Scraped Surface Heat Exchanger Research Articles

A computational investigation for heat and fluid transport with electro-osmosis phenomenon in a scraped surface heat exchanger

Scraped surface heat exchangers (SSHEs) have prominently shown their eminence in various food, chemical and in pharmaceutical industries when the regular processing of fluids and pertinent materials is encountered. The heat transfer analysis of Williamson fluid flow with electro osmotic effects in a narrow-gap SSHE is designed by implementing constant temperature difference between the gaps of the rotor and the stator. A fluid model is established by using lubrication approximation theory and Debye-Huckel simplifications. The computational solution is elaborated by implementing renowned BVP4C technique in MATLAB. Exact solution of Poisson-Boltzmann equation for different scenarios of SSHE is gathered, whereas solution for velocity, stream functions and temperature in various parts of SSHE are explored computationally. Impact of various crucial physical flow parameters like, Weissenberg number, mobility of the medium number, electro osmotic parameter on the velocity profile, stream function, temperature profile, and pressure gradient has been explored graphically. The numerical solution is compared with artificial neural network (ANN) and an absolute alignment of BVP4C solution is observed with ANN solution. It is reported that fluid flow is lifted with enhancing the viscoelastic behavior and exhibits dual behavior for electroosmosis phenomenon and mobility of medium parameter. Also, it is seen that temperature of the fluid is significantly declines with Weissenberg number and is surges with enhancing mobility of medium and Brinkman number. By increasing the Brinkman number conduction phenomenon is slow down and heat produced due to viscous dissipation, raises the temperature of the fluid. The viscoelastic effect could be of enormous significance in applications, like Polymer processing in certain heat exchangers, and in mixing and blending foodstuffs etc.

Parametric study of a scraped surface heat exchanger for latent energy storage for domestic hot water generation

In this work, a parametric study of a Scraped Surface Heat Exchanger (SSHE) for solar Latent Thermal Energy Storage (LTES) has been conducted. The primary challenge in Phase Change Material (PCM) heat exchangers is the formation of a solid layer along the heat transfer surfaces during the latent energy release phase. This reduction in the energy release rate is resolved through the scraping of the solidified PCM, making SSHE systems suitable for domestic hot water generation. Experiments have been performed to evaluate the influence of various operational parameters, including the heat transfer fluid (HTF) mass flow rate, the phase change characteristics of the PCM, the temperature difference between the HTF and the PCM, and the scraping velocity. It has been observed that a HTF Reynolds number (Re) of 100 will require three times more time compared to Re = 600. Moreover, the significance of maintaining a HTF to PCM differential temperature between 20 °C and 25 °C has been experimentally verified to improve the PCM solidification process. Furthermore, the existence of a critical scraping frequency has been demonstrated, beyond which increasing the frequency does not yield to significant improvements in energy extraction. Finally, a correlation has been proposed to predict solidification time as a function of the non-dimensional operational parameters involved, where 95 % of the results fall within an interval of 10 %.

Crystallization behavior of monoglyceride oleogels: A comparison between a fully hydrogenated palm oil and a fully hydrogenated rapeseed oil based monoglycerides

