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TABLE OF CONTENTS

NO.

TITLEALLOCATED MARKS (%)PAGES

1Abstract/Summary52

2Introduction53

3Aims54

4Theory54

5Apparatus/Materials59

6Procedure109

7Results1010

8Calculations1014

9Discussion2015

10Conclusion1017

11Recommendations517

12Reference518

13Appendices519

1.0ABSTRACTIn this experiment, we use as pandan leaves a sample. This is because pandan leaves take short time to dry and decrease the moisture content faster with time. The measurement of the moisture content is based on the weight of the sample which inversely proportional with the temperature and time. The weight of water was recorded every ten minutes until there was no more water in the sample (Reaching the equilibrium). Thus, the drying rate of the sample can be determined. Based on the data from the experiment, the mass and moisture content is decreasing with time, whereas the drying rate is varying rapidly with time.

2.0INTRODUCTIONDrying is a process of removal of relatively small amounts of water from material. In drying the water is usually removed as a vapor by air. Besides, some water also can be removed by mechanically from solid materials by presses, centrifuging and other methods. This method is much cheaper than drying by thermal means for removal of water. When a wet solid is subjected to thermal drying, two processes occur simultaneously; first is the transfer of energy, mostly as heat from the surrounding environment to evaporate the surface moisture, and second is the transfer of internal moisture to the surface of the solid and its subsequent evaporation due to the first process.Drying processes can be classified as batch, where the material is inserted to the drying equipment and drying proceeds for a given period of time, or as continuous, where the material is continuously added to the dryer and dried material continuously removed.The common type of dryer in many industrial applications that involve drying operation is tray dryers (or cabinet dryers). The dryers are made of trays held in a cabinet, which is connected to a source of heated air by gas, diesel or biomass. The food, which is to be dried, is spread out, generally quite thinly, on trays which the drying takes place.Most tray dryers are heated by air, which also removes the moist vapours. The dryer trays are tight-fitting in the cabinet to prevent air from bypassing the material to be dried. Tray dryers require low capital and maintenance costs but have relatively poor control and produces more variable product quality. However, in recirculation designs, the moisture laden air, after evaporating water from food, would have to be dried before being undergo recirculation, or else it would soon become saturated and further drying of the food would stop.One of the most important problems encountered is not to supply the same drying rate at the all position within the tray dryers. The other is the fast drying of food in the position where the air first enters to the system and the slow drying of food in the other position. Therefore, additional heaters and fans may be placed above or alongside the trays to increase the rate of drying. Tray dryer are used for small-scale production or for pilot-scale work.3.0OBJECTIVESTo determine the drying rate of the sample by drying method using tray dryer

4.0THEORY

4.1Principle of dryingThe purpose of drying is to remove the liquid adhering to a material and contained within it. The drying curve depends on the form in which the moisture is present in the material to be dried. The surface moisture is evaporated first and carried away by the drying air as it surrounds the materials to be dried as a thin film.The drying process proceed more slowly for the moisture that is located in capillaries and pores within the material. This is because the capillary forces or diffusion resistance must be overcome.The removal of the water of crystallization contained in the material to be dried is even more difficult as it is bonded by relatively strong molecular forces. To expel it, the material to be dried has to be intensely heated. The drying curve is therefore divided into several stages. In the first drying stage, the liquid adhering to the surfaces of the material to be dried evaporates rapidly at a uniform drying rate.Drying of the capillaries is followed by drying in the pores. To do this, the liquid situated there must be evaporated so that it can diffuse through the material to be dried. This process is relatively slow and thus further reduces the drying rate. Intense heating of the material to be dried over longer period of time finally expels the liquid bonded within the crystal structure. In most technical drying does not continue to absolute dryness but to an agreed residual moisture level.

