Comparative Analysis Between Water and Nanofluids as Working Fluids in Photovoltaic Thermal Collectors

2014 ◽  
Author(s):  
Bahy S. A. Abdel-Mesih ◽  
Ahmed A. Abdelrehim ◽  
Amr M. H. Khobeiz
Keyword(s):  
Heat Transfer ◽  
Comparative Analysis ◽  
Heat Exchange ◽  
Hybrid System ◽  
Exchange Process ◽  
Hot Water ◽  
Working Fluid ◽  
Working Fluids ◽  
Heat Transfer Augmentation ◽  
Heat Exchange Process

Photovoltaic thermal collectors (PV/T) are devices that produce both electrical and thermal energies simultaneously. Water acts as the working fluid that cools down the PV cells, thus improving their electrical efficiency, and at the same time hot water is produced due to the heat exchange process. As a consequence heat transfer augmentation is an important issue that affects the performance of such a hybrid system. The objective of the current study is to evaluate the effect of using a nanofluid on the performance of a photovoltaic thermal (PV/T) collector. The performance of the water cooled PV/T collector without nanofluid is first evaluated and then additional correlations are incorporated to include the nanofluid properties. Results showed that the use of nanofluid enhanced the rate of heat transfer which resulted in improvement in the performance of the PV/T collector. However, such improvement was not found to be significantly high to shift for nanofluids as working fluids in PV/T collectors.

scholarly journals Numerical analysis of heat exchange process in the biomass carbonisation reactor

2019 ◽  
Vol 252 ◽  
pp. 05019 ◽  
Author(s):  
Robert Zarzycki ◽  
Justyna Jędras
Keyword(s):  
Heat Transfer ◽  
Heat Exchange ◽  
Numerical Analysis ◽  
Exchange Process ◽  
Geometrical Model ◽  
Heating Time ◽  
Heating Process ◽  
Hot Air ◽  
Cyclic Operation ◽  
Heat Exchange Process

The study presents the problem of heat exchange in the biomass carbonisation reactor with cyclic operation. Based on the actual parameter of the biomass carbonisation reactor, a geometrical model was developed, and the computation of the heating process was conducted for two cases: an empty reactor and a filled reactor. Its result demonstrated that for the analysed configuration of the reactor, the process of heating biomass in the containers is limited by the capability of heat transfer to the biomass in the container. The results suggest opportunities for the improved heat exchange in the reactor and, accordingly, shortening heating time through installation of the system that forces circulation of hot air inside the reactor.

scholarly journals NOVEL TRENDS OF DEVELOPMENT AND PERFECTION THE MODERN HEAT EXCHANGERS

2019 ◽  
pp. 54-65
Author(s):  
B.S. Soroka
Keyword(s):  
Heat Transfer ◽  
Heat Exchange ◽  
Exchange Process ◽  
Combustion Products ◽  
Reynolds Analogy ◽  
Heat Exchange Equipment ◽  
Heat Exchange Process ◽  
Heat Transfer Phenomenon ◽  
Relative Change

Some actual aspects of advancement the problem of improvement the heat exchange equipment are considered in the paper. First of all the actual items related to middle and high temperature recuperators are discussed with proper up-to — date approaches. The classification of flue gases heat recovery appliances has been proposed along with the statement and analysis of the main characteristics of the recovery plants and option the ways of optimization the mentioned characteristics. The problem of Reynolds analogy (similarity of relative change the heat transfer phenomenon and variation the hydraulic resistance) within the channels of different purpose and of various cross-section supplied with and without the obstacles has been analyzed in application to separate cases of flow along the surfaces equipped with the cavities (dimples) or the convex elements. Thermal Performance Factor (TPF) of the heat exchange process is qualitatively like to Reynolds analogy factor and is highly depended upon rate of heat transfer and of friction factor in conditions of the scheme under consideration for flow over the surface or flow within the channel. The various media has been compared used as a working body in the heat exchanger’s channels: gaseous, liquid and the nanofluids, the last appeared in practice since 2000. Analysis has been carried out on effect of using the secondary energy emitters (SEE) arranged inside the tube channels, on resulting heat flux by heat exchange between outward flow of combustion products and the inner air flow. Bibl. 23, Fig. 6.