AbstractFat polymorphism plays a crucial role in many fat‐rich food products (e.g., margarine, chocolate). Due to this, polymorphism of triglycerides is widely investigated. During the previous years, the interest of using monoglyceride oleogels to replace margarine is increasing due to its structure, reduced amount of saturated fatty acids, stability and application potential. However, polymorphism of monoglyceride oleogels is less investigated. This research shows the effect of the composition (C18:0 or C18:0 and C16:0), temperature (25°C–20°C–10°C) and production process (static or lab‐scale scraped surface heat exchanger) on the crystallization behavior of monoglyceride oleogels (MO) by using differential scanning calorimetry, (synchrotron) X‐ray scattering and polarized light microscopy. Based on time‐resolved synchrotron WAXS, it was found that the rapeseed oil based MO (MO‐C18) occurred in four different polymorphs. During crystallization, transitions from an inverse lamellar phase (Lα) toward sub‐α1 and sub‐α2 could be established. Upon storage, a polymorphic transition toward β occurred. For the palm oil based MO (MO‐C18/C16), only two polymorphs were found during crystallization (Lα, sub‐α), followed by a polymorphic transition to β upon storage. By applying high shear and cooling rates during the production of MO‐C18 (dynamic production), the polymorphic transition from sub‐α2 to β occurred much faster compared to the static production method. When comparing the dynamically produced MO‐C18 and MO‐C18/C16, the thickness of 1 lamella, the crystal nanoplatelet and the fat crystals were smaller for MO‐C18/C16. This research clearly illustrates that the composition and the applied crystallization conditions have an impact on the properties from nano‐ to microscale.Practical Application: This research illustrates the importance of engineering monoglycerides oleogels to obtain food products with an improved nutritional balance. Hereby, the manuscript focuses on the crystallization behavior of monoglyceride oleogels by changing the composition and the crystallization procedure. The acquired insights go beyond the state of the art. It was found that applying high cooling rates and high shear rates by using a lab‐scale scraped surface heat exchanger affected the crystallization behavior of monoglyceride oleogels. These are crucial experiments to verify the application potential of monoglyceride oleogels in the food industry. Moreover, different polymorphic transitions occurred for the two types of monoglycerides. This is the starting point to investigate the effect of polymorphism on a final food product in order to improve the nutritional balance in fat‐rich food products.

Numerical investigation of entropy generation of Joule heating in non-axisymmetric flow of hybrid nanofluid towards stretching surface

Abstract The industrial sector has shown a growing interest in hybrid nanofluids affected by magnetohydrodynamics (MHD) owing to their wide range of applications, including photovoltaic water heaters and scraped surface heat exchangers. The main purpose of this study is to look at how entropy is created in a hybrid nanofluid of ${\rm{A{{l}_2}{{O}_3}{-}Cu}}$ mixed with ${\rm{{{H}_2}O}}$ at a non-axisymmetric stagnation point flow with Joule heating and viscous dissipation. By using appropriate non-similarity transformations, the partial differential equations (PDEs) governing the boundary layer region of this issue are transformed into a set of non-linear PDEs. The BVP4c MATLAB program, which uses local non-similarity and additional truncation, may fix the problem. The velocity profiles in both directions grow when the values of ${{\phi }_2},\ M,\lambda $, and A parameters increase. The temperature profile rises as the values of A and $Ec$ grow and lowers as ${{\phi }_2}$ and M increase. The obtained numerical findings demonstrate significant impacts on both the heat transfer rate and fluid flow parameters of the hybrid nanofluid. When the concentration of nanoparticles and the magnetic parameter are heightened, there is an enhancement seen in the skin friction coefficient and decline in heat transfer rate. In addition, the entropy production profile shows an increasing tendency as a function of the parameters ${{\phi }_2},\ M,$ and $Br,$ while demonstrating a decreasing tendency of function of the parameter $\alpha $. The Bejan number profile has a positive correlation with the parameter $\alpha $ but shows a negative correlation with the variables ${{\phi }_2},\ M,$ and $Br$.

Recent Advances in Lipid Crystallization in the Food Industry.

This review discusses fundamental concepts of fat crystallization and how various processing conditions such as crystallization temperature, cooling rate, and shear or agitation affect this process. Traditional methods used to process fats, such as the use of scraped surface heat exchangers, fractionation, and interesterification, are described. Parameters that affect fat crystallization in these systems, such as shear, crystallization temperature, type of fat, and type of process, are discussed. In addition, the use of minor components to induce or delay fat crystallization based on their chemical composition is presented. The use of novel technologies, such as high-intensity ultrasound, oleogelation, and high-pressure crystallization is also reviewed. In these cases, acoustic and high-pressure process parameters, the various types of oleogels, and the use of oleogelators of differing chemical compositions are discussed. The combination of all these techniques and future trends is also presented.

