Use of a Shroud and Baffle to Improve Natural Convection to Immersed Heat Exchangers

2011 ◽  
Vol 134 (1) ◽  
Author(s):  
Sandra K. S. Boetcher ◽  
F. A. Kulacki ◽  
Jane H. Davidson
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
High Performance ◽  
Discharge Process ◽  
Thermal Systems ◽  
Transfer Rates ◽  
Water Storage Tank ◽  
Flow Control Devices ◽  
Commercial Applications ◽  
Thermal Stores

Optimizing heat transfer during the charge and discharge of thermal stores is crucial for high performance of solar thermal systems for domestic and commercial applications. This study models a sensible water storage tank for which discharge is accomplished using a heat exchanger immersed in the storage fluid. The heat exchanger is a two-dimensional isothermal cylinder in an adiabatic enclosure with no initial stratification. An adiabatic shroud and baffle whose geometry is parametrically varied is placed around and below the cylinder. Transient numerical simulations of the discharge process are obtained for 105 < RaD < 107, and estimates of the time needed to discharge a given fraction of the initial stored energy are obtained. We find that a short baffle is least effective in increasing heat transfer rates. The performance benefit is greatest early in the transient discharge period when the buoyant flow in the store is strongest. As with all flow control devices, the benefit decreases as energy is extracted from the tank and the temperature difference driving the flow decreases. The use of a shroud increases the transient Nusselt number by as much as twentyfold.

Use of a Shroud and Baffle to Improve Natural Convection to Immersed Heat Exchangers

2010 ◽  
Author(s):  
S. K. S. Boetcher ◽  
F. A. Kulacki ◽  
Jane H. Davidson
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Storage Tank ◽  
High Performance ◽  
Discharge Process ◽  
Thermal Systems ◽  
Water Storage Tank ◽  
Nusselt Numbers ◽  
Commercial Applications ◽  
Thermal Stores

Optimizing heat transfer during the charge and discharge of thermal stores is crucial for high performance of solar thermal systems for domestic and commercial applications. This study models a sensible water storage tank for which charge and discharge are accomplished using a heat exchanger immersed in the storage fluid. The objective is to investigate the use of a baffle and shroud as a means to improve convective heat transfer and thermal stratification. The immersed heat exchanger is modeled as a two-dimensional isothermal cylinder which is situated near the top of a storage tank with adiabatic walls. Transient numerical simulations of the discharge process are obtained for 105 < RaD < 107. An adiabatic shroud and baffle whose geometry is parametrically varied is placed around and below the cylinder. Transient Nusselt numbers are calculated for different baffle-shroud geometries and Rayleigh numbers. Results indicate that a long baffle with a high shroud height is optimal.

scholarly journals Execution of a Smart Prediction Tool to Evaluate Thermal Performance in a heat exchanger by using Single Elliptical Leaf Strips with altered Angle

2019 ◽  
Vol 8 (11) ◽  
pp. 123-131
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Thermal Performance ◽  
Heat Exchangers ◽  
Industrial Applications ◽  
Generalized Regression Neural Network ◽  
Prediction Tool ◽  
Pressure Drops ◽  
Transfer Rates ◽  
Mass Flow Rates

Heat exchangers are prominent industrial applications where engineering science of heat transfer and Mass transfer occurs. It is a contrivance where transfer of energy occurs to get output in the form of energy transfer. This paper aims at finding a solution to improve the thermal performance in a heat exchanger by using passive method techniques. This experimental and numerical analysis deals with finding the temperature outlets of cold and hot fluid for different mass flow rates and also pressure drop in the tube and the annular side by adding an elliptical leaf strip in the pipe at various angles. The single elliptical leaf used in experiment has major to minor axes ratios as 2:1 and distance of 50 mm between two leaves are arranged at different angular orientations from 0 0 to 1800 with 100 intervals. Since it’s not possible to find the heat transfer rates and pressure drops at every orientation of elliptical leaf so a generalized regression neural network (GRNN) prediction tool is used to get outputs with given inputs to avoid experimentation. GRNN is a statistical method of determining the relationship between dependent and independent variables. The values obtained from experimentation and GRNN nearly had precise values to each other. This analysis is a small step in regard with encomiastic approach for enhancement in performance of heat exchangers

scholarly journals Heat transfer rates in hot shell, cold tube inclined baffled small shell, and tube heat exchanger using CFD and experimental approach

