High temperature flames, which can be produced via oxygen-enriched combustion, potentially have improved the combustion characteristics over air-only combustion flames due to their substantially higher flame temperatures. These conditions necessitate the use of non-intrusive optical measuring methods to measure the temperature and the chemical species in the flame. To develop an optical measurement calibration burner that can be used at high pressure and temperature conditions, a new calibration burner which employed water-cooled multi-hole nozzle was developed in this study. Premixed CH4/O2/N2 oxygen-enriched conditions were selected to investigate both the heat-resisting properties of the developed burner nozzle and the burner’s flame characteristics. OH-Planar Laser-Induced Fluorescence (OH-PLIF) measurements were conducted on the flames to observe the OH distributions. The flame temperature at 0.10 MPa was derived using a Boltzmann-plot for the OH fluorescence excitations. To verify the variation of molecular concentration with equivalence ratio for the experimental flames qualitatively, the experimentally acquired OH and CH chemiluminescence intensities were compared with the simulated partial pressure of OH* and CH*, respectively. Experimental results showed that the CH4/O2/N2 flames were stabilized on the burner nozzle in a wide range of oxygen-enrichment ratio, from 0.40 to 1.0 at atmospheric pressure. At an oxygen-enrichment ratio of 0.45, the flames were also stabilized in pressure conditions up to 0.49 MPa, while the inner nozzle temperature was lower than 400 K. The OH-PLIF images showed that the OH was distributed almost uniformly along the axial direction of the burner, and demonstrated similar characteristics to that of a flat flame. The derived maximum flame temperature at atmospheric pressure was approximately 2650 K at an oxygen-enrichment ratio of 0.80. The variation of the OH and CH chemiluminescence intensities with change of equivalence ratios corresponded roughly with the simulated partial pressures of OH* and CH* at each pressure condition.
The purpose of this paper is to investigate the effect of the wettability on MPCM suspensions thermal conductivity. The wettability of the capsules, characterized by contact angle between solid capsules and carrying fluid, was modified by mixing two selected surfactants into the suspensions, i.e.,cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate(SDS) and changing such surfactants’ additive amount. Meanwhile, the Hot Disk 2500s thermal analyzer was applied to test the static thermal conductivity of the MPCM suspensions in which the mass fraction of capsules is 10wt.% and obtained the relation between the thermal conductivity and the contact angle. The results indicated, when the mass fraction of surfactants falls into the range of 0 -0.05wt.%, the effect of the CTAB is more significant than the SDS. However, when the mass fraction of surfactants continue to increase from 0.05wt.%, the significance of the SDS exceeded the CTAB. It was also found that the decrease in the contact angle led to the growth in thermal conductivity for both Maxwell model’s theoretical value and experimental results. When the contact angle fell into the range of 45°-95°, the Maxwell model’s theoretical results of the thermal conductivity could predict the thermal conductivity of MPCM suspensions with a good accuracy, but inversely when the contact angles were smaller than 45°, a significant gap was found between the two results. To remove such gap a correction factor “A” which is associated with contact angles was proposed.
In order to study the thermal performance of a single U-tube VBHE in multiple-layer substrates, the similarity principle was used to build an indoor comprehensive miniature bench of single U-tube VBHE innovatively, and effects of inlet water temperature and hydrogeological geology on the thermal performance of VBHE were analyzed. In addition, numerical simulation was used to assist in the research. The results indicate that to build a laboratory-scale GSHP system model test apparatus based on the similarity principle will achieve long-term test of GSHP system with smaller human and material resources and a shorter experimental cycle. It's more efficient and convenient. The simplified use of uniform soil thermal and physical properties can cause great deviation. Heat flux per unit pipe of the VBHE increases linearly with the temperature difference's increasing between the inlet water and initial soil. The water temperature along the tube under thermal conductivity increasing and decreasing conditions does not decrease as linearly as the temperature's decreasing under the uniform thermal conductivity condition.
Fundamental experiments were conducted on a cooling tube with an obstacle using liquid nitrogen as the coolant under a frost-formation condition. The background of this study is the development of a heat exchanger for an air-breathing engine, which cools the air using a cryogenic fuel. The obstacle is located in front of the cooling tube. The main purpose of the obstacle is to protect the cooling tube against damages due to foreign objects. The experimental results obtained using an obstacle with a V-shaped cross section show that the obstacle helps in reducing the pressure loss and improving the heat-transfer performance if the distance between the obstacle and the cooling tube is optimally selected. The experiments conducted using obstacles with several types of cross sections show that one of these obstacles with an arrowhead cross section is effective in suppressing the pressure loss, mitigating an adverse effect on the heat-transfer performance, and protecting the cooling tube against damages due to foreign objects.