Thermal performance of hydronic radiator with flow plsation Nmerical investigation Embaye, Mebraht; Al-Dadah, Raya; Mahmod, Saad DOI: 10.1016/j.applthermaleng.2014.12.056 License: Other (please specify with Rights Statement Docment Version Peer reviewed version Citation for pblished version (Harvard: Embaye, M, Al-Dadah, R & Mahmod, S 2015, 'Thermal performance of hydronic radiator with flow plsation Nmerical investigation' Applied Thermal Engineering, vol 80, pp. 109-117. DOI: 10.1016/j.applthermaleng.2014.12.056 Link to pblication on Research at Birmingham portal Pblisher Rights Statement: NOTICE: this is the athor s version of a work that was accepted for pblication in Applied Thermal Engineering. Changes reslting from the pblishing process, sch as peer review, editing, corrections, strctral formatting, and other qality control mechanisms may not be reflected in this docment. Changes may have been made to this work since it was sbmitted for pblication. A definitive version was sbseqently pblished in Applied Thermal Engineering, Vol 80, April 2015, DOI: 10.1016/j.applthermaleng.2014.12.056. Eligibility for repository checked March 2015 General rights Unless a licence is specified above, all rights (inclding copyright and moral rights in this docment are retained by the athors and/or the copyright holders. The express permission of the copyright holder mst be obtained for any se of this material other than for prposes permitted by law. Users may freely distribte the URL that is sed to identify this pblication. Users may download and/or print one copy of the pblication from the University of Birmingham research portal for the prpose of private stdy or non-commercial research. User may se extracts from the docment in line with the concept of fair dealing nder the Copyright, Designs and Patents Act 1988 (? Users may not frther distribte the material nor se it for the prposes of commercial gain. Where a licence is displayed above, please note the terms and conditions of the licence govern yor se of this docment. When citing, please reference the pblished version. Take down policy While the University of Birmingham exercises care and attention in making items available there are rare occasions when an item has been ploaded in error or has been deemed to be commercially or otherwise sensitive. If yo believe that this is the case for this docment, please contact UBIRA@lists.bham.ac.k providing details and we will remove access to the work immediately and investigate. Download date: 29. Jn. 2018
Accepted Manscript Thermal Performance of Hydronic Radiator with Flow Plsation Nmerical Investigation M. Embaye, R.K. AL Dadah, S. Mahmod PII: S1359-4311(1401185-5 DOI: 10.1016/j.applthermaleng.2014.12.056 Reference: ATE 6250 To appear in: Applied Thermal Engineering Received Date: 12 Jly 2014 Revised Date: 22 December 2014 Accepted Date: 22 December 2014 Please cite this article as: M. Embaye, R.K. AL Dadah, S. Mahmod, Thermal Performance of Hydronic Radiator with Flow Plsation Nmerical Investigation, Applied Thermal Engineering (2015, doi: 10.1016/j.applthermaleng.2014.12.056. This is a PDF file of an nedited manscript that has been accepted for pblication. As a service to or cstomers we are providing this early version of the manscript. The manscript will ndergo copyediting, typesetting, and review of the reslting proof before it is pblished in its final form. Please note that dring the prodction process errors may be discovered which cold affect the content, and all legal disclaimers that apply to the jornal pertain.
