Investigation of Reverse Thermosyphoning in an Indirect SDHW System

2010 ◽  
Vol 133 (1) ◽  
Author(s):  
Cynthia A. Cruickshank ◽  
Stephen J. Harrison
Keyword(s):  
Heat Exchanger ◽  
Thermal Energy ◽  
Heat Exchangers ◽  
Reverse Flow ◽  
Numerical Models ◽  
Storage System ◽  
Relative Magnitude ◽  
Temperature Profiles ◽  
Heating Systems ◽  
And Storage

Thermal energy storages with thermosyphon natural convection heat exchangers have been used in solar water heating systems as a means of increasing tank stratification and eliminating the need for a second circulation pump. However, if the storage system is not carefully designed, under adverse pressure conditions, reverse thermosyphoning can result in increased thermal losses from the storage and reduced thermal performance of the system. To investigate this phenomenon, tests were conducted on single tank and multitank thermal storages under controlled laboratory conditions. Energy storage rates and temperature profiles were experimentally measured during charge periods, and the effects of reverse thermosyphoning were quantified. Further objectives of this study were to empirically derive performance characteristics, to develop numerical models to predict the performance of the heat exchanger during reverse thermosyphon operation, and to quantify the relative magnitude of these effects on the energy stored during typical daylong charge periods. Results of this study show that the magnitude of the reverse flow rate depends on the pressure drop characteristics of the heat exchange loop, the system temperatures, and the geometry of the heat exchanger and storage tank. In addition, the results show that in the case of a multitank thermal storage, the carryover of energy to the downstream thermal energy storages depends on the effectiveness of the exchangers used in the system.

Investigation of Reverse Thermosyphoning in an Indirect SDHW System

2009 ◽  
Author(s):  
Cynthia A. Cruickshank ◽  
Stephen J. Harrison
Keyword(s):  
Heat Exchanger ◽  
Thermal Energy ◽  
Reverse Flow ◽  
Numerical Models ◽  
Storage System ◽  
Thermal Storage ◽  
Relative Magnitude ◽  
Typical Day ◽  
Carry Over ◽  
And Storage

Thermal energy storages with thermosyphon natural convection heat exchangers have been used in solar water heating systems as a means of increasing tank stratification and eliminating the need for a second circulation pump. However, if the storage system is not carefully designed, under adverse pressure conditions, reverse thermosyphoning can result in increased thermal losses from the storage and reduced thermal performance of the system. To investigate this phenomenon, tests were conducted on a single tank and multi-tank thermal storage under controlled laboratory conditions. Energy storage rates and temperature profiles were experimentally measured during charge periods, and the effects of reverse thermosyphoning were quantified. A further aspect of this study was to empirically derive performance characteristics and to develop numerical models to predict the performance of the heat exchanger during reverse thermosyphon operation, and to quantify the relative magnitude of these effects on the energy stored during typical day-long charge periods. Results of this study show that the magnitude of the reverse flow rate depends on the pressure drop characteristics of the heat exchange loop, the system temperatures and the geometry of the heat exchanger and storage tank. In addition, the results show that in the case of a multi-tank thermal storage, the carry over of energy to the downstream thermal energy storages depend on the effectiveness of the exchangers used in the system.

The Optimum Design of Stratified Thermal Energy Storage Systems—Part II: Completion of the Analytical Model, Presentation and Interpretation of the Results

1992 ◽  
Vol 114 (3) ◽  
pp. 204-208 ◽  
Author(s):  
R. J. Krane ◽  
M. J. M. Krane
Keyword(s):  
Energy Storage ◽  
Heat Exchanger ◽  
Analytical Model ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Storage System ◽  
Energy Storage System ◽  
Thermal Energy Storage System ◽  
Thermal Energy Storage Systems ◽  
Performance Gains

This investigation is presented in two parts. The basic analytical model is developed in Part I. Part II includes the completion of the analytical model and the results of an optimization study performed with this model. The results show that: 1) Significant performance gains, that is, reductions in the entropy generation number on the order of 10 percent, are possible by employing perfectly stratified thermal energy storage systems that are designed on the basis of the second law of thermodynamics. 2) These performance gains are mainly due to the complete elimination of the entropy generation due to heat transfer through finite temperature differences within the storage element. 3) In general, the optimum design of a perfectly stratified thermal energy storage system requires the use of a very large heat exchanger; however, it is possible to employ a much smaller than optimum heat exchanger without seriously degrading the superior performance of the system. 4) The operation of a stratified system is quite flexible because it has no optimum storage time. 5) The optimum values of the capacity rate ratios, (φR)opt and (φR)opt, for a perfectly stratified thermal energy storage system are in general not equal to unity; however, this finding is shown to be in concert with Bejan’s theory of “remanent” irreversibilities for a heat exchanger.