A review of the use of scraped surface heat exchangers to crystallize fats and fat‐based products

AbstractScraped surface heat exchangers (SSHE) are very important in many industries including chemical, cosmetic, pharmaceutical, and food. Some of the applications of SSHE in the food industry are to control the crystallization process in fats and frozen desserts, among other applications. This can be achieved because of the scraping action of the fixed blades that continuously rotate within the cooling surface removing the crystallized product from the surface, improving heat transfer, preventing crystal build‐up on the wall, and accelerating the crystallization process. There are many process parameters that can be controlled in the SSHE to control and tailor the fat crystallization process, and many fat‐based products can benefit from this machine, such as shortenings, spreads, and chocolates. Moreover, SSHE have recently been coupled to other processing devices such as high intensity ultrasound (HIU), high pressure homogenizers, and others to improve the crystallization process even further. This review focuses on the importance of SSHE in fat and fat‐based products and discusses the importance of the parameters of the SSHE in the crystallization process, as well as how they affect the physical properties of different fat sources and spreads.

Heat transfer analysis in a heat exchanger with two coaxial tubes for sustainable aseptic processing of foods

Thermal-based approaches in food sterilization techniques principally utilize the heating process until the desired sterilization level of the food can achieved. More specifically, aseptic processing allows for a more cost-effective and time-efficient method for preserving food without degrading the food quality. In this work, we propose a heat transfer analysis of a scraped surface heat exchanger with two coaxial tubes that provides a simplified prototype of a sustainable aseptic processing system. The heat exchanger is installed with scraped blades to allow a stirring mechanism that can only oscillate back and forth at certain angles called oscillating angles. In this simulation, water and solid food particles are put in the system. Moreover, simple regression models are used to find the relation between the mechanical properties of the stirring process with the heat transfer properties. Therefore, experimental data of the temperature and heat transfer coefficient during the heating are used for model fitting. The model fit shows that the angle, frequency, and velocity of the stirring affect the temperature trend and the heat flow rate inside the system. Establishing a comprehensive heat transfer modelling can help to improve the traditional sterilization approach to focus on optimizing energy efficiency and reducing environmental impacts.

Influence of pH on particle size of thermomechanical stabilized whey protein-pectin complexes for technical scale production

Whey protein-pectin complexes (WPPC) with particle sizes d90,3 10 μm can be applied as fat replacer enhancing creaminess in fat reduced products. For the formation of process stable WPPC initial whey protein-pectin coacervates are formed via pH adjustment and denatured via thermomechanical treatment. The formation of WPPC was recently scaled up based on a reference process established at a batch lab scale scarped surface heat exchanger (90 °C, 675 s−1, 130 mL, pH 6.1). The application of three different whey protein sources was investigated resulting in poor applicability at previously established pH of 6.1 at the continuous technical scale scraped surface heat exchanger (90 °C, 675 s−1, 130 L⋅h−1). Based on ζ-potential and turbidity a pH range between 4.75 and 5.5 was chosen as suitable for the investigation in technical scale. While temperature and representative shear rate were maintained, whey protein pectin coacervate dispersions with pH between 4.75 and 6.0 were processed at the scraped surface heat exchanger. Depending on whey protein source a pH adjustment between 5.0 and 5.5 was necessary, to result in suitable particle sizes in targeted complex size d90,3 ∼10 μm. The pH can be applied as additional parameter, besides representative shear rate, temperature and biopolymer concentration, to tailor WPPC size for different product matrices for high perceived creaminess.

Processing of whey protein-pectin complexes: Upscaling from batch lab scale experiments to a continuous technical scale process

Whey protein-pectin complexes can be applied as fat replacers contributing to creaminess, while adding a source of protein and fiber. Production of these complexes was previously conducted via thermomechanical treatment (90 °C, 675 s−1, 19.5 min) on lab scale in small batches (∼130 mL). To apply these fat replacers in food products a continuous large scale process at a scraped surface heat exchanger (90 °C, 675 s−1) at a throughput of 130 L h−1 was established. Process stable whey protein-pectin complexes were achieved, whereas broader complex size distributions were obtained in technical scale process due to differences in residence times and temperature profiles. However, the influence of representative shear rate on complex size could be predicted for technical scale application by pre-experiments on lab scale. In both scales particle size decreased with increasing representative shear rate from 105 to 675 s−1 making it possible to tailor complex size.