Thermal Performance of Hydronic Radiator with Flow Plsation Nmerical Investigation ABSTRACT M. Embaye, R. K. AL Dadah*, S. Mahmod School of Mechanical Engineering University Of Birmingham, Birmingham, Edgbaston. B5 7NQ *Corresponding Athor: Tel. 00441214143513, Email r.k.al-dadah@bham.ac.k Improving the heat otpt of hydronic central heating system in bildings can play a major role in energy saving. Crrent panel radiators of central heating systems are operating at constant flow strategy with thermostat control device. Sch operating mode is not efficient in terms of energy consmption; therefore an alternative operating scenario is reqired to enhance the heat otpt of the panel radiator. The main aim of this research is to investigate the effect of plsed flow inpt on the energy consmption of panel radiators while maintaining the target panel srface temperatre. CFD modelling of two hydronic panel radiators with constant and plsating flows were developed sing the conjgate heat transfer modle in COMSOL Mltiphysics software. The radiators sed were one with single finned srface (type 11 and the second is withot fins (type 10, both with the dimensions of 500mm long and 300mm high. The CFD reslts of the constant flow conditions were compared to pblished experimental work showing good agreement with maximm deviation of 2.4% in the heat otpt. To investigate the effects of plsating flow on the performance of the two panel radiators, a wide range of inpt plsating flows with amplitde ranging from 0.027m/s to 0.051 m/s and freqency ranging from 0.0523 rad/s to 0.209rad/s while the flow spply temperatre remained constant at 75 o were simlated. The simlation reslts showed that sing plsed flow can redce the energy consmption of panel radiators by p to 20% compared to constant flow operating condition while maintaining the same radiator srface temperatre of 50 o C. Sch reslts highlight the potential of sing plsed flow to redce the energy consmption of central heating systems in bildings withot compromising the ser comfort. Keywords: Energy saving, CFD modelling, COMSOL Mltiphysics, Flow plsation, Constant flow
1. Introdction Bilding energy tilization has important impact on energy consmption and greenhose gas emission all over the world. The energy statistical data indicates that arond 50% of the total energy consmed in the developed contries is for bildings sage [1]. This prodces significant amonts of CO 2 emission and other environmental polltants which contribte to global warming [2]. This has led the Eropean Union to legislate for redcing its energy consmption by 20% before 2020 which was adopted by the member states [3]. Enhancing the efficiency of domestic central heating system is an important factor in achieving this target. Considerable research has been carried ot in order to improve the domestic central heating systems. The stdies were carried ot based on the heat sorces and heating appliances. Heat sorces inclde Heat pmp, District heating, Boiler (Combi boiler, Condensing boiler, and CHP (Combined Heat and Power. Heating appliances inclde panel radiators with convective fins and withot convective fins, floor heating and air heating, skirting s (baseboard. Hydronic (water based heating radiators are predominantly sed for internal heat emission within the residential sector in Erope [4]. The advantages of the heating panel radiator as a heat emitter are: compact design, less space reqirement in the rooms and ease of installation to new bildings or retrofits. Varios research works have been carried ot to enhance the central heating system performance based on design optimization of the panel radiator. Myhren and Halberg [5] achieved improvement in the heat transfer otpt from panel radiators by increasing the air flow on its heat transferring srfaces. They conclded that, sing ventilation-radiators the desired thermal climate cold be achieved with a radiator srface temperatre as mch as 7.8 o K lower than standard vales. The possibility of enhancing the heat otpt from the panel radiator by coating the wall behind the radiator in different colors with different emissivity vales was also stdied by [6]. The stdy conclded that, the wall coated with higher emissivity (smooth black srface material can improve the heat otpt of the heating panel radiator by p to 26%. Beck et al [7] investigated the heat transfer enhancement of panel radiations by placing one or two high emissivity metal sheets between the interior srfaces of doble panel radiators. They conclded that placing two high emissivity metals in the interior side of the doble
