Frost Formation Phenomenon in a Fin-and-Tube Heat Exchanger

A transient two-dimensional mathematical model of frost formation on a fin-and-tube heat exchanger has been developed and numerically solved. The mathematical model and numerical procedure have been experimentally validated. The results have shown that frost layer formation significantly influences heat transfer between air and a refrigerant. Frost layer growth is faster with higher inlet air humidity. Using the developed mathematical model, the algorithm and the computer code, which have been experimentally validated, it is possible to predict frost layer growth on fin-and-tube heat exchangers under different operating conditions

Analiza prijelaza topline unutar grijaće ploče s mnogostrukim izvorima topline

3D numerical study of transient heat transfer phenomenon on a solid plate with complex heat sources has been carried out. In order to validate the chosen numerical model, a set of thermographic measurements have been performed on a heating plate sample. The infrared camera provided a number of thermograms showing the development of transient temperature fields on the plate surface. Satisfactory agreement between thermograms and numerically obtained temperature fields has been achieved. Based upon the validated numerical model, an approach involving thermographic measurements has been used to estimate the position of heat sources inside the plate. Numerically obtained temperature distributions have been used for calculation of effective transient heating output. The unsteady behavior of the heating plate with complex heat sources has been numerically studied for different plate materials. It has been concluded that the temperature fields and transient heating outputs depend on physical properties of the plate material. However, when a steady state has been achieved, different plate materials give equivalent steady heating outputs despite different temperature distributions.Provedena je 3D numerička analiza nestacionarnog prijelaza topline u grijaćoj ploči s mnogostrukim izvorima topline. Valjanost odabranog numeričkog modela provjerena je usporedbom s termografskim snimcima koji su načinjeni na uzorku grijaće ploče. Infracrvena je kamera osigurala dovoljan broj termograma koji prikazuju nestacionarne temperaturne raspodjele na površini ploče. Usporedbom termograma i numeričkim putem dobivenih temperaturnih raspodjela utvrđena je dobra podudarnost termografskih mjerenja i numeričkih simulacija. Temeljeći se na provjerenom numeričkom modelu, razvijen je postupak za određivanje položaja izvora topline u grijaćoj ploči pomoću termografskih mjerenja. Numeričkim putem dobivene temperaturne raspodjele na površini ploče korištene su za određivanje toplinskog učina grijaće ploče. Nestacionarno ponašanje temperaturnih raspodjela na grijaćoj ploči s mnogostrukim izvorima topline ispitivano je numeričkim putem za različite materijale ploče. Zaključeno je da raspodjele temperatura i nestacionarni toplinski učini ovise o fizikalnim svojstvima materijala ploče. Međutim, kada se postigne stacionarno stanje, različiti materijali ploče daju jednake toplinske učinke usprkos različitim temperaturnim raspodjelama

Analiza prijelaza topline unutar grijaće ploče s mnogostrukim izvorima topline

3D numerical study of transient heat transfer phenomenon on a solid plate with complex heat sources has been carried out. In order to validate the chosen numerical model, a set of thermographic measurements have been performed on a heating plate sample. The infrared camera provided a number of thermograms showing the development of transient temperature fields on the plate surface. Satisfactory agreement between thermograms and numerically obtained temperature fields has been achieved. Based upon the validated numerical model, an approach involving thermographic measurements has been used to estimate the position of heat sources inside the plate. Numerically obtained temperature distributions have been used for calculation of effective transient heating output. The unsteady behavior of the heating plate with complex heat sources has been numerically studied for different plate materials. It has been concluded that the temperature fields and transient heating outputs depend on physical properties of the plate material. However, when a steady state has been achieved, different plate materials give equivalent steady heating outputs despite different temperature distributions.Provedena je 3D numerička analiza nestacionarnog prijelaza topline u grijaćoj ploči s mnogostrukim izvorima topline. Valjanost odabranog numeričkog modela provjerena je usporedbom s termografskim snimcima koji su načinjeni na uzorku grijaće ploče. Infracrvena je kamera osigurala dovoljan broj termograma koji prikazuju nestacionarne temperaturne raspodjele na površini ploče. Usporedbom termograma i numeričkim putem dobivenih temperaturnih raspodjela utvrđena je dobra podudarnost termografskih mjerenja i numeričkih simulacija. Temeljeći se na provjerenom numeričkom modelu, razvijen je postupak za određivanje položaja izvora topline u grijaćoj ploči pomoću termografskih mjerenja. Numeričkim putem dobivene temperaturne raspodjele na površini ploče korištene su za određivanje toplinskog učina grijaće ploče. Nestacionarno ponašanje temperaturnih raspodjela na grijaćoj ploči s mnogostrukim izvorima topline ispitivano je numeričkim putem za različite materijale ploče. Zaključeno je da raspodjele temperatura i nestacionarni toplinski učini ovise o fizikalnim svojstvima materijala ploče. Međutim, kada se postigne stacionarno stanje, različiti materijali ploče daju jednake toplinske učinke usprkos različitim temperaturnim raspodjelama

