Effect of Several Combinations of Infrared Radiative and Hot-Air Convective Drying on Drying Rate and Energy Consumption

ISSN 0973-4562 Volume 6, Number 24 (2011) pp. 2751-2763 © Research India Publications

http://www.ripublication.com/ijaer.htm

Effect of Several Combinations of Infrared Radiative

and Hot-Air Convective Drying on Drying Rate and

Energy Consumption

Abd El-Hamid A. El-Sayed and 2Ahmed A. Hanafy

1

Mechanical Eng. Dept, Faculty of Engineering, Alexandria University, Egypt

E-mail: [email protected]

2

Arab Academy for Science, Technology and Maritime Transport, Alexandria, Egypt

E-mail: [email protected]

Abstract

A prototype of combined IR and hot air drying system was developed to study the different drying parameters. A conveyorised drying system was fitted with infrared lamps for radiative heating. Through-flow hot air was provided for convective mode heating. As a part of this paper, a spread sheet program has been developed in order to calculate the drying rate, Product Temperature, and energy consumption per kg of dried food. Effect of Several combinations of infrared radiative and hot-air convective drying on drying rate and energy consumption was studied. The results show that, the optimum conditions in combined infrared radiative and hot-air convective drying of onion was that infrared radiative intensity of 0.771 kW/m2 combined with hot-air velocity of 0.5 m/s. So the better way to save energy in combined infrared and hot air drying system is to dry food at low speed of air.

Keywords: Infrared drying, Hot-air convection, Onion.

Introduction

2752 Abd El-Hamid A. El-Sayed and Ahmed A. Hanafy Convective drying is a common method used to preserve agricultural products in hot humid countries. Hot air drying of food is energy-efficient but has a long drying time during the falling rate period. Because of the low thermal conductivity of food materials during this period, the heat transfer rate during Convective drying is limited. The desire to eliminate this problem – in order to preserve products quality, and achieve faster and more effective thermal processing – has resulted in the increased use of other methods such as microwave and infrared drying. (Paradorn) [2]

Infrared drying technology is based on a property of water to absorb infrared (IR) radiation. Infrared radiation has a wavelength range from 0.75 to 100 µm and is subdivided into short-wave IR (0.75–2 µm), medium wave IR (2–4 µm), and long-wave IR (4–100 µm). The mechanism of bio-product drying is mass diffusion of water out of the bio-product and into the surrounding air. The infrared rays penetrate to certain depth into the bio-products and increase its temperature. As a result of this temperature increase, the diffusion rate of water through the bio-product is increased and the water is vaporized at the surface of the material. The moisture is taken up by the drying air and provides in a fast rate of drying. (Dilip 2004) [3]

A combined infrared (IR) and hot air drying system is an efficient and rapid drying method compared to the usage of IR and hot air drying separately. It has some advantages such as improved quality of dried product and good drying characteristics. Heat and mass transfer can take place more efficiently and, consequently, drying time dramatically reduces, energy efficiency increases, and specific energy consumption decreases. Because the temperature of the product being dried is kept relatively low during the dying process, thermal degradation of heat sensitive products can be retained to a higher degree than by convective hot air drying. Therefore, it can be seen as an alternative to the drying of heat-sensitive products. From the final product quality perspective, it is observed that this method is superior to the separate use of IR and hot air drying. Also, energy and operating cost of the combined drying mode for several food and agricultural products is lower than convective drying system. (Habib, 2011)[1]

A continuous combined infrared and hot air drying system reduced the processing time dramatically (48%), in addition to consuming less energy (63%) for water evaporation compared to hot air drying (H. Umesh Hebbar) [4].

Combined FIR-HA drying was a potential method for mulberry leaf drying, providing shorter drying time and uniform colour. The optimum conditions in combined FIR-HA drying of mulberry leaf was that infrared radiative intensity of 4 kW/m2 combined with hot-air temperature at 40 ◦C and hot air velocity of 1 m/s. Under these conditions, the quality of mulberry tea was satisfactory. (Wanyo, P) [5]

The combined infrared and hot air drying of whole longan shows both constant and falling drying rate periods. The infrared power, air temperature and air velocity significantly influenced the drying rate, product temperature and drying time. An increase of infrared power and air temperature had an effect on increasing the drying rate and reducing drying time. But the drying rate was reduced with increasing air velocity (Paradorn Nuthong) [2]