panel radiator can prodce an improvement of abot 88% compared to the doble panel radiator. Enhancement of hydronic heating system sing baseboard device integrated air spply was reported by Ploskic and Holmberg [4, 8]. The aim of their work was to minimize the spply temperatre by pre-heating the incoming ventilation airflow and conclded that the heat otpt of their proposed system can prodce abot 21% more heat compared to the traditional hydronic baseboard heating system [4, 8]. Myhren and Holmberg [9] carried ot a stdy to enhance the energy efficiency in exhast-ventilated bildings with warm water heating system sing ventilation radiator combined with heat emission device. A CFD model of the proposed system was developed and reslts showed that the heat otpt can be increased by 20% compared to traditional radiators. The hydronic baseboard heating system was stdied by [10]. The aim of the stdy was to investigate the capability of the baseboard spplied at low temperatre ranges 40 o C - 45 o C to sppress strong downdraghts. They conclded that the baseboard at these range of temperatre is nable to spress the strong downdraght instead they have sed a spply temperatre of 55 o C and that was able to overcome the downdraghts to comfort level. Optimization of heat otpt of the ventilation radiator was stdied by varying the distribtion of the vertical longitdinal convection fins sing comptational flid dynamics (CFD [11]. They showed that heat transfer can be enhanced by p to 17% by changing the geometrical design of the fins, decreasing the fin to fin distance and ctting the middle section of the fin array. Sanjay and Avanic [12] investigated the se of phase change material to optimize the heat otpt from the hydronic panel radiator and conclded that 20-25% of energy can be saved compared to the traditional radiators. Kerriganaet et al [13] investigated the se of heat pipes to improve the performance of panel radiators at spply temperatre as low as 55 o C.The power density of the tested panel radiator fitted with heat pipes was nearly tripled compared to the traditional panel radiator. Therefore the researchers conclded that the heat pipe based natrally aspirated radiator is a possible alternative to replace traditional panel radiators particlarly when low temperatre water heating systems sch as heat pmps are sed. Extensive stdy has been carried ot by varios researchers to enhance the heat transfer of varios heat emitting devices. Flow plsation is a method of heat transfer enhancement applied in varios indstrial applications inclding heat exchangers, plse combstors, electronic cooling devices and cooling of nclear reactors [14]. A stdy was
carried ot by [15] to enhance the heat transfer of the parallel and conter flow heat exchangers sing ball valve as plsar device. Reslts showed that sing plsed flow, the heat transfer can be enhanced by 20% for the parallel flow heat exchangers and 90 % for the conter flow ones. The effect of flow plsation in heat transfer enhancement of the doble pipe steam water heat exchangers sing solenoid valve triggered by pressre switch was stdied by [16]. The test was performed at Reynolds nmber ranges from 500 to 5000; and freqency of 1.5 Hz and conclded that the overall heat transfer coefficient was increased by 80% depending on closeness of the solenoid valve to the test section. Effect of plsed pertrbation on convective heat transfer for laminar flow on co-axial cylindrical tbe heat exchangers was experimentally investigated by [17]. The test was performed at lower Reynolds nmber ranging from 150 to 1000; freqency of 0 to 2Hz with reciprocating pmp was sed as plsating device. Based on the reslts they conclded that the heat transfer coefficient can be enhanced by 300% sing the strong plsed pertrbations. Experimental stdy was carried ot to explore the convective heat transfer enhancement from heated cylinder in a plsating flow. A series of experiments was condcted to compare the heat transfer enhancement for plsed air jet and steady flow air jet and reslts showed that abot 50% heat transfer enhancement was achieved with the plsed jet compared to the steady flow jet [18]. Sailoret al [19] investigated the potential of embedding plsating heat pipes for space or terrestrial applications. The enhancement techniqe was based on the selection of Biot nmber that minimizes the condctive resistance of the thermal radiator. They conclded that effective thermal condctivities of 400W/mK- 2300W/mK can be achieved de to the applied plsed flow. Despite the nmber of stdies reported for sing plsating flow to enhance heat transfer of heating or cooling devices, there are limited stdies regarding its se to improve panel radiators in hydronic heating systems. Therefore, this work aims to investigate the heat transfer enhancement de to flow plsation in panel radiator based hydronic central heating system sing comptational flid dynamics modelling with COMSOL mlti-physics software. The work investigates the energy saving by sing flow plsation in two types of panel radiators namely; type 10 withot fins and type 11 single fined panel radiators.
