LTspice Electro-Thermal Model of Joule Heating in High Density Polyethylene Optical Fiber Microducts

Abstract

At present, optical fiber microducts are joined together by mechanical type joints. Mechanical joints are bulky, require more space in multiple duct installations, and have poor water sealing capability. Optical fiber microducts are made of high-density polyethylene which is considered best for welding by remelting. Mechanical joints can be replaced with welded joints if the outer surface layer of the optical fiber microduct is remelted within one second and without thermal damage to the inner surface of the optical fiber duct. To fulfill these requirements, an electro-thermal model of Joule heat generation using a copper coil and heat propagation inside different layers of optical fiber microducts was developed and validated. The electro-thermal model is based on electro-thermal analogy that uses the electrical equivalent to thermal parameters. Depending upon the geometric shape and material properties of the high-density polyethylene, low-density polyethylene, and copper coil, the thermal resistance and thermal capacitance values were calculated and connected to the Cauer RC-ladder configuration. The power input to Joule heating coil and thermal convection resistance to surrounding air were also calculated and modelled. The calculated thermal model was then simulated in LTspice, and real measurements with 50 µm K-type thermocouples were conducted to check the validity of the model. Due to the non-linear transient thermal behavior of polyethylene and variations in the convection resistance values, the calculated thermal model was then optimized for best curve fitting. Optimizations were conducted for convection resistance and the power input model only. The calculated thermal parameters of the polyethylene layers were kept intact to preserve the thermal model to physical structure relationship. Simulation of the optimized electro-thermal model and actual measurements showed to be in good agreement. Author Contributions: Conceptualization, K.B., S.A., and J.S.; methodology, S.A. and K.B.; software, S.A. and K.B.; validation, S.A. and K.B.; formal analysis, S.A. and K.B.; investigation, S.A. and K.B.; resources, K.B. and J.S.; data curation, K.B., S.A. and J.S.; writing-original draft preparation, S.A.; writing-review and editing, J.S.; visualization, S.A.; supervision, K.B. and J.S.; project administration, J.S.; funding acquisition, K.B. and J.S.Funding: This research work is part of the project FIBER, funded through the European Regional Development Fund. Conflicts of Interest:The authors declare no conflict of interest.

Design and Development of a Battery Powered Electrofusion Welding System for Optical Fiber Microducts

“…The authors have previously developed and validated an LTspice electro-thermal model of joule heating in highdensity polyethylene optical fiber microducts [17]. The developed thermal model was based on thermal to electrical analogy that uses the thermal resistance as electrical resistance and thermal capacitance as electrical capacitance [18].…”

“…This way, the internal temperatures of the optical fiber microduct made of HDPE and its surrounding layers of LDPE were computed. The thermal properties of HDPE and LDPE materials are not constant in the temperature range 25˚C to 180˚C [11], therefore the computed LTspice thermal model was optimized to give the best fit for the measured temperatures with 50µm K-type thermocouples [17]. The optimized LTspice thermal model of heat generation and propagation inside the optical fiber microduct [17] is reproduced in Figure 6 [17].…”

“…The power input part models the input power to joule heating wire, whereas the thermal model part models the resulting temperature at different layers inside the HDPE and LDPE material due to given power input. One of the results of the simulation and validation experiment in [17], with a power input of 13.2 volt × 5.42 ampere = 71.54 watts, is reproduced here in Figure 7. In Figure 7, the red curve, i.e.…”

“…Based on the thermal modeling theory and methods presented in S. Akram et al [17] and shortly described in the previous section, a new type of OFEF joint and its complete welding system was modeled in LTspice. Simulation results of the LTspice welding model were used to fabricate prototype OFEF joints and their controller board.…”

“…In the validation experiments of S. Akram et al [17], 14 turns of 0.1 mm diameter copper wire were wound as joule heating wire. If this same wire is wound on each side of the EF joint shown in Figure 3, it becomes a direct transformation of the experimental results shown in Figure 7.…”