2021 ◽  
Vol 9 (4B) ◽  
Author(s):  
Devanand D. Chillal ◽  
◽  
Uday C. Kapale ◽  
N.R. Banapurmath ◽  
T. M. Yunus Khan ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Liquid Flow ◽  
Cfd Analysis ◽  
Transfer Coefficients ◽  
Transfer Rates ◽  
Tube Heat Exchanger ◽  
Heat Transfer Coefficients ◽  
Shell And Tube ◽  
Cold Liquid

The work presented is an effort to realize the changes occurring for convective coefficients of heat transfer in STHX fitted with inclined baffles. Effort has been undertaken using Fluent, a commercially available CFD code ona CAD model of small STHX with inclined baffles with cold liquid flowing into the tubes and hot liquid flowing in the shell. Four sets of CFD analysis have been carried out. The hot liquid flow rate through shell compartments varied from 0.2 kg/sec to 0.8 kg/sec in steps of 0.2 kg/sec, while keeping the cold liquid flow condition in tube at 0.4 kg/sec constant. Heat transfer rates, compartment temperatures, and overall heat transfer coefficients, for cold liquid and hot liquid, were studied. The results given by the software using CFD approach were appreciable and comparatively in agreement with the results available by the experimental work, which was undertaken for the same set of inlet pressure conditions, liquid flow rates, and inlet temperatures of liquid for both hot and cold liquids. The experimental output results were also used to validate the results given by the CFD software. The results from the CFD analysis were further used to conclude the effect of baffle inclination on heat duty. The process thus followed also helped realize the effects of baffle inclination on convective heat transfer coefficient of the liquid flow through the shell in an inclined baffle shell and tube heat exchanger. The temperature plots for both cold and hot liquid were also generated for understanding the compartmental temperature distributions inclusive of the inlet and outlet compartments. The heat duty for a heat exchanger has been found to increase with the increase in baffle inclinations from zero degree to 20 degrees. Likewise, the convective heat transfer coefficients have also been found to increase with the increase in baffle inclinations.

Performance analysis of screw compressors – numerical simulation and experimental verification

2011 ◽  
Vol 226 (4) ◽  
pp. 968-980 ◽  
Author(s):  
S H Hsieh ◽  
Y C Shih ◽  
W-H Hsieh ◽  
F Y Lin ◽  
M J Tsai
Keyword(s):  
Heat Transfer ◽  
Screw Compressor ◽  
Pressure Curve ◽  
Discharge Process ◽  
Transfer Rates ◽  
Outlet Port ◽  
Total Process ◽  
The Difference ◽  
Verification Process ◽  
Empirical Constants

This article describes a theoretical model and computer program for calculating the pressure–volume ( PV ) diagram and the efficiency of an oil-injected screw compressor. The proposed model considers the mass and energy conservation laws, the heat transfer between air and oil, the leakages through various paths, and the discharges of air and oil. The proposed program, which uses seven empirical constants to account for the difference between the flow and the heat-transfer rates in the screw compressor and those estimated by available correlations, solves for the efficiency and the pressure curve of the compressed air. A systematic methodology for the determination of the seven empirical constants is presented in this article. Optimization is carried out to determine the seven empirical constants. With the empirical constants, which are determined with four sets of experiments, the maximum difference between the calculated and measured results in the training process, the verification process and the total process is 2.0 per cent for the volumetric and isentropic efficiencies and 5 per cent for the pressure curve. In the discharge process, the pressure in the compression chamber is noted to be affected by the area of the outlet port and the pressure in the neighbouring chambers.

