Pre-Cooling Concrete System in Massive Concrete Production: Energy Analysis and Refrigerant Replacement

Several techniques for cooling mass concrete structures were developed in order to increase structural integrity and reduce the influence of cement hydration, which sometimes causes cracking in concrete structures, negatively affecting their durability. This research focuses on cooling system design, initial investment, and the influence of different refrigerants on cooling system performance aims in producing higher quality massive concrete. Cooling aggregates in massive concrete structures such as desert dams can be performed by employing cooled air from an air conditioning duct system or chilled water. The experimental study illustrates the relationship between the coefficient of performance COP, the evaporator temperature, cooling capacity, and refrigerant mass flow rate as a function of the evaporator temperature, cooling capacity, and refrigerant mass flow rate. The findings of the experiments were utilized to verify a numerical model developed utilizing engineering equation solver (EES) software. The performance of the vapor compression of the cooling systems was compared using alternative refrigerants, including R22, R32, and R410a at different operating conditions. This study revealed that R22 refrigerant has a higher coefficient of performance than R32 and R410A, while R32 has the highest cooling capacity among other refrigerants.


Introduction
Thermal control plans are required for mass concrete constructions such as desert dams or bridge members in order to regulate the flow of heat generated by exothermic hydration processes in the concrete. When water is added to cement, a chemical process called hydration occurs, resulting in high temperatures and stresses in the core of massive concrete members. It is generally known that concrete has limited tensile strength and thermal conductivity, resulting in large stresses as a consequence of the high-temperature differential between the layers of massive concrete, and structural fractures as a result of the surface's expansion and contraction at various rates [1]. Concrete cracking reduces the durability and serviceability of concrete [2,3]. Furthermore, if the temperature of the cement paste core rises beyond 57.2 • C, it loses strength, produces larger void pores, and therefore increases permeability [4]. Cooling the concrete components or utilizing additional materials that emit less heat can help to limit the substantial increase in temperature [5,6].
Precooling concrete components after they have been mixed results in a considerable increase in their durability and compressive strength [6]. Improving the quality of the concrete increases the structure's safety and lowers its maintenance costs. The main cause of reduced concrete durability and the source of structural weakness is inadequate massive concrete quality. Furthermore, inferior concrete quality combined with insufficient concrete energy efficiency than R410A under the conditions examined, but they have a minimal environmental effect due to their lower GWP. Ahmed et al. [33] studied in terms of exergy efficiency for R407A, R600A, R410A, and R134A. The results indicated that the hydrocarbon mixtures with R134A performed better than the other refrigerants. The compressor has the highest amount of exergy losses among the components of the vapor compression system. Fajar et al. [34] investigated the energy and exergy of a conventional refrigeration system by replacing the R410A with R290. The results showed that as compared to the system's full charge quantity R410A, the compressor's power consumption and refrigerating capacity dropped by 35.7 and 31.3%, respectively.
The utilization of chillers that operate with refrigerants that are particularly harmful to the environment is one of the primary difficulties generated by pre-cooling concrete in the Middle East. As a result, we attempted to alleviate the hydration problem that causes thermal cracking in mass concrete structures in this study by using a cooling system with low environmental effects and excellent performance through refrigerant substitution. There is a scarcity of knowledge on the design of cooling systems and which of these systems is the most efficient. The current study is the first of its kind to go into depth into the impact of concrete pre-cooling systems. The refrigerants R22 and R410a, which have a global warming potential of 1810 and 1725, have been widely employed in residential airconditioning systems. R32, which has a low global warming potential of 675, is considered as a substitute for R22 and R410a. The goal of this study is to examine the performance of a vapor compression system with several alternative refrigerants, such as R22, R32, and R410a, under various operating situations.
The laboratory examination of pre-cooling concrete utilizing the continuous aggregate cooling method and chilled water method will be detailed in the following sections. Following that, the influence of such approaches on the engineering qualities of the resulting concrete will be explored. The authors will also present the findings of their numerical analysis of alternate refrigerants in the pre-cooling process under various operating circumstances.

