• Energy Research

Abstract Experimental investigation of heat transfer and friction factor characteristics of thermosyphon solar water heater with full length Left–Right twist, twist fitted with rod and spacer at the trailing edge for lengths of 100, 200 and 300 mm for twist ratio 3 and 5 has been studied. The experimental data for plain tube collector has been compared with fundamental equation within a discrepancy of ±7.41% and ±14.97% for Nusselt number and friction factor, respectively. Result shows that the Nusselt number decreases by 11% and 19% for twist fitted with rod and twist with spacer, respectively, when compared with full length twist. Friction factor also decreases by 18% and 29% for twist fitted with rod and spacer, respectively, as compared with full length twist. The heat enhancement in twist fitted with rod at the trailing edge is maximum when compared with twist fitted with spacer because the swirl flow is maintained throughout the length of rod.

The Salt gradient solar pond (SGSP) is used for process heating, power generation and to achieve refrigeration. In this paper the performance of an in-pond heat exchanger of a laboratory model SGSP was analyzed both experimentally and computationally. A laboratory model solar pond was fabricated using GI sheet of 1.5 mm thick for the dimension 600 × 500 × 500 mm and the performance of the pond was experimentally determined under solar irradiated condition. The experiment was conducted for a period of 10 days and the hourly variations of the temperatures of inlet, outlet, storage zones and ambient were measured and analyzed. To computationally analyze the performance of the SGSP, a model was developed using software tools CATIA and HYPERMESH and the performance of the modeled in-pond heat exchanger of the solar pond was determined using FLUENT software. The performance of the SGSP was analyzed for laminar and turbulent flow conditions. The experimental results were compared with computational results and close agreement was observed.

Authors, Rose, Singh, Tassou, Suresh and Anathraman, thankfully acknowledge the UKIERI-DST grant (IND/CONT/E/14-15/381) which made this research possible.

Abstract This paper reports experimentally measured thermal and optical properties of Al2O3-Therminol®55 nano heat transfer fluid (nHTF) in conjunction with a specially developed line focusing Fresnel lens based solar thermal concentrator. Solar collector tests were conducted under real life outdoor ambient and solar radiation conditions. A range of volumetric proportions of Al2O3 (0.025–0.3 vol%) have been covered. Highest thermal conductivity and refractive index were measured for nHTF with 0.1 vol% concentration of Al2O3 with higher concentrations (>0.1 vol%) concluded to be unfit for their use in the solar collector applications due to likely agglomeration and sedimentation in the hours of low or nil sunshine when fluid is not circulating. Thermal conductivity enhanced by 11.7% for 0.1 vol% Al2O3 concentration nHTF. A highest temperature of 132.8 °C was delivered by the solar collector using 0.1% concentration Al2O3 nHTF at a flow rate of 0.5 lps. This was 44.7 °C higher than that achieved by pure Therminol®55 (88.1 °C) even though the DNI during 0.1% nHTF test was considerably lower than that for the later. The solar concentrator thermal efficiency increased with the proportion of NPs attaining a maximum of 52.2% for 0.1 vol% Al2O3 nHTF. Directly absorbing nHTFs along with the solar collector developed in this study are predicted to be strong candidate to replace conventional metallic tube receiver using concentrators due to advantages of size compaction and higher thermal conversion efficiency.

Abstract Experimental investigations on thermophysical properties and forced convective heat transfer characteristics of various nanofluids are reviewed and the mechanisms proposed for the alteration in their values or characteristics due to the addition of nanoparticles are summarized in this review. A comprehensive review on the experimental works on specific application of nanofluids is also presented. As the literature in this area is spread over a span of two decades, this review could be useful for researchers to have an accurate screening of wide range of experimental investigations on thermophysical properties, forced convective heat transfer characteristics, the mechanisms involved and applications of various nanofluids.

Improving the performance of pool boiling with critical heat flux of pool boiling and enhancing the coefficient of heat transfer through surface modification technique have gained a lot of attention. These surface modifications can be done at different scales using various techniques. However, along with the performance improvement, the durability and stability of the surface modification are very crucial. Laser machining is an attractive option in this aspect and is gaining a lot of attention. In the present experimentation research work, pool boiling attributed performance of copper-grooved surfaces obtained through picosecond laser machining method is investigated. The performance of the modified surfaces was compared with the plain surface serving as reference. In this, three square grooved patterns with the same pitch (100 μm) and width (100 μm) but different depths (30, 70, and 100 μm) were investigated. Different depths were obtained by varying the scanning speed of the laser machine. In addition to the microchannel effect, the grain structuring during the laser machining process creates additional nucleation sites which has proven its effectiveness in improving the pool boiling performance. In all aspects, the pool boiling performance of the grooved laser-textured surface has showed increased surface characterisation as compared with the surface of copper.

