In practical 1, we learnt about the workings of a coffee maker as well as how a bubble pump works.
Here is our findings:
Written Assessment
Having completed the necessary reverse engineering work, you have to analyse the data gathered and answer the following questions.
Describe, with the aid of schematic diagram(s), the operating principles of BD100® coffee maker. (10 marks)
Describe the bubble pump mechanism that is used in BD100® and how it represents a simple, effective and yet inexpensive design solution to artificial gas lifting. (10 marks)
The water enters the heating element and is vapourised. Since water vapour has a much lower density as compared to water, it expands and pushes water up easily. Water is also heated up at the same time which saves energy. As compared to other mechanisms that use mechanical means to move a fluid, the bubble pump mechanism is driven mainly by thermal energy, hence components are simpler and lesser, resulting in a lower equipment cost.
Present all the data collected in a Table 1. Show sample calculations whenever appropriate. (20 marks)
Time interval(s) | Temperature (°C) | Energy (kWh) |
0 | 25.3 | 745.1 |
30 | 35.6 | 745.1 |
60 | 49.1 | 745.1 |
90 | 62.4 | 745.1 |
120 | 74.5 | 745.1 |
Mass of dry coffee filter paper (g) | 1.193 |
Mass of coffee powder used (g) | 20 |
Volume of water used (ml) | 300 |
Volume of coffee brewed (ml) | 482.62-219.72=262.9 |
Mass of condensate on lid (g) | 1.46 |
Mass of Wet Coffee filer & spent coffee powder (g) | 482.62 |
Temperature of brewed coffee (°C) | 74.5 |
Average temperature of coffee powder (°C) | 25.3 |
Time taken to brew the coffee (s) | 214 |
Power (WATT) | 44.3 |
Average energy reading (Wh) | 745.1 |
Wet tissue before (g) | 6.14 |
Wet tissue after (g) | 7.60 |
Mass of condensate collected (g) | 7.60-6.14=1.46 |
Dry tissue (g) | 1.94 |
Calculate the approximate amount of energy transferred to the coffee in BD100®. (15 marks)
Latent heat of water: 1.46g x 2,258 J/g =2396.68J
Sensible heat of water: (100-25.3)°C x 4.18J/g°C x (300-1.193)g = 93301J
Total energy used: 93301 + 2396.68 = 95697J
Calculate the percentage of energy consumed by BD100® that was actually transferred to the coffee. Comment on the result. (15 marks)
956971 / (745.1 x 3600) x 100% = 35.7% (3s.f.)
The energy efficiency of the coffee maker is low because more than half of the energy is wasted.
Describe two ways to improve the percentage value that was calculated in Question 5. (10 marks)
One of the way to improve the percentage value is by using a better conductor of heat. This will ensure that lesser heat is loss during the transfer from the heating element to the water, thus resulting in higher percentage of energy consumed that was actually transferred to the coffee.
Another way to improve the percentage value is by using insulation outside of the coffee maker casing so that it minimizes heat loss to the surrounding. With insulation, lesser heat will be lost to the surrounding meaning that more heat energy will go to the coffee therefore there will be a higher percentage of energy consumed that was actually transferred to the coffee.
State the assumptions that your team have made to simplify the calculations above. (10 marks)
Heat capacity are constants for the temperature a range of this study.
Black water has the same specific heat capacity as water.
Black water has the same density as water.
Negligible amount of water is left on the filter paper.
List down the sources of error in the data collection and calculation (10 marks)
When finding temperature of coffee powder when boiling, one must open the lid to stick thermometer inside. By doing so, heat and steam is lost to the environment so temperature is not fully accurate.
The lost steam may affect the weight of the wet tissue.
Wet tissue did not fully cover the steam escaping from the vent so weight of wet tissue may be affected.
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