4.2Drying processDrying is the process of thermally removing volatile substances (e.g. moisture) to yield a solid product. Mechanical methods for separating a liquid from a solid are not considered in thermal drying. When a wet solid is subjected to thermal drying, two processes occur simultaneously. First, is the transfer of energy, mostly as heat from the surrounding environment to evaporate the surface moisture, and second is the transfer of internal moisture to the surface of the solid and its subsequent evaporation due to the first process.Drying occurs with the help of evaporation by supplying heat to the wet feedstock. There are two option for medium of heat transfer that is through convection by direct driers or conduction by contact or indirect driers. The removal of water from drying is to inhibit the growth of microorganisms and therefore the food is well preserved besides reducing the weight and bulk of food for cheaper transport and storage. When carried out correctly, any alternation of nutritional quality, colour, flavour and texture of rehydrated foods will not be affected to much.Drying methods and processes can be classified as batch, where the material is inserted into the drying equipment and drying proceeds for a given period of time, or as continuous, where the material is continuously added to the dryer and dried material continuously removed. Drying processes can also be categorized according to the physical conditions used to add heat and remove water vapour. In the first category, heat is added by direct contact with heated air at atmospheric pressure, and the water vapour formed is removed by the air. In vacuum drying, the evaporation of water proceeds more rapidly at low pressure, and the heat is added indirectly by contact with a metal wall or by radiation (low temperature can also be used under vacuum for certain materials that may decolourize or decompose at higher temperature). Infreeze drying, water is sublimed from the frozen material.

Figure 4.1: Drying process

The first consideration in selecting a dryer is its operability. The equipment must produce the desired product in the form at the desired rate. The quality required in a final product, and its necessary physical characteristics, are determined by its end use. The final choice is then made on the basis of capital and operating costs. Attention must be paid, however, to the costs of the entire isolation system, not just the drying unit alone.Thermally sensitive materials must be dried at low temperature under vacuum, with a low-temperature heating medium, or very rapidly. The dryer must also operate reliably, safely, and economically. Operation and maintenance costs must be excessive, pollution must be controlled, energy consumption must be minimised. As far as the drying operation itself is concerned, adiabatic dryer are generally less expensive than non-adiabatic dryers, in spite of the lower thermal efficiency of adiabatic units. Unfortunately there is usually a lot of dust carry over from adiabatic dryers, and these entrained particles must be removed almost quantitatively from the drying gas.In herbs and medicinal industry, most medicinal and culinary herbs are sold dried. When drying large quantities of herbs for commercial sale, growers should use a forced-air dryer to preserve their colour, flavour, oil content, and medicinal properties. To achieve this, good air circulation with in the dryer is important, as it reduces drying time and allows the use of lower temperature, both of which can prevent the degradation of chemical constituents during the drying process. Therefore, dependable temperature control and the ability to provide high air flow throughout the plant material are important. Drying temperature and times differ by plants, and plant parts, thus most herbs should be dried at low temperatures, ideally around 90-100F. When outside conditions are hot and humid, however, it may be necessary to raise temperatures to as high as 130F. The size of the dryer should be based on the herb production area and how much will be harvested at one time.The dryer should have well-spaced racks to ensure that all sides of the plant receive sufficient air flow and the plant material dries evenly. Then shelves should be constructed of food grade screens or covered with an acceptable food grade material. The dryer should be free of dust, dirt, insects, and rodents. Evidence of any of these in the final product can lower its value or render it unmarketable (University, 2008).The dryer should be able to hold an entire harvest and dry it fast enough that the crop does not spoil. Efficiency and economic concerns must be taken into consideration to ensure the cost-effectiveness of its operation. Likewise, a dryer can be constructed from a new or existing shed outfitted with a heater, fan, and dehumidifier. Additionally, a grower may choose to construct one from scratch. In this experiment, pandan leaves are chosen as herbs that undergo drying process by operating tray dryer. The best method to dry herb will depend largely on the physical characteristics of the material, the volume of herb in the dryer, and the relative humidity of the outside air.Different herbs will require different temperatures. Typically, the higher the ambient humidity, the higher the temperature that is required to dry the material thoroughly. Introducing drier air will reduce the amount of time the material is in the dryer, thus reducing the cost of drying the material. The moisture content of dried products is very important, and if it is too high, moulds and yeasts tend to grow. The moisture content may be checked using content may be checked using scales and an oven. The following is the expression that we may use in order to calculate the moisture content of our drying tea leaves.The most important key figure in drying is the moisture content V of the material to be dried. This is defined as :V= ............. Equation (1) = mass of liquid in kg = mass of solid in dry state in kgThe change in the moisture content during the drying process can be used to derive the drying rate v.V = ............. Equation (2)v = Change in moisture contentt = Drying time for this change

4.3The Mollier h,x diagramThe Mollier diagram provides information about the loading of the air with water, depending on the temperature and the relative humidity. This diagram only applies at atmospheric pressure. The loading X describes the mass ratio of water vapour in the air to the mass of the dry air .X = .....................Equation (3)The axis labels have the following meanings:X : Loading [g/kg] : Relative humidity [hPa/hPa] : Temperature of moist air [C]h : Specific enthalpy of air [kJ/kg]h/ X : Change in enthalpy for 1 kg absorbed water vapour [kJ/kg]The lines in the Mollier diagram have the following meanings:1. Lines of constant temperature (isotherms)2. Lines of constant specific enthalpy (isenthalps)3. Lines of constant relative humidity, 4. Lines of constant loading XAs we move along a line in the Mollier diagram, the corresponding variables does not change.

