Heat Transfer with Chemical Reaction in Wall Heated Packed Bed Reactor

2014 ◽  
Vol 625 ◽  
pp. 722-725
Author(s):  
Duvvuri Subbarao ◽  
Reem Hassan Abd Elghafoor Hassan ◽  
Marappagounder Ramasamy
Keyword(s):  
Heat Transfer ◽  
Model Equation ◽  
Packed Bed ◽  
Packed Bed Reactor ◽  
Wall Heat Transfer ◽  
Transfer Coefficients ◽  
Exothermic Reactions ◽  
Packed Bed Reactors ◽  
Heat Transfer Coefficients ◽  
Endothermic Reactions

Information on wall heat transfer to packed bed reactors operating with exothermic or endothermic reactions is scarce. Overall wall heat transfer coefficients in a packed bed reactor in presence of an endothermic reaction are measured and observed to be smaller than the expected in the absence of reaction. This observation is in contrast with the reported observations with exothermic reactions in packed beds. A model equation based on energy balance is presented to explain the observations.

A Network-of-Voids Model to Assess Wall Flow Patterns and Heat Transfer for Low Aspect Ratio Packed-Bed Reactors

2008 ◽  
Vol 6 (1) ◽  
Author(s):  
Peter I Chigada ◽  
Reginald Mann
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Fluid Flows ◽  
Packed Bed ◽  
Wall Heat Transfer ◽  
Transfer Coefficients ◽  
Catalytic Reactors ◽  
Heat Transfer Coefficients ◽  
Low Aspect Ratio ◽  
Random Placement

Exothermic packed bed catalytic reactors are usually characterised by a low diameter-aspect ratio to facilitate heat transfer. In operation, these reactors often exhibit localized regions with much higher temperatures referred to as hot spots. A new model based on a 2-D network-of voids (NoV) has been devised to explore wall heat transfer behaviour for such low aspect ratio packed tubes. Random placement of (packing) particles is used to provide a simple NoV framework for implicitly creating the tortuous fluid flows amongst the resulting randomized inter-connecting voids. This is a computationally tractable strategy for exploring the haphazard appearance of individual tube pin-hole burn-outs amongst the typically thousands, or tens of thousands, of tubes within high temperature industrial multi-tubular configurations. Although presently limited to 2-D, the model captures many natural features of the flow and heat transfer of randomly packed tubes, especially huge variations in wall and cross flows and consequently massive variations in local wall heat transfer coefficients along the length of individual tubes. The model is potentially superior to those based upon averaged properties, which do not properly distinguish the solid and fluid phases. The network-of-voids concept is readily extended to 3-D, in order to achieve geometric congruence of the model and assemblies of individual particles.

scholarly journals Experimental Heat Transfer Investigation of Stationary and Orthogonally Rotating Asymmetric and Symmetric Heated Smooth and Turbulated Channels

1992 ◽  
Author(s):  
H. A. El-Husayni ◽  
M. E. Taslim ◽  
D. M. Kercher
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Rotation Number ◽  
Symmetric Case ◽  
Wall Heat Flux ◽  
Heated Wall ◽  
Wall Heat Transfer ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Smooth Channel

An experimental investigation was conducted to determine the effects of variations in wall thermal boundary conditions on local heat transfer coefficients in stationary and orthogonally rotating smooth wall and two opposite-wall turbulated square channels. Results were obtained for three distributions of uniform wall heat flux: asymmetric, applied to the primary wall only; symmetric, applied to two opposite walls only; and fully-symmetric, applied to all four channel walls. Measured stationary and rotating smooth channel average heat transfer coefficients at channel location L/Dh = 9.53 were not significantly sensitive to wall heat flux distributions. Trailing side heat transfer generally increased with Rotation number whereas the leading wall results showed a decreasing trend at low Rotation numbers to a minimum and then an increasing trend with further increase in Rotation number. The stationary turbulated wall heat transfer coefficients did not vary markedly with the variations in wall heat flux distributions. Rotating leading wall heat transfer decreased with Rotation number and showed little sensitivity to heat flux distributions except for the fully-symmetric heated wall case at the highest Reynolds number tested. Trailing wall heat transfer coefficients were sensitive to the thermal wall distributions generally at all Reynolds numbers tested and particularly with increasing Rotation number. While the asymmetric case showed a slight deficit in trailing wall heat transfer coefficients due to rotation, the symmetric case indicated little change whereas the fully-symmetric case exhibited an enhancement.

