Experimental investigation of temperature-field evolution and heat-accumulation characteristics in goaf under U-type and Y-type ventilation conditions

To examine the temperature-field evolution and heat-accumulation characteristics in a goaf under U-type and Y-type ventilation, a similarity-simulation experimental system was established. Temperature-field responses were compared under two U-type air-leakage (AL) conditions and two Y-type airflow-direction conditions in a gob-side entry retaining model. The measured temperatures were model-scale experimental values and were used for relative comparison rather than direct conversion to prototype goaf temperatures. Under U-type ventilation with AL only at the upper and lower corners, the heated region was mainly concentrated in the central goaf, and the maximum model temperature reached 89 °C. When all AL points along the working face were open, the maximum model temperature was close to that of the baseline case (88 °C), whereas the area above the reference threshold (T ≥ 76 °C) increased and shifted toward the deeper goaf. Under Y-type ventilation, the gob-side entry retaining intake-airflow case produced a maximum model temperature of 86 °C and a relatively limited area above the reference threshold. In the gob-side entry retaining return-airflow case, the maximum model temperature increased to 96 °C, and the above-threshold area also increased, indicating stronger heat accumulation under the present ventilation condition. Overall, airflow direction, leakage path, and heat-storage conditions jointly controlled the model-scale temperature-field distribution. The results provide an experimental basis for comparing relative heat-accumulation tendencies in goafs under different ventilation conditions.