Other important parameter for drying process is the drying rates, v (min-1)

V =

5.0APPARATUS1. Tray dryers2. Analytical balance3. Pandan leaves4. Anemometer

6.0PROCEDURE1. All of the equipment which used in this experiment were switched on.2. Rinse the empty tray using water before start.3. The mass of the empty tray were measured and tare. The data was recorded.4. The dry pandan leaves were sprinkled with enough of water to make it wet.5. The pandan leaves were placed onto the empty tray and put into the tray dryers to be prepared to be dried.6. The initial mass of the wet tea herbs were measured and recorded being dried.7. The initial temperature and humidity which shown on the tray dryers taken and recorded. The initial air flow inside the tray dryers were measured using the anemometer and the readings was recorded.8. The drying process is started by pressing the HEAT button on the tray dryers.9. All of the data read and recorded every 10 minutes in one hour thirty minutes of the drying process of the pandan leaves.10. The moisture content and the drying rate were calculated.11. The graph of drying rate against moisture content was plotted.

7.0RESULTS

7.1DataInitial values:Weight of tray (4 trays) = 1390.2 gInitial weight of sample pandan = 120.5 gInitial Temperature 1 = 27.4 CInitial Temperature 2 = 42.3 CInitial Humidity 1 = 42.5 %rFInitial Humidity 2 = 00.5 %rFMoisture content = 43.8 gTable 7.1: The data during 90 minutesTime (mins)Weight (g)Temperature 1(C)Temperature 2(C)Humidity 1(%rF)Humidity 2(%rF)Velocity(m/s)Moisture content(g)DryingRate(g/min)

10.0117.843.642.608.006.70.4741.10.270

20.0111.344.944.207.506.60.6634.60.460

30.0105.845.546.907.506.61.2829.10.490

40.0100.245.845.207.506.61.4323.50.506

50.094.446.045.407.506.61.5117.70.522

60.089.845.845.207.506.61.4913.10.512

70.085.646.145.607.506.61.508.90.499

80.081.745.845.407.506.61.555.00.485

90.076.746.846.307.506.61.380.00.487

7.2Graph

Figure 7.1: Graph of weight against time

Figure 7.2: Graph of Temperatures 1 and 2 against time

Figure 7.3: Graph of Humidity 1 and 2 against time

Figure 7.4: Graph of velocity against time

Figure 7.5: Graph of moisture content against time

Figure 7.6: Graph of drying rate against time

8.0CALCULATIONS8.1Calculation of moisture content:To calculate the total moisture content of the sample pandan leaves, the following formula is used:

To calculate moisture content at certain time, the following formula is used:

Where mt is the mass of pandan sample at a certain time t. For example, to calculate moisture content at 30 minutes:

8.2Calculation of Drying Rate:To calculate the overall drying rate of the tray dryer, the following formula is used:

To calculate the drying rate at a certain time range, the following formula can be used:

For example, to calculate the drying rate at t=40 mins:

To calculate drying rate from t=20 mins to t=50 mins:

9.0DISCUSSIONBased on the graphs plotted, for graph A, which is mass of pandan sample versus time, the mass of pandan sample decreases with time. This is due to the loss of moisture content during the drying process, in which we can observe from graph E, which is graph of moisture content versus time. These two graphs show similar patterns, that is they both show declining slope.The moist content in the pandan leaves sample decreases with time by evaporation process. During the first 10 minutes, the drying rate is relatively low, compared to the drying rates after that. The best explanation for this is, at this time, the heat is being transferred by various methods to the sample and the moist content in it. Heat is transferred by conduction from the trays. Heat is also transferred via convection with the moving air surroundings. Besides that, heat is also transferred by radiation with the air surroundings. This heat will cause the moist in the pandan sample to migrate to the surface of the sample. This explains the small decrease in weight and moisture content, as the moist particles are mostly still within the sample.After the 10-minute period, we can observe from graph F, drying rate against time, starts to increase drastically. This pattern is also related to the pattern in graphs A and E, where the mass of sample and moisture content starts to show a larger decrement. This is because, at this stage, the moist content, which has already migrated to the surface of the sample, starts to evaporate to the surroundings. Thus, the moisture content in the pandan sample becomes lesser as the drying is conducted. At this stage as well, the velocity of the dryer starts to increase rapidly, thus increasing the rate of evaporation. This is because at high speeds, the moisture particles surrounding the pandan leaves sample will be pushed away from the sample, thus leaving more space for more moist particles to be evaporate from the pandan.As for the humidity in the dryer, it is observed that after the 10-minute mark, the humidity shows a much lower value than compared to before the 10-minute mark. Low humidity also promotes faster evaporation rate. Low humidity means that there is low moist content in the dryer surroundings. This means that there is not much space in the air which is occupied by moist particles, thus allowing the moist from the pandan to evaporate quicker, as there is less barrier in the air surrounding it. It is also observed that the humidity remains constant throughout the process, after the 10-minute mark.