2. CFD Simlation CFD three dimensional simlations of panel radiators type 10 and 11 were carried ot sing conjgate heat transfer physics within COMSOL mlti-physics [20]. The Navier Stokes eqations (Eqs. (1-(3 of continity, momentm and energy sed to simlate the heat transfer and flid flow within the panel radiators and the srrondings [21]. F I I pi t T T T = ] 3 2. ( ( 3 2 ( ( (.[. ( ρκ µ µ µ ρ ρ (1 Where: ε κ ρ µ µ 2 C T = 0.( = V t ρ ρ (2 Q T k T V C dt dt C p p =.(. ρ ρ (3 The k-ε Reynolds Average Navier Stokes (RANS trblent model was sed to model the trblent flow inside the radiator channels [20, 21]. The vales for the trblence model of κ (trblent kinetic energy,ε(trblent dissipation rate, and the pressre are calclated sing Eqs. (4, (5 and (6 respectively. ρε κ σ µ µ κ ρ κ ρ κ κ = p t T ] [(. ( (4 κ ε ρ κ ε ε σ µ µ ε ρ ε ρ ε κ ε ε 2 2 1 ] [(. ( C p C t T = (5 p T T. 3 2 ]. ( 3 2 ( ( : [ 2 = ρκ µ κ (6
Where: ρ, C P,T,, p, Q, I, F,ε, μ T, μ, p k, K, V and k are density, specific heat capacity, temperatre, velocity vector, pressre, heat sorce other than viscos, identity matrix of [3*3], total force acting per volme, the trblence dissipation rate, trblence dynamic viscosity, dynamic viscosity, trblent kinetic pressre, heat condctivity, volme and the trblence kinetic energy respectively. Fig. 1 shows the 3D model of panel radiator (type11 with the selected mesh concentration for the water flow domain and the fins. Table 1 presents the thermal properties of the materials sed in the panel radiator. The panel radiator model incldes the rectanglar dcts, 15mm side with thickness of 1mm, and fins 270 mm high with thickness of 0.5mm. The radiator model was meshed based on the geometrical strctre of each component; swept rectanglar mesh was generated for the fins (478080 elements and tetrahedral mesh was selected for the water domain and the flow channels (1759121 elements. Assmptions sed to simlate the panel radiators in both plsed and constant flow conditions inclde: Natral convection cooling was applied on the air side srface of the radiator Constant hot water spply temperatre of 75 o C was considered Heat transfer de to radiation was applied at constant emissivity vale of 0.85. The heat transfer coefficient of the air side srface of the radiator was considered as natral convection and was calclated sing the well-known empirical correlation given in Eq. (7 [4]. N = hl k where : = 0.59( Ra 3 g. β ( Ts Tamb L (7 Ra = Gr.Pr = (.Pr 3 ν g. β ( Ts T h = 0.59. 3 ν 1/ 4 amb 3. L.Pr 1/ 4. k L Where: N, Gr, h, L, Ra, T s, T amb, g, Pr, k, and β are the Nsselt nmber, Grashof nmber, convection heat transfer coefficient, characteristics height, Rayleigh nmber, srface temperatre, ambient temperatre, gravitational acceleration, Prandtl nmber (0.71 for air, thermal condctivity, and expansion coefficient (which is 1/T average respectively.
3. CFD Simlation of the radiators at constant flow rate In this section, nmerical simlation of two panel radiators (type 10 and type 11 at constant flow rate was carried ot to predict the radiators temperatre distribtion and the heat otpt. Sch prediction will be sed as a reference case for the proposed plsed flow analysis and for validation reasons since experimental data is available for constant flow scenario. The radiators were nmerically simlated at constant hot water inlet mass flow rate of 0.00434kg/s for type 10 and 0.00571kg/s for type 11, constant inlet temperatre of 75 o C and ambient air temperatre of 20 o C. Sch flow rates were determined to prodce water otlet temperatre of 65 o C and radiators average srface temperatre of 50 o C as recommended by BS EN 442 [22-25]. Fig. 2 shows the radiators local srface temperatre distribtion at constant hot water inlet flow rate for both radiators. Fig. 3 shows the variation of flow otlet temperatre, radiator average srface temperatre and the rate of heat otpt from the radiators with time for type 10 (Fig. 3(a and type 11 (Fig. 3(b. It is clear from Fig. 3 that the average srface temperatre for both radiators achieved the target average srface temperatre of 50 o C and water otlet temperatre of 65 o C as recommended by BS EN 442. However, radiator type 11 prodced higher heat otpt rate de to the increased srface area prodced