Utilization of a Graphite Foam Radiator on a Natural Gas Engine-Driven Heat Pump

2002 ◽  
Author(s):  
R. D. Ott ◽  
A. Zaltash ◽  
J. W. Klett
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Pump ◽  
Gas Engine ◽  
Natural Gas Engine ◽  
Overall Heat Transfer Coefficient ◽  
Bulk Thermal Conductivity ◽  
Graphite Foam

A natural gas engine-driven heat pump was outfitted with a graphite foam radiator to demonstrate its thermal efficiency and compare it with that of a conventional radiator. A sequence of tests was performed with the graphite foam radiator operating in series with the standard aluminum radiator. Most aluminum air-to-water radiators exhibit an overall heat transfer coefficient up to 100 W/(m2·K). Laboratory experiments have demonstrated that a graphite foam radiator can achieve an overall heat transfer coefficient up to an order of magnitude larger. The mesophase pitch derived graphite foam is a material that offers excellent thermal management capability. The foam has an accessible surface area of 4 m2/g and an open cell structure with graphitic ligaments aligned parallel to the cell walls, giving it an overall bulk thermal conductivity of up to 175 W/(m·K). The bulk thermal conductivity of aluminum is 180 W/(m·K). The density of the graphite foam is a fifth of that of aluminum and its thermal diffusivity is three times greater than aluminum. These properties allow the graphite foam to be utilized in radiator, or any other heat exchanger, designs that are more efficient than conventional radiators. A graphite foam radiator designed to reject a given amount of heat will be smaller in size, weigh less, require less cooling air, and be quicker at removing heat than a conventional aluminum radiator.

scholarly journals Performance Analysis of Shell and Tube Type Heat Exchanger Using Aluminium Oxide (Al2O3) Nano-Particle

2021 ◽  
Vol 9 (9) ◽  
pp. 157-164
Author(s):  
Paritosh Singh
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Transfer Coefficient ◽  
Heat Exchanger ◽  
Transfer Coefficient ◽  
Solid Particles ◽  
Tube Heat Exchanger ◽  
Overall Heat Transfer Coefficient ◽  
Shell And Tube ◽  
Evacuated Tube

Abstract: Research in convective heat transfer using suspensions of nanometer sized solid particles in a base fluid started only over the past decade. Recent investigations on nanofluids, as such suspensions are often called, indicate that the suspended nanoparticles markedly change the transport properties and heat transfer characteristics of the suspension. The very first part of the research work summarizes about the various thermo physical properties of Al2O3 Nanofluid. In evacuated tube solar water heating system nanofluids are used as primary fluid and DM water as secondary fluid in Shell and Tube Heat Exchanger. The experimental analysis of Shell and Tube heat exchanger integrated with Evacuated tube solar collector have been carried out with two types of primary fluids. Research study of shell and tube heat exchanger is focused on heat transfer enhancement by usage of nano fluids. Conventional heat transfer fluids have inherently low thermal conductivity that greatly limits the heat exchange efficiency. The result of analysis shows that average relative variation in LMTD and overall heat transfer coefficient is 24.56% and 52.0% respectively. The payback period of system is reduced by 0.4 years due to saving is in replacement cost of Evacuated Tube Collector. Keywords: ETC; Nanofluid; LMTD; Thermal Conductivity; Overall heat transfer coefficient

Utilizing the Waste Polystyrene to Enhance the Thermal Insulation of the Local Buildings

2013 ◽  
Vol 652-654 ◽  
pp. 1191-1200 ◽  
Author(s):  
Khaled S. AlQdah ◽  
Mubarak AlGrafi
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Low Cost ◽  
Compression Stress ◽  
Overall Heat Transfer Coefficient ◽  
Heating And Cooling ◽  
Waste Polystyrene ◽  
Structure Versus

