Energy Efficient Refrigerators: The Effect of Door Gasket and Wall Insulation on Heat Transfer

2003 ◽  
Author(s):  
Mir-Akbar Hessami ◽  
Arnd Hilligweg
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Energy Efficiency ◽  
Power Consumption ◽  
Thermal Efficiency ◽  
Air Temperatures ◽  
Insulation Thickness ◽  
Two Stages ◽  
Experimental Rig ◽  
The Doors

The energy efficiency of refrigerators not only depends on the efficiency of the various components used in the cycle but also on their thermodynamics cycle efficiency as well the thermal efficiency of the cabinet housing the components. Efficiency improvements to the thermodynamics cycle and refrigerator components have been the subject of various papers published in the open literature. Not many researchers have looked at reducing the heat leakage into the refrigerator cabinet with the explicit objective of reducing the power consumption of the unit and hence improving its thermal efficiency. This paper is based on an experimental study of this topic, and includes information on the experimental rig used and the results obtained. This research was performed in two stages: The first stage was focused on improving the energy efficiency by changing wall insulation while the second stage was to study the heat transfer through the doors’ gaskets. For the first part, a domestic refrigerator was instrumented with many thermocouples and heat flux meters to measure the inside and outside air temperatures and the heat transfer through the wall of the unit, respectively. These measurements were taken under different environmental conditions as well as different insulation thickness in the walls of the cabinet. For the second part, using a specially designed and manufactured experimental rig, various door gaskets were placed between a warm and a cold chamber and heat transfer through the gasket was measured. The results showed that by adding 30 mm polystyrene insulation to the walls of the refrigerator, the heat transfer through the walls reduced by around 35%. The power consumption data agreed very well with the measured heat flux through the walls. The percentage heat transfer through the doors’ gaskets was confirmed to be about 13% of the total heat transferred into the unit.

High Flux Microscale Solar Thermal Receiver for Supercritical Carbon Dioxide Cycles

2015 ◽  
Author(s):  
Thomas L’Estrange ◽  
Eric Truong ◽  
Charles Rymal ◽  
Erfan Rasouli ◽  
Vinod Narayanan ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Carbon Dioxide ◽  
Heat Flux ◽  
Supercritical Carbon Dioxide ◽  
Surface Temperature ◽  
Thermal Efficiency ◽  
Solar Thermal ◽  
Fluid Temperature ◽  
Thermal Receiver ◽  
Supercritical Carbon

Characterization of a microchannel solar thermal receiver for a supercritical carbon dioxide (sCO2) is presented. The receiver design is based on conjugate computational fluid dynamics and heat transfer simulations as well as thermo-mechanical stress analysis. Two receivers are fabricated and experimentally characterized — a parallel microchannel design and a microscale pin fin array design. Lab-scale experiments have been used to demonstrate the receiver integrity at the design pressure of 125 bar at 750°C surface temperature. A concentrated solar simulator was designed and assembled to characterize the thermal performance of the lab scale receiver test articles. Results indicate that, for a fixed exit fluid temperature of 650°C, increase in incident heat flux results in an increase in receiver and thermal efficiency. At a fixed heat flux, efficiency decreased with an increase in receiver surface temperature. The ability to absorb flux of up to 100 W/cm2 at thermal efficiency in excess of 90 percent and exit fluid temperature of 650°C using the microchannel receiver is demonstrated. Pressure drop for the pin array at the maximum flow rate for heat transfer experiments is less than 0.64 percent of line pressure.

Thermal Performance of a Receiver Tube for a High Concentration Ratio Parabolic Trough System and Potential for Improved Performance With Syltherm800-CuO Nanofluid

2015 ◽  
Author(s):  
Aggrey Mwesigye ◽  
Zhongjie Huan ◽  
Josua P. Meyer
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Thermal Performance ◽  
Thermal Efficiency ◽  
Concentration Ratio ◽  
Low Flow ◽  
Fluid Temperature ◽  
Parabolic Trough ◽  
High Concentration ◽  
Flow Rates

In this paper, the thermal performance of a high concentration ratio parabolic trough system and the potential for improved thermal performance using Syltherm800-CuO nanofluid were investigated and presented. The parabolic trough system considered in this study has a concentration ratio of 113 compared with 82 in current commercial systems. The heat transfer fluid temperature was varied between 350 K and 650 K and volume fractions of nanoparticle were in the range 1–6%. Monte-Carlo ray tracing was used to obtain the actual heat flux on the receiver’s absorber tube. The obtained heat flux profiles were subsequently coupled with a computational fluid dynamics tool to investigate the thermal performance of the receiver. From the study, the results show that with increased concentration ratios, receiver thermal performance degrades, with both the receiver heat loss and the absorber tube circumferential temperature differences increasing, especially at low flow rates. The results further show that the use of nanofluids significantly improves receiver thermal performance. The heat transfer performance increases up to 38% while the thermal efficiency increases up to 15%. Significant improvements in receiver thermal efficiency exist at high inlet temperatures and low flow rates.

