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.

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.

scholarly journals EXPERIMENTAL STUDY ON BED-TO-TUBE HEAT TRANSFER COEFFICIENTS IN BUBBLING FLUIDIZED BED

2021 ◽  
Vol 15 (2) ◽  
pp. 139-149
Author(s):  
Bamiji Zacheous Adewole
Keyword(s):  
Heat Transfer ◽  
Particle Size ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Fluidized Bed ◽  
Particle Sizes ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Bubbling Fluidized Bed ◽  
Coconut Shells

The overall bed-to-tube heat transfer coefficients of the blends of Lafia-obi coal and coconut shells have been investigated in a bubbling fluidized bed combustor. Experiments were performed at five different particle sizes of coal (5, 10, 15, 20 and 25 mm) and five different particle sizes of coconut shells (2, 6, 10,14 and 18 mm) for different blend proportions of 10%, 20%, 30%, 40% and 50%. Results obtained showed that the overall bed-to-tube heat transfer coefficient decreased with increasing coconut shell particle size in the blends. Combined effects of high radiation from large particle size of coal (25 mm) and high convection heat from small particle size of coconut shell (2 mm) at blend proportion of 10 and 50% produced the maximum bed-to-tube heat transfer coefficient. Due to the importance of heat exchange in the fluidized bed, it is observed that the contribution of biomass co-firing with coal is significant, hence, co-firing at optimal particle size and biomass blend ratio is imperative for achieving higher bed-to-tube heat transfer in the fluidized bed boiler.

scholarly journals Systematic heat transfer measurements in highly viscous binary fluids

2021 ◽  
Author(s):  
Ann-Christin Fleer ◽  
Markus Richter ◽  
Roland Span
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Volatile Component ◽  
Test Tube ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Low Viscosity ◽  
The Heat Transfer Coefficient

AbstractInvestigations of flow boiling in highly viscous fluids show that heat transfer mechanisms in such fluids are different from those in fluids of low viscosity like refrigerants or water. To gain a better understanding, a modified standard apparatus was developed; it was specifically designed for fluids of high viscosity up to 1000 Pa∙s and enables heat transfer measurements with a single horizontal test tube over a wide range of heat fluxes. Here, we present measurements of the heat transfer coefficient at pool boiling conditions in highly viscous binary mixtures of three different polydimethylsiloxanes (PDMS) and n-pentane, which is the volatile component in the mixture. Systematic measurements were carried out to investigate pool boiling in mixtures with a focus on the temperature, the viscosity of the non-volatile component and the fraction of the volatile component on the heat transfer coefficient. Furthermore, copper test tubes with polished and sanded surfaces were used to evaluate the influence of the surface structure on the heat transfer coefficient. The results show that viscosity and composition of the mixture have the strongest effect on the heat transfer coefficient in highly viscous mixtures, whereby the viscosity of the mixture depends on the base viscosity of the used PDMS, on the concentration of n-pentane in the mixture, and on the temperature. For nucleate boiling, the influence of the surface structure of the test tube is less pronounced than observed in boiling experiments with pure fluids of low viscosity, but the relative enhancement of the heat transfer coefficient is still significant. In particular for mixtures with high concentrations of the volatile component and at high pool temperature, heat transfer coefficients increase with heat flux until they reach a maximum. At further increased heat fluxes the heat transfer coefficients decrease again. Observed temperature differences between heating surface and pool are much larger than for boiling fluids with low viscosity. Temperature differences up to 137 K (for a mixture containing 5% n-pentane by mass at a heat flux of 13.6 kW/m2) were measured.

