6 K solid state Energy Storage Unit

A cryogen-free cold source for temperature below 6 K without mechanical, thermal and electromagnetic perturbations would be welcome in many sensitive applications. This article describes such a device (Energy Storage Unit-ESU) built to store 36 J between 3 K and 6 K. This ESU consists of a solid state enthalpy reservoir connected to a cryocooler by a heat switch. Its different parts as well as the experimental results are presented. The choice of Gd₂O₂S (GOS) as high specific heat solid material for the enthalpy reservoir is discussed. Tests in different conditions were performed. A very good agreement was found between the experimental data and those predicted using the heat switch characteristics and the specific heat measurements of the GOS used in this experimental set-up. A stable 6 K temperature was maintained during more than 50 min in a completely silent environment. A semi-continuous operation for this cold source was successfully tested during 2.5 h.     

Modelling of the borehole filling of double U-pipe heat exchangers

A new model MISOS is proposed for the simulation of the borehole filling (grout) of double U-pipe heat exchangers. When simulating ground-coupled heat pumps, a suitable model of the filling is necessary because the temperature of the filling effects the temperature of the heat carrier fluid. The filling is divided into three elements whose geometry corresponds to the different temperature zones. For each time step, the temperatures of the filling elements can be calculated from energy balances. MISOS is very fast compared to computational fluid dynamics (CFD) algorithms. CFD calculations were performed for different shank spacings, and results compared with those obtained from MISOS. If the pipe shanks are situated between the axis and the wall of the borehole, nearly the same difference of the fluid temperature between inlet and outlet is predicted by MISOS and CFD. For a minimal shank spacing, heating is overpredicted by about 6% for an extraction period of 3 h while an underprediction of about 9% is obtained for maximal shank spacing.     

The Role of Nonuniformity in Convective Heat and Mass Transfer through Porous Media,Part 2

Nonuniformities in porous materials can play a significant role in the convective and diffusive transport of fluid, heat, and mass. This study provides experimental results and corresponding numerical simulation results. The experiments report continuous data in transient test runs with measurements of temperature and velocity at distributed locations in the domain immediately downstream of the porous materials. An increasing degree of nonuniformity was found to produce a lower drying rate as well as an earlier onset of falling rate drying. The numerical model provides results of the effects of different nonhomogeneities such as distributed holes or distributed regions of varying permeability and moisture content. Comparisons between numerical and experimental test results indicate general agreement with differences with regard to details of the drying curve features. This provides a tool for studying the role of nonuniformity in fluid flow and heat and mass transfer in porous media.     

Investigating the trade-off between operating revenue and CO2 emissions from crude oil distillation using a blend of two crudes

Blending of different crude types is frequently used in petroleum refineries to improve their profitability and products yields. However, energy consumption and consequential CO₂ emissions strongly depend on the types of crude being processed. The trade-off between CO₂ emissions and economic objectives, such as net revenue, is investigated for cases of different crude blends using the multi-objective optimization approach. The first objective is the minimization of CO₂ emissions whilst the second objective is maximizing the net revenue from the crude distillation unit (CDU). A rigorous model is used to estimate CO₂ emissions from different sources within the CDU. This emissions model incorporates pinch analysis for heat integration, to optimize the distribution of utilities related to emissions. Blends of two crudes, 36 API and 27.7 API, are used as feedstock to a rigorous CDU model of the atmospheric crude tower, vacuum tower and heat exchanger network. Lighter crude blends recorded higher CO₂ emissions and net revenue compared with the heavier blend due to the greater distilled fraction. However, CO₂ emissions did not vary linearly with the fraction of each crude, as the heat exchanger network also influenced the degree of heat recovery and consequently the level of CO₂ emissions. The multi-objective solutions show the influence of all 13 of the process variables on the objectives.     

RADIATION EFFECTS ON MHD AXISYMMETRIC STAGNATION POINT FLOW TOWARDS A HEATED SHRINKING SHEET

In this article, a comprehensive numerical study of MHD axisymmetric stagnation point flow with radiation effects towards a heated shrinking sheet immersed in an electrically conducting incompressible viscous fluid in the presence of a transverse magnetic field is analyzed. The governing continuity, momentum, and heat equations together with the associated boundary conditions are first transformed to a set of self-similar nonlinear ordinary differential equations and are then solved by a method based on finite difference discretization. Some significant features of the flow and heat transfer in terms of normal and horizontal velocities and temperature field for various values of the governing parameters are analyzed, discussed, and presented through tables and graphs. The present investigations predict that the shear stresses increase and the thermal boundary layer becomes thinner by applying a strong magnetic field. The heat loss per unit area from the sheet decreases with an increase in the shrinking parameter. The thermal boundary layer thickness decreases with increasing values of the radiation parameter. The present results may be beneficial in flow and thermal control of polymeric processing.     

