Rajesh Maithani

Experimental determination of enhancement of heat transfer in a multiple square perforated twisted tape inserts heat exchanger tube

ABSTRACT This paper presents an experimental determination of Nusselt number and friction factor of heat exchanger tube with multiple square perforated twisted tape inserts. The effect of geometrical parameters, especially, perforation width ratio and twist ratio, has been investigated. The perforation width ratio and twist ratio have been varied from 0.083 to 0.333 and 2.0 to 3.5, respectively. The optimum values of parameters for multiple square perforated twisted tape inserts arrangement have been obtained and discussed. The effect of multiple square perforated twist tape inserts has been investigated for the range of Reynolds number from 5,000 to 27,000. The effect of important parameters on the and has been discussed, and the results are compared with the results of without square perforated multiple twisted tape inserts and smooth surface heat exchanger tube under similar flow conditions. The optimum values of parameters for multiple square perforated twisted tape inserts heat exchanger tube arrangement have been obtained and discussed. The maximum enhancement is observed at a of 0.250 and of 2.5, respectively.

Investigation of thermal and hydrodynamic performance of impingement jets solar air passage with protrusion with combination arc obstacle on the heated plate

ABSTRACT In this article an experimental analysis has been conducted to study the effect obstacle parameters on thermal and hydrodynamic performance of impingement jets solar air passage having protrusion with combined arc obstacles on the heated surface. The study has involved the values of Reynolds number from 4000 to 18000, relative height ratios () from 0.8 to 1.7, relative pitch ratios () from 9.0 to 12, angle of arc () from 40 to 80, stream wise variation () from 0.39 to 0.56, and span wise variation () from 0.82 to 0.99, and jet diameter ratio of 0.065 respectively. Experimental data pertinent to Nusselt number () and friction factor () were generated for various sets of roughness and flow parameters. The highest improvement is obtained at a range of =1.1,=10, =60°, =0.43, =0.86, and 0.065 respectively. The maximum value of the thermal hydrodynamic performance was found to be 1.50 for the range of parameters investigated.

Convective heat transfer enhancement techniques of heat exchanger tubes: a review

ABSTRACT Heat exchangers are widely used in almost all industrial activities. Turbulent promoters used in heat exchanger tubes are an effective way of enhancing the performance. This paper summarises various investigations using twisted tapes, wire coil ribs, baffles, and swirl flow generators. The main objective of this paper is to review various studies, in which different obstacle roughness elements are used to enhance the rate of heat transfer in the heat exchanger tubes. It has been found that a lot of experimental and analytical studies reported in the literature. On the basis of correlations developed by various investigators an attempt has been made to compare the thermal hydraulic performance of obstacles in heat exchanger tubes. In this work, a comparative study is also carried out to select the best obstacle roughness shapes for higher heat transfer rate and low pressure drop losses.

Effect of square wing with combined solid ring twisted tape inserts on heat transfer and fluid flow of a circular tube heat exchanger

ABSTRACT This work presents the heat transfer and friction characteristics of turbulent circular tube flow through a square wing with combined solid ring twisted tape inserts have been analyzed experimentally. Experiments have been carried out for the range of Reynolds number (Re) from 3000 to 21000, number of twisted tape inserts from 1.0–4.0, ring pitch ratios from 0.5 to 2.0, wing pitch ratios from 2.0 to 3.5, wing depth ratios from 0.083 to 0.333 and ring diameter ratio from 0.831 to 0.932. The experimental results show that the heat transfer is increased around 5.66 times higher than plane circular heat exchanger tube. The optimum value of thermal hydrodynamic performance has been found corresponds to = 3.0, = 1.0,= 3.0, = 0.167 and . The finest value of thermal and hydrodynamic performance has been found to be 2.74 for of 3,000 within the range of the parameters investigated.

DEVELOPMENT OF NEW CORRELATIONS FOR NUSSELT NUMBER AND FRICTION FACTOR OF TiO_2/WATER BASED NANOFLUID FLOW IN V-PATTERN PROTRUSION RIBBED SQUARE CHANNEL

Nanofluids play important roles in the heat transfer and flow characteristics in ribbed square channels. Systematic experiments are conducted to measure heat transfer enhancement and TiO H O based nanofluid flow characteristics on a protruded with combined V-type ribbed square channel. Reynolds number studied in the channel range from 4000-18000. Investigational parameters of square channel contain, volume fraction range of 1.04.0%, particle diameter range of 30nm-45nm, relative protruded rib height range of 0.10-0.25, ratio of protruded height to print diameter range of 0.82.0, relative protruded rib pitch ratio range of 2.0-3.5 and angle of attack of 30-75 respectively. Results indicates that the thermal performance of the protruded combined V-type ribbed square channel falls with increasing Reynolds number. The highest value of thermal hydraulic performance parameter is found to be 3.21for the range of parameters investigated. Correlations predicting Nusselt number and friction factor as a function of volume fraction, particle diameter range, relative protruded rib height, ratio of protruded height to print diameter, relative protruded rib pitch ratio, angle of attack and flow parameter. The correlations for Nusselt number and friction factor have also been developed on the basis of experimental data with considerable good accuracy.

Heat transfer and fluid flow behaviour of a rectangular duct roughened with V-ribs with symmetrical gaps

ABSTRACT In the present work, artificial roughness in the form V-ribs with symmetrical gaps have been applied on the heated surface to enhance the heat transfer in the limbs of V-ribs. Symmetrical gaps on both legs were provided by varying the relative gap width from 1 to 5 and number of gaps from 1 to 5. The relative roughness pitch, relative roughness height and aspect ratio of the rectangular duct are kept constant to the value of 10, 0.0433 and 12, respectively. The Nusselt number and friction factor of the artificially roughened absorber plates has been determined experimentally and corresponding values were compared with that of the smooth duct for the range of flow Reynolds number 4000–18,000. The maximum enhancement in Nusselt number was reported for relative gap width of 4 and Number of gaps of 3. The thermohydraulic enhancement factor was found to be in order of the 1.54–2.39.

Performance evaluation of solar air heater having V-ribs with symmetrical gaps in a rectangular duct of solar air heater

ABSTRACT An investigation has been carried out to evaluate the performance of a solar air heater duct roughened with V-ribs with symmetrical gaps to enhance heat transfer. The roughness produced for enhancing heat transfer from the absorber plate also enhances pressure drop due to increased friction. Heat transfer enhancement of the absorber plate has been experimentally determined by using V-ribs with symmetrical gaps. The duct has a relative roughness height (e/D) of 0.0433, a relative roughness pitch (P/e) of 10 and an angle of attack (α) of 60°. Relative gap width (g/e) and number of gaps (Ng) were varied in the range of 1–5. The maximum enhancement in the Nusselt number and friction factor is observed to be 2.59 and 2.87 times, respectively, as compared to the smooth duct. The relative gap width of 4 and the number of gaps of 3 show the maximum value of thermohydraulic performance parameter.