The effect of shell side and coil side volume flow rate on overall heat transfer coefficient, effectiveness, pressure drop and exergy loss of shell and helical coil heat exchanger were studied experimentally under steady state conditions. The working fluid, i.e., water was allowed to flow at three different flow rates of 1, 2, and 3 l/min on shell side (cold water) and at 1, 1.5, 2, 2.5, and 3 l/min on coil side (hot water) for each shell side flow rate at the temperatures of 298±0.4K and 323±0.4K, respectively. The results found that the overall heat transfer coefficient increased with increasing both shell side and coil side volume flow rates. The inner Nusselt number significantly increased with the coil side Dean number.

The paper presents analytical relationships based on the theory of Green’s functions. The relationships refer to instantaneous and continuous as well as point and ring heat sources which are discussed. The relationship relating to continuous ring source is the basis for modelling and designing of spiral ground heat exchangers. Heat transfer in the infinite and semi-infinite body was considered. In the latter case, the image method was discussed. Using the results of measurements regarding heat transfer in the ground with a heat exchanger in the form of a single coil installed, a comparison of calculated ground temperatures with measured values was presented.

The arc suppression coil determines whether it can effectively extinguish the arc when it is grounded in the neutral non-effective grounding system. An artificial grounding test is an importantway to verify its performance. In this study, 13 substations with the 10 kV system in the Ningxia areawere selected and considered. Based on the artificial single-phase grounding test, the residual current, the compensation current and the off-resonance degree were measured in the arc suppression coil, and the performance of the arc suppression coil in the 10 kV system was verified. The experimental results show that the error of arc suppression coil automatic measurement is large, the off-resonance degree is large, the resistive component in the compensation current is excessive, the harmonic component exists in the compensating current and capacitive current. To solve these problems, this paper puts forward the corresponding countermeasures for reference.

The article proposes the method of synthesis of active elements with time-varying parameters R(t), C(t) and L(t). In order to construct the elements, it is necessary to use operational amplifiers, multipliers and classic RLC components. The variability in time of the elements results from applying voltage to control terminals. Assuming that the parameters of elements R(t), L(t), C(t) are exponentially varying, dependencies describing the control voltage waveforms which enable such a parameter variability were determined. The obtained results were illustrated with examples and PSpice simulations.

Helical coil heat exchangers are widely used in a variety of industry applications such as refrigeration systems, process plants and heat recovery. In this study, the effect of Reynolds number and the operating temperature on heat transfer coefficients and pressure drop for laminar flow conditions was investigated. Experiments were carried out in a shell and tube heat exchanger with a copper coiled pipe (4 mm ID, length of 1.7 m and coil pitch of 7.5 mm) in the temperature range from 243 to 273 K. Air – propan-2-ol vapor mixture and coolant (methylsilicone oil) flowed inside and around the coil, respectively. The fluid flow in the shell-side was kept constant, while in the coil it was varied from 6.6 to 26.6 m/s (the Reynolds number below the critical value of 7600). Results showed that the helical pipe provided higher heat transfer performance than a straight pipe with the same dimensions. The convective coefficients were determined using theWilson method. The values for the coiled pipe were in the range of 3–40 W/m2 ·K. They increased with increasing the gas flow rate and decreasing the coolant temperature.

Pot-cored coils are commonly used as probes in eddy current testing. In this paper, an analytical model of such a coil placed over a three-layer plate with a hole has been presented. The proposed solution enables the modelling of both magnetic and non-magnetic conductive plates that contain different types of hole, i.e. a through, a surface, an inner or a subsurface hole. The problem was solved by using the truncated region eigenfunction expansion (TREE) method. The analysis was carried out in a cylindrical coordinate system in which the solution domain was radially limited. With the employment of the filamentary coil, the expressions for the magnetic vector potential, and subsequently for the impedance of the cylindrical coil were obtained. The final formulas were presented in a closed form and then implemented in Matlab. The resistance and reactance values were compared with the results obtained in the experiment and using the finite element method in the Comsol Multiphysics package. In each of the cases, good agreement was obtained.

This paper presents and assesses an inverse heat conduction problem (IHCP) solution procedure which was developed to determine the local convective heat transfer coefficient along the circumferential coordinate at the inner wall of a coiled pipe by applying the filtering technique approach to infrared temperature maps acquired on the outer tube’s wall. The data−processing procedure filters out the unwanted noise from the raw temperature data to enable the direct calculation of its Laplacian which is embedded in the formulation of the inverse heat conduction problem. The presented technique is experimentally verified using data that were acquired in the laminar flow regime that is frequently found in coiled−tube heat−exchanger applications. The estimated convective heat transfer coefficient distributions are substantially consistent with the available numerical results in the scientific literature.