International Journal of Engineering Advanced Research eISSN: 2710-7167 | Vol. 4 No. 3 [September 2022]
Journal website: http://myjms.mohe.gov.my/index.php/ijear
BEST REFRIGERANT FOR ICE CREAM MAKING PROCESS
Nazahiah S1*, Noorilyana A. B.2 and Zuhaila M3
1 2 3 Jabatan Kejuruteraan Mekanikal, Politeknik Ibrahim Sultan, Johor Bahru, MALAYSIA
*Corresponding author: nazahiahsalleh@gmail.com
Article Information:
Article history:
Received date : 8 August 2022 Revised date : 25 August 2022 Accepted date : 5 September 2022 Published date : 25 September 2022
To cite this document:
Nazahiah, S., Noorilyana, A. B., &
Zuhaila, M. (2022). BEST REFRIGERANT FOR ICE CREAM MAKING PROCESS. International Journal of Engineering Advanced Research, 4(3), 90-102.
Abstract: Refrigerant is a medium or working substance in a cooling and refrigeration system. The refrigerant run through all the inner parts of the refrigerator. The use of the right refrigerant in the system is important because it can help to shorten the time of ice cream process and the can increase the production as well. The system optimization will help to ensure the system is working in an optimal condition where there is no energy loss happened. At the same time, the total power usage can be reduced because the system operates in its normal condition and no need of extra loads or works to support the system requirement. The objectives of this project are to identify which of two refrigerants (R134a and R404a) is better in term of cooling rate for ice cream making process using the test rig. The test rig was built using standard refrigeration system components. Three experiments have been carried out to record the time taken for each refrigerant to reach the ice cream freezing temperature and temperature reading for every 10 minutes interval in one hour. The data are then have been analysed using Minitab software to find out the better refrigerant and proving the theoretical assumptions.
Keywords: Refrigerant, Refrigeration system, System Optimization, Cooling Rate.
1. Introduction
It is widely acknowledged that demand for energy is constantly increasing and industries are finding it increasingly difficult to stay competitive because companies in every market are looking for new ways to maximize efficiency while lowering energy costs and improving their environmental image (Adrian et al., 2021). Internal combustion engine, steam engine, steam turbine, boiler and refrigerator are the equipment that directly depends on thermal efficiency. In the case of refrigeration, thermal efficiency is the ratio of net heat output for heating or removal for cooling, to the energy input (known as coefficient of performance).
Thermal efficiency is a dimensionless performance measure of a device of system that uses thermal energy to operate (MAN, 2017). Thermal efficiency concept has been used widely in many ways.
As for this study, the focus is in the ice cream making process using ice cream rolling maker. It is a unit of ice cream maker which used a common components and basic cooling system to produce ice cream. In this study, the effects of different refrigerants on the ice cream making process will be studied. The focus is how different type of refrigerants affect the rate of freezing time for the ice cream.
Currently, most of the refrigeration systems using lower Global Warming Potential (GWP) refrigerants may not perform optimally with various loads because of the different thermodynamic properties of the refrigerants which would affect the optimum operation of the heat pumps. In order to select what refrigerant to use, it is important that their performance range is characterized and aligned with the demands of the refrigeration system so as to achieve energy efficiency for overall operation.
2. Literature Review
In Malaysia, ice cream can be categorized as a popular dessert for all ages especially children. We can buy ice cream easily at any time. It also become a source of additional income to small traders which sells their handmade ice cream during ceremony or occasions. Some of them, sells their ice cream in the booth at several places such as pasar malam.
The meaning of the term “ice cream” varies from country, due to different regulations and traditions and, thus, covers a wide range of ingredients and composition, as well as product texture and manufacturing processes (Giudici et. al.., 2021). Maryam and Mostafa (2011) defined ice cream as a complex food consists of small air cells dispersed in a partially frozen, continuous aqueous phase. Its desired quality is achieved by both proper processing and formulation. Perera (2021) stated that the main ingredients of ice cream are milk, cream, sweeteners, natural flavorings, and other optional ingredients such as eggs, nuts, fruits, chocolate and candy. Both the flavorings and the sweeteners are imparting sweet sensation to the ice cream.
