us a good surface area to volume (amount of air inside to be heated) ratio. Also, spray painting the toilet roll matt black would give us a pretty useful emissibility (close to 1).
The handy hand provides a good compromise. It has flexible arms attached to a stand, which allows for different angles and the magnifying glass is not too big. If it were too large in diameter, it would have to be a lot thicker in width to have a short f number (focal length). No doubt a larger diamtere of glass would allow for more sunlight to be concentrated on one spot, the handy hand, with a timing of 12s in noon sun to burn paper, was a good compromise.
Verdict:
This set up was good, clocking 1 minute 2 seconds on our trail run. The warmed environment in the toilet roll also ensured that the magnifying glass’ concentrated radiated heat energy would nburn the chocolate chip. Melting is breaking the intermolecular bonds to allow the chocolate chip turn from solid to liquid where burning occurs along with other chemical reactions which might
result in the hardening of the chocolate instead. Due to technical problems with the datalogger we are not able to produce a graph of the temperature recorded. Howewe realized that there was an exponential curve. This could be due to the green house effect where heated air is built up in the chamber. However this(using a green house chamber) still proved to be pretty ineffective at rapidly melting the chocolachip. This gave rise to our second and final design
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5| the final design introduction/overview:
In our final design, we decided to go all out by using mirrors to redirect sunlight through a lens and onto a specific point on the chocolate chip (the point where the second toothpick was attached). We used a total of 4
sets(mirror + lens) placed on the ground around the chocolate chip. Each mirror and lens was tuned to have the most pin-point accurate focal point of sunlight on the chocolate chip. The handy hand is then placed over the chocolate chip to add an additional focal point of sunlight onto the chocolate chip.
Set up:
As seen in the photo below, 4 sets of mirrors and lens were placed around the chocolate chip, which was, itself, placed on a mirror. Each lens was placed at it’s focal length distance (sun, though reflected by the mirror, is assumed to be at infinity) to the chocolate chip. The angles of each lens was tuned(second picture) such that all of their focal points landed on the chocolate chip itself. After these were established, individual mirrors were placed. The mirrors had to be placed individually to compensate for the lens’ angle and position relative to the direction of the sun. they were held in place by paper clips and blue tack. After all of these were set up, the handy hand was placed over the chocolate chip to add an additional magnifying glass over the chocolate chip
a dummie object was placed in position of the chocolate chip to make sure all focal points landed on the same spot.
Rationale:
In our practise setup, we tried to keep a good control over the thermal energy at the chocolate chip, trying to ensure that the chocolate melts and not burns. We did this by reducing the magnitude of intense, focused sunlight on the chocolate chip, and surrounding the chocolate chip with a mild heat source (the black box + air for conduction). However what te chip (not burn) despite using 5
sets of lenses to focus the sun’s light on the it. HOW? Convection is the mass movement of molecules from one area to another. From previous studies, we have seen that the movement of liquids and air around certain objects allows the system to cool/heat an object more easily. During our trial, we realized that the roof we were working on actually has pretty good wind conditions. The photo above gives great testimony to the ability for convection (of air, in this case) to cool an object.
What is happening is the 5 lenses are focusing so much ligh
we realized is it is possible to melt the chocola
t on the end of a
n
ll three methods of heat transfer. adiati t out
le
toothpick (bare toothpick) that it is glowing red-hot. However, the toothpick is not bursting into open flames nor charring quickly. This is because, the intense radiationfrom the sun focused on the tip of a toothpick is radiating a lot of thermal energy into the toothpick. However, the convection of air (that is of lower temperature thathe toothpick) allows heat to conduct away from the toothpick at a constant rate (the movement of air maintains a constant gradient) and thus the toothpick is kept at a very comfortable temperature.
Our system utilized the concept of aR on is the main heating source in the system. However, conduction of heaof the toothpick and the movement of air (as well as the free convection of air upwards after it has been heated) allows the temperature to be quite comfortabfor melting.
Summary:
Materials/design
Mirrors Surface is shiny and bright, low radiation emissitivity n’s therefore will be good at reflecting almost all of the su
radiant energy Lenses t energy is targeted at the lenses. The lens Reflected radian
focuses radiant energy on a pin-point to melt the chocolate Handy hand on
t up
Acts as an additional lens to focus the sun’s radiant energy the chocolate chip. It has a larger diamter thus is able to redirect a lot more sunlight at the chocolate chip to heat imore quickly
Open air design esign (lack of container) aids the chocolate chip The open air dsuch that it will melt and not burn. This will help us to achieve a soft state of chocolate rather than it being fried(burnt) and going solid.
No ‘fixed box’ ave to be aimed individually due to the position of
nduct
All mirrors hthe sun across the sky, the team’s given position on the roof, the placement of lenses and other factors. Also aids in providing an open air design for free air movement to coheat away.
Types of heat transfer Radiation Main source of thermal energy. Sunlight is focused on the
chocolate chip. This provides radiant energy in the form of infrared waves to the chocolate chip which heats it up.
Conduction Heat is conducted away from the point to the surrounding air to prevent burning.
Convection d to move freely and thus away The heated air is allowefrom the heat source allowing cooler air to move closer and constantly take the heat away from the chocolate chip.
Operation steps Step 1 Placed the lenses at focal length from the chocolate chip placed on
a toothpick held up by bluetack which is placed on a mirror. It is advised that the lenses aren’t place in the direction of the sun relative to the chocolate chip
Step 2 rors, one for each lens. The mirrors
Individually place and tune mirshould be placed at an angle such that the 3 dimensional angle of incidence is equal to the required angle of reflection such that thesunlight can be reflected onto the lens.
