Habib H. Al-Ali

On the effective heat transfer parameters in a packed bed

In this study, wall-to-fluid heat transfer coefficient h w and effective radial thermal conductivity k er have been determined for a packed bed with 4.5<d e /d p <7.5 in the region of 200<Re<1450. Two values of Nu based on the bulk as well as the extrapolated fluid temperature at the wall have been determined and compared.

A REVIEW OF NON-CONVENTIONAL METHODS FOR THE DESULFURIZATION OF RESIDUAL FUEL OIL

ABSTRACT Sulfur removal from residual fuel oil has received increasing attention in recent years mainly for the preparation of clean feedstocks for downstream conversion units and to meet the new specifications for petroleum products. This review presents discussion of non-conventional methods of fuel oil desulfurization other than hydrodesulfurization (HDS). These methods include oxidation, electrochemical, sodium, alkali, chemical treatment, and biodesulfurization.

Thermodynamic analysis of convective heat transfer in a packed duct with asymmetrical wall temperatures

Abstract Combination of the first and second law of thermodynamics has been utilized in analysing the convective heat transfer in a rectangular packed duct. Raschig ring type of packing in the air flow passage is used to enhance the heat transfer from uniformly heated front wall to air when the other walls are adiabatic. The packing increases wall to fluid heat transfer considerably, hence reduce the entropy generation due to the heat transfer across a finite temperature difference. However, the entropy generation due to fluid flow friction increases. The net entropy generations resulting from the above effects provide a new criterion in analysing the system. Using the Ergun equation for pressure drop estimation, an expression for the volumetric rate of entropy generation has been derived for a vertical 0.675 m long packed duct ( H/W = 0.31). This expression has been displayed graphically to show the influences of physical and geometric parameters on the entropy generation. Introduction of packing proves to be a thermodynamically sound augmentation technique of convective heat transfer.

Packing size and shape effects on forced convection in large rectangular packed ducts with asymmetric heating

An experimental and numerical investigation of fully developed forced convection in large rectangular packed ducts is presented. The horizontally oriented ducts have the length-to-separation distance ratio of L/H=16 with two aspect ratios of W/H=8 and 4. A constant heat flux is supplied to the top wall, while the bottom and side walls are insulated. Packing of hard polyvinyl chloride Raschig rings with outside diameters of 48 and 34 mm, and expanded polystyrene spheres with diameters of 48, 38 and 29 mm are used in the air flow passage. The experiments are carried out for 200 < (Rep=udp/nf) < 1450, and 4.5 < de/dp < 9.0. The pressure drop, the heat flux, axial and transverse temperature profiles of air flow inside the ducts are measured at the steady state. Similar experiments have also been carried out with empty ducts. Numerical predictions of two-dimensional quasi-homogeneous model are found to be in agreement with the experimental results of the packed ducts. The correlation equations for the Nusselt number are obtained. It is found that the introduction of packing into the air flow passage yields about a three times increase in the wall-to-air heat-transfer rate compared with that of the empty duct. # 1999 Elsevier

Enhancement of convection heat-transfer in a rectangular duct

Characteristics of wall-to-air heat transfer for a fully developed forced convection have been studied in a large rectangular packed duct with 160 cm heated length, 40 cm width, and for low bed equivalent diameter to particle diameter ratio. The separation distance between the top and bottom walls is 10 cm. A uniform heat flux is supplied at the top wall, while the bottom wall is insulated. Raschig rings in two and spherical packing in three sizes have been used in the air flow passage to investigate the enhancement of heat transfer due to packing. Temperature profiles for the steady and unsteady states have been measured. In modeling, the Ergun equation and energy equations are solved to calculate the temperature profile for the steady-state only. It has been found that the introduction of the packing into the air flow passage increases the wall-to-fluid heat transfer approximately three times compared with that of empty bed. This finding can enhance the rational use of energy from solar air heaters, chemical reactors, electronic cooling and many other engineering applications.

