Study a new atmospheric freeze drying system incorporating a vortex tube and multi mode heat input 3

Chapter-3 Experimental Apparatus and Procedure CHAPTER EXPERIMENTAL APPARATUS AND PROCEDURE An experimental investigation was undertaken to evaluate the drying performance of a vibrated atmospheric freeze drying by varying over a range of possible parameter values. The test setup was designed and constructed to allow testing of multimode or intermittent heat input together with variable pressure of the compressed air supplied to the vortex tube to provide different subzero temperature inside the drying chamber. The experimental program, including the design and construction of the test set-up, the instrumentation and the measurements is presented in this chapter. Experiments were also conducted using a laboratory freeze dryer and a heat pump dryer in order to carry out a comparison with the newly developed proposed AFD system. 3.1 Experimental Apparatus A schematic of the atmospheric freeze drying system along with a photograph of the test rig is shown in Figures 3.1 and 3.2, respectively. It consists of a vibrator with variable amplitude (1-5 mm) and frequency (1-25 Hz), a screw compressor, a vortex tube cooler, a noise muffler, a ceramic radiation heater assembly, a conduction plate, an insulated dryer drum, freezer and insulated dryer exhaust. Details of the major components of the set-up are described in the next section. 29 Chapter-3 Experimental Apparatus and Procedure Figure 3.1 Schematic layout of the atmospheric freeze drying system 30 Experimental Apparatus and Procedure Chapter-3 Figure 3.2 Photograph of the experimental setup 3.1.1 Drying chamber Figure 3.3 is a photograph of the AFD dryer. The dryer was constructed of a horizontally oriented drum, made of acrylic and insulated with Armoflex. Length, inner radius and wall thickness of the dryer were 300mm, 200mm and 5mm, respectively. Two O-rings of different radious (115mm and 125mm) and equal thickness (3mm) were used with a flange type fitting on one side of the drum to seal it properly. Exit air from the drying chamber passed through the open area of a 3mm circumferential gap between the acrylic drum and the flange. The drying chamber was well insulated with 5mm thick Armoflux insulation material. A rectangular tray made of the aluminum sheet was placed approximately at the middle position inside the drum to hold the samples. 31 Experimental Apparatus and Procedure Chapter-3 mm gap Figure 3.3 Photograph of the dryer The length and width of the tray were about 300mm and 150mm, respectively. The tray was seated on a strip made of an acrylic sheet of 5mm thickness and 280mm length. The strip was fixed to the wall of the dryer on both sides using adhesive cement. 3.1.2 Conduction and radiant heater The drying samples received heat by conduction through the heated tray or by radiation. A silicon rubber heater (300 W) was attached to the bottom of the tray to heat the plate by conduction. The dimensions of the conduction heater were 245 mm x 147 mm. 32 Chapter-3 Experimental Apparatus and Procedure Radiant heater Conduction plate Figure 3.4 Radiant and conduction heater (below the aluminum plate) inside the drying chamber For radiation heating, a quartz heater (245 mm x 147 mm) was fixed above the tray. The capacity of the heater was 300 W. A photograph of the heater inside dryer is shown in Figure 3.4. 3.1.3 Vortex tube A vortex tube cooler (Model 3240, EXRIR Corporation, Cincinnati, Ohio) with 0.82 kJ/s refrigeration capacity and 0.018876 m3/s air flow at STP was used to supply subzero temperature air to the dryer is shown in Figure 3.5. It is made of stainless steel material. The vortex tube is a device for producing hot and cold air when compressed air is made to flow tangentially into the vortex chamber through properly designed the 33 Chapter-3 Experimental Apparatus and Procedure Figure 3.5 Photograph of the vortex tube used in experimental setup Figure 3.6 Lateral section of vortex tube showing a graphical view of the cold and hot air flows inlet nozzles. This causes a complex swirling motion within the vortex tube. The cold air in the core region of the tube flows out through an orifice plate in the direction 34 Experimental Apparatus and Procedure Chapter-3 opposite to that of the hot air near the shorter tube wall flowing out through the core. A cross sectional view of the vortex tube is shown in Figure 3.6. Control of air temperature can be achieved by controlling supply the air pressure or by controlling the amount of cold air released. 