Abstract: An Energetic and exergetic analysis is conducted on a
Steam Turbine Power Plant of an existing Phosphoric Acid Factory.
The heat recovery systems used in different parts of the plant are also
considered in the analysis. Mass, thermal and exergy balances are
established on the main compounds of the factory. A numerical code
is established using EES software to perform the calculations
required for the thermal and exergy plant analysis. The effects of the
key operating parameters such as steam pressure and temperature,
mass flow rate as well as seawater temperature, on the cycle
performances are investigated. A maximum Exergy Loss Rate of about 72% is obtained for the
melters, followed by the condensers, heat exchangers and the pumps.
The heat exchangers used in the phosphoric acid unit present
exergetic efficiencies around 33% while 60% to 72% are obtained for
steam turbines and blower. For the explored ranges of HP steam
temperature and pressure, the exergy efficiencies of steam turbine
generators STGI and STGII increase of about 2.5% and 5.4%
respectively. In the same way optimum HP steam flow rate values,
leading to the maximum exergy efficiencies are defined.
Abstract: The aim of the study is to improve the understanding
of latent and sensible thermal energy storage within a paraffin wax
media by an array of cylindrical tubes arranged both in in-line and
staggered layouts. An analytical and experimental study is carried out
in a horizontal shell-and-tube type system during melting process.
Pertamina paraffin-wax was used as a phase change material (PCM),
while the tubes are embedded in the PCM. From analytical study we
can obtain the useful information in designing a thermal energy
storage such as: the motion of interface, amount of material melted at
any time in the process, and the heat storage characteristic during
melting. The use of staggered tubes is proposed compared to in-line
layout in a heat exchanger as thermal storage. The experimental study
is used to verify the validity of the analytical predictions. From the
comparisons, the analytical and experimental data are in a good
agreement.
Abstract: Operation enhancement in an air cooler depends on
rate of heat transfer, and pressure drop. In this paper for a given heat
duty, study of the effects of FPI (Fin Per Inch) and fin type (circular
and hexagonal fins) on heat transfer, and pressure drop in an air
cooler in Iran, Arvand petrochemical. A program in EES
(Engineering Equations Solver) software moreover, Aspen B-JAC
and HTFS+ softwares are used for this purpose to solve governing
equations. At first the simulated results obtained from this program is
compared to the experimental data for two cases of FPI. The effects
of FPI from 3 to 15 over heat transfer (Q) to pressure drop ratio
(Q/Δp ratio). This ratio is one of the main parameters in design, and
simulation heat exchangers. The results show that heat transfer (Q)
and pressure drop increase with increasing FPI steadily, and the Q/Δp
ratio increases to FPI=12 and then decreased gradually to FPI=15,
and Q/Δp ratio is maximum at FPI=12. The FPI value selection
between 8 and 12 obtained as a result to optimum heat transfer to
pressure drop ratio. Also by contrast, between circular and hexagonal
fins results, the Q/Δp ratio of hexagonal fins more than Q/Δp ratio of
circular fins for FPI between 8 and 12 (optimum FPI)
Abstract: In the present paper the design of plate heat exchangers
is formulated as an optimization problem considering two
mathematical modelling. The number of plates is the objective
function to be minimized, considering implicitly some parameters
configuration. Screening is the optimization method used to solve the
problem. Thermal and hydraulic constraints are verified, not viable
solutions are discarded and the method searches for the convergence to
the optimum, case it exists. A case study is presented to test the
applicability of the developed algorithm. Results show coherency with
the literature.
Abstract: The development of electric vehicle batteries have
resulted in very high energy density lithium-ion batteries. However,
this progress is accompanied by the risk of thermal runaway, which
can result in serious accidents. Heat pipes are heat exchangers that
are suitable to be applied in electric vehicle battery thermal
management for their lightweight, compact size and do not require
external power supply. This paper aims to examine experimentally a
Flat Plate Loop Heat Pipe (FPLHP) performance as a heat exchanger
in thermal management system of lithium-ion battery for electric
vehicle application. The heat generation of the battery was simulated
using a cartridge heater. Stainless steel screen mesh was used as the
capillary wick. Distilled water, alcohol and acetone were used as
working fluids with a filling ratio of 60%. It was found that acetone
gives the best performance that produces thermal resistance of 0.22
W/°C with 50°C evaporator temperature at heat flux load of 1.61
W/cm2.
