Development of Ohmic Heating Apparatus for Extraction - IJIRST

IJIRST –International Journal for Innovative Research in Science & Technology| Volume 2 | Issue 11 | April 2016 ISSN (online): 2349-6010

Development of Ohmic Heating Apparatus for Extraction of Rapeseed Oil Kautkar Sheshrao Sakharam Research Scholar Department of Post-Harvest Process & Food Engineering G. B. Pant University of Agriculture & Technology, Pantnagar (Uttarakhand)

Jai Prakash Pandey Professor Department of Post-Harvest Process & Food Engineering G. B. Pant University of Agriculture & Technology, Pantnagar (Uttarakhand)

Anupama Singh Professor Department of Post-Harvest Process & Food Engineering G. B. Pant University of Agriculture & Technology, Pantnagar (Uttarakhand)

Anil Kumar S. R. O. Department of Food Science & Technology G. B. Pant University of Agriculture & Technology, Pantnagar (Uttarakhand)

Anil Kumar Shukla Professors Department of Mathematics, Statistics & Computer G. B. Pant University of Agriculture & Technology, Pantnagar (Uttarakhand)

Abstract Ohmic heating is a process in which alternating electric current is passed through liquid-particulates foods to heat them. The heating occurs in the form of internal energy generation within the product. Voltage is applied directly to the electrodes at both ends of the product body which cause internal energy generation within the food material. This technology has wide range of applications in the area of food processing. In the present investigation, a laboratory scale ohmic heater was developed to use it for extraction of rapeseed oil. Keywords: Ohmic Heating, Rapeseed Oil, Electrical Conductivity, Heating Power, Heating Rate _______________________________________________________________________________________________________ I.

INTRODUCTION

All over the world, an ever-increasing demand for oil from edible oilseed is being witnessed. Oil and oilseeds constitute a major portion of agricultural products. India is the largest producer of oilseeds with the production of 32.88 million tonnes of oilseeds during 2013-14 which accounts for 9.6 percent of world’s total oilseed production from largest area of over 28 million ha of land in the world, but still deficient as far as production of oil is concerned. Groundnut, rapeseed/mustard, caster seed, sesame, linseed, safflower, sunflower and soybean are the major oilseeds produced in the country with groundnut, rapeseed and soybean accounting for major chunk of the output [1]. Among all the oilseeds produced in the country, Rapeseed (Brassica rapa L.) is one of the major oilseed crop. It belongs to the family Cruciferae with large number of species and sub species cultivated in the country with different names like sarso, rai, pili sarso, gobhi sarso, mohari etc. India is the third largest rapeseed producer in the world followed by China and Canada with 19.29 % of total acreage and 12 per cent of production. Rapeseed contains high-quality oil (38–46%) and protein (20–30%) as well as some antinutritional compounds, such as glucosinolates, phenols, and phytic acid [2], [3]. Being a rich source of unsaturated fatty acid and with low concentration of saturated fatty acid, now-a-days the oil of rapeseed has become nutritionally better than other oilseeds. Several oil extraction methods have been employed to extract oil from oil seeds which include mechanical or expeller pressing, hydraulic pressing, organic solvent extraction and enzymatic extraction. In present investigation a novel and green extraction process has been developed to extract rapeseed oil by combined ohmic heating and enzyme assisted aqueous extraction technique. Therefore an ohmic heating apparatus is designed and development in the development laboratory of Department of Post-Harvest Process and Food Engineering, G. B. Pant University of Agriculture & Technology, Pantnagar, Uttarakhand (India). Ohmic heating also called as electric heating or joule heating is a process wherein alternating electric current (AC) is passed through liquid-particulates foods with primary purpose of heating them. The heating occurs in the form of internal energy generation within the product [4]. AC voltage is applied directly to the electrodes at both ends of the product body which cause internal energy generation within the food material. The rate of heating is directly proportional to the square of the electric field strength, and the electrical conductivity of material [5]. The electrical conductivity increases with increasing temperature, suggesting that ohmic heating becomes more effective as temperature increases. This technology has various applications in food processing and used by various researchers for rice bran stabilization [6] [7], Blanching [8], Sterilization, Juice extraction, oil extraction [9], pasturization [4], evaporation, fermentation [10], Peeling [11], Thawing [12].

