Experimental study on thermal performances of heat pipes for air-conditioning systems influenced by magnetic nanofluids, external fields, and micro wicks

• The influences on thermal resistance and critical heat flux were studied.
• The tested working fluids were magnetic nanofluids (MNFs) and deionized water.
• The tested heat pipes (HPs) were sintered- and grooved- wick HPs, and no-wick HPs.
• Combing MNFs and either wick HP improved thermal resistance and critical heat flux.
• The modulation of magnetic fields ineffectively reduced the thermal resistance.

Previous studies have typically indicated that only one composition factor, such as wick structures or working fluids, affects the thermal resistance or critical heat flux of heat pipes. In this study, the composition factors influencing thermal performance, such as wick structures, working fluids, the modulation fields of working fluids, and combinations of these factors, were thoroughly investigated. The evaluated materials comprised microgrooved, sintered, and wickless heat pipes; magnetic nanofluids exhibiting volumetric fractions (vol.) of 0.16%–3.20%; and deionized water. A strong magnetic field of 200 Oe was applied. The results indicated that combining grooved heat pipes and a 0.80% vol. of magnetic nanofluids or sintered heat pipes and a 0.16% vol. of magnetic nanofluids yielded the optimal promotions: the thermal resistance was reduced by approximately 80% and the critical heat flux was enhanced 2.7-fold compared with general wickless heat pipes filled with deionized water. These findings should serve as a valuable reference when designing heat pipe exchangers for use in air-conditioning systems.