Abstract: The thermal control in many systems is widely
accomplished applying mixed convection process due to its low cost,
reliability and easy maintenance. Typical applications include the
aircraft electronic equipment, rotating-disc heat exchangers, turbo
machinery, and nuclear reactors, etc. Natural convection in an inclined
square enclosure heated via wall heater has been studied numerically.
Finite volume method is used for solving momentum and energy
equations in the form of stream function–vorticity. The right and left
walls are kept at a constant temperature, while the other parts are
adiabatic. The range of the inclination angle covers a whole revolution.
The method is validated for a vertical cavity. A general power law
dependence of the Nusselt number with respect to the Rayleigh
number with the coefficient and exponent as functions of the
inclination angle is presented. For a fixed Rayleigh number, the
inclination angle increases or decreases is found.
Abstract: Meeting the growth in demand for digital services
such as social media, telecommunications, and business and cloud
services requires large scale data centres, which has led to an increase
in their end use energy demand. Generally, over 30% of data centre
power is consumed by the necessary cooling overhead. Thus energy
can be reduced by improving the cooling efficiency. Air and liquid
can both be used as cooling media for the data centre. Traditional
data centre cooling systems use air, however liquid is recognised as a
promising method that can handle the more densely packed data
centres. Liquid cooling can be classified into three methods; rack heat
exchanger, on-chip heat exchanger and full immersion of the
microelectronics. This study quantifies the improvements of heat
transfer specifically for the case of immersed microelectronics by
varying the CPU and heat sink location. Immersion of the server is
achieved by filling the gap between the microelectronics and a water
jacket with a dielectric liquid which convects the heat from the CPU
to the water jacket on the opposite side. Heat transfer is governed by
two physical mechanisms, which is natural convection for the fixed
enclosure filled with dielectric liquid and forced convection for the
water that is pumped through the water jacket. The model in this
study is validated with published numerical and experimental work
and shows good agreement with previous work. The results show that
the heat transfer performance and Nusselt number (Nu) is improved
by 89% by placing the CPU and heat sink on the bottom of the
microelectronics enclosure.
Abstract: This article is trying to determine the status of flue gas
that is entering the KWH heat exchanger from combustion chamber
in order to calculate the heat transfer ratio of the heat exchanger.
Combination of measurement, calculation and computer simulation
was used to create a useful way to approximate the heat transfer rate.
The measurements were taken by a number of sensors that are
mounted on the experimental device and by a thermal imaging
camera. The results of the numerical calculation are in a good
correspondence with the real power output of the experimental
device. That result shows that the research has a good direction and
can be used to propose changes in the construction of the heat
exchanger, but still needs enhancements.
Abstract: A thermosyphon system is a heat transfer loop which
operates on the basis of gravity and buoyancy forces. It guarantees a
good reliability and low maintenance cost as it does not involve any
mechanical pump. Therefore, it can be used in many industrial
applications such as refrigeration and air conditioning, electronic
cooling, nuclear reactors, geothermal heat extraction, etc. But flow
instabilities and loop configuration are the major problems in this
system. Several previous researchers studied that stabilities can be
suppressed by using nanofluids as loop fluid. In the present study a
rectangular thermosyphon loop with end heat exchangers are
considered for the study. This configuration is more appropriate for
many practical applications such as solar water heater, geothermal
heat extraction, etc. In the present work, steady-state analysis is
carried out on thermosyphon loop with parallel flow coaxial heat
exchangers at heat source and heat sink. In this loop nanofluid is
considered as the loop fluid and water is considered as the external
fluid in both hot and cold heat exchangers. For this analysis onedimensional
homogeneous model is developed. In this model,
conservation equations like conservation of mass, momentum, energy
are discretized using finite difference method. A computer code is
written in MATLAB to simulate the flow in thermosyphon loop. A
comparison in terms of heat transfer is made between water and
nanofluid as working fluids in the loop.