3.1.4 Muffler Vortex tube generates a unacceptance level of noise. A muffler was used at both ends of the vortex tube to reduce the emitted noise to an exceptable limit. It was made of an aluminum material. A photograph of muffler is as shown in Figure 3.7. Figure 3.7 Photograph of muffler used to reduce noise level 3.1.5 Pressure regulator A pressure regulator was used to control and measure the air pressure at the inlet of the vortex tube as well as inside the drying chamber. It was used to control the carrier gas 35 Chapter-3 Experimental Apparatus and Procedure temperature inside the drying chamber by controlling the inlet air pressure. 3.1.6 Vibrator The drying chamber was vibrated mechanically by using a magnetic coil vibrator (Model 406, Ling Dynamic, Germany) of variable frequency (3-30 Hz) and amplitude (0-5mm) was placed directly under the drying chamber. Vibrator was fixed up in such way so that it only vibrates the tray to allow a gentle vibration of the samples in vertical directions. Maximum load of the vibrator of kg with a vibration factor ( aω / g ) in between 3-7. Detailed of the system component specifications are listed in Table 3.1. Table 3.1 Components specification and characteristics of the system parameters 1. Drying chamber a. Material b. Shape c. Dimension d. O-ring e. Flange f. Insulation material 2. Tray a. Material b. Dimension : Acrylic sheet : Drum type : Length: 300mm Inner diameter: 200mm Thickness: 5mm : 1) Inner radius: 115 mm Thickness: mm 2) Inner radius: 125 mm Thickness: mm : Material – Acrylic sheet Radius: 145 mm Thickness: 5mm : Armoflax; Thickness: 5mm : Aluminum sheet : Length: 300mm Width: 150 mm 3. Conduction heater a. Type b. Dimension c. Capacity : Silicon rubber heater : 245 mm x 147 mm : 300W, 240V 4. Radiant heater a. Type b. Dimension c. Capacity : Infrared heater : 245 mm x 60 mm : 300W, 240V 36 Chapter-3 Experimental Apparatus and Procedure 5. Vortex tube a. Model b. Flow rate c. Refrigeration capacity : 3240 : 0.0188 m3/sec : 706 Kcal/hr 6. Vibrator a. Type b. Model c. Capacity d. Frequency e. Amplitude : Magnetic coil vibrator : 406 : Kg : -30 Hz : mm (Max) 3.1.7 Freeze dryer In this study a laboratory scale freeze dryer (Model-Heto Lyolab 3000) was used to conduct the experiment for a comparative study with AFD. The condensation coil was maintained at a temperature of -56°C for vacuum freeze-drying. Vacuum was maintained inside the chamber at 0.0235 mbar. Samples were taken out every 30 minutes for weight measurements. 3.1.8 Heat pump dryer In the heat pump drying runs the air temperature was set at 45°C with an air velocity and relative humidity (RH %) of about 1.45 m/sec and 18%, respectively. Reductions of mass of sample during the course of experiments were measured at a regular interval of 30 minutes. A full description and experimental procedure for the heat pump dryer can be found in Lan et al. (2005). 37 Chapter-3 Experimental Apparatus and Procedure 3.2 Experimental Procedure 3.2.1 Fixed bed couple with vortex tube and multimode heat input Potato and carrot were used as the model drying materials as properties of this material are well documented. Samples in the form of discs (16mm diameter x mm thickness) were washed, peeled and cut for the AFD experiments. To avoid enzymatic browning, the slices were immersed in a 5% sodium bicarbonate solution at a temperature of 96oC ± 2oC, for about two minutes and carefully wiped using tissue paper before start the drying run. Potato samples were cooled down immediately to stop possible gelatinization. Samples were weighed after blanching and placed on a wire mesh tray in a freezer at -22°C for approximately 18 hours. The product temperature was noted to be about -20°C. The samples were weighed again before placing them inside the drying chamber to measure the reduction of weight during freezing. Prior to start of the drying experiment the temperature of the chamber