An experimental study on heat transfer for a tilted semi-cylindrical cavity with inclined ribs

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1 An experimental study on heat transfer for a tilted semi-cylindrical cavity with inclined ribs #1 Mr. Wagh Prasad R., #2 Dr. Borse Sachin L. #1 ME Student Department of Mechanical Engineering, Rajarshi Shahu College of Engineering, Savitribai Phule Pune University, Pune, India. #2 Professor Department of Mechanical Engineering, Rajarshi Shahu College of Engineering, Savitribai Phule Pune University, Pune, India. ABSTRACT In this paper an experimental investigation to be performed to study the effect of inclination on heat transfer co-efficient for semi-cylindrical cavity, with inclined ribs inserted. Heat transfer measurements to be carried out on both smooth and rough surfaces for different tilt angles. Conduction and radiation losses have been taken into account during the analysis. It is expecting that in all cases heat transfer co-efficient decreases with increase in inclination and minimum when hot surface facing down. The results are compared with and without ribs inserted. The ribs of 0.002m diameter are inserted along the length of the cavity. Keywords Heat transfer, Semi-cylindrical cavity, inclined ribs, Nusselt number. I. INTRODUCTION Study of natural convection plays an important role in open cavities due to it is more important in case of solar thermal receiver system. Also its study helps in building insulation, household refrigerators, electronic cooling, and many others where a heat loss affects the performance of the system. Natural convection heat transfer from an inclined surface and in cavities is very frequently encountered in engineering devices and the natural environment. Previous researchers have conducted the numerical simulation and experimental observations. II. LITERATURE REVIEW Martorell et al. [2003] work deals with the natural convection flow and heat transfer from a horizontal plate cooled from above.. Authors found that Nusselt number does not significantly affected with the aspect ratio of the plate and temperature distribution is more uniform in case of copper plate, due to the high conductivity of the metal. The study of natural convection heat transfer between parallel plates by changing the inclination and plate spacing were investigated, [N. Onur, et al 1997], it can be stated that Nusselt number depends on the separation distance between the plates. M. Havet done numerical study of a natural convection flow along a non-isothermal vertical plate immersed in an isothermal fluid. He found that heat transfer is greatly influenced by the wall temperature distribution. Various researchers has make study of experimental effect of opposing wall on natural convection along an inclined hot plate facing downward.[onur and Aktas, et al, 1998]. Different studies on effect of roughness on heat transfer for semicylindrical and rectangular cavity has been done. Walid Chakroun et al [2001] has studies the heat transfer mechanism inside cavity, in their research they concluded that in some cases of the smooth walled enclosure has more heat transfer rate than a rough surfaces, since the rough wall delays the onset of convection motion. Experimental Setup The experimental setup is as shown in fig.1 Fig.1. Experimental Setup. 2015, IERJ All Rights Reserved Page 1

2 The cavity is mounted on a stand. It is supported by two arms. The design of arms and the stand are to minimize the disturbance of the airflow and it will ensure good physical stability. The cavity can be rotated about its longitudinal axis. About the vertical axis the angle of rotation was measured. The semi-cylindrical cavity is made up of aluminium material. The dimensions of cavity are as radius R is of 0.15 m and length l is of 0.9 m and the thickness of cavity is 0.00 m. The dimensions are chosen in the way that it will give two dimensional flow inside the cavity. The heat is supplied to the cavity by using silicon rubber heaters. The heating pads are self-adhesive and fixed at back of the cavity. Outside of the cavity there are different layers such as first layer is of glass wool of 0.02 m thick, then 0.03 m thick layer of hard polystyrene insulation and then again the 0.02m thick layer of glass wool is placed at the top. This is a smooth semi-cylindrical cavity. Fig.2. Cross-section of the cavity. For rough semi cylindrical cavity aluminium rods are placed along the length of cavity. The rods are fixed to the upper part of the surface such that they will act as a rough surface. The heat input is controlled by electric circuit and by a voltage regulator. The thermocouples are connected at different point to measure the temperature. All the thermocouples are connected to the digital recorder. The readings are taken at different interval until steady state is reached. The readings were taken at different tilt angles of the cavity and recorded. Nusselts number calculation The average Nusselt number from the cylindrical cavity is defined as- hr Nu (1) k Where, h is the average heat transfer coefficient between the cavity and the surroundings, R is the radius of the cavity and k is the thermal conductivity of air in the cavity. Eq. (1) can be rewrite in terms of the local heat transfer coefficient h as- H 1 R N u hds (2) H k 0 Where H R. When the cavity is heated at constant heat flux, the local heat transfer coefficient is given by the equation- qc" ( TwT) h (3) Where, Tw is the local temperature of the cavity surface and qc is heat transfer rate per unit area of the cavity surface due to convection. As we dividing the wall into five equal sections, Equations. (2) and (3) can be added to give 5 R qc" 5k i T Nu () 1 ( Twi ) Where i is the order of various sections of the heated surface. To calculate qc IV = HL (qc + qcd + qr ) (5) Where VI is the Voltage and current supplied. qcd is heat lost due to conduction, qr heat lost due to radiations. The heat lost due to radiation from hot surface is calculated as 1 1 qr" [ Tw 273] ( T 273) ( ) Fpa (6) Where, Tw is the average temperature of the cavity surface, is its emissivity and Fpa is the configuration factor between the plate and the aperture. 2015, IERJ All Rights Reserved Page 2