Experimental Study of Evaporation Heat Transfer Characteristics and Pressure Drops of R410A and R134a in a Multiport Mini-Channel

2009 ◽  
Author(s):  
Jatuporn Kaew-On ◽  
Somchai Wongwises
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Transfer Coefficients ◽  
Pressure Drops ◽  
Heat Transfer Coefficients ◽  
Evaporation Heat ◽  
Evaporation Heat Transfer ◽  
R 134A

The evaporation heat transfer coefficients and pressure drops of R-410A and R-134a flowing through a horizontal-aluminium rectangular multiport mini-channel having a hydraulic diameter of 3.48 mm are experimentally investigated. The test runs are done at refrigerant mass fluxes ranging between 200 and 400 kg/m2s. The heat fluxes are between 5 and 14.25 kW/m2, and refrigerant saturation temperatures are between 10 and 30 °C. The effects of the refrigerant vapour quality, mass flux, saturation temperature and imposed heat flux on the measured heat transfer coefficient and pressure drop are investigated. The experimental data show that in the same conditions, the heat transfer coefficients of R-410A are about 20–50% higher than those of R-134a, whereas the pressure drops of R-410A are around 50–100% lower than those of R-134a. The new correlations for the evaporation heat transfer coefficient and pressure drop of R-410A and R-134a in a multiport mini-channel are proposed for practical applications.

Calculation of Hourly Output of a Solar Still

1993 ◽  
Vol 115 (4) ◽  
pp. 231-236 ◽  
Author(s):  
V. B. Sharma ◽  
S. C. Mullick
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Balance ◽  
Solar Still ◽  
Balance Equations ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Hourly Output ◽  
The Heat Balance

An approximate method for calculation of the hourly output of a solar still over a 24-hour cycle has been studied. The hourly performance of a solar still is predicted given the values of the insolation, ambient temperature, wind heat-transfer coefficient, water depth, and the heat-transfer coefficient through base and sides. The proposed method does not require graphical constructions and does not assume constant heat-transfer coefficients as in the previous methods. The possibility of using the values of the heat-transfer coefficients for the preceding time interval in the heat balance equations is examined. In fact, two variants of the basic method of calculation are examined. The hourly rate of evaporation is obtained. The results are compared to those obtained by numerical solution of the complete set of heat balance equations. The errors from the approximate method in prediction of the 24-hour output are within ±1.5 percent of the values from the numerical solution using the heat balance equations. The range of variables covered is 5 to 15 cms in water depth, 0 to 3 W/m2K in a heat-transfer coefficient through base and sides, and 5 to 40 W/m2K in a wind heat-transfer coefficient.

The Measurement of Full-Surface Internal Heat Transfer Coefficients for Turbine Airfoils Using a Non-Destructive Thermal Inertia Technique

2002 ◽  
Author(s):  
Nirm V. Nirmalan ◽  
Ronald S. Bunker ◽  
Carl R. Hedlung
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
External Surface ◽  
Internal Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Turbine Airfoils ◽  
Non Destructive ◽  
Internal Heat Transfer

A new method has been developed and demonstrated for the non-destructive, quantitative assessment of internal heat transfer coefficient distributions of cooled metallic turbine airfoils. The technique employs the acquisition of full-surface external surface temperature data in response to a thermal transient induced by internal heating/cooling, in conjunction with knowledge of the part wall thickness and geometry, material properties, and internal fluid temperatures. An imaging Infrared camera system is used to record the complete time history of the external surface temperature response during a transient initiated by the introduction of a convecting fluid through the cooling circuit of the part. The transient data obtained is combined with the cooling fluid network model to provide the boundary conditions for a finite element model representing the complete part geometry. A simple 1D lumped thermal capacitance model for each local wall position is used to provide a first estimate of the internal surface heat transfer coefficient distribution. A 3D inverse transient conduction model of the part is then executed with updated internal heat transfer coefficients until convergence is reached with the experimentally measured external wall temperatures as a function of time. This new technique makes possible the accurate quantification of full-surface internal heat transfer coefficient distributions for prototype and production metallic airfoils in a totally non-destructive and non-intrusive manner. The technique is equally applicable to other material types and other cooled/heated components.

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.

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