Search

The present paper analyzes the feasibility of an exhaust gas driven jet-ejector cooling system for charge air cooling of turbocharged gasoline engines in addition to the conventional charge air cooler to increase the engine efficiency. Thereto, steady-state experiments of a jet-ejector cooling system and an exhaust gas heat exchanger prototype working with the refrigerant R134a are used to analyze the operation and control of the compound system and determine feasible cooling capacities, charge air temperatures, thermal COP th and hydraulic COP h . Moreover, the cooling system is rated regarding its power densities and engine backpressure. The exhaust gas waste heat recovery, system power densities, and engine backpressure are acceptable. However, the hydraulic COP h and the amount of reject heat need to be improved, necessitating for instance a multi-staging of the jet-ejection. [ABSTRACT FROM AUTHOR]

Abstract: Since the late seventies of the 20th century, several analytical models for combined heat and mass transfer in laminar falling film absorption have been proposed. Nevertheless the analytical solutions obtained with the Fourier method for the coupled process are complex and for short flow length a certain instability occurs which have been explained with the inconsistency of the initial and boundary conditions. Therefore boundary layer models have been justified in order to solve the transfer problem for short flow length. Moreover a linear approximation of the phase equilibrium is required. The analytical solutions for heat and mass transfer presented in this paper are obtained by using the Laplace transform to solve the partial differential equations for an isothermal as well as impermeable wall. An originally unknown constant temperature and mass fraction boundary condition at the interface are set. The temperature and mass fraction profile across the film are obtained formally independently. In order to determine the yet unknown interface temperature and mass fraction the phase equilibrium and the interface energy balance are applied, using averaged gradients with regard to the streamwise coordinate. The interface temperature and mass fraction obtained with this procedure are interpreted and treated as mean values. From the known evolution of the mean interface temperature and mass fraction, the local values are derived by inverting the first mean value theorem for integration. The results show very good agreement to the established analytical solutions. The solving procedure does not depend on the input parameters such as the Lewis number for instance, which is needed in order to determine the eigenvalues within the Fourier method. Moreover arbitrary correlations for the phase equilibrium are applicable. The present solution is mathematically stable and offer explicit expressions in order to calculate the mean heat and mass fluxes directly. Therefore this solution is favourable to implement entire absorption process simulation, yet describing the coupled heat and mass transfer process comprehensively. [Copyright &y& Elsevier]

The relevant low-frequency modes of plan-asymmetric tall buildings and those of bridges consist of coupled translational and torsional motions. We consider the locations of the modal centers of velocity of either the rigidly assumed floors or of the bridge cross-sections to be crucial for selecting the design and the “optimal” position of the liquid absorbers. Such a tuned liquid column-gas damper, TLCGD consists of a sealed rigid piping system that is partially filled with liquid (preferably water), whose dynamics can be derived using the nonstationary Bernoulli equation properly extended to account for the relative streamline in a moving reference system. Although both the construction and working principle of TLCGDs differ from tuned mass dampers (TMD), a geometric analogy exists between these absorber types. Consequently, in a first step modal tuning is performed by means of a transformation of the TMD optimal parameters, e.g., of the Den Hartog formulas, possibly followed in a second step by fine-tuning in state-space. Such a U- or V-shaped sealed liquid column-gas damper, i.e., with the gas-spring effect taken into account, is found suitable for applications in moderately plan-asymmetric buildings (the floors’ modal center of velocity falls outside of the floor plan) and for bridges with dominant horizontal vibrations. The novel design of a torsional sealed liquid column-gas damper, TTLCGD, turns out to have even higher efficiency in effectively damping strongly asymmetric buildings, where the floors’ modal centers of velocity lie inside of the floor plan: in that case of an alternative design, the mid-plane of the U-shaped TLCGD is bent to a cylindrical surface that might be “nearly closed” such that the trace in the floor becomes approximately a loop. For bridges with dominating vertical flexural vibrations, a novel pipe-in-pipe design of the VTLCGD provides the vertical control force rendering the additional efficient damping. The evident features of TLCGDs are no moving mechanical parts, cheap and easy implementation into civil engineering structures, simple modification of the natural frequency and even of the damping properties, low maintenance costs, little additional weight in those cases where a water reservoir is required, e.g., for the sake of fire fighting, and with a performance comparable to that of TMDs of the spring-mass- (or pendulum-)-dashpot type. [ABSTRACT FROM AUTHOR]