Electroosmosis oriented flow of Jeffrey viscoelastic model through scraped surface heat exchanger

Scraped surface heat exchanger (SSHE) is vibrantly utilized in various industries. The heat exchanger devices play pivotal role in the energy transfer phenomenon between the fluids, and it improves the efficient use of energy. The steady isothermal flow of a rheological aqueous ionic solution in a narrow gap scraped surface heat exchanger is explored. The mathematical model is established with the aid of lubrication approximation theory and extracted analytical solution. Exact analytical expressions are gathered for velocities, volume fluxes, pressure gradients, pressure at the edges of the blades and stream functions in the various stations of SSHE. Strength of significant flow parameters on the velocities, volume fluxes, pressure gradients, pressure at the edges of the blades and stream functions is revealed with aid of various plots. Significant enhancement in the velocity profile is observed in main domain of the flow with increasing ratio of relaxation to retardation time parameter and Helmholtz Smoluchowski velocity. While, it is observed that electro-osmotic parameter creates impediments to the flow.

Carnauba Wax and Beeswax as Structuring Agents for Water-in-Oleogel Emulsions without Added Emulsifiers.

This research aims to explore the potential of waxes as ingredients in the formulation of food-grade water-in-oleogel emulsions without added emulsifiers. The effects of the wax type, wax concentration and water concentration were tested on systems containing exclusively water, sunflower oil, and wax. Beeswax and carnauba wax were used in the formulation of water-in-oleogel emulsions with 20%, 30% and 40% w/w of water. For the continuous phase, three different levels of wax were used, namely 50%, 100%, and 150% of the critical gelling concentration. More specifically, carnauba wax emulsions were prepared at 2.5%, 5.0% and 7.5% of wax, while concentrations of 0.75%, 1.5% and 2.25% of wax were utilized for the beeswax experiments. Samples were assessed over time regarding stability, rheology and microstructure (polarized light microscopy, cryo-scanning electron microscopy and confocal scanning laser microscopy). Our findings suggest that, if present in sufficient concentration, carnauba wax and beeswax can stabilize emulsions in the absence of additional added emulsifiers. The resulting systems were inherently different based on the wax used, as crystal morphology and droplet configurations are determined by wax type. The yield strain was dictated by the nature of the wax, while the complex modulus was mostly influenced by the wax concentration. To test the scaling-up potential, systems were crystallized in a pilot-scale scraped surface heat exchanger, resulting in notably smaller crystal sizes, reduced rigidity and a storage stability of over one year. These findings represent a starting point for the formulation of scalable water-in-oleogel emulsions without added emulsifiers.

Enhanced thermal-hydraulic performance in tubes of reciprocating scraped surface heat exchangers

An experimental study of pressure drop and heat transfer in tubes of reciprocating scraped surface heat exchangers is presented. Inside the tube, a concentric rod which mounts an array of equally-spaced semi-circular blades is fitted. The reciprocating motion of the rod induces the continuous scraping of the inner tube wall, enhancing heat transfer through the removal of the thermal boundary layer, the promotion of mixing of the bulk flow and the mitigation of fouling. Using propylene-glycol as working fluid, friction factor results in isothermal conditions are obtained for 15<Reh<1500 and velocity ratios 0<ω<2. Early transition to turbulence for Reh<150 is detected. Pressure drop augmentations of the order of 20, with respect to the smooth tube, are found in laminar regime for ω=2. In the turbulent flow regime, this pressure drop increase rises up to 400 times. In laminar regime, results for ω=0.1 lead to heat transfer augmentation of 30 % compared with the smooth tube. When increasing from ω=0.1 to ω=1, the Nusselt number is doubled. However, when increasing from ω=0.1 to ω=2 the Nusselt number is only increased by 2.8 times. The beneficial influence of higher scraping amplitudes on heat transfer have been demonstrated, as well as their negligible impact on the friction characteristics.