The Deeper the Better? A Thermogeological Analysis of Medium-deep Borehole Heat Exchanger Efficiency in Crystalline Rocks

2022 ◽  
Author(s):  
Kaiu Piipponen ◽  
Annu Martinkauppi ◽  
Sami Vallin ◽  
Teppo Arola ◽  
Nina Leppäharju ◽  
...  
Keyword(s):  
Fluid Flow ◽  
Heat Exchanger ◽  
Thermal Energy ◽  
Heat Production ◽  
Heat Exchangers ◽  
Energy Production ◽  
Crystalline Rocks ◽  
Deep Borehole ◽  
Deep Well ◽  
Borehole Heat Exchangers

Abstract The energy sector is undergoing a fundamental transformation, with significant investment in low-carbon technologies to replace fossil-based systems. In densely populated urban areas, deep boreholes offer an alternative over shallow geothermal systems, which demand extensive surface area to attain large-scale heat production. This paper presents numerical calculations of the thermal energy that can be extracted from the medium-deep borehole heat exchangers of depths ranging from 600-3000 m. We applied the thermogeological parameters of three locations across Finland and tested two types of coaxial borehole heat exchangers to understand better the variables that affect heat production in low permeability crystalline rocks. For each depth, location, and heat collector type, we used a range of fluid flow rates to examine the correlation between thermal energy production and resulting outlet temperature. Our results indicate a trade-off between thermal energy production and outlet fluid temperature depending on the fluid flow rate, and that the vacuum-insulated tubing outperforms high-density polyethylene pipe in energy and temperature production. In addition, the results suggest that the local thermogeological factors impact heat production. Maximum energy production from a 600-m-deep well achieved 170 MWh/a, increasing to 330 MWh/a from a 1000-m-deep well, 980 MWh/a from a 2-km-deep well, and up to 1880 MWh/a from a 3-km-deep well. We demonstrate that understanding the interplay of the local geology, heat exchanger materials, and fluid circulation rates is necessary to maximize the potential of medium-deep geothermal boreholes as a reliable long-term baseload energy source.

Failure Analysis of Heat Exchangers

2021 ◽  
pp. 3-19
Author(s):  
Dusan P. Sekulic
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Failure Analysis ◽  
Thermal Energy ◽  
Solid Surface ◽  
Heat Exchangers ◽  
Heat Transfer Surface ◽  
Tubular Heat Exchanger ◽  
Erosion Corrosion ◽  
Different Temperatures

Abstract Heat exchangers are devices used to transfer thermal energy between two or more fluids, between a solid surface and a fluid, or between a solid particulate and a fluid at different temperatures. This article first addresses the causes of failures in heat exchangers. It then provides a description of heat-transfer surface area, discussing the design of the tubular heat exchanger. Next, the article discusses the processes involved in the examination of failed parts. Finally, it describes the most important types of corrosion, including uniform, galvanic, pitting, stress, and erosion corrosion.

Numerical Investigation on the Characteristic of the Reverse Flow Phenomenon in a Z-Type Parallel Compact Heat Exchanger With Large Number of Tubes

2018 ◽  
Author(s):  
Jian Zhou ◽  
Ming Ding ◽  
Haozhi Bian ◽  
Yinxing Zhang ◽  
Zhongning Sun
Keyword(s):  
Heat Exchanger ◽  
Pressure Distribution ◽  
Coming Out ◽  
Heat Exchangers ◽  
Cooling System ◽  
Reverse Flow ◽  
Flow Distribution ◽  
Flow Phenomenon ◽  
Compact Heat Exchangers ◽  
Geometry Design

The parallel compact heat exchangers have been widely applied in the various fields such as heat exchangers in chemical engineering, the solar collector, fuel cells and the passive removal heat exchanger in passive containment cooling system (PCCS), etc. The heat exchangers in the PCCS removes out the heat brought by the steam coming out from the broken reactor or primary cooling system. Therefore, the performance of the passive containment cooling system heat exchanger (PCCS HX) will greatly influence the safety and integrity of the containment. In previous investigations on the parallel compact heat exchangers, attentions are focused on the pressure distribution and flow distribution in the heat exchangers. A bad flow distribution in the heat exchanger will reduce the heat performance. More seriously, the coolant in some tubes may boils and the tubes will be overheated, resulting in explosion of tubes. Therefore, the characteristic of pressure distribution and the flow distribution should be investigated for a uniform flow distribution. In the past studies of the compact heat exchangers, the numbers of tube are almost under 72 which is relatively small, while the number of tubes PCCS HX is usually over than 100. And the pressure distribution in compact heat exchangers is assumed that the pressure recovery plays a leading role. However, the more numbers of tube will bring more flow maldistribution, if the geometry design is selected inappropriately. The reverse flow may occur in the heat exchanger, which means that in some tubes, the coolant flows from the tube outlet to the inlet. This phenomenon of reverse flow have never been mentioned in previous studies. The occurrence of the reverse flow will significantly decrease the performance of the heat exchanger and cause a bad influence on the safety of the containment. In the PCCS, the Z-type heat exchanger is one of the choice of PCCS HX (heat exchanger) design. Therefore, the present study focus on the characteristic of reverse flow phenomenon in Z-type heat exchangers. The pressure distribution and the flow distribution have been separately investigated deeply. The conclusion of this study will provide a guide to the geometry design of the PCCS HX with large number of tubes.