Abstract: An important drawback of solid sorption systems which are operated in batch mode against liquid sorption systems is the imperfect heat exchange between loaded and unloaded adsorbent, as compared to the almost perfect counter-flow solution heat exchanger. We will discuss a simple hardware solution for a significant improvement. We divide the batch reactors into several compartments, not with respect to the refrigerant side, but with respect to the heat transfer medium (heat exchanger loop). If these compartments have individual and arbitrary heat exchange possibilities with each other the efficiency of heat recovery can be improved from a co-flow characteristic to a cross-flow characteristic. We want to stress that this is different from a multi-bed or multistage arrangement. The method is explained, and an algorithm for deriving the exchange efficiency is given. Although this paper is only meant for outlining the basic mechanism, a proposition for realisation of the external hydronic circuit is given in addition. [Copyright &y& Elsevier]

Abstract: We present a model describing simultaneous heat and mass transfer of an absorbing or desorbing laminar liquid film flowing over a vertical isothermal plate. We start with a formulation which is comparable to established models by using simplifying assumptions such as homogeneous velocity and constant film thickness. In contrast to those, we allow for effects like change in properties and differential heat of solution within the bulk of the film. Additionally, enthalpy transport due to interdiffusion is accounted for. The impact of the considered effects are discussed and compared. The numerical solution is obtained by utilising a Newton–Raphson scheme to solve the finite difference formulation of the governing equations. Since the temperature gradients adjacent to wall and phase boundary are expected to be large, we discretise the equations on an irregular grid. The results of the model agree very well with established analytical models. It is found that the influence of released differential heat of solution within the bulk is relatively small. However, the impact on the temperature distribution is in the same order of magnitude as the one of a change in properties. Moreover, when comparing desorption with absorption under equivalent conditions, the mass transfer rate during absorption is higher than during desorption. [Copyright &y& Elsevier]

In this paper the dynamic response of compound bridges under moving loads is analyzed. The main structure is modeled as a two-layer beam consisting of a steel girder connected elastically to the concrete deck. The governing sixth-order partial differential equation of motion of the homogenized beam is extended to include uncertainty in the mechanical property of the interface. The slip modulus is considered to be a random variable, whose probability density function is considered to be zero outside of a given interval, that is, it is a member of a fuzzy set with bounded uncertainty. The analysis of the illustrative problem is based on the interval representation with a triangular membership function of the slip modulus assigned. Membership functions of the random natural frequencies are determined. Both, fuzzy peak deflection and acceleration are derived for a single-span compound bridge subjected to a single moving load as well as to a series of repetitive moving loads traveling with constant speed. [ABSTRACT FROM AUTHOR]

The theorem on the unique decomposition of eigenstrain provides the tool to construct prescribed displacements inside and (or) at the surface of a linear elastic body in two novel ways (e.g., in connection with shape control). The first approach applies Maysel’s formula and renders the linear relationship between nodal displacements and impotent eigenstrain in discrete or discretized systems. The second, alternative approach can be applied to continuous systems as well, and allows controlling the shape of the body. Both approaches do not require the solution of the associated boundary value problem with prescribed eigenstrain, thus circumventing the possibly cumbersome (numerical) solution, which can present some difficulties with respect to its convergence. [ABSTRACT FROM AUTHOR]

Background and purpose Charcot−Marie−Tooth ( CMT) 1C due to mutations in LITAF/ SIMPLE is a rare subtype amongst the autosomal dominant demyelinating forms of CMT. Our objective was to report the clinical and electrophysiological characteristics of 18 CMT1C patients and compare them to 20 patients with PMP22 mutations: 10 CMT1A patients and 10 patients with hereditary neuropathy with liability to pressure palsies ( HNPP). Methods Charcot−Marie−Tooth 1C patients were followed-up in referral centres for neuromuscular diseases or were identified by familial survey. All CMT1A and HNPP patients were recruited at the referral centre for neuromuscular diseases of Pitié-Salpêtrière Hospital. Results Two phenotypes were identified amongst 18 CMT1C patients: the classical CMT form (' CMT-like', 11 cases) and a predominantly sensory form ('sensory form', seven cases). The mean CMT neuropathy score was 4.45 in CMT1C patients. Motor nerve conduction velocities in the upper limbs were significantly more reduced in CMT1A than in CMT1C patients. On the other hand, the motor nerve conduction velocity of the median nerve was significantly lower in CMT1C compared to the HNPP group. Distal motor latency was significantly more prolonged in CMT1A patients compared to the CMT1C and HNPP groups, the latter two groups having similar distal motor latency values. Molecular analysis revealed five new LITAF/ SIMPLE mutations (Ala111Thr, Gly112Ala, Trp116Arg, Pro135Leu, Arg160Cys). Conclusions Our study delineates CMT1C as mostly a mild form of neuropathy, and gives clinical and electrophysiological clues differentiating CMT1C from CMT1A and HNPP. Delineating phenotypes in CMT subtypes is important to orient molecular diagnosis and to help to interpret complex molecular findings. [ABSTRACT FROM AUTHOR]