Ice cream starting to freeze when the mixture of ice cream reaches its freezing point. Freezing is a phase transition in which liquid turns into a solid when its temperature is lowered below its freezing point. Khaliduzzaman et al. (2012) proved that the freezing point for different mixture ice creams is between -20C to -40C while Murtaza et al. (2004) stated the ice cream was frozen at temperature of -10C to -90C along with the whipping of air into the mix by agitation in hand operated ice cream
freezer or machine. The freezing points might be different because of the content of the mixture, but generally below than 00C. Trgo et al., (1999) has derive information on the technological influences on the ice crystallization in ice cream during the sensitive temperature range from the freezing point to -80C.
According to Rossi (2020), refrigeration systems aim to transfer thermal energy from a low- temperature source to a high-temperature sink while utilizing the least amount of work for a given capacity and source and sink temperatures. It has many applications including but limited to household refrigerators, industrial freezers, cryogenics, air conditioning and heat pumps. In order to satisfy the Second Law of thermodynamics, some form of work must be performed to accomplish this (Dhankar, 2012). The work is traditionally done by mechanical work.
Refrigeration is actually applied the concept of energy conversion. According to Jung (2000), heat pump are highly attractive energy conversion devices, since they offer an efficient means to reduce primary energy consumption by utilizing heat recovery. Heat pumps are widely used for refrigeration, air-conditioning, space heating, hot water production, heat upgrading or waste water recovery (Arpagaus et al., 2016). It used Carnot cycle concept in its operation.
Sands D. (2021) defined that the remarkable feature of the dynamic Carnot cycle just described is its simplicity. In refrigeration system, the Carnot cycle considered is reversed Carnot cycle.
Knowing that a heat engine working on Carnot engine has the highest efficiency, a refrigeration system is working on the reversed cycle and has the maximum coefficient of performance.
Thakar et al. (2017) defined that the working substance used to make refrigeration is called the refrigerant while Mark and Marcia (2020) defined that refrigerants are the vital working fluids at the heart of the vapor-compression cycle, moving heat from a lower to higher temperature. The refrigerant run through all the inner parts of the refrigerator. It is the refrigeration that carries out the cooling effect in the evaporator. It absorbs the heat from the body to be cooled in the evaporator and throws it to the atmosphere via condenser. The refrigerant keeps on recalculating through all the inner parts of the refrigerator in cycle.
Refrigerant R134a
R134a is a refrigerant that has some good content, non-toxic, non-flammable, relatively stable and environment friendly. Commonly used in the vehicle’s air conditioning system and commercial refrigerators.
Refrigerant R404a
This type of refrigerant has some good characteristics which are non-toxic, non-flammable and relatively stable. R404a is an environmentally friendly refrigerant and recently used in the cooling system due to its high cooling rate.
2.1 Problem Statement
The quantity of ice cream can be produced is limited since the ice cream making process needs times to ensure the ice cream is ready to be served. At peak time, the ice cream needs to be produced quickly to fulfil the demand of the customers. Meaning that the time taken to produce the ice cream must be accelerated.
The major issue for these ice cream makers is the time taken for ice cream to completely freezes and according to Trgo et al (1999), the freezing point of ice cream is -8oC. Sometimes, the customer needs to wait to have and ice cream but not all customers willing to waste their time just for a cone of ice cream. So, there is a lost of sales happened. By improving the process of making ice cream, the benefits are:
• Shorten the time of making ice cream
• Improve the number of cycles of making ice cream
• Increase the productivity
This study will focus on how different type of refrigerants will affected the ice cream hardening process.
3. Method
This project involves several stages starting from the stage of collecting relevant information, designing the machine, conducting experiments, data collection and up to data analysis. All these stages can be illustrated with the diagram below:
Figure 1: Process Flow Chart
3.1 The Ice Cream Making Machine
In designing the project, several criteria such as size, design, material and components selection must be defined properly. This is important to produce an ice cream making machine that optimized the ice cream hardening process since it was used as the main resource to collect the data needed for the analysis. The idea was developed and illustrated using AutoCAD software.
Figure 2: Design in 3D View (Basic Dimension)
System test is important to make sure the system can operate properly and effectively. The standard procedure such as flushing process, leak test, vacuum and charging must be conducted before the system test run. The objective of conducting test run is to make sure the system can reach the desired temperature (freezing point temperature). If the system fails to achieve the desired temperature, some modification must be made until the system operates as required.
