Mohammed Lachi

The time constant of double pipe and one pass shell-and-tube heat exchangers in the case of varying fluid flow rates

In this paper we try to characterise the behaviour of a double pipe or shell and tube heat exchanger in transient phase when a sudden change of the flow rate is imposed at the entrance of one of the two inlets. A simplified model is proposed: a two parameter model with a time lag and a time constant. An analytical expression of the time constant is obtained by using the energy balance equation. Experimental investigations show a good agreement with theoretical results. This method can be generalised to describe the response of any variation of the flow rates at the entrance of the heat exchanger.

Development and performance evaluation of a hemp–starch composite

This article describes the results of a research project carried out at the University of Reims Champagne-Ardenne. The aim of this article is to develop a new insulating material produced by bonding hemp shives with wheat starch as a binder and to characterize its physical properties such as sorption isotherm, water vapour permeability, thermal conductivity, heat capacity and porosity. The equations of coupled heat and moisture transfer within the panels are introduced. These governing equations are applied on the room level in order to assess the hygrothermal behaviour of the panels and its impact on energy consumption and indoor comfort. Simulations are performed for Nancy (France) winter conditions with the simulation environment Simulation Problem Analysis and Research Kernel (SPARK) suited for complex problems.

Mechanical and hygrothermal characterisation of cork concrete composite: experimental and modelling study

Abstract The paper aims to present a new insulating material based on cork aggregates and cement designed for building applications. Samples are prepared by mixing natural cork aggregates, sand, cement and water. Four cork volume dosages are considered, 0, 25, 50 and 75% (relative to the sand). Samples are characterised in terms of hardened density, compressive and flexural strength, as well as thermal conductivity and hydric properties (moisture content, vapour permeability, moisture buffering value and absorption by partial immersion). Results show that increasing cork granule amount tends to increase moisture retention and buffering value but decreases density, thermal conductivity and mechanical properties. Depending on the cork content, cork concrete mixture can be used as thermal insulator or as a structural component.

Transient Conjugated Conduction: External Convection With Front Face Imposed Wall Heat Flux

This work presents hybrid numerical-analytical solutions for transient laminar forced convection over flat plates of non-negligible thickness, subjected to arbitrary time variations of applied wall heat flux at the interface fluid-solid wall. This conjugated conduction-convection problem is first simplified through the employment of the Coupled Integral Equations Approach (CIEA) to reformulate the heat conduction problem on the plate by averaging the related energy equation in the transversal direction. As a result, a partial differential formulation for the average wall temperature is obtained, while a third kind boundary condition is achieved for the fluid in the heat balance at the solid-fluid interface. From the available velocity distributions, the solution method is then proposed for the coupled partial differential equations, based on the Generalized Integral Transform Technique (GITT) under its partial transformation mode, combined with the method of lines implemented in the Mathematica 5.2 routine NDSolve.© 2007 ASME

Hygrothermal and Acoustical Performance of Starch-Beet Pulp Composites for Building Thermal Insulation

This article deals with the elaboration and the characterization of an innovative 100% plant-based green composite made solely of beet pulp (BP) and potato starch (S). Using this type of material in insulation applications seems a good solution to reduce the CO2 gas emissions in building. The influence of the starch amount on composite characteristics was studied. Four mixtures were considered with different S/BP mass ratios (0.1, 0.2, 0.3 and 0.4). The physical properties of these materials were studied in terms of porosity, apparent and absolute densities, thermal conductivity, and hygric properties. The influence of humidity content on acoustical properties was studied as a function of frequency. Test results show a real impact of both starch and humidity contents on the hygrothermal and acoustical properties of the studied material due to the porosity. The composite with the lowest amount of starch (S/BP = 0.1) seems to be the optimal composition in terms of the hygrothermal and acoustical behaviors.

Numerical Study of Tread Defects' Impact on the Static and Dynamic Behavior of a Railway Wheel

To ensure security and diminish the service charges in the railway systems, it is necessary to characterize the mechanical behavior of the zone containing tearing of metal resulting into breaks and high vibrations caused by a manufacturing defect. The influence of these defects, present in the metal of the wheel, was first studied by simulating three geometrical forms: circular defect, elliptical defect and any other form defect. The constraints and distortions were analyzed, strictly, around these defects. The calculations were performed for a load level corresponding to the weight of the trailer of the new railcars in Algeria, using a code of calculation by finished elements (ANSYS). The Second study concerns the dynamic behavior; initially with a modal analysis of two cases; wheel with and without defects on the tread using Ansys workbench 14.0

Non-Isothermal Fluid Flow in a Continuous Casting Tundish

Temperature variation phenomena observed inside the metallurgical tundish in the continuous casting is principally due to several factors, high temperature of the ladle metal jet, important thermal losses, heat transfer between molten steel and tundish walls and more still, in contact with the slag layer at bath surface and if necessary cooling or warming in refining composition operations. A numerical simulation using the CFD code “Fluent” is realised. Investigation of heat transfer—which has a great importance in the natural convection and the inclusions floating at slag surface—, is proposed. Results are presented for three arrangements of the tundish, where the interest and role of the control devices is improved.Copyright