For the temperature inside the dryer, for temperature 2, which is the temperature after the tray and samples, is nearly constant throughout the entire process. As for temperature 1, which is the temperature before the tray and samples, before the 10-minute mark, the temperature is quite low, as compared to the temperature after t=10 minutes. After 10 minutes, both temperatures show similar values, which are in the range 40C < T < 50C, which is quite high. This can be related to the larger decrease in moist content and mass of samples during the same period of time. High temperatures promote faster evaporation, thus explaining the higher drying rate at this time interval.However, after the 50-minute mark, the drying process starts to become slower. From graph A and E, the decrement in weight and moist content respectively, starts to become smaller, as compared to before this time period. A similar pattern is observed for graph F, graph of drying rate. The drying rate starts to decrease after t=50 minutes. These conditions occur, as the rate of evaporation has become the limiting factor. The evaporation rate as a limiting factor, means that unless the rate of evaporation increases, the drying rate will remain nearly constant. The rate of evaporation at this period starts to slow down, as the moist content at this time has become very low, thus less moist particles evaporate from the pandan leaves. Although the temperature remains high, the humidity remains low and the air velocity remains high, these factors give no effect as the evaporation rate has become the limiting factor.

10.0CONCLUSIONThe mass of pandan sample decreases with time. The moist content in the pandan leaves sample decreases with time by evaporation process. During the first 10 minutes, the drying rate is relatively low. As for the humidity in the dryer, it is observed that after the 10-minute mark, the humidity shows a much lower value than compared to before the 10-minute mark.For the temperature inside the dryer, for temperature 2, which is the temperature after the tray and samples, is nearly constant throughout the entire process. As for temperature 1, which is the temperature before the tray and samples, before the 10-minute mark, the temperature is quite low, as compared to the temperature after t=10 minutes. After 10 minutes, both temperatures show similar values, which are in the range 40C < T < 50C, which is quite high.Although the temperature remains high, the humidity remains low and the air velocity remains high, these factors give no effect as the evaporation rate has become the limiting factor.

11.0 RECOMMENDATIONThere are several steps of recommendation to be considered in this experiment to get an accurate data and progressing smoothly. Firstly, general step-up must be conducted as given, then followed by the experiment procedures and end with the general shut-down procedures. It is to make sure that the experiment can be performing successfully. Besides, use a proper knife or scissor to cut pandan leaves. Do not operate this unit in cold condition. In addition, during taking the reading of weight of pandan leaves by using digital weighing balance, the reading of weight should be taking in more significant figures so that to avoid any error and get result more accurate in order the true values could be minimized. Moreover, the average weight of pandan leaves should be calculated by taking weight of pandan leaves in three or two time in order to get more accurate value.

12.0REFERENCES

Limiting Factor. (n.d.). Retrieved from Wikipedia: http://en.wikipedia.org/wiki/Limiting_factorThe Rate of a Chemical Reaction. (n.d.). Retrieved from ChemWiki: http://chemwiki.ucdavis.edu/Physical_Chemistry/Kinetics/Reaction_Rates/Reaction_Rate/The_Rate_of_a_Chemical_ReactionUniversity, N.C.S. (2008) 'Dryer for Commercial Herb Growers', October, pp. 1-8.Bird, R.B, Steward. WE, and Lightfoot, EN, Transport Phenomena, John Wiley and Sons, Inc, 1960.Lab manual (2014). Chemical engineering Laboratory 1.

13.0APPENDICES

Figure 13.1: Control panelFigure 13.2: Fan

Figure 13.3: Pandan leavesFigure 13.4: Dryer

Figure 13.5: AnemometerFigure 13.6: Tray dryer unit