Step 3 e chocolate chip and
lens and the chocolate chip
Place a dummie object in the place of thindividually tune the: 1)distance between the
2) angle of the mirrors 3)pitch of the lenses To ensure that it is a PIN-POINT focal point of light at the chocolate chip
Step 4 hand perpendicular to the light rays from the sun to Place the handythe chocolate chips. Ensure the magnifying glass has its focal point on the chocolate chip.
Step 5 p on the tip of the toothpick and start timing Place the chocolate chiStep 6 Stop timing once the melting has completed and the toothpick has
fallen from the chocolate chip
6 | data and analysis This is the results of our data logger put into the position of the chocolate on the trial day.
Chocolate Time Temperature
0 46.8889 10 47.312 20 47.325 30 47.366 40 47.389 50 47.699 60 47.778 70 48.111 80 48.534 90 48.783 100 49 110 49.32 120 49.667 130 49.889 140 50.25 150 50.467 160 50.733 170 50.924 180 51.222 190 51.455 200 51.666 210 51.739 220 51.988 230 52.111 240 52.222 250 52.33333 260 52.44444 270 52.44444 280 52.66667 290 52.88889 300 53 310 53.33333 320 53.55556 330 53.77778
340 53.88889 350 54 360 54 370 54.11111 380 54.33333
This is the graph of the estimated temperature of the chocolate against the time taken.
Basically, based on the trendline of the most appropriate temperatures for a certain time, the temperature started off at 47.06 degrees Celsius. On average, for every second, the temperature increased by about 0.0204 degrees Celsius. At the end, it was approximately 54.812 degrees Celsius. In total, the temperature increased by about 7.752 degrees Celsius over a period of 380 seconds, or six minutes and twenty seconds.
y = 0.0204x + 47.06
4647484950515253545556
0 100 200 300 400
Chocolate Temperature
Chocolate Temperature
Linear (Chocolate Temperature)
As you can see, the gradient of the graph is very high at first, with a higher rate of increase in temperature. However, as the temperature gets higher, the temperature starts to increase slower. This is because at the start, the environmental temperature is much higher than that of the data logger, so the temperature will increase faster. However, as time passes by, the difference between the temperature of the environment and the data logger is not as high, so the temperature gradient is less steep, hence there is slower transfer of heat, so the increase in temperature is lesser.
However, this may not be the actual temperature. Chocolate is made up of a few different substances, out of which none of them are metal, which the data logger is made of. Since all substances have a different specific heat capacity, the
difference in substance will cause a difference in temperature since the rate of increase in temperature is different. Also, the temperature is affected by a few different factors, including environmental factors (such as wind, surrounding temperature, humidity, sunlight). As the environmental conditions maybe different on any given day, thus the temperatures reading may not be very accurate.
The final time taken to melt the chocolate chip was 43 seconds which was a great improvement from our original design. The picture below(though blurry) shows that the chocolate was slightly burnt. However compared to a previous test where we tried shutting off air flow(we tried out best to cover any free moving air to prevent heat loss from the chocolate chip) it is a vast improvement as the chocolate chip burnt too quickly, hardened and the toothpick wouldn’t fall.
Conclusions:
Pros • Final time of 43 seconds ranks us 6th • The system uses all 3 modes of heat transfer • The system used duplicates of the same materials
and apparatus rather than multiple different ones • This makes the system very focused in concept –
using as much focused radiant energy to melt the chocolate chip
• A focused point of sunlight is better than just mirrors or just a shiny bowl where the sunlight might be a lot more diffused.
• Free air flow around the system helped melt the chocolate and not burn it
Cons • The chocolate turned out still slightly charred • The system has a lot of “on the spot” tuning • Because the system was so open, it’s more
susceptible to environmental variables. To Be Improved • The system could be more of a “machine” rather
than parts • Mirrors, though required to be tuned, could be
placed on hinges in a complete system. • More mirrors and lenses could have been set up
and focused on other points of the chocolate so that it doesn’t get burnt but turns molten and liquid more quickly
• A larger magnifying glass could have been attached to the handy hand
Learning outcome Although conventional melters use a certain form of heat transfer(conduction) to melt chocolate and does so well, it is also possible to melt chocolate via other methods of heat transfer. We have also learnt to be more open to new ideas and test them all out. In the beginning both methods seemed as promising but eventually one worked a lot better than the other.
Reflections Throughout the course of this problem-based learning (PBL) project, We have gained a lot, in the fields of both research and experience.
Firstly, before We started this module, we had no idea that there was such an appliance used to melt chocolate, and we had absolutely no idea how one worked. So, the only way we could find out more was by doing research. In addition to reading the brief description provided on the Physics platform website, we also conducted our own research and read up on different designs of chocolate melters, how they worked, and other things. After that, our knowledge about the chocolate melter greatly increased. Also, during the course of the research, we have developed much better research skills, as we needed to find multiple sources to find what we was searching for, and we also needed to refine my search terms to change what kind of results we wanted to find.
Secondly, we have gained a lot of experience. When we first started off, we did not have much experience in this field or experiments. However, after spending time with our groupmates discussing and also spending time on our own doing our own research, we have learnt a lot on thermal experiments and other concepts related to thermal physics, including the three main types of heat transfer: conduction, convection and radiation.
References http://www.mansfieldct.org/schools/mms/staff/hand/convcondrad.htm
http://en.wikipedia.org/wiki/Conduction_(heat)
http://candy.about.com/od/workingwithchocolate/a/meltchocolate.htm
http://en.wikipedia.org/wiki/Melting
http://www.ornl.gov/info/ornlreview/v30n3-4/solids.htm
http://www.recipelink.com/cookbooks/2001/0767906071_1.html