In this investigation, waste polystyrene boxes were collected and treated before mixed with common concrete in especial dies to produce new brick called poly-brick. The main tests performed these tests include the measurement of thermal conductivity, overall heat transfer coefficient and the compression stress. It can be seen that the thermal conductivity of the poly-brick increased with increasing the percentage of waste polystyrene and vary from 0.78 (W/mk) at 0% Polystyrene to 0.227 (W/mk) at 50% and the overall heat transfer coefficient reduced from 7.85 to 2.77 W/m2k. Comparisons between common building structure versus the new Poly-Brick was made and it indicates that the heat transfer rate reduced from 1413 to 498.6 Watt at 50% ratio of the mixture which means 64.7% of energy saving. On the other hand, the compression stress found to be less than that for the common brick. Reduction in energy consumption, which means that low cost of heating and cooling needs, safer, clean and comfortable environment achieved. It is also leads to getting rid of the waste material and has resolved numerous design challenges such as mould.

Enhancement of Heat Transfer Characteristics in an Absorber Tube of a Solar-Based Energy System Using Nanofluids

2015 ◽  
Author(s):  
Adnan Alashkar ◽  
Mohamed Gadalla
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Thermophysical Properties ◽  
Volume Fraction ◽  
Effective Density ◽  
Heat Transfer Characteristics ◽  
Overall Heat Transfer Coefficient ◽  
Transfer Characteristics

In this present paper, nanoparticles are dispersed into a base fluid, their effect on the thermophysical properties and overall heat transfer coefficient of the fluid inside a circular tube representing an absorber tube of a Parabolic Trough Solar Collector (PTSC) is studied. Different models are used to predict the effective density, specific heat capacity, viscosity and thermal conductivity of the nanofluids. For the analytical analysis, Alumina (Al2O3), Copper (Cu) and Single Wall Carbon Nanotubes (SWCNT) nanoparticles are dispersed into Therminol VP-1 oil. The resulting nanofluids are compared in terms of their thermophysical properties, their convective heat transfer characteristics and their overall heat transfer coefficient. Moreover, the effect on increasing the volume fraction on the properties and the heat transfer coefficient is studied. The computational analysis results show that the thermal conductivity increases with the increase of the volume fraction. In addition Therminol/SWCNT showed the highest thermal conductivity enhancement of 98% for a volume fraction of 3%. Further, the overall heat transfer coefficient increases with the increase of volume fraction, and Therminol/SWCNT showed the highest enhancement with 72% compared to Al2O3/Therminol and Cu/Therminol that showed an enhancement of 29% and 43% respectively.

Study of Circuit Number on the Evaporator in CO2 Heat Pump Water Heater

2011 ◽  
Vol 71-78 ◽  
pp. 2266-2270 ◽  
Author(s):  
Kang Liu ◽  
Jing Lv ◽  
Song Bo Zhang ◽  
Jie Yang
Keyword(s):  
Heat Transfer ◽  
Carbon Dioxide ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Pump ◽  
Temperature Difference ◽  
Water Heater ◽  
Overall Heat Transfer Coefficient ◽  
Heat Pump Water Heater ◽  
Simulation Package

In the design of a carbon dioxide heat pump water heater evaporator, the effect of the circuit number on the evaporator is investigated numerically by EVAP-COND 3.0 version simulation package of American National Institute of Standards and Technology. It is found that as the circuit number increases the temperature difference between the air and the refrigerant increases, but it reduces the overall heat transfer coefficient. The evaporator capacity will rise firstly, and then drop with the circuit number and achieve the maximum in the optimum circuit number. Therefore, selecting the appropriate circuit number of the evaporator can significantly improve the efficiency and optimize the design.

Algal Biomass Harvesting Using Low-Grade Waste Heat: Evaluation of Overall Heat Transfer Coefficient in a Heat Exchanger

2020 ◽  
Vol 143 (1) ◽  
Author(s):  
Temesgen Garoma ◽  
Ramin E. Yazdi
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Nusselt Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Waste Heat ◽  
Low Grade ◽  
Cfd Analysis ◽  
Overall Heat Transfer Coefficient ◽  
Nusselt Number Correlation

