scholarly journals Development of a Condensation Model and a New Design of a Condensation Hood—Numerical and Experimental Study

Energies ◽  
2021 ◽  
Vol 14 (5) ◽  
pp. 1344
Author(s):  
Mieszko Tokarski ◽  
Arkadiusz Ryfa ◽  
Piotr Buliński ◽  
Marek Rojczyk ◽  
Krzysztof Ziarko ◽  
...  
Keyword(s):  
Heat Exchanger ◽  
Numerical Model ◽  
Transport Model ◽  
Measurement Data ◽  
Computation Time ◽  
High Heat ◽  
Condensation Process ◽  
Proposed Model ◽  
Flow Heat ◽  
High Heat Load

The development of a numerical model and design for the innovative construction of a heat exchanger (HE) used in a condensation hood (being a part of the combi-steamer) are described in this work. The model covers an air-steam flow, heat transfer, and a steam condensation process. The last two processes were implemented with the use of an in-house model introduced via User Defined Functions (UDF). As the condensate volume is negligible compared to the steam, the proposed model removes the condensate from the domain. This approach enabled the usage of a single-phase flow for both air and steam using a species transport model. As a consequence, a significant mesh and computation time reduction were achieved. The new heat exchanger is characterised by reorganised fluid flow and by externally finned pipes (contrary to the original construction, where internally finned pipes were used). This allowed a reduction in the number of the pipes from 48 to 5, which significantly simplifies construction and manufacturing process of the HE. The redesigned HE was tested in two cases: one simulating normal working conditions with a combi-steamer, the other with extremely high heat load. Measurement data showed that the numerical model predicted condensate mass flow rate (3.67 g/s computed and 3.56 g/s measured) and that the condensation capability increased at least by 15% when compared to the original HE design.

scholarly journals Investigation of flow non-uniformities in the cross-flow heat exchanger with elliptical tubes

2019 ◽  
Vol 108 ◽  
pp. 01009 ◽  
Author(s):  
Stanisław Łopata ◽  
Paweł Ocłoń ◽  
Tomasz Stelmach
Keyword(s):  
Heat Exchanger ◽  
Measurement Data ◽  
Cross Flow ◽  
Flow Distribution ◽  
Transitional Flow ◽  
Working Fluid ◽  
Elliptical Cross ◽  
Flow Heat ◽  
The Cross ◽  
Inflow Conditions

In heat exchangers, especially those with the cross-flow arrangement, it is nearly impossible to achieve the uniform distribution of the working fluid in the tubular space with the currently used inlet and outlet chambers (in some constructions as well). The improper inflow conditions to individual tubes, including those with an elliptical cross-section - often used because of their favorable features compared to round tubes, is the cause of improper heat transfer. In this respect, transitional flow is of particular importance. This flow regime is complex and challenging to model. Therefore, it is necessary to perform experimental verification. For this purpose, an appropriate stand was built, allowing to investigate the flow of the working fluid (water) to the elliptical tubes in the cross-current heat exchanger. The paper presents the results of measurements for manifold geometry, which are currently used in practice (for heat exchanger constructions). The analysis of the measurement data confirms the nonuniform flow distribution to individual tubes of the heat exchanger.

Co-Flowing Ammonia Desorption in a Fractal-Like Branching Heat Exchanger

2007 ◽  
Author(s):  
Greg Mouchka ◽  
Mario Apreotesi ◽  
Keith Davis ◽  
Deborah Pence
Keyword(s):  
Heat Exchanger ◽  
Mass Flow ◽  
Mass Fraction ◽  
High Heat ◽  
Ammonia Solution ◽  
High Heat Flux ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Flow Rates ◽  
Flow Heat

