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Numerical analysis on cooling of Jaggery by using heat exchanger
1Kalyani H. Nikam, 2Balaji D. Nelge
1,2Mechanical Department, Savitribai Phule Pune University, Maharashtra Email: 1[email protected], 2[email protected] Abstract—Jaggery is produced by evaporating water from
sugarcane juice. Jaggery industry is one of the most important cottage industries in India. Jaggery is prepared mostly by small and marginal farmers. The production process of jaggery involves crushing of cane, boiling and concentration of juice, moulding into the standard shapes and sizes and packaging in suitable packages. The consistency of the juice becomes thick on concentration by boiling and then it is poured into moulds to make jaggery blocks on cooling. The efficiency of crushing and concentration process is 60% and 14.75% respectively. The low efficiency is depends on the usage of open pans for concentration and using moulds for cooling. Apart from combustion improvement to increase overall performance, further research may have a scope on design of heat exchanger to reduce time for solidification process of jaggery. Also it is helpful to waste heat recovery at the end of drying process of jaggery and to save bagasse. In this paper numerical analysis is done on cooling of jaggery by using heat exchanger.
Index Terms— Jaggery, Moulds, Heat exchanger, CFD, Heat recovery.
NOMENCLATURE English Symbol
p pressure force
u,v,w velocity in x, y, and z components Greek Symbols
ρ density field
τ viscous shear stresses
I. INTRODUCTION
A manufacturing process for jaggery requires mechanical and thermal energy. Mechanical energy is used for juice extraction by passing the sugarcane stalks through a 3 or 5 roller crusher drawn by animal power or by electric motor or by an oil engine. The thermal energy for condensation of juice is provided by combustion of bagasse. The juice should be boiled immediately after extraction in open pan by using bagasse as fuel which is a biomass generated during sugarcane crushing.[2]. During boiling vegetable clarificants are added to remove the suspended impurities as scum. After the boiling mass has reached the striking point at which the boiling is regarded as complete and it is fit to be taken out of the pan for cooling. The striking point is of temperature that normally ranges in between 118 to 123 degree Celsius. The proper concentration of juice is judged by applying one of the following methods.
1. A small quantity of concentrated juice is taken from pan and is thrown into cold water. If it takes the shape of a ball with the metallic sound it is considered to be complete i.e.
completion of the process of boiling of juice. At the striking point, if the boiling mass is stirred, it does not stick the pan. 2. At the striking point the sticking mass forms a long silky thread which does not fall in drops. [4].
Thus, by applying one of the above methods to find the striking point or appropriate point of concentration of juice, the pan is then removed immediately from the furnace and is stirred for some time. The boiled liquid jaggery (kakavi) is transferred into a cooling pan. As the temperature falls, the jaggery begins to crystallize. By stirring the juice slowly and intermittently to avoid the loss of granular structure, the semi solid mass is then put into moulds when the jaggery solidifies it is removed by inverting the moulds. [1].
Temperatures of sugarcane juice during jaggery making process with respect to time are studied practically by Prof. G.S. Nevekar.
These lumps or moulds are made to take the shape of a bucket of different weights. These buckets are of 30 kg, 20, 19, 10, or 5 kg etc. these buckets are of different size but uniform shape having different weights of jaggery lumps. Even very small sizes of jaggery lumps is available in the shape of small balls locally called modak or laddoes but are not very famous as other heavy weighing lumps or moulds. The moulds are made to take the shape of a bucket of different weights. The cooling process of mould from 76 degree to normal room temperature is done by natural convection.
Table I. Temperature, time and processes during jaggery formation
Time (min)
Temp
(Degree) Process
5 28 Normal Temp. use of Calcium oxides (lime)
30 86 Removal of first black Scum
35 92 Boiling Continue
100 99
Start formation of Second Golden Scum
115 100
Boiling of Juice with bubble cream layer
130 101 Breaking of upper cream
layer
150 105 Juice ready for liquid Jaggery 155 107
Use of Hydrous or Cooking Oil
170 118 Formation of Jaggery 175 118
Transfer of Juice to cooling pan
180 96
Stirring of hot Juice first pattern
190 91
Stirring of hot Juice Second pattern
195 89
Start collection and pouring concentrated Juice
210 78 Moulding Jaggery
Therefore this heat is waste to atmosphere. To recover this waste heat and also to reduce cooling time of mould in this experiment mould is replaced by heat exchanger.