scholarly journals ANALISIS PASOKAN PANAS PADA PRODUKSI HIDROGEN PROSES STEAM REFORMING KONVENSIONAL DAN NUKLIR

2015 ◽  
Vol 17 (1) ◽  
pp. 11 ◽  
Author(s):  
Siti Alimah ◽  
Djati Hoesen Salimy
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Hydrogen Production ◽  
Natural Gas ◽  
Steam Reforming ◽  
Thermal Efficiency ◽  
Energy Supply ◽  
Nuclear Energy ◽  
Fossil Fuels ◽  
Temperature And Pressure

ABSTRAK ANALISIS PASOKAN PANAS PADA PRODUKSI HIDROGEN PROSES STEAM REFORMING KONVENSIONAL DAN NUKLIR. Telah dilakukan analisis pasokan energi panas pada produksi hidrogen dengan proses steam reforming gas alam. Tujuan studi adalah untuk memahami sistem pasokan energi panas konvensional dan dengan nuklir. Metodologi yang digunakan adalah kajian literatur dan analisis berdasar perbandingan. Hasil studi menunjukkan bahwa proses dengan sumber panas bahan bakar fosil (gas alam) mampu memberikan kondisi operasi optimum temperatur 850-900oC dan tekanan 2-3 MPa, serta dengan perpindahan panas didominasi oleh perpindahan panas radiasi, sehingga fluks panas yang dapat dicapai pada tabung katalisator relatif tinggi (50-80 kW/m2) dan menghasilkan efisiensi thermal yang tinggi yaitu sekitar 85%. Sedang pada sistem dengan energi nuklir, karena tuntutan keselamatan, proses beroperasi pada kondisi yang kurang optimum temperatur 800-850oC dan tekanan 4,5 MPa, serta dengan perpindahan panas didominasi oleh perpindahan panas konveksi, sehingga fluks panas yang dapat dicapai pada tabung katalisator jauh lebih rendah (10-20 kW/m2) dan menghasilkan efisiensi thermal yang rendah sekitar 50%. Modifikasi reformer dan utilisasi panas mampu meningkatkan fluks panas sampai 40 kW/m2 sehingga efisiensi thermal dapat mencapai 78%. Meskipun demikian, aplikasi energi nuklir untuk produksi hidrogen dengan proses steam reforming mampu menghemat pembakaran bahan bakar fosil yang berimplikasi pada potensi penurunan laju emisi CO2 ke lingkungan. Kata kunci: produksi hidrogen, steam reforming, reformer, HTGR ABSTRACT HEAT SUPPLY ANALYSIS OF STEAM REFORMING HYDROGEN PRODUCTION PROCESS IN CONVENTIONAL AND NUCLEAR. The analysis of heat energy supply in the production of hydrogen by natural gas steam reforming process has been done. The aim of the study is to compare the energy supply system of conventional and nuclear heat. Methodology used in this study is an assessment of literature and analysis based on the comparisons. The study shows that the heat sources of fossil fuels (natural gas) is able to provide optimum operating conditions of temperature and pressure of 850-900oC and 2-3 MPa, as well as the heat transfer is dominated by radiation heat transfer, so that the heat flux that can be achieved on the catalyst tube relatively high (50-80 kW/m2) and provide high thermal efficiency of about 85%. While in the system with nuclear energy, due to the demands of safety, process operating at less than optimum conditions of temperature and pressure of 800-850oC and 4.5 MPa, as well as the heat transfer is dominated by convection heat transfer, so that the heat flux that can be achieved catalyst tube is relatively low (10- 20 kW/m2) and it provides a low thermal efficiency of about 50%. Modifications of reformer and heat utilization can increase the heat flux up to 40 kW/m2 so that the thermal efficiency can reach 78%. Nevertheless, the application of nuclear energy to hydrogen production with steam reforming process is able to reduce the burning of fossil fuels which has implications for the potential decrease in the rate of CO2 emissions into the environment. Keywords: hydrogen production, steam reforming, reformer, HTGR 

Quasi Two-Dimensional Cyclone-Jet Cooling Configuration: Evaluation of Heat Transfer and Pressure Losses

2001 ◽  
Author(s):  
Artem A. Khalatov ◽  
Nick Syred ◽  
Philip J. Bowen ◽  
Rashed Al-Ajmi
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Stagnation Point ◽  
Thermal Efficiency ◽  
Leading Edge ◽  
Swirl Flow ◽  
Hydraulic Performance ◽  
Two Dimensional ◽  
Pressure Losses ◽  
Cyclone Chamber

