Final Steady-state Temperature Research Articles

Reducing thermal contact resistance by a novel elastomeric polyethylene glycol/unsaturated polyester resin/graphene thermal interface materials

Reducing thermal contact resistance (TCR) is an important way to enhance heat dissipation of electronic devices. Elastomer is easy to deform, increase the contact area and reduce the TCR, but its wetting condition is not satisfying. In this work, a novel elastomeric thermal interface materials (TIMs) polyethylene glycol/unsaturated polyester resin/graphene (PEG/UPR/G) was designed and prepared. With the increase of temperature, PEG near surface of PEG/UPR/G was released due to phase transformation, and a thin molten layer would be attached to the surface. By this way, the micro bumps on the solid surface were all soaked by the thin layer of molten PEG, which greatly reduced the TCR. In addition, the effect of temperature and pressure on TCR of elastomeric PEG/UPR/G were studied. When the pressure increases from 10 Psi to 50 Psi (65 °C), TCR decreases from 11–14 K ∙ cm2/W to 2–4 K ∙ cm2/W. The TCR will be further reduced to 0.7–0.9 K ∙ cm2/W (75 °C) due to the phase transition of PEG. Moreover, the heat dissipation effect of PEG/UPR/G was evaluated by infrared thermal imager. These results demonstrate that the total thermal resistance is the decisive factor for the final steady-state temperature and the time of unsteady heat transfer.

PISCES-RF: a liquid-cooled high-power steady-state helicon plasma device

Radio-frequency (RF) driven helicon plasma sources can produce relatively high-density plasmas (n > 1019 m−3) at relatively moderate powers (<2 kW) in argon. However, to produce similar high-density plasmas for fusion relevant gases such as hydrogen (H), deuterium (D) and helium (He), much higher RF powers are needed. For very high RF powers, thermal issues of the RF-transparent dielectric window, used in the RF source design, limit the plasma operation timescales. To mitigate this constraint, we have designed, built and tested a novel helicon plasma source assembly with a fully liquid-cooled RF-transparent window which allows steady state operations at high power (up to 20 kW) and successfully produces high-density plasma with both argon and H. Deionized (DI) water, flowing between two concentric dielectric RF windows, is used as the coolant. We show that a full azimuthal blanket of DI water does not prevent high-density plasma production. From calorimetry on the DI water, we measure the net heat removed by the coolant at steady state conditions. Using infra-red imaging, we calculate the constant plasma heat deposition and measure the final steady state temperature distribution patterns on the inner surface of the ceramic layer. The heat deposition pattern follows the helical shape of the antenna. We also show the consistency between the heat absorbed by the DI water, as measured by calorimetry, and the total heat due to the combined effect of the plasma heating and the absorbed RF. These results are being used to answer critical engineering questions for the 200 kW RF device materials plasma exposure experiment being designed at the Oak Ridge National Laboratory as a next generation plasma material interaction device.

An experiment investigation of temperature control performance for machine tool oil coolers with hot-gas bypass temperature control scheme and inverter temperature control scheme

Following the machine tool with demands of high-speed, high-precision machining and multi-axis, the heat generation of machine tool will lead to thermo growth of spindle, thermal error, etc. Therefore, the machine tool oil cooler has been frequently adopted for thermal management of heat generation for machine tool. However, it will be quite challenging to develop high-precision machining without suitable temperature control scheme. And, the machine tool oil cooler with on-off control is difficult to control the oil temperature accurately. Therefore, in this paper, the machine tool oil cooler with hot-gas bypass temperature control scheme and inverter temperature control scheme based on the PID control logic have been proposed to solve the oil temperature control problem for machine tool oil cooler. Furthermore, the temperature control performance (i.e. thermo growth of spindle, oil temperature control accuracy, and EER) of hot-gas bypass temperature control scheme and inverter temperature control scheme has been compared by means of experiment. The experimental results shows that the inlet oil temperature control accuracy can be maintained ±0.2 °C during spindle operation by using the hot-gas bypass temperature control scheme (HGB cooler) and inverter temperature control scheme (INV cooler). Furthermore, the thermo growth of spindle of HGB cooler is about 14 % smaller than the INV cooler because of hot-gas bypass temperature control scheme with thermal compensation function. However, the total power consumption of HGB cooler is about 0.18 kW higher than the INV cooler. Hence, the energy efficiency ratio (EER) of INV cooler reveals about 10.9 % higher than the HGB cooler at steady state. Furthermore, when oil flow rate declined to about half, the temperature difference between initial and final steady state temperature of the spindle is increased around 94.3 %, and the thermo growth of spindle is increased 58.7 %.