was kept below the freezing point of the samples to prevent melting which can cause damage to the structure of the product. Four heat input schemes were compared experimentally: case1: single stage-pure convection, case2: two-stage-pure convection, case3: twostage-radiation coupled with convection and case4: two stage-radiation-conduction coupled with convection. Samples were then placed on a wire mesh tray seated on the heated conduction plate. Weight of the samples was measured at a regular interval of hours by taking them out of the drying chamber. Time required to measure the samples weight at different stages of drying was about 45 seconds. Table 3.2 shows details of the experiments performed in this work. At the end of each experiment, the dried samples were placed in an oven at 105oC for 24 hours to measure their bone-dry 38 Experimental Apparatus and Procedure Chapter-3 weight. Drying kinetic data are presented in dimensionless moisture content verses drying time plots. Table 3.2 Schedule of experiments performed using fix bed dryer Process Products Drying conditions Convective Single stage: -11°C (0 to hr- heating (case-1) convection) Convective Two stage: -11°C (0 to hr- heating (case-2) convection) and -6°C (after to Dimension hr-convection) Convective with Potato Two stage: -11°C (0 to hr- Disc shape: Radiation and convection) and -6°C (after hr to 16 mm (D)x1mm heating (case-3) carrot hr – convection and radiation Rectangle shape: (12°C) heat input) (10x 5x 1)mm Multi-mode Two stage: -11°C (0 to hr- (Radiation and convection) and -6°C (after hr to Conduction) hr – convection, radiation and heating (case-4) conduction heat input ) Vacuum freeze Chamber temperature: -56oC drying Heat pump Air Temperature & velocity : drying 42oC, 1.45 m/sec & RH 65% 3.2.1 Osmotic dehydration Atmospheric freeze drying is plagued with the problem of long drying time. Osmotic dehydration can help reduce the initial moisture content of the products that are to be atmospheric freeze dried and thus improve the performance. In addition, usually a porous structure is developed during drying of products in freeze drying process, which will provide more room for moisture to travel through the product to the carrier 39 Chapter-3 Experimental Apparatus and Procedure gas inspite of clogging the passage through precipitation of the osmotic agents. These phenomena will also contribute to enhance the drying rate in AFD process. Therefore, osmotic dehydration as a pretreatment to AFD method for materials of biological origin (fruit in sucrose, fish and meat in salt) were undertaken to examine the effect of osmotic agents on AFD Samples of the materials were cut to discs type of 26mm diameter and 1mm thickness by using a special cutter and a knife. Same initial weight 0.75 gm was taken for each material for all drying experiment. 10 gm of sugar is mixed with gm of water at room temperature (24oC) to obtain a concentrated sucrose solution while gm of salt is mixed with 50 gm of water to obtain a concentrated salt solution for the osmotic pretreatment of the samples. Banana, carrot and potato samples were immersed in sucrose solution, while beef liver, beef meat and cod fish samples were immersed in the salt solution for 30 minutes for the osmotic pretreatment. The samples were then taken out and removed the surface moisture by using tissue paper. The weight of the osmotic pretreated samples was then measured to determine the loss of moisture due to the osmosis process. The samples were then kept in a refrigerator at -22ºC for 18 hours on a wire mesh tray before being placed inside the atmospheric freeze dryer or the vacuum freeze dryer. 