combination of hot air and far-infrared. The heat and the mass transfer coefficients were analyzed by heat–mass analogy. Naret Meeso [7] investigated the Effects of combined far-infrared radiative and hot-air convective drying on drying characteristics and physical properties of banana. Michale M. [8] compared the drying and quality characteristics of onion dried with catalytic infrared (CIR) heating and forced air convection (FAC) heating. D.G. Praveen [9] study the drying behavior of Onion slices were dried under different processing conditions applying infrared radiation assisted by hot air and tested Thin layer models such as Page, modified Page, Fick’s and Exponential models, which are used to describe the drying kinetics of food materials, for the combination mode drying. G.P. Sharma [10] developed an infrared dryer and infrared radiation thin layer drying of onion slices was carried out at different infrared power, air temperatures and air velocities. Hasan [11] examined the effect of drying temperature on drying rates of apple slice at different temperature. Dorota [12] designed Laboratory dryer in such a way that drying could be done either with infrared energy or by convection and compared the infrared drying with convective drying for apple slices. Meza-Jimenez J. [13] proposed solar drying system for Jamaica was designed to decrease product dehydration time substantially and diminish pollutants acquired during the traditional drying process. JUCKAMAS [14] investigated IR drying behavior of paddy at different initial moisture content levels and IR peak wavelengths.

A conveyorised drying system was fitted with infrared lamps for radiative heating to study optimal operating conditions for combined IR and hot air drying has been studied.

Basic Equations of Combined IR and Hot Air Drying

The basic equation of Combined IR and Hot Air Drying is given by Enrique [15] and ASHRAE [16]:

Figure 1: Scheme of a drying process

Sensible Heat

2754 Abd El-Hamid A. El-Sayed and Ahmed A. Hanafy

Latent Heat

Material water removal = Air moisture gain = kc dA (wi-wa) (2)

QL = ma hfg dwa = kc dA (wi - wa) hfg (3)

Total Heat

ma dha = kc dA (hi - ha) (4)

Material side heat:

[

]

[

]

[

]

(

)

}

{

(

)

}

{

mat mat mat mat mat mat

s m C T in m C T out Q QL QR t ⎡ ⎤ ⎣ _{⎦ = +} Δ (7) Where: mmat = md + mw (8) mmat Cmat = md Cd + mw Cw (9)

Experimental Setup

Drying was done in a prototype laboratory infrared dryer presented on figure (2). The dryer was designed in such a way that convective or infrared drying could be done individually or in combination. The dryer with overall dimensions of 1.77 (L), 0.7(B), 1.65 (H) m has a load of 5 kg/m2 of raw vegetables. The major specifications of the developed dryer are provided in Table (1).

Figure 2: Prototype of continuous infrared and hot air dryer. 1- Blower 2- Air heater

Infrared Heat Source

The dryer was equipped with four infrared lamps with power 250 W for each lamp.

Main Chamber

The dryer has a heating chamber of dimension (0.94 m, 0.52 m). Heating chamber is provided with an arched roof and mirror polished inner surface for maximum reflection of the radiation on to the material bed. Figure (2) shows the arrangement of infrared lamps inside the heating chamber. The chamber walls were insulated (glass wool, 40 mm thickness) to prevent heat loss. A vent was provided at the top of the chamber for the exit of moist air.

Air Heating System

An electrical heater and variable speed centrifugal blower formed the hot air generation and distribution system. A finned tube heater was used for heating the air to a temperature between (35–45 ◦C) up to 62 ◦C with IR lambs. Electric heaters are arranged in three rows, each one have three electric heaters of (300w) each.

Material of Conveyor

A rubber mesh conveyor was used to carry the material through the heating chambers. The conveyor speed was controlled by a variable speed motor.

The air temperature was measured by thermocouple wire was kept inside an aluminum rod which served as a shield from radiation. Temperature of the material undergoing drying was measured with thermocouples with diameter 0.5 mm.

Table 1: Specification of the Continuous Infrared and Hot Air Dryer.

Description Specification

Overall dimension 1.77 (L)×0.7( B)×1.65 (H) m Dimension of drying chamber 0.94m×0.52m

Infrared heat source Infrared lamps Power input for IR heating 1000W

Conveyor mesh conveyor with roller chain edges Conveyor drive motor 1HP helical geared motor

Residence time 30 min to 8 hrs

Blower variable speed centrifugal blower

Experimental Procedures

Materials

2756

Sample Preparation

Red Onion was brought peeled, cut into slices of knife with two measurem Vernier caliper and their a

Procedures

The infrared dryer was ru respect of the pre-set expe experiments were, therefo temperatures of 39 °C and The initial and final m balance. The conveyor ve temperature was maintaine under different condition o the inlet and outlet dry temperature were measure

Data Reduction

As a part of this paper, calculate the drying rate program also performs ca per kg of dried food. Th program. The spreadsheet item is a drying method "I been used for the spreadsh

Figure 3: Expe

Abd El-Hamid A. El-Sayed and Ahm

from the local Egyptian market. The oni approximately 6 mm thickness with a sharp ments were made on each slice for its thic average values were considered.

un empty for about 30 minute to achieve a erimental drying conditions before each dryin ore, conducted at 1000 W infrared powers; an d air velocities of 5.25, and 3.5 m/s.