by the fins. The CFD reslts of both type 10 and type 11 radiators were validated based on the experimental reslts reported in [23-25]. Validation was carried ot based on the radiator hot water otlet temperatre, the average srface temperatre and the rate of heat otpt according to the BS EN 442. The rate of heat otpt from the radiator can be calclated sing Eq. (8. Q, ot = U rad. Arad LMTD (8 rad. Where U rad is overall heat transfer coefficient of the panel radiator determined sing Eq. (9 as: qrad Urad = (9 LMTD and LMTD is the log mean temperatre difference given in Eq. (10 as: LMTD = T T ln( T w, in w, in w, ot T T w, ot T ind ind (10
q rad is the total heat flx obtained from the srface of the panel radiator. Tables 2 and 3 compare the simlation reslts to the experimental vales [24] in terms of the water otlet temperatre, the radiator average srface temperatre and the rate of heat otpt for both radiators. The deviation between the experimental and simlation reslts is determined sing Eq. (11. Exp CFD Dev% = *100 (11 Exp As shown in Tables 2 and 3 the maximm deviation were 0.27% for the water otlet temperatre, 1.20% for the radiator average srface temperatre and 2.44% for the rate of heat otpt. Sch low deviation vales indicate good agreement between the experimental and the CFD analysis which highlights the validation of the nmerical simlation approach. 4. CFD simlation of plsed flow radiator This section presents the CFD investigation of the two panel radiators sing plsed flow inpt conditions. Fig. 4 shows the general profile of the plsed flow sed in this investigation where it is governed by two major parameters namely; the amplitde (amp [m/s] and freqency (freq [Hz]. Strohal nmber is a dimensionless parameter that describes plsating flow mechanisms and relates the freqency of plsation to the velocity of the flow as shown in Eq. (12. freq. L St = (12 V For heat transfer enhancement applications, Strohal nmber vales between 0 to 1 are recommended to achieve significant heat transfer enhancement de to flow plsation [26]. For each radiator, the maximm flow rate is specified by its manfactrer depending on the heat otpt, size and type. For type10, the maximm mass flow rate is 0.0043 kg/s while for type11 it is 0.005710 kg/s [22, 27]. Sch maximm flow rates limit the vale of the flow plsation amplitde. Also, there are limitations on the flow freqency that can be sed de to noise and vibration considerations for hman threshold of hearing [28]. Based on these velocity amplitde and freqency limitations, the range of Strohal nmber that can be sed for radiators type10 and 11 are 0.343 to 0.89 and 0.23 to 0.65 respectively. Also, the Reynolds nmber (Eq.(13 associated with these flow conditions for both types of radiators
is below 2300 indicating that the flow is laminar. Finally, the inlet hot water temperatre and ambient temperatre were fixed at 75 o C and 20 o C respectively for both types of radiators. ρvd Re = h µ where; D h = (13 4A Per Table 4 shows the varios flow amplitdes and average hot water mass flow rate at constant freqency of 0.209rad/s corresponding to maximm Strohal nmber. Fig. 5 shows the specific heat otpt of the two types of radiators at varios plsating flow amplitdes shown in Table 4. The specific heat otpt is the ratio of heat otpt rate to the spplied mass flow rate based on Eq. (14. It can be seen from Fig. 5 that the plsating flow with amplitde of 0.031m/s prodces the highest specific heat otpt for radiator type 10 and the flow with amplitde of 0.041m/s gave the highest specific heat otpt for radiator type 11. Q otpt Q SP.otpt = (14 m& inpt Where: Q SP.otpt is the specific heat otpt (J/kg, Q otpt is the rate of heat otpt from the radiator (W and is the inlet mass flow rate (kg/s. Fig. 6 shows the specific heat otpt of the best plsed flow amplitde while varying the flow freqencies for both radiators (a type10 and (b type11. As shown in Fig. 6 the highest specific heat otpt was prodced at operating freqency of 0.209rad/s for both type10 and type11 radiators. Fig. 7 shows the local srface temperatre contors, the average srface temperatres, the otlet water temperatre and the heat otpt of both type 10 and type 11 radiators at the selected operating flow amplitde and freqency. It is clear from this figre that target temperatres were achieved with panel radiator srface temperatre of 50 o C and hot water otlet temperatre of 65 o C. The energy saving de to flow plsation can be calclated sing Eq. (15. % ES = m& CF m& m& CF PF * 100 (15