scholarly journals Heat transfer in fluidized and fixed beds of adsorption chillers

2019 ◽  
Vol 128 ◽  
pp. 01003 ◽  
Author(s):  
Jaroslaw Krzywanski ◽  
Karolina Grabowska ◽  
Marcin Sosnowski ◽  
Anna Zylka ◽  
Anna Kulakowska ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Fluidized Bed ◽  
Fluidized Beds ◽  
Fixed Bed ◽  
Wall Heat Transfer ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Innovative Idea ◽  
Fixed Beds

An innovative idea, shown in the paper constitutes in the use of the fluidized bed of sorbent, instead of the conventional, fixed-bed, commonly used in the adsorption chillers. Bed–to–wall heat transfer coefficients for fixed and fluidized beds of adsorbent are determined. Sorbent particles diameters and velocities of fluidizing gas are discussed in the study. The calculations confirmed, that the bed–to–wall heat transfer coefficient in the fluidized bed of adsorbent is muchhigher than that in a conventional bed.

Split Flow Modified Packed Bed Reactor for Cobalt Oxide Based High-Temperature TCES Systems

2019 ◽  
Author(s):  
Nasser Vahedi ◽  
Alparslan Oztekin
Keyword(s):  
Heat Transfer ◽  
High Temperature ◽  
Pressure Drop ◽  
Energy Density ◽  
Redox Reaction ◽  
Packed Bed ◽  
Packed Bed Reactor ◽  
Flow Ratio ◽  
Packed Bed Reactors ◽  
Split Flow

Abstract The new generation of Concentrated Solar Power (CSP) plants requires high temperature and high energy density storage system with good cyclic stability. The potential solution satisfying such requirements is the thermochemical energy storage (TCES) using gas-solid redox reaction. Design of efficient storage reactor is very critical for applications of such storage systems. Packed bed reactors have a simpler design with no moving components and are more cost-effective compared to other available moving bed design configurations while having high-pressure drop is their main drawback. Any improvement in the pressure drop makes the design more suitable for commercial applications, especially at high temperature operating conditions. Cobalt oxide redox reaction has been considered for this study because of its unique features, especially high enthalpy of reaction (energy density) and high reaction temperature. A rectangular cross-section packed bed reactor with a large aspect ratio is selected as a reference conventional packed bed reactor. The novel split-flow packed bed reactor design configuration is proposed in which a portion of heat transfer fluid is passed through adjacent side channels. The split flow ratio of 1/3 has been considered for the case study. The transient two-dimensional numerical model is developed for solving mass, momentum, and energy equations for both gas and solid phases using suitable reaction kinetics for the reversible reduction and re-oxidation process. Complete storage cycle, including both the charging and discharging mode, has been simulated using finite element method. The split flow design performance is compared with the reference case considering the same size of the reaction bed. It is shown that the conversion time is increased while the pressure drop reduced below half of the pressure loss of the conventional design. Reduced mass flow rate passing through the bed results in considerable improvement in required pressure work with a penalty of storage performance. Further study is needed to optimize the split flow ratio and the surface heat transfer characteristics of the bed. The proposed design configuration could be a breakthrough in packed bed reactors, especially for high-temperature storage applications.

New Approach to Determine the Heat+transfer Coefficients for Cooling Tower Packing

1989 ◽  
Vol 203 (2) ◽  
pp. 75-84 ◽  
Author(s):  
M A Younis
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Cooling Tower ◽  
Empirical Relationship ◽  
Packed Bed ◽  
Transfer Coefficients ◽  
Water Contact ◽  
Heat Transfer Coefficients ◽  
Tower Packing

The heat input response technique was developed to determine the heat-transfer coefficients for a forced draught cooling tower packing. The method was applied to a counter current type air-water contact system in a packed bed. A temperature change was alternately imposed on inlet air at the tower bottom and on inlet water at the tower top. Outlet temperatures of air and water were measured with time. From zeroth moments of these temperature changes, water-film and air-film heat-transfer coefficients have been estimated. Finally, the effect of the water/air loading ratio and the packing material, such as wood, aluminium wire netting and plastic PVC on the values of the heat-transfer coefficients was experimentally tested. An empirical relationship between the gas-side heat-transfer coefficient, liquid-side heat-transfer coefficient and water/gas ratio has been established within the range of the tested data.

