Applied thermodynamics & heat transfer

Applied thermodynamics & heat transfer

We specialize in thermodynamics and heat transfer doing experimental and numerical research.

We specialize in thermodynamics and heat transfer doing experimental and numerical research.

 

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Compact heat exchangers

Background

Compact heat exchangers are used in a great variety of applications. They allow for an increased heat transfer rate, require less volume and weigh less compared to other heat exchanger types. The disadvantage is the higher pressure drop. They are clearly the preferred choice for applications which require a high heat transfer rate in a limited volume such as air conditioning devices, heat pumps, automotive radiators, etc. In these applications the main thermal resistance is located on the airside. To improve the heat transfer rate different strategies are used such as the addition of fins at the airside (e.g. plain fins, louvered fins, slit fins, offset strip fins, ...), the use of vortex generators or the application of novel materials (e.g. metal foams, polymer heat exchangers, …). Only a limited number of fin designs or configurations with novel materials have been studied and described in open literature, as a large set of experiments is required to acquire sufficient data and the parameter space considered is very large. Currently these experiments are performed on actual heat exchangers or scaled versions. However, as the computational power and accuracy of simulation codes increase, more and more research is being done through 'numerical experiments', i.e. computational fluid dynamics (CFD). Careful benchmarking remains very important, especially when performing heat exchanger optimization.

Scope of research

This research aims to investigate the interaction between the flow behaviour and the resulting thermodynamics within compact heat exchangers (fin structures) in order to optimize and design better units for specific applications. Both experimental and numerical studies are performed, seeking a strong synergy between these disciplines. The experimental data (water tunnel and wind tunnel experiments, hotwire measurements, Laser Doppler Anemometry (LDA), infrared (IR) thermography, ...) are used to develop heat transfer and pressure drop correlations. They also provide reliable benchmarking data for numerical codes (cycle simulations, full scale heat exchanger simulations or CFD flow field and thermal hydraulic computations). The numerical results provide a more detailed look into the flow physics. This combined approach is currently used to study junction flows and the use of vortex generators in compact heat exchangers (H. Huisseune), the use of metal foams for heat exchanger applications (P. De Jaeger) and the performance characteristics of different enhancement techniques (B. Ameel).

Wind tunnelWater tunnel

Two phase flow heat transfer

Background

Evaporation is a very effective heat transport mechanism due to the latent heat transfer. An evaporating fluid extracts this heat from its surroundings. The flow behavior has a strong influence on the two phase flow heat transfer and pressure drop. In compact fin and tube heat exchanger the refrigerant flows through a tube which is folded up in to a series of hairpins. Very little is known about the influence of these hairpins on the flow behavior. Most known correlations and models for the two phase heat transfer and pressure drop are only valid for undisturbed flow in straight tubes. Yet, qualitative studies have shown that the effect of the bends could significantly affect the flow behavior.

Scope of research

This research aims to investigate the effect of the geometry on the two phase flow behavior. The evolution of the flow behavior and the pressure drop through a hairpin is studied. The research is solely experimental. In previous research a capacitive sensor was developed to study the flow behavior is straight tubes. In this work the flow behavior is studied with this capacitive sensor and with flow visualizations. The flow behavior is studied to acquire more insight on the mechanisms causing the evolution of the pressure drop in a hairpin. These insights together with the pressure drop measurements are then used to develop a more accurate model for the two phase flow pressure drop in a hairpin. Using this model the effect of the hairpins can better be accounted for in the heat exchanger design. This improved design will reduce the oversizing of the heat exchanger and increase the coefficient of performance.

Hairpin

Heat, air and moisture (HAM) transfer in buildings

Background

Humidity of indoor air is an important factor influencing the indoor air quality, energy consumption of buildings, conservation of valuable objects and durability of building components. The relative humidity in buildings depends on several factors such as moisture sources, air change, possible condensation and absorption and release of vapor by porous materials. Porous materials are characterized by their possibility to store moisture in a liquid phase even at a relative humidity below 100% and can be found in most buildings (e.g. in the building envelope, furnishings, books, wooden objects, textiles, ...). In order to predict the relative humidity in a detailed way, the effect of moisture buffering needs to be integrated into heat and airflow simulation tools. Heat Air and Moisture (HAM) models allow describing coupled heat and mass transfer in porous materials. The research conducted in this field mainly focuses on coupling HAM models with CFD-tools (Computational Fluid Dynamics) or BES-tools (Building Energy Simulation) to predict either the local indoor humidity around objects or the indoor humidity in multizone buildings.