Abstract Integrated and efficient circuitry has become a crucial part of modern technology which urged the necessity in development of efficient and robust Thermal Management (TM) system for its steady operation under higher heat dissipation. Thus the research work aims to analyse the heat transfer performance of a novel wall-less heat sink packed with highly stable synthesised Hexamethylene Diisocyanate cross-linked Polyethylene Glycol-6000 based Form-Stable Phase Change Material (FS-PCM) for its suitability in passive TM systems with chemical and thermal stability till 1000 thermal cycles. An inclusion of 1 wt% (Multi-Wall Carbon Nano Tubes /Graphene nano Platelets) in FS-PCM improved its thermal conductivity by 61.73% (0.448 W/m-K) and 84.48% (0.511 W/m-K) respectively. The characterisation was carried out for its micro and nano structural morphology, elemental composition, chemical composition and thermal properties like thermal degradation, phase transition attributes, specific heat and thermal conductivity via Field Emission Scanning Electron Microscope, Energy Dispersive X-ray Spectroscopy, Carbon Hydrogen Nitrogen analyser, Fourier Transform Infrared Spectroscopy, Thermogravimetric Analysis, Differential Scanning Calorimetry and KD2 pro analyser respectively. The transient heat transfer study of square pin finned heat sink was performed under a set of ON/OFF duty cycles for various heat rates with different aspects of FS-PCMs. In addition, the effect of nanoparticle reduced the thermal difference of FS-PCM in heat sink. Furthermore, involvement of FS-PCM in energy storage characteristics was improved reducing the heat sink base temperature to a maximum of 9.77%. Finally, the experimental results were numerically validated using COMSOL software establishing its reliability for real-time avionics TM application.

Effective cooling of blades with a nominal pressure drop is essential for performance augmentation and thermal management of gas turbines. Hence, present work is aimed at determining the heat transfer enhancement and friction for W- and V-shaped ribs inside a rectangular cooling channel having hydraulic diameter ( D h ) of 0.048 m and aspect ratio ( AR ) 1 : 4. Ribs are fixed facing downstream with angle of attack ( α ) 45° on opposite walls. Pitch ( P ) between two successive ribs is 25 mm for both cases. Continuous V- and W-shaped ribs with height to channel hydraulic diameter ratio ( e / D h ) 0.052 and 0.0416 and pitch to height ratio ( P / e ) 10 and 12.5, respectively, have been examined for Reynolds number ( Re ) range 20000-80000. Heat transfer augmentation achieved at Re 80000 is 1.94 and 1.8 times higher than Re 20000 for V- and W-shaped ribs, respectively. Streamwise and spanwise variations in local Nusselt number ratio are highest for V-shaped ribs, which are estimated to be 31% and 12%. For W-shaped ribs, variations are 17.5% and 3.5%. Nusselt number ( Nu ) is highest along span length 0.5 w for V-shaped ribs due to dominance of apex induced secondary flow. For W-shaped ribs, Nusselt number along the span lengths is found to be nearly same view uniformity in secondary flow. Maximum enhancement ( Nu / N u o ) estimated for both the rib shapes is 3.9 at Re 20000. Due to increased rib height, friction losses for V-shaped ribs are higher than W-shaped ribs. Maximum friction loss increment is estimated to be 85% for V-shaped ribs and 42% for W-shaped ribs between Re 20000 and 40000. For both rib shapes, impact of ribs is found to be greatest at Re 40000. Thermohydraulic performance ( THP ) for W-shaped ribs is superior to V-shaped ribs. Best THP achieved for W- and V-shaped ribs are 3.7 and 3.4 at Re 20000.

The aim of this paper is to observe the Nusselt number and friction factor behavior of the circular tube with conical strip inserts as turbulators in a laminar flow condition, using staggered and non-staggered conical strips with three different twist ratios (Y = 2, 3 and 5). The conical strip is inserted in the forward and backward direction individually compared to the flow of water which is the working fluid. The results indicate that the conical strip inserts increases the Nusselt number when compared to the plain surface tube. It is observed that the strip geometry has a major effect on the thermal performance of the circular tube. On examination of different strips for determining the enhancement of Nusselt number, the staggered conical strip with the twist ratio of Y = 3 has given a better result compared to the other two strips. Finally, correlations have been derived using regression analysis for predicting the Nusselt number and friction factor.