mass of the samples were measured by a di elocities of 0.72 m/hr and 1.35m/hr are us ed at 51°C for the two Experiments. The sam of air and conveyor velocity at a loading den ying air temperature, relative humidity an ed at interval time.

a spread sheet program has been develop for a food. In addition to draying rate ca alculations of product temperature, and energ his section attempts to give over-view of th program has a hierarchical data structure. Th IR, hot air or both". Figure (3) shows the hie heet

erimental and theoretical moisture ratio for on

med A. Hanafy

ons were hand p stainless steel ckness, using a

steady state in ng run. The two nd at drying air igital electronic ed. The drying mples were dried

nsity of 5 kg/m2 nd ambient air ped in order to alculations, the gy consumption he spread sheet he highest level erarchy that has

Checking the validity of the program

In order to check the validity of the spread sheet program. Figure (4) represents a comparison between the predicted moisture content obtained by the program and the experimental. the comparison shows that the difference between the two solutions is not noticeable and the results of this program are very close to those of experimental work. The predicted data generally banded around the straight line which showed the suitability of the program

Figure 4: Hierarchy that has been used for the Spreadsheet.

Results and discussion

The moisture content and the drying rate versus drying time at various infrared radiation powers of 1.85, 1.75, 1.65 and 1.55 kW, air velocity of 0.5 m/s and air temperature of 39 C are shown in Figs. (5 to 8). As shown in figure 5 the drying rate increase rapidly in the first 30 minutes and then constant, also the higher drying rate with high IR power. As shown in figures 5 & 6 , the drying time was reduced by about 14 % with the IR power 1.85 kW compared to IR 1.55 kW for onion also the power consumption per kg product was reduced by about 0.56 % . The drying times to reduce the moisture content of onion from the 82% to 3.35 % in the final product were 267, 280, 295 and 311 minute at 1.85, 175, 1.65 and 1.55 kW respectively.

75 76 77 78 79 80 81 82 83 75 76 77 78 79 80 81 82 83

Moisture Content % - Experimental

2758 Abd El-Hamid A. El-Sayed and Ahmed A. Hanafy

Figure 5: Drying rate curves of Onion at various IR power and constant other

parameters.

Figure 6: Moisture Content %db. of Onion at various IR power and constant other

parameters. 0 0.0005 0.001 0.0015 0.002 0.0025 0.003 0 50 100 150 200 250 300 350 Time (min.) D ry in g R a te ( g w a te r / k g s o li d .m in )

air velocity = 0.5m/s & IR = 0.771 kW/m2 air velocity = 0.5m/s & IR = 0.729 kW/m2 air velocity = 0.5m/s & IR = 0.688 kW/m2 air velocity = 0.5m/s & IR = 0.646 kW/m2

0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400 420 440 460 480 0 50 100 150 200 250 300 350 Time (min.) Mo is tu re C ont e n t ( % d. b. )

Figure 7: Moisture Content % w.b. of Onion at various IR power and constant other

parameter.

Figure 8: Moisture Content % w.b. of Onion at various air velocity and constant IR

power. 0 10 20 30 40 50 60 70 80 90 0 50 100 150 200 250 300 350 Time (min.) M o is tu re C o n te n t %

air velocity = 0.5m/s & IR = 0.771 kW/m2 air velocity = 0.5m/s & IR = 0.729 kW/m2 air velocity = 0.5m/s & IR = 0.688 kW/m2 air velocity = 0.5m/s & IR = 0.646 kW/m2

0 10 20 30 40 50 60 70 80 90 0 50 100 150 200 250 300 350 Time (min.) M o is tu re C o n te n t %

2760 Abd El-Hamid A. El-Sayed and Ahmed A. Hanafy The results show that the IR power had a significant effect on the drying rate of onion. With the increase of the IR power, the time required to achieve a certain moisture content decreased at constant air velocity. On the other hand the several combinations modes of various IR power and various air velocity were done to obtain the same final moisture content and almost the same drying rate. As shown in figure (9) the drying time is the same in all combinations modes but the specific energy consumption and final product temperature are different as seen in table (2).

Table 2-a: Drying conditions versus energy consumption and final product

temperature observed "constant IR power" Air Velocity (m/s) Infrared Power (kW/m2) Final Product Temperature ( C) Time (Sec.) Energy Consumption (kWh/kg product) 0.5 0.633 38.59 315.7 5.6365 1 0.633 36.75 301.5 5.7512 2 0.633 35.25 284.2 5.8174 3.5 0.633 34.25 268.3 5.844

Table 2-b: Drying conditions versus energy consumption and final product

temperature observed "constant air velocity" Air Velocity (m/s) Infrared Power (kW/m2) Final Product Temperature ( C) Time (Sec.) Energy Consumption (kWh/kg product) 0.5 0.771 40.25 266.6 5.5984 0.5 0.729 39.75 279.85 5.6062 0.5 0.688 39.25 294.4 5.6177 0.5 0.646 38.74 310.5 5.6298

Table 2-c: Drying conditions versus energy consumption and final product

Figure (9): Drying rate curve of Onion at various combinations modes of various IR

power and air velocity.

