This study presents the methodology to eliminate oil residual in copper pipe due to rolling process for manufacturing coil used in air conditioner. The pressure caused by Nitrogen flow rate was applied starting from 0, 5, 10, and 15 bar, respectively which was depending on time delay and pipe length. The developed system was divided into 2 modules: Parallel pressure ladder module (PPLM) [1] and Serial pressure ladder module (SPLM) which were experimented with 2 sizes of copper pipe: diameter 7.29 mm, thickness 0.25 mm, and length 10 km, and diameter 8 mm, thickness 0.25 mm, and length 10 km. From experiment, it can be noted that PPLM would perform better in elimination of oil residual compared to SPLM. About 97.44% (0.04 mg/m) and 97.59% (0.05 mg/m) of oil residual can be respectively eliminated from diameter 7.29 mm pipe and diameter 8 mm pipe which exceeded the standard allowance of 30% or 0.1 mg/m. Moreover, the cost of Nitrogen can be reduced by 6.25% per month.
In copper pipe manufacturing process, oil residual would significantly remain in the pipe that may lead to the further applications of copper pipe such as difficulty in welding pipe, corrosion and leakage [
This study used Nitrogen in different pressure levels to purge out oil residual from copper pipe. It is also necessary to maintain the pressure by considering flow rate of Nitrogen simultaneously based on the size and the length of copper pipe after ironing process as shown in
where x is the length of Nitrogen flowing in horizontal direction (m);
d is the diameter of pipe (m);
t is the flowing time of Nitrogen (s).
The length of vertical drop due to Nitrogen flowing through the pipe can be calculated by Equation (2) where 9.81 is the earth’s gravity (g) [
Design of oil residual purging system after ironing process should consider the appropriate quantity of Nitrogen supplied as well as the size of copper pipe in order to obtain the optimum capacity and to estimate the cost of Nitrogen to be used in each month. These can be calculated by analyzing flow rate of Nitrogen supplied as shown in Equations (3) and (4), respectively.
where Q is the flow rate of Nitrogen (l/min).
A is the cross section area of copper pipe (m2).
The velocity of Nitrogen through pipe f 7.29 mm and pipe f 8 mm can be calculated by using Equation (3) where x = 1.5 m, y = 1.5 m. Therefore, the velocity of Nitrogen through pipe f 7.29 mm = 0.2436 m/s, which through pipe f 8 mm = 0.2496 m/s, and the average velocity of Nitrogen (vavg) through both pipes is 0.2466 m/s. From Equation (4), flow rates of Nitrogen through pipe f 7.29 mm and pipe f 8 mm are 0.0461 l/min.
Design of oil residual purging system was applied the ladder technique which was dependent on the flow rate of Nitrogen. This study was separated into two systems: the parallel pressure ladder module (PPLM) and the serial pressure ladder module (SPLM) which was performed by using the same methodology. The experiment was used two sizes of copper pipe f 7.29 mm and f 8 mm, thickness of 0.25 mm and length of 10 km. The system developed was divided the pressure levels into 3 ranges regarding to the flow rate of Nitrogen and the appropriate delay time which was a function of copper pipe length. The initial range of the Nitrogen was maintained at the specific pressure (5 bar), supplied to copper pipe, and then delayed for 5 minutes for the pipe length of 0 to 500 m. The second range was 10 bar Nitrogen which was fed through copper pipe and delayed for 10 minutes for the pipe length of 500 m to 1000 m. The third range was 15 bar of Nitrogen supplied through the copper pipe length of 1000 m to 10,000 m and then delayed for 90 minutes. All processes would be taken about 105 minutes for 1 copper roll (10 km of pipe length). The previous studies on flow rate and Nitrogen pressure control have been proposed by using several methodologies such as a control procedure for eliminating the mal flow rate distribution of evaporating flow in parallel pipes, monitoring and control of gas flow rate in a Pyrocarbon coating furnace for heart valves, a novel method of using a control valve for measurement and control of flow and cavitation flow instability of subcooled liquid Nitrogen in converging diverging nozzles [4-7].