CHARACTERISTICS OF HEAT TRANSFER FROM A SPHERICAL SOLID BODY UNDER PULSATING FORCED CONVECTION

Heat transfer from a solid sphere having a Biot number Bi ? 0.1 to a flow medium in a cooling process under pulsating forced convection is experimentally examined. In the experiment, two kinds of pulse modes, which are the type of pulsating forced convection with continuous feed and the feed type mixing forced and natural convection, are considered as a pulse feed technique. Initially, the evaluation method of the Nusselt number Nu is derived in the cooling process and the validity of that method is verified by comparison with the experimental results. With regard to the effect of pulsating feed, it is shown that the pulsating feed conditions have a great influence on the characteristics of the heat transfer. The enhancement of heat transfer under the condition of the forced convection pulsatively fed with continuous feed is recognized, and the characteristics of heat transfer for the pulsating feed including natural convective heat transfer region are aggravated. Besides, it is clear that the decrease in the heat transfer characteristics is dependent on the duration of the natural convective heat transfer. Furthermore, Ranz-Marshall correlations for each pulsating feed condition are presented.     

A NONDESTRUCTIVE METHOD TO MEASURE RESIDUAL ADSORPTION CAPACITY OF CHARCOAL FILTERS

High surface area charcoal bed filters have been used for over a half a century to adsorb undesirable vapors from gas streams. One problem encountered when using these niter beds is that there is presently no simple, reliable, nondestructive method to measure their Residual Adsorption Capacity, RAC. This is particularly critical in situations where harmful vapors are being adsorbed.

An investigation has been underway to use pulses of weakly adsorbed gases such as ethane and/or methane to measure RAC. The hypothesis being that these weakly adsorbed gases will “count” unoccupied adsorption sites. In the present study, dimethyl methylphosphonate (DMMP) was used to “irreversibly” occupy available siles to various extents on different niters. The Reduced Retention Time. θ, (the ratio of the adjusted retention time to the space time) and the Resolution (R) between peaks of methane and ethane were found to correlate to RAC under dry and wet (humid) conditions.     

HOMOTOPY ANALYSIS OF FREE CONVECTION BOUNDARY LAYER FLOW WITH HEAT AND MASS TRANSFER

A steady two-dimensional laminar boundary layer flow of an incompressible viscous fluid over a semi-infinite surface is considered to investigate the accuracy of the homotopy analysis method. The governing coupled nonlinear system of differential equations is solved by means of the HAM approach. Explicit analytical series solutions are obtained and compared with numerical solutions. Good agreement is observed between the numerical results and HAM analytical solutions.     

加热预处理减轻茄子冷害的效果

将茄子分别用３０、３５、４０、４５℃经２４ｈ加热预处理后，在１℃冷藏１５ｄ。结果表明：加热预处理抑制了茄子的呼吸速率，减缓了总酚类物质含量的下降以及由于冷害引起的电解质渗漏率增加，有效地抑帛最茄子在低温贮藏时所出现的果皮凹陷，果肉及种子在症状，其中以４５℃处理２４ｈ后的效果最明显。     

TRACE qualification via analysis of the EIR gas-loop experiments with smooth rods

Several gas-loop experimental programs were carried out during the 1970–1980s at the Eidgenössisches Institut für Reaktorforschung (EIR, now PSI), Switzerland. In the present work, a wide range of thermal–hydraulics tests for smooth rods, which form part of the experiments conducted at the time, have been reanalyzed with the aim of qualifying the TRACE code. The latter constitutes the thermal–hydraulics module of PSI’s FAST code system, currently being applied to the multi-physics analysis of advanced fast reactor systems, including the Generation IV Gas-Cooled Fast Reactor (GFR). It is shown, from the present analysis, that the built-in TRACE heat transfer and friction correlations are indeed quite suitable for gas cooling under prototypic GFR conditions.