Numerical and experimental investigation of melting of paraffin in a hemicylindrical capsule

2021 ◽  
pp. 1-19
Author(s):  
Nabeel S. Dhaidan ◽  
Abbas F. Khalaf ◽  
Jay M. Khodadadi
Keyword(s):  
Wall Temperature ◽  
Conduction Mechanism ◽  
Initial Period ◽  
Operating Conditions ◽  
Melting Time ◽  
Cell Diameter ◽  
Stored Energy ◽  
Storage Unit ◽  
Charging Rate ◽  
Buoyancy Driven Convection

Abstract Phase change of paraffin in a hemicylindrical storage unit is investigated numerically and experimentally. The predicted findings are confirmed by comparison with the experimental results of the present work. Good agreements are achieved between the two approaches. The influence of the hot wall temperatures of 80, 85 and 90 °C is examined. The conduction mechanism is dominant only during the initial periods of the charging process, while buoyancy-driven convection is prevalent at later stages. The charging rate and stored energy both increased, whereas the melting time is reduced as the wall temperature increases. The Nusselt number increases sharply at the initial period of the fusion process, followed by a decaying trend with time until it stabilizes when the charging process is terminated. Increasing the cell diameter from 20 to 40 cm will raise the melting time by 300% for the wall temperature of 90 °C. In addition, under the same operating conditions, the melting of the PCM inside the hemicylindrical cell is faster than that observed in a rectangular one with equivalent volume. Savings in melting time due to using hemicylindrical container instead of a rectangular one of equivalent PCM volume are about 7.1, 8.3 and 11.7% for hot-wall temperatures of 65, 75 and 85 °C, respectively.

Thermal Energy Storage Through Melting of a Commercial Phase Change Material in an Annulus with Radially Divergent Longitudinal Fins

2020 ◽  
Vol 7 (1) ◽  
Author(s):  
Tonny Tabassum Mainul Hasan ◽  
Latifa Begum
Keyword(s):  
Energy Storage ◽  
Phase Change ◽  
Phase Change Material ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Storage System ◽  
Operating Conditions ◽  
Melting Time ◽  
Bottom Part ◽  
Change Material

This study reports on the unsteady two-dimensional numerical investigations of melting of a paraffin wax (phase change material, PCM) which melts over a temperature range of 8.7oC. The PCM is placed inside a circular concentric horizontal-finned annulus for the storage of thermal energy. The inner tube is fitted with three radially diverging longitudinal fins strategically placed near the bottom part of the annulus to accelerate the melting process there. The developed CFD code used in Tabassum et al., 2018 is extended to incorporate the presence of fins. The numerical results show that the average Nusselt number over the inner tube surface, the total melt fraction, the total stored energy all increased at every time instant in the finned annulus compared to the annulus without fins. This is due to the fact that in the finned annulus, the fins at the lower part of the annulus promotes buoyancy-driven convection as opposed to the slow conduction melting that prevails at the bottom part of the plain annulus. Fins with two different heights have been considered. It is found that by extending the height of the fin to 50% of the annular gap about 33.05% more energy could be stored compared to the bare annulus at the melting time of 82.37 min for the identical operating conditions. The effects of fins with different heights on the temperature and streamfunction distributions are found to be different. The present study can provide some useful guidelines for achieving a better thermal energy storage system.

scholarly journals Exergy analysis of a biomass-based multi-energy system

2019 ◽  
Vol 113 ◽  
pp. 02017
Author(s):  
Mariagiovanna Minutillo ◽  
Alessandra Perna ◽  
Alessandro Sorce
Keyword(s):  
Exergy Analysis ◽  
Energy System ◽  
H2 Production ◽  
Operating Conditions ◽  
Processing Unit ◽  
Storage Unit ◽  
Fuel Processing ◽  
Fuel Processor ◽  
Energy Processes ◽  
And Storage

