Enhancing the performance of paraffin's phase change material through a hybrid scheme utilizing sand core matrix (2024)

Characterization of composite

XRD

The XRD diffractogram of the core sand material, the paraffin PCM and the core sand/paraffin PCM are investigated and explored in Fig.2a,b and c, respectively. The crystalline phase of core sand substance is recognized and the XRD pattern displays numerous diffraction peaks. Hematite and quartz crystal structures are recognized in the material diffraction pattern.Figure2a shows strong broadening peaks from the small crystalline areas of such phases. Therefore, it might be deduced that the silica reinforced iron material comprises of a crystalline silica core augmented hematite shell possess barely precise small crystalline domain. The signified phases of silicon oxide, iron oxide, iron, iron aluminium oxide and iron silicate. Intense peaks of silicon oxide are assigned in the graph since the sand is mainly compromises of silica and that may be the source of those quartz particles. Also, the suspended materials in the iron-based waste are mainly the source of iron and iron oxides that appear as iron oxide, iron and aluminium oxide and iron silicate. Due to the calcination iron augmented with silica and formed iron silicate^38,39.

Also, the crystallization of paraffin wax is investigated through XRD and the data displayed in Fig.2b. It is clear from the data exhibited in such Figure that paraffin wax has two sharp diffraction peaks at 2θ values of 21.6° and 24.0° that are attributed to the typical diffractions crystal planes of [110] and [200] that signified paraffin wax, respectively⁴¹. Furthermore, Fig.2c is representing the core sand/paraffin PCM composite. The sharp peaks indicate that the composite has a crystalline structure. The XRD pattern of the core sand/paraffin PCM composite shows the same peaks as that of paraffin wax. Also, the other peaks can be observed are for the core sand phase presented in the pristine material. Such results confirm the presence of the iron core sand material with the paraffin wax PCM.

SEM and EDX

Figure3a,b,c and d illustrates the SEM micrographs images at different magnification of the prepared core sand composite substance to explore its morphology. The SEM micrograph illustrates that mixed shape of the sand particles that is augmented semi-spherical dispersed particles of the iron material on the surface of the core sand.

Additionally, elemental analysis of the organized core sand composite substance is exposed through the Energy Dispersive X-Ray Analysis(EDX). The data displayed in Fig.3e and f exposed the composite sample compromises of the dominant elements of O, Si, Al and Fe which conforms their presence in the improvement the PCM system.

Thermal analysis of flat plate collector and the PCM system

As previous studies^13,16,40 projected, the city that the study is carried out on is in the North of Egypt, Shebin El-Kowm city, Menoufia governorate, is well gifted with high intensity of renewable solar radiation, thereby such place is signified this geographical collection as a superior candidate for gaining a high implementations of solar-energy systems. The location of the study in the north of Egypt is categorized as one of the predominant and plentiful of solar energy towns in the country of Egypt throughout all the seasons especially in the summer periods. The daylight time is ranged from nine to eleven hours per day at the place of the study. The place is located on the latitude of 30.5¹⁶. Experimental data from the recorded solar energy intensity of the sun radiation in the city of the study of experiment through the hot months of the season of summer is displayed (Fig.4) and the recorded highest solar radiation is around the solar noon and recorded 1162w/m². Furthermore, the monitored ambient temperature, T_a, is explored and recorded an average value of 35°C.

The air, PCM, water temperatures are measured using digital processing thermocouples thermometers at six locations. Two measuring points are arranged for the inlet and outlet solar collector as well as the air temperature under the glass cover of the collector that is recorded with extra thermocouple. Ambient air temperature surrounding the collector is taken to represent the air temperature at the place of the study. In addition, one thermocouple thermometer was mounted inside the heat exchanger to monitor the PCM temperature through time intervals. The recording interval is one minute. Hot water collected after the discharging cycle is also observed and its temperature is recorded. Furthermore, the solar meter that records the solar radiation intensity is mounted above the ground in the east-south direction at the open area of the location where the solar collector is mounted using Eppley Black-and-White Pyranometer.

Heat charging/discharging of PCM system

In such part, the results achieved from the current work are examined for the concept of investigating and proposing a proficient TES design. The data investigated are explored in expressions of heat transfer improvement and advancement that attained from melting/solidification cycles. Analysis upgrading by applying the implementation indicator for different proportions of core sand supported PCM systems using various concentrations.

