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Characterisation and modelling of thermal stratification in hot water storage tanks
Thesis (PhD)--Stellenbosch University, 2024.
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Stellenbosch : Stellenbosch University
2025
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| _version_ | 1867613735665795072 |
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| access_status_str | Open Access |
| author | Van Schalkwyk, Pieter Daniel |
| author2 | Booysen, M. J. |
| author_browse | Booysen, M. J. Van Schalkwyk, Pieter Daniel |
| author_facet | Booysen, M. J. Van Schalkwyk, Pieter Daniel |
| author_sort | Van Schalkwyk, Pieter Daniel |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description |
Thesis (PhD)--Stellenbosch University, 2024. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/131960 |
| institution | Stellenbosch University (South Africa) |
| last_indexed | 2026-06-10T12:40:52.447Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2025 |
| publishDateRange | 2025 |
| publishDateSort | 2025 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/131960 Characterisation and modelling of thermal stratification in hot water storage tanks Van Schalkwyk, Pieter Daniel Booysen, M. J. Engelbrecht, J. A. A. Meyer, J. P. Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering. Heat storage Computational fluid dynamics Water heaters Thermodynamics -- Mathematical models UCTD Thesis (PhD)--Stellenbosch University, 2024. ENGLISH ABSTRACT: As the world strives to reduce greenhouse gas emissions and move towards more sustainable energy systems, the importance of improving the efficiency of domestic heating technologies has become increasingly evident. Electric water heaters and hot water buffer tanks, key components in thermal energy storage, are widely used for providing hot water worldwide. However, the horizontal orientation of these tanks, especially in countries like South Africa, Australia, and China, has been understudied, particularly concerning thermal stratification and energy efficiency. This thesis addresses this research gap by investigating the thermal distribution and stratification in horizontally orientated electric water heaters and buffer tanks. Through the development of a custom-built experimental test bench, detailed temperature distribution data were collected under various operational conditions. These data were used to create a validated thermal state-space model that accurately predicted thermal behaviour, achieving a precision of 90.6% for the normalised stratification factor and 94.6% for the exergy number. The model was extended to incorporate dynamic scenarios with uni- and bidirectional flow, amounting to an overall accuracy of 91.5%, applicable to both electric water heaters and cogeneration buffer tanks. The high accuracy of these analytical models makes them particularly suitable for practical applications in energy management and optimisation. Additionally, a validated computational fluid dynamics model was developed to simulate three common operational modes in horizontally orientated electric water heaters: heating, heating with water draw, and heat transfer between layers. The model, validated with a mean relative error of 4.6%, revealed the impact of heating coil placement on thermal stratification and provided a description of convective flow path from the heating coil. Simulations showed that the active heating coil during water withdrawal enhanced thermal stratification, improving the stratification factor by up to 11.5%. The final scenario demonstrated a gradual convergence towards thermal equilibrium, providing insights for future research on thermal models and bacterial proliferation under varying conditions. The research findings from this thesis contribute to a better understanding of the thermal behaviour of hot water storage tanks and provide accurate analytical and numerical models to further aid future development in this field. AFRIKAANSE OPSOMMING: Soos wat die wˆereld streef om kweekhuisgasvrystellings te verminder en na meer volhoubare energiestelsels te beweeg, word die belangrikheid van die verbetering van die doeltreffendheid van huishoudelike verhittingstegnologie ¨e toenemend duidelik. Elektriese waterverwarmers en warmwaterbuffertenks, sleutelelemente in termiese energiestoor, word wyd gebruik vir die voorsiening van warm water wˆereldwyd. Die horisontale ori¨entasie van hierdie tenks, veral in lande soos Suid-Afrika, Australi¨e en China, is egter onderbestudeer, veral met betrekking tot termiese stratifikasie en energiedoeltreffendheid. Hierdie tesis spreek hierdie navorsingsgaping aan deur die termiese verspreiding en stratifikasie in horisontaal geori¨enteerde elektriese waterverwarmers en buffertenks te ondersoek. Deur die ontwikkeling van ’n eksperimentele toetsopstelling, is temperatuurverspreidingsdata onder verskeie operasionele toestande ingesamel. Hierdie data is gebruik om ’n gevalideerde termiese “state space” model te skep wat termiese gedrag akkuraat voorspel het, met ’n presisie van 90.6% vir die genormaliseerde stratifikasiefaktor en 94.6% vir die “exergy number”. Die model is uitgebrei om dinamiese gevalle met uni- en bidirectionele vloei in te sluit, wat gelei het tot ’n algehele akkuraatheid van 91.5%, van toepassing op beide elektriese waterverwarmers en warmwaterbuffertenks. Die ho¨e akkuraatheid van hierdie analitiese modelle maak dit veral geskik vir praktiese toepassings in energiebestuur en optimalisering. Verder is ’n gevalideerde rekenaarsvloei dinamika model ontwikkel om drie algemene operasionele gevalle in horisontaal geori¨enteerde elektriese waterverwarmers te simuleer: verhitting, verhitting met wateronttrekking, en hitte-oordrag tussen lae. Die model, gevalideer met ’n gemiddelde relatiewe fout van 4.6%, het die impak van spiraalplasing op termiese stratifikasie onthul en ’n beskrywing van die konvektiewe vloei pad vanaf die verhittingsspiraal verskaf. Simulasies het getoon dat die aktiewe verhittingsspiraal tydens wateronttrekking termiese stratifikasie verbeter het, wat die stratifikasiefaktor met tot 11.5% verbeter het. Die finale geval het ’n geleidelike konvergensie na termiese ewewig gedemonstreer, wat insigte bied vir toekomstige navorsing oor termiese modelle en bakteriese proliferasie onder verskillende toestande. Die navorsingsbevindinge van hierdie tesis dra by tot ’n beter begrip van die termiese gedrag van warmwatertenks en verskaf akkurate analitiese en numeriese modelle om verdere ontwikkeling in hierdie veld te ondersteun. Doctoral 2025-05-02T08:57:35Z 2025-05-02T08:57:35Z 2024-12 Thesis https://scholar.sun.ac.za/handle/10019.1/131960 Stellenbosch University xiv, 112, 17 pages : illustrations application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Heat storage Computational fluid dynamics Water heaters Thermodynamics -- Mathematical models UCTD Van Schalkwyk, Pieter Daniel Characterisation and modelling of thermal stratification in hot water storage tanks |
| title | Characterisation and modelling of thermal stratification in hot water storage tanks |
| title_full | Characterisation and modelling of thermal stratification in hot water storage tanks |
| title_fullStr | Characterisation and modelling of thermal stratification in hot water storage tanks |
| title_full_unstemmed | Characterisation and modelling of thermal stratification in hot water storage tanks |
| title_short | Characterisation and modelling of thermal stratification in hot water storage tanks |
| title_sort | characterisation and modelling of thermal stratification in hot water storage tanks |
| topic | Heat storage Computational fluid dynamics Water heaters Thermodynamics -- Mathematical models UCTD |
| url | https://scholar.sun.ac.za/handle/10019.1/131960 |
| work_keys_str_mv | AT vanschalkwykpieterdaniel characterisationandmodellingofthermalstratificationinhotwaterstoragetanks |