查看更多>>摘要：As a newly-developed microchannel heat exchanger， printed circuit heat exchanger (PCHE) is employed as the primary LNG vaporizer in floating storage and re-gasification unit for high efficiency and compactness。 In this paper， thermal-hydraulic characteristics of trans-critical NG through the improved staggered S-shaped fin channels were numerically investigated。 Variation tendencies of fin performance under different operating pressures and a wide range of Reynolds numbers were analyzed。 Sensitivity analyses on the effect of various thermophysical properties on heat transfer around pseudo-critical temperature revealed that heat transfer capacity were deeply affected by specific heat， and effects of thermal conductivity and viscosity could be canceled each other。 Additionally， to further estimate forced convective heat transfer mechanism， common features of HTC and f factor distributions were analyzed and some reasonable criteria were also discussed。 The results showed that except for a few data points across critical temperature affected by entrance effect， the peak HTC always appeared in the vicinity of the pseudo-critical points。 Furthermore， the Bo of 10-5 and q+ of 5 x 10 - 4 could be adopted to analyze buoyancy and flow acceleration influences qualitatively。 The simulated results agreed with the predictions from Ngo Correlation within 16。32% and 12。36% errors respectively for HTC and f factors， which implied that though the drastic local changes of performance tendency could not be predicted well， suitable correlations were sufficiently accurate for engineering applications。
查看更多>>摘要：Superconducting high-field magnets working in He II are usually immersed in a pressurized static He II bath。 This pressurized He II bath is then connected through a heat exchanger to a saturated He II bath acting as a cold source。 Due to the peculiar He II properties (very high heat conductivity)， the conventional heat exchanger designs are not suitable here。 Additionally， a compact design is often mandatory， as space inside cryostats is always an issue。 In a recent paper [1]， we presented different configurations of optimized multi tube heat exchangers depending on the available horizontal or vertical space。 Such an optimized compact heat exchanger prototype has been built to fulfill the cooling needs and the integration constraints of the HL-LHC superconducting D2 recombination dipole [2]。 The chosen design with hundred oxygen-free high-purity copper horizontal tubes penetrating inside the extremity of the D2 cold mass vessel is an efficient solution offering significant operating margins。 From the thermal analysis， it appears that the profile and value of the temperature difference across the heat exchanger really depends on the ratio of the transverse conductance to the longitudinal conductance， the first being determined by the conductivity of the copper and the Kapitza conductance。 Therefore， optimization and prediction of the thermal performance of such a heat exchanger is only possible when these thermal properties (i。 e。， the heat conductivity and Kapitza conductance of the copper tubes) or the sum of these three thermal resistances in series are well known。 For that purpose， we built a dedicated test bench to perform these transverse resistance measurements on a pipe sample。 The experimental results obtained on a single pipe were then used to infer the behavior of the complete heat exchanger。 The comparison of the predictive code and the cryogenic measurements shows excellent agreement over a wide range of cryogenic operating conditions (temperatures， pressures， heat loads)。 This paper presents a guideline for designing compact and efficient He II/He II heat exchanger as well as a method to predict the performance of such heat exchanger accurately。
查看更多>>摘要：A launch vehicle that operates using cryogenic liquid propellants will require a pressurization process for a propellant tank。 Usually， helium stored at cryogenic temperatures passes through the engine， is heated， and pressurizes the tank。 Low-temperature helium is heated in a heat exchanger using high-temperature combustion gas from an engine。 For the accurate performance prediction and weight optimization of the launch vehicle， the performance of the heat exchanger should be evaluated before launching。 This study presents an evaluation method for predicting the performance of a heat exchanger in a launch vehicle。 The heat exchanger performance was measured at a constant helium flow rate under actual engine operating conditions。 A numerical analysis model for predicting the heat exchanger performance was developed and compared to the test results。 The tests were conducted at different inlet temperatures。 The test results and analysis confirmed that the effectiveness increased with the inlet temperature。 Further analyses revealed that a change in the heat transfer coefficient， as well as the inlet temperature， changed the effectiveness by 6%。 To accurately predict the performance of the launch vehicle， it was necessary to accurately predict the change in the heat transfer coefficient with temperature。 A design method for the heat exchanger of a launch vehicle was also discussed。 The heat-transfer area and weight should be optimized under the required conditions。
查看更多>>摘要：Hysteresis effect on thermal contact conductance due to load cycling is well documented for joints at ambient temperature。 However very limited information is available at cryogenic temperature。 The thermal cycling of joints to cryogenic temperature is also an unexplored area。 In addition， the change in heat flow direction on thermal contact conductance across joints formed by dissimilar materials， which is referred as rectification， is an important parameter in maintaining desired thermal contact conductance across the joints。 In the present study， these factors are experimentally evaluated for joints formed by stainless steel， aluminium alloy and titanium alloy over a temperature range of 150 K to 300 K at low interface loading。 The present study reveals that the thermal contact conductance at cryogenic temperature is less affected by hysteresis by an average of 8% and 16% with thermal and mechanical loading cycles respectively。 However， Rectification effect in thermal contact conductance is prominently observed in bi-metallic joints。 More than 60% change in thermal contact conductance is observed with change in direction of heat flow。 The study points out that rectification can be effectively utilised for controlling the thermal contact conductance at cryogenic temperature in joints subjected to low contact pressure， where the use of other controlling methods is constrained。
NSTL
Elsevier