Numerical investigation and experimental validation of heat transfer in a small size shell and tube heat exchanger

Heat exchangers are integrated in all process and energy plants. Shell and tube heat exchanger designs are most commonly used. The efficiency and performance of the device can be determined both experimentally and numerically. In this study, a numerical model of heat transfer in a small size shell and tube heat exchanger is presented, and the results are compared with experimental data. The problem with laminar flow and steady state heat transfer was solved using the finite volume method. Three experiments were performed, and all of them showed a high match between outlet fluid temperatures. As additional validation, heat flux balance was set and calculated for both methods, which also showed a considerable match. It can be concluded that the model accurately predicts physical phenomena in analyzed heat exchanger, and can be used in further studies

A three-dimensional numerical analysis of complete crossflow heat exchangers with conjugate heat transfer

In this paper, a three dimensional numerical analysis of turbulent fluid flow and heat transfer on the air-side and water-side of plain fin-and-tube heat exchangers is performed in order to obtain their heat transfer characteristics with non-constant physical properties. Besides convection heat transfer on water and air sides, the heat conduction through pipe walls and fins is also considered in the study. The two types of heat exchangers having cascade and in-line flat tube arrangements are presented.. Heat exchangers have been numerically simulated for different inlet air temperatures and velocities. As crossflow has been taken into account, the heat exchangers have been modeled with all fins considering the temperature changes on both sides. Numerical values are compared to the results obtained by analytical calculations of the heat exchangers, and good agreement of results is derived. The heat transfer characteristics are observed to be better for the heat exchanger with cascade tube arrangement for all of the analyzed conditions

Numerical analysis of heat transfer in air-water heat exchanger with microchannel coil

This paper presents numerical analysis of fluid flow and heat transfer in the heat exchanger with microchannel coil (MCHX). In accordance with previously published experimental results, 3D mathematical model has been defined and appropriate numerical simulation of heat transfer has been performed. Geometry and working parameters of cross-flow air-water heat exchanger with microchannel coil, installed in an open circuit wind tunnel and used in experimental investigations, have been applied in numerical analysis in order to validate the mathematical model. 3D model with air and water fluid flow and heat transfer domains has been used, as it gives more precise results compared to models that assume constant temperatures or constant heat fluxes on the pipe walls. Developed model comprised full length of air and water flows in the heat exchanger. Due to limitations of computational capacity, domain has been divided in multiple computational blocks in the water flow direction and then solved successively using CFD solver Fluent. Good agreement between experimentally measured and numerically calculated results has been obtained. The influence of various working parameters on heat transfer in air-water heat exchanger has been studied numerically, followed with discussion and final conclusions

A thermodynamic analysis of heat storage in a latent heat storage unit

U radu je analiziran fizikalni proces nestacionarne izmjene topline unutar latentnog spremnika. Postavljeni je matematički model, kojeg čine diferencijalne jednadžbe strujanja i prijelaza topline fluida, diferencijalna jednadžba provođenja topline kroz stijenku te diferencijalna entalpijska jednadžba akumulatora topline, uz definirane početne i rubne uvjete, diskretiziran primjenom numeričke metode kontrolnih volumena, a dobiveni su sustavi algebarskih jednadžbi riješeni iteracijski kompjuterskim programom napisanim u programskom jeziku Fortran-u. Usporedbom rezultata dobivenih numeričkim i eksperimentalnim putem za konstruirani model latentnog spremnika utvrđeno je dobro međusobno slaganje. Za određivanje iskoristivosti primijenjena je eksergijska analiza. Numeričkim su proračunom dobivena temperaturna polja te fronte širenja područja taljenja odnosno skrućivanja u različitim vremenskim intervalima čime je simulirano toplinsko ponašanje spremnika pri spremanju i korištenju topline. Nizom numeričkih proračuna u radu je analiziran i utjecaj različitih pogonskih uvjeta i konstrukcijskih parametara na količinu spremljene odnosno iskorištene topline te eksergijsku iskoristivost latentnog spremnika.A physical process of transient heat transfer during charging and discharging of the latent heat storage unit has been analysed in this paper. A mathematical model has been set by observing heat phenomena of the conjugate problem of transient forced convection between heat transfer fluid and the wall, heat conduction through the wall and the heat exchange of the phase change material in the elementary storage section. Differential equations of flow and heat transfer of the heat transfer fluid, differential equation of heat conduction through the wall and differential enthalpy equation of the phase change material, with initial and boundary conditions, have been discretised by a control volume approach. The obtained set of algebraic equations has been solved by Fortran software using the iterative procedure. Numerical analysis has been applied to the model of latent heat storage unit, used in experimental investigations, to validate the defined numerical model. Mutual agreement has been established between numerically and experimentally obtained timewise temperature variations. An exergy analysis, based on the second law of thermodynamics, has been applied for determining the efficiency of the storage unit. Temperature fields and melting i.e. solidification fronts in different time periods have been obtained by numerical calculation of transient heat transfer in the storage unit and thermal behaviour of the heat storage unit has been simulated. A series of numerical procedures has been performed in order to analyse the influence of different operating conditions and construction parameters on the amount of charged i.e. discharged energy and exergy efficiency of the latent heat storage unit