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Development of Ohmic Heating Apparatus for Extraction of Rapeseed Oil (IJIRST/ Volume 2 / Issue 11/ 040)

II. MATERIALS AND METHODS Principle of ohmic heating The ohmic heater is a device which uses products own electrical resistance to generate the heat [13]. Heat is produced directly within the fluid itself by Joule heating as alternating electric current (I) is passing through a conductive material of resistance (R), with the result energy generation causing temperature rise [14]. Fig.1 describes the principle of ohmic heating. In most commonly used heating techniques, heating the product is depending on heat transfer from a hot surface. This heat can be generated directly by heating element or indirectly from a hot medium like steam or hot water via a heat exchanger. These methods require a temperature gradient to heat the product and as such the surfaces are at a higher temperature than the product. This can cause fouling of the heating surfaces which reduces heat transfer rates and adversely affecting the nutritional quality of the product. Ohmic heating does not involve such problems because it eliminates the hot surface from the apparatus and hence produce a quality product.

Fig. 1: Principle of Ohmic Heating

Development of ohmic heating Setup: For development of an ohmic heating apparatus for enzyme assisted oil extraction of rapeseed, the factors such as material of construction of chamber, material of electrode, cementing material, wiring, transformer, thermostat are important. Therefore the criteria for development of ohmic setup are given as; Ohmic heating chamber Selection of suitable material for ohmic heating chamber is very important for efficient heating and as safety concern. The material for construction of ohmic heating chamber should be electrically nonconductive, it should able to withstand higher temperature, it should be of light weight, it should be chemically inert and it should not affect the quality of the product and should be easily available at reasonable [15]. On the basis of these factors ohmic heating chamber can be constructed by perspex sheet, acrylic sheet, PVC pipes, wood, glass etc. Considering all the important factors PVC pipes of 7 cm diameter, 16.8 cm length and 2 mm thickness has been selected for construction of the ohmic heating chamber. Circular ohmic heating chamber has its advantage of minimum heat loss than rectangular geometry and it also avoid the leakage of rapeseed slurry from the cylinder as there is absence of any joint or fitting in the chamber. The size of ohmic heating chamber will be decided on the basis of volume and density of the rapeseed slurry. By determining the volume and density of rapeseed slurry the capacity of ohmic heating chamber was determined and accordingly other dimensions of setup like length, breath and thickness of chamber was decided. Rapeseed slurry was made by mixing 100 gm dehusked and grinded rapeseeds with sufficient amount of water (1:3 w/v as per experimental design) and used for determination of capacity of ohmic heating chamber. Electrodes Selection of electrode is an important parameter to be considered in the design of an ohmic heater [16], [17], [18], [19] Different type of conductive materials such as titanium, stainless steel, platinized-titanium, aluminium and graphite can be used as electrodes on the basis of price, availability and correction resistance which may affect the efficiency of the ohmic heater [17]. The situations where the product quality is not essential, low carbon electrodes are preferred but for processing the product with keeping their quality intact, metals such as stainless steel are preferred. The electrodes should be of good grade, non-corrosive, chemically inert and should provide smooth finish [20], [15]. Considering these factors stainless steel (SS), plate of grade SS-316 with 5.5 cm diameter was selected as electrode material because of its suitability for food products handling. The distance between two electrodes has been kept as 14 cm to pass maximum voltage gradient of 16.5 V/cm from Indian household electric supply of 230 V. Nuts and bolts made of SS 316 are used for attaching the wire with the electrodes. Lid The Teflon coated lid having 3.5 cm diameter and 2 cm length made for connecting the electrodes with the power supply. It can withstand higher temperatures of about 6000 °C [15].