Local and average interphase heat transfer coefficients in a randomly packed bed of spheres

AIChE Journal ◽  
1968 ◽  
Vol 14 (3) ◽  
pp. 483-490 ◽  
Author(s):  
Bernard M. Gillespie ◽  
Edward D. Crandall ◽  
James J. Carberry
Keyword(s):  
Heat Transfer ◽  
Packed Bed ◽  
Transfer Coefficients ◽  
Interphase Heat Transfer ◽  
Heat Transfer Coefficients

scholarly journals CONSIDERING THE ISSUE OF RENOVATING PUBLIC BUILDINGS WITH REFERENCE TO IN-KIND INVESTIGATIONS INTO WALL HEAT TRANSFER COEFFICIENTS / VISUOMENINIŲ PASTATŲ ATNAUJINIMO PROBLEMOS NAGRINĖJIMAS REMIANTIS NATŪRINIAIS SIENŲ ŠILUMOS PERDAVIMO KOEFICIENTŲ TYRIMAIS

2013 ◽  
Vol 5 (2) ◽  
pp. 82-91 ◽  
Author(s):  
Robertas Volvačiovas ◽  
Zenonas Turskis ◽  
Česlovas Ignatavičius ◽  
Leonas Ustinovičius ◽  
Audrius Ruzgys
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Hot Water ◽  
Wall Heat Transfer ◽  
Transfer Coefficients ◽  
Public Buildings ◽  
Heat Transfer Coefficients ◽  
Before And After ◽  
The Heat Transfer Coefficient

This article raises the problem of high energy consumption stimulated by heating buildings and preparing hot water. The paper shortly revises the state of renovating public buildings in Lithuania. A number of scientists devote close attention to examining various aspects of building renovation (technical regulations on constructions, subsidies provided by the state, cost-effectiveness, factors influencing building renovation, etc.). The article presents a few studies by foreign scientists, lists factors that determine public building renovation (unsatisfactory indoor air hygiene and floor temperature, indoor relative humidity, indoor air velocity, indoor carbon dioxide concentration, physical deterioration of a large building, poor aesthetic appearance of the building, etc.) and demonstrates a few practical examples. In accordance with Lithuanian design codes, a methodology for determining heat transfer coefficients in public buildings is provided. Besides, investigations into heat transfer coefficients before and after the renovation of public buildings have been conducted. A few nursery school buildings in Lithuania have been examined applying laboratory equipment before and after renovation. It was found that the wall heat transfer coefficient of properly designed and insulated buildings falls by more than 4–5 times to reach the normal value of the heat transfer coefficient (value of the heat transfer coefficient falls from 1.12 to 0.22 W/(m2·K)). A comparison of an external thermal insulation plastering composite system with an external aeration heat-insulated system has been done. The estimation has revealed that due to lower costs, better results of thermal resistance obtained using the external thermal insulation plastering composite system can produce better wall heat transfer coefficient values. The obtained results have been determined referring to better wall insulation tightness. The paper also summarizes data on heating buildings and consumption of prepared hot water before and after renovation. On the basis of the findings acquired employing the degree-day–method, public building energy consumption for heating and hot water preparation decreased from 41.30 to 43.73%. Santrauka Straipsnyje trumpai apžvelgta pastatų energinio efektyvumo problematika, visuomeninių pastatų atnaujinimo situacija Lietuvoje, pateikiami keli užsienio valstybių mokslininkų darbų, kuriuose nagrinėjama pastatų atnaujinimo tematika, pavyzdžiai. Be praktinių pavyzdžių, nurodomi veiksniai, lemiantys visuomeninės paskirties pastatų atnaujinimą. Taip pat pateikiami visuomeninės paskirties pastatų sienų šilumos perdavimo koeficientų tyrimų, atliktų naudojant laboratorinę įrangą, rezultatai, ištyrus kelis visuomeninės paskirties pastatus Lietuvoje prieš ir po pastatų atnaujinimo. Palyginta išorinė tinkuojama sudėtinė termoizoliacinė sistema su išorine vėdinamąja termoizoliacine sistema, apibendrinta nagrinėjamų pastatų sąnaudų šildyti ir karštam vandeniui ruošti ekonominė nauda prieš ir po pastatų atnaujinimo taikant dienolaipsnių metodiką.

Sign in / Sign up

Export Citation Format

Share Document