Where ES is the energy saving; sbscripts CF and PF are for constant and plsed flow respectively. In this analysis, the energy saving is related to the mass flow rate becase the hot water inlet and otlet temperatres are constants. Fig. 8 compares the specific heat otpt of the two types of radiators for constant and plsed flow conditions. The shaded areas in Fig. 8 represent the amont of enhancement in specific heat otpt achieved de to sing flow plsation. Using Eq. (15, sch enhancement leads to energy saving of 17% for type 10 radiator and of 20% for radiator type 11 which is de to the redction in the mass flow rate of the plsed flow. The higher energy saving achieved in type 11 radiator is de to the extra srface area of the attached fins which highlight the advantages of sing plsed flow with finned radiators. In this investigation, it is envisaged that the energy saving achieved in the plsed flow is de to the heat transfer enhancement cased by the changes in the velocity distribtion inside the flow channels of the radiators. Fig. 9 shows the velocity contors of radiator type 11 and the velocity distribtion at varios selected channels. Fig. 9a shows the velocity contors for the plsed flow condition and the location of the selected channels. Figs. 9b to 9d compares the velocity distribtion for plsed and constant flow scenarios at the selected channels shown in Fig. 9a. These channels are channel 1 at 90mm, channel 2 at 196mm, channel 3 at 302mm and channel 4 at 408mm. The shaded part of Figs. 9b to 9d show the improvement in the average velocity of the plsed flow compared to the constant flow. The higher flow velocity in the channels de the plsed flow leads to higher Reynolds nmber that creates flow trblence and breaks the bondary layers along the water side srface of the radiator channels. Prodcing higher velocity in the radiator channels reslts in higher heat transfer coefficient as shown in Fig. 10 leading to higher heat transfer rate. The convective heat transfer coefficient shown in Fig. 10 was calclated sing Eq. (16 qconv h = T T sr (16 Where; h is the convection heat transfer coefficient, q conv is the convective heat flx, T is the average blk hot water temperatre and T sr is the average internal srface temperatre of the radiator channels. Fig. 10 shows an enhancement in the heat transfer coefficient de to plsation of p to 50% can be achieved at the steady state condition.
5. Conclsions In this work, flow plsation techniqe was investigated for enhancing the heat transfer performance of two types of panel radiators sed in central heating systems throgh CFD modelling. The simlation reslts for constant flow inpt case were compared to pblished experimental work showing good agreement with maximm deviation of 2.44% in the heat otpt. The radiators were simlated sing wide range of inpt plsating flow conditions with velocity amplitde ranging from 0.027 m/s to 0.057 m/s and freqency ranging from 0.052 rad/s to 0.209rad/s. Reslts showed higher average velocity was achieved in the channels of the radiators de to the plsed flow compared to the constant flow velocity reslting in high convective heat transfer coefficient at the water side and higher specific heat otpt of the radiator. Energy saving of p to 17% (for type10 radiator and 20% (for type11 radiator can be achieved withot affecting the radiator srface temperatre. This overall energy saving can be attribted to the increase in the flow velocity vales inside the radiator channels leading to high heat transfer coefficient (p to 50% and redced flow rate. The reslts from this work highlight the potential of sing plsed flow to enhance the heat transfer of panel radiators and redce the energy consmption of central heating systems in bildings withot compromising the ser comfort. Nomenclatre Symbols A area [m 2 ] D h hydralic diameter [m] ES energy saved [%] Eq. eqation freq freqency [Hz]