A thermodynamic analysis of heat storage in a latent heat storage unit

U radu je analiziran fizikalni proces nestacionarne izmjene topline unutar latentnog spremnika. Postavljeni je matematički model, kojeg čine diferencijalne jednadžbe strujanja i prijelaza topline fluida, diferencijalna jednadžba provođenja topline kroz stijenku te diferencijalna entalpijska jednadžba akumulatora topline, uz definirane početne i rubne uvjete, diskretiziran primjenom numeričke metode kontrolnih volumena, a dobiveni su sustavi algebarskih jednadžbi riješeni iteracijski kompjuterskim programom napisanim u programskom jeziku Fortran-u. Usporedbom rezultata dobivenih numeričkim i eksperimentalnim putem za konstruirani model latentnog spremnika utvrđeno je dobro međusobno slaganje. Za određivanje iskoristivosti primijenjena je eksergijska analiza. Numeričkim su proračunom dobivena temperaturna polja te fronte širenja područja taljenja odnosno skrućivanja u različitim vremenskim intervalima čime je simulirano toplinsko ponašanje spremnika pri spremanju i korištenju topline. Nizom numeričkih proračuna u radu je analiziran i utjecaj različitih pogonskih uvjeta i konstrukcijskih parametara na količinu spremljene odnosno iskorištene topline te eksergijsku iskoristivost latentnog spremnika.A physical process of transient heat transfer during charging and discharging of the latent heat storage unit has been analysed in this paper. A mathematical model has been set by observing heat phenomena of the conjugate problem of transient forced convection between heat transfer fluid and the wall, heat conduction through the wall and the heat exchange of the phase change material in the elementary storage section. Differential equations of flow and heat transfer of the heat transfer fluid, differential equation of heat conduction through the wall and differential enthalpy equation of the phase change material, with initial and boundary conditions, have been discretised by a control volume approach. The obtained set of algebraic equations has been solved by Fortran software using the iterative procedure. Numerical analysis has been applied to the model of latent heat storage unit, used in experimental investigations, to validate the defined numerical model. Mutual agreement has been established between numerically and experimentally obtained timewise temperature variations. An exergy analysis, based on the second law of thermodynamics, has been applied for determining the efficiency of the storage unit. Temperature fields and melting i.e. solidification fronts in different time periods have been obtained by numerical calculation of transient heat transfer in the storage unit and thermal behaviour of the heat storage unit has been simulated. A series of numerical procedures has been performed in order to analyse the influence of different operating conditions and construction parameters on the amount of charged i.e. discharged energy and exergy efficiency of the latent heat storage unit

PARAMETRIC STUDY OF OPERATING AND GEOMETRY CHARACTERISTICS EFFECT ON HEAT TRANSFER IN ANNULAR FINNED TUBE HEAT EXCHANGER

U radu je opisana trodimenzijska numerička analiza laminarnog strujanja fluida i izmjene topline u cijevnom izmjenjivaču topline s prstenastim lamelama. Definirani numerički postupak provjeren je usporedbom s objavljenim numeričkim i eksperimentalnim rezultatima i uočeno je njihovo dobro slaganje. Niz numeričkih proračuna izvršen je s ciljem analize utjecaja različitih pogonskih i geometrijskih parametara na polja brzina i temperatura te na vrijednosti prosječnih koeficijenata prijelaza topline i izmijenjenih specifičnih toplinskih tokova unutar izmjenjivača.A three-dimensional numerical analysis of laminar heat transfer and fluid flow in an annular finned tube heat exchanger has been performed. The numerical procedure has been validated by comparison with published numerical and experimental results and good agreement has been observed. A series of numerical calculations have been carried out in order to analyse the influence of various operating and geometric characteristics on the velocity and temperature fields as well as on the average heat transfer coefficients and specific heat fluxes within a heat exchanger

A three-dimensional numerical analysis of complete crossflow heat exchangers with conjugate heat transfer

In this paper, a three dimensional numerical analysis of turbulent fluid flow and heat transfer on the air-side and water-side of plain fin-and-tube heat exchangers is performed in order to obtain their heat transfer characteristics with non-constant physical properties. Besides convection heat transfer on water and air sides, the heat conduction through pipe walls and fins is also considered in the study. The two types of heat exchangers having cascade and in-line flat tube arrangements are presented.. Heat exchangers have been numerically simulated for different inlet air temperatures and velocities. As crossflow has been taken into account, the heat exchangers have been modeled with all fins considering the temperature changes on both sides. Numerical values are compared to the results obtained by analytical calculations of the heat exchangers, and good agreement of results is derived. The heat transfer characteristics are observed to be better for the heat exchanger with cascade tube arrangement for all of the analyzed conditions