Semiempirical Method of Boiling Expectation Time Calculation in Falling Wavy Liquid Film

2012 ◽  
Vol 7 (3) ◽  
pp. 78-83
Author(s):  
Andrey Chernyavskiy ◽  
Aleksandr Pavlenko
Keyword(s):  
Heat Transfer ◽  
Heat Exchange ◽  
Thermal Conductivity Coefficient ◽  
Exchange Process ◽  
Semiempirical Method ◽  
Liquid Films ◽  
Wave Characteristics ◽  
Time Calculation ◽  
Heat Exchange Process ◽  
The Mathematical Model

The Mathematical model which allows to calculate boiling expectation times in falling wavy liquid films on nonsteady heat release has been represented. It has been shown that it is necessary to take a convective constituent of a heat transfer into account in heat exchange modeling in falling films. The effective thermal conductivity coefficient which invlolves a convective constituent of a heat transfer calculated from average wave characteristics using Vorontsov method has been used. The method of accounting of the wave moving influence on a heat exchange process has been presented. The comparison of results of a numerical simulation and experimental data has been done

scholarly journals Experimental Determination of the Influence of Shape on the Heat Transfer Process in a Crushed Granite Storage Bed

Energies ◽  
2020 ◽  
Vol 13 (24) ◽  
pp. 6725
Author(s):  
Magdalena Nemś
Keyword(s):  
Heat Transfer ◽  
Heat Exchange ◽  
Flow Rate ◽  
Exchange Process ◽  
Heat Transfer Analysis ◽  
Crushed Rock ◽  
Storage Material ◽  
Flow Rates ◽  
Actual Surface ◽  
Heat Exchange Process

The article presents the problem of modelling the charging of a constant-phase bed storage in the first hours of the process. The places of errors in the heat transfer calculations for the packed beds were indicated. Granite in the shape of spheres and crushed rocks, with a characteristic dimension of 50 mm, was used for the experimental tests. The material was subjected to tomographic examination and then used as a storage material. The charging process was carried out for three flow rates: 0.006, 0.008 and 0.010 m3/s. After three hours of testing, the temperature of the outlet air for the granite sphere as the storage material was the same as for the granite crushed rock. However, the biggest differences occurred after 1 h of charging. They were equal to: 40.4% for the flow rate of 0.006 m3/s, 22.0% for the flow rate of 0.008 m3/s, and 18.5% for the flow rate of 0.010 m3/s. The differences were greater than the uncertainty of the measurements. As a result, different temperatures of the storage material were obtained. After three hours, they were equal to: 25.2%, 12.3% and 8.6% for the lowest, medium, and highest airflow, respectively. The conducted heat transfer analysis and the relationship Nu = f(Re) was determined. The influence of the calculated and actual surface of the crushed rock on the heat exchange process was explained. For all the tested air flow rates through the bed, higher thermal parameters were obtained for the crushed rock than for the sphere. The maximum differences in the Nu number were: 222.6%, 151.4% and 161.3% for the flow of 0.006, 0.008 and 0.010 m3/s, respectively. This means that the description of the heat exchange process in the piled beds would require a parameter that takes into account the geometry of the storage material.

scholarly journals Analysis of the Issue of Recovery of Low-Potential Energy at Small-Scale Energy Facilities

2021 ◽  
Vol 19 (2) ◽  
pp. 100-106
Author(s):  
A. V. Dmitrenko ◽  
M. I. Kolpakov
Keyword(s):  
Heat Exchange ◽  
Potential Energy ◽  
Power Plants ◽  
Waste Heat ◽  
Organic Rankine Cycle ◽  
Hot Water ◽  
Working Fluid ◽  
Small Scale ◽  
Working Fluids ◽  
Heat Exchange Equipment