g gravity [m/s 2 ] h C p K L convective transfer coefficient [w/(m 2.K] specific heat capacity [J/(kg.K] thermal condctivity [w/(m.k] characteristics length [m] LMTD Log mean temperatre difference [K] mass flow rate [kg/s] Per perimeter [m] Q q heat energy [W] heat flx [W/m2] Re Reynolds nmber [-] St Strohal nmber [-] s T t U V seconds temperatre [K] time [s] Total coefficient of heat transfer [W/(m 2 K] velocity [m/s] Greek symbols ρ density [kg/m 3 ] ν μ Δ Sbscripts CF kinetic viscosity dynamic viscosity difference constant flow conv convective in inlet ot otlet PF plsed flow rad radiator sp. specific heat otpt
sr srface area w water 6. References [1] A. Novoselac, Combined airflow and energy simlation program for bilding mechanical system design. PhD dissertation The Pennsylvania State University USA, 2005. [2] http://www.levolx.com/l_misc/40%25_energy_consmption.htm[accessed 30/01/2014]. [3] D. Dineen, B.P. Ó Gallachóir Modelling the impacts of bilding reglations and a property bbble on residential space and water heating. Energy and Bilding 2011;43: 166-178. [4] A. Ploskic, S. Holmberg. Low temperatre baseboard heaters with integrated air spply analytical and nmerical investigations. Energy and Environment2011; 46: 176-186. [5] J. A. Myhren, S.Halberg. Design Consideration with ventilation-radiators comparisons to traditional two-panel radiators. Energy and bildings 2009; 41: 92-100. [6] K. Bangert. Radiator heat transfer agmentation by changes to wall srface roghness and emissivity. The University of Sheffield 2010. [7] S.M.B. Beck, S.C. Grinsted, S.G. Blakey, K. Worden. Novel design for panel radiators. J. ApplThermEng 2004; 24: 1291 1300. [8] A. Ploskic, S.Holmberg.Performance evalation of radiant baseboards (skirtings for room heating-analitical and experimental approach. Applied Thermal Engineering 2014; 62: 382-389. [9] J. A. Myhren, S.Holmberg. Performance evalation of ventilation radiator. Thermal Science and Technology 2012; 32, 2,63-71. [10] A.Ploskic, Stre Holmberg. Heat emission from thermal skirting boards. Bilding and Environment 2010; 45: 1123-1133. [11] J. Are Myhren H.Stre. Improving the thermal performance of ventilation radiators The role of internal convection fins. International Jornal of Thermal Science 2011; 50: 115-123.
[12] K. Sanjay Roy, B. L. Avanic.Optimization of a space radiator with energy storage. Heat and Mass Transfer 2006; 33: 544-551. [13] K. Kerrigana, H. Joharab, G.E. O, Donnella, A.J. Robinsona. A natrally aspirated convector for domestic heating application with low water temperatre sorces. Energy and Bilding 2013; 67:187-194. [14] G. Li, Y. Zheng, G. H, Z. Zhang. Experimental investigation on heat transfer enhancement from an inclined heated cylinder with constant heat inpt power in infrasonic plsating flows. ETF 2013. [15] A.E. Zohir. The Inflence of Plsation on Heat Transfer in a Heat Exchanger for Parallel and Conter Water Flows. New York Science Jornal 2011; 4(6:61-71. [16] R.Lemlich. Vibration and plsation boost heat transfer. Chemical Engineering 1961; 171-176. [17] X.Shai,S. Cheng,G. Antonini. Plsation effects on convective heat transfer in the laminar flow of a viscos flid. The Canadian Jornal of Chemical Engineering 1994; 72: 468 475. [18] D.J. Sailor, D.J.Rohli, Q. F. Effect of variable dty cycle flow plsations on heat transfer enhancement for an impinging air jet. I.J. Heat and Flid flow 1999; 574-580 [19] V. A. Hemadri, A. Gpta, S.Khandekar. Thermal radiator with embedded plsating heat pipes; Infra-red thermography and simlations. Applied Thermal Engineering 2011; 31: 1332-1346. [20] COMSOL Mltiphysics version 4.3 [21] N. Yakah. Heat Exchanger Design for a Solar Gas-Trbine Power Plant. RTM indstrial engineering and management Stockholm 2012. [22] E. Aydar, I. Ekameci. Thermal efficiency estimation of the panel type radiator with CFD analysis. Thermal science and Technology 2012; 32: 63-71. [23] A. Berkan. Simlation of the heater test room defined by EN442 standard and virtal testing of different type of heaters. PhD thesis (PDF 2011. [24] T. Üçokerkek, A. Güngör. Experimental performance evalation of PCM thermal storage in a panel radiator Mediterranean Congress of Climatization. Istanbl, 3-4 October, 2013. [25] Comparative thermal performance of test on tworeflective panels forms radiators. BSRIA April 2003.