Two phase cooling with nano-fluid for highly dense electronic systems-on-chip – A pilot study

In recent days, electronics gadgets need to design for higher functionalities with dense populated systems in order to meet the demands like lower in size, weight and power consumption. Even industrial electronic component and system design also prefer same slim fashion. On other hand the overheating of electronic components reduces its performance, life and by the way the reliability of such electronic product/system is greatly affected due to overheating. The conventional cooling methods failed to offer best performances. Hence this part of research proposed a effective two phase cooling technique with nano-fluid. The objective of this research is to maintain the maximum temperature at the junction and hot spots in order to break a new ground in the cooling of electronic systems. The Maximum permissible operating temperature for any commercial electronic applications is only upto 70 °C (equal to 343.15 K) and above which most of the inherent electronic circuits may malfunction and destroy the entire application.The HotSpot Simulator-6.0 software employed for establish, verify the simulated model and trial runs to answer many ‘what if’ questions. In the simulation, hottest spot has been found in Int_Reg region, where the steady temperature grows beyond the threshold temperature level. The temperature has to be decreased in order to provide reliable working environment. Hence, HFO 1234ze nano-fluid employed with flow rate of 1100 ml per minute. The nanofliuid minimizes the temperature of the simulated electronic circuit from 351.80 K to 326.86 K in UUT. The proposed two phase nano-fluid cooling system for 3-D Unit-Under Test (UUT) was verified and validated with real system and simulated for experiments. Thus, a high range of temperature difference from the initial and final steady state temperature has been evidently shown in the proposed two phase nano fluid cooling method. The system found outperforms as best of both the worlds. The nanofluid cooling system can be used in thermal-aware systems and highly dense systems to maintain the temperature not much than 343.15 K, even at full load conditions.

INTERFACE OF A DIGITAL TEMPERATURE MICROCONTROLLER WITH AN ANALOG INCUBATOR

A plug-and-play type digital temperature control system was developed and tested. The software designed for the controller implemented 100% duty cycle for temperature errors of 2°C or more and a 25% duty cycle for temperature errors of 1°C. This produced an initial rate of change of temperature of 0.170°C s−1 at a 100% duty cycle and 0.0040°C s−1 at a 25% duty cycle. The temperature rates were invariant for both positive and negative temperature gradients. The system was also able to make the incubator reach the final steady state temperature in less than 70 s.

1D heat transfer through a flat plate submitted to step changes in heat transfer coefficient

The thermal response of an infinite flat plate is considered, when the heat transfer coefficients on both the exposed surfaces undergo step changes. The configuration is a simplified model for the heat transfer through the separating wall in the Isochoric Counter-Current Heat Exchanger. The step change in the second surface appears with a time delay with respect to the first. The plate temperature, surface heat fluxes and accumulated energy perturbations are evaluated for both the thermally thick and thin cases and the corresponding results are compared. The results show a significant influence of both the delay time and the Biot numbers perturbations. It is shown that for a specific combination of Biot number magnitudes the plate is brought suddenly into a steady state condition and as soon as the second step appears. In addition, an inner point may be defined where the final steady state temperature perturbation becomes zero, separating the plate into two oppositely thermally stressed regions.

X-ray beam/biomaterial thermal interactions in third-generation synchrotron sources.

Third-generation synchrotron sources generate strong X-ray beams. The beam's interaction with biomaterials gives rise to concerns related to thermal damage and radiation damage. Of the two issues, the thermal interaction is conducive to rigorous analysis from first principles, although this has not been performed to date in a comprehensive manner. In this study, the interaction of the X-ray beam emanating from a third-generation synchrotron with a typical frozen biocrystal is theoretically studied, focusing specifically on the resulting unsteady (time-dependent) and steady heat-transfer phenomena. A unique regime map is developed to explain and to identify, on the basis of Fourier and Biot numbers as governing parameters, the applicable mathematical models that predict the subsequent thermal behavior. Depending on the values of these parameters, some simplified but realistic 'generic' solutions are generated that are suitable for that particular domain of applicability. Classical heat-transfer theory was used to describe the third-generation X-ray beam and biomaterial thermal interaction. Besides the generalized approach presented, numerous illustrative cases were solved and the resulting temperature levels are explicitly presented. Overall, the resulting thermal behavior of the system, i.e. peak and local temperature distribution, during both early transient development and for sustained long-time steady-state conditions, depends on a number of factors including the amount of energy absorbed, convective heat-transfer film coefficient and gas temperature, the sample size and shape, and the thermophysical properties of the sample and cooling gas. Results of the analysis revealed the strong influence that convection has on the transient and final steady-state temperature of the sample and the impact of internal heat conduction. The characteristic timescales of the important and dominant thermal processes with respect to the two types of thermal models are clearly identified.

Thermodynamic analysis of Collins helium liquefaction cycle

The present paper gives a thermodynamic analysis of the Collins helium liquefaction cycle with two reciprocating expanders. The results of the analysis make it clear that, for a given efficiency of expanders and effectiveness of heat exchangers, there exists an optimum mass flow fraction of total helium gas mass flow rate that should be diverted through the expanders for which liquid yield is maximum and net power input is minimum. The analysis quantitatively studies the effect of expander efficiency and heat exchanger effectiveness on the performance of the liquefier. It gives final steady state temperature distribution across the cycle, which is essential data for carrying out the preliminary design of various components in the cycle.

The gas temperature in a tungsten electrothermal atomizer

The gas temperature of a tungsten electrothermal atomizer (WETA-82) has been studied both theoretically and experimentally. Optical pyrometry was used to determine the surface temperature of the tungsten tube atomizer. The model proposed in an earlier paper predicts that the rate of increase of the predicted weighted-average gas temperature will be slower than that of the predicted surface temperature during the first few ms of the heating cycle for all the heating rates considered. However, the experimental results show that the rate of increase in the gas temperatures follows the surface temperature of the atomizer. The above-mentioned model also predicts a large temperature gradient between the gas and the surface temperature of the atomizer for the final steady-state temperature. However, the experimentally determined gradient between the temperature of the gas and the atomizer surface was smaller than that predicted.