This paper presents the results of an experimental investigation of heat transfer and friction in the flow of air in rectangular ducts having multi v-shaped rib with gap roughness on one broad wall. ...The investigation encompassed Reynolds number (Re) from 2000 to 20,000, relative gap distance (Gd/Lv) values of 0.24–0.80, relative gap width (g/e) values of 0.5–1.5, relative roughness height (e/D) values of 0.022–0.043, relative roughness pitch (P/e) values of 6–12, relative roughness width ratio (W/w) values of 1–10, angle of attack (α) range of 30°–75°. The optimum values of geometrical parameters of roughness have been obtained and discussed. For Nusselt number (Nu), the maximum enhancement of the order of 6.74 times of the corresponding value of the smooth duct has been obtained, however the friction factor (f) has also been seen to increase by 6.37 times of that of the smooth duct. The rib parameters corresponding to maximum increase in Nu and f were Gd/Lv=0.69, g/e=1.0, e/D=0.043, P/e=8, W/w=6 and α=60°. Based on the experimental data, correlations for Nu and f have been developed as function of roughness parameters of multi v-shaped with gap rib and flow Reynolds number.
•Nu and f of multi v-shaped rib with gap roughened solar air heater duct are investigated.•There exist optimum, Gd/Lv, g/e, W/w, P/e, α and e/D for which Nu and f are highest.•Correlations developed for Nu and f predict values with reasonable accuracy.
The use of artificial roughness on the underside of the absorber plate is an effective and economic way to improve the thermal performance of a solar air heater. Several experimental investigations, ...involving different types of roughness elements, have been carried out to improve the heat transfer from the absorber plate to air flowing in solar air heaters. This paper presents an experimental investigation carried out to study the effect of multiple v-rib roughness on heat transfer coefficient and friction factor in an artificially roughened solar air heater duct. The experiment encompassed Reynolds number (Re) from 2000 to 20000, relative roughness height (
e/
D) values of 0.019–0.043, relative roughness pitch (
P/
e) range of 6–12, angle of attack (
α) range of 30–75° and relative roughness width (
W/
w) range of 1–10. Extensive experimentation has been conducted to collect data on heat transfer and fluid flow characteristics of a rectangular duct roughened with multiple v-ribs. Using these experimental data, correlations for Nusselt number and friction factor in terms of roughness geometry and flow parameters have been developed.
Because of intermittent nature of solar energy, storage is required for uninterrupted supply in order to match the needs. Packed beds are generally used for storage of thermal energy from solar air ...heaters. A packed bed is a volume of porus media obtained by packing particles of selected material into a container. A number of studies carried out on packed beds for their performance analysis were reported in the literature. These studies included the design of packed beds, materials used for storage, heat transfer enhancement, flow phenomenon and pressure drop through packed beds. This paper presents an extensive review on the research carried out on packed beds. Based on the literature review, it is concluded that most of the studies carried out are on rocks and pebbles as packing material. A very few studies were conducted on large sized packing materials. Further no study has been reported so far on medium sized storage elements in packed beds.
► Nu and f of Multi-v with gap rib roughened solar air heater duct are investigated. ► There exist optimum Gd/Lv, g/e for which Nu and f are highest. ► Discuss thermo hydraulic performance parameter.
...In this work, results of an experimental investigation of the effect of geometrical parameters of Multi v-shaped ribs with gap on heat transfer and fluid flow characteristics of rectangular duct with heated plate having rib roughness on its underside have been reported. The range of parameters for this study has been decided on the basis of practical considerations of the system and operating conditions of solar air heaters. The experimental investigation encompassed the Reynolds number (Re) range from 2000 to 20,000, relative width ratio (W/w) of 6, relative gap distance (Gd/Lv) of 0.24–0.80, relative gap width (g/e) of 0.5–1.5, relative roughness height (e/D) of 0.043,relative roughness pitch (P/e) of 10, angle of attack (α) of 60°. The maximum enhancement in Nusselt number and friction factor is observed to be 6.32–6.12 times of that of the smooth duct, respectively. The thermo-hydraulic performance parameter is found to be the best for the relative gap distance of 0.69 and the relative gap width of 1.0.
In this work, the effect of geometrical parameters of the V-shaped perforated blocks on heat transfer and flow characteristics of rectangular duct, has been investigated experimentally. The ...experimental investigation encompassed the geometrical parameter namely, relative blockage height (e/H) of 0.4-1.0, relative pitch ratio (P/e) of 4-12 and open area ratio (beta) of 5-25% at a fixed angle of attack (alpha) of 60degrees. The effect of V-shaped perforated blockages has been investigated for the range of Reynolds number from 2000 to 20,000. The maximum enhancement in Nusselt and friction factor has been found to be 6.76 and 28.84 times to that of smooth duct, respectively. Thermohydraulic performance of V-shaped perforated block-ages is also compared to that of V-shaped solid blockages for same geometrical parameters.