3.2 Experiment
The flow in collecting data from the experiment is illustrated in Figure 3.7. In this stage, the experiment was conducted in two conditions using different type of refrigerant. The procedures for both two conditions are similar where the time and temperature are the output responses to be recorded.
Figure 3: Data Collection Process
The first experiment used R134a as a refrigerant for the ice cream making process. The data collected is the time taken for the ice cream reach its freezing temperature which is set at -80C as mentioned in Chapter 2 by Murtaza et al. (2004). The other data that was recorded is the temperature reading for every 10 minutes. Then, the experiment is repeated using R404a as a refrigerant.
3.3 Data Analysis
Two sample t-test in Minitab is one of the most commonly used hypothesis tests to study whether there is a statistically significant difference between the means of two set of data. The t-test tells how significant the different are or in other words it lets the users know if those differences could have happened by chance.
Null Hypothesis (H0) : µ1 = µ2 Alternative Hypothesis (Ha) : µ1 ≠ µ2
Where: µ1 is the mean of one set of data and µ2 is the mean of the other set of our interest.
3.3.1 P–Approach
The P-value approach is used to determine the ‘likely’ or ‘unlikely’ by determining the probability.
It is used to assume the null hypothesis were true by observing more extreme test statistic in the direction of the alternative hypothesis than the one observed. In most of analysis, the value of alpha being use is 0.10 as the cut off for significance. If the P-value is less than 0.10, we reject the null hypothesis that is no difference between the means and conclude that a significant difference does exist. If the P-value is below 0.10, it is significant but if over 0.10, it is not significant.
4. Results and Discussion
In this study, two types of refrigerant been used as a cooling medium in ice cream making process.
By using the ice cream rolling machine, the ability or cooling rate of these two refrigerants have been compared using Minitab software. Each experiment was performed separately using R134a refrigerant and R404a refrigerant. The aim of the experiment is to record the temperature at every 10 minutes intervals and time taken for the system to reach the ice cream freezing temperature which is taken as -8oC.
Table 1: Data Taken from Experiments Time
(minutes)
Pan Plate Temperature
Experiment 1 Experiment 2 Experiment 2
R134A R404A R134A R404A R134A R404A
10 8 10 8 9 8 9
20 1 -2 2 -1 2 -1
30 -5 -6 -6 -8 -6 -8
40 -12 -14 -14 -16 -14 -16
50 -14 -17 -18 -21 -18 -21
60 -18 -20 -21 -25 -21 -25
Table 2: Time Taken to Reach Freezing Temperature Time taken to reach -8 oC (minutes)
Experiment 1 Experiment 2 Experiment 2
R134A R404A R134A R404A R134A R404A
34 32 33 30 32 30
4.1 Data Analysis and Discussion
A two-sample t-test helps to determine whether these to population means are different. The test uses the sample standard deviations to estimate α for each population. If the different between the ample means is large relative to the estimated variability of the sample means, then the population means are unlikely to be the same.
In two-sample t-test, continuous data from two independent random sample will be used. Samples are independent if observations from one sample are not related to the observations from the other sample. The test also assumes that the data come from normally distributed populations.
A paired t-test helps determine whether the mean difference between paired observations is significant. A paired t-test can also be used to evaluate whether the mean difference is equal to a specific value. Basically, paired t-test is used to evaluate the following hypotheses:
• H0: The mean difference between paired observations in the population is zero.
• H1: The mean difference between paired observations in the population is not zero.
4.1.1 Discussion: Time Taken to Reach Freezing Point Temperature Using Two Sample T- Test
From Figure 4, the different between the sample means (2.33) is an estimate of the difference between the population means (µR134a - µR410). The confidence interval for difference is based on this estimate and the variability within the samples. The mean is between 0.258 and 4.409 higher in R134a than R404a. The t-value for the test is 2.65, which is associated with a p-value of 0.077. Thus, reject the null hypothesis at the α = 0.10 level and it can be concluded that there is a statistically significant difference between the mean of the populations.
Figure 4: Two Sample T-Test from Minitab
The significant difference between these two populations is shown in Individual Value Plot in Figure 5 and Boxplot in Figure 6. From the figures, it is clear that there was a significant value between these two refrigerants.