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Temperature controller and thermocouple Bestronics made digital temperature controller with stainless steel probe was used monitor the temperature inside the heating chamber. Teflon coated, J type thermocouple which can withstand a temperature of 0-600 °C [21] is placed at the geometric centre of the ohmic heating cylinder to control the temperature during ohmic heating. Power supply The single phase power supply from alternating current (AC) mains (220 V, 50 Hz) was used in the experimental set-up. A 4 amp variac which varies the voltage in the range of 0-270 V was used to provide required voltage to the system according to the experimental design. A constant voltage stabilizer is used before the autotransformer to control voltage fluctuations. The electrical variables were recorded using digital ammeter, voltmeter and wattmeter. Important parameters in the designing of the power supply system were personal safety and equipment safety to avoid accidents during ohmic heating. Base, control panel and stand An iron stand having height of 17.5 cm is used to fix the ohmic heating apparatus at stationary position. The stand also has an arrangement to loosen the apparatus by simply opening the screw for the purpose of cleaning and washing the PVC cylinder after each operation. A wooden frame with 42 cm length, 30 cm width, 4 cm height and 1 cm thickness is used as base to fix entire ohmic setup and control panel. The control panel with 44 cm length, 12 cm width and 11.5 cm height was made up of wooden to fix temperature controller, ammeter, and voltmeter. Determination of heating characteristics There are some important heating characteristics like electrical conductivity, heating power, heating rate, energy efficiency and power factor that must be continuously monitored and determined during the ohmic heating process that are. Electrical conductivity The electrical conductivity (σ) is a very important factor in ohmic heating and is a measure of how well a material accommodates the movement of an electric charge or it is materials ability of how efficiently it flow electric current through it [13]. It is the ratio of the current density to the electric field strength. Its SI unit is Siemens per meter (S/m). It can be calculated from the following equation [14], [22]. L I σ= × (1) A V Electrical conductivity of any sample is varies continuously and it is dependent on or directly proportional to the temperature, voltage gradient and the ionic contain of the material. Energy or heating power (P) The energy (P) given to the ohmic heater at a given temperature can be calculated by using the current (I) and voltage (V) values during heating time (Δt). It can be calculated by equation given below [23]; P = ΣVIΔt (2) Heating rate (𝑄) Electrical current passed through the material to be heated can cause generation of sensible heat in to the material, due to which the temperature of the material can rise from initial temperature (T i) to final temperature (Tf). Therefore the amount of heat given to the system can be calculated from the following equation [24]; Q = m Cp (Tf – Ti) (3) Energy efficiency (∈) Energy efficiency is used to evaluate the performance of an ohmic heating system. It is defined as the ratio of total energy utilized to heat the sample to total input energy and it can be calculated by following equation [25]; Energy utilized to heat the sample Energy efficiency = Total input energy m Cp (Tf − Ti) ∈= (4) ΣVIΔt Power factor Power factor is useful in determining wattage requirement of ohmic unit. Hence it is an important property in terms of power consumption. It can be defined as [26]; 𝑊 cosφ = (5) V×I III. RESULTS AND DISCUSSION Ohmic heating is continuously gaining much importance from the researchers and professionals in the food processing institutions because of its advantages over conventional heating technologies. It produce superior quality product with minimal nutritional or quality degradation, allows uniform and faster heating, simple process and fabrication of ohmic heater is also relatively simple task. The development of ohmic heater was done using materials like stainless steel food grade 316 for components which are in direct contact with food materials and PVC pipe for the ohmic heating chamber as shown in Fig. 2. The capacity of the ohmic heater was decided on the basis of volume of the rapeseed slurry fed to the chamber.


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Fig. 2: Ohmic Heater

Capacity: Capacity of the ohmic heating equipment refers to the weight of the rapeseed slurry fed to the chamber per unit time. The chamber with cylindrical geometry was finalized to construct in order to avoid leakage of slurry from the system. Following were recorded and used to construct the ohmic heating chamber; - Weight of the rapeseed flour taken = 100 g - Flour to water ratio = 1:3 - Density of the rapeseed slurry = 1.0273 g/cm3 Volume of the rapeseed slurry = 384 cm3 - Volume of the cylinder = π r2 h On the basis of these data, length, diameter and thickness of the ohmic chamber has been decided to keep 16, 6 and 0.5 cm respectively. Instead of designing the chamber for rapeseed slurry with the volume of 384 cm3, the ohmic chamber was designed for the volume of 450 cm3 considering boiling and expansion of the slurry inside the chamber when heated up to 100 ˚C. Capacity of ohmic apparatus was calculated as; - Weight of the sample taken = 384 g - Time taken = 6 min Weight of the sample Capacity = kg/hr (6) Time taken (384 ×60)

=

(6 ×1000)

= 3.84 kg/hr.

Therefore the capacity of the ohmic heating equipment was tested for rapeseed slurry was found to be 3.84 kg/hr. IV. SUMMARY AND CONCLUSION The designed laboratory model of ohmic heating showed good performance when used for ohmic and enzyme assisted aqueous extraction of rapeseed oil. In this setup the liquid particulate food could be heated from 20˚C to 100˚C in a minute at a voltage gradient of 16 V/cm. The heating was uniform for all practical purposes. Boiling and expansion of rapeseed slurry during ohmic heating should be given serious attention, especially when the liquid temperature exceeds above 60°C. Digital measuring accessories like temperature controller, thermocouple, ammeter, volt meter make it simple, easy to handle, and safe to operate. Ohmic heating is one of the fast growing technologies in food industries. It allows for the production of new, high value, shelf stable products with a better quality. REFERENCES [1] [2] [3] [4] [5] [6] [7]

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