The design of an evaporator/absorber and thermodynamic analysis of a vapor absorption chiller driven by solar energy

An experimental absorption cooling system is being developed, driven by the heat generated by the solar energy collection system installed at Coventry University. The proposed absorption cooling system comprises an evaporator/absorber cell and a generator/condenser cell. These components are housed in evacuated glass cylinders to allow the processes involved to be observed. The refrigerant-absorbent pair used is water and Lithium Bromide since a low temperature heat source can be used to drive the refrigerant from the carrier fluid. A thermodynamic analysis of the absorption cooling cycle has been performed to study the effect of various operating conditions on the thermal performance. This paper presents the design of the evaporator/absorber cell and the results of the thermodynamic analysis.

Momentum and heat transfer in the entrance region of a parallel plate channel: developing laminar flow with constant wall temperature

A new integral method of solution is presented for developing laminar flow and heat transfer in the entrance region of a parallel plate channel with uniform surface temperature. Unlike earlier Karman-Pohlhausen analyses, the new analysis provides solutions which are free from jump discontinuities in the gradients of the velocity and temperature distributions throughout and at the end of the entrance region. The hydrodynamic and thermal results from the present analysis therefore join smoothly and asymptotically to their fully-developed values. The heat transfer results obtained are further found to agree well with previously published numerical solutions.

ENTROPY GENERATION OF CONVECTION HEAT TRANSFER IN AN ASYMMETRICALLY HEATED PACKED DUCT

An expression for the volumetric rate of entropy generation has been derived and displayed graphically to analyze the convection heat transfer for a fully established flow in a rectangular packed duct with L/H=16 and H/W=0.125. The top and bottom walls of the duct are heated by constant, asymmetric heat fluxes, while the other walls are insulated that is the L2 thermal boundary conditions. Entropy generation maps reveal the regions where excessive entropy generation occurs due to physical and geometric parameters for a specified task within the system.

SIMULTANEOUS DEVELOPMENT OF VELOCITY AND TEMPERATURE PROFILES IN THE ENTRANCE REGION OF A PARALLEL PLATE CHANNEL: LAMINAR FLOW WITH UNIFORM WALL HEAT FLUX

Available boundary layer type solutions to the combined hydrodynamic and thermal entrance region problem are known to exhibit a discontinuity in the gradients of the velocity and temperature distributions in the entrance region. A new solution is presented which alleviates this shortcoming. The new solution is based on the hydrodynamic inlet-filled region concept originally proposed by Ishizawa (1966) and later adopted by Mohanty and Das (1982) to hydrodynamically developing flow in a channel. This concept is extended to the combined entry length problem by dividing the thermal entrance length into two lengthwise regions, a thermal inlet region and a thermally filled region. In the former, the effect of heat transfer between fluid and wall is confined within the thermal boundary layer developing along the wall. At the end of the thermal inlet region, the thermal boundary layers meet at the duct axis but the temperature profile is not yet developed. In the thermally filled region, the heat effects propagat...

SIMULTANEOUSLY DEVELOPING LAMINAR FLOW AND HEAT TRANSFER IN THE ENTRANCE REGION OF A CIRCULAR TUBE WITH CONSTANT WALL TEMPERATURE

The developing flow and heat transfer in the entry region of a heated circular tube is analyzed for the case of constant wall temperature. An integral or boundary-layer solution is presented which has a number of advantages over earlier Karman-Pohlhausen integral analyses. Thus, in the present analysis, the velocity and temperature distributions, the local and mean drag coefficients, and the local and mean Nusselt numbers approach their fully-developed values asymptotically. The new analysis is based on the hydrodynamic inlet-filled region concept originally proposed by Ishizawa (1966) and later adopted by Mohanty and Asthana (1978) to flow through a circular tube. This concept is extended to the combined entry-length problem by introducing a thermal transition region, herein called the thermally-filled region, between the thermal inlet boundary-layer region and the thermally fully-developed region. A thermal shape factor is also introduced which ensures smooth transition of all pertinent thermal quantiti...