Numerical Modelling and Experimental Verification of New Observations of the Two Phases Interaction in a Vertical and Inclined Closed Wickless Heat Pipe

 الأنابيب الحرارية واحدة من الحلول الحديثة لتحرير الطاقة الحرارية من المصادر ذات درجات الحرارة العالية أو للحصول على توزيع منتظم للحرارة في المستودعات السائلة أو الصلبة. ان التداخل بين الطورين السائل والغازي في داخله قد تم فرضه بطريقة تقليدية من قبل الباحثين ولم يتم الكشف عنه بدقة. في هذه الدراسة تم اجراء تقريباً 480 حل رياضي وفحص تجريبي مختبري لتأكيد المشاهدات التي نشرناها سابقاً حول انماط الجريان الفضائية غير المنتظمة لكل من الطورين داخل انبوب حراري مصنوع من النحاس وبدون فتيلة يعتمد على التدوير الحراري ومملوء جزئيا بالماء. تم الحصول على النتائج الرياضية من موديل رياضي حسابي ديناميكي انتقالي بالابعاد الثلاثية تم تضمينه مختلف المتغيرات لتقريبه للحالة الواقعية على الرغم من التعقيد في طرق الحسابات وزيادة المدة اللازمة لاكمال التشغيل للمحاكاة الرياضية. ان نسبة التوافق العالية بين نتائج الموديل الرياضي والفحص المختبري لطريقة وقيم التوزيع الحراري تؤكد صحة نتائج الموديل الرياضي.  ان المخططات الكنتورية المستحصلة من الموديل الرياضي والخاصة بنمط جريان وتوزيع الطورين داخل الأنبوب الحراري، تبين ان الطورين يجريان بنمط فضائي غير منتظم وغير مستقر وغير مستمر على شكل واحد. كلا الطورين يعانيان من انتقال للحرارة وتغير بالطور مع بعضهما خلال الجريان للاعلى (البخار) او الجريان للاسفل (السائل المتكثف). ازداد الاداء الحراري بنسبة (+10%) نتيجة الميلان من الوضع العمودي الى زاوية º60، ومن ثم انخفض الاداء الحراري بنسبة (-15%) بزاوية º15 (هذه القيم عند نسبة ملئ 50% وطاقة حرارية مسلطة 200 واط). هذا بسبب كون ميلان الانبوب الحراري يؤدي الى تنظيم نمط الجريان الفضائي وتقريبه الى الدوران المنتظم، كما أنه يؤدي الى عدم تجانس عمليتي التبخر والتكثف وبالتالي يؤدي الى انخفاض الاداء الحراري ككل.Heat pipes are one of the modern solutions for heat release from hot sources or for heat homogeneity in liquid or solid reservoirs. The interactions between the two phases of its working fluid are suggested classically by researchers and still not discovered deeply. In this study about 480 experimental and numerical tests are carried out to confirm the previous published observation of spatial flow patterns of the two phases inside a wickless copper Thermosyphon Heat Pipe THP partially filled with water. Numerical results are gotten from a three dimensional transient Computational Fluid Dynamics 3DCFD numerical solution. Different factors are included into 3DCFD model to reach reality in results and suffering from complex calculation procedures and increase simulation running time. The high agreement percentages between the experimental and 3DCFD for the temperatures distribution profile and magnitudes confirm the 3DCFD results. 3DCFD solution contours of steam volume fractions SVF show that both phases flow in a 3D spatial, non-steady and non-continues flow streams. Both phases suffering phase change and heat transfer from each to other during flow up (steam) and flow down (condensate). Thermal performance increase about (+ve. (10%)) due to inclination from vertical to 60º then falling to (-ve. (15%)) at 15º (for filling ratio 50% and heat supplied 200W). that’s because inclination lead the complex spatial flow to be a uniform circulation flow, hence it’s lead to non-homogeneity in evaporation and condensation processes and finally result in reduction of thermal performance

Study of Heat Pipe Thermal Performance with Internal Modified Geometry

The aim of this study was to investigate the effect of inserting a new internal tube packing (TP) on the thermal performance of a thermosyphon heat pipe (THP). The THP pipe was made from copper with an inner diameter of 17.4 mm and length of 600 mm. The new internal tube packing (TP) had a central copper disc with two copper tubes soldered onto both sides to transport vapor and condensate. The upper tube or riser had an inner diameter of 8.3 mm and was 300 mm long; it was connected to a hole in the disc from the upper side to transport the steam to the condenser section. The lower tube or downcomer had an inner diameter of 5 mm, was 225 mm long and was connected to the lower side of the disc to collect the condensate and transport it to the evaporator. The TP was inserted inside the THP to complete the design of the improved heat pipe (TPTHP). Experimental results showed that the TPTHP reduces the transit time from 16 to 11 min and the thermal resistance by 17–62% based on the input power and depending on the conditions of the THP. The results also showed that the inclination angle and filling ratio have no effect on the thermal resistance of the TPTHP

THERMAL PERFORMANCE ENHANCEMENT OF A VERTICAL THERMOSYPHON HEAT PIPE BY FLOW CONTROL OF THE TWO PHASES

Heat Pipe (THP) has a continues evaporation/ condensation cycles of the working fluid. The flow patterns of the two phases is founds by previous published articles, as a non-steady complex spatial flow pattern. This type of the flow blocks the easy moving of the two-phases and limits the thermal performance of the THP. In this study, a copper tubes packing (TP) is simulated numerically to control/manage the flow streams of the two phases inside the THP. The simulated THP is 600mm length made of copper partially filled with water. The TP is consist of a two copper tubes attached contrary to each other with a neighboring openings. The upper tube (Riser tube) facilitate the moving of steam streams from evaporator section to the top of the condenser section. The lower tube (Down-comer tube) facilitate the moving of the condensate streams from the condenser section to the bottom of the evaporator section. The tested filling ratios are (40,50,55,60 and 70) % of evaporator section volume. The supplied heats are (50,75,100,150 and 200) W. The Computational Fluid Dynamics solution are done for a three dimensional model (3DCFD) using ANSYS/ Fluent R19.0 software. The simulation result of the steam volume fractions contours shows that the insertion of TP control the flow streams of both phases. Also prevent the formation of complex flow patterns then enhance the axial velocity vectors and reduce cross velocity vectors. The inserted TP provide a regular circulation paths for the working fluid phases and enhance evaporation /condensation processes. Hence it’s reduce the thermal resistance of the THP about 55% and enhance the thermal performance with the same percentage. In addition, the thermal performance of the enhanced TPTHP is not/a little influence due to the variation of the filling ratio