Abstract: Cross flow water tube heat exchanger can be designed
and made operational using methods of model building and
simulation of the system. This paper projects the design and
development of a model of cross flow water tube heat-exchanger
system, simulation and validation of control analysis of different
tuning methods. Feedback and override control system is developed
using inputs acquired with the help of sensory system. A
mathematical model is formulated for analysis of system behaviour.
The temperature is regulated at the desired set point automatically.
Abstract: Solar air heater is a type of heat exchanger which
transforms solar radiation into heat energy. The thermal performance
of conventional solar air heater has been found to be poor because of
the low convective heat transfer coefficient from the absorber plate to
the air. It is attributed to the formation of a very thin boundary layer
at the absorber plate surface commonly known as viscous sub-layer.
Thermal efficiency of solar air heater can be improved by providing
the artificial roughness on absorber plate is the most efficient
technique. In this paper an attempt is made to provide artificial
roughness by incorporating inclined multiple V-ribs in the underside
of the absorber plate. 60˚V – ribs are arranged inclined to the
direction of air flow. Performance of collector estimated theoretically
and experimentally. Results of the investigation reveal that thermal
efficiency of collector with multiple V-ribs increased by 14%.
Abstract: Using cold EGR method with variable venturi and
turbocharger has a very significant effect on reduction of NOX and
grime simultaneously. EGR cooler is one of the most important parts
in the cold EGR circuit. In this paper optimum design of cooler for
working in different percentages of EGR and for determining
optimum temperature of exhausted gases, growth of efficiency,
reduction of weight, dimension, expenditures, sediment and also
optimum performance by using gasoil which has significant amounts
of brimstone are investigated and optimized.
Abstract: The thermo-mechanical behaviour of concrete energy
pile foundations with different single and double U-tube shapes
incorporated was analysed using the Comsol Multi-physics package.
For the analysis, a 3D numerical model in real scale of the concrete
pile and surrounding soil was simulated regarding actual operation of
ground heat exchangers (GHE) and the surrounding ambient
temperature. Based on initial ground temperature profile measured in
situ, tube inlet temperature was considered to range from 6oC to 0oC
(during the contraction process) over a 30-day period. Extra thermal
stresses and deformations were calculated during the simulations and
differences arising from the use of two different systems (single-tube
and double-tube) were analysed. The results revealed no significant
difference for extra thermal stresses at the centre of the pile in either
system. However, displacements over the pile length were found to
be up to 1.5-fold higher in the double-tube system than the singletube
system.
Abstract: Heat transfer from flat tube is studied numerically. Reynolds number is defined base on equivalent circular tube which is varied in range of 100 to 300. In these range of Reynolds number flow is considered to be laminar, unsteady, and incompressible. Equations are solved by using finite volume method. Results show that increasing l/D from 1 to 2 has insignificant effect on heat transfer and Nusselt number of flat tube is slightly lower than circular tube. However, thermal-hydraulic performance of flat tube is up to 2.7 times greater than circular tube.
Abstract: A 3D-conjugate numerical investigation was conducted to predict heat transfer characteristics in a rectangular cross-sectional micro-channel employing simultaneously developing Tow-phase flows. The sole purpose for analyzing two phase flow heat transfer in rectangular micro channel is to pin point what are the different factors affecting this phenomenon. Different methods and techniques have been undertaken to analyze the equations arising constituting the flow of heat from gas phase to liquid phase and vice versa.Different models of micro channels have been identified and analyzed. How the geometry of micro channels affects their activity i.e. of circular and non-circular geometry has also been reviewed. To the study the results average Nusselt no plotted against the Reynolds no has been taken into consideration to study average heat exchange in micro channels against applied heat flux. High heat fluxes up to 140 W/cm2 were applied to investigate micro-channel thermal characteristics.
Abstract: In industrial environments, the heat exchanger is a
necessary component to any strategy of energy conversion. Much of
thermal energy used in industrial processes passes at least one times
by a heat exchanger, and methods systems recovering thermal
energy.