II. LITERATURE REVIEW
2014: Kiran Y. Shiralkar et al. examined comparative study of the energy efficiency of the existing single pan jaggery units and existing four pan jaggery units. Based on the findings authors recommended that four pan units are more productive than single pan units are more productive than single pan units due to their semi- continuous nature.[7].
2013: Pankaj K Arya et al. studied on improved plant of three pan furnace which compared with conventional plant on the basis of four parameters viz. jaggery production, bagasse consumption, emissions and temperature of exhaust. The Improved unit resulted in about 12% reductions in bagasse consumption, about 23% increases in jaggery production capacity, lesser emissions and comparatively lower exhaust gas temperature.[12]
2010: Vishal R. Sardeshpande et al. studied the procedure of four pan jaggery processing furnace including of four pan jaggery processing furnace including mass and energy balance. A controlled fuel feeding based on the oxygen percentage in the fuel gases is proposed and demonstrated. Fuel feeding rate reduced in specific fuel consumption from 2.73 kg bagasse/kg jaggery to 1.73 kg bagasse/kg jaggery. That means the rate of bagasse addition has a strong impact on efficiency. [2]
2010: Anwar conducted performance trials with evaporation of water in a two pan furnace with and without external fins on flue gas heating side. His study reports increase in the efficiency from 20% to about 29%
cemented with earth clay and a vertical chimney of rectangular cross section without any brickwork at the bottom or fire grate. Improved furnace was designed with use of fire brickwork at the bottom or fire grate. Improved furnace was designed with use of fire brick with refractory cement and a chimney of circular cross- section of optimum height to create sufficient draft. Improved chimney also included sliding dampers for draft control, firing platform for easy feeding of bagasse, fire grate for mixing of air with fuel. The specific bagasse consumption in traditional furnace was about 2.24 kg/kg jaggery which was improved to 1.96 kg/kg jaggery.[9]
2004: Dr. R. D. Singh et al. Report the performance evaluation of improved two-pan furnace in comparison with single pan furnace. The second pan (termed as gutter pan) in the improved furnace is installed in the flue gas path of the first pan (termed as boiling pan). Other improvements were air preheating and installation of stepped grate. The study reports an improvement of furnace efficiency from 16% for single pan traditional furnace to 29% for improved furnace.[10]
III. EXPERIMENTAL SETUP AND PROCEDURE
The design of the traditional cooling of the jaggery was the hot jaggery kept in the bucket and cooled by naturally.
So this heat can be used to preheat the juice ultimately plant thermal efficiency increases and bagasse consumption per batch reduces. To study the making process of jaggery plant survey was carried in Nahvi, Pune.
Fig. 1. Set up diagram of jaggery process plant.
The schematic diagram of the experimental setup used in the experiments is shown in Fig. 1. Heat exchanger is manufactured on the basis of standard size of jaggery of half kg of SS304. Experiment will conduct on site where main focus of experiment is on drying of jaggery process.
lower pan of heat exchanger is connected by connecting pipes.
This experimentation of jaggery drying will conduct at jaggery making plant. This involves fresh juice heated with all process which is ready to dry. Time required to solidifying the juice in heat exchanger and heat recovery at the outlet of heat exchanger will calculate by this experimentation.
A. Test methodology
Fig. 2. Actual setup
The procedure to conduct experiment is as follows.
The fresh sugarcane juice is stored in storage tank and supplied to heat exchanger by connecting pipes. The flow is adjusted by using flow control valve. Rota meter gives the flow rate of juice.
Thick syrup of juice at 76 degree is filled manually in upper pan of heat exchanger. The fresh sugarcane juice gets preheated which come in contact with thick syrup.
This preheated juice is collected in collecting tank. The measurements include total duration of one batch, temperature of jaggery during solidification process, temperature of inlet and outlet of heat exchanger flow rate of juice.
Schematic of the heat exchanger for measurement is shown in fig.2. K-type thermocouples are place to measure temperature at that particular point.
To evaluate the effect of hot thick syrup on fresh sugarcane juice and thus on thermal efficiency, experiments were performed by keeping flow rate of juice static and continuous. In next section the numerical analysis is done on cooling of jaggery and the preheating of the juice.
IV. NUMERICAL MODELING
A. Governing equations
The governing equations of the problem are the continuity equation, the momentum equation and the energy equation. In this study, the equations are written given below.