3.2.2 Fibro-fluidized bed: Sample mixed with an adsorbent Vibration was applied to the drying chamber using a magnetic coil vibrator of adjustable frequency (f) and amplitude (A). An analyzer and amplifier were used to measure the amplitude (3-4 mm) and frequency (17-22 Hz) values of vibrationparameter (3.5-6.4), respectively. As noted earlier mm cube of potato and carrot were 40 Experimental Apparatus and Procedure Chapter-3 used as samples weighted about 1.3 gm. Blanching of the product was carried out to avoid enzymatic browning. Silica gel beads were used as adsorbent particles. This material shows good characteristics of adsorption even at low air humidity. Gel particles with an average diameter of mm and an adsorbent-to-product mass ratio of 1:1 were used. Experiments were conducted using both cooled and ambient temperature adsorbent. Prior to start of the experiment, the temperature of the chamber was kept below the freezing point of the samples. Table 3.3 Schedule of experiments performed using the vibrating bed dryer Process Drying condition Product Adsorbent dimension • Multimode-Two stage: -11°C and -6°C (case-4) Vibration: f - 20 Hz, A – 4mm and 3mm • Multimode-Two stage: -11°C and -6°C (case-4) Vibration: f-22 Hz, A - 4mm • Multimode -Two stage: -11°C and -6°C (case-4) Vibration: f -17 Hz, A - 4mm • Vibrating factor: 3.5, 4.8, 5.8 and 6.4 • Potato & Carrot Cube: 2mm cubic Comparison • Literature data: Two stage: with -8°C and 20°C (convection heat literature input - using heat pump) results • Proposed AFD: Multimode heat input-Two stage: -8°C and 20°C (Heat input using convection-radiation coupled with conduction); Without vibration; With vibration (f-20 Hz, A-3mm) and adsorbent • Potato & Carrot Cube: 2mm cubic • Cod: 5mm cubic Vibrating bed dryer Vacuum freeze drying Chamber temperature: -56oC Silica gel Spherical shape: D1mm • Without Adsorbent • With Adsorbent • Adsorbent refreshing Silica gel Spherical shape: D1mm • Without Adsorbent • With Adsorbent Adsorbent refreshing • Potato & Carrot Cube: 2mm cubic 41 Chapter-3 Experimental Apparatus and Procedure Frozen samples were then mixed with the adsorbent particles and placed on a wire mesh tray seated on the hot plate. At a regular interval of hours during the course of drying, product samples were separated from adsorbent for weight measurement. Experiments were also carried out by charging with new adsorbent. Experiment with a fresh dry adsorbent at regular intervals (2 hours) is termed as “adsorbent refreshing”. Table 3.3 shows the schedule of the experiments performed in this study. The quality of the dried products was characterized as indicated in the following section. 3.3 Quality Parameters 3.3.1 Rehydration The following procedure was adopted to test the rehydration property of the dried samples (Giri et al. 2005). Dried samples were rehydrated in 300ml boiling water for an interval of minute. The ratio of sample to water was 1:50 (w/w). It was then taken out from water and carefully wiped with tissue paper to remove surface moisture. Samples were then weighed to determine the gain in mass. The relative mass index was used to quantify rehydration quality, which is defined as a ratio of the weight of rehydrated samples to the weight of the dry product after the end of each experiment. 3.3.2 Color A Minolta spectral magic spectrophotometer (Model CM-3500d) was used to determine the colour change due to drying as shown in Figure 8. The following difference formula from CIELAB was used to quantify change of color from the original to the dried product. 42 Experimental Apparatus and Procedure Chapter-3 ΔL = L−L*, Δa = a−a*, Δb = b−b* ⎡ ⎤2 ΔE*ab = ⎢ΔL2 +Δa2 +Δb2 ⎥ ⎣ ⎦ here L, a, and b denote reference color and L*, a* and b* denote target color, respectively. Smaller value of ∆E*ab, indicates closer color of the dried product to its original color. 3.3.3 Scanning electron micrographs (SEM) SEM tests were performed on a JSM5600 machine. Samples were cut horizontally as well as vertically across the surface to visualize the structures on different sides of the product. Due to non conductive properties of the samples, a thin film of gold was coated over the food samples using a coating machine. A magnification power of 40 to 80 was used for observation of the sample microstructure. 3.3.4 Freezing point depression The freezing point depression was estimated using a method given by Strommen et al. 2005. The Schwartzberg equation was modified to estimate the freezing temperature as a function of the solid fraction as follows. E⎛ ⎞ ⎟ = (1 + b) + ⎜⎜ WS k ⎝ TO − T ⎟⎠ O and solid fraction; Here k = M W ΔH WS RTO = Solid Weight Solid + Water Weight Mw=Molecular weight of water = 18.0153g/mol, Δ Ho=Molar enthalpy = 333.55J/g, R=gas constant (8.314kJ/kmol-K), To=freezing temperature of pure water (273.15K). A plot of ⎛ ⎞ E ⎟⎟ yields a linear equation of which the gradient is versus ⎜⎜ WS k ⎝ TO − T ⎠ 43 Chapter-3 Experimental Apparatus and Procedure and the y-intercept is (1+b). A plot of WS against T°C gives the estimated value of the freezing point depression of the product. 