Abstracts:Due to the low thermal inertia and poor thermal insulation of ultrathin envelope in tents, its indoor temperature environment is extremely bad and its occupants are tormented. Especially under the high solar radiation, both indoor air temperature and inner surface radiation temperature increase rapidly. And thereby, decreasing radiation heat gain in summer is necessary to refine indoor temperature environment in tents. Retro-reflective materials make it a reasonable choice due to their high reflectivity for solar radiation. To reveal the temperature environment improvement of tents by integrating with retro-reflective materials, a comparative experiment is carried out under the summer climatic conditions of Chengdu city, China. Experimental results show that due to integrating with retro-reflective materials, indoor air peak temperature in the tent can be reduced by more than 7.7°C, while inner surface radiant temperature can be lowered up to 4.8°C in the day time. It shows retro-reflective materials could refine indoor temperature environment in tents. Through a comparison of the walls in different orientations, on which retro-reflective materials are covered, the top, east and north walls are found to be better choices, while the north wall is the worst one for retro-reflective materials.

Abstracts:In this study, numerical investigation has been carried out for a range of system and operating parameters in order to analyze the effect of protrusion obstacles on heat and fluid flow characteristics of nanopartical ${\mathrm{Al}}_2{\mathrm{O}}_3$ with concentration 4.0% and diameter 30 $\mathit{nm}$ in square mini channel. The square mini channel has, stream wise spacing ($X_s/d_p$) range of 1.4–2.6, span wise spacing ($Y_s/d_p$) range of 1.4–2.6, ratio of protrusion height to print diameter ($e_p/d_p$) of 1.67 and Reynolds number (${\mathit{Re}}_n$) ranges from 4000 to 18,000. Simulations were carried out to obtain heat and fluid flow behaviour of smooth and rough tube, using commercial CFD software, ANSYS 16.0 (Fluent). Renormalization $k-\epsilon$ model was employed to assess the influence of protrusion on turbulent flow and velocity field. Simulation results show that, the enhancement of 3.73 times in heat transfer and 4.25 times enhancement in pressure drop as a function of $X_s/d_p$ and $Y_s/d_p$ of 1.8 respectively.

Abstracts:In the present study, the effect of operational and geometrical parameters on the thermal effectiveness of shell and helically coiled tube heat exchangers was investigated. Analysis was performed for the steady state. The working fluid of both sides is water, that its viscosity and thermal conductivity were assumed to be dependent on temperature. Based on the results, two correlations have been developed to predict the thermal effectiveness, for wide ranges of mass flow rates ratio, dimensionless geometrical parameters and product of Reynolds numbers. Furthermore, it was found for same values of NTU and Cr, the effectiveness is averagely 12.6% less than the effectiveness of parallel flow heat exchangers and this difference is approximately constant.

Abstracts:In order to improve the efficiency of the adsorption refrigeration cycle, this study proposes a triple-effect adsorption refrigeration cycle equipped with a compressor. This cycle can run in order to create a large variation in adsorbent concentration range by the compressor, even if there is little temperature variation in the desorption and adsorption processes. The objective of this study is to clarify the effect that regulating adsorption pressure using a compressor has on the adsorption refrigeration cycle, and to that end cycle efficiency was calculated using a static analysis based on a state of equilibrium. As a results from the simulation, the triple-effect cycles can operate by regulating adsorption pressure. Both COP and exergy efficiency can be improved by a factor of 1.2 if the cycled is regulated the adsorption pressure of each cycle rather than using a shared adsorption pressure. For heat sources in the temperature range of 70–100°C, this method is superior in terms of COP and exergy efficiency. COP values of approximately 1.7–1.8 can be obtained, which is three times higher than single-effect cycles. The triple-effect cycles have one-third the SCE of single-effect cycles but about the same SCE as double-effect cycles.

Abstracts:The utilization of corrugation for improvement in heat transfer is increasingly becoming interesting recently due to its combined advantages such as extended surfaces, turbulators as well as roughness. This study employed the use of both numerical as well as experimental settings on the water flowing at lower Reynolds numbers in a corrugated tubes with spiral shape to evaluate the performance of heat in a newly designed corrugation style profile. The total performance of the heat for the corrugation tubes were determined and the mathematical information generated from both the Nusselt number and the factors of friction were equated with those of the experimentally generated outcome for both standard smooth as well as the corrugated tubes. Analysis of the dat generated revealed improvements in heat transfer ranges of (2.4–3.7) times those 0btained from the smooth tubes with significant increase in the friction factors of (1.7–2.3) times those of the smooth tubes. Based on the findings of study, it was concluded that for extended period and extensive range use, tubes with severity index values at 36.364×10^–3 could produce better heat performance (1.8–3.4) at Reynolds numbers ranging from 100 to 1300. This was an indication that the geometric expression with spiral corrugation profile could significantly enhance the efficiency of heat transfer with significantly increased friction factors.