The continuity equation
……. (1) x momentum :
……. (2) y momentum :
……. (3) z momentum :
……. (4) B. Computational domain
Computational domain for preheating of juice in heat exchanger analysis was created in design modeler software of ANSYS 15. This geometry included a box of dimension of 120*120*100 in which juice domain was created and at the center the glass type domain was created for the domain of jaggery. Inlet and outlet pipe was provided for the fluid flow from these pipes, and the computational domain can be seen in fig.3.
Dimensions:
1. Juice domain : Box type shape
∗ Length=125 mm *Height=10 mm *Breadth=125 mm
2. Jaggery domain: Cylinder type shape
∗ Length= 85 mm * Diameter=95 mm
∗ Draft= 10 degree
Fig. 3. Computational domain C. Mesh Generation
Discretizing or dividing the full computational domain in smaller elements is known as meshing. This process is very crucial as we need an optimum number of fine grids to solve the Navier-stokes equation at each and every nodes of mesh elements. Here, meshing is done in Ansys software with tetrahedral mesh elements. Since, the simulation is carried in 3-D geometry; triangular dominant grid generation was done. Here, fig.4. shows the meshing of the computational domain.
Fig. 4. Grid generation Meshing specifications are:
Triangular grid dominant meshing
∗ Nodes = 12,314
∗ Elements = 30,382
Grid independency test has been performed for various mesh counts and it was verified that for mesh counts more than 44,946 variations in flow parameters were very less.
D. Initial, boundary and operating condition
mass flow rate at atmospheric pressure conditions and the fluid is incompressible hence pressure based solver was selected along with energy equation as on so as to get the temperature profiles near the solid object and fluid domain. The complete solver settings along with boundary conditions are as follows:
Solver settings:
Pressure based solver
Energy equation - ON
Viscous laminar
Boundary conditions:
∗ Inlet – Velocity ∗ Outlet- Atm. Pressure
E. Solution method
In Ansys 15, explicit formulation method was selected along with AUSM flux type. Spatial discretization was selected as follows:
Gradient - Least square cell based
Flow - Second order upwind
Turbulent Kinetic Energy - First order upwind
Specific dissipation rate - First order upwind
Post processing of velocity vectors and contours of pressure and temperature are done in next chapter of results and discussions.
V. RESULTS AND DISCUSSION
A. Validation of numerical results
For the validation of the numerical results, these results compare with the experimental results and the numerical error associated with these results calculated.
Results were validated as shown in Fig.5. Variation between those two temperature lines is 4.7 % because simulated value of temperature in experiment results is less due to less heat losses occurs through the SS wall where in numerical analysis heat losses through the SS wall is not considered.
B. Preheating of juice in heat exchanger 1) At flow rate of 30 LPH
At different time interval preheating of juice in heat exchanger was studied for the mass flow rate of 30 LPH as shown in figure 6.
a) Preheating of juice after 10 min:
Temperature contour was observed in the heat exchanger to analyze the preheating of juice, it is observed that when fresh juice passes through the jaggery wall it gets heated due to heat transfer by convection and conduction through the wall.
Fig.6. Preheating of juice after 10 min (30LPH) Red zone shows very high temperature of the wall and near wall the faint blue color indicates that the heating of the juice. The temperature of the juice rises up to 307 K after 10 min. time interval. Thus, heat is transferred to the juice and its get preheated. Also the temperature of jaggery is reduced due to cooling by sugarcane juice. The average reduction of the jaggery temperature up to 339 k which is initially temperature of the jaggery is 351 k as shown in temperature contour.
b) Preheating of juice after 20 min:
The temperature contour for 20 min. in the heat exchanger shown in figure, It is observed that when fresh juice passes through the jaggery wall it gets heated due to heat transfer by convection and conduction through the wall.
Fig.7. Temperature contour for preheating of juice after 20 min (30LPH)
Red zone shows very high temperature of the jaggery at the center and near wall the faint blue color indicates that the heating of the juice. The temperature of the juice rises up to 310 K after 20 min. time interval. Thus, heat is transferred to the juice and its get preheated. Also the cooling of jaggery is seen in the temperature contours.
The jaggery temperature is 332 k after 20 min time interval.
c) Preheating of juice after 30 min:
The temperature contour for 30 min. in the heat exchanger is shown in fig.8.
Fig.8. Temperature contour for preheating of juice after 30 min (30LPH)
It is observed that when fresh juice passes through the jaggery wall it gets heated due to heat transfer by convection and conduction through the wall. Red zone shows very high temperature of the jaggery at the center and near wall the faint blue color indicates that the heating of the juice. The temperature of the juice rises up to 308 K after 30 min. time interval. Thus, heat is transferred to the juice and its get preheated. Also the cooling of jaggery is seen in the temperature contours. The jaggery temperature is 326 k after 30 min time interval. Here we can also see that the cold juice comes near to the outlet.