This paper focuses on a biofuel-based Multi-Energy System generating electricity, heat and hydrogen. The proposed system, that is conceived as refit option for an existing anaerobic digester plant in which the biomass is converted to biogas, consists of: i) a fuel processing unit, ii) a power production unit based on the SOFC (Solid Oxide Fuel Cell) technology, iii) a hydrogen separation, compression and storage unit. The aim of this study is to define the operating conditions that allow optimizing the plant performances by applying the exergy analysis that is an appropriate technique to assess and rank the irreversibility sources in energy processes. Thus, the exergy analysis has been performed for both the overall plant and main plant components and the main contributors to the overall losses have been evaluated. Moreover, the first principle efficiency and the second principle efficiency have been estimated. Results have highlighted that the fuel processor (the Auto-Thermal Reforming reactor) is the main contributor to the global exergy destruction (9.74% of the input biogas exergy). In terms of overall system performance the plant has an exergetic efficiency of 53.1% (it is equal to 37.7% for the H2 production).

Influence of fin parameters on melting and solidification characteristics of a conical shell and tube latent heat storage unit

2021 ◽  
pp. 1-37
Author(s):  
Lokesh Kalapala ◽  
Jaya Krishna Devanuri
Keyword(s):  
Cylindrical Shell ◽  
Latent Heat ◽  
Conical Shell ◽  
Heat Storage ◽  
Melting Time ◽  
Storage Unit ◽  
Latent Heat Storage ◽  
Efficient Operation ◽  
Shell And Tube ◽  
Melting And Solidification

Abstract Augmenting meting and solidification rates of latent heat storage unit (LHSU) is very much essential for its efficient operation. By the effective utilization of natural convection, rate of heat transfer can be enhanced and the conical shell is beneficent in this regard. Employing fins further improves the charging and discharging rates. Hence the current study is focused on analyzing melting and solidification characteristics of a conical shell and tube LHSU along with the effect of fin parameters viz. fin diameter and number of fins. Numerical analysis is chosen for this purpose and the performance is compared via melting/solidification times, energy stored, energy/exergy efficiencies. Initially the performance of unfinned conical shell is compared with the cylindrical shell without fins and then the effect of fin parameters is presented. For melting process conical shell is found to be superior to cylindrical shell. 34.46% reduction in melting time is noted by employing conical shell and rate of energy stored is also higher for conical shell. Increase in fin diameter caused an increase in melting time when 20 number of fins are used, whereas melting time got decreased with the increase in fin diameter when 5 number of fins are used. Hence, when a greater number of fins are employed lesser diameter is preferred for melting. For discharging process, conical shell took 60% more time than cylindrical shell. Even after employing fins, solidification time is not drastically reduced in comparison to cylindrical shell.

Influence of Gas-to-Wall Temperature Ratio on By-Pass Transition

2017 ◽  
Author(s):  
Tânia S. Cação Ferreira ◽  
Tony Arts
Keyword(s):  
Heat Flux ◽  
Wall Temperature ◽  
Analog Circuits ◽  
Guide Vane ◽  
Operating Conditions ◽  
Wall Heat Flux ◽  
Bypass Transition ◽  
Temperature Ratio ◽  
Isentropic Compression ◽  
Pressure Transducers

An investigation of thermal effects on bypass transition was conducted on the highly-loaded turbine guide vane LS89 in the short-duration isentropic Compression Tube (CT-2) facility at the von Karman Institute for Fluid Dynamics (VKI). Measurements from high response surface-mounted thin films coupled with analog circuits provided the time-resolved wall heat flux history whereas pneumatic probes, differential pressure transducers and thermocouples allowed the accurate definition of the inlet and outlet flow conditions. The gas-to-wall temperature ratio, ranging from 1.11 to 1.55, was varied by changing the inlet total temperature. The isentropic exit Mach number ranged from 0.90 to 1.00 and the global freestream turbulence intensity value was set at 0.8, 3.9 and 5.3%. The isentropic exit Reynolds number was kept at 106. The onset of transition was tracked through the wall heat flux signal fluctuations. Within the present operating conditions, no significant effect of the gas/wall temperature ratio was put in evidence. At the present (design) transonic exit conditions, the local free-stream pressure gradient appears to remain the main driver of the onset of transition. A wider range of operating conditions must be considered to draw final conclusions.