Heat transfer and pressure losses have been studied in a cyclone-jet chamber to evaluate its the thermal efficiency and thermal-hydraulic performance. The cyclone chamber simulates the leading edge area, it is 4.2 mm in diameter and 35 mm long and has four injecting and five discharging round-shaped holes evenly spread and facing the chamber stagnation point. Such a configuration generates a quasi two-dimensional swirl flow pattern accompanied with flow separation effects. Three test sections with various inlet and outlet hole diameter have been studied to evaluate the effect of boundary conditions. The Heating in Melted Metal (HMM) experimental technique has been employed to measure heat transfer parameters. The local spanwise heat flux distribution has a periodical characteristic with a maximum opposite the injecting holes and a minimum in between them. The non-uniformity of the heat flux depends on the diameter of inlet holes and the air mass flow rate. The angular distribution of an averaged spanwise heat transfer is asymmetrical with respect to the chamber stagnation point; it is either actually a ‘flat curve’ or has a maximum at the stagnation point. An average heat transfer in the cyclone chamber is 2.61 – 3.54 higher compared with its axial counterpart. The basic heat transfer correlations are presented in addition to the thermal efficiency and thermal-hydraulic performance evaluation made. The proposed cyclone-jet design is as good as a serpentine cyclone cooling and some advanced cooling techniques, but more simple production technology is an undoubted advantage of this configuration.

scholarly journals Numerical Modelling of a Photovoltaic Thermal (PV/T) System Using Nanofluid With Parallel Flow Thermal Absorber

2021 ◽  
Vol 945 (1) ◽  
pp. 012013
Author(s):  
J. Kubenthiran ◽  
S. Baljit ◽  
A. S. Tijani ◽  
Z. A. K. Baharin ◽  
M.F. Remeli ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Energy Efficiency ◽  
Thermal Efficiency ◽  
Pure Water ◽  
Fluid Velocity ◽  
Parallel Flow ◽  
Working Fluid ◽  
Volume Percentage ◽  
Electrical Efficiency ◽  
T System

Abstract In the present study, a numerical model of photovoltaic thermal (PV/T) system using alumina (Al2O3) nanofluid, and pure water are used as working fluid. The proposed PV/T model consists of parallel riser tubes that are connected to two header tubes and it is attached to an absorber plate to simulate the conduction and convection heat transfer mechanism of a conventional PV/T system. The energy efficiency of the PV/T model is analyzed by varying the solar radiation (Heat Flux), inlet fluid velocity, and the volume percentage of the nanofluids. The numerical simulation is performed by using a conjugate heat transfer method with a computational fluid dynamics (CFD) software. According to the simulation data, the energy efficiency and the heat transfer coefficient of the PV/T system increased by increasing the inlet fluid velocity. In comparison with water, alumina nanofluid showed better thermal and electrical efficiency due to its high thermal conductivity. The thermal efficiency increased by 5.55% for alumina, compared to pure water and the electrical efficiency increased by 0.15% for alumina. Moreover, the effect of inlet fluid velocity ranging from 0.04m/s to 0.2m/s was also evaluated, and the results showed that the increase in thermal efficiency for pure water and alumina are 18.15% and 25.77%, respectively. Subsequently, the electrical efficiency increased by 0.52% and 0.56% for pure water and alumina using the new parallel flow thermal absorber, respectively.

THE MECHANISM OF RAISING AND QUANTIFICATION OF SPECIFIC HEAT FLUX AT BOILING OF NANOFLUIDS IN FREE CONVECTION CONDITIONS

2017 ◽  
pp. 25-34
Author(s):  
V.N. Moraru
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Capacity ◽  
Specific Heat ◽  
Chemical Properties ◽  
Heating Surface ◽  
Physical Models ◽  
Superheated Liquid ◽  
Two Phase ◽  
Boiling Process

The results of our work and a number of foreign studies indicate that the sharp increase in the heat transfer parameters (specific heat flux q and heat transfer coefficient _) at the boiling of nanofluids as compared to the base liquid (water) is due not only and not so much to the increase of the thermal conductivity of the nanofluids, but an intensification of the boiling process caused by a change in the state of the heating surface, its topological and chemical properties (porosity, roughness, wettability). The latter leads to a change in the internal characteristics of the boiling process and the average temperature of the superheated liquid layer. This circumstance makes it possible, on the basis of physical models of the liquids boiling and taking into account the parameters of the surface state (temperature, pressure) and properties of the coolant (the density and heat capacity of the liquid, the specific heat of vaporization and the heat capacity of the vapor), and also the internal characteristics of the boiling of liquids, to calculate the value of specific heat flux q. In this paper, the difference in the mechanisms of heat transfer during the boiling of single-phase (water) and two-phase nanofluids has been studied and a quantitative estimate of the q values for the boiling of the nanofluid is carried out based on the internal characteristics of the boiling process. The satisfactory agreement of the calculated values with the experimental data is a confirmation that the key factor in the growth of the heat transfer intensity at the boiling of nanofluids is indeed a change in the nature and microrelief of the heating surface. Bibl. 20, Fig. 9, Tab. 2.

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