Abstract This study is part of a broader study on a novel method for harvesting algae by evaporation, and it investigated the feasibility of heating algal biomass using low-grade waste heat in a heat exchanger. Computational fluid dynamic (CFD) analysis was performed with ansysfluent, and the results were verified with experiments. The results of CFD analysis showed the overall heat transfer coefficient increased by 4, 13, and 100% as inlet gas temperature increased from 150 to 245 °C, liquid mass flow rate increased from 1.82 to 9.1 g/s, and gas mass flow increased from 2.2 to 13.2 g/s, respectively. It was also observed the overall heat transfer coefficient was not significantly affected with variations of properties of the liquid (thermal conductivity, density, and viscosity), thermal conductivity of the tube wall, and thickness of the tube banks, but it was sensitive to thermal conductivity of the gas. The experimental data were analyzed with logarithmic mean temperature difference (LMTD), number of transfer units (NTU), and Nusselt number correlation methods. There was an excellent agreement between the overall heat transfer coefficient calculated with the LMTD and NTU methods. The coefficients calculated with the LMTD method and Nusselt number correlation exhibited slight variations. This is likely because the LMTD is a theoretical method covering all experimental conditions and material properties, but Nusselt number correlation is an empirical approach based on correlations. The overall heat transfer coefficient calculated by CFD was slightly overestimated because the CFD analysis assumed complete insulation.

Overall Heat Transfer Coefficient of Functionally Graded Hollow Cylinder

2017 ◽  
Vol 267 ◽  
pp. 177-181 ◽  
Author(s):  
Ali Ozturk
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Transfer Coefficient ◽  
Circular Cylinder ◽  
Transfer Coefficient ◽  
Material Parameter ◽  
Functionally Graded ◽  
Cylinder Wall ◽  
Overall Heat Transfer Coefficient ◽  
Hollow Circular Cylinder

This paper presents how to calculate the overall heat transfer coefficient of a very long functionally graded hollow circular cylinder subjected to steady state heat transfer. Thermal conductivity coefficient of the functionally graded cylinder (FGC) vary radially and continuously according to an exponential form, which is supposed to be independent of the temperature. Overall heat transfer coefficient is found analytically in terms of the radial coordinate, thermal conductivity, material parameter, inner surface and outer surface temperatures of the cylinder. Once the overall heat transfer coefficient is found, calculation of the heat transfer rate across the cylinder wall is quite straightforward. The equation derived for the overall heat transfer coefficient can be applied to any type of functionally graded hollow circular cylinder playing with the material parameter term.

Development of a New Correlation and Post Processing of Heat Transfer Coefficient and Pressure Drop of Functionalized COOH MWCNT Nanofluid by Artificial Neural Network

2018 ◽  
Vol 14 (2) ◽  
pp. 104-112 ◽  
Author(s):  
Mohammad Hemmat Esfe ◽  
Somchai Wongwises ◽  
Saeed Esfandeh ◽  
Ali Alirezaie
Keyword(s):  
Neural Network ◽  
Heat Transfer ◽  
Thermal Conductivity ◽  
Artificial Neural Network ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Regression Coefficient ◽  
New Correlation ◽  
The Neural Network

Background: Because of nanofluids applications in improvement of heat transfer rate in heating and cooling systems, many researchers have conducted various experiments to investigate nanofluid's characteristics more accurate. Thermal conductivity, electrical conductivity, and heat transfer are examples of these characteristics. Method: This paper presents a modeling and validation method of heat transfer coefficient and pressure drop of functionalized aqueous COOH MWCNT nanofluids by artificial neural network and proposing a new correlation. In the current experiment, the ANN input data has included the volume fraction and the Reynolds number and heat transfer coefficient and pressure drop considered as ANN outputs. Results: Comparing modeling results with proposed correlation proves that the empirical correlation is not able to accurately predict the experimental output results, and this is performed with a lot more accuracy by the neural network. The regression coefficient of neural network outputs was equal to 99.94% and 99.84%, respectively, for the data of relative heat transfer coefficient and relative pressure drop. The regression coefficient for the provided equation was also equal to 97.02% and 77.90%, respectively, for these two parameters, which indicates this equation operates much less precisely than the neural network. Conclusion: So, relative heat transfer coefficient and pressure drop of nanofluids can also be modeled and estimated by the neural network, in addition to the modeling of nanofluid’s thermal conductivity and viscosity executed by different scholars via neural networks.

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