The heat and fluid flow characteristics of rectangular duct having its one broad wall heated and roughened with periodic ‘discrete V-down rib’ are experimentally investigated. Reynolds number (Re) ...has been varied from 3000–15000 with relative gap width (
g/
e) and relative gap position (
d/
w) range of 0.5–2.0 and 0.20–0.80 respectively. The respective variation in relative roughness pitch (
P/
e), angle of attack (
α) and relative roughness height (
e/
D
h
) have been 4–12, 30°–75° and 0.015–0.043. The effect of roughness parameters on Nusselt number (Nu) and friction factor (
f) has been determined and the results obtained were compared with those of smooth duct. The maximum increase in Nu and
f over that of smooth duct was 3.04 and 3.11 folds respectively. The rib parameters corresponding to maximum increase in Nu and
f were d/
w = 0.65,
g/
e = 1.0,
P/
e = 8.0,
α = 60° and
e/
D
h
= 0.043. Correlations for the Nu and
f in terms of Re and rib parameters have been developed.
► Nu and
f of discrete V-down rib-roughened solar air heater duct are investigated. ► There exist optimum
P/
e,
d/
w,
α and
g/
e for which Nu and
f are highest. ► Correlations developed for Nu and
f predict values with reasonable accuracy.
Thermal energy storage has recently attracted increasing interest related to thermal applications such as space and water heating, waste heat utilization, cooling and air-conditioning. Energy storage ...is essential whenever there is a mismatch between the supply and consumption of energy. Use of phase change material (PCM) capsules assembled as a packed bed is one of the important methods that has been proposed to achieve the objective of high storage density with higher efficiency. A proper designing of the thermal energy storage systems using PCMs requires quantitative information about heat transfer and phase change processes in PCM. This paper reviews the development of available latent heat thermal energy storage technologies. The different aspects of storage such as material, encapsulation, heat transfer, applications and new PCM technology innovation have been carried out.
•Heat and fluid flow characteristics of V-ribs with symmetrical gaps investigated.•Nusselt number and friction factor is maximum for Ng=3 and g/e=4.•Correlation for Nusselt number and friction factor ...developed.
An experimental study has been carried out for enhancement of heat transfer coefficient of a solar air heater having roughened air duct artificially roughened in the form of V-ribs with symmetrical gaps as turbulence promoter. In present work an experimental investigation of heat transfer and friction of artificial roughness in the form of V-ribs with symmetrical gaps were investigated. The investigation encompassed Reynolds number (Re) ranging from 4000 to 18,000, Number of gaps (Ng) values of 1–5, relative gap width (g/e) values of 1–5, relative roughness pitch (P/e) values of 6–12, angle of attack (α) range of 30–75° and relative roughness height (e/D) values of 0.043. For Nusselt number (Nu), the maximum enhancement of the order of 3.6times that of smooth duct has been obtained, similarly friction factor (f) also increases by 3.67 folds of that of the smooth duct. The rib parameters corresponding to maximum increase in Nu and f were Ng=3, g/e=4, P/e=10 and α=60°. Based on the experimental data, correlations for Nu and f have been developed as function of roughness parameters of V-ribs with symmetrical gap and flow Reynolds number.
Solar air heaters form the major component of solar energy utilization system which absorbs the incoming solar radiation, converting it into thermal energy at the absorbing surface, and transferring ...the energy to a fluid flowing through the collector. The efficiency of flat plate solar air heater has been found to be low because of low convective heat transfer coefficient between absorber plate and the flowing air which increases the absorber plate temperature, leading to higher heat losses to the environment resulting in low thermal efficiency of such collectors. Artificial roughness in the form of repeated ribs is the most effective and economic way of improving the thermal performance of solar air heater. This paper presents an extensive review on the research carried out on artificial roughened solar air heater ducts. The objective of this paper is to review various studies, carried out on thermal as well as hydraulic performance of artificial roughened solar air heater ducts. The review presented in this paper will be useful for the researchers working in this area.
Energy and material saving considerations, as well as economic incentives, have led toward making effort for producing more efficient heat exchange equipment such as solar air heaters, heat ...exchangers. In order to enhance the heat transfer rate to flowing air in the duct of solar air heater and heat exchangers various turbulence generators viz. ribs, baffles and delta winglets are considered as an effective technique. Investigators reported on various turbulators in literature for studying heat transfer and friction characteristics in a duct of solar air heaters and heat exchangers. An attempt has been made in this paper to carry out an extensive literature review of various turbulators investigated for enhancing heat transfer and friction in solar air heaters and heat exchangers. The correlations developed for heat transfer and friction factor in solar air heaters and heat exchangers by various investigators have been presented and reviewed.
•An intensive review on turbulators has been performed.•Role of turbulators in solar air heaters as well as heat exchangers has been studied.•Comparison between artificial roughness and turbulators has been done.•Perforated ribs and delta winglets have also been included in the study.
