Keyur C. Patel a *, Vikas J. Lakhera b, Dilip Sarda c

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1 Available online at Procedia Engineering 51 ( 013 ) Chemical, Civil and Mechanical Engineering Tracks o 3 rd Nirma University International Conerence (NUiCONE 01) Thermal optimization o an ice cream hardening process Keyur C. Patel a *, Vikas J. Lakhera b, Dilip Sarda c a Assistant Proessor, Gandhinagar Institute o Technology, Gandhinagar-3871, India b Proesssor, Institute o Technology, Nirma University, Ahmedabad-38481, India c Director, Synergy Agrotech Pvt Ltd, Ahmedabad , India Abstract The conservation o energy is an essential step that can be taken towards mitigating the issues o energy crisis and environmental degradation. Excessive use o energy and energy loss are usually associated with many industrial establishments worldwide-specially in the ood processing industry, where a substantial amount o energy is consumed. Enormous potential exists or the cost eective improvement in existing energy consuming equipment. In the present work, an ice cream hardening machine or batch production is taken into consideration. The system consists o shell and tube condenser and evaporator coils as a part o primary rerigeration cycle along with the air blower. The optimization or the shape o ice cream boxes during hardening process is done. The combined eect o various parameters like velocity and temperature o blowing air, orientation o ice cream box and spacing between the ice cream boxes on the reezing time is studied to ind the energy eicient and economic option. The results obtained by the theoretical model are evaluated by comparing with the experimental data The Published Authors. by Published Elsevier by Ltd. Elsevier Selection Ltd. Open and/or access peer-review under CC BY-NC-ND under responsibility license. o the Institute o Technology Nirma University, Selection and Ahmedabad. peer-review under responsibility o Institute o Technology, Nirma University, Ahmedabad. Keywords: Freezing time, ice cream hardening, cooling load. Nomenclature C Speciic heat (kj/kg K) C lv Volumetric speciic heat o unrozen ood (J/m 3 K) C sv Volumetric speciic heat o ully rozen ood (J/m 3 K) D Slab thickness (m) H 10 Volumetric enthalpy dierence between initial reezing point o ood and -10 C (J/m 3 ) H 18 Volumetric enthalpy dierence between initial temperature o ood item and -18 C (J/m 3 ) h Surace heat transer coeicient (W/m K) k s Thermal conductivity o rozen ood (W/m K) L Volumetric latent heat o usion (J/m 3 ) P Parameter deining the geometry o the ood R Parameter deining the geometry o the ood Initial reezing point o the ood ( C) t * Keyur C. Patel. Tel.: address: keyur.patel6786@gmail.com The Authors. Published by Elsevier Ltd. Open access under CC BY-NC-ND license. Selection and peer-review under responsibility o Institute o Technology, Nirma University, Ahmedabad. doi: /j.proeng