Heat activated cooling provides an opportunity to recover and utilize wasted heat. In terms of thermal management of electronics, a heat-activated cooling cycle could be used to thermally manage a space such as a central computing facility. A microscale, fractal-like branching flow heat exchanger was designed and used to desorb ammonia from an aqueous ammonia solution. The fractal-like pattern employed in the present study was previously studied for high heat flux single-phase and two-phase boiling flow heat sink applications. For compatibility, the desorber was fabricated in 316 stainless steel. The desorber is compact, approximately 38 mm in diameter and 6.4 mm thick, and lightweight, weighing 20 grams. Heating was accomplished using Paratherm NF oil between 350 and 400 K. The mass fraction of ammonia in the strong solution inlet stream was 0.30 and the temperature was 300 K. Given a range of inlet solution mass flow rates between 0.42 and 0.92 g/s and oil flow rates between 1.67 and 10 g/s, the mass flow rate of vapor generated varied from 0.02 to 0.13 g/s. The mass fraction of ammonia in the exiting vapor stream varied between 0.8 and 0.96 while circulation ratios varied between 3.5 and 20. Heat exchanger performance is presented using LMTD and ε-NTU analyses. Overall heat transfer coefficients ranged from 7500 to 15,000 for the flow rates and driving temperature differences investigated. The configuration of the desorbers is such that the oil stream can be introduced to flow parallel or counter to the ammonia solution stream. The nature of the microchannels is such that desorption occurs in a co-flowing manner, limiting the vapor mass fraction. However, the advantages of the present design are lightweight, compact, modularity and orientation independence.

Modeling of Supercritical Co2 Shell-and-Tube Heat Exchangers Under Extreme Conditions. Part 2: Heat Exchanger Model

2022 ◽  
Author(s):  
Akshay Bharadwaj Krishna ◽  
Kaiyuan Jin ◽  
Portnovo Ayyaswamy ◽  
Ivan Catton ◽  
Timothy S. Fisher
Keyword(s):  
Heat Exchanger ◽  
Numerical Model ◽  
Heat Exchangers ◽  
Supercritical Co2 ◽  
Critical Role ◽  
Computation Time ◽  
Efficient Estimation ◽  
Working Fluid ◽  
Computationally Efficient ◽  
Thermal Cycles

Abstract Heat exchangers play a critical role in supercritical CO2 Brayton cycles by providing necessary waste heat recovery. Supercritical CO2 thermal cycles potentially achieve higher energy density and thermal efficiency operating at elevated temperatures and pressures. Accurate and computationally efficient estimation of heat exchanger performance metrics at these conditions is important for the design and optimization of sCO2 systems and thermal cycles. In this paper (Part II), a computationally efficient and accurate numerical model is developed to predict the performance of STHXs. Highly accurate correlations reported in Part I of this study are utilized to improve the accuracy of performance predictions, and the concept of volume averaging is used to abstract the geometry and reduce computation time. The numerical model is validated by comparison with CFD simulations and provides high accuracy and significantly lower computation time compared to existing numerical models. A preliminary optimization study is conducted and the advantage of using supercritical CO2 as a working fluid for energy systems is demonstrated.

Simulation of particle concentration distribution in primary clarifiers

1985 ◽  
Vol 12 (3) ◽  
pp. 454-463 ◽  
Author(s):  
Sameh Abdel-Gawad ◽  
John A. McCorquodale
Keyword(s):  
Numerical Model ◽  
Differential Equations ◽  
Removal Efficiency ◽  
Transport Model ◽  
Concentration Profiles ◽  
Steady Flows ◽  
Integral Technique ◽  
Solids Concentration ◽  
Proposed Model ◽  
Fifth Order

A numerical model to simulate the performance of both rectangular and circular primary clarifiers is presented. The proposed model is restricted to those mean steady flows that are isothermal, of neutral density, low in solids concentration, and nearly two-dimensional.The strip integral technique is used to reduce the partial differential equations of continuity, momentum, and mass transport to a set of ordinary differential equations. The resulting set of equations is numerically integrated using a fifth-order, Runge–Kutta method.The full numerical model contains a hydrodynamic submodel and a transport submodel. The hydrodynamic submodel predicts the velocity field and dispersion characteristics within the clarifier, which are prerequisite for the transport submodel.The model, as presented here, was used to simulate the circular tanks used in the cities of Windsor, Ontario and Waterloo, Ontario. The predicted concentration profiles and removal efficiency were in good agreement with the measured values. Key words: numerical model, primary clarifiers, strip integral technique, transport model, concentration profiles, removal efficiency.

PERFORMANCE ANALYSIS OF MICROCHANNEL COUNTER FLOW HEAT EXCHANGER USING DIFFERENT NANOFLUIDS

2018 ◽  
Author(s):  
Bharath P ◽  
Doddamani Hithaish ◽  
Saravanan Venkatesh ◽  
C K Umesh
Keyword(s):  
Heat Exchanger ◽  
Performance Analysis ◽  
Counter Flow ◽  
Flow Heat
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