Description of the Pre-Cooling Concrete Mixture Systems
Two pre-cooling procedures for massive concrete desert dam projects were investigated in the Jordanian city of Ghores-Safi, near Karak. The air-cooling system is depicted in Figure 1a, which includes the main duct, four cooling coils, and a fan to circulate air. The 18,000 volumetric flow rate centrifugal fan circulates air via a filter and four fins-and-tube cooling coils, which progressively cool the air to around 0. To reach the aggregates hopper, this cooled air passes through ducts. The air is then cooled as it flows through drilling holes established within pipes inserted in the aggregate hopper's lower section illustrated in the upper left side of Figure 1a.
The typical layout of an aggregate cooling system consists of (i) main duct, elbows, connectors, and air duct damper to control the air mass flow rate installed in the main duct (ii) the refrigeration cycle illustrated in Figure 2, the cycle consists of four cooling coils to cool air inside the main duct connected with two compressors, a component for heat rejection (condenser), and four expansion valves to control the refrigerant flow inside the refrigeration system and change of higher pressure to lower pressure. (ii) The aggregate hopper to cool the aggregate (a). During the cooling process, tons of aggregates are maintained within the hopper. The cooled aggregates can then be transported to the concrete manufacturing plant through the outlet belt conveyor. Table 1 shows the major components of the system as well as the initial investment in US Dollars (USD).
Another way of pre-cooling concrete mixtures utilizing the chilled water system is shown in Figure 1b. The water chiller which utilizes 55 HP (40.45 kW) reciprocating hermetic compressors placed in two industrial refrigeration circuits to cool up to 65.1 nominal tons of refrigeration (228.95 kW), is the main component of the cooling system. A centrifugal pump circulates water from storage tanks storing water at a temperature of 20 • C to the chiller. Two types of K-thermocouples with a precision of ±1 are fitted at the water storage tank, and water flows out of the chiller. The cooled water was around 4 • C exited from the chiller in all cases. The concrete mixer received chilled water through 2-inch (50.8 mm) steel pipes. Water volumetric flow rates of up to 250 GPM (1.136 m 3 /min) are provided. Table 2 depicts the system components and their initial investment.
Another way of pre-cooling concrete mixtures utilizing the chilled water system is shown in Figure 1b. The water chiller which utilizes 55 HP (40.45 kW) reciprocating hermetic compressors placed in two industrial refrigeration circuits to cool up to 65.1 nominal tons of refrigeration (228.95 kW), is the main component of the cooling system. A centrifugal pump circulates water from storage tanks storing water at a temperature of 20 °C to the chiller. Two types of K-thermocouples with a precision of ±1 are fitted at the water storage tank, and water flows out of the chiller. The cooled water was around 4 °C exited from the chiller in all cases. The concrete mixer received chilled water through 2-inch (50.8 mm) steel pipes. Water volumetric flow rates of up to 250 GPM (1.136 m /min) are provided. Table 2 depicts the system components and their initial investment.

