Design and Experimental Analysis Of a Direct Solar Dryer With Thermal Energy Storage Equipped With a New Heat Recovery System.

Abstract

This postgraduate thesis investigates the performance of two preliminary models of natural convection solar dryers, one equipped with a heat recovery system and the other without this system. The aim of the study is to enhance the efficiency of solar dryers by addressing the challenge of insufficient solar energy during certain periods. To overcome this limitation, a heat recovery system was integrated to reduce heat loss, and the dryers were equipped with paraffin wax (PCM) boxes for thermal energy storage, enabling effective drying even under low solar energy conditions. Experimental tests were conducted at the Applied Renewable Energies Research Unit (URAER) in Ghardaia, under real weather conditions. The initial models were subjected to no-load tests, and the internal air temperature reached 87 degrees Celsius in the solar dryer with the heat recovery system, and 65 degrees Celsius in the solar dryer without the heat recovery system. The average absorber temperatures were recorded as 75 degrees Celsius in the dryer with heat recovery and 66 degrees Celsius in the dryer without heat recovery. Performance evaluation of natural convection greenhouse dryers was conducted using peppers as drying products. Ten mathematical models were used to describe the drying kinetics of the thin layer of peppers. The results indicated that the Logarithmic and Midilli-Kucuk models were the most suitable for describing the solar drying process of the products in the tested preliminary models. The moisture content of the peppers decreased from 93% to 11% within a period of three to four days. The dryer with the heat recovery system resulted in faster drying up to one day and a gain in drying temperature approximately 30% up to 20 degrees. The efficiency of the preliminary models was determined to be 40% for the dryer with heat recovery and 30.76% for the second dryer without heat recovery. Overall, this study demonstrates the potential of integrating heat recovery and thermal energy storage systems into solar dryers to improve their performance during periods of low solar energy availability. The results provide valuable insights for improving the design and operation of solar greenhouse dryers for effective drying of agricultural products with reduced energy consumption.

تبحث مذكرة التخرج هذه في أداء نموذجين أوليين من المجففات الشمسية ذات الحمل الحراري الطبيعي ، أحدهما مزود بنظام إعادة تدوير الحرارة والآخر غير مزود بهذا النظام . الهدف من الدراسة هو تعزيز كفاءة المجففات الشمسية من خلال مواجهة التحدي المتمثل في عدم كفاية الطاقة الشمسية خلال فترات معينة. للتغلب على هذا القيد ، تم دمج نظام إعادة تدوير الحرارة لتقليل فقد الحرارة ،كما تم تزويد المجفف بعلب من البرافين (pcm) لتخزين الطاقة الحرارية وبالتالي تمكين التجفيف الفعال حتى في ظروف الطاقة الشمسية المنخفضة. تم إجراء الاختبارات التجريبية في وحدة أبحاث الطاقات المتجددة التطبيقية (URAER) في غرداية ، في ظل ظروف جوية حقيقية. تم إخضاع النماذج الأولية لاختبار عدم التحميل ، ووصلت درجة حرارة الهواء الداخلي إلى 87 درجة مئوية في المجفف الشمسي المزود بنظام اعادة التدوير و 65 درجة مئوية في المجفف الشمسي الغير مزود بنظام إعادة التدوير . تم تسجيل متوسط درجات حرارة الامتصاص في المجفف الشمسي مع اعادة التدوير بـ 75 درجة مئوية و المجفف بدون اعادة التدوير 66 درجة مئوية على التوالي. تم إجراء تقييم أداء مجففات الدفيئة بالحمل الحراري الطبيعي باستخدام الفلفل كمنتجات تجفيف. تم استخدام عشرة نماذج رياضية لوصف حركية تجفيف الطبقة الرقيقة للفلفل. أشارت النتائج إلى أن نموذج Logarithmic ونموذج Midilli-Kucuk هما الأنسب لوصف عملية التجفيف الشمسي للمنتجين في النماذج الأولية التي تم فحصها. انخفض المحتوى الرطوبي للفلفل من 93٪ إلى 11٪ خلال فترة ثلاثة إلى أربعة أيام. نتج عن المجفف المزود بنظام استرداد الحرارة تجفيف أسرع يصل إلى يوم واحد وزيادة درجة حرارة التجفيف حتى 20 درجة المقدرة ب 30.76٪ بشكل عام ، توضح هذه الدراسة إمكانية دمج نظام إعادة تدوير الحرارة وتخزين الطاقة الحرارية في المجففات الشمسية لتحسين أدائها خلال فترات انخفاض توافر الطاقة الشمسية. توفر النتائج رؤى قيمة في تحسين تصميم وتشغيل مجففات الدفيئة الشمسية من أجل التجفيف الفعال للمنتجات الزراعية مع تقليل استهلاك الطاقة.

This postgraduate thesis investigates the performance of two preliminary models of natural convection solar dryers, one equipped with a heat recovery system and the other without this system. The aim of the study is to enhance the efficiency of solar dryers by addressing the challenge of insufficient solar energy during certain periods. To overcome this limitation, a heat recovery system was integrated to reduce heat loss, and the dryers were equipped with paraffin wax (PCM) boxes for thermal energy storage, enabling effective drying even under low solar energy conditions. Experimental tests were conducted at the Applied Renewable Energies Research Unit (URAER) in Ghardaia, under real weather conditions. The initial models were subjected to no-load tests, and the internal air temperature reached 87 degrees Celsius in the solar dryer with the heat recovery system, and 65 degrees Celsius in the solar dryer without the heat recovery system. The average absorber temperatures were recorded as 75 degrees Celsius in the dryer with heat recovery and 66 degrees Celsius in the dryer without heat recovery. Performance evaluation of natural convection greenhouse dryers was conducted using peppers as drying products. Ten mathematical models were used to describe the drying kinetics of the thin layer of peppers. The results indicated that the Logarithmic and Midilli-Kucuk models were the most suitable for describing the solar drying process of the products in the tested preliminary models. The moisture content of the peppers decreased from 93% to 11% within a period of three to four days. The dryer with the heat recovery system resulted in faster drying up to one day and a gain in drying temperature approximately 30% up to 20 degrees. The efficiency of the preliminary models was determined to be 40% for the dryer with heat recovery and 30.76% for the second dryer without heat recovery. Overall, this study demonstrates the potential of integrating heat recovery and thermal energy storage systems into solar dryers to improve their performance during periods of low solar energy availability. The results provide valuable insights for improving the design and operation of solar greenhouse dryers for effective drying of agricultural products with reduced energy consumption.