3 The conduction heat loss is the heat loss through hard wall insulation and is given by the equation- kin ( Ti To) qcd" R Ln( ro/ ri) (7) Where kin is the thermal conductivity of hard insulation. Ti and To are average inner and outside surface temperatures of the hard wall insulation, respectively. By considering equation. (6) and (7), the Eq. (2)for Nusselts number can be written as- Nu R 5k 5 i1 IV kin ( Ti To) { HL R Ln( Ti To) [( Tw 273) ( T 273) 1 ]( ) (8) 1 1 Fpa III. RESULTS The results of semi-cylindrical cavity should be tested on both smooth as well as rough that is aluminium rod inserted. The Nusselts numbers are carried out at different inclinations of the semi-cylindrical cavity. The results are compared with the both smooth and rough surfaces. Here some of the graph shows the variation of the Nusselts number with respect to time interval. When steady state reached the rough wall shows higher value for the average Nusselt number than that of smooth wall and this is mainly due to the increase in surface area. At other tilt angles, roughness gives a large effect on heat transfer inside the cavity. Roughness increases drag resulting in less amount of heat transfer, but it also increases turbulence which will increases heat transfer rate. These factors are depends on the inclination of the cavity. Fig.3. Variation of Nusselts number with respect to time at tilt angle Fig.. Variation of Nusselts number with respect to time at tilt angle , IERJ All Rights Reserved Page 3

4 Fig.5. Variation of Nusselts number with respect to time at tilt angle Fig.6. Variation of Nusselts number with respect to time at tilt angle 0 0. IV. CONCLUSIONS 1) The experiment presents the results of heat transfer for smooth as well as rough semi-cylindrical cavity. 2) The cavity is facing down it should gives the minimum value of Nusselt number. 3) At minimum inclination it will causes increase in heat transfer rate but as inclination increases heat transfer rate increases in average. ) As the inclination increases heat transfer rate is more for rough semi-cylindrical cavity than the smooth cavity for same tilt angle. V. REFERENCES S. Siddiqa, S. Asghar, M.A. Hossain, (2010), Natural convection flow over an inclined flat plate with internal heat generation and variable viscosity, Mathematical and Computer Modelling, pp M. Mahdavi, M. Sharifpur, H. Ghodsinezhad, J.P. Meyer, Experimental and numerical study of the thermal and hydrodynamic characteristics of laminar natural convective flow inside a rectangular cavity with water, ethylene glycol water and air, Experimental Thermal and Fluid Science, Volume 78, November 2016, Pages Amit Sarswat, Ankit Verma, Sameer Khandekar, Malay K Das, Latent Heat Thermal Energy Storage In A Heated Semi- Cylindrical Cavity: Experimental Results And Numerical Validation, International ISHMT-ASTFE Heat and Mass Transfer Conference, pp B. Premachandran, C. Balaji, (2006),correlation for mixed convection heat transfer from converging, parallel and diverging channels with uniform volumetric heat generating plates, International Communications in Heat and Mass Transfer 33,pp , IERJ All Rights Reserved Page

5 Li Guoneng,, Xu Zhihua, Zheng Youqu, Guo Wenwen, Dong Cong, (2016),Experimental study on convective heat transfer from a rectangular flat plate by multiple impinging jets in laminar cross flows, International Journal of Thermal Sciences, Volume 108,, pp Mark F. Tachie and Martin Agelinchaab (2010), Turbulent Flows over Aligned and Inclined Ribs, Springer Science+Business Media B.V. 2010,pp Ingrid Martorell, Joan Herrero, Francesc X.G rau,(2003), Natural convection from narrow horizontal plates at moderate Rayleigh numbers, International Journal of Heat and Mass Transfer 6, pp N. Onur, M. Sivrioglu, M. K. Akta(1997), An experimental study on the natural convection heat transfer between inclined plates (Lower plate isothermally heated and the upper plate thermally insulated as well as unheated), Heat and Mass Transfer 32, pp N. Onur,, M. K. Akta (1998), an experimental study on the effect of opposing wall on natural convection along an inclined hot plate facing downward, Int. Comm. Heat Mass Transfer, Vol. 25, No. 3, pp , M. Havet, D. Blay (1999), Natural convection over a non-isothermal vertical plate, International Journal of Heat and Mass Transfer 2, pp Xiaowei FAN, Yuemei Wang, Huifan Zheng, Ruiliang yang, (2007), Numerical and experimental study on heat transfer and fluid flow characteristics of the holed baffles, International Congress of Refrigeration, Beijing. B S.V. Karmare, A.N. Tikekar, (2010),Analysis of fluid flow and heat transfer in a rib grit rough ended surface solar air heater using CFD, Solar Energy 8, pp Walid Chakroun, Mir Mujtaba A. Quadri, (2002),Heat transfer measurements for smooth and rough tilted semi-cylindrical cavities, Int. J. Therm. Sci. 1, pp , IERJ All Rights Reserved Page 5