scholarly journals Development of a Pattern Recognition Methodology with Thermography and Implementation in an Experimental Study of a Boiler for a WHRS-ORC

2019 ◽  
Author(s):  
Concepción Paz ◽  
Eduardo Suarez ◽  
Miguel Concheiro ◽  
Antonio Diaz
Keyword(s):  
Pattern Recognition ◽  
Wall Temperature ◽  
Waste Heat ◽  
Combustion Engine ◽  
Organic Rankine Cycle ◽  
Exhaust System ◽  
Rankine Cycle ◽  
Operating Conditions ◽  
Cycle Performance ◽  
Working Fluid

Waste heat dissipated in the exhaust system in a combustion engine represents a major source of energy to be recovered and converted into useful work. A waste heat recovery system (WHRS) based on an Organic Rankine Cycle (ORC) is a promising approach, and has gained interest in the last few years in an automotive industry interested in reducing fuel consumption and exhaust emissions. Understanding the thermodynamic response of the boiler employed in an ORC plays an important role in steam cycle performance prediction and control system design. The aim of this study is therefore to present a methodology to study these devices by means of pattern recognition with infrared thermography. In addition, the experimental test bench and its operating conditions are described. The methodology proposed identifies the wall coordinates, traces paths, and tracks wall temperature along them in a way that can be exported for subsequent post-processing and analysis. As for the results, through the wall temperature paths on both sides (exhaust gas and working fluid) it was possible to quantitatively estimate the temperature evolution along the boiler and, in particular, the beginning and end of evaporation.

Control of Dielectric Fluid Flow Distribution in Micro-Tubes With EHD Conduction Pumping: Numerical Study

2011 ◽  
Author(s):  
Miad Yazdani ◽  
Jamal Seyed-Yagoobi
Keyword(s):  
Fluid Flow ◽  
Electric Field ◽  
Conduction Mechanism ◽  
Numerical Study ◽  
Fluid Motion ◽  
Flow Distribution ◽  
Operating Conditions ◽  
Dielectric Fluid ◽  
Total Flow ◽  
Flow Through

The control of fluid flow distribution in micro-scale tubes is numerically investigated. The flow distribution control is achieved via electric conduction mechanism. In electrohydrodynamic (EHD) conduction pumping, when an electric field is applied to a fluid, dissociation and recombination of electrolytic species produces heterocharge layers in the vicinity of electrodes. Attraction between electrodes and heterocharge layers induces a fluid motion and a net flow is generated if the electrodes are asymmetric. The numerical domain comprises a 2-D manifold attached to two bifurcated tubes with one of the tubes equipped with a bank of uniquely designed EHD-conduction electrodes. In the absence of electric field, the total flow supplied at the manifold’s inlet is equally distributed among the tubes. The EHD-conduction, however, operates as a mechanism to manipulate the flow distribution to allow the flow through one branch surpasses the counterpart of the other branch. Its performance is evaluated under various operating conditions.

A Thermal Model for Concentric-Tube Overfire Air Ports

2009 ◽  
Vol 1 (1) ◽  
Author(s):  
Larry W. Swanson ◽  
David K. Moyeda
Keyword(s):  
Heat Source ◽  
Wall Temperature ◽  
Tube Wall ◽  
Operating Conditions ◽  
Transfer Model ◽  
Radiation Boundary Condition ◽  
Temperature Distributions ◽  
Airflow Distribution ◽  
Highly Nonlinear ◽  
Tube Wall Temperature

A quasisteady multimode heat-transfer model for boiler concentric-tube overfire air ports has been developed that predicts the effect of geometry, furnace heat source and heat sink temperatures, axial injector wall conduction, and coolant flow rate on the tube wall temperature distributions. The model imposes a radiation boundary condition at the outlet tip of the ports, which acts as a heat source. The model was validated using field data and showed that both the airflow distribution in the ports and tube diameter can be used to control the maximum tube wall temperature. This helps avoid tube overheating and thermal degradation. For nominal operating conditions, highly nonlinear axial temperature distributions were observed in both tubes near the hot outlet end of the port.