The temperature of charging, T_c, and the corresponding temperature of discharging, T_d, for the varied PCM systems are consistence for the melting and solidification cycles are demonstrated and exhibited in Fig. 5a and b, respectively at distinctive time profiles. Different mass segments of core sand/PCM systems are attained by adding various proportions of core sand materials, 0.5, 1.0, 1.5 and 2.0% and labeled as 0.5%-sand core-PCM, 1.0%-sand core-PCM, 1.5%-sand core-PCM and 2.0%-sand core-PCM are embedded for the base organic paraffin wax material to assess the optimal mass addition (%) to the pristine PCM.

Notably, as displayed in Fig.5a, the fraction of sand core embedded into the PCM system explores a diverse range of melting temperatures profile. A thermal enhancement is detected via the supplement of core sand into the wax up to 1.5%. But, extra addition of core sand into the PCM-system retards the temperature elevation. The T_c of the system extended to 71°C in comparison to 54°C for the pristine wax. Exceptionally, according to the previous work cited by various researchers in literature^24,33,41, the addition of materials into the pristine was PCM supports in a persuade alteration in the profile of the heat flow compared to the pure PCM based wax material. Hence, such change might adapt the significance of the melting temperature of the PCM-phase change wax substance than compromised with core sand. Furthermore, it is projected that the compromised core sand in wax substance improves its latent heat. Moreover, it might be stated that the presence of hematite/silica materials in the phase change substances controls its photodegradation due to it concessions of various components as achieved from EDX examination (Fig.3e and f), that suggests the representative signals of iron, silica and aluminum materials that are indicated with their photoactivity^27,42.

The results of the discharging cycle of the different kinds of pure wax PCM as well as wax augmented with varies quantities of core sand is displayed in Fig.5b. It is notably from such curves displayed in the figure that elevating the PCM melting temperature, subsequently increases the solidification temperature of its corresponding PCM by 19°C. However, it is noteworthy to mention that PCM wax embedded with core sand material in comparison to the pristine wax possesses a higher solidification temperature. Also, the temperature variation is dependable on the varied amount of the embedded core sand.

Additionally, according to the results distinguished in Fig.5b and a remarkable comparative improvement with the core sand amount addition is linked to the increase in the composite-PCM solidification time. Consequently, the heat attained and acquired through the solidification cycle is additionally elevated. The various system enhancements are achieved through the discharging temperatures of corresponding to the 1.5% mass proportions. This might be associated with the existence of the core sand discrete in the host paraffin organic PCM wax that delivering more inorganic sites that enhances the possibility of absorbing heat that is leading to intensification of the latent heat of fusion of the paraffin wax implanted substance.

But, it is significant that extra upsurge in the added material mass portion leading to a decline in the solidification temperature that makes the procedure undesirable. Previous investigators are previously mentioned such results in their PCM system^14,22,31,42. This can be demonstrated by the extra supplement of the enhancement materials can decrease the constancy of the PCM rather refining it. In this case the consequence is agglomeration/sedimentation, which might further deduce the PCM effectiveness. Consequently, selecting the optimal enhancers value is vital for charging/discharging system performance to reach to the optimum global system routine. Notably, it is estimated according to the data in Fig.4b that the discharging time is increased for the 1.5% core sand addition compared to the other proportions and the pristine PCM. Hence, this takes longer time to complete the discharging cycle.

Transient temperature profiles of core sand PCM existing an extra-designated to represent the melting process. Heat transfer is lasted during conduction from the beginning of the heating cycle till the wax temperature ranges the melting temperature. Thereby, the preliminary melting of core-sand Wax-PCM is fashioned via a complex combination of conduction and convection heat transfer together. But, with the processing of the melting system, the temperature elevation is relatively augmented. This might be investigated and explored by the enhancement in natural convection of the melted wax substance. Previous work is reported previously by other workers^21,43.

The above-mentioned experimental data suggest that the heat storage density is associated with the quantity of the proportions of core sand embedded into the system and the perfect amount portion is recorded at 1.5wt%. Previous work is previously published in literature⁴⁴.

Heat storage capacity

To attain the thermal consistency of the core sand PCM-Wax system, after discharging cycle, both the amount of heat (Q_g) and the temperature gained (T_g) are monitored. According to the solar heating fluid, water, heating is being in increment. The optimal import to the phase change wax substance is comparably important concerning the quantity of heat multiplied. The data exhibited in Fig.6a and b reveals that the augmented core sand wax-PCM might attain an elevated temperature range gained from the PCM that might be stored. The existence of core sand with paraffin wax in an optimized value addition fraction ratio (1.5%) might increase the heat storing temperature. Thereby, the heat stored in comparison to the pure wax is increased. According to the data displayed in Fig.6b advancement in the heat achieved from the storing process in the preliminary time interval, which is extended only to 2.2kJ/min for the pristine paraffin wax configuration.