2 Keyur C. Patel et. al / Procedia Engineering 51 ( 013 ) t m T c T i Freezing medium temperature ( C) Final centre temperature o ood item ( C) Initial temperature o ood item ( C) Greek symbols Freezing time (s) 1. Introduction Preservation o ood is one o the most signiicant applications o rerigeration. It is known that cooling and reezing o ood eectively reduces the activity o micro-organisms and enzymes, thus retarding deterioration. In addition, crystallization o water reduces the amount o liquid water in ood items and inhibits microbial growth[1]. In order or cooling and reezing operations to be cost-eective, it is necessary to optimally design the rerigeration equipment to it the speciic requirements o the particular cooling or reezing application. The design o such rerigeration equipment requires estimation o the cooling and reezing times o oods and beverages, as well as the corresponding rerigeration loads. Numerous methods or predicting the cooling and reezing times o oods[] are available, including those based on numerical, analytical and empirical analysis. This paper ocuses upon the method which is applicable to regularly shaped ice cream boxes. The perormance o this method is evaluated by comparing their results to experimental reezing time data obtained rom the literature. The ice cream is cooled as quickly as possibly down to a holding temperature o less than -5 C. The temperatures and time o cooling will depend on the type o storage reezer, shape o packets, arrangement o packets, material o packets, low rate o air and surrounding temperature. Rapid cooling will promote quick reezing o water and create small ice crystals, which ultimately increases the quality o an ice cream Packaging o an ice cream Generally packaging o ice cream is done beore hardening. In ew cases it is done ater hardening. When ice cream is drawn rom the reezer, it is usually collected in containers, which give it the desired shape or size or convenient handling during hardening, storage and marketing. The important requirements o packages or ice cream are: Protection against contamination Attractiveness Ease o opening and re-closure Ease o disposal Desirable requirements o packages are: Protection against moisture Protection against temperature luctuations. Theoretical model.1. Freezing time Number o methods or predicting the cooling time and reezing time o oods are available, based on numerical, analytical, and empirical analysis. One o the most widely known simple methods or estimating reezing times o oods and beverages is developed by Plank[3]. In this method, convective heat transer is assumed to occur between the ood item and the surrounding cooling medium. In addition, the temperature o the ood item is assumed to be at its initial reezing temperature and that this temperature is constant throughout the reezing process. Furthermore, a constant thermal conductivity or the rozen region is assumed. Plank's reezing time estimation is as ollows: L PD RD (1) t tm h ks

3 65 Keyur C. Patel et. al / Procedia Engineering 51 ( 013 ) Since this equation does not include the times below and above the reezing itsel, several attempts have been made to improve it by adding new terms and parameters, to make it suitable or the entire reezing process. Cleland and Earle[4] improved upon Plank's model by incorporating corrections to account or the removal o sensible heat both above and below the initial reezing point o the ood as well as temperature variation during reezing. Regression equations were developed to estimate the geometric parameters, P and R, or ininite slabs, ininite cylinders, spheres and rectangular bricks. In these regression equations, the eects o surace heat transer, precooling and inal sub cooling are accounted or by means o the Biot number Bi, the Plank number Pk, and the Stean number Ste. The latent heat L in Plank s equation is replaced with the volumetric enthalpy change o the ood H 10 between the reezing temperature T and inal center temperature assumed to be -10 C. Thus, the modiied Plank equation takes the orm ΔH 10 PD RD () t tm h ks Hung and Thompson[5] obtained Plank-like ormulas through the regression analysis o reezing data. Their equation incorporates the volumetric change in enthalpy H 18 or the reezing process as well as a weighted average temperature dierence between the initial temperature o the ood and the reezing medium temperature. This weighted average temperature dierence T is given as ollows: Clv ( T t ) ( t T ) Csv i c Δ T = ( t t ) m + ΔH18 (3) The reezing time prediction model is based on ollowing equation: 3. Experimental set up and methodology 3.1. Air blast reezer ΔH 18 PD RD (4) ΔT h k s Air blast reezer is a rerigerated space in which ice cream boxes are to be kept. The vapor compression system cools the rerigerant R 404a which low through the cooling coil. Fans are provided to circulate the air. Air passes across the cooling coil, get cooled and lows through the arrangement o the ice cream boxes to cool them. Ice cream is taken to the temperature o -18 ºC. The schematic o an air blast reezer is shown in Fig 1. Fig. 1. Schematic o Air blast reezer