Conclusions

In this study, Effect of Several combinations of infrared radiative and hot-air convective drying on drying rate and energy consumption was investigated.

Drying energy depends mainly on the infrared energy and the air velocity. The air velocity is an important variable; the air velocity more effective than the infrared power on energy consumption of drying of onion.

Adjusting distance between infrared lamps and the slice surface as well as air velocity, can be easily controlled.

The optimum conditions in combined infrared radiative and hot-air convective drying of onion was that infrared radiative intensity of 0.771 kW/m2 combined with hot-air velocity of 0.5 m/s. So the better way to save energy in combined infrared and hot air drying system is to dry food at low speed of air.

Nomenclature

A = heat and mass transfer area m2 Cd = dry material specific heat J/kg oC

Cmat = material specific heat J/kg oC

Cp = air specific heat J/kg oC

Cw = water specific heat J/kg oC

ha = air enthalpy kJ/kg 0 0.0005 0.001 0.0015 0.002 0.0025 0.003 0 50 100 150 200 250 300 Time (min.) D ry in g R a te ( g w a te r / kg s o lid .m in )

2762 Abd El-Hamid A. El-Sayed and Ahmed A. Hanafy hc = heat transfer coefficient W/m2 oC

hi = interfacial enthalpy kJ/kg

hfg = latent heat of evaporation kJ/kgv

kc = Mass transfer coefficient kg/m2 s

ma = air mass rate kg/s

md = dry material mass kg

mmat = material mass kg

mw = water mass kg

QL = Latent heat kJ

QR = Radiation heat kJ

QS = Sensible heat kJ

Ta = air dry bulb temperature oC

Ti = interfacial temperature oC

Tmat = material temperature oC

wa = air moisture content kgv/kg

wi = interfacial moisture content kgv/kg

References

[1] Habib Kocabiyik (2011) Infrared Heating for Food and Agricultural Processing. CRC Press 2011- Pages 101–116

[2] Paradorn Nuthong ֛, Aree Achariyaviriya, Kodkwan Namsanguan, Siva Achariyaviriya, Kinetics and modeling of whole longan with combined infrared and hot air. Journal of Food Engineering 102 (2011) 233–239

[3] Dilip Jain; Pankaj B. Pathare (2004). Selection and Evaluation of Thin Layer Drying Models for Infrared Radiative and Convective Drying of Onion Slices. Biosystems Engineering (2004) 89 (3), 289–296

[4] H. Umesh Hebbar *, K.H. Vishwanathan, M.N. Ramesh (2004). Development of combined infrared and hot air dryer for vegetables. Journal of Food Engineering 65 (2004) 557–563

[5] Wanyo, P., Meeso, N., Dondee, S. and Siriamornpun, S. (2009). Feasibility of Mulberry Tea Drying using Combination of Far- infrared Radiation and Air Convection. Agricultural Sci. J. 40 : 1 (Suppl.) : 497-500 (2009)

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[9] D.G. Praveen Kumar, H. Umesh Hebbar, M.N. Ramesh, Suitability of thin layer models for infrared–hot air-dryingof onion slices, LWT 39 (2006) 700– 705

[10] G.P. Sharma , R.C. Verma , Pankaj Pathare, Mathematical modeling of infrared radiation thin layer drying of onion slices, Journal of Food Engineering 71 (2005) 282–286

[11] Hasan Tog˘rul, Simple modeling of infrared drying of fresh apple slices, Journal of Food Engineering 71 (2005) 311–323

[12] Dorota Nowak, Piotr P. Lewicki, Infrared drying of apple slices, Innovative Food Science and Emerging Technologies 5 (2004) 353– 360

[13] Meza-Jimenez J., Ramirez-Ruiz J. J., and Diaz-Nunez J. J., The design and proposal of a thermodynamic drying system for the dehydration of Rosell (Hibiscus Sabdariffa) and other agro-industrial products, African Journal of Agricultural Research Vol. 3 (2008), pp. 477-485

[14] Juckamas Laohavanichi and Seree Wongpichet, Drying Characteristics and Miliing Quality Aspects of Paddy Dried with Gas-Fired Infrared, Journal of Food Process Engineering 32 (2009) 442–461.

[15] Enrique Rotstein, R. Paul Singh, and Kenneth J. Valentas, Handbook of food engineering practice, 1997, ISBN 0-8493-8694-2

[16] ASHRAE applications handbook.