3.4 Measuring Equipment To evaluate the drying performance, it is necessary to measure the weight of the product, temperature of the drying chamber as well as product, to control the temperature of the conduction and radiant heater and to measure the amplitude and frequency of the vibrator. The instruments used for this measurement are described below. 3.4.1 Analytical balance Weight of the drying product was measured with a high precision analytical balance (Model B-320C, Explorer OHAUS, and USA) to an accuracy of +0.0001 gm. The weighing plate on which the product is placed to take the measurement was fully surrounded with transparent material to avoid the effect of natural airflow during measurement. 3.4.2 Temperature measurements T-type copper-constantan thermocouples (Omega, USA) were used to measure the temperatures of the carrier gas in the drying chamber, conduction and radiant heater temperature and product temperature. Thermocouples were inserted in the middle of the product to measure the local temperature of the product. All thermocouples were calibrated in a bath using a standard liquid (ethylene glycol) with an accuracy of ±0.050C. 44 Chapter-3 3.4.3 Experimental Apparatus and Procedure PID controller Two PID controllers (Model HT-400, Hot Temp) were used to control the temperature of the conduction and radiant heater, respectively. 3.4.4 Analyzer and power amplifier To measure the amplitude of the vibrator an analyzer (Model: CF-840; Uno Sokn, Japan) was used. An amplifier (Model: PA-100; Ling Dynamic System, UK) was used to change and fix up the frequency (Hz) during the course of experiment. 3.4.5 Data Acquisition system A data acquisition system consisting of a high-speed data logger (Hewlett Packard, Model 34970A) and a computer was connected to the experiment set-up. The data logger can accommodate a maximum of three detachable multiples of modules and each module can accept a combination of twenty thermocouples signals. For data acquisition and on-line monitoring of the system variables during the experiment, a software program (DATALINK) supplied by the manufacturer was used. All thermocouples were connected to the data logger. 3.5 Experimental Uncertainty The main errors in this experiment arise in weight measurement of samples at regular intervals during the course of the experiments. Re-absorption of moisture is another source of uncertainty when samples were exposed to ambient for measurement of their mass. Due to sudden exposure of the samples from subzero temperature of the drying chamber to the humid ambient air there possibility of condensation on the sample 45 Experimental Apparatus and Procedure Chapter-3 surface. All sources of uncertainty mentioned were considered and they are described below. 3.5.1 Uncertainty in mass measurement In the present work, we are concerned with the uncertainty associated with the moisture content measurement. At first, we have to relate this uncertainty to those independent uncertainties involved as shown Tables 3.3; follow Moffatt’s (1988) methodology. Table 3.4 Fixed error of sensors based on manufacturer’s specifications and calibration error Sensor Electronic weighing scale Thermocouple Percentage error ± 0.0001 gm ± 1.32 Fixed error based on manufacturer Calibrated error For moisture content on dry basis we have ΔX m mΔmO Δm = − Xm m − mO (m − mO )mO The relative uncertainty associated with the measurement of moisture content of sample can be expressed as: ⎛ ⎛ Δm ⎞ ⎛ mΔm ⎞ O ⎟⎟ + ⎜⎜ ⎟ = ⎜ ⎜⎜ ⎜ ⎝ m − mO ⎠ ⎝ (m − mO )mO ⎟⎠ ⎝ e Xm ⎞ ⎟ ⎟ ⎠ m - initial moisture, mo - final moisture 46 Experimental Apparatus and Procedure Chapter-3 As illustration, the following values were obtained from the balance, whose accuracy is given in Table 3.4. The measured values and the uncertainty of sets of the experimental results were evaluated from the equations, e xm are found to be negligible. See Table 3.5. Table 3.5 Uncertainty of moisture content measurement in the temperature