4 Keyur C. Patel et. al / Procedia Engineering 51 ( 013 ) Experimental methodology The methodology or experimentation was as ollowing: The setup was run by switching on the power supply or no load conditions till the air achieve the desired temperature. Measure the velocity o air by anemometer. The ice cream boxes were placed in the air blast reezer. The arrangement and spacing between the boxes depend on the space available. The temperature sensor was placed at the centre o an ice cream box. The temperatures were recorded and the time taken or achieving the desired inal ood centre temperature was noted Uncertainity in measurement The experimental uncertainities in the measurements conducted were as ollowing: Temperature sensors ±1 ºC Pressure gauges ±0.01 bar. Anemometer ±0.01 m/s 4. Results and discussion 4.1 Analytical results The geometric shape o an ice cream box is one o the most important parameter taken under consideration. A cube is the best shape or the box type geometry and it takes minimum time or reezing. A cylinder takes hal the time and a sphere takes one third time to reeze or a same characteristic dimension D but these shapes are not practically convenient to sell in the market. So a rectangular shape is the best option available or one liter ice cream packet. Orientation o ice cream box is also important. Flow parallel to the length takes more time than the low perpendicular to the length as the boundary layer separation is more in case o the low parallel to the length o box. For a uniorm air distribution and better heat transer, a spacing between the two consecutive boxes is desirable. Table 1. An economic comparison o combined eect o velocity and temperature on total power (kw) or 90 minutes running time Temperature (ºC) Velocity (m/s) Generally or rapid reezing, the temperature o the system is taken towards the lowest possible range. This procedure increases the power consumption. It is observed that an increase in velocity eectively decreases the total power. This also increases the an power but the an power is much lesser than the compressor power. From Table 1 it is observed that or desired time o reezing, total power is less in case o the increase in velocity than the decrease in temperature. So it is more beneicial to increase the air velocity than to decrease the air temperature. As an example, or reezing time o 90 minutes, it is beneicial to select the combination (Velocity 4 m/s; Temperature -0 ºC) than the combination (Velocity 1.5 m/s; Temperature -40 ºC). It results in a power saving o 0.41 kw. 4. Comparison o experimental and theoretical results To validate the theoretical calculations, experiments were perormed or two dierent boxes having the dierent volume and dimensions.

5 654 Keyur C. Patel et. al / Procedia Engineering 51 ( 013 ) The comparison o reezing time or both the boxes (box ml and box ml) in the exposer o an air at -5 ºC and velocity 1 m/s is shown in Fig. The theoretical results are less than the experimental results since the conductivity o packing material is not considered in the theoretical calculations. Fig.. Comparison o reezing time o ice cream boxes 5. Conclusions Based on the study conducted, the ollowing conclusions are drawn. The hardening o ice cream depends on various parameters but the shape and orientation o ice cream boxes along the low plays a major role. The characteristic length (length parallel to the low o air) is the most important actor. It should not be too long as due to the boundary layer proile created, it results in a decrease o heat transer. The temperature and the velocity o the blowing air directly aects the power consumption. It is preerable to increase the velocity rather than decrease the temperature o blowing air. For the same reezing time, a combination o velocity and temperature should be selected in such a way that it contains maximum velocity (keeping pressure drop o air against the cooling coil in consideration) since the power consumption o an is very low as compared to the power consumption o the compressor. The spacing between the two consecutive boxes is also an important parameter to be taken under consideration. For the uniorm air low, minimum 5 cm spacing is advisable. Acknowledgements This present study was experimentally supported by Synergy Agrotech Pvt Ltd, Ahmedabad, Gujarat, India. Reerences [1] Heldman, D. R Predicting the Relationship Between Unrozen Water Fraction and Temperature During Food Freezing Using Freezing Point Depression, Transactions o the ASAE 17(1), pp [] ASHRAE, 00. ASHRAE Handbook-Fundamentals. Atlanta, Georgia: American Society o Heating, Rerigerating and Air-Conditioning Engineers. [3] Plank, R. (1941). Beitrage zur Berechnung und Bewertung der Geriergeschwindigkeit von Lebesnmitteln (Calculation and validation o reezing velocities in oods). Beihete zur Zeitschrit ur die gesamte Kalte-Industrie, 3(10), pp.1-4. [4] Cleland, A. C., & Earle, R. L. (1979b). Prediction o reezing times or oods in rectangular packages, Journal o Food Science, 44, pp [5] Hung, Y. C., & Thompson, D. R. (1983). Freezing time prediction or slab shape oodstus by an improved analytical method, Journal o Food Science, 48(), pp