Abstracts:The paper investigates some heat and mass transfer parameters (HMTPs) of three varieties of cocoyam slice and their vitamin B retention level in convective drying. The varieties include Colocasia esculenta (COE) and xanthosoma sagittiffolium (white flesh – NX01, red flesh – NX02). The objective is to generate HMTPs for process model development, applied in dryer design. The oven and sun drying procedures were employed where temperatures were maintained between 50 and 70°C (oven drying) and sun drying, the readings were observed at every one hour. The results obtained show that the mass transfer coefficient for the three varieties lies between 1.01044×10⁻⁶ and 3.44876×10⁻⁶ m/s while the heat transfer coefficient ranged from 1.17973 to 3.58284W/m² K. The specific energy consumption for drying was estimated at 14.15, 25.16 and 35.07 kWh/kg for NX02, NX01, and COE respectively, at drying temperature (DT) of 60°C. However, at DT range between 50 and 70°C the moisture extraction rate was varied from 0.047 to 0.185kg/kWh, for NX02, 0.070–0.258kg/kWh for NX01 and 0.099–1.42kg/kWh for COE, with vitamin B retention level ranging from 70.13% to 100% at all DTs for the varieties.

Abstracts:This article present an experimental investigation of varied mass charges of Liquefied Petroleum Gas (40g, 50g, 60g and 70g) enhanced with varied TiO2 nanoparticle/mineral oil concentrations (0.2g/L, 0.4g/L and 0.6g/L nano-lubricants) in a R134a compressor of a domestic refrigerator. Performance tests investigated at steady state included: pull down time, power consumption, compressor power input, cooling capacity and coefficient of performance (COP). Analysis was based on temperature and pressure readings obtained from appropriate gauges attached to the test rig. Refrigerant property characteristics were obtained using Ref-Prop NIST 9.0 software. Results obtained showed almost equal evaporator air temperatures and reduction in power consumption for all tested nano-lubricant concentrations except at 70g charge of LPG using 0.6g/L nano-lubricant. Furthermore, the lowest compressor power input was found to be 21W and obtained using 70g of LPG with either of 0.2g/L or 0.4g/L nano-lubricants. At 70g of LPG using 0.6g/L concentration of nano-lubricant, highest cooling capacity index of 65W was obtained while the highest COP of 2.8 was obtained with 40g charge of LPG using 0.4g/L concentration of nanolubricant. In conclusion, LPG-TiO2 nano-lubricant mixture works safely and efficiently in domestic refrigerators without modification of capillary tube length, but requires adequate optimization.

Abstracts:The limited thermal properties of liquids have led to the addition of solid nanoparticles to liquids in many industrial applications. In this paper, the friction factor and forced convection heat transfer of TiO2 nanoparticles dispersed in water in a car radiator was numerically determined. Four different nanofluid volume concentrations (1%, 2%, 3% and 4%) were used, and the resulting thermal properties were evaluated. The Reynolds number and inlet temperature ranged from 10000 to 100000 and from 60 to 90°C, respectively. The results showed that the friction factor decreases as the Reynolds number increases and increases as the volume concentration increases. Additionally, the Nusselt number increases as the Reynolds number and volume concentration of the nanofluid increases. The TiO2 nanofluid at low concentrations can enhance the heat transfer efficiency up to 20% compared with that of pure water. There was good agreement among the CFD analysis and experimental data available in the literature.

Abstracts:Energy consumption of liquefied petroleum gas (LPG) in ceramic firing process accounts for about 15–40% of production cost. Biomass derived producer gas may be used to replace LPG. In this work, a premixed burner originally designed for LPG was modified for producer gas. Its thermal performance in terms of axial and radial flame temperature distribution, thermal efficiency and emissions was investigated. The experiment was conducted at various gas production rates with equivalence ratios between 0.8 and 1.2. Flame temperatures of over 1200°C can be achieved, with maximum value of 1260°C. It was also shown that the burner can be operated at 30.5–39.4kWth with thermal efficiency in the range of 84 – 91%. The maximum efficiency of this burner was obtained at producer gas flow rate of 24.3 Nm³/h and equivalence ratio of 0.84.

Abstracts:A two-dimensional numerical simulation of the melting process in a rectangular enclosure for different inclination angles, has been carried out. Galium as a phase change material (PCM) with low Prandtl number is used. A numerical code is developed using an unstructured mesh, finite-volume method and an enthalpy porosity technique to solve for natural convection coupled to solid–liquid phase change. The validity of the numerical code used is ascertained by comparing our results with previously published results. The effect of the inclination angle on the flow structure and heat transfer characteristics is investigated in detail. It is found that the melting rate inside the rectangular cavity increases by decreasing the inclination angle from 90° to 0°.