Three-Dimensional Numerical Modeling of Heat and Moisture Transfer in Natural Rubber Sheet Drying Process

The effects of heat and moisture transfer on rubber sheet drying were investigated by 3-D modeling using computational fluid dynamics (CFD). Complexities arose due to the inclusion of moisture transport. Local convective heat transfer coefficients for the sheets were predicted and then used to determine the mass transfer coefficients using the Chilton–Colburn analogy. Deviations between experimental and simulated temperatures were observed to range from 4.0 to 7.7°C. Temperature and moisture content of the rubber sheets were accurately predicted, and agreement between the experimental and simulated results was acceptable. This is useful for the design of an efficient rubber sheet drying chamber.     

Energy efficiency enhancement of natural rubber smoking process by flow improvement using a CFD technique

A non-uniform flow and large temperature variation in a natural rubber smoking-room cause an inefficient use of energy. Flow uniformity and temperature variation can be improved by using a computational fluid dynamics (CFD) simulation. The effects of the size, position and number of gas supply ducts and ventilating lids which were at the inlets and the outlets of the smoking-room were investigated. The optimal rubber smoking-room of size 2.6 m × 6.2 m × 3.6 m contains 154 50 mm-diameter hot gas supply ducts, and four 0.25 × 0.25 m and four 0.25 × 0.20 m ventilating lids. The velocity distribution of this model in the rubber-hanging area was rather uniform. The average monitoring temperature of 54 positions was 62.1 °C. This model could reduce the temperature variation by a factor of three from the original room model, i.e., from 15 to 5.5 °C. In a further study, the heat input of an appropriate room model was finely adjusted to obtain a suitable temperature (60 °C) for the smoking process. It was found that an appropriate heat supply at this temperature is 11 kW. At this rate, the temperature variation is 5.3 °C. This improved model should help the rubber smoking cooperatives to achieve at least a 31.25% saving in energy.     

Effect of cross-flow velocity on flow and heat transfer characteristics of impinging jet with low jet-to-plate distance

An effect of cross-flow velocity on flow and heat transfer characteristics of impinging jet in the case of low jet-to-plate distance at H = 2D was experimentally and numerically investigated. In the experiments, the air jet from orifice impingement on the wall of wind tunnel while a cross-flow was simultaneously induced normal to the jet flow. The jet velocity was fixed while the cross-flow velocity was varied corresponding to velocity ratios (jet velocity/cross-flow velocity) VR = 3, 5 and 7. The temperature distribution on an impinged surface was visualized by using thermochromic liquid crystal sheet (TLCs), and Nusselt number distribution was evaluated by using image processing method. The flow pattern on impingement surface was visualized by using oil film technique. The numerical simulation was carried out for a better understanding of the jet flow in the cross-flow. The results show that Nusselt number peak shifts downstream and the Nusselt number peak increases with increasing cross-flow velocity.     

Local heat transfer characteristics of array impinging jets from elongated orifices

The aim of this research is to enhance the heat transfer on an impinged surface under an impinging jet array by minimizing a cross-flow effect. Conventional round orifices (aspect ratio, AR = 1) are substituted by the elongated orifices with aspect ratio AR = 4 and 8 with the same jet exit area. Two types of orifice arrangements; in-line and staggered arrays are compared. The experimental investigation was carried out at constant distance from orifice plate to impinged surface H = 2D_E (D_E is equivalent diameter of orifice). The heat transfer characteristic was visualized using thermochromic liquid crystal sheet (TLCs) and the Nusselt number distribution was evaluated by an image processing technique. The flow characteristic on the impinged surface was also visualized by oil film technique. The results show that the cross-flow in a case of the jets issued from the orifices with AR = 4 is considerably less significant than that in cases of the ones delivered from the orifices with AR = 1 and 8. At Reynolds number of 13,400, the Nusselt numbers for the jet arrays issued from the elongated orifices with AR = 4 with in-line and staggered arrangements are respectively 6.04% and 12.52% higher than those for the case of AR = 1.