Parallel ladder system aims to regulate the Nitrogen flow rate by using parallel pressure supplying method for purging oil residual inside the pipe after manufacturing processes. This system consists of a control module which is a PLC controller to switch 3 sets of control valves on and off at low pressure (5 bar), normal pressure (10 bar), and high pressure (15 bar) as shown in
From
The procedure is started by releasing Nitrogen though the system via a 3/4 inch solenoid valve at the specific pressure (40 bar), and using valve V4, V5 and V6 to regulate pressure levels supplied to copper roll. Valve V4, valve V5, and valve V6 were for controlling pressure level of 5 bar, 10 bar, and 15 bar, respectively. After finishing the last procedure, oil residual inside the pipe was measured and recorded by using database program via data logger.
The Serial pressure ladder module (SPLM) system was used in order to regulate the Nitrogen flow rate by using
serial pressure supplying method to purge oil residual inside the pipe after manufacturing processes. The experiment of SPLM was performed similarly to PPLM. In case of SPLM, the system aims to regulate the Nitrogen flow rate by using serial pressure supplying method to purge oil residual inside the pipe after manufacturing processes. Only one set of regulator valve (VR1) and solenoid valve (SO1) were used for adjusting pressure levels into the system. The initial length (from 0 to 500 m) was supplied the pressure of 5 bar Nitrogen, fed through copper pipe, and then delayed for 5 minutes. After that, the 10 bar Nitrogen was then fed through copper pipe with the length of 500 m to 1000 m and delayed for 10 minutes. The final range was for the pipe with the length of 1000 m to 10,000 m. Nitrogen with the pressure of 15 bar was supplied through copper pipe and then delayed for 90 minutes (as shown in
Experimental results from both systems developed were converted from pressure value to voltage (P to V) by using the pressure transmitter [
Reliability and efficiency of the system can be analyzed from experiments and data of oil residual inside the pipe. Comparison and analysis of collected data were conducted by using oil content analyzer (HORIBA model OCMA-20) for the range of 5 to 20 PPM. Experiments were performed 20 times for each size of copper pipe with the length of 1 m as shown in Equation (5).
Therefore, A can be calculated by Equation (6).
where Eavg is mean value of experiments.
do is the outer diameter of pipe (mm).
Experiment using PPLM system for purging oil residual inside the copper pipe was performed with f 7.29 mm pipe. To evaluate the precision of the system developed, repeatability analysis was also carried out by repeatedly
experimented with 20 rolls of copper pipe at the pressure levels of 5 bar, 10 bar, and 15 bar. Each roll of copper pipe would contain oil residual about 1.58 mg/m in average after ironing process. From experiment, the amount of oil residual inside copper pipe after using the PPLM system was reduced to 0.04 mg/m or 2.56% on average.
Therefore, the PPLM can eliminate oil residual from copper pipe about 1.54 mg/m or 97.44% on average.
Considering an amount of oil residual from 20 rolls of the f 7.29 mm copper pipe, it can be noted that the difference between the minimum and maximum of oil quantity remaining inside the copper pipe was approximately ±2.9%. After ironing process, the oil remaining inside of each roll copper was uneven as shown in
Efficiency analysis for evaluating appropriate pressure exploitation was performed by specifying the initial pressure level to be supplied through the copper pipe at 5 bar and then increasing 2 bar interval until reaching 15 bar. For every step of pressure level tested, there were 3 repeated experiments as shown in
Experiment using SPLM system to purge oil residual inside the f 7.29 mm copper pipe was performed by repeatedly measuring the results from 20 rolls of copper pipe. Precision and repeatability of the system developed were then estimated. Each roll of copper pipe would contain oil residual after ironing process approximately 1.13 mg/m on average. From experiment, an amount of oil residual inside copper pipe after using SPLM system was reduced to 0.29 mg/m or 25.23% on average.
Therefore, the system developed can purge oil residual out from copper pipe by 0.85 mg/m or 74.77% on average. Considering an amount of oil residual remaining inside the roll copper, it can be noted that the difference between the minimum and maximum amount of oil remaining inside the rolls of copper pipe was approxi- mately ±10.09% as shown in