Numerical Analysis on the Heat Transfer Characteristics of Supercritical Water in Vertically Upward Internally Ribbed Tubes

Internally ribbed tubes (IRTs) with better heat transfer capability have been widely applied in many fields. Several studies focused on the flow and heat transfer in IRTs with special structure configurations, but there is still lack of clear understanding regarding the influence of spiral ribs/grooves on the local flow structure and heat transfer capability of supercritical water. In the present paper, numerical simulation on turbulent heat transfer of supercritical water through a vertically upward IRTs is investigated. It is found at low heat fluxes, heat transfer enhancement occurs; the temperature of IRT is lower than that in the smooth tube by 6~7 °C, but at high heat fluxes; deteriorated heat transfer occurs in ST rather than in IRTs; the maximum temperature difference reaches 36 °C. The heat transfer ratio between IRT and ST is about 1.81 in the pseudocritical region, where the velocity deviation is about 20–50%. Once the deterioration heat transfer exists, a thin layer with high temperature but low density and low thermal conductivity so that (with a 20% reduction) fluids will be covered on the surfaces. Effects of rib height, width, lift angle and threads on turbulent heat transfer are analyzed, an optimum rib structure based on the performance evaluation criteria is obtained (α = 50°, e = 0.58 mm, S = 3.5 mm, m = 6), which can achieve the best performance.

Experimental Evaluation on the Effect of Nanofluids Physical Properties With Different Concentrations on Grinding Temperature

This chapter is proposed to solve the insufficient MQL cooling and heat transfer capability based on the heat transfer enhancement theory of solid. Adding nanoparticles into the base fluid can significantly elevate heat conductivity coefficient of the base fluid and enhance convective heat transfer capability of the grinding area. Researchers have carried out numerous experimental studies on nanofluids with different concentrations. However, the scientific nature of MQL cooling has not been explained. Degradable, nontoxic, low-carbon, and environmentally friendly green grinding fluid, palm oil taken as the base fluid, grinding force, grinding temperature and proportionality coefficient of energy transferred to workpiece of nanofluids with different volume fractions, are investigated in this chapter. Based on the analysis of the influence of physical characteristics of nanofluids on experimental results, cooling and heat transfer mechanism of NMQL grinding is studied. The experimental study can provide a certain technical guidance for industrial machining.

Experimental Evaluation on the Effect of Nanofluids Physical Properties With Different Concentrations on Grinding Temperature

This chapter is proposed to solve the insufficient MQL cooling and heat transfer capability based on the heat transfer enhancement theory of solid. Adding nanoparticles into the base fluid can significantly elevate heat conductivity coefficient of the base fluid and enhance convective heat transfer capability of the grinding area. Researchers have carried out numerous experimental studies on nanofluids with different concentrations. However, the scientific nature of MQL cooling has not been explained. Degradable, nontoxic, low-carbon, and environmentally friendly green grinding fluid, palm oil taken as the base fluid, grinding force, grinding temperature and proportionality coefficient of energy transferred to workpiece of nanofluids with different volume fractions, are investigated in this chapter. Based on the analysis of the influence of physical characteristics of nanofluids on experimental results, cooling and heat transfer mechanism of NMQL grinding is studied. The experimental study can provide a certain technical guidance for industrial machining.

Investigation of heat transfer in porous channels

Purpose This paper aims to investigate the heat transfer in porous channels. Design/methodology/approach Finite element method is used to simulate the heat transfer in porous channels. Findings The number and width of channels play a key role in determining the heat transfer of the porous channel. The heat transfer is higher around the channel legs. Smaller base height is better to get higher heat transfer capability. Originality/value This study represents the original work to investigate heat transfer in a porous domain having multiple channels.