scholarly journals The influence of main parameters of regenerative heat exchanger on its energy efficiency

2020 ◽  
Vol 178 ◽  
pp. 01024
Author(s):  
Nikolay Monarkin ◽  
Anton Sinitsyn ◽  
Mikhail Pavlov ◽  
Timur Akhmetov
Keyword(s):  
Energy Efficiency ◽  
Heat Capacity ◽  
Heat Exchanger ◽  
Wall Thickness ◽  
Thermal Energy ◽  
Thermal Efficiency ◽  
Heat Exchangers ◽  
Regenerative Heat ◽  
Flow Through ◽  
Geometric Length

The influence of various parameters of stationary switching regenerative heat exchangers used for ventilation on its thermal efficiency was studied. Considered are the geometric (length, diameter and wall thickness of a single equivalent nozzle channel), thermophysical (density and heat capacity of the nozzle material) and operation (air flow through the regenerator and the time of one stage of accumulation/regeneration of thermal energy) parameters.

scholarly journals Evaluation and Improvement of Thermal Energy of Heat Exchangers with SWCNT, GQD Nanoparticles and PCM (RT82)

2020 ◽  
Vol 79 (1) ◽  
pp. 153-168
Author(s):  
Mohammadreza Hasandust Rostami ◽  
Gholamhassan Najafi ◽  
Ali Motevalli ◽  
Nor Azwadi Che Sidik ◽  
Muhammad Arif Harun
Keyword(s):  
Energy Storage ◽  
Heat Exchanger ◽  
Heat Exchange ◽  
Phase Change ◽  
Thermal Energy ◽  
Thermal Efficiency ◽  
Heat Exchangers ◽  
Phase Change Materials ◽  
Single Wall Carbon Nanotubes ◽  
In Series

Today, due to the reduction of energy resources in the world and its pollutants, energy storage methods and increase the thermal efficiency of various systems are very important. In this research, the thermal efficiency and energy storage of two heat exchangers have been investigated in series using phase change materials (RT82) and single wall carbon nanotubes (SWCNT) and graphene quantum dot nanoparticles (GQD) In this research, two heat exchangers have been used in combination. The first heat exchanger was in charge of storing thermal energy and the second heat exchanger was in charge of heat exchange. The reason for this is to improve the heat exchange of the main exchanger (shell and tube) by using heat storage in the secondary exchanger, which has not been addressed in previous research. The results of this study showed that using two heat exchangers in series, the thermal efficiency of the system has increased. Also, the heat energy storage of the double tube heat exchanger was obtained using phase change materials in the single-walled carbon nanotube composition of about 3000 W. The average thermal efficiency of the two heat exchangers as the series has increased by 52%. In general, the effect of the two heat exchangers on each other was investigated in series with two approaches (energy storage and energy conversion) using fin and nanoparticles, which obtained convincing results.

Performance and Modeling of Thermosyphon Heat Exchangers for Solar Water Heaters

1997 ◽  
Vol 119 (3) ◽  
pp. 193-200 ◽  
Author(s):  
S. D. Dahl ◽  
J. H. Davidson
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Heat Exchangers ◽  
Operating Conditions ◽  
Heating Systems ◽  
Solar Water ◽  
Water Heaters ◽  
Prandtl Numbers ◽  
Area Product ◽  
Solar Water Heaters

Determining the performance of indirect solar heating systems that use thermosyphon heat exchangers requires knowledge of how thermosyphon flow rate and heat exchanger performance vary with operating conditions. In this paper, measured performance of a two-pass, tube-in-shell, double-wall heat exchanger is discussed in terms of modeling issues. Thermosyphon heat exchangers may operate in the developing, mixed convection regime where natural convection effects can significantly influence overall heat transfer and friction coefficients. Existing models which assume the thermal and hydraulic behaviors of thermosyphon heat exchangers are only functions of the thermosyphon and collector flow rates may not be suitable for all heat exchanger types. For example, the overall heat-transfer coefficient-area product for the two-pass, tube-in-shell heat exchanger is best expressed as a function of Reynolds, Grashof, and Prandtl numbers on the thermosyphon side of the heat exchanger. It is proposed that annual simulations of solar water heaters with thermosyphon heat exchangers use this type of relationship to characterize heat transfer in the heat exchanger.

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