Studying the issues of recovery of low-potential energy at smallscale energy facilities allowed to show the promising character of the organic Rankine cycle (ORC) technology as a technology for recovery or conversion of low-potential energy.The most promising developments in the field of the use and recovery of waste heat are described regarding application of ORC, which is widely used in geothermal sources, hot water boilers, gas turbine plants. Due to the constantly growing diversity of working fluids, ORC can be used within a wide temperature range from 100°C to over 350°C. Also, developments are underway in the design of ORC generators to increase reliability of its individual system units, such as turbines and expanders. Based on the above factors, it can be concluded that with a deeper study of the problems of adopting ORC technologies, they can become a very promising direction in development of heat power engineering.It has been determined that the main factor hindering the widespread adoption of the ORC technology is associated with high cost of heat exchange equipment due to increased heat exchange surfaces. It is shown that design of mini power plants and energy centres based on the use of low-potential energy requires improvement of mathematical modelling methods to reliably determine operating modes and characteristics of each of the units. Methods for modelling evaporation and condensation systems, including turbines and expanders using organic low-boiling working fluids, should be considered among the methods that are highly sought after. The methods for selecting a working fluid for ORC devices also have a significant impact on characteristics of the installation determining the range of cycle operating temperatures and pressures. The solution of the above problems can lead to a reduction in the cost of heat exchange equipment, and, consequently, to a decrease in costs for design of ORC generators. 

scholarly journals PECULIARITIES OF THE THERMAL REGIME OF THE SURFACE SEDIMENTS IN LAKE TAPELIAI

2010 ◽  
Vol 2 (5) ◽  
pp. 66-70
Author(s):  
Anastasija Moisejenkova ◽  
Nikolaj Tarasiuk ◽  
Aloyzas Girgždys
Keyword(s):  
Heat Transfer ◽  
Heat Exchange ◽  
Bottom Sediments ◽  
Bottom Water ◽  
Surface Sediments ◽  
Exchange Process ◽  
Water Layer ◽  
Bottom Water Layer ◽  
Mineral Substances ◽  
Heat Exchange Process

The article discusses the process of heat transfer in the water sediment system having an impact on the input of nutrients and mineral substances from sediments to the bottom water layer. Therefore, conductivity sharply increases on the surface of bottom sediments and reaches more than 400 μS∙cm–1. The heat exchange process is analyzed in Lake Tapeliai classified as a “temporally warm” lake (see K. Kilkus). The paper defines heat transfer from bottom sediments to water applying the convection method and describes isotherm deepening of 4 ºC into sediments. The temperature of surface sediments in Lake Tapeliai was 3,3–3,9 ºC in 2007–2009, whereas the isotherm of 4 ºC slid 20–30 cm deeper to bottom sediments.

scholarly journals Mathematical model of heat transfer through a conductive pipe

2021 ◽  
Author(s):  
Eduard Marusic-Paloka ◽  
Matko Ljulj ◽  
Igor Pazanin ◽  
Josip Tambaca
Keyword(s):  
Heat Transfer ◽  
Mathematical Model ◽  
Heat Exchange ◽  
Asymptotic Analysis ◽  
Exchange Process ◽  
Heat Exchange Process ◽  
Effective Description

The standard engineer's model for heat transfer between the fluid flowing through the pipe and the exterior medium neglects the effects of the pipe's wall. The goal of this paper is to prove that they are not always negligible. Comparing the ratio between diffusivities of the fluid and the wall with the wall's thickness, using rigorous asymptotic analysis, we find five different models for effective description of the heat exchange process.

scholarly journals INTEGRATION OF THE HEAT PUMP HEAT EXCHANGE PROCESS FOR HOT WATER SUPPLY AND HEATING

2019 ◽  
Vol 41 (3) ◽  
pp. 41-44
Author(s):  
Yu.A. Selikhov ◽  
V.A. Kotsarenko ◽  
O.V. Kostenko
Keyword(s):  
Heat Exchange ◽  
Water Supply ◽  
Heat Pump ◽  
Exchange Process ◽  
Hot Water ◽  
Fuel Oil ◽  
Private House ◽  
Heat Exchange Process ◽  
Hot Water Supply ◽  
Automation Tools

A developed and implemented project of replacing a universal boiler with a fuel oil burner for a dual-circuit solar installation for hot water supply and a «ground-water» heat pump for heating a private house is presented. A system automation scheme has been developed using a workstation and technical automation tools have been selected.

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