Fig.9. Velocity vectors for preheating of juice after 10 min (30LPH)
Velocity vectors was observed and analyzed in the full domain and near the wall of jaggery Fig.9. shows the velocity vectors in the juice domain, which shows that juice impinging on the wall and then diverging sideways after getting interacted from the wall. Velocity contours by temperature is shown in the figure, here the dark blue arrows at the inlet shows the cold juice and sky blue arrows shows the preheated juice.
2) At flow rate of 50 LPH
At different time interval preheating of juice in heat exchanger was studied for the mass flow rate of 50 LPH as shown in figure
a) Preheating of juice after 10 min:
Temperature contour was observed in the heat exchanger to analyze the preheating of juice, it is observed that when fresh juice passes through the
Fig.10. Temperature contour for preheating of juice after 10 min (50LPH)
jaggery wall it gets heated due to heat transfer by convection and conduction through the wall. Red zone shows very high temperature of the wall and near wall the faint blue color indicates that the heating of the juice. The temperature of the juice rises up to 307 K after 10 min.
time interval. Thus, heat is transferred to the juice and its
b) Preheating of juice after 20 min:
The temperature contour of the heat exchanger for 20 min is shown in figure 10.
Fig.11. Temperature contour for preheating of juice after 20 min (50LPH)
It is observed that when fresh juice passes through the jaggery wall it gets heated due to heat transfer by convection and conduction through the wall. Red zone shows very high temperature of the jaggery at the center and near wall the faint blue color indicates that the heating of the juice. The temperature of the juice rises up to 307 K after 20 min. time interval. Thus, heat is transferred to the juice and its get preheated. Also the cooling of jaggery is seen in the temperature contours. The jaggery temperature is 333 k after 20 min time interval.
3) Preheating of water in heat exchanger:
At different time interval preheating of water in heat exchanger was studied for the mass flow rate of 30 LPH as shown in fig.12.
a) Preheating of water in heat exchanger after 5 min Temperature contour was observed in the heat exchanger to analyze the preheating of water. It is observed that when fresh water passes through the jaggery wall it gets heated due to heat transfer by convection and conduction through the wall
the water. The temperature of the juice rises up to 306 K after 5 min. time interval. Thus, heat is transferred to the water and its get preheated. The heat transfer rate is higher for the water compare to the juice due to higher thermal conductivity of water but temperature rise of water is less compare to the juice due to higher heat capacity of the water compare to the juice. Also the temperature of jaggery is reduced due to cooling by sugarcane juice.
b) Preheating of water in heat exchanger after 25 min
The temperature contour for 25 min. in the heat exchanger shown in fig
Fig.13. Temperature contour for preheating of water after 25 min
It is observed that when fresh juice passes through the jaggery wall it gets heated due to heat transfer by convection and conduction through the wall. Red zone shows very high temperature of the jaggery at the center and near wall the faint blue color indicates that the heating of the juice.
In above section the preheating of juice and water was analyzed numerically at different mass flow rate by using computational fluid dynamics software. In that we can see the temperature contours, velocity plot by temperature vectors for different fluid and mass flow rate. Also validation of these results with the experimental results was done. In next chapter analytical model was developed to calculate the cooling rate of the jaggery by using transient conduction analysis.
VI. CONCLUSION
Preheating of juice was analyzed by experimentally, analytically and numerically.
1. Preheating of the fresh sugarcane juice before it passes for Jaggery production achieved using heat exchanger experimentally.
2. In static condition the juice is heated by 12 degree Celsius and water is heated by 8 degree Celsius also in
dynamic condition the juice is heated up to by 6 degree Celsius and water is heated up to by 4 degree Celsius.
3. Due to passing of juice or water in heat exchanger the temperature of jaggery reduces with respect to time resulting reduction in cooling rate of jaggery.
4. Numerical analysis for Velocity and Temperature distribution on jaggery and preheated juice in heat exchanger was done and results validate with experimental results.
5. Numerical analysis is helps to show how heat is transferred between juice and jaggery. Velocity plot by temperature vectors shows that the how fluid is flow and it gets heated.
6. Numerical analysis also helps to study the preheating of juice at different mass flow rate and different size of heat exchanger.
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