range -11°C and -6°C Two stage -11°C and -6°C -11°C and -6°C (R) -11°C and -6°C -11°C and -6°C (R) 3.5.2 Potato Potato Carrot Carrot m 4.215 4.764 11.713 10.977 mo 0.373 0.366 0.530 0.239 /\Xm/Xm -0.268% -0.273% -0.188% -0.418% exm 0.295% 0.297% 0.198% 0.428% Uncertainty in mass gain on exposure to ambient air To determine gain in moisture due to exposure in ambient air during mass measurement, potato sample of the same weight and dimension were put in the drying chamber and dried for upto 8hrs without taking them out of the drying chamber. The result was compared under these two conditions viz: with and without taking them out of the chamber. A minor increase in weight was observed due to re-absorbed moisture from the ambient in the case of taking out for measurement. This procedure causes an expectable error of about 4.70%. These results are tabulated in Table 3.6. Table 3.6 Uncertainty of weight gain in ambient air during measurement Initial weight Without measurement 0.4882 Final weight after hours 0.1252 Error 4.70% With measurement 0.4991 0.1314 47 Experimental Apparatus and Procedure Chapter-3 3.5.3 Uncertainty due to condensation of on product during measurement To measure the error caused by condensation of water vapor due to exposure to ambient air during mass measurement, a potato sample was taken out from the drying chamber and placed on the weighing scale to measure the increase in weight due to condensation. The sample was left on the weighing scale for a maximum time of min. However, during actual experiments the samples were seldom left outside for more 45 seconds. It was found that the gain in mass was negligible and the findings are tabulated in Table 3.7. This is probably due to low thermal conductivity and low heat capacity of the product. Table 3.7 Uncertainty due to condensation during measurement 3.6 Hours Mass, gm 1min 2min 0.243 0.186 0.139 0.077 0.073 0.244 0.187 0.139 0.077 0.073 0.244 0.187 0.139 0.077 0.073 Reproducibility test Replicate experiments were conducted using potato samples under the two stage drying condition of -11°C & -6°C for a fixed bed and a vibrating bed dryer to investigate the reproducibility of the experimental data. Figure 3.8 and 3.9 show that the data are within +6% and +3%, respectively, for the fixed bed and the vibrated bed equipments. 48 Experimental Apparatus and Procedure Chapter-3 Dimensionless moisture content 1.0 o 0.9 o Two stage: -11 C & -6 C Potato sample 0.8 0.7 0.6 0.5 0.4 Experiment 0.3 Reproducible Experiment 0.2 0.1 0.0 Time, hr Figure 3.8 Variation of dimensionless moisture content with time in fixed bed dryer Dimensionless moisture content 1.0 0.9 Experiment 0.8 Reproducible experiment 0.7 0.6 0.5 0.4 Two stage: Multimode heat input 0.3 ( -11 C & -6 C) Vibrating bed dryer ( VF-5.8) No adsorbent Potato cube (2mm) 0.2 0.1 0.0 10 Time, Figure 3.9 Variation of dimensionless moisture content with time in vibrated bed dryer 49 Experimental Apparatus and Procedure Chapter-3 3.7 Summary Atmospheric freeze drying (AFD) in a vibro-fluidized bed dryer coupled with an adsorbent and multimode heat input is proposed for dehydration of food products at lower cost than the traditional freeze-drying process under vacuum. An experimental setup was designed and built to permit simultaneous application of convection, conduction and radiation heat input to the drying material above its freezing point to ensure sublimation. Detailed experimental program to evaluate the viability of the new proposed atmospheric freeze drying system for drying of heat sensitive materials was presented. Experimental apparatus and procedure, quality parameters (color, rehydration, SEM test) measuring equipments, experimental uncertainty, reproducibility and detailed schedule of experiment conducted were illustrated. 50 [...]... was applied to the drying chamber using a magnetic coil vibrator of adjustable frequency (f) and amplitude (A) An analyzer and amplifier were used to measure the amplitude (3- 4 mm) and frequency (17-22 Hz) values of vibrationparameter (3. 