Experimental Work
The purpose of these tests is to acquire a better understanding of the continuous aggregate cooling system and, in particular, to validate the numerical model discussed later in Section 3. Figure 3 depicts the thermodynamic cycle of the vapor-compression refrigeration plant. It essentially comprises two semi-hermetic reciprocating compressors coupled in parallel to compress a 3.40 mass flow rate refrigerant. Chlorodifluoromethane fluid R22 was utilized as a refrigerant in the experimental device. The fluid's characteristics are depicted in Table 3. The condenser unit is used to reject heat with air, causing the gaseous refrigerant inside the condenser to condense into a liquid. The condenser is connected to a liquid receiver and cartridge filter, as well as four expansion valves for lowering the refrigerant pressure. Each expansion valve is connected to a cooling coil through fins and a tube evaporator. Four parallel cooling coils in gradation lower the temperature of the ducted air and operate as a heat collector, picking up heat from the ducted air and transferring it to the refrigerant within the tube in this system.  Table 4 lists the sensors used to monitor the refrigerant's temperature, mass flow rate, and pressure. T-type thermocouples, which generate an output voltage signal in the range of 1 to 5 Volts, are used to record refrigerant temperatures. To measure the temperature of aggregates, a Testo 830 infrared thermometer was acquired. Pressure gauges were used to record the refrigerant gauge pressure datum, and a volumetric Coriolis flowmeter was used to monitor the volumetric flow rates in the refrigeration loop. Two data acquisition    Table 4 lists the sensors used to monitor the refrigerant's temperature, mass flow rate, and pressure. T-type thermocouples, which generate an output voltage signal in the range of 1 to 5 Volts, are used to record refrigerant temperatures. To measure the temperature of aggregates, a Testo 830 infrared thermometer was acquired. Pressure gauges were used to record the refrigerant gauge pressure datum, and a volumetric Coriolis flowmeter was used to monitor the volumetric flow rates in the refrigeration loop. Two data acquisition modules, the National Instruments ±21.5, Current Analog Input, 16 Channels Module (NI 9208) are used to transform physical circumstances into digital form, which is then stored and analyzed. At the entrance and exit of each device during the refrigeration cycle, the pressure and temperature of the working fluid are detected and recorded. The gauge pressure is measured with a ±1% accuracy and can measure up to 500 psi (34.47 bar) using the fluid gauge pressure. The mass flow rate of R22 refrigerant was measured at the liquid receiver's output, which was located downstream of the condenser. A hot-wire anemometer with a diameter of 10 µm, brand Dantec 55P31, was used to monitor the speed of ducted airflow within the range of 0.05-500 m/s and its temperature.
Inside the condenser, the maximum mass flow rate of the refrigerant was set at 3.4 kg/s, and the temperature and gauge pressure at points 1 to 15 were recorded, as shown in Figure 2 and Table 5. The mass flow rate in the evaporator was fixed at 0.85 kg/s, which was a quarter of the mass flow rate in the condenser. The temperature and speed of the ducted air after and before the cooling coils were also recorded in parallel. The temperature of the aggregates was also monitored using an infrared thermometer model Testo 830 placed on the aggregates' upper surface. For aggregates with a diameter of 30 to 40 mm, the steady-state temperature was between 1 and 2 • C at a distance of 0.5 m from the hopper's top. The cooling fan's mass flow rate was maintained at 18,000 m 3 /h at all times. The same experimental setup was performed and repeated with different mass flow rates of 2.8, 3, and 3.172 kg/s using a gate valve.
The single cooling coil capacity Q L can be calculated by using the equation: .
From the ratio of the net cooling capacity ( . Q L,total ) and the drive power ( . W in ), the coefficient of performance COP can be calculated as,

Numerical and Experimental Analysis and Discussion
This section deals with a numerical analysis that intends to investigate the use of several alternative refrigerants under various operating conditions in the refrigeration cycle.

Physical and Chemical Properties of Refrigerates
There are many different types of refrigerants in the market. The working conditions, as well as favorable physical and chemical qualities, should be considered when selecting a suitable refrigerant for a refrigeration system to obtain the largest cooling capacity and coefficient of performance. There is no one refrigerant that has all of the desirable features and can be utilized in the refrigeration system under all working situations. We chose three types of refrigerants for our research: R22, R32, and R410a. Table 3 shows the most important physical and chemical parameters that determine vapor compression performance for three types of selected refrigerants. Appendix A offers a detailed comparison of several types of refrigerants based on their thermodynamic characteristics. The following observations may be drawn based on an extensive assessment of different types of refrigerants in terms of R22, R410A, and R32: (i) Among the various refrigerants, R22 offers significant advantages in terms of specific heat for the liquid phase, freezing point, and liquid phase density; (ii) R410A has superior properties such as conductivity, vapor phase density, compression temperature, oil miscibility, and liquid phase viscosity compared to other refrigerants; (iii) R32, on the other hand, has the best enthalpy of vaporization, specific heat for the vapor, and viscosity for the liquid and vapor phases compared to other refrigerants; (iv) All refrigerants meet the critical pressure, evaporator, and condenser pressure requirements; (v) R22 and R410A are non-flammable refrigerants, however R32 is a moderately flammable refrigerant; (vi) R22 and R32 are non-toxic, however R410A is a toxic compound.

