biofuel (experiment 1)

8/20/2019 Biofuel (Experiment 1)

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DIFFERENCE BETWEEN HEAT FLUX OF STARCH SOLUTION AFTER HEATED BY HOT

PLATE AND MICROWAVE OVER TIME IN COOLING PROCESS

Heng Joe Shen

Department of Chemical Engineering

University of Malaya

50603 Kuala Lumpur

Email: [email protected]

Abstract

The main objective to carry out this experiment is to investigate the difference between heat flux of starch

solution after heated by hot plate and microwave over time in cooling process respectively. A graph of

temperature against time taken and heat flux against time are plotted. Nearly similar trends are observed in both

methods although there are significant differences in the heat flux initially.

Keywords: hot plate, microwave, starch solution and heat flux .

1.0 THEORY

From the definition of heat capacity, the rate of heat loss of the starch solution is given by …(1)

Since there is no direct value given for the specific heat capacity of starch solution, we assumed that the heat

capacity of the starch solution is nearly identical with that of water, 4.178 J/g ºC. This is because the starch

solution used is very dilute, 2%.

Under continuous mixing by magnetic stirrer, instantaneous rate of heat flux, q can be calculated by

…(2) where

= Mass of the solution

= Specific heat capacity of solution

= Temperature difference

= Cross sectional area of the beaker

= Time taken



2

2.0

METHODOLOGY

2.1 Apparatus and Materials

Two 100ml beakers, tissue papers, spatula, balance, magnetic stirrer, hot plate, microwave, thermometer, ruler

and stopwatch. Deionized water, ethanol solution and tapioca flour.

2.2 Conditions1. The fan is switched off during the whole experiment to prevent inaccurate results. The heat loss is purely by

natural convection.

2. Both beakers are allowed to cool down on the same table to prevent deviations due to direct contact with the

outside environment.

2.3 Procedure

1. All the apparatus and materials needed are collected and washed with deionized water.

2. Ethanol solution is sprayed onto tissue papers. The tissue papers are then used to wipe the inner walls of all

the apparatus to ensure all viruses are killed.

3. Two beakers are labeled with ‘hot plate’ and ‘microwave’ respectively. Their weights are recorded

respectively.

4. 2 grams of tapioca flour is added into each beaker and their weights are recorded respectively.

5. 100 ml of deionized water is poured into each beaker. Their weights are then recorded again respectively.

6. The heights of the starch solution in the beakers, the inner and outer diameter of beakers are measured.

7.

The beaker labeled with ‘hot plate’ is heated using hot plate and continuously stirred using magnetic stirrer

until 80ºC. On the other hand, the beaker labeled with ‘microwave’ is heated in microwave w ith magnetic

stirrer until 80ºC. Once they reached 80ºC, the beaker is immediately taken out respectively.

8. oth are allowed to cool down by themselves to 2 C. At particular temperatures during cooling, the time

taken to reach particular temperatures for each beaker is recorded respectively.

9. All the data is tabulated and plotted in graphs.



4

0 1000 2000 3000 4000 5000 6000 7000 800020

30

40

50

60

70

80

90

Time taken (s)

Temperature_hotplate

Temperature_microwave

time1 time2

0 800 1600 2400 3200 4000 4800 5600 6400 7200 80000

200

400

600

800

1000

1200

1400

1600

1800

2000

Time taken (s)

H e a t f l u x ( J /

s * m 2 )

Heat_flux_hotplate_wbeaker

Heat_flux_microw ave_wbeaker

Heat_flux_hotplate_woutbeaker

Heat_flux_microw ave_woutbeaker

time1 time2 time1 time2

Graph 1: Graph of temperature against time taken by starch mixture to decrease from 80˚C to 29˚C.

Graph 2: Graph of temperature against time taken by starch mixture to decrease from 80˚C to 29˚C.

4.0 DISCUSSION

From graph 1, both starch solution heated using hotplate and microwave show almost similar trend although

overall, the starch solution heated using hotplate took 7615 seconds to reach 29ºC compared to 6066 seconds

only using microwave.



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From both graph, it is observed that the starch solution heated using hotplate cools down faster initially but the

heat flux eventually drops below that of microwave at some points. Both the heat flux eventually reached a

nearly identical value towards the end. The difference varies from as small as 16.02% at 70ºC to as large as

44.63% at 29ºC.

Similar trends are observed when we exclude the mass and surface area of beaker in the calculation. The

difference varies from as small as 16.01% at 70ºC to as large as 45.24% at 29ºC.

Errors involved in the experiment

In this experiment, there may be several errors that cause experimental results to deviate from theoretical

values.

Since one beaker is measured using thermocouple while another using thermometer, there may be slight

deviation in the time taken. There is possibility of parallax error too in using thermometer.

Since both beakers are not covered with aluminium foil to prevent heat loss via conduction, there is

possibility that some solution evaporated in the process or particles in the air contaminate the solution.

5.0 CONCLUSIONS

1. Both starch solution cools down in a similar trend.

2. There is a significant difference in heat flux between starch solution heated using hotplate and microwave

respectively.

6.0 REFERENCES

1. Azmi, A., Hasan, M., Mel, M. Ngoh, C. Single-step bioconversion of starch to bioethanol by the coculture of

ragi tapai and Saccharomyces cerevisiae. Deparment of Chemical Engineering, University of Malaya, Kuala

Lumpur & Biotechnology engineering, Kulliyah of Engineering, International Islamic University Malaysia

Kuala Lumpur.

2. Saelim, K., Dissara, Y. & Kittikun, A.H. Saccharification of cassava starch by Saccharomycopsis fibuligera

YCY1 isolated from Loog-Pang (rice cake starter). Department of Industrial Biotechnology, Faculty of Agro

Industry & Department of Microbiology, Faculty of Science, Prince of Songkla University, Hat Yai

Songkhla, 90112 Thailand.

3. Ko, S.D. Tape Fermentation. Agricultural University, Department of Food Science, Wageningen

Netherlands.

4. Borglum, G.B. Starch Hydrolysis for Ethanol Production. Miles Laboratories, Inc. Industrial Products

Group, Elkhart, Indiana.

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