Maximum Likelihood Method for Energy Balance Error Correction in Heat Exchanger Data

2017 ◽  
Author(s):  
Young-Gil Park ◽  
Liping Liu ◽  
Anthony M. Jacobi
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Performance Indicators ◽  
Performance Data ◽  
Likelihood Method ◽  
Transfer Rates ◽  
Engineering Standards ◽  
Mass Flow Rates ◽  
Minimum Uncertainty ◽  
Balance Error

Heat exchanger performance data commonly contain redundant heat transfer rate measurements. Due to measurement uncertainties involved in the experiments, these redundant heat transfer rates have some discrepancies. While it is a common practice and adopted by engineering standards to use the arithmetic mean of heat transfer measurements, the resulting performance indicators of heat exchangers do not result in a minimum uncertainty possible. Also, this approach fails to resolve discrepancies in resulting transport performance parameters depending on the use of UA-LMTD method or effectiveness-NTU method. In this paper, heat exchanger performance data with two heat transfer measurements from hot and cold fluid streams are combined to produce a least uncertainty of the performance indicators. Individual measurements of mass flow rates and temperatures are corrected by most likely errors based on their respective uncertainties. The validity of this method has been demonstrated by Monte-Carlo simulations. Using air conditioning heat exchanger performance data under dry and wet surface conditions, it is demonstrated that the proposed method leads to a minimum uncertainty of the calculated variables.

Characteristics of Inclined Fin-Tube Heat Exchanger for Compact Air Conditioner

2002 ◽  
Author(s):  
Haruaki Kanematsu ◽  
Kazuhiko Murakami
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
High Performance ◽  
Flow Direction ◽  
Numerical Approach ◽  
Air Conditioner ◽  
Large Space ◽  
Tube Heat Exchanger ◽  
Fin Tube ◽  
Inclined Angle

For saving space at an office or a clean room, it is needed to reduce the space of an air conditioner. It is effective to miniaturize a heat exchanger because it occupies the large space in the air conditioner. Three types of a heat exchanger that are an in-line tube and cut fins type, a staggered tube and cut fins type and a staggered tube and uncut fins type were investigated as four inclined angle tests of 0, 45, 60 and 80 degrees in a heat wind tunnel. The coefficients of flow friction and heat transfer rates were obtained from these experiments, and the characteristics of inclined heat exchanger were clarified by effects of tube arrangements, fin types and inclined angles against flow direction. As a numerical approach, two-dimensional steady models were applied on the staggered tube and the in-line tube by using BFC (Boundary-Fitted Coordinate Method); BFC is available to make grids for any install angle of the heat exchanger. The results of the numerical analysis visualized flow patterns and heat transfer in these heat exchangers. In case of 80-degrees angle, the flow makes dead area in a part of the heat exchanger, and it causes reducing performance of the heat exchanger. These results are available for improve a compact high performance heat exchanger.

Design Optimization of Micro-channel Heat Exchanger embedded in LTCC

2012 ◽  
Vol 2012 (1) ◽  
pp. 000857-000865
Author(s):  
Aparna Aravelli ◽  
Singiresu S. Rao ◽  
Hari K. Adluru
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Thermal Management ◽  
Optimization Technique ◽  
Thermal Design ◽  
Transfer Rates ◽  
Design Variables ◽  
Micro Heat Exchanger ◽  
Micro Systems ◽  
Silver Metal

Increase in the density of electronic packaging leads to the investigation of highly efficient thermal management systems. The challenge in these micro-systems is to maximize heat transfer per unit volume. In the author's previous work, experimental and computational analysis has been performed on LTCC substrates using embedded silver vias. This novel technique of embedding silver vias along with forced convection resulted in higher heat transfer rates. The present work further investigates into the optimization of this model. A Multi-objective optimization problem has been formulated for the heat transfer in the LTCC model. The Log Mean Temperature Difference (LMTD) method of heat exchangers has been used in the formulation. Optimization is done based on maximization of the total heat transferred and minimization of the coolant pumping power. Structural and thermal design variables are considered to meet the manufacturability and energy requirements. Demanded pressure loss and volume of the silver metal are used as constraints. The classical optimization technique Sequential Quadratic Programming (SQP) is used to solve the micro-heat exchanger problem. The optimal design is presented and sensitivity analysis results are discussed.

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