Heat Transfer Characteristics of Various Gun Barrels Under Different Operating Conditions

2019 ◽  
Author(s):  
Mohamed Gadalla ◽  
Muhammad Jasim ◽  
Omar Ahmad
Keyword(s):  
Heat Transfer ◽  
Thermal Management ◽  
Cross Section ◽  
Wall Temperature ◽  
Circular Cross Section ◽  
Typical Case ◽  
Operating Conditions ◽  
Firing Process ◽  
Transfer Model ◽  
Gun Barrel

Abstract The thermal stability parameter is an important parameter for predicting the lifespan of structures. In this paper, a two-dimensional transient heat transfer model of machine gun barrels undergoing continuous firing developed and analyzed for different geometries and thermal properties. The model for the transient thermal analysis is based on the forced convection heat transfer at the inner surface of the gun barrel. Finite element simulations were performed to predict the interior and exterior barrel temperature profiles and temperature contours after continuous firing process. The incomplete Cholesky Conjugate Gradient (ICCG) solver was adopted in solving unsymmetrical thermal transient analyses. The material thermal behavior studied for the basic circular cross section of gun barrels showed that the lowest inner wall temperature was for high rounds was achieved in steel barrels due to the rapid conducted and convective heat transfer to the environment. While the highest inner wall temperature was recorded for ceramic STK4 barrels and an increase of inner wall temperature by 17% was observed as compared to the typical case of circular cross section steel barrel. In general, a higher inner temperature in the gun barrel is undesirable and harm due to the possibility of reaching the cook-off scenario at earlier rounds. Results concluded that non-circular geometries with constrained cross section areas of typical case improve thermal management and the hexagonal geometry had the best thermal management and could provide more rounds for users. In addition, titanium barrels would have a weight drop of 41% while the overall barrel’s temperature increases by 49%.

Design Optimization of a Single Fluid, Solid Sensible Heat Storage Unit

1977 ◽  
Vol 99 (2) ◽  
pp. 174-179 ◽  
Author(s):  
F. W. Schmidt ◽  
R. R. Somers ◽  
J. Szego ◽  
D. H. Laananen
Keyword(s):  
Design Optimization ◽  
Heat Storage ◽  
Operating Conditions ◽  
Minimum Length ◽  
Complex Method ◽  
Fluid Temperature ◽  
Sensible Heat ◽  
Storage Material ◽  
Storage Unit ◽  
Flowing Fluid

The optimization of the design of a solid sensible heat storage unit initially at a uniform-temperature is presented. The storage unit is composed of a number of rectangular cross-sectional channels for the flowing fluid, connected in parallel and separated by the heat storage material. The complex method for constrained nonlinear optimization as presented by M. J. Box is utilized, with some modifications. The design optimization is based upon achieving maximum utilization of the heat storage or removal capabilities of the material for a given set of operating conditions. This is achieved by varying the storage unit’s geometry while placing constraints on the maximum and minimum length of the unit, fluid channel size, storage material thickness, maximum and minimum outlet fluid temperature, and the minimum amount of heat to be stored.

scholarly journals Role of honeycomb structure in improving the melting process of a phase change material inside a latent heat storage unit

2021 ◽  
Vol 19 ◽  
pp. 589-592
Author(s):  
M. Hariss ◽  
◽  
M. El Alami ◽  
A. Gounni
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Numerical Study ◽  
Melting Process ◽  
Honeycomb Structure ◽  
Melting Time ◽  
Storage Unit ◽  
Latent Heat Storage ◽  
The Impact

In this work, a numerical study is performed to analyze the impact of honeycomb structure on heat transfer within the PCM. The modeling is based on a transient calculation making it possible to analyze the phase change of the paraffin using the commercial software "Fluent" based on the enthalpy-porosity model. The results showed that the impregnation of a metal matrix in a rectangular enclosure helps to decrease the melting time and thus improve the heat transfer within the PCM.

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