Figure 5: Individual Value Plot from Minitab
Figure 6: Boxplot from Minitab
Although the variability for the two refrigerants is almost similar, the confidence interval provides a reasonable estimate of what the mean difference might be. The difference of 2.33 are statistically significant and from the boxplots, it is clearly show that there was a significant difference between these two refrigerants. Refrigerant R404a provides higher cooling rate since it reached freezing point temperature faster compare to R134a refrigerant.
4.1.2 Discussion: Temperature Reading at Every 10 Minutes Using Paired T-Test
Figure 6: Paired T-test from Minitab
The mean number of temperatures is -6.67 for refrigerant R134a and -8.17 for refrigerant R404a for 10 minutes interval in an hour. The 90% confident interval is roughly -0.039 to 3.039 degree Celsius. The test gives a t-statistic of 1.96 with an associated p-value of 0.10. Thus, reject the null hypothesis at 0.10 α-level and conclude that refrigerant R404a cooling rate is better than R134a.
4.1.3 Time Series Plot
Figure 7 show the time series plots for all three experiments. From these figures, we can see refrigerant R404a showed better cooling rate where in all experiments, refrigerant R404a reach the freezing temperature faster than refrigerant R134a.
Figure 7: Test for Time Series from Minitab
The graph showed that the cooling rate at the early stage was higher and became slower when the temperature decreased. This situation complied with Newton’s Law of Cooling that states the rate of changes of the temperature of an object is proportional to the difference between its own temperature and the ambient temperature (Cengel, 2019).
The result shown in the time series plots indicate that the cooling rate of R404a refrigerant is better than R134a. From the plots, we can see that R404a refrigerant reach the ice cream freezing temperature (-8oC) faster than R134a refrigerant.
5. Conclusion
It can be concluded that the type of refrigerant has effect on cooling rate in ice cream making process. Different refrigerant with different properties will achieve the freezing point temperature at different time rate. As for in this project, the R134a refrigerant and R404a refrigerant have been used to collect the data and the data has been analysed using Minitab software. The two-sample t- test and paired t-test shows that there was a significant difference between these two refrigerants.
The cooling rate of the ice cream machine can be improved by the used of suitable refrigerant.
Although the variability for the two refrigerants is almost similar, the confidence interval provides a reasonable estimate of what the mean difference might be. The difference between these two types of refrigerant are statistically significant which is 2.33 and from the time series plots, it is clear R404a refrigerant provides higher cooling rate compare to R134a refrigerant.
With the used of the same test rig, by using R404a refrigerant, the time taken to produce ice cream can be reduced as from the experiment shows that the time taken to achieve freezing point temperature using R410 refrigerant is shorter than using R134a refrigerant in all three experiments.
The use of the right refrigerant is important because it can help to shorten the time of ice cream process and the can increase the production as well. As for the users, they can produce more ice cream in the particular period. The system optimization will help to ensure the system is working in an optimal condition where there is no energy loss happened. At the same time, the total power usage can be reduced because the system operates in its normal condition and no need of extra loads or works to support the system requirement. The findings also comply with the cooling rate stated by Danfoss (2006) which is shown in Table 3.
Table 3 : Refrigerant Description (Danfoss, 2006)
Refrigerant Description
R134a Having a normal boiling point of -26.1 °C. The thermodynamic properties that make it suitable as conditioning for simple temperature applications such as domestic cool create.
R404a
Boiling point at -46.7 °C, which is slightly lower than the R22 which is -40.8 °C. Thermodynamic properties make it suitable as a coolant for low and medium temperature applications in commercial refrigeration
Theoretically, based on characteristic and properties offers by these two types of refrigerant, R404a will give a better result because of its’ boiling point starts at -46.7 0C while R134a boiling point starts at -26.1 0C, by using R404 as a refrigerant, the ice cream freezing point can be achieved faster than R134a. With the analysis that has been made by using the data taken from the experiments, the results fulfilled the description stated by Danfoss (2006).
In overall, besides refrigerant R134a, refrigerant R404a is a better alternative which offer higher cooling rate. It is not limited to the commercial or bigger application such as for chiller in supermarket but also can be used for a small ice cream machine application.
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