Simulation and Validation of the Numerical Work
Engineering Equation Solver (EES) was used to model the performance of the conventional refrigeration cycle utilizing various refrigerant types and operating variables. The following assumptions were used to model the vapor compression system in order to simplify the analysis: (i) All components in a refrigeration system operate in a steady-state condition, so all processes are steady flow processes; (ii) all changes in potential kinetic energy in all components are ignored; (iii) pressure drops in the pipelines as condenser and evaporator are ignored; and finally, (iv) isenthalpic process in throttle valve and Isentropic process in the compressor. Figure 3 depicts the flow chart of a system modeling approach for a typical vapor compression refrigerator. Table 5 shows an example of the measured temperature and the gauge pressure at different points inside the refrigeration cycle illustrated in Figure 2. After the compressors at point 1 in Figure 2, the highest gage pressure was 2.14 MPa and the extreme temperature was 75 • C, as displayed in Figure 2. Before the compressor at point 15, the lowest pressure was 0.027 MPa. The pressure loss inside the condenser was about 1 kPa, while the pressure loss inside the cooling coils was between 0.2 and 0.8 kPa. As shown between points 3 and 7, the pressure drop inside the expansion valves was greatest through the first expansion valve. Between points 6 and 10, the fourth expansion valve had the lowest pressure drop. After the expansion valves, the lowest temperature in the refrigeration cycle was −35 • C.
To calculate the errors, we utilized the following formulae [35,36].
Standard error of the mean; where; the standard deviation x i n . The results of the EES model were validated using the experimental results at the same operating condition for conventional refrigeration systems. The experimental results for COP, cooling capacity, and mass flow rate as a function of evaporative temperature for R22 refrigerant are compared to the current experimental data in Figure 4. The predicted COP, cooling capacity, and mass flow rate all agreed well, with average relative errors of 6.3%, 4.56%, and 2.1%, respectively. For the predicted COP, cooling capacity, and mass flow rate, the standard error of the mean was 0.08, 2.44, and 0.008, respectively.   Table 6 shows the operating conditions employed in our analysis. At a constant condensing temperature, Figures 5 and 6 show the fluctuation of COP, cooling capacity, and mass flow rate through the refrigeration system with evaporation temperature for three   Table 6 shows the operating conditions employed in our analysis. At a constant condensing temperature, Figures 5 and 6 show the fluctuation of COP, cooling capacity, and mass flow rate through the refrigeration system with evaporation temperature for three types of refrigerants: R22, R32, and R410a. For all types of refrigerants, the COP, cooling capacity, and mass flow rate increase as the evaporator temperature rises because the compressor works less as the area under the pressure-volume curve shrinks. On average, the COP for R22 is 6.51% and 17.65% better in comparison to R32 and R410a, respectively. While, on average, the cooling capacity for R32 is 37.6% and 20% higher in comparison to R22 and R410a, respectively, because it has the highest enthalpy of vaporization as depicted in Table 3. To achieve the same evaporative temperate, the recirculation mass flow rate through a refrigeration cycle should be increased on average by 3.6% and 43.5% for R32 and R410a compared to R22. Table 6. Operating Conditions were employed in this study.

Parameter
Nominal Value Parametric Range       Table 7 shows a brief comparison of our present research with others [30,31,[37][38][39][40]. Despite the fact that comparing our results with others is challenging due to differences in parameters variation such as ambient temperature, mass flow rates, operating state parameters, and instrument accuracy.   Table 7 shows a brief comparison of our present research with others [30,31,3 Despite the fact that comparing our results with others is challenging due to differ in parameters variation such as ambient temperature, mass flow rates, operating sta rameters, and instrument accuracy. Figure 7 indicates the effects of condenser temperature on both COP and coolin pacity for several refrigerant types. The COP and cooling capacity of the vapor com sion refrigeration system both decrease as the condenser temperature rises, as sho this figure. This occurs because as the condenser temperature rises, the quality/dr fraction of the refrigerant at the exit from the throttle rises, lowering the COP and co capacity. In comparison to R32 and R410a, the COP of R22 is % and 18.3% higher, re tively. While R32 has a cooling capacity that is 37.4% larger and 20.5% higher tha and R410a, respectively.    Figure 7 indicates the effects of condenser temperature on both COP and cooling capacity for several refrigerant types. The COP and cooling capacity of the vapor compression refrigeration system both decrease as the condenser temperature rises, as shown in this figure. This occurs because as the condenser temperature rises, the quality/dryness fraction of the refrigerant at the exit from the throttle rises, lowering the COP and cooling capacity. In comparison to R32 and R410a, the COP of R22 is % and 18.3% higher, respectively. While R32 has a cooling capacity that is 37.4% larger and 20.5% higher than R22 and R410a, respectively.