Accelerated testing methods to analyse long term stability of a Phase Change Material under the combined effect of shear stress and thermal cycling

The long-term stability of a Phase Change Material (PCM) is a key point for its selection in energy storage devices. This work studies the suitability of a commercial paraffin wax in an active scraped surface heat exchanger for solar energy storage purposes. In these devices, the continuous scraping of inner walls during solidification removes PCM and increases the released heat. Hence, the PCM is affected by a high level of shear stress. In order to study a potential degradation of the paraffin, a novel accelerated procedure has been designed for obtaining samples with a different number of thermal and scraping cycles. The procedure allows to evaluate the effect of shear stresses, thermal cycles and their combined effects separately. Up to 3000 cycles have been generated, which accounts for around 8 years of continuous daily work in the heat exchanger. The measurements through Differential Scanning Calorimetry, rheometry and thermal conductivity analysis have shown that neither the thermal nor the scraping cycling have a significant impact on the paraffin thermo-physical properties. According to the findings reported in this work, paraffin wax RT44HC can be successfully used in scraped surface heat exchangers. It is expected that other commercial paraffins would be also suitable since most of them share the fact of being blends of alkanes and other hydrocarbons.

Effect of processing by batch type scraped surface heat exchanger (SSHE) onsensory attributes of bottle gourd (Lagenaria siceraria) halwa

The awareness among consumers for healthier and functional food has led to increase in the market size for valued added products. The present study was undertaken to manufacture valued added Indian indigenous dairy product, bottle gourd halwa in a multipurpose batch type SSHE. The performance of the developed SSHE was evaluated at three different steam pressures (1, 1.5 and 2 kg/cm2), scraper speeds (10, 20 and 30 rpm) by keeping batch size constant (5kg) during manufacturing of bottle gourd halwa. The products were evaluated for sensory characteristics with a 9-point Hedonic scale. The overall acceptability of the product was considered on the basis of sensory attributes. The bottle gourd halwa prepared in SSHE at 1kg/cm2 steam pressure and 30 rpm scraper speed (P1S3) had the score of 7.9 for flavour, 7.85 for body and texture and 7.4 for colour &amp; appearance and the highest overall acceptability score (7.72)  as compared to the products prepared at other operating conditions. However, it was not equivalent to control for these attributes.

Thermal and electrical energy analysis of scraped surface heat exchangerduring Kheer making

Kheer is a cereal based sweetened and concentrated milk confection, very well-liked in India. The present investigation was undertaken to study the energy consumption of the developed batch type scraped surface heat exchanger (SSHE) for kheer making. The kheer was prepared by using SSHE at different levels of steam pressure (1.0, 1.5 and 2.0 kg/cm2), scraper speed (10, 20 and 30 rpm) and batch size (10, 15 and 20 kg). The thermal and electrical energy consumptions were determined. The rate of evaporation increased with increase in operating variables. The average rate of evaporation ranged from 11.84 to 25.65 kg water evaporated/h. The specific steam consumption by the SSHE during kheer making ranged between 1.568 and 1.702 kg steam/kg of water evaporated under different operating conditions of the machine. The total heat losses during manufacture of kheer in SSHE ranged from 12.9 to 18.9 %. The electrical power consumption of the machine during manufacturing of kheer varied from 230.1 to 260.5 W.

Experimental performance of a novel scraped surface heat exchanger for latent energy storage for domestic hot water generation

In this work, a novel design of a real scale Scraped Surface Heat Exchanger (SSHE) for solar LTES has been developed and experimentally tested. The main issue in PCM heat exchangers is the growth of a solid layer at the heat transfer walls during the latent energy extraction/discharging, that lowers heat transfer. The removal of the solidified PCM through scraping increases the heat transfer rate with nearly constant heat flux. Those characteristics make it suitable for domestic hot water generation. Discharging tests have been performed in scraping and no scraping modes (SM and nSM). The heat release rate in SM has shown to be between two and three times higher than in nSM. Moreover, in SM there is a complete extraction of the available latent energy (11.9 MJ) in a short period, compared to nSM. Additionally, a performance comparison between the developed SSHE and those available in open literature has been done. The results of heat release density (4 kW/m2) and overall heat transfer coefficient (1000 W/m2K) have shown similar values, though the scraping mechanism, the rotational speed, the size and their energy capacity are different. The developed design is an appropriate technology to increase the efficiency in solar LTES.

Numerical investigation of heat treatment of an olive paste within a scraped surface heat exchanger equipped with helix screw

Numerical investigation of heat treatment of an olive paste within a scraped surface heat exchanger equipped with helix screw

Influence of Freezing Parameters on the Formation of Internal Porous Structure and Its Impact on Freeze-Drying Kinetics

The main objective of this study was firstly to investigate the influence of freezing process parameters on the formation of the internal structure of frozen coffee granules. It was investigated how these frozen internal structures affect the drying kinetics during freeze-drying. A design of experiment study was carried out using the response surface method to quantify the influence of the freezing step that occurs in a scraped surface heat exchanger (SSHE). Therefore, the coffee extract at a concentration of 30% w/w is entering the SSHE as a liquid and gets partially crystallized up to a weight-based ice content of 0.364. During this step, the influence of factors like cooling temperature, scraper rotation speed and temperature cycles on ice crystal structure was investigated. In a second freezing step, the influence of freezing rates during hardening of the product by air-blast freezing is investigated, where the freezing rate is significantly affected by the cake thickness. The produced frozen granules were freeze-dried in single layer experiments. During drying the influence of internal structure on the drying kinetics was investigated. Results show that all factors have a significant impact on structure parameters for 30% w/w coffee solutions. A lower degree of supercooling during freezing in an SSHE, a higher number of temperature cycles (2 to 8 times) and lower freezing rates during hardening (2 °C/min to 10 °C/min) were leading to increased crystal size. This increase accelerates the primary drying rate and decreases the total drying time. A higher number of temperature cycles leads to a significant increase of crystal size and therefore larger pore size at the end of the primary drying. Furthermore, in combination with temperature cycles in the SSHE, it was found that high freezing rates during air blast freezing generally lead to a second nucleation step of ice crystals.

Integrated and intelligently controlled unit for suspension freeze concentration: design and experimental verification

Suspension freeze concentration (SFC) can avoid denaturation while concentrating thermal-sensitive aqueous solutions. However, the complex treatment process and high capital cost severely limit its application in large-scale production. In this paper, a compact and integrated unit is devised to overcome these shortcomings and improve the operability of SFC. The unit is in a vertical layout and supports multistage treatment to successively condense the solution. Several innovative designs are made for the key components, including the helical blades in the scraped surface heat exchanger and a dual-use column for recrystallization and washing. The former helps to establish the circulation of solution and impose forces to compress the ice column, while the latter enables seamless switch between different processes. As the whole process of SFC is well known to be time-consuming and labor-intensive, an intelligent controlling system is installed on the unit to realize on-site and/or remote monitoring and adjustment of the treatment. A concentration experiment using apple juice was conducted to verify the design and demonstrate the advantages. The results show that high-quality solutions were obtained with this unit. The recovery yields of the soluble solids and nutrients components are over 98.5% and 80.0%, respectively. Based on the work principles of the freezing and washing process in this design, the mechanism behind the superior recovery yields is analyzed. This study opens up a potential route for scaling up SFC and is expected to stimulate further work to achieve industrial application.

A review of the usage of highly viscous fluids in industrial applications

Highly viscous fluids (HVF) are used in food sector as raw materials (melted vegetable, animal fats) or finished products (chocolate, sorbets), in construction sector as liquid state of Phase Change Materials (PCM) used to store thermal energy inside building structure or building materials such as liquid concrete, bitumen and tar, in automotive industry as PCMs used to passively cool batteries, and many others. Some applications are rather new and lot of research has been done, in the last decade, to find mathematical models for predicting HVF behaviour, in heat and mass transfer processes in scraped surface heat exchangers, in vegetable fat melters and in waxy crude oil transport pipelines. Better results could be obtained by enhancing HVF thermal properties such as increasing the thermal conductivity of PCMs by adding metallic powders, or by finding new natural materials (vegetable fats) which can replace more expensive and harmful ones (waxes) for PCMs. This study was performed to shortly present the main applications in which HFVs are being used, the main advances and findings made in the last years and the current challenges and research possibilities which are likely to be explored in the future.