Scope of research

The 3D CFD-HAM model, which was previously developed, is limited to vapor diffusion in porous materials. To be able to account for condensation in building materials, this model needs to be expanded. This research project forms a continuation of the previous work and focuses both on numerical modeling and experimental validation.

A model for film condensation will be developed. Film condensation is a phenomenon in which a liquid film is formed at the surface of non-hygroscopic materials such as tiles. In a next phase this model will be extended to describe droplet condensation. Run-off of droplets will be taken into account. Both newly developed models will be implemented in the currently existing CFD-HAM model. Thirdly the CFD-HAM model will be extended to liquid moisture flow. In this way a complete coupled model is established which allows to combine liquid moisture transport, air transport and interstitial condensation. This model will be used to compare numerical modeling results with in-situ measurements.

Each of the different modeling steps will be extensively validated by means of laboratory experiments. An experimental setup is built which can be used to validate the newly developed coupled model. To validate the original CFD-HAM model, laboratory tests in a climatic chamber where a conditioned air jet enters at the opposite side of a test sample are performed. The newly developed models describing film condensation and droplet condensation in CFD, will be validated by using free water surface experiments and experiments on a cold impermeable surface respectively.

This research is performed in cooperation with the Building Physics Research Group of the Department of Architecture and Urban Planning at the Ghent University.

Schematic representation of the climatic chamber.

Heat transfer in engines

Background

The focus of the research on hydrogen as an alternative fuel at Ghent University has shifted from experimental to numerical research with the development of a thermodynamic model of the engine cycle, the GUEST-code (Ghent University Engine Simulation Tool). GUEST enables a cheap and fast optimization of engine settings for operation on hydrogen. Several sub models are necessary to solve the conservation equations of energy and mass including a combustion, a turbulence and a heat transfer model.

GUEST will be expanded with emission calculations of oxides of nitrogen. These emissions can occur in hydrogen internal combustion engines at high loads and they are an important constraint for power and efficiency optimization. The heat transfer sub-model is important to accurately simulate the emissions of oxides of nitrogen because they are influenced by the maximum gas temperature.

Scope of research

Several heat transfer models for internal combustion engines (ICE) exist in the literature. Most of these models have been developed for fossil-fuelled engines. However, the heat transfer process of hydrogen differs a lot compared to that of a fossil fuel so the models have to be evaluated for hydrogen and adjustments will be made if necessary.

Measurements of heat transfer and wall temperatures are necessary to evaluate the heat transfer models. Measuring heat transfer in a combustion engine is complex because it is a fast transient process where high temperatures are involved, and there is strong cycle to cycle variation. The first part of the research is therefore focused on the development and comparison of different measurement methods. Three types of local heat flux sensors are being compared: a coaxial type, an eroding ribbon type and a film type. The engine used for the heat transfer measurements is a four-stroke single-cylinder spark ignited gas engine based on a CFR (Cooperative Fuel Research) engine operated at a constant speed of 600 rpm. It is equipped with port fuel injection (PFI) and has a variable compression ratio.

This research is performed in cooperation with the Research Group Transport Technology.

Small scale energy production systems

Fuel cells

Fuel Cells are one of the future technologies for small scale high efficiency production. In order to better understand the thermal behavior and develop strategies for thermal management, thermodynamic models are developed for AFC, SOFC, MCFC and PEMFC. Current research is focusing on the application of Alkaline Fuel Cells for building coupled CHP.

Organic Rankine Cycle (ORC)

Organic Rankine cycles are an interesting technology for waste heat recovery. Several industrial realizations are known. There are still a lot of issues to be looked at in order to realize higher efficiencies and better performance. Research focuses on thermodynamic modeling of eg supercritical ORCs, control strategies and the design of heat exchangers for ORC cycles.