Conclusions
In this paper, a detailed methodology for the design of cooling systems oriented to produce high-quality massive concrete and lower the cement hydration heat has been presented. The aim of cooling is to increase the durability of massive concrete by reducing the impact of the heat of the hydration. The researchers expect significant progress in applying the findings of this study into the design and construction methods of local mass concrete projects, such as desert dams. In this methodology, different kinds of systems such as duct air cooling systems or chilled water are discussed in order to achieve accurate designs enough to cool tons of concrete before mixing. The novelty of this research is that the study not only discussed the design and the initial cost of the cooling systems, but also the impact of particularly harmful to the environment refrigerant replacement with less harmful refrigerants on the coefficient of performance. Two simple designs of cooling systems have been introduced to cope with the problems of cooling concrete components.
First, A simple effective design of the cooling system was introduced for cooling continuous aggregate using four cooling coils, a fan-duct system, and a heat exchanger inside the aggregate hopper. This method depends upon the speed and temperature of the airflow through the coarse aggregate, the size, the amount and the type of the aggregate, ambient temperatures, relative humidity, and the time of cooling and design of the hopper. Sub-zero air is used to reduce the aggregate temperature. However, the cooling system is designed to be flexible in order to decrease the final temperature of the aggregate based on the design of the concrete mix, the amount of concrete, and the ambient temperature. The air temperature can be controlled by selecting the number of active cooling coils, valves, and air dampers to control the flow rate of air. The paper discussed in detail the initial cost of the air conditioning system, ducts, fan, and hopper.
Use of chiller to produce cold water around 4 • C. Many water storage tanks are required for the production of large volumes of concrete. The method is suitable when fast and large temperature reductions are needed. The installation cost using a mechanical refrigeration chiller is high, but it has a relatively low operational cost. The initial cost for the chilled water-cooling system is reduced by 10% compared with the air conditioning system case.
The issue of harmful refrigerant replacement in the industry with minimal global warming potential is necessary and Mandatory in many countries. Discuss the impact of refrigerant replacement on the performance of the cooling system has discussed in this research in the industrial application used for pre-cooling concrete. The experimental work with a continuous aggregate cooling system utilized refrigerant R22. The results show a good agreement between the experimental and numerical results. New HFC fluids R32, R410a were used in the simulation as an alternative refrigerant with a lower environmental impact. It concluded that the performance of a vapor compression refrigerating unit operating with R22, and its performance compared with new refrigerants R32. The results show that still, refrigerant R22 has more COP than new HFC fluids due to the thermophysical properties of the refrigerant.
Finally, it could be stated that applying the proposed methodologies, an efficient cooling system has been designed. To lower the impact of the cement hydration heat that may reduce the safety and durability of the structure. The researchers recommend a future investigation of moist aggregate cooling approaches and their impact on the properties of concrete mixes under different environmental conditions. The influence of wet aggregate absorption on evaporative cooling and concrete quality, in particular, has to be thoroughly investigated.   To achieve a high heat transfer at a constant temperature to reduce power consumption by the refrigeration system Critical Pressure It should be positive and moderate All refrigerants achieve the criteria In case of high pressure, the refrigeration system will be a heavy and bulky. In case of low pressure, the increase possibility of air leakage into the system.

Enthalpy of Vaporization
It should be large as possible 3 1 2 To reduce the mass flow rate per ton of refrigeration.
To reduce the area under the curve for superheat and the area reduction due to the throttling process.

Conductivity
It should be high as possible 3 2 1 To control of a size of the condenser and evaporator without any difficulties Specific Heat for the liquid It should be small as possible 1 3 2 To minimize the irreversibilities corresponding to throttle process, which leads to increase the liquid subcool.
Specific Heat for the vapor It should be high as possible 3 1 2 To be less superheating of the vapor.

Evaporator and Condenser Pressure
It should be above atmospheric pressure All refrigerants achieve the criteria To prevent the air leakage into refrigeration system which reduce the refrigeration system capacity and the moisture air leads to corrosive tubing of the refrigeration system.