5-6.4), respectively As noted earlier 2 mm cube of potato and carrot were 40 Experimental Apparatus and Procedure Chapter -3 used as samples weighted about 1 .3 gm Blanching... Experimental Apparatus and Procedure Chapter -3 3.7 Summary Atmospheric freeze drying (AFD) in a vibro-fluidized bed dryer coupled with an adsorbent and multimode heat input is proposed for dehydration of food products at lower cost than the traditional freeze- drying process under vacuum An experimental setup was designed and built to permit simultaneous application of convection, conduction and radiation heat. .. Potato Two stage: -11°C (0 to 4 hr- Disc shape: Radiation and convection) and -6°C (after 4 hr to 16 mm (D)x1mm heating (case -3) carrot 8 hr – convection and radiation Rectangle shape: (12°C) heat input) (10x 5x 1)mm Multi- mode Two stage: -11°C (0 to 4 hr- (Radiation and convection) and -6°C (after 4 hr to Conduction) 8 hr – convection, radiation and heating (case-4) conduction heat input ) Vacuum freeze. .. system A data acquisition system consisting of a high-speed data logger (Hewlett Packard, Model 34 97 0A) and a computer was connected to the experiment set-up The data logger can accommodate a maximum of three detachable multiples of modules and each module can accept a combination of twenty thermocouples signals For data acquisition and on-line monitoring of the system variables during the experiment, a. .. -17 Hz, A - 4mm • Vibrating factor: 3. 5, 4.8, 5.8 and 6.4 • Potato & Carrot Cube: 2mm cubic Comparison • Literature data: Two stage: with -8°C and 20°C (convection heat literature input - using heat pump) results • Proposed AFD: Multimode heat input- Two stage: -8°C and 20°C (Heat input using convection-radiation coupled with conduction); Without vibration; With vibration (f-20 Hz, A- 3mm) and adsorbent... measure the temperatures of the carrier gas in the drying chamber, conduction and radiant heater temperature and product temperature Thermocouples were inserted in the middle of the product to measure the local temperature of the product All thermocouples were calibrated in a bath using a standard liquid (ethylene glycol) with an accuracy of ±0.050C 44 Chapter -3 3.4 .3 Experimental Apparatus and Procedure... heat input to the drying material above its freezing point to ensure sublimation Detailed experimental program to evaluate the viability of the new proposed atmospheric freeze drying system for drying of heat sensitive materials was presented Experimental apparatus and procedure, quality parameters (color, rehydration, SEM test) measuring equipments, experimental uncertainty, reproducibility and detailed... the balance, whose accuracy is given in Table 3. 4 The measured values and the uncertainty of sets of the experimental results were evaluated from the equations, e xm are found to be negligible See Table 3. 5 Table 3. 5 Uncertainty of moisture content measurement in the temperature range -11°C and -6°C Two stage -11°C and -6°C -11°C and -6°C (R) -11°C and -6°C -11°C and -6°C (R) 3. 5.2 Potato Potato Carrot... (Model HT-400, Hot Temp) were used to control the temperature of the conduction and radiant heater, respectively 3. 4.4 Analyzer and power amplifier To measure the amplitude of the vibrator an analyzer (Model: CF-840; Uno Sokn, Japan) was used An amplifier (Model: PA-100; Ling Dynamic System, UK) was used to change and fix up the frequency (Hz) during the course of experiment 3. 4.5 Data Acquisition system. .. was measured with a high precision analytical balance (Model B -32 0C, Explorer OHAUS, and USA) to an accuracy of +0.0001 gm The weighing plate on which the product is placed to take the measurement was fully surrounded with transparent material to avoid the effect of natural airflow during measurement 3. 4.2 Temperature measurements T-type copper-constantan thermocouples (Omega, USA) were used to measure . Chapter -3 Experimental Apparatus and Procedure CHAPTER 3 EXPERIMENTAL APPARATUS AND PROCEDURE An experimental investigation was undertaken to evaluate the drying performance of a vibrated. conduction heater were 245 mm x 147 mm. 32 Chapter -3 Experimental Apparatus and Procedure Radiant heater Conduction plate Figure 3. 4 Radiant and conduction heater (below the aluminum plate). 3. 2 Experimental Procedure 3. 2.1 Fixed bed couple with vortex tube and multimode heat input Potato and carrot were used as the model drying materials as properties of this material are