This survey paper tries to presents in a systemic way an sample
control of a heat exchanger by comparison between three controllers
LQR (linear quadratic regulator), PID (proportional, integrator and
derivate) and Pole Placement. All of these controllers are used mainly
in industrial sectors (chemicals, petrochemicals, steel, food
processing, energy production, etc…) of transportation (automotive,
aeronautics), but also in the residential sector and tertiary (heating, air
conditioning, etc...) The choice of a heat exchanger, for a given
application depends on many parameters: field temperature and
pressure of fluids, and physical properties of aggressive fluids,
maintenance and space. It is clear that the fact of having an
exchanger appropriate, well-sized, well made and well used allows
gain efficiency and energy processes.
Abstract: The subject of this paper is the design analysis of a single well power production unit from low enthalpy geothermal resources. A complexity of the project is defined by a low temperature heat source that usually makes such projects economically disadvantageous using the conventional binary power plant approach. A proposed new compact design is numerically analyzed. This paper describes a thermodynamic analysis, a working fluid choice, downhole heat exchanger (DHE) and turbine calculation results. The unit is able to produce 321 kW of electric power from a low enthalpy underground heat source utilizing n-Pentane as a working fluid. A geo-pressured reservoir located in Vermilion Parish, Louisiana, USA is selected as a prototype for the field application. With a brine temperature of 126 , the optimal length of DHE is determined as 304.8 m (1000ft). All units (pipes, turbine, and pumps) are chosen from commercially available parts to bring this project closer to the industry requirements. Numerical calculations are based on petroleum industry standards. The project is sponsored by the Department of Energy of the US.
Abstract: The problem of magnetohydrodynamics boundary layer flow and heat transfer on a permeable stretching surface in a second grade nanofluid under the effect of heat generation and partial slip is studied theoretically. The Brownian motion and thermophoresis effects are also considered. The boundary layer equations governed by the PDE’s are transformed into a set of ODE’s with the help of local similarity transformations. The differential equations are solved by variational finite element method. The effects of different controlling parameters on the flow field and heat transfer characteristics are examined. The numerical results for the dimensionless velocity, temperature and nanoparticle volume fraction as well as the reduced Nusselt and Sherwood number have been presented graphically. The comparison confirmed excellent agreement. The present study is of great interest in coating and suspensions, cooling of metallic plate, oils and grease, paper production, coal water or coal-oil slurries, heat exchangers technology, materials processing exploiting.
Abstract: The ice rink floor is the largest heat exchanger in an ice rink. The important part of the floor consists of concrete, and the thermophysical properties of this concrete have strong influence on the energy usage of the ice rink. The thermal conductivity of concrete can be increased by using iron ore as ballast. In this study, the Transient Plane Source (TPS) method showed an increase up to 58.2% of thermal conductivity comparing the improved concrete to standard concrete. Moreover, two alternative ice rink floor designs are suggested to incorporate the improved concrete. A 2D simulation was developed to investigate the temperature distribution in the conventional and the suggested designs. The results show that the suggested designs reduce the temperature difference between the ice surface and the brine by 1-4˚C, when comparing with convectional designs at equal heat flux. This primarily leads to an increased coefficient of performance (COP) in the primary refrigeration cycle and secondly to a decrease in the secondary refrigerant pumping power. The suggested designs have great potential to reduce the energy usage of ice rinks. Depending on the load scenario in the ice rink, the saving potential lies in the range of 3-10% of the refrigeration system energy usage. This calculation is based on steady state conditions and the potential with improved dynamic behavior is expected to increase the potential saving.
Abstract: A mathematical heat transfer model for the prediction of transient heating of the slab in a direct-fired walking beam type reheating furnace has been developed by considering the nongray thermal radiation with given furnace environments. The furnace is modeled as radiating nongray medium with carbon dioxide and water with five-zoned gas temperature and the furnace wall is considered as a constant temperature lower than furnace gas one. The slabs are moving with constant velocity depending on the residence time through the non-firing, charging, preheating, heating, and final soaking zones. Radiative heat flux obtained by considering the radiative heat exchange inside the furnace as well as convective one from the surrounding hot gases are introduced as boundary condition of the transient heat conduction within the slab. After validating thermal radiation model adopted in this work, thermal fields in both model and real reheating furnace are investigated in terms of radiative heat flux in the furnace and temperature inside the slab. The results show that the slab in the furnace can be more heated with higher slab emissivity and residence time.