[26] M. Jafari, M. Farhadi, K. Sedighi. Plsating flow effects on convection heat transfer in a corrgated channel A LBM approach. International Commnications in Heat and Mass Transfer 2013; 45: 146 154 [27] http://www.screwfix.com/c/heating-plmbing/radiators/cat830960 (accessed on 30/04/2014 [28] Y. S. Sininger, C. Abdala, B. Cone-Wesson. Aditory threshold sensitivity of the hman neonate as measred by the aditory brainstem response. Hearing Research 1997: 104: 27 38
Table 1 the material properties hydronic panel radiatormodel and water Domain type Table 2 the CFD and experimental reslts and inpt vale of type10 radiator Specifications CFD Exp Diff % Flow rate (kg/s 0.0174 0.0174 Ambient temperatre ( o C 19.89 19.89 Inlet temperatre ( o C 75.23 75.23 Otlet temperatre ( o C 65.28 65.10 0.27 Mean temperatre ( o C 70.255 70.17 0.12 LMTD ( o C 50.5 50.28 0.7 Radiator heat otpt (W 720.09 736.51 2.23 Table 3 the CFD and experimental reslts and inpt vale of the single panel radiator with attached fins (type11 Specifications CFD Exp Diff % Flow rate (kg/s 0.023 0.0228 Ambient temperatre ( o C 19.89 19.89 Inlet temperatre ( o C 74.76 74.76 Otlet temperatre ( o C 64.83 64.71 0.15 Mean temperatre ( o C 69.79 69.76 0.043 LMTD ( o C 49.25 49.76 1.20 Radiator heat otpt (W 992.1 968.42 2.44 Table 4 Plsed flow amplitdes and average mass flow rate sed at constant freqency of 0.209rad/s Type 11 radiator Materials type incompressible Water Flid medim Channels Steel (AISI 4340 Fins Steel(AISI 4340 K C p, ρ [W/m.K] [J/kg.m] [kg/m 3 ] 0.58 4180 1000 44.5 475 7850 44.5 475 7850 Type 10 radiator Amplitdes [m/s] Average mass [kg/s] Amplitdes [m/s] Average mass [kg/s] 0.03552 0.003997 0.027 0.0030 0.0406 0.004568 0.031 0.0037 0.04568 0.005138 0.035 0.0039 0.05074 0.005710 0.039 0.0043
Figre 1 dimensions of the panel radiator geometry and the mesh concentration of the designed radiators Figre 2 local srface temperatre distribtions of the radiator (a type10 and (b type11 at constant flow condition Figre 3 time variation of otlet hot water temperatre, rate of heat otpt and average srface temperatre of the radiators (a type10 and (b type11 at constant flow condition
Figre 4 flow inpt profile of the proposed plsating flow strategy Figre 5 the rate of heat otpts and specific heat otpts of both type11 and typ10 radiators sing varios flow plsation amplitdes while maintaining constant freqency of 0.209 rad/s Figre 6 specific heat otpts of (a type 10 and (b type 11 radiators sing varios freqencies while maintaining constant amplitdes of 0.031m/s and 0.0406m/s respectively
Figre 7 contor of local srface temperatre distribtion ( o C; average srface temperatre; water otlet temperatre and rate of heat otpt at best plsation freqencies and amplitdes for both radiators of (a type 10 and (b type 11 Figre 8 specific heat otpt and enhanced heat otpt de to the plsed flow case compared to the constant flow case of radiators (a type10 and (b type11
Figre 9 velocity distribtion profiles and the enhanced velocity of the proposed plsed flow compared to the constant flow along the waterside internal skin of the sampled channels indicated in figre9(a
Figre10 the enhanced convective heat transfer coefficient on the waterside (internal channel walls de to the plsed flow compared to constant flow
Paper Highlights 1- CFD simlation of type 10 and type 11 panel radiators with constant and plsed flow conditions. 2- Plsating the flow enhances the heat transfer performance of panel radiators. 3- As flow plsating freqency increases, the specific heat otpt of panel radiators increases. 4- Plsating the flow reslted in energy saving of p to 17% for type 10 and 20% for type 11 radiators.