Education

The research group Applied Thermodynamics and Heat Transfer is responsible for the following courses at the Ghent University:

Course information for students can be found at the Minerva website.

Michel De Paepe is coordinator of the Lecture Series on Energy Efficiency in Industry at the Institute of Permanent Education (IVPV) of the UGent. This lecture series is meant to give the participants insight into the complex matter of energy use in industry.

Michel De Paepe is guest professor at the University of Antwerp (UA) for the bachelor course of Thermodynamics and Fluid Mechanics and the master course in Fluid Machines at the Faculty of Applied Economics of the University of Antwerp.

Support to industry

Services to industry research group Applied Thermodynamics & Heat Transfer

The Research Group Applied Thermodynamics and Heat Transfer provides advisory work to industry in its field of research. Companies in need of advice on problems in thermal engineering are welcome to contact us.

This work is conducted under the coordination of the Sustainable Energy Technologies (SET) consortium of the UGent. Please contact the SET responsible (Jeroen De Maeyer) for information on contracting, confidentiality, government support, etc.

The research group also has testing facilities which are available for industry:

  • Guarded hot plate method for the determination of the thermal conductivity of insulation and building materials (ISO 8302 and NBN B 62-201);
  • Parallel hot wire method for the determination of the thermal conductance of building materials (NBN B 62-202);
  • Determination of the autoignition temperature of materials.

Team

Head of the research group

Professor Michel De Paepe (Bibliography)

Michel De Paepe (°1972) is professor of Thermodynamics in the Faculty of Engineering and Architecture at Ghent University.

He graduated as Master of Science in Electro-Mechanical Engineering at Ghent University in 1995. In 1999 he obtained the PhD in Electro-Mechanical Engineering at Ghent University, graduating on ‘Steam Injected Gas Turbines with Water Recovery’. In 2005 he spent 3 months as a visiting professor at the University of Pretoria (South Africa), doing research on flow regime detection.

Tenured Academic Staff

 

Scientific staff & PhD students

  • Zaaquib Ahmed - 3D modeling of the slab in a walking-beam furnace
  • Wim Beyne - 3D modeling of PCM-foam thermal storage systems
  • Filip Bronchart - development of efficient dehumidification device for greenhouses (Bibliography)
  • Willem Faes - Strategies for the design and predictive maintenance of heat exchangers used in geothermal applications
  • Alihan Kaya - heat transfer and pressure drop of working fluids in subcritical ORCs (Bibliography)
  • Marija Lazova - heat transfer and pressure drop of working fluids in supercritical ORCs (Bibliography)
  • Hugo Monteyne - methodology for affordable sustainable building design for hot and humid climates
  • Jasper Nonneman - test engineer
  • Aditya Pillai
  • Wito Plas
  • Katarina Simić - Development of dynamic heat pump and TES models
  • Ilya T'Jollyn - advanced cooling of power electronics (Bibliography)
  • Jera Van Nieuwenhuyse
  • Judith Vander Heyde

Supporting staff

  • Thomas Blancke
  • Frederik Martens

Former scientific staff

  • Marijn Billiet - gas-liquid distribution of refrigerants in compact heat exhangers (Bibliography)

Who are we?

Mission

We provide to society excellent education, revolutionary research and expert knowledge in thermal engineering for a sustainable world.

 

History & Vision

The research Group Applied Thermodynamics and Heat Transfer (ATHT) was founded by Prof. Michel De Paepe in 2002 as a part of the Ghent University Faculty of Engineering and Architecture. ATHT focuses on systems where thermal energy transfer is the main energy transfer mode. The aim is to develop more energy efficient systems. By doing this, the research contributes to formulating technical solutions for the reduction of CO² emissions in compliance with the 20-20-20 directive of the European Union and 2030 framework for climate and energy policies.

 

Team

 

 

 

What do we do?

Main research topics research group Applied Thermodynamics & Heat Transfer Ghent University