It is noteworthy to mention that such heat amount is increased to reach 7.4kJ/min for augmented core-sand PCM system storing heat system. This might be illustrated by the role of hematite and silica, which are mainly compromising the core sand substance, the improving the thermal transfer tendency that is the key reliable of a remarkable prospective in enriching the global energy storage efficacy³⁶.

According to data exhibited in Fig.6b, base pristine wax-PCM scheme achieves minimal heat rate expanded examined through the attained collected hot working fluid “water” that is in comparison to the embedded core sand into the composite PCM system, which is elevated and increased, with the quantity of inserted substance added till the portion of 1.5% mass fraction. Such investigated might be illustrated by the superior thermal conductivity of the managed hybridized scheme⁴².

Overall PCM process efficiency

Generally, all the investigated PCM-systems in the present current study, the whole overall heat attained from the systems are calculated and the investigated data are clearly displayed in Fig.7a. The heat rate gained by the PCM is the heat assigned by the working fluid “water” as the heat transfer carrier substance and is investigated through the following Eq.(1).

where \(\dot{\dot{w}}\): mass flow rate of heat transfer fluid (g/s); T: Temperature range between inlet and outlet water entering and leaving the collector ad C_w: Specific heat capacity of the heat transfer fluid (4.18kJ/kg K).

As the results displayed in Fig.7a, the solo paraffin wax PCM system and that inserted system with the core sand filler elucidates the embedded system improves the global heat rate gained from the PCM configuration. The experimental data revealed that the useful rate of heat attained is greater for combination core sand paraffin wax substance (7kJ/min), which exhibited a noticeable outcome than the heat attained by the pristine paraffin wax (48kJ/min). Such comparative investigation revealed the noteworthy extra significant pronounced heat rate attained as a result of the enhancement in the heat transfer. This might be attributed by the higher thermal conductivity of the embedded filler in the hybridized PCM mixture, and the rate of heat attained is significant than the solo PCM wax. Moreover, it is important to mention that the heat rate gained could be rises equitably by the upsurge in the core sand weight fraction. Also, throughout the discharging cycle, the overall temperature difference and the quantities of hot water stored are greater. Consequently, the useful heat recorded from the system of the core sand paraffin wax process is higher. Aforementioned examiners in the literature described similar data^9,13,36.

Similarly, the global solar energy thermal storing efficacy of such energy storing PCM embedded with the core sand filler system added at different weight mass fractions is investigated and competed as displayed in Fig.7b. Concerning the amount of the heat gained via the stored water as the heat transfer carrier is calculated from Eq.(1) and the heat gained from the core sand substance that is attained from the relation described in Eq.(2). Thereby, the overall PCM efficacy, \(\text{Y}\), can be calculated. Process efficacy is recorded from the calculations according to Eq.(3) that describes the useful energy achieved from the heat transfer fluid to that gained from the PCM⁴⁵.

where, \({m}_{\text{PCM}}\) is the mass of phase change material (Kg), \({C}_{\text{PCM}}\) is the specific heat capacity of PCM (kJ/kg.K), \({\theta }_{PCM}\) is consequent to the T_PCM, temperature alteration of inlet and outlet temperatures of the heat exchanger involving core sand/Wax phase change material and L_f is the latent heat of fusion of PCM (kJ/kg)^46,47.

It is noticeable from Fig.7b that the achieved efficacy is enhanced according to the mass fraction of the core sand supplemented to the pure paraffin’s wax-PCM. The highest overall efficacy, 92%, is corresponding to core sand/Wax compromised of 1.5% weight fraction added. Consequently, such data confirms the greatest storing capacity that is equivalent to the added 1.5% core sand of weight proportion embedded into the paraffin organic PCM wax^48,49,50.

Comparative investigation

Numerous paraffin wax-PCM systems enhanced through various system fillers described by different researchers reported in the cited work that are previously published are compared with the current study. The type of system improvement achieved is described in Table 2. Moreover, the maximum temperatures’ recorded for charging PCM are presented in Table 2 to arrange the progress attained from the current investigation. According to the results exhibited, a significant improvement is attained through the core sand supplement enhancers. The temperatures form the current studied PCM-system accordingly is signified as the greatest values. By applying such metals capsulations as the supplement substance exhibited excellent thermal performance in comparison to the pristine paraffin thermal performance. Although, it is noteworthy to notate that a higher achievement is gained from other reported systems than the current core sand systems; the current study is